WO2019040277A1

WO2019040277A1 - Supercritical water oxidation systems for energy recovery and use thereof

Info

Publication number: WO2019040277A1
Application number: PCT/US2018/045643
Authority: WO
Inventors: Michael Modell
Original assignee: Michael Modell
Priority date: 2017-08-22
Filing date: 2018-08-07
Publication date: 2019-02-28

Abstract

Herein disclosed is a supercritical water oxidation (SCWO) system, comprising a preheating zone including at least one heat exchanger with at least one process fluid (PF) inlet and one PF outlet and at least one heat exchange fluid (HEF) inlet and one HEF outlet, wherein the PF inlet is configured to receive a process fluid feed stream; a SCWO reaction zone including at least one SCWO reactor with at least one PF inlet and one PF outlet; a steam generation zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one water inlet and one steam outlet; and a first cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet.

Description

SUPERCRITICAL WATER OXIDATION SYSTEMS FOR ENERGY RECOVERY AND USE THEREOF

FIELD OF THE INVENTION

[0001] The present invention is related generally to supercritical water oxidation (SCWO) and more specifically to the configuration and design of SCWO systems for the purpose of energy recovery.

BACKGROUND

[0002] Supercritical water oxidation (SCWO) is an oxidation process that occurs at thermodynamically supercritical conditions wherein water is the reaction medium. The critical point of water is about 374°C and 22 MPa (220 bar), above which water becomes supercritical and exhibits various unique properties, such as: (1) the density of supercritical water is between that of water vapor and liquid at standard conditions; (2) supercritical water possesses high gas-like diffusion rates and high liquid-like solubilities; and (3) supercritical water is a superb solvent for both organics and gases. Because of these unique properties, supercritical water (SCW) is able to provide an excellent medium to oxidize organic and biological materials virtually completely to benign products without the need for stack gas scrubbing and without the need to create coal ash ponds. Heavy metals contained in the feed are also recovered as stabilized solids after SCWO processing, along with the sand and clay present in the feed.

[0003] For example, SCWO is an excellent solution for destruction of sewage sludges: carbon and hydrogen from organic and biologic substances are oxidized to CO2 and H2O; nitrogen, sulfur and phosphorus (from e.g. biological materials) form N₂, SO4² and PO4³ , respectively; organic chlorides are converted to CI^", and heavy metals are oxidized to the corresponding oxides. Some representative reactions are shown below:

Hydrocarbons C₆H₆ + 7.5 0₂ 6 CO2 + 3 H2O

[Benzene]

Biological Matter CH_aObN_dS_ePf [Bacteria] + (l+a/4-b/2+3/2e+5/4f) O2

CO2 + (a/2-e-3/2f) H2O + d/2 N₂ + e H2SO4 + f H3PO4 Organic Chlorides C12H4O2CI4 + 11 O2 --> 12 C0₂ + 4 HC1

[Dioxin]

Heavy Metals Zn²⁺ + ½ 0₂ ZnO

[0004] At 25 MPa and 600°C, typical conditions for SCWO, almost all of these reactions have been shown to reach conversions of 99.9999% at 600°C with a residence time of 30 sec or less. Effective oxidation at the relatively mild temperatures of SCWO is made possible by high pressure and the presence of water as the reaction medium in its supercritical state. Supercritical water (SCW) dissolves organic materials and gases and reacts with organics and reforms them to small molecules - without the formation of char. These small molecules are readily oxidized if oxygen is present with the organic-SCW mixture. Furthermore, SCWO is an exothermic process; thermal energy is generated by oxidation reactions. Generated thermal energy has the potential to produce steam and hot water, which may be used to power turbines for electricity generation and to provide heating for facilities, respectively. Estimates of sewage production in the United States range from 60 to 115 gallons per person per day (227 to 435 liters) excluding industrial effluents. For example, New York City alone produces about 1,200 tons of sewage sludge every day.

[0005] These principles are also applicable to other organic energy sources, such as coal and lignite. Therefore, it is of great value and interest to develop SCWO systems to recover energy from SCWO processes in a safe, environment-friendly, efficient, and economical manner.

SUMMARY

[0006] Herein disclosed is a supercritical water oxidation (SCWO) system, comprising a preheating zone including at least one heat exchanger with at least one process fluid (PF) inlet and one PF outlet and at least one heat exchange fluid (HEF) inlet and one HEF outlet, wherein the PF inlet is configured to receive a process fluid feed stream; a SCWO reaction zone including at least one SCWO reactor with at least one PF inlet and one PF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said preheating zone PF outlet; a steam generation zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one water inlet and one steam outlet, wherein the PF inlet is configured to receive SCWO process fluid from said reaction zone PF outlet; and a first cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said steam generation zone PF outlet, and the HEF inlets and outlets of said first cooling zone and said preheating zone are connected to form a recirculation loop for a heat exchange fluid, constituting a regenerative heat exchange system.

[0007] In an embodiment, the system comprises a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet; and at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to the water inlet of said steam generation zone.

[0008] In an embodiment, the system comprises a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet; and at least one HEF inlet and HEF outlet are configured to be fluidly connected to said HEF inlets and outlets of said first cooling zone and said preheating zone to form said recirculation loop for said heat exchange fluid as the regenerative heat exchange system.

[0009] In an embodiment, the system comprises a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet; and at least one HEF inlet is configured to receive a second heat exchange fluid and at least one HEF outlet is configured for said second heat exchange fluid to exit the system.

[0010] In an embodiment, the system comprises a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet; at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to the water inlet of said steam generation zone; and at least one HEF inlet is configured to receive a second heat exchange fluid and at least one HEF outlet is configured for said second heat exchange fluid to exit the system. [0011] In an embodiment, the system comprises at least one turbine, which is configured to receive the steam effluent from said steam outlet of the steam generation zone to produce electricity. In an embodiment, the SCWO reactor in the reaction zone is thermally insulated. In an embodiment, the heat exchangers include cross-flow tube- and-shell heat exchangers, cocurrent double pipe heat exchangers, and countercurrent double pipe heat exchangers. In an embodiment, the heat exchangers include countercurrent double pipe heat exchangers.

[0012] In an embodiment, said SCWO system comprises a series of double pipes with fluidly connected inner pipes having the same inner diameter and a smooth inner surface; said preheating zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for a first HEF with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet is configured to receive a process fluid feed stream; said reaction zone comprises a thermally insulated SCWO tubular reactor as the passage for the PF with an inlet and an outlet, wherein the inlet of said tubular reactor is fluidly connected to the IP outlet of preheating zone double pipe; said steam generation zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for water with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet of steam generation double pipe is fluidly connected to the outlet of the tubular reactor; said first cooling zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for said first HEF with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet of first cooling zone double pipe is fluidly connected to the IP outlet of steam generation zone double pipe; one annulus inlet is fluidly connected to one annulus outlet of preheating zone double pipe; and one annulus outlet is fluidly connected to one annulus inlet of preheating zone double pipe; said second cooling zone comprises a countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for said first HEF with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet of second cooling zone double pipe is fluidly connected to the IP outlet of first cooling zone double pipe; one annulus inlet is fluidly connected to a water feed and one annulus outlet is fluidly connected to one annulus inlet of steam generation zone double pipe; and a second annulus inlet is fluidly connected to a second HEF feed, which exits the system via a second annulus outlet.

[0013] In an embodiment, the system comprises a scale cleaner. In an embodiment, the system comprises a multiport oxygen injection system in the reaction zone. In an embodiment, adjacent oxygen injection ports in the multiport oxygen injection system are configured to provide a residence time of no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds.

[0014] Also discussed is a supercritical water oxidation (SCWO) system, comprising a preheating double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the PF inlet is configured to receive a process fluid feed stream; a SCWO tubular reactor with at least one PF inlet and one PF outlet, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said preheating double pipe heat exchanger; a steam generation double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one water inlet and one steam outlet on the annulus, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said SCWO tubular reactor; and a first cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said steam generation double pipe heat exchanger, and at least one HEF inlet is fluidly connected to the HEF outlet of said preheating double pipe heat exchanger; and at least one HEF outlet is fluidly connected to the HEF inlet of said preheating double pipe heat exchanger.

[0015] In an embodiment, the system comprises a second cooling double pipe heat exchanger with at least one pf inlet and one pf outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the pf inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; and at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to said water inlet of said steam generation double pipe heat exchanger.

[0016] In an embodiment, the system comprises a second cooling double pipe heat exchanger with at least one pf inlet and one pf outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the pf inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; and at least one HEF inlet and HEF outlet are fluidly connected to said HEF inlets and outlets of said first cooling and preheating double pipe heat exchangers to form a recirculation loop for a heat exchange fluid as the regenerative heat exchange system.

[0017] In an embodiment, the system comprises a second cooling double pipe heat exchanger with at least one pf inlet and one pf outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; and at least one hef inlet is configured to receive a heat exchange fluid and at least one hef outlet is configured for said heat exchange fluid to exit the system.

[0018] In an embodiment, the system comprises a second cooling double pipe heat exchanger with at least one pf inlet and one pf outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the pf inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; one HEF inlet is configured to receive water feed and one HEF outlet is configured to be fluidly connected to said water inlet of said steam generation double pipe heat exchanger; and a second hef inlet is configured to receive a heat exchange fluid and a second hef outlet is configured for said heat exchange fluid to exit the system.

[0019] Further discussed is a method of recovering energy from a SCWO reaction, comprising pressurizing an oxidant and a feed stream to a pressure greater than 220 bar; mixing pressurized oxidant and feed stream to form a process fluid; preheating said process fluid in a first heat exchange system to its kindling temperature to form preheated process fluid; introducing preheated process fluid into a reactor wherein SCWO reactions take place to oxidize a substantial portion of the organic material in the process fluid to form a reacted process fluid; introducing reacted process fluid into a second heat exchange system to increase the thermal energy to desalinated water that is circulating in said second heat exchange system, whereby the circulating water becomes steam; and introducing process fluid effluent from said second heat exchange system into a third heat exchange system to increase the temperature of a heat exchange fluid, wherein said heat exchange fluid is recirculated to said first heat exchange system to preheat the process fluid.

[0020] In an embodiment, the method comprises introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system, wherein desalinated water that is circulating in said second heat exchange system is preheated so as to facilitate steam generation. In an embodiment, the method comprises introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system to provide thermal energy to the heat exchange fluid that is recirculated in said first and third heat exchange system so as to facilitate the preheating of the process fluid.

[0021] In an embodiment, the method comprises introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system to generate hot water; or to cool down process fluid effluent to near room temperature; or both. In an embodiment, the method comprises introducing steam effluent generated into a turbine to produce electricity.

[0022] In an embodiment, said oxidant includes air and oxygen. In an embodiment, said feed stream is a mixture of trimming water and a feedstock. In an embodiment, said trimming water and feedstock are either mixed first and then pressurized to greater than 220 bar or pressurized to greater than 220 bar first and then mixed. In an embodiment, said feedstock is selected from the group consisting of activated raw sludge from a municipal sewage treatment plant; sludge from manufacturing facilities which produce at least one product selected from the group consisting of pulp, paper, pharmaceuticals, foods, beverages, and chemicals; a military waste selected from the group consisting of chemical warfare agents, explosives, rocket propellant, and radioactive materials; pulverized coal with a particle size of 200 μιτι or less or 100 μιτι or less; biomass; and combinations thereof. In an embodiment, said feedstock comprises algae.

[0023] In an embodiment, said SCWO reactor is thermally insulated. In an embodiment, said SCWO reactor is constructed with a material selected from the group consisting of Inconel 625, Hastelloy C-276, and HAYNES® 230® ALLOY. In an embodiment, the temperature of reacted process fluid exiting SCWO reactor is in the range of from 550°C to 700°C. In an embodiment, the pressure of the steam effluent generated is in the range of from 1 bar (14.5 psia) to 276 bar (4000 psia).

[0024] In an embodiment, each one of said heat exchange systems comprises at least one heat exchanger. In an embodiment, each heat exchanger of said heat exchange systems is operated with a minimal average temperature difference between the two fluids that are in thermal communication in the heat exchanger. In an embodiment, said minimal average temperature difference is 150 °C or less. In an embodiment, the rate of energy recovery from SCWO reactions for steam generation is 80% or more. [0025] Disclosed herein is a method of recovering energy from a SCWO reaction, comprising forming a feed stream comprising an organic material and water with a pressure greater than 220 bar; preheating the feed stream to its kindling temperature to form preheated process fluid; introducing preheated process fluid into a reactor wherein SCWO reactions take place, wherein an oxidant is provided via multiple injection ports placed along the length of the reactor; oxidizing a substantial portion of the organic material in the process fluid to form a reacted process fluid; introducing reacted process fluid into a heat exchange system to increase the thermal energy to desalinated water that is circulating in said heat exchange system, whereby the circulating water becomes steam; and using the steam to produce electricity.

[0026] In an embodiment, said organic material comprises pulverized coal and said oxidant comprises air or oxygen. In an embodiment, the multiple injection ports are configured to control reaction rates, to adjust oxidant concentration profile in the reactor, to adjust temperature profile in the reactor, to prevent run-away reactions, to prevent spontaneous combustion, to prevent explosion, or to prevent char formation. In an embodiment, residence time in the reactor is no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds. In an embodiment, residence time between adjacent ports of the multiple injection ports is no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds. In an embodiment, the method comprises periodic use of a pipe cleaner in the reactor. In an embodiment, said heat exchange system is configured to minimize entropy generation. In an embodiment, said heat exchange system is configured to maximize steam generation. In an embodiment, the reacted process fluid becomes an effluent from the heat exchange system, wherein said effluent is separated by phase and then depressurized. In an embodiment, there is no or minimal char formation. In an embodiment, 99% or more of the organic material is oxidized.

[0027] Discussed herein is a three-phase separator comprising an inlet tube configured to receive a three-phase mixture; a vessel; a gas effluent outlet; at least two heat exchangers, each of which being in fluid communication with the vessel and in fluid communication with the gas effluent outlet; and valves configured to control fluid flow. In an embodiment, the inlet tube has a diverging inner diameter. In an embodiment, the smallest inner diameter of the inlet tube is large enough to allow a cleaner to pass through. [0028] In an embodiment, the vessel is tall enough to contain liquid at the bottom and froth at the top with gas phase above the froth. In an embodiment, the cross-section of the froth region vessel is large enough to provide for a slow rise of the vapor phases. In an embodiment, the heat exchangers are jacked pipes or double pipe heat exchangers. In an embodiment, the heat exchangers are configured to receive a coolant during a cooling cycle or a heating medium during a heating cycle. In an embodiment, the heat exchangers are configured in parallel and operated in a semi-batch fashion.

[0029] In an embodiment, the separator comprises a liquid level monitor in communication with the liquid and the froth in the vessel. In an embodiment, the valves are operated such that the heat exchangers are used in alternating cooling and heating cycles. In an embodiment, the vessel has a conical bottom. In an embodiment, the bottom of the vessel is jacketed and maintained at a temperature slightly above the freezing point of the least volatile component of the mixture. In an embodiment, the separator comprises a liquid outlet at the bottom of the vessel.

[0030] The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:

[0032] Figure 1 is a schematic flow diagram, illustrating a SCWO system capable of using the thermal energy of the reaction zone effluent to preheat the feed stream, to produce high pressure steam for electricity generation, and to produce hot water for heating, in accordance with embodiments of the disclosure. The solid arrows represent the flow of the process fluid and the dashed arrows represent the flow of a heat exchange fluid. [0033] Figure 2 is an exemplary process flow diagram of a SCWO system such as that shown in Figure 1, and which is capable of using the thermal energy of the reaction zone effluent to preheat the feed stream, to produce high pressure steam for electricity generation, and to produce hot water for heating, in accordance with embodiments of the disclosure.

[0034] Figures 3a-3c present the relationship between heat duty and temperature in three heat exchangers. Figure 3a shows this relationship in heat exchanger 200 shown in Figure 2. Figure 3b shows this relationship in heat exchanger 300 shown in Figure 2. Figure 3c shows this relationship in heat exchanger 500 shown in Figure 2.

[0035] Figure 4a illustrates the design of a tubular reactor assembly as an exemplary configuration of a Preheating Zone and a Reaction Zone of a SCWO system, as shown in Figure 1, in accordance with embodiments of the disclosure.

[0036] Figure 4b illustrates the design of a tubular reactor assembly as an exemplary configuration of a Steam Generation Zone, a Cooling Zone (I), and a Cooling Zone (II) of a SCWO system as shown in Figure 1, in accordance with embodiments of the disclosure.

[0037] Figure 4c illustrates exemplary designs of the layout of tubular reactor assemblies as shown in Figure 4a and Figure 4b.

[0038] Figure 5 illustrates the design of a SCWO system for coal oxidation and recovery of energy according to an embodiment of this disclosure.

[0039] Figure 6 illustrates a three-phase separator according to an embodiment of this disclosure.

NOTATION AND NOMENCLATURE

[0040] In this document, the term 'reactor assembly' not only refers to a reactor itself, but also includes a sequence of heat exchangers that are thermally or fluidly connected to the reactor itself either directly or indirectly, such as a preheater upstream of the reactor and heat recovery exchanger(s) downstream of the reactor. The term 'solids', when referring to the feed, is utilized in its meaning as known to one skilled in the art. When referring to the non-aqueous content of the feed, the term 'solids' includes actual solid material plus dissolved solids. The term "coupled to" or "coupled with" is used herein to refer to thermal or fluid communication either directly or indirectly between vessels, regions, or compartments. The terms "thermally coupled" and "fluidly coupled" are generally used to differentiate the usage unless they are clearly differentiated by the context.

[0041] The terms "process fluid" and "reaction mixture" are used interchangeably to refer to the mixture for a SCWO process, which may include organics, inorganics, water, and an oxygen source. The term "reaction mixture" is used with an emphasis on the mixture related to SCWO reactions. The term "process fluid" is used with respect to every stage of the mixture in a SCWO system.

[0042] Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function.

[0043] In the following description and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to... ".

DETAILED DESCRIPTION

[0044] I. Overview. Embodiments of the present invention describe the configuration and design of a SCWO system. In some embodiments, the reactor assemblies generate high pressure steam for electricity production. In some embodiments, the reactor assemblies provide hot water for heating. In some embodiments, the reactor assemblies provide both power and heating. In some embodiments, the SCWO system is configured as tubular reactor assemblies.

[0045] The above features and other details of the apparatus and method of the invention will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular embodiments of the invention are shown by way of illustration and not as limitations of the invention. The principle features of this invention can be employed in various embodiments without departing from the scope of the invention.

[0046] Referring to Figure 1, a SCWO process fluid passes in sequence through Preheating Zone, Reaction Zone, Steam Generation Zone, Cooling Zone (I), and optionally Cooling Zone (II), as shown by solid arrows. The reaction zone comprises at least one SCWO reactor. Each of the Preheating Zone, Steam Generation Zone, Cooling Zone (I), and Cooling Zone (II) includes at least one heat exchanger. Examples of heat exchangers are cross-flow tube-and-shell heat exchangers, cocurrent or countercurrent double pipe (or tube-in-tube) heat exchangers. In embodiments, double pipe heat exchangers are used. In embodiments, countercurrent double pipe heat exchangers are utilized because they provide the most effective heat exchange. In embodiments, to maintain a constant temperature difference between the two fluids that are in thermal communication, as much as possible, across the entire length of a countercurrent double pipe heat exchanger, water is used as the heat exchange fluid in the annulus of the double pipe heat exchanger at a flow rate that is comparable to that of the process fluid in the inner pipe.

[0047] The heat exchangers are operated with small temperature difference between the two fluids that are in thermal communication to achieve high heat exchange efficiency. Furthermore, since the rate of scale formation on the wall of the heat exchangers increases with increasing temperature gradient across the wall, each one of the heat exchangers in the disclosed SCWO system is operated at an average temperature difference (between the two fluids in thermal communication) that is as low as practical. In some cases, the heat exchanger is operated with an average temperature difference of 50°C or less. In some cases, the heat exchanger is operated with an average temperature difference of 100°C or less. In some cases, the heat exchanger is operated with an average temperature difference of 150°C or less. In some cases, the heat exchanger is operated with an average temperature difference of 200°C or less. Because small temperature difference is utilized in the heat exchangers, the heat exchange area of each heat exchanger needs to be sufficiently large so as to achieve the desired heat duty. Ideally, the bigger the heat exchange area, the smaller the temperature difference may be used, the slower the scale formation, and the higher the heat transfer rate. But practically, the bigger the heat exchange area, the higher the cost of construction. Therefore, there is a balance between the size of the heat exchangers and the minimum average temperature difference with which a series of heat exchangers may be operated.

[0048] In embodiments, the reaction zone effluent is used in the Steam Generation Zone to provide thermal energy to turn water into steam. In exemplary embodiments, purified (desalinated) water is used as the heat exchange fluid in the one or more heat exchangers of Steam Generation Zone as shown by the dashed arrows. In certain embodiments, the temperature of the steam generated is in the range of from 400°C to 650°C. In some cases, the temperature of the steam generated is in the range of from 500°C to 650°C. In some other cases, the temperature of the steam generated is in the range of from 550°C to 650°C. In yet other cases, the temperature of the steam generated is in the range of from 600°C to 650°C. In certain embodiments, the pressure of the steam generated is in the range of from 300 psia (21 bar, 2.1 MPa) to 4000 psia (276 bar, 27.6 MPa). In some cases, the pressure of the steam generated is in the range of from 450 psia (31 bar, 3.1 MPa) to 3700 psia (255 bar, 25.5 MPa). In some other cases, the pressure of the steam generated is in the range of from 900 psia (62 bar, 6.2 MPa) to 3700 psia (255 bar, 25.5 MPa). In yet other cases, the pressure of the steam generated is in the range of from 1200 psia (83 bar, 8.3 MPa) to 3700 psia (255 bar, 25.5 MPa). The pressure of generated steam for electricity production may be tailored according to the types of steam turbines that are practically available. In certain embodiments, the rate of energy recovery from SCWO reactions for steam generation is 80% or more. In certain embodiments, the rate of energy recovery from SCWO reactions for steam generation is 90% or more. In certain embodiments, the rate of energy recovery from SCWO reactions for steam generation is 95% or more.

[0049] Referring still to Figure 1, after the thermal energy of the reaction zone effluent is used for steam generation, the effluent enters Cooling Zone (I) and increases the thermal energy of a heat exchange fluid, which is recirculated to one or more heat exchangers of the Preheating Zone to preheat the feed stream of the SCWO process fluid. In exemplary embodiments, water is the heat exchange fluid that is recirculated in Cooling Zone (I) and Preheating Zone shown as dashed arrows. Any other suitable heat exchange fluid may be used as known to one skilled in the art, such as silicone oil. The process fluid exits Cooling Zone (I) and enters Cooling Zone (II) to provide heat to a heat exchange fluid, such as water. In certain embodiments, the temperature of the hot water produced is 85°C or higher. In some cases, the temperature of the hot water produced is 50°C-85°C. In some cases, the temperature of the hot water produced is 60°C-85°C. In some cases, the temperature of the hot water produced is 70°C-85°C. In some cases, the temperature of the hot water produced is 80°C-85°C. In certain embodiments, the temperature of the process fluid exiting Cooling Zone (II) is near room temperature, such as 30 to 40°C, depending upon the lowest temperature of cooling water available.

[0050] II. An Exemplary SCWO System Design. Now referring to Figure 2, an exemplary SCWO system is presented, which is designed to (1) provide sufficient energy for preheating the feed by extracting heat from the reactor effluent and recycling that energy to the preheater; and simultaneously (2) recover excess thermal energy of the reactor effluent as high pressure steam to drive steam turbines for power generation; and optionally (3) produce hot water to heat facilities. Proper sequencing of heat exchangers is needed to generate high pressure steam and hot water from the excess energy contained in the reactor effluent, which also provides thermal energy to preheat the process fluid feed stream. In Figure 2, the heat exchangers are illustrative only and do not necessarily represent the type of heat exchangers used. For example, in some embodiments, double pipe heat exchangers are used as heat exchangers as shown in Figure 2.

[0051] 1. Preparation of Process Fluid Feed Stream. The process fluid comprises organic materials with or without inorganic materials as the feedstock, a trimming or diluting agent (e.g., water), and an oxygen source (e.g., air, oxygen). Organic and inorganic materials as the feedstock are included in, for example, activated raw sludge from a municipal sewage treatment plant, sludge from manufacturing facilities for pulp, paper, pharmaceuticals, foods, beverages and chemicals, or military wastes, such as chemical warfare agents, explosives, rocket propellant, or radioactive materials. In some embodiments, the feedstock comprises coal. In some cases, coal is pulverized to particles with a size of 100 μηι or less. In some embodiments, the feedstock comprises biomass (either a particular type or a mixture of different types of biomass). The source of biomass includes agriculture (e.g., rice husk, rice straw, wheat straw, vegetable residue), livestock (e.g., animal waste, butchery waste), forestry (e.g., forest residue, thinned wood, processing waste, sawdust), fishery (e.g., processing waste, bowel, dead fish), industry (e.g., sewage sludge, organic processing waste), household (e.g., garbage, human waste), continental plantation (e.g., grain, plant, vegetable, fat, oil), and water plantation (e.g., algae, photosynthetic bacteria). In some cases, the feedstock comprises algae.

[0052] A feed mixture is formed by mixing and grinding and pressurizing or by mixing and pressurizing the feedstock and water to an absolute pressure of greater than about 218 atmospheres (i.e., 220 bar). In some cases, the feedstock is mixed with water first and then the formed mixture is pressurized. In some other cases, water and the feedstock are pressurized separately to the same pressure level (> 220 bar) and then mixed. The mixing ratio between water and the feedstock depends on the heating value of the organics contained in the feedstock to ensure that for a given flow rate (1) the SCWO reaction produces sufficient thermal energy for subsequent tasks, and (2) the adiabatic flame temperature of the SCWO reaction is controlled so that the material with which the SCWO reactor is constructed is able to withstand said temperature. Examples of suitable heating values are in the range of from about 300 to about 2500 Btu/lb. In embodiments, the concentration of the organics is adjusted to 8-20 wt%. In certain embodiments, the concentration of the organics is adjusted to 10-15 wt%. In certain embodiments, the feedstock is sufficiently dilute that no trimming water is necessary. In some cases, the water-feedstock mixture is neutralized to a pH in the range of from about six to about ten by a suitable means known to one skilled in the art.

[0053] Oxygen (liquid or gaseous) is separately pressurized to the same pressure level as the water-feedstock mixture (> 220 bar), which is then introduced to the water-feedstock mixture to form a reaction mixture (i.e., a process fluid). In some cases, trimming water, feedstock, and the oxygen source are separately pressurized to the same level (>220 bar) and mixed to form the SCWO process fluid. As shown in Figure 2, the trimming water stream SI is fed into pump 5 to be pressurized and becomes stream S2. The feedstock stream S3 is pressurized in pump 15 and becomes stream S4. Liquid oxygen feed stream S5 is pressurized in pump 25 and becomes stream S6. Oxygen stream S6 passes through a flash drum 35 to become gaseous oxygen stream S7 with no or minimum pressure decrease. Streams S2, S4 and S7 are at the same pressure level (> 220 bar) and mixed at point 40, forming the SCWO reaction mixture (i.e., SCWO process fluid) feed stream S8. Mixing point 40 represents a suitable mixing means known to one skilled in the art, without limitation.

[0054] 2. Preheating Zone. The formed SCWO process fluid is preheated in the at least one heat exchanger of the Preheating Zone to its kindling temperature so as to initiate the SCWO reactions. The kindling temperature depends on the composition and concentration of the organics in the process fluid feed stream. In some cases, the kindling temperature is in the range of from 200°C to 350°C. In some other cases, the kindling temperature is in the range of from 250°C to 350°C. In yet other cases, the kindling temperature is in the range of from 300°C to 350°C. Preheating of the process fluid feed stream to its kindling temperature is predominantly achieved by utilizing the thermal energy of the SCWO reaction effluent in a regenerative manner [details in section 5. Cooling Zone (I)]. To start up the SCWO process, a facilitative heating means is included. Said facilitative heating may be accomplished by passing the process fluid through a vessel wherein an electric heater or a heating jacket is provided. Said facilitative heating may also be accomplished by additionally heating the heat exchange fluid in the at least one heat exchanger of the Preheating Zone. Said additional heating is by a suitable heating means known to one skilled in the art, without limitation. Once the SCWO process is in full operation wherein the regenerative thermal energy of the SCWO reaction effluent is sufficient to raise the process fluid to its kindling temperature, said facilitative heating is terminated.

[0055] In exemplary embodiments, as shown in Figure 2, the Preheating Zone comprises a heat exchanger 100. In other embodiments, the use of more than one heat exchanger in the Preheating Zone is contemplated. The process fluid feed stream S8 is preheated to become stream S9 in heat exchanger 100, wherein a heat exchange fluid is introduced into heat exchanger 100 via stream S16 and increases the temperature of the process fluid to its kindling temperature, and then exits as stream SI 7. In embodiments, said heat exchange fluid is water. Stream S17 is recirculated by pump 45 to a heat exchanger in Cooling Zone (I) as stream SI 8, wherein stream S18 is heated by the SCWO reaction effluent to become stream S19 with increased thermal energy. In embodiments, stream SI 9 is fluidly coupled to stream S16 (not shown in Figure 2), forming a recirculation loop as a regenerative heat exchange system. In some embodiments, a facilitative heating means is added between stream SI 9 and stream S16 for SCWO process startup as described in the above paragraph.

[0056] 3. Reaction Zone. After the process fluid is heated to its kindling temperature, oxidation reactions of some organic material take place and because these reactions are exothermic, the temperature of the process fluid (i.e., reaction mixture) increases and reaches a temperature that is above the supercritical temperature for water (374°C), wherein SCWO reactions are enabled. In some cases, the pressure for SCWO reactions in the Reaction Zone is in the range of from 220 bar (3200 psia) to 290 bar (4200 psia). In some other cases, the pressure for SCWO reactions in the Reaction Zone is in the range of from 234 bar (3400 psia) to 262 bar (3800 psia). In yet other cases, the pressure for SCWO reactions in the Reaction Zone is in the range of from 250 bar (3626 psia) to 262 bar (3800 psia).

[0057] In embodiments, the reaction zone comprises one or more SCWO reactors. These reactors are constructed with a suitable material that is able to withstand SCWO reaction conditions, including factors such as temperature, pressure, and oxidative reactants. The extent and processing capacity of a SCWO process, and the temperature of the reaction effluent practically obtainable are limited by the construction material one may find for SCWO reactors. For example, if the SCWO reactor material is able to withstand a temperature up to 600°C, the heating value and flow rate of the process fluid need to be adjusted so that the reaction mixture does not exceed 600°C. In some cases, the reactor is designed so that the reaction mixture exits the reactor before reaching the temperature limit of the material. In some other cases, a cooling means is provided for the SCWO reactor to prevent material failure. Such a cooling means is known to one skilled in the art without limitation. Examples of construction material for a SCWO reactor are Inconel 625 and Hastelloy C-276. Another exemplary construction material for SCWO reactors is HAYNES® 230® ALLOY, which is a Ni-Cr-W-Mo alloy that is able to withstand temperature up to 700°C with excellent oxidation resistance, long term stability, and good fabricability. Other alloys with similar properties, as will be understood by those of skill in the art, may be successfully used without departing from the spirit of the invention. In embodiments, SCWO reactors are thermally insulated with a suitable insulation material known to one skilled in the art, without limitation. In this context, air is considered as a thermal insulation material for SCWO reactor.

[0058] In exemplary embodiments, as shown in Figure 2, the Reaction Zone comprises a SCWO reactor 150. In other embodiments, the configuration of more than one SCWO reactor in the Reaction Zone is contemplated. Reactor 150 is thermally insulated as an approximately adiabatic reactor. Preheated process fluid S9 is introduced into Reactor 150 and the organic material contained therein is substantially oxidized within Reactor 150, after which a reaction effluent is formed as stream S10.

[0059] 4. Steam Generation Zone. The Steam Generation Zone comprises at least one heat exchanger, wherein water is utilized as the heat exchange fluid and is transformed into steam by the thermal energy of the SCWO reaction effluent. In embodiments, purified (desalinated) water is utilized for steam generation so that no or minimal scale forms in the heat exchanger(s) of the Steam Generation Zone.

[0060] In exemplary embodiments, as shown in Figure 2, the Steam Generation Zone comprises heat exchanger 200 and heat exchanger 300. Reaction effluent stream S10 is introduced into heat exchanger 200 and exits as stream SI 1. Stream Sl l is further cooled in heat exchanger 300 and becomes stream SI 2. In certain embodiments, heat exchanger 300 is configured to receive a heated water stream S22 to generate steam as stream S23. In some cases, stream S22 is heated by SCWO reaction effluent [details in section 6. Cooling Zone (II)]. In some other cases, stream S22 is heated by a suitable heating means known to one skilled in the art, without limitation. In yet other cases, stream S22 is not heated. Steam stream S23 is then introduced into heat exchanger 200 and super-heated to become steam stream S24. Stream S24 is then introduced into turbine 55 to generate electricity and exits as stream S25. In certain embodiments, more than one turbine is contemplated in the configuration for electricity generation. In certain embodiments, stream S25 is recycled as water feed for steam generation. For example, stream S25 may be fluidly coupled to stream S20 (not shown in Figure 2).

[0061] 5. Cooling Zone (I). SCWO reaction effluent exiting the Steam Generation Zone still has a significant amount of thermal energy, which energy is able to preheat the process fluid feed stream to its kindling temperature. Therefore, process fluid exiting Steam Generation Zone is introduced to Cooling Zone (I), which comprises at least one heat exchanger. In exemplary embodiments, as shown in Figure 2, Cooling Zone (I) includes heat exchanger 400. In other embodiments, the configuration of more than one heat exchanger in the Cooling Zone (I) is contemplated. Reaction effluent stream S12 is introduced into heat exchanger 400 and exits as stream SI 3. In heat exchanger 400, a heat exchange fluid is recirculated between the Preheating Zone and Cooling Zone (I). In certain embodiments, as described in section 2. Preheating Zone, water is recirculated as the heat exchange fluid. Stream S18 is heated in heat exchanger 400 by SCWO reaction effluent stream S12 and becomes stream S19 with increased thermal energy. Stream SI 9 is fluidly coupled to stream S16 either directly or indirectly (not shown in Figure 2), forming said recirculation loop as a regenerative heat exchange system. In some embodiments, a facilitative heating means is added between stream S19 and stream SI 6 to start up the SCWO process. Once the SCWO process is at steady state wherein the regenerative thermal energy of the SCWO reaction effluent is sufficient to raise the process fluid to its kindling temperature, said facilitative heating is terminated.

[0062] 6. Cooling Zone (II). In certain embodiments, the process fluid exiting Cooling Zone (I) has a temperature in the range of from 100°C to 200°C, suggesting that further energy recovery is possible and valuable. Cooling Zone (II) accomplishes the following three purposes: (1) to further recover heat for steam generation; (2) to generate hot water with the remaining thermal energy; and (3) to cool the process fluid to near room temperature (e.g. 30 to 40°C), depending upon the lowest temperature of cooling water available. In some embodiments, Cooling Zone (II) is coupled to Preheating Zone as the regenerative heat exchange system. In some other embodiments, Cooling Zone (II) is coupled to both Preheating Zone and Cooling Zone (I) as the regenerative heat exchange system.

[0063] In exemplary embodiments, such as shown in Figure 2, Cooling Zone (II) comprises heat exchanger 500 and heat exchanger 600. SCWO reaction effluent stream S13 is introduced into heat exchanger 500 and exits as stream SI 4, which is then sent to heat exchanger 600 and exits the SCWO system as stream S15. Heat exchanger 500 is utilized in this exemplary case to raise the temperature of a purified water stream S21 for steam generation. Stream S21 is heated in heat exchanger 500, becomes stream S22, and is introduced to heat exchanger 300 of Steam Generation Zone. In some cases, water stream S21 is obtained by pressurizing purified water feed stream S20 via pump 65. In heat exchanger 600, the temperature of the process fluid is cooled to near room temperature (e.g. 30 to 40°C), depending upon the lowest temperature of cooling water available. Said cooling water is introduced into heat exchanger 600 as stream S26 and exits as stream S27. In some cases, the temperature of stream 27 is in the range of from 50°C to 100°C. In some other cases, the temperature of stream 27 is in the range of from 60°C to 95°C. In yet other cases, the temperature of stream 27 is in the range of from 70°C to 95°C. In certain embodiments, the temperature of stream 27 is in the range of from 80°C to 95°C. In certain embodiments, stream S27 is directly utilized to provide heating for facilities, e.g., dormitories, office buildings, residential buildings.

[0064] 7. Disposal of Process Fluid. After the process fluid passes through the described SCWO system, the effluent mixture is a combination of three phases. A first phase is gaseous and typically includes, as major constituents: carbon dioxide; unreacted oxygen; and, if air is used as the oxidant, nitrogen. Minor constituents of the gaseous phase may include, for example: carbon monoxide and nitrous oxide. A second phase is liquid and generally includes water with carbon dioxide and inorganic salts dissolved therein. Such inorganic salts include, for example, calcium sulfate, sodium chloride, sodium phosphate, sodium carbonate, sodium sulfate, and potassium sulfate. A third phase includes solid particulates that may include, for example, oxides, carbonates, and other inorganic materials which are water- insoluble.

[0065] Upon discharge from heat exchanger 600 (Figure 2), the effluent stream S15 is directed to a three-phase separation system (not shown in Figure 2). Said separation system allows separation of the gaseous, liquid and solid effluent components into separate streams prior to depressurization. The resulting solid, liquid, and gaseous effluent streams are then depressurized separately, thereby avoiding depressurization of a multi-phase effluent mixture.

[0066] In certain embodiments, effluent mixture stream S15 passes through a separator (not shown in Figure 2), wherein the gaseous phase is vented from the upper part of the separator and then depressurized to below the critical pressure of water by means known to one skilled in the art, without limitation. The solids settle and collect at the bottom of the separator and are periodically removed from the separator via, for example, a bottom outlet. Such solids may include transition metals, heavy metals, rare earth metal oxides and metal carbonates, and insoluble inorganic salts. The rest of the effluent mixture, which contains the liquid phase and some solid particulates, exits said separator via another outlet disposed at the lower portion of the separator. The solid particulates are separated from the liquid via a proper means known to one skilled in the art without limitation. The liquid phase is then depressurized via a suitable means, such as a back-pressure regulator or a flow control valve. In some cases, the liquid phase passes through further processing, including removal of dissolved inorganic salts by conventional methods, such as evaporation or reverse osmosis.

Example 1

[0067] According to the exemplary design of a SCWO system shown in Figure 2, an exemplary experiment is carried out by software ASPEN to generate the results shown in Table 2 and Table 3. Table 1 shows the composition of the process fluid feed stream (S8 and S9). The calculations are based on a throughput of 5-15 Dry Tons Per Day (DTPD) of sludge processing capacity with 80% of the organics available for SCWO reactions.

[0068] Table 2 summarizes the heat duty of flash drum 35; heat exchanger 100, 200, 300, 400, 500, and 600; and reactor 150 shown in Figure 2. Table 2 also presents the work power of pump 5, 15, 25, 45, and 65; and turbine 55 shown in Figure 2. In Table 2, positive numbers represent duty or power input into the SCWO system; negative numbers represent duty or power output from the SCWO system. In this example, turbine 55 produces 351295 W (i.e., 0.35 MW) of power based on a 6 total Dry Tons Per Day (DTPD) of sludge processing capacity. Table 3 presents the temperature, pressure, mass flow rate, and vapor fraction of each stream (S1-S27) shown in Figure 2.

[0069] Heat exchanger 200, 300, and 500 collectively produce high quality steam (stream S24: 615°C, 31 bar) utilizing the thermal energy of the SCWO reaction effluent. Heat exchanger 200 is used to super-heat the generated steam from heat exchanger 300, which receives the heated water stream from heat exchanger 500. The temperature profile of heat exchanger 200 shown in Figure 2 is illustrated in Figure 3a; the temperature profile of heat exchanger 300 is illustrated in Figure 3b; the temperature profile of heat exchanger 500 is illustrated in Figure 3c. In Figures 3a-3c, the top curve represents the temperature of the process fluid and the bottom curve represents the temperature of the heat exchange fluid. The average temperature difference between the process fluid and the heat exchange fluid in heat exchanger 200 is 91°C; the average temperature difference in heat exchanger 300 is 149°C; and the average temperature difference in heat exchanger 500 is 39°C.

Table 1

Stream S8 Flow Rate (kg/hr)

C₆H₈N2 72.16

C₆H₆ 1.64

H₂0 1685.544

Total without inorganic solids 1,874.88

Inorganic solids (S1O2) 47.34

Total with inorganic solids 1,922.22

Total solids without water 236.68

Organics in total solids 80.00

Total dry solids 236.68

Sludge concentration (wt%) 12.31

Stream S9 Temperature 250

Table 2

[0070] Furthermore, it is to be noted that stream S14 (effluent from heat exchanger 500) has a temperature of 92°C, which provides heat to stream S26 in heat exchanger 600 to produce hot water stream S27. In this example, heat exchanger 600 produces hot water stream S27 at 61 °C. By varying the design parameters of heat exchanger 600, hot water at a higher temperature may be produced, for example, hot water having a temperature of 80-85 °C.

Table 3

S8 33 250 2341 0.12

S9 250 247 2341 0.15

S10 675 243 2341 0.99

Sll 613 240 2341 0.99

S12 315 236 2341 0.22

S13 156 233 2341 0.09

S14 92 229 2341 0.09

S15 35 226 2341 0.09

S16 300 228 1911 0.00

S17 67 214 1911 0.00

S18 69 241 1911 0.00

S19 300 238 1911 0.00

S20 30 1 1223 0.00

S21 31 41 1223 0.00

S22 139 38 1223 0.00

S23 491 34 1223 1.00

S24 615 31 1223 1.00

S25 80 0 1223 1.00

S26 25 14 3276 0.00

S27 61 14 3276 0.00

Example 2

[0071] According to the exemplary design of a SCWO system shown in Figure 2, further experiments are carried out by software ASPEN to generate the results shown in Table 4, wherein some results of Run 1 are shown also in Table 2 and Table 3. Table 1 shows the composition of the process fluid feed stream (S8 and S9) for Run 1-4. All calculations are based on a throughput of 6 Dry Tons Per Day (DTPD) of sludge processing capacity with 80% of the organics available for SCWO reactions.

Table 4

Stream S25 [turbine exhaust] vapor fraction 1.00 0.99 0.97 0.87

Stream S14 temperature (°C) 92 92 92 90

Stream S24 [steam] pressure (psia) 450 900 1200 3700

Turbine 55 power (W) 351,295 375,929 385,743 417,262

[0072] By varying the heat exchanger design parameters, different qualities of steam may be produced, for example, steam (stream S24) at pressures of 450 psia, 900 psia, 1200 psia, and 3700 psia. The higher the pressure of the steam, the more electricity is generated via turbine 55, for example, 0.35 MW, 0.38 MW, 0.39 MW, and 0.42 MW, all based on a 6 total Dry Tons Per Day (DTPD) of sludge processing capacity. Therefore, it is envisaged that steam at any pressure in the range of from 300 psia (21 bar, 2.1 MPa) to 4000 psia (276 bar, 27.6 MPa) may also be generated by the exemplary design of the SCWO system. As a result, the pressure of generated steam for electricity production may be tailored according to the types of steam turbines that are practically available at any given time.

[0073] It is further noted that stream S24, the effluent from heat exchanger 500, has a temperature of 92°C or 90°C. By varying the design parameters of heat exchanger 600, hot water of varying temperatures may be produced. For example, in certain embodiments, the temperature of the hot water produced is 85°C or higher. In some cases, the temperature of the hot water produced is 50°C-85°C. In some cases, the temperature of the hot water produced is 60°C-85°C. In some cases, the temperature of the hot water produced is 70°C-85°C. In some cases, the temperature of the hot water produced is 80°C-85°C. In some scenarios, hot water produced therein is directly utilized to provide heating for various facilities.

[0074] III. Tubular Reactor Assembly Configuration. Now referring to Figures 4a-4c, a tubular reactor assembly configuration is presented for an exemplary SCWO system as shown in Figure 1, which is able to (1) produce steam of various pressures for electricity generation; (2) produce hot water for facility heating; and (3) preheat the process fluid feed stream in a regenerative manner for the SCWO system. Figure 4a illustrates the Preheating Zone and Reaction Zone of the tubular reactor assembly. Figure 4b illustrates the Steam Generation Zone, Cooling Zone (I), and Cooling Zone (II) of the tubular reactor assembly. Figure 4c illustrates exemplary layouts of the tubular reactor assembly.

[0075] The tubular reactor assembly is constructed as a series of double pipes (tube-in-tube pipes) with fluidly connected inner pipe as the process fluid passage and fluidly connected annulus, which annulus is designed to be either thermally insulated or to block or allow passage of a heat exchange fluid. The connected inner pipe has one process fluid inlet at the beginning of the series of double pipes (i.e., the tubular reactor assembly) and one process fluid outlet at the end, with a constant inner diameter (ID) and substantially smooth inner surface. The connected annulus has many inlets and outlets for the heat exchange fluid, positioned according to the desired heat exchange needs. In embodiments, some of the inlets and outlets of the annulus are blocked so as to continue the flow of the heat exchange fluid in the next section of the annulus. In some cases, the function of an inlet and outlet pair is switched to reverse the direction of the flow of the heat exchange fluid if desired.

[0076] In some embodiments, the radius of the inner pipe of the tubular reactor assembly is 2 inches. In some other embodiments, the radius of the inner pipe of the tubular reactor assembly is 1 inch. In embodiments, the pressure of the heat exchange fluid in the annulus is close to the pressure of the process fluid in the inner pipe. Such a pressure balance enables the use of a thin wall for the inner pipe, which in turn reduces the heat transfer resistance across the inner pipe wall. During startup and shutdown, caution must be exercised to insure that such a pressure balance is maintained.

[0077] SCWO process fluid contains substances that may settle as solid particulates to form deposits/scale on the inner surface of the apparatus, such as silica, alumina, and oxides and carbonates of transition metals, heavy metals, and rare earth metals. In most cases, such substances are insoluble in water above or below its supercritical point. Over time, the accumulated deposits and scale within the SCWO system cause the heat transfer rate to decrease and thus necessitate cleaning of apparatus. To reduce the rate of scale/deposit build-up, the process fluid is passed through in the inner pipe at a velocity sufficient to prevent settling of a substantial portion of solid particles from the process fluid.

[0078] Furthermore, after a long duration of operation, the inner pipe of the tubular reactor assembly is cleaned by a suitable means known to one skilled in the art. For example, a mechanical cleaning brush is sent to pass through the inner pipe of the tubular reactor assembly. The bristles of the cleaning brush may be constructed of, for example, Inconel 625, Hastelloy C-276, stainless steel, or nylon. When using the on-line cleaning method, the entire brush is constructed from the same material used for tubular reactor assembly so as to preserve the integrity of brush at the operating condition of the system. When using the off-line cleaning method, bristle materials are chosen to provide adequate friction to remove the hardest solid deposits likely to be encountered. Other solids removal means includes high velocity cleaning spray. The cleaning spray includes a gas or a liquid from the effluent mixture or other suitable material at supercritical conditions. Finely dispersed solids may also be sprayed by a nozzle, either alone or dispersed within a fluid, to remove solids collected within the tubular reactor assembly. Cleaning of the inner pipe by a brush, spray or by other means is performed periodically so that formation of hardened scale (for example, sodium sulfates and calcium sulfates) is thereby substantially reduced.

[0079] In the section of the annulus of the double pipe assembly for steam generation, for example, Steam Generation Zone and part of Cooling Zone (II), purified (desalinated) water is passed through as the heat exchange fluid. Consequently, there is no expectation of scale formation in this section of the annulus. For the Preheating Zone, Cooling Zone (I), and part of Cooling Zone (II) of the annulus of the double pipe assembly, because the average temperature difference between the heat exchange fluid in the annulus and the process fluid in the inner pipe is below 100°C or even below 50°C, scale formation is very slow or negligible. In some cases, if purified (desalinated) water is used in these parts of the annulus, no scale formation is expected to take place. The annulus of the Reaction Zone of the double pipe assembly is thermally insulated either with air or with a suitable insulation material known to one skilled in the art, without limitation.

[0080] The double pipe reactor assembly is constructed with suitable material such as stainless steel, Inconel 625, Hastelloy C-276, and HAYNES® 230® ALLOY. For the sections wherein the SCWO process fluid is at high temperature (500-700°C, for example, sections close to the Reaction Zone) double pipe is constructed with Inconel 625, Hastelloy C-276, or HAYNES® 230® ALLOY. The rest of the double pipe reactor assembly may be constructed with these materials or stainless steel, wherein economic factors are to be considered.

[0081] 1. Preheating Zone and Reaction Zone. Referring now to Figure 4a, the Preheating Zone and the Reaction Zone of the double-pipe reactor assembly is represented by assembly 2000. The Preheating Zone of the double-pipe reactor assembly is represented by zone Zl, comprising the first three runs of the double pipes (1^st, 2^nd, and 3^rd). The Reaction Zone of the double-pipe reactor assembly is represented by zone Z2, comprising the next four runs of the double pipes (4^th, 5^th, 6^th, and 7^th). Process fluid feed stream S201 enters inner pipe 290 via inlet 210 located on the 1^st run and exits inner pipe 290 as stream S202 via outlet 220 located on the 7^th run. The U-bends that connect the runs of the double pipe have a mild bend radius to allow smooth passage of cleaners inside inner pipe 290. For example, the bend radius of the U-bends is 1-2 feet.

[0082] The heat exchange fluid (e.g., water) enters the annulus of the double pipe as stream S203 via inlet 211 located on the 3^rd run; passes through the first 3 runs of the double pipe; and exits the annulus of the double pipe as stream S204 via outlet 212 located on the 1^st run. The heat exchange fluid flows in the direction opposite that of the process fluid, constituting a double pipe countercurrent heat exchanger. Dark dots 219 represent the blocked-off inlets/outlets of the annulus. Grid area 230 represents the annulus passage for the heat exchange fluid. Shaded area 240 represents void or thermally insulated annulus for the Reaction Zone of the SCWO system. The support structure 250 for assembly 2000 may be any known to one skilled in the art.

[0083] Comparing Figure 4a with Figure 2, stream S201 is stream S8 in Figure 2; stream 202 is stream S10 in Figure 2; stream 203 is stream S16 in Figure 2; and stream 204 is stream S17 in Figure 2. Zone Zl composed of the first three runs of the double pipe in Figure 4a is heat exchanger 100 in Figure 2. Zone Z2 composed of the next four runs of the double pipe in Figure 4a is reactor 150 in Figure 2.

[0084] 2. Steam Generation Zone, Cooling Zone (I) and (II). Referring now to Figure 4b, the Steam Generation Zone, Cooling Zone (I) and (II) of the double-pipe reactor assembly is represented by assembly 3000. Steam Generation Zone of the double-pipe reactor assembly comprises the 1^st, 2^nd, and 3^rd runs of the double pipe; the 6^th run of the double pipes is part of Cooling Zone (II), which facilitates steam generation. Cooling Zone (II) of the double-pipe reactor assembly also comprises the 7^th run of the double pipe to produce hot water. Cooling Zone (I) of the double-pipe reactor assembly comprises the 4^th and 5^th runs of the double pipes to preheat the process fluid feed stream in a regenerative manner for the SCWO system. [0085] Process fluid feed stream S301 enters inner pipe 390 via inlet 310 located on the 1^st run and exits inner pipe 390 as stream S302 via outlet 320 located on the 7^th run. The U-bends that connect the runs of the double pipe have a mild bend radius to allow smooth passage of a cleaning device inside inner pipe 390. For example, the bend radius of the U-bends is 1-2 feet. Comparing Figure 4b with Figure 2, stream S301 is stream S10 in Figure 2; and stream 302 is stream S15 in Figure 2.

[0086] For steam generation, a purified (desalinated) water feed stream S305 enters the annul us of the double pipe via inlet 311 located on the 6^th run; exits via outlet 312 also located on the 6^th run into cross-over pipe 360; re-enters the annulus of the double pipe via inlet 313 located on the 3^rd run; passes through the first 3 runs of the double pipe; and finally exits as steam stream S306 via outlet 314 located on the 1^st run of the double pipe. Water flows in the direction opposite that of the process fluid, constituting a double pipe countercurrent heat exchanger. Comparing Figure 4b with Figure 2, stream S305 is stream S21 in Figure 2; and stream 306 is stream S24 in Figure 2. The 6^th run of the double pipe in Figure 4b is heat exchanger 500 in Figure 2 as part of Cooling Zone (II); the 1^st, 2^nd, and 3^rd runs of the double pipe in Figure 4b altogether accomplish the tasks of heat exchanger 200 and heat exchanger 300 in Figure 2 as the Steam Generation Zone shown in Figure 1.

[0087] With respect to Cooling Zone (I), a heat exchange fluid stream (e.g., water) S303 enters the annulus of the double pipe via inlet 315 located on the 5^th run; passes through the 5^th and the 4^th runs of the double pipe; and finally exits as stream S304 via outlet 316 located on the 4^th run of the double pipe. The heat exchange fluid flows in the direction opposite that of the process fluid, constituting a double pipe countercurrent heat exchanger. Comparing Figure 4b with Figure 2, stream S303 is stream S18 in Figure 2; and stream 304 is stream S19 in Figure 2. The 4^th and 5^th runs of the double pipe in Figure 4b is heat exchanger 400 in Figure 2. Therefore, the 4^th and 5^th runs of the double pipe assembly 3000 in Figure 4b and the first three runs of the double pipe assembly 2000 in Figure 4a constitute the regenerative heat exchange system to preheat the process fluid feed stream to its kindling temperature.

[0088] With respect to Cooling Zone (II), a heat exchange fluid stream (e.g., water) S307 enters the annulus of the double pipe via inlet 317 located on the 7^th run and exits as stream S308 via outlet 318 also located on the 7^th run of the double pipe. The heat exchange fluid flows in the direction opposite that of the process fluid, constituting a double pipe countercurrent heat exchanger. Comparing Figure 4b with Figure 2, stream S307 is stream S26 in Figure 2; and stream 308 is stream S27 in Figure 2. The 7^th run of the double pipe in Figure 4b is heat exchanger 600 in Figure 2 as part of Cooling Zone (II) shown in Figure 1.

[0089] Dark dots 319 represent the blocked-off inlets/outlets of the annulus. Grid area 330 represents the annulus passage for the heat exchange fluids. Shaded area 340 represents blanked-off annulus sections, wherein no passage is provided for the heat exchange fluids. The support structure 350 for assembly 3000 may be any known to one skilled in the art.

[0090] 3. Layouts of Tubular Reactor Assembly. Figure 4c present exemplary illustrations of the layout of the tubular reactor assembly.

[0091] The upper part of Figure 4c illustrates an exemplary layout 4000 for the double pipe reactor assembly. In certain embodiments, the inner pipe of double pipe reactor assembly 2000 shown in Figure 4a, represented by A410, is connected to the inner pipe of double pipe reactor assembly 3000 shown in Figure 4b, represented by A420, via S-shape connecter 450, providing a continuous passage for the process fluid. In certain embodiments, the Preheating Zone of the double-pipe reactor assembly comprises the top three runs of double pipe shown in Figure 4a with a total length of 240 feet; the Reaction Zone of the double-pipe reactor assembly comprises the 320-foot long bottom four runs of double pipe shown in Figure 4a and a 80-foot long S-shape connecter with a total length of 400 feet. In some cases, S-shape connecter 450 is also utilized to provide passage for the effluent from the double pipe reactor assembly to a separation system (not shown in Figure 4c). In embodiments, S-shape connecter 450 is constructed with a suitable material, such as stainless steel, Inconel 625, Hastelloy C-276, and HAYNES® 230® ALLOY, without limitation. The suitable material for constructing S-shape connecter 450 is based on the highest temperature of the process fluid that passes through the connecter. In embodiments, the inner diameter (ID) of S-shape connecter 450 is the same as the ID of the inner pipe of the double pipe reactor assemblies. In certain embodiments, S-shape connecter 450 is expandable and contractible so that the SCWO system may be constructed within the available space.

[0092] The lower part of Figure 4c illustrates another exemplary layout for the double pipe reactor assembly with 5000 as the front view and 5000' as the side view of said layout. This layout enables the construction of a SCWO system in a compact space. Support frame 550 is constructed with any suitable material known to one skilled in the art without limitation, such as concrete. In some embodiments, a suitable thermal insulation material is added to support frame 550. In embodiments, double pipes are placed in support frame 550 horizontally. In exemplary embodiments, the double pipes are connected to one another at the two ends via U- bends 510 and 520. As illustrated by side view 5000', U-bends may be placed horizontally, vertically, or diagonally, depending on the fluid connection needed. U- bends 510 and 520 have the same inner diameter and outer diameter as the double pipe. The inner pipe of U-bends 510 and 520 also has a smooth inner surface and a mild bend radius that provides passage for cleaners.

[0093] The layouts in Figure 4c are for illustration purposes only and are not drawn to be exact. Furthermore, these layouts are also not to be limiting because one skilled in the art is able to design many different layouts based on the disclosure provided herein. Therefore, these layouts are to be considered as equivalents, which are within the scope of this disclosure.

[0094] IV. Processing Capacity and Design Variables. Example 2 (Run 1-4) illustrates that 6 Dry Tons Per Day (DTPD) of sludge is able to generate steam at pressures of 450 psia, 900 psia, 1200 psia, and 3700 psia, which respectively generate in a turbine 0.35 MW, 0.38 MW, 0.39 MW, and 0.42 MW of power. It is understood that the disclosed exemplary configurations may be scaled for larger processing capacity or multiple configurations may be operated in parallel to process greater amounts of sludge. Small conventional steam turbines that operate at 800 to 900 psi typically range from 0.5 to 3 MW. Thus, 900 psi steam generation matches conventional turbines for a SCWO system with processing capacity of 5 to 25 Dry Tons Per Day (DTPD) of wastewater treatment sludge.

[0095] The flow rate of water used to generate steam is a design variable that may be chosen over a broad range. However, this flow rate impacts the amount of energy recovered and degree of superheat attainable for the steam produced. For example, increasing the water flow rate increases the energy recovered as steam but decreases the degree of superheat. The pressure of the steam generated is a design variable that ranges from 1 bar (14.5 psia) to 276 bar (4000 psia), thus providing steam at low to high pressure. In some embodiments, SCWO systems for power generation (for example, from conventional or non-conventional fuels) have throughput as high as 100 to 1,000 tons per day (using multiple parallel units if necessary). For such cases, high pressure steam (1200 psi to 3500 psi) is produced as a desired product. The configuration illustrated in Figure 2 may be used for such cases, for example.

[0096] V. SCWO Process for Energy Recovery/Production. Referring to Figure 5, a design of a SCWO system for energy production from an organic matter is illustrated. In an embodiment, the organic matter comprises coal or lignite. The feed comprises pulverized coal (e.g., 100-500 micron or 0-200 micron particles) and water with no oxygen. The feed slurry is pumped through a preheater and/or a startup heater to a suitable pressure (e.g., 220 bar or higher) and temperature (e.g., ignition or kindling temperature) to initiate the oxidation reactions. Oxygen is provided through the multiport oxygen injection system, which is placed along the length of the reactor. The use of the multiport oxygen injection system enables more precise and accurate control of the oxidation reaction rate and helps to prevent run-away reactions, spontaneous combustion, possible explosion, and char formation. The oxygen profile in the reactor is also controlled by such multiport oxygen injection system. In an embodiment, the use of multiport oxygen injection system reduces the amount of oxygen needed. In an embodiment, the residence time of the process fluid between adjacent oxygen injection ports in the multiport oxygen injection system is no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds.

[0097] In an embodiment, the reactor is designed for adiabatic reaction/oxidation. In an embodiment, the residence time of the process fluid in the reactor is no more than 2 minutes. In an embodiment, the residence time of the process fluid in the preheater and reactor is no more than 2 minutes. In an embodiment, the residence time of the process fluid in the preheater and reactor is no more than 1 minute. In an embodiment, the residence time of the process fluid in the preheater and reactor is no more than 30 seconds. In an embodiment, the residence time of the process fluid in the preheater and reactor is no more than 20 seconds. The residence time affects reactor design, e.g., it is a factor determining how long the reactor is. The content (e.g., wt%) of organics in the feed affects the reactor effluent temperature.

[0098] In an embodiment, the temperature in the reactor for the oxidation of coal is in the range of 500-950°C or 650-700°C or 600-650°C or 550-600°C. In an embodiment, the percentage of coal oxidized in the reactor is more than 90% or 95% or 99% or 99.9%. In an embodiment, the SCWO of coal avoids char formation. In the reactor, the settling solids at high velocities have a slow build up/scale. This is a particulate scale, not crystalline scale. As shown in Figure 5, a pigging device is used periodically to remove the particulate scale, e.g., a few minutes per day or per shift or every other shift. In an embodiment, the pigging device is used 1-20 minutes/day, 5-10 minutes/day, or 5 minutes/day. Any frequency of the use of such pigging device is contemplated. Any other suitable descale devices or pipe cleaners are also contemplated.

[0099] Following the reactor is a series of tube-in-tube heat exchangers. In an embodiment, the heat exchangers are operated counter-currently with approximately the same ΔΤ (average temperature difference) throughout. The heat exchangers are operated so as to keep the entropy generation minimum. In an embodiment, the reactor assembly is 200-ft long made from 40-ft long pipes.

[00100] The sequence of the heat exchangers is designed so as to maximize power generation through steam turbine by taking heat from the process stream at its hottest point. The heat extracted from the process stream may be used for (1) preheating the process stream; (2) making clean steam for the high pressure turbine by completely oxidizing the organic in the process stream; (3) generating clean hot water (e.g., about 180°C) for other uses (e.g., providing for household use, hotel use).

[00101] The effluent from the heat exchangers comprises three phases. In an embodiment, the gas phase comprises C and CC , the aqueous phase comprises salts; the solid phase comprises particulates. The effluent exits at high pressure and needs to be depressurized (e.g., from 250 atm to 1 atm). The effluent is separated by phase at high pressure, after which each phase is depressurized separately.

[00102] The SCWO process almost completely consumes coal without producing char or harmful S-, N- gases. Heavy metals are oxidized to the highest state and exit with the aqueous effluent that is clean. Silica and alumina are the main solids (95%) from waste water. The rest are inorganic oxides (e.g., 5%), calcium sulfate (e.g., 4%). In an embodiment, the solid/particulate is an orange color stream containing calcium sulfate. In an embodiment, particle size in the solids residue has a range of 0.5-200 micron, which is insoluble in water and could be used for other purposes, e.g., roofing, construction.

[00103] VI. Three-Phase Separator. The effluent from a SCWO process usually contains a mixture of three phases: vapor, liquid, and solid, all at an elevated pressure and relatively low temperature (e.g., pressure greater than about 250 bar and temperature in the range of from about 25°C to about 100°C). The major components of the fluid phases are O2, H2O, and CO2. Depressurization of this mixture presents severe erosion problems, from either or both of liquid droplets in gas or solids dispersed in liquid. Depressurizing the vapor phase is enhanced by first removing moisture and then depressurizing it. The resulting product is a 2-phase mixture of liquid CO2 and gaseous O2 at -51°C. The liquid CO2 purity is above 99%. However, the drying step by conventional means (e.g., fixed bed adsorption) is costly. The 3- phase separator and its use as described herein is able to separate and remove the least volatile component (e.g., H2O) of a mixture by freezing out that component on the inner wall of a jacketed pipe and subsequently scraping and/or melting the solid off of the wall. The freezing-melting process operates as a semi-batch process and requires two jacketed parallel pipes, one doing the freezing while the other is regenerated by melting. In some embodiments, the freezing-scraping or freezing- melting process is operated continuously: the solid scraped off of the inner surface of a jacketed cylindrical vessel falls into the conical bottom of the vessel, which is also jacketed and maintained at a temperature slightly above the freezing point, thereby melting the solid so that the liquid is removed from the conical bottom while the more volatile components exit the top of the vessel.

[00104] Referring to Figure 6, a 3-phase separator is shown for the separation and depressurization of 3-phase mixtures at high pressures and moderate temperatures. For example, the 3-phase mixture contains water, oxygen, and carbon dioxide at high pressures and moderate temperatures, as one might find as the effluent of a SCWO process. Such a separator can be used in the flow path at the end of the process fluid pipe, after cooling down to a temperature in the range of 25°C to 100°C. The steps proceed in the following order: (1) removal of inorganic solids by filtration; (2) separation of liquid and vapor by gravity settling; (3) removal of moisture from the gas by freezing, and finally depressurization of each of the fluid phases (not shown).

[00105] The apparatus shown in Figure 6 is a VLS (vapor-liquid-solid) separator or a 3-phase separator. The separator comprises an expanding inlet tube, a vessel, a liquid level detector (or a liquid level measurement device), two heat exchangers fluidly connected to the vessel, and valves to control fluid flow. The vessel of the VLS separator is tall enough to contain liquid at the bottom and froth at the top with gas phase above the froth. The expanding inlet has a diverging inner diameter to slow down the feed stream entering the separator. In some embodiments, the two heat exchangers are jacketed pipes wherein the jacket is configured to receive either a coolant or a heating medium/fluid. In some embodiments, the two heat exchangers are double pipe heat exchangers configured to receive either a coolant or a heating medium/fluid. In an embodiment, the two heat exchangers are configured to be in parallel to one another with one being used in a cooling cycle and the other being used in a heating cycle. When ice buildup in the cooling-cycle heat exchanger needs to be melted, the cooling cycle heat exchanger is switched to the heating cycle and the heating cycle heat exchanger is switched to the cooling cycle. In some embodiment, the VLS separator comprises more than two heat exchangers. Each of the heat exchangers is fluidly connected to a gas effluent outlet.

[00106] The primary function of the VLS separator is to separate the effluent phases so that each can be depressurized without eroding the depressurizing valve. It receives the effluent from the reactor after cooling it in several heat exchangers. In an embodiment, the last heat exchanger cools this stream to a temperature in the range of 30°C to 40°C. At this temperature, the effluent consists of three phases: an aqueous liquid phase (PI) with inorganic solids (P2) dispersed in it, and CO2 dissolved in it, and a light fluid phase (P3) which is mostly CO2 with water dissolved in it.

[00107] The incoming fluid mixture for the VLS separator enters an expanding inlet, which slows down the flow rate to allow light and heavy phases to disengage from one another. This slow-down process is initiated by using an inlet tube with a diverging inner diameter. In some embodiments, the smallest inner diameter of the inlet tube is large enough to accept the cleaning device on its passage to the bottom of the vessel.

[00108] The two fluid phases then disengage from one another in the space labelled "Froth". The cross-section of the froth region is large enough to provide for a slow rise of the vapor (CC -rich) phases. The rising vapor carries with it a small amount of moisture equal to the solubility of water in equilibrium with CO2 at the bulk fluid temperature of the liquid in the device. The stream leaving through the top of the device will ice up on the depressurization valve's (not shown) inner surface of the exit tube and the solid buildup will eventually clog that tube.

[00109] As shown in Figure 6, the exit vapor stream is intercepted in a tube-in-tube heat exchanger. Ice is formed on the inner surface of the tube-in-tube heat exchanger by passing a coolant through the annulus of the exchanger. The coolant temperature will determine how fast the inner tube will clog. The time-to-clog is used to calibrate empirically the cycle time.

[00110] While the left half of the device is cooling and depressurizing, the right half is defrosting. In the switch-over, the tube-in-tube exchanger on the right has had warm water flowing through it. The water droplets settle to the bottom of the vessel, along with the cleaning devices.

[00111] The 3-phase separator or the VLS separator as discussed herein directs the flow of the gaseous effluent to a vertical double pipe heat exchanger. A coolant flows through the annulus and moisture is condensed on the inside surface of the inner pipe. Ice crystals and liquid droplet either fall back down into the gas/liquid- solid separator or they build up on the inner pipe. When enough solids form to reduce flow out of the top of the double pipe exchanger, flow is switched to a second vertical double pipe exchanger, which has coolant running through it. The coolant flow to the first exchanger is then stopped and warm water is passed through the first vertical exchanger. Ice formed in the first exchanger is melted and falls back down into the gas/liquid-solid exchanger vessel.

[00112] VII. Advantages. Conventional processes use severe oxidation conditions (for example, temperatures greater than 1000°C). Such high temperatures produce toxic and hazardous intermediates which require costly add-on processing (e.g., stack gas scrubbing). Conventional oxidation processes also produces char, which ends up contaminating vast acreage as coal ash slurry. The process as described herein is directed at oxidizing organic materials without producing toxic or hazardous intermediates or by-products. The oxidation is conducted under the relatively mild conditions of supercritical water oxidation (e.g., temperature in the range of from about 250°C to about 650°C). At these mild temperatures and at high pressures, water behaves as a supercritical solvent that can dissolve both organic matter and gases, thereby eliminating mass transfer limitations for oxidative processes. The lower temperatures of oxidation, as taught herein, increase the residence time from milliseconds to seconds, but the higher densities compensate to make the reactor volumes acceptable.

[00113] The tubular reactor configuration and the pipe-in-pipe double pipe heat exchanger are both operated at a fluid velocity high enough to keep most solids in suspension. The remainder of the solids is removed by using cleaners periodically (e.g., using Conco cleaners once a day for a few minutes).

[00114] The hot effluent of the reaction is cooled by heat transfer to preheat feed, generate steam and, to make hot water. The effluent from the last heat exchanger is a mixture of three phases, which is separated by the 3-phase separator as discussed herein. In this design, the gas phase is separated from aqueous effluent and then depressurized. The configuration and use of the 3-phase separator as disclosed herein also addresses ice build-up and/or liquid CO2 formation resulting from the depressurization process. Such ice build-up and/or liquid C02 formation, in conventional methods and systems would clog the depressurization valve. The 3- phase separator as discussed herein is a cost-effective solution to clogging of the gas depressurization problem.

[00115] The inclusion or discussion of a reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent they provide background knowledge; or exemplary, procedural or other details supplementary to those set forth herein.

[00116] While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations, of the term "optionally" with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like. [00117] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention.

Claims

CLAIMS I CLAIM:

1. A supercritical water oxidation (SCWO) system, comprising

a. a preheating zone including at least one heat exchanger with at least one process fluid (PF) inlet and one PF outlet and at least one heat exchange fluid (HEF) inlet and one HEF outlet, wherein the PF inlet is configured to receive a process fluid feed stream;

b. a SCWO reaction zone including at least one SCWO reactor with at least one PF inlet and one PF outlet, wherein the PF inlet is configured to receive SCWO process fluid from said preheating zone PF outlet;

c. a steam generation zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one water inlet and one steam outlet, wherein the PF inlet is configured to receive SCWO process fluid from said reaction zone PF outlet; and

d. a first cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein i. the PF inlet is configured to receive SCWO process fluid from said steam generation zone PF outlet, and

ii. the HEF inlets and outlets of said first cooling zone and said preheating zone are connected to form a recirculation loop for a heat exchange fluid, constituting a regenerative heat exchange system.

2. The system of claim 1 further comprising a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein

a. the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet; and

b. at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to the water inlet of said steam generation zone.

3. The system of claim 1 further comprising a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein

b. at least one HEF inlet and HEF outlet are configured to be fluidly connected to said HEF inlets and outlets of said first cooling zone and said preheating zone to form said recirculation loop for said heat exchange fluid as the regenerative heat exchange system.

4. The system of claim 1 further comprising a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein

b. at least one HEF inlet is configured to receive a second heat exchange fluid and at least one HEF outlet is configured for said second heat exchange fluid to exit the system.

5. The system of claim 1 further comprising a second cooling zone including at least one heat exchanger with at least one PF inlet and one PF outlet and at least one HEF inlet and one HEF outlet, wherein

a. the PF inlet is configured to receive SCWO process fluid from said first cooling zone PF outlet;

b. at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to the water inlet of said steam generation zone; and

c. at least one HEF inlet is configured to receive a second heat exchange fluid and at least one HEF outlet is configured for said second heat exchange fluid to exit the system.

6. The system of claim 1 further comprising at least one turbine, which is configured to receive the steam effluent from said steam outlet of the steam generation zone to produce electricity.

7. The system of claim 1 wherein the SCWO reactor in the reaction zone is thermally insulated.

8. The system of claim 1 wherein said heat exchangers include cross-flow tube-and- shell heat exchangers, cocurrent double pipe heat exchangers, and countercurrent double pipe heat exchangers.

9. The system of claim 5 wherein

a. said SCWO system comprises a series of double pipes with fluidly connected inner pipes having the same inner diameter and a smooth inner surface;

b. said preheating zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for a first HEF with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet is configured to receive a process fluid feed stream;

c. said reaction zone comprises a thermally insulated SCWO tubular reactor as the passage for the PF with an inlet and an outlet, wherein the inlet of said tubular reactor is fluidly connected to the IP outlet of preheating zone double pipe;

d. said steam generation zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for water with at least one annulus inlet and at least one annulus outlet, wherein the IP inlet of steam generation double pipe is fluidly connected to the outlet of said tubular reactor;

e. said first cooling zone comprises at least one countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for said first HEF with at least one annulus inlet and at least one annulus outlet, wherein

i. the IP inlet of first cooling zone double pipe is fluidly connected to the IP outlet of steam generation zone double pipe;

ii. one annulus inlet is fluidly connected to one annulus outlet of preheating zone double pipe; and

iii. one annulus outlet is fluidly connected to one annulus inlet of preheating zone double pipe; f. said second cooling zone comprises a countercurrent double pipe heat exchanger with the inner pipe (IP) as the passage for the PF with one IP inlet and one IP outlet and the annulus as the passage for said first HEF with at least one annulus inlet and at least one annulus outlet, wherein

i. the IP inlet of second cooling zone double pipe is fluidly connected to the IP outlet of first cooling zone double pipe;

ii. one annulus inlet is fluidly connected to a water feed and one annulus outlet is fluidly connected to one annulus inlet of steam generation zone double pipe; and

iii. a second annulus inlet is fluidly connected to a second HEF feed, which exits the system via a second annulus outlet.

10. The system of claim 1 comprising a scale cleaner.

11. The system of claim 1 comprising a multiport oxygen injection system in the reaction zone.

12. The system of claim 11 wherein adjacent oxygen injection ports in the multiport oxygen injection system are configured to provide a residence time of no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds.

13. A supercritical water oxidation (SCWO) system, comprising

a. a preheating double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein the PF inlet is configured to receive a process fluid feed stream; b. a SCWO tubular reactor with at least one PF inlet and one PF outlet, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said preheating double pipe heat exchanger;

c. a steam generation double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one water inlet and one steam outlet on the annulus, wherein the PF inlet is configured to receive SCWO process fluid from the PF outlet of said SCWO tubular reactor; and d. a first cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein

i. the PF inlet is configured to receive SCWO process fluid from the PF outlet of said steam generation double pipe heat exchanger, and

ii. at least one HEF inlet is fluidly connected to the HEF outlet of said preheating double pipe heat exchanger; and

iii. at least one HEF outlet is fluidly connected to the HEF inlet of said preheating double pipe heat exchanger.

14. The system of claim 13 further comprising a second cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein

a. the PF inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; and

b. at least one HEF inlet is configured to receive water feed and at least one HEF outlet is configured to be fluidly connected to said water inlet of said steam generation double pipe heat exchanger.

15. The system of claim 13 further comprising a second cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein

b. at least one HEF inlet and HEF outlet are fluidly connected to said HEF inlets and outlets of said first cooling and preheating double pipe heat exchangers to form a recirculation loop for a heat exchange fluid as the regenerative heat exchange system.

16. The system of claim 13 further comprising a second cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein

a. the PF inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger; and b. at least one HEF inlet is configured to receive a heat exchange fluid and at least one HEF outlet is configured for said heat exchange fluid to exit the system.

17. The system of claim 13 further comprising a second cooling double pipe heat exchanger with at least one PF inlet and one PF outlet on the inner pipe and at least one HEF inlet and one HEF outlet on the annulus, wherein

a. the PF inlet is configured to receive SCWO process fluid from the PF outlet of said first cooling double pipe heat exchanger;

b. one HEF inlet is configured to receive water feed and one HEF outlet is configured to be fluidly connected to said water inlet of said steam generation double pipe heat exchanger; and

c. a second HEF inlet is configured to receive a heat exchange fluid and a second HEF outlet is configured for said heat exchange fluid to exit the system.

18. A method of recovering energy from a SCWO reaction, comprising

a. pressurizing an oxidant and a feed stream to a pressure greater than 220 bar;

b. mixing pressurized oxidant and feed stream to form a process fluid;

c. preheating said process fluid in a first heat exchange system to its kindling temperature to form preheated process fluid;

d. introducing preheated process fluid into a reactor wherein SCWO reactions take place to oxidize a substantial portion of the organic material in the process fluid to form a reacted process fluid;

e. introducing reacted process fluid into a second heat exchange system to increase the thermal energy to desalinated water that is circulating in said second heat exchange system, whereby the circulating water becomes steam; and

f. introducing process fluid effluent from said second heat exchange system into a third heat exchange system to increase the temperature of a heat exchange fluid, wherein said heat exchange fluid is recirculated to said first heat exchange system to preheat the process fluid.

19. The method of claim 18 further comprising introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system, wherein desalinated water that is circulating in said second heat exchange system is preheated so as to facilitate steam generation.

20. The method of claim 18 further comprising introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system to provide thermal energy to the heat exchange fluid that is recirculated in said first and third heat exchange system so as to facilitate the preheating of the process fluid.

21. The method of claim 18 further comprising introducing process fluid effluent from said third heat exchange system into a fourth heat exchange system to generate hot water; or to cool down process fluid effluent to near room temperature; or both.

22. The method of claim 18 further comprising introducing steam effluent generated in step e into a turbine to produce electricity.

23. The method of claim 18 wherein said oxidant includes air and oxygen.

24. The method of claim 18 wherein said feed stream is a mixture of trimming water and a feedstock.

25. The method of claim 24 wherein said trimming water and feedstock are either mixed first and then pressurized to greater than 220 bar or pressurized to greater than 220 bar first and then mixed.

26. The method of claim 24 wherein said feedstock is selected from the group consisting of

a. activated raw sludge from a municipal sewage treatment plant;

b. sludge from manufacturing facilities which produce at least one product selected from the group consisting of pulp, paper, pharmaceuticals, foods, beverages, and chemicals;

c. a military waste selected from the group consisting of chemical warfare agents, explosives, rocket propellant, and radioactive materials;

d. pulverized coal with a particle size of 200 μιτι or less;

e. biomass; and

f. combinations thereof.

27. The method of claim 24 wherein said feedstock comprises algae.

28. The method of claim 18 wherein said SCWO reactor is thermally insulated.

29. The method of claim 18 wherein said SCWO reactor is constructed with a material selected from the group consisting of Inconel 625, Hastelloy C-276, and HAYNES® 230® ALLOY.

30. The method of claim 18 wherein the temperature of reacted process fluid exiting SCWO reactor is in the range of from 550°C to 700°C.

31. The method of claim 18 wherein the pressure of the steam effluent generated in step e is in the range of from 1 bar (14.5 psia) to 276 bar (4000 psia).

32. The method of claim 18 wherein each one of said heat exchange systems comprises at least one heat exchanger.

33. The method of claim 18 wherein each heat exchanger of said heat exchange systems is operated with a minimal average temperature difference between the two fluids that are in thermal communication in the heat exchanger.

34. The method of claim 33 wherein said minimal average temperature difference is 150 °C or less.

35. The method of claim 18 wherein the rate of energy recovery from SCWO reactions for steam generation is 80% or more.

36. A method of recovering energy from a SCWO reaction, comprising

a. forming a feed stream comprising an organic material and water with a pressure greater than 220 bar;

b. preheating the feed stream to its kindling temperature to form preheated process fluid; c. introducing preheated process fluid into a reactor wherein SCWO reactions take place, wherein an oxidant is provided via multiple injection ports placed along the length of the reactor;

d. oxidizing a substantial portion of the organic material in the process fluid to form a reacted process fluid;

e. introducing reacted process fluid into a heat exchange system to increase the thermal energy to desalinated water that is circulating in said heat exchange system, whereby the circulating water becomes steam; and

f. using the steam to produce electricity.

37. The method of claim 36 wherein said organic material comprises pulverized coal and said oxidant comprises air or oxygen.

38. The method of claim 36 wherein the multiple injection ports are configured to control reaction rates, to adjust oxidant profile in the reactor, to prevent run-away reactions, to prevent spontaneous combustion, to prevent explosion, or to prevent char formation.

39. The method of claim 36 wherein residence time in the reactor is no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds.

40. The method of claim 36 wherein residence time between adjacent ports of the multiple injection ports is no more than 2 minutes, or no more than 1 minute, or no more than 30 seconds, or no more than 20 seconds.

41. The method of claim 36 comprising periodic use of a pipe cleaner in the reactor.

42. The method of claim 36 wherein said heat exchange system is configured to minimize entropy generation.

43. The method of claim 36 wherein said heat exchange system is configured to maximize steam generation.

44. The method of claim 36 wherein the reacted process fluid becomes an effluent from the heat exchange system, wherein said effluent is separated by phase and then depressurized.

45. The method of claim 36 wherein there is no or minimum char formation.

46. The method of claim 36 wherein 99% or more of the organic material is oxidized.

47. A three-phase separator comprising

an inlet tube configured to receive a three-phase mixture;

a vessel;

a gas effluent outlet;

at least two heat exchangers, each of which being in fluid communication with the vessel and in fluid communication with the gas effluent outlet; and

valves configured to control fluid flow.

48. The separator of claim 47 wherein the inlet tube has a diverging inner diameter.

49. The separator of claim 48 wherein the smallest inner diameter of the inlet tube is large enough to allow a cleaner to pass through.

50. The separator of claim 47 wherein the vessel is tall enough to contain liquid at the bottom and froth at the top with gas phase above the froth.

51. The separator of claim 50 wherein the cross-section of the froth region vessel is large enough to provide for a slow rise of the vapor phases.

52. The separator of claim 47 wherein the heat exchangers are jacked pipes or double pipe heat exchangers.

53. The separator of claim 47 wherein the heat exchangers are configured to receive a coolant during a cooling cycle or a heating medium during a heating cycle.

54. The separator of claim 47 wherein the heat exchangers are configured in parallel and operated in a semi-batch fashion.

55. The separator of claim 47 comprising a liquid level monitor in communication with the liquid and the froth in the vessel.

56. The separator of claim 47 wherein the valves are operated such that the heat exchangers are used in alternating cooling and heating cycles.

57. The separator of claim 47 wherein the vessel has a conical bottom.

58. The separator of claim 57 wherein the bottom of the vessel is jacketed and maintained at a temperature slightly above the freezing point of the least volatile component of the mixture.

59. The separator of claim 47 comprising a liquid outlet at the bottom of the vessel.