AU2014240146B2

AU2014240146B2 - Method and apparatus for ash cooling

Info

Publication number: AU2014240146B2
Application number: AU2014240146A
Authority: AU
Inventors: John D. Winter
Original assignee: Synthesis Energy Systems Inc
Current assignee: Synthesis Energy Systems Inc
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2018-09-20
Anticipated expiration: 2034-03-14
Also published as: CN105247018B; US20140311031A1; WO2014152073A3; CN105247018A; WO2014152073A2; AU2014240146A1

Abstract

Systems and methods for step-wise cooling high pressure and high temperature ash discharged from the gasifier used for gasification of carboneous materials, wherein a high pressure cooler cools the ash under the operating pressure of the gasifier, which may be followed by a depressurizer which brings the cooled ash to safe-handling temperature. A low temperature ash cooler may also be optionally used. Also provided is a system where a wet scrubber is used to clean the syngas from the gasifier, the waste water blow down from the scrubber is used to cool the hot ash either in the high temperature ash cooler, or the low temperature ash cooler. Steam generated in the ash coolers is supplied back to the gasifier to reduce steam consumption

Description

FIELD OF THE INVENTION [0002] The present invention relates to coal gasification using fluidized bed reactor. More specifically, the present invention relates to a method and apparatus for cooling and handling high temperature and high pressure ash discharged from a fluidized bed gasification reactor. The present invention also relates to a method and apparatus for using waste water from a syngas scrubber in the cooling of hot ash discharged from the gasifier.

BACKGROUND OF THE INVENTION [0003] Gasification of carbon containing or carbonaceous materials is used to produce syngas, a mixture of carbon monoxide, hydrogen, carbon dioxide, and other components. Various types of gasifiers are known and used, including a moving bed gasifier, entrained flow gasifier, and fluidized bed gasifier.

[0004] Carbonaceous feed materials often contains an appreciable ash content,

e.g. above 5 wt%. Non-slagging gasifiers used to convert these feed materials commonly operate at temperatures just below the melting point of the ash, and the ash discharged from the gasifier is at a temperature ranging from 500 °C to 1200 °C, and under a high pressure (up to 6 bar). This ash must be cooled to ambient temperature, or at least not more than 300 °C for storage and subsequent handling and disposal.

[0005] It has been technically challenging to cool such hot ash under high pressure, because existing equipment capable of handling hot solids under high pressure is expensive, difficult to build and operate, unreliable, and requires frequent maintenance. For example, conventional valves are not reliable in high temperature, high pressure flowing solids service.

[0006] Furthermore, thermal energy of the hot ash is not efficiently used or not used at all, imposing a net energy penalty on the system. Often, the ash is discharged

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PCT/US2014/026919 directly into water at low or ambient pressures generating steam that is either not recovered or has very limited utility and value due to its low pressure and contamination;

or the thermal energy of the hot ash is somehow transferred into cooling water, or using relatively expensive heat transfer equipment to generate low temperature/low pressure steam which is also of low value.

[0007] There is thus a further need for improved hot ash cooling methods and equipment.

[0008] U.S. Pat. App. No. 13/532,769 provides an apparatus and a method for capturing and recycling small fines for fluidized bed reactors or gasifiers operated at high temperatures and pressures in a reliable and simple manner. However, even after such deliberate steps of solids removal, the raw syngas still contains a significant amount of solids and must undergo further cleaning processes, for the removal of residual solids and undesired gas phase contaminants, such as sulfur compounds, before it can be used in power generation or the production of chemicals. A wet scrubber or water scrubber is commonly used for this purpose, generating a wastewater stream containing salts, dissolved gases and vapors, and suspended solids. In SES process described in U.S. Pat. App. No. 13/532,769 (“the SES process”), solids are first removed and recycled to the gasifier using cyclones, then a filter is used to remove further solids, and a wet scrubber is lastly used to remove some gas phase contaminants such as halides and any solids that have passed through the filter due to their small particle size or failure of filter elements. To prevent buildup of salts and acids or bases in the scrubber water and to limit the concentration of solids in the scrubber, the scrubbing liquid, typically water, is continually added to and removed from the scrubber, and is henceforth called “makeup” and “blowdown.” [0009] Currently, the wastewater stream resulting from the scrubber blowdown is treated and then discharged. The treatment of wastewater is costly, and the discharged wastewater represents a substantial portion of the overall water consumption of the gasification process. There is therefore a need to more fully utilize the carbon content in the wastewater stream from the scrubber, and to reduce the water consumption.

SUMMARY OF THE INVENTION

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2014240146 07 Aug 2018 [0010] As discussed above, handling high temperature, high pressure flowing solids is not only costly but also not reliable. Some attempts have been made to make improvement, but the results have not been satisfactory. Additionally, these improved cooling solutions also result in waste of thermal energy and water recourse. The a method and apparatus in the present invention can solve the technical problems as mentioned above and also raise the overall efficiency of the gasification process.

[0010a] According to a first aspect, the present disclosure provides a gasification system comprising:

a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable hot ash under pressure are discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and a high temperature ash cooler connected to the gasifier and into which the flowable hot ash under pressure is discharged, wherein the high temperature ash cooler comprises a water supplying apparatus that provides atomized water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized water completely and instantaneously vaporized upon contact with the flowable hot ash.

[0010b] According to a second aspect, the present disclosure provides a gasification system comprising:

a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable hot ash under pressure are discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants, a wet scrubber for removing the pollutants from the product gas stream and producing a waste water stream, a high temperature ash cooler connected with the gasifier to receive the flowable hot ash from the gasifier; and a connection to deliver at least a portion of the waste water stream to the high temperature ash cooler,

2014240146 07 Aug 2018 wherein the high temperature ash cooler comprises a water supplying apparatus that atomizes the waste water stream from the wet scrubber and provides the atomized waste water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized waste water completely and instantaneously vaporized upon contact with the flowable hot ash.

[0010c] According to a third aspect, the present disclosure provides a method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable hot ash under pressure are discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, the method comprising:

providing atomized water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment in a high temperature ash cooler which is connected to the gasifier and into which the hot ash under pressure is discharged, with the atomized water completely and instantaneously vaporized upon contact with the flowable hot ash.

[OOlOd] According to a fourth aspect, the present disclosure provides a method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable ash under pressure are discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants, the method comprising:

removing the pollutants from the product gas stream and producing a waste water stream with a wet scrubber, delivering at least a portion of the waste water stream from the wet scrubber to a high temperature ash cooler connected with the gasifier which receives the flowable hot ash from the gasifier, and atomizing the waste water and providing the atomized waste water to be in direct contact with the flowable hot ash in the high temperature ash cooler in an amount for cooling the

3A

2014240146 07 Aug 2018 flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized wastewater completely and instantaneously vaporized upon contact with the flowable hot ash.

[0011] According one aspect of the present invention, this present invention provides a gasification system comprising a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable ash is discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash, and under a pressure not less than 6 bar gauge, and a high temperature ash cooler which is connected to the gasifier and into which the hot ash under pressure is discharged, wherein the high temperature ash cooler comprises a water-supplying apparatus that provides water for cooling the flowable ash, wherein the flowable ash is cooled to a temperature suitable for the ash to be handled with conventional carbon steel equipment.

[0012] In some embodiment of the gasification system, the water supplying apparatus supplies the cooling water to the high temperature ash cooler to be in direct contact with the flowable ash, and wherein the system further comprises a controller to control the water supplying apparatus so that the water is vaporized upon direct contact with the ash to generate steam, and the flowability of the ash is maintained, and the flowable ash is cooled to a temperature not lower than the pre-determined threshold temperature.

[0013] In some embodiment of the gasification system, the cooling water is supplied to the high temperature ash cooler and cools the ash via indirect heat transfer.

[0014] In some embodiment of the gasification system, the high temperature ash cooler comprises a cooling jacket, or cooling coils, or a cooling panel through which the cooling water flows and absorbs heat indirectly from the hot ash.

[0015] In some embodiment of the gasification system, a portion of the cooling water is supplied to the high temperature ash cooler in direct contact with the flowable ash, and wherein the system further comprises a controller to control the water supplying apparatus so that the water is vaporized upon direct contact with the ash to

3B

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PCT/US2014/026919 generate steam, and the flowability of the ash is maintained; and a portion of the cooling water is supplied to the high temperature ash cooler where the cooling water cools the ash via indirect heat transfer; and wherein the flowable ash is cooled to a temperature not lower than the pre-determined threshold temperature.

[0016] In some embodiment of the gasification system, the system further comprises a connection between the high temperature ash cooler and the gasifier, wherein steam generated from the water supplied to the high temperature ash cooler and is supplied to the gasifier.

[0017] In some embodiment of the gasification system, the system further comprises a depressurizing device which is connected to the high temperature ash cooler to receive the cooled high pressure ash from the high temperature ash cooler, and which is able to reduce the pressure of the ash to ambient pressure.

[0018] In some embodiment of the gasification system, the depressurizing device comprises a double sealed lock hopper.

[0019] In some embodiment of the gasification system, the system further comprises a second ash cooler device which is connected to the high temperature ash cooler to receive the cooled high pressure ash from the high temperature ash cooler, and which is able to further lower the temperature of the ash to ambient temperature.

[0020] In some embodiment of the gasification system, the system further comprises a second ash cooler device which is connected to the depressurizing device to receive the ash from the high temperature ash cooler, and which is able to further lower the temperature of the ash to ambient temperature.

[0021] In some embodiment of the gasification system, the system further comprises a depressurizing device which is connected to the second ash cooling device to receive the ash from the second ash cooling device, and which is able to reduce the pressure of the ash to ambient pressure.

[0022] In some embodiment of the gasification system, the high temperature ash cooler comprises a fluidized bed or a moving bed wherein the high pressure ash makes direct contact with the water from the water supplying apparatus.

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PCT/US2014/026919 [0023] In some embodiment of the gasification system, the water supply apparatus comprises means to disperse the liquid into the ash such as spray nozzles, atomizing spray nozzles, microporous pipes.

[0024] According to another aspect of the present invention, this invention further provides a gasification system comprising a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable ash are discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash, and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants, a wet scrubber for removing the pollutants from the product gas stream and producing a waste water stream, an ash cooler connected with the gasifier to receive hot ash from the gasifier; and a connection to deliver at least a portion of the waste water stream to the ash cooler, wherein the waste water stream is converted into steam.

[0025] In some embodiment of the gasification system, the ash cooler comprises a high temperature ash cooler connected directly with the gasifier.

[0026] In some embodiment of the gasification system, the ash cooler further comprises a low temperature ash cooler, and wherein the waste water is delivered to the low temperature ash cooler.

[0027] In some embodiment of the gasification system, the waste water makes direct contact with the ash and steam generated from the contact is delivered to the gasifier.

[0028] According to another aspect of this present invention, some embodiment provide a method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable ash is discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash, and under a pressure not less than 6 bar gauge, the method comprising cooling the flowable ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment in a high temperature ash cooler which is connected to the gasifier and into which the hot ash under pressure is discharged, wherein the high temperature ash cooler comprises a water-supplying apparatus that provides water for cooling the flowable ash.

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PCT/US2014/026919 [0029] In some embodiment of the method, wherein the water supplying apparatus supplies the cooling water to the high temperature ash cooler to be in direct contact with the flowable ash, and the method further comprises controlling the water supplying apparatus so that the water is vaporized upon direct contact with the ash to generate steam, and the flowability of the ash is maintained, and the flowable ash is cooled to a temperature not lower than the pre-determined threshold temperature .

[0030] In some embodiment of the method, the method further comprises receiving the cooled high pressure ash from the high temperature ash cooler, and reducing the pressure of the ash to ambient pressure with a depressurizing device which is connected to the high temperature ash cooler.

[0031] In some embodiment of the method, the method further comprises receiving the cooled ambient pressure ash from the a depressurizing device, and further lowering the temperature of the ash to ambient temperature with a second ash cooler device which is connected to the depressurizing device.

[0032] Further, certain embodiments provide a method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable ash are discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash, and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants, the method comprising removing the pollutants from the product gas stream and producing a waste water stream with a wet scrubber, and delivering at least a portion of the waste water stream from the wet scrubber to a ash cooler connected with the gasifier which receives hot ash from the gasifier, wherein the waste water stream is converted into steam.

[0033] In some embodiment of the method, the ash cooler comprises a high temperature ash cooler connected directly with the gasifier.

[0034] In some embodiment of the method, the ash cooler further comprises a low temperature ash cooler, and wherein at least a portion of the waste water is delivered to the low temperature ash cooler.

[0035] In some embodiment of the method, the waste water makes direct contact with the ash and steam generated from the contact is delivered to the gasifier.

BRIEF DESCRIPTION OF THE DRAWING

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PCT/US2014/026919 [0036] For the present disclosure to be easily understood and readily practiced, the present disclosure will now be described, for purposes of illustration and not limitation, in conjunction with the following figures.

[0037] Figure 1 schematically shows an exemplary overall arrangement of the syngas production system of the present invention, which comprises a gasifier 1, a high temperature ash cooler 6, and a low temperature ash cooler 7. One or more cyclones 2 are provided for recovery and recycle of entrained solids from the crude syngas, with or without heat recovery in a syngas cooler 3 in which boiler feed water is introduced and out of which process steam is produced, with or without filters 4 to further clean the syngas. A wet scrubber 5 downstream of the gasifier is provided to clean the syngas. Wastewater from the scrubber 5 can be fed to a high temperature ash cooler 6 or a low temperature ash cooler 7, or both. When using direct contact cooling, upon contact with the hot ash, either in the high temperature ash cooler 6 or in the low temperature ash cooler 7, steam is generated. This steam can be fed back into the gasifier l(e.g. shown in the high temperature ash cooler 6), or be filtered in filter 8 and outputted for other purposes (e.g. shown in the low temperature ash cooler 7).

[0038] Figure 2 is a block diagram illustrating the sequential arrangement of steps to cool and depressurize the gasifier ash from gasifier conditions to conditions suitable for safe and inexpensive ash handling, according to one embodiment of the present invention.

[0039] Figure 3 illustrates the basic structure of a fluidized bed gasifier according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0040] A fluidized bed gasifier, as shown in Figure 3, comprises a vessel housing a headspace 2 above a fluidized bed 1 of the solid material being gasified and a conical perforated gas distribution grid 7 below the bed through which the gasifying medium is introduced at sufficient velocity to fluidize the solid feed material in the gasifier. The gasifying medium (steam and/or oxygen) is introduced into the gasifier from the plenum space 4 through the grid 7 to fluidize and partially oxidize the solid feed stock.

[0041] A passage such as a pipe 6 (center jet pipe) in the center region at the bottom of the grid cone introduces oxidant with diluting gas to the bed. Gas velocity of

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PCT/US2014/026919 the centre jet pipe 6 is normally greater than the average superficial velocity of gas in the fluidized bed 1. An ash discharge device 5 comprising an annular passage is provided around this center jet pipe 6 for coal ash agglomerated withdrawal and also for provision of additional gas, such as steam, which may serve to cool and protect the center jet pipe 6. The ash discharge device 5 is often configured to comprise a venture 3 device for sorting the ash particles at the upside of the passage. A classifier 8 can be intergraded with the ash discharge device 5. A gas stream, such as steam, moving upwards through the classifier, is often used to separate the ash particles, re-entraining those lighter and/or smaller particles whose carbon content is not yet depleted and returning them back into the reaction region, [0042] As indicated above, handling of hot ash from the ash discharge device 5 under high temperature as well as high pressure has been technically challenging in the coal gasification field. The present invention provides methods and related systems whereby the ash cooling process is separated into respective steps and the first step is a first cooling step under high pressure at high temperature. As shown in Figure 1, the first cooling step under high pressure may be by indirect heat transfer of ash with using indirect cooling medium or by direct contacting using direct evaporative cooling liquid. After the first cooling step processed by the high temperature ash cooler (also referred as “high pressure ash cooler”), the temperature of the ash is low enough for the use of conventional equipment. Therefore, further steps such as a depressurization step can be handled at low or medium temperature with equipments of lower cost, thus the investment of equipments is reduced and the reliability of all of the remaining ash handling equipment is also increased.

[0043] In some embodiment, as shown in Figure 2 , if a depressurization step is further performed, after depressurizing, the cooled and depressurized ash can then be cooled further in a low temperate ash cooler 7 and handled using conventional methods. The stepwise system of the present invention recovers heat from said ash in such a manner as to raise the overall efficiency of the gasification process.

[0044] A feature of the present inventive process is to first cool the ash exiting the gasifier in a high temperature cooler 6 at the gasifier pressure. The temperature of the ash after this high pressure ash cooling step may be determined based on two criteria. First the temperature is high enough such that any steam generated from the high temperature ash cooling has sufficient pressure and can be used to replace part of the

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PCT/US2014/026919 fluidizing and reacting steam needed for the gasifier. Second, the temperature of the ash is low enough to allow use of conventional carbon steel equipment, such as vessels, valves, pipes, and conveyors, for the subsequent ash handling. This lowers the cost and increases the reliability of all of the remaining ash handling equipments, particularly the equipment used to remove the ash from a high pressure environment to ambient pressure.

[0045] Although above two criteria are provided, it is understood so long as at least one of two criteria are satisfied after this high pressure ash cooling step, the overall efficiency or reliability of the gasification system can be improved. Also those skilled in the art can understand that control the operating conditions in the ash coolers, such as the introduction of cooling liquid or medium, by techniques in the prior art, e.g. valves, and other device for the adjustment etc., to control the ash temperature after the high pressure ash cooling step.

[0046] The gasification process requires a large amount of steam referred as process steam which is either be generated independently or by cooling the syngas produced in the gasifier such as in a syngas cooler 3, as shown in Figure 1, in the prior art, which is imposing a net energy penalty on the system. In comparison, in some embodiment of this present invention, the steam generated in the high temperature ash cooler can be used as port of the process steam, thereby allowing more steam to be exported from the gasification process, or reducing the need of independent steam generation. Thus, at least part of the energy penalty on the gasifier system is released.

[0047] In some embodiment, referring Figure 2, after the high temperature ash cooling, the lower-temperature ash is then depressurized using lower cost higher reliability equipment, such as carbon steel lock hoppers. A low temperature ash cooling system follows, as shown as a low temperature ash cooler 7 in Figure 2, which further cools the ash for ordinary solids handling and disposal. The stepwise process of the present invention lowers capital cost, improves reliability, and improves the overall efficiency of the gasification process.

[0048] In one aspect of the present invention, the system for gasifying a carbonaceous material comprises: 1) a gasifier into which the carbonaceous material and gas feeds are fed and gasified to produce a crude syngas product leaving the gasifier from the top and also produce high temperature ash under the operating pressure of the gasifier discharged from the bottom of the gasifier, 2) an ash cooler, as such the high

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PCT/US2014/026919 temperature ash cooler, connected with the gasifier, wherein the ash cooler comprises i) a vessel to contain the ash during cooling and ii) an apparatus to cool the ash either via indirect heat transfer or direct contact cooling, and iii) a connection to deliver the steam(“vapor”) generated in step ii) back into the gasifier.

[0049] In one embodiment, the step-wise process of the present invention for cooling the high temperature and high pressure ash discharged from the gasifier comprises a first step wherein the free-flowing ash from the gasifier at the operating temperature of the gasifier is discharged, e.g. by gravity in the case of a fluidized bed gasifier, into a compartment or vessel, in which the ash is cooled. The operating temperature of the gasifier is usually a temperature just below the melting point of the ash e.g. 1200 °C. The high-temperature ash cooling compartment itself may be configured as a fluid bed or as a moving bed.

[0050] In one embodiment the high temperature ash cooler may be a direct contact cooler wherein water or other direct evaporative cooling liquid is directly contacted with the hot ash and converted to steam, which flows countercurrent to the ash discharge into the gasifier via a channel connecting the gasifier to the high temperature ash cooler. In this way, the heat energy contained in the ash is used to generate steam which is used directly in the gasification reactor.

[0051] Direct contact may be affected by many methods well-known to those skilled in the art. For example, water, preferably atomized, may be injected into the hot ash so long as the flow-ability of the ash is maintained. This may be done via a water supply apparatus which comprises means to disperse the water into the ash such as spray nozzles, atomizing spray nozzles, microporous pipes, which for example may be made from sintered metal powder or fibers, pipes or other flow channels with drilled holes. This direct contact cooling step can be achieved in either a moving bed or fluid bed ash cooler.

[0052] Indirect cooling can be used in combination with or instead of direct contact cooling. Whether this is means of jacketing of the vessel, cooling coils, or cooling panels or any other common means of indirect heat transfer, a indirect cooling medium is heated or evaporated in a flow channel separated from the ash. Steam is generated in the flow channel and is relatively clean compared to the steam generated via direct contact. Preferably, the steam is at a pressure higher than that of the gasifier and can be used in the gasifier or for other uses.

io

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PCT/US2014/026919 [0053] After the high temperature cooler, the ash reaches a temperature at which any further handling or processing can be accomplished using e.g. ordinary carbon steel materials, which function well and reliably at a temperature below 500 °C, preferably below 350 °C. In one embodiment, after the high temperature ash cooler, the ash may be reduced in pressure, e.g. in a depressurizer, to ambient pressure for any further handling or cooling. This can be achieved by a variety of means, such as via valves and lock-hoppers well-known to those skilled in the art. These are conventional equipment and can operate rather reliably at a temperature of 300-550 °C even under the operating pressure of the gasifier.

[0054] A lock hopper is a well-known depressurizing device, and generally comprises a vessel into and out of which the ash flows by gravity, with valves at the top and bottom that seal against pressure and solids flow, and means to pressurize and depressurize the vessel, and associated valves and controls to regulate the gas flow.

[0055] The cooled and depressurized ash may optionally undergo a further cooling step using a second cooler, or a low temperature ash cooler, for ease of handling or safe disposal, e.g. to not more than 140 °C for handling via belt conveyors. Any commonly available low pressure solids cooler, including a direct contact or indirect heat transfer cooler, e.g. a screw cooler, can be used as the low temperature ash cooler.

[0056] In the low temperature ash cooling step after depressurization, a scrubber blowdown (described below in detail) may be used in direct contact with the ash to provide cooling, transfer salts and suspended solids to the ash, and further recover water without salt for reuse, thus lowering wastewater treatment and reducing overall water consumption.

[0057] In some embodiment, a two-step cooling process (i.e. a high pressure cooling followed by depressurizing) of the present invention thus allows the overall cost of an ash cooling and depressurization system to be lowered, its reliability increased, and the bulk of the heat available in the ash, which is the heat of the ash from gasifier operating temperature to the exit temperature of the high temperature ash cooler, is directly converted to process steam. As mentioned above, the process steam converted has the highest value possible for a gasifier system, for use in the gasifier without any addition steam handling.

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PCT/US2014/026919 [0058] In one embodiment, the high temperature cooler may also be designed to cool the ash to a lower temperature such that a low temperature ash cooler is not needed. Such a process may be desired if high process efficiency is needed, especially when the gasifier feed has high ash content. Such a lower temperature may be achievable even with direct contact cooling, so long as the water saturation pressure at the exit temperature of the high temperature ash cooler is above the gasifier operating pressure.

[0059] In one embodiment, the high temperature cooler may also be designed to cool the ash to a lower temperature and the cooled ash is cooled by a low temperature ash cooler. In this embodiment, the depressurizer is not needed. Such a process may be desired when the pressure of the cooled ash is needed.

[0060] The above mentioned and other features of this invention and the manner of obtaining and using them will become more apparent, and will be best understood, by reference to the following drawing and description.

[0061] Referring to Figure 1, hot ash passes from the gasifier 1 into the ash cooling apparatus. Depending on the operating conditions of the gasifier 1, the hot ash may be at a temperature from 500° to 1200°C at the discharge point from the gasifier 1. The temperature of the ash leaving the ash cooling device is determined by the operating pressure of the gasifier. As long as the saturation pressure of water at the ash exit temperature is above the gasifier operating pressure, water can be injected directly into the moving or fluid ash.

[0062] The pre-determined threshold temperature may be determined by the following two factors. Firstly, in order to keep the flowability of the ash, liquid water should be avoided in the ash cooler. Thus, the temperature of the cooled ash (TJ should be kept at least above the boiling point of water at the ash cooling pressure. Preferably, the temperature is at or above the critical temperature of water (i.e. 374°C). Secondly, since the steam generated flows into the gasifier (more detail below), the pressure of the steam should be above the pressure of the points at which the steam is introduced into the gasifier. Thus, the temperature of the cooled ash (T2) should be high enough. Therefore, the pre-determined threshold temperature should not be lower than either T1 or T2.

[0063] In a preferred embodiment of the invention, the rate and amount of water is controlled so that it is dispersed and mixes with the hot solids properly, and

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PCT/US2014/026919 completely evaporates without affecting the flowability of the ash. The steam thus generated moves up into the reacting zone of gasifier.

[0064] The flow of the cooling water can controlled by a flow control device such as a control valve where the flow of the water is controlled by temperature or pressure measurement in the ash cooler to regulate to the amount of cooling desired.

[0065] In this manner, the thermal energy contained in the hot ash is used to generate steam needed for the gasification reaction, thus displacing the amount of clean, high pressure steam otherwise needed in the gasification reaction and typically generated in a separate boiler. It should be noted that the steam generated by direct contact with the ash is a “dirty” steam containing a variety of contaminants, making it unsuitable for most other purposes, but suitable for use in the gasification process.

[0066] The steam generated by direct or indirect contact can be introduced in the gasifier through various points of the gasifier. As shown in Figure 3, the steam can flow into the plenum space 4 via a channel and then be introduced in the gasifier through the grid 7, or be introduced into the center jet pipe 6 as part of the jet gas, or through the classifier 8 integrated with the ash discharge device 5. Since steam generated by direct contact contains ash which may cause grid plug problem for the grid 7, this direct contacting steam, preferably, is introduced to the classifier 8, such as through the classifier gas inlet on the classifier 8.

[0067] For example, in a SES gasifier (U.S. 13/532,769), if a 10 wt% ash feed stock is used, and the exit ash temperature is 1000°C, and is cooled to 400°C. Almost lkg of steam can be generated using the present invention for each 7kg of ash which accounts for an appreciable fraction of the total gasification steam required.

[0068] Referring to Figure 2, which illustrates the sequential arrangement of steps of one embodiment of the present process, the ash is first cooled to reach a temperature typically in the region of 300 to 550 °C in a vessel of the high temperature ash cooler 6 at a pressure close to the gasifier pressure. The ash is then depressurized to ambient pressure via equipment such as lock-hoppers. Regardless of the depressurizing method used, for safety and maintenance purposes, some form of isolation valve may be required between the high pressure region and the low pressure region and this valve is far less expensive and more reliable at the exit temperature of the high temperature ash cooler than a valve specified for service at temperatures (800 to 900 °C) near the

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PCT/US2014/026919 gasifier temperature (typically 1000 °C for the SES gasifier). Once the ash is at atmospheric pressure, it can be further cooled in a low temperature ash cooler 7 to safe handling temperatures, typically 50 to 140 °C, in any number of manners using readily available solids cooling equipment.

[0069] Accordingly another aspect of the present invention, in another embodiment, the invention further provides a method and system of coal gasification wherein at least a part of wastewater stream generated from one or more of the gas cleaning steps (e.g. the scrubber blowdown water) is recycled and applied to the hot ash residue from the gasification process, in such a manner that the salts and suspended solids in the waste water remain with the ash, wherein steam is generated in the process, which steam may be used for several purposes such as being fed back to the gasification process. The amount of water sent to wastewater treatment of the system is reduced.

[0070] In one embodiment, the invention provides a system for gasifying a carbonaceous material, referring to Figure 1, wherein the system comprises:

[0071] 1) a gasifier 1 into which the carbonaceous material such as coal is fed and gasified to produce a crude syngas containing gaseous and particulate pollutants;

[0072] 2) optionally, at least one device to remove a portion of the particulate pollutants and recycle the solids in the crude syngas such as cyclone 2, cool the crude syngas such as syngas cooler 3;

[0073] 3) optionally, another device to further remove solids from the gas stream, such as filter 4 as shown in Figure 1;

[0074] 4) a scrubber 5, wherein the cooled and partially cleaned syngas is further cleaned to produce a waste water stream;

[0075] 5) at least one ash cooler connected with the gasifier to receive hot ash under pressure from the gasifier, such as the high temperature ash cooler 6;

[0076] 6) a connection to deliver at least a portion of the waste water stream to the ash cooler, wherein all or part of the waste water stream is converted into steam; and [0077] 7) a connection to deliver the steam generated in the ash cooler back into the gasifier.

[0078] According to an embodiment of the present invention, the waste water stream from the scrubber can be delivered to either or both of the high temperature ash

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PCT/US2014/026919 cooler or low temperature ash cooler. Because the ash temperature is much higher than the boiling point of water in either of the ash coolers, the water in the waste water stream, along with other volatile components will evaporate, to generate a supply of steam, while leaving the particulate pollutants and other non-volatile components behind with the ash particles. The supply of steam from the high temperature ash cooler is directed to the gasifier and supplements the steam supply needed for the gasification process. Steam generated from the wastewater used in the low temperature ash cooler may be condensed in use as a low temperature heat source or the condensate used as process water makeup.

[0079] In one embodiment, this invention deals with the recycle of waste water emanating from a water scrubber used for removing solids from product syngas from e.g. a fluidized bed coal gasification process. Typically, a water scrubber follows the cyclones and filters (e.g. bag house filters or candle filters) used to remove solids from the gas. This scrubber captures most, or nearly all, of the halide, ammonia, cyanides, remaining particulate matter not removed in the cyclones and filters, and some trace gas species that are at least partially water soluble.

[0080] Scrubbers, or wet scrubbers suitable for the present invention, are common and well-known devices that use liquid to wash and remove unwanted particulate and/or gas pollutants from a gas stream. There are a diverse group of such devices that can be used. Scrubbers are one of the primary devices that control gaseous emissions, especially acid gases. Scrubbers can also be used for heat recovery from hot gases by flue-gas condensation. Wet scrubbing works via the contact of target compounds or particulate matter with the scrubbing solution, which may simply be water. Water soluble toxic and/or corrosive gases like HC1, H2S, SO2 or ammonia (NH₃) can be removed very well by a wet scrubber. The water spray may also condense certain condensables such as tar and oil. Removal efficiency of pollutants is improved by increasing residence time in the scrubber or by the increase of surface area of the scrubber solution by e.g. spraying.

[0081] According to one embodiment of the present invention, a portion (which includes all or none) of the waste water stream from the scrubber which contains the removed contaminants may be applied directly to contact with hot gasifier ash at the gasifier operating pressure which is typically, but not restricted to, 10 to 60 bar. Alternatively, the waste water stream may be applied in indirect heat transfer against the

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PCT/US2014/026919 hot ash, and substantially evaporated. In either case, the steam generated from the cooling or the hot ash and any contaminants in the wastewater stream that evaporate with the steam, can be re-introduced into the gasifier as part of the required steam for gasification purposes, reducing the overall water requirements for the gasification plant.

[0082] In another embodiment, a portion or all of the wastewater stream can be applied to the ash directly in a low pressure ash cooling step. In this case, some of the water may be used to partially hydrate the ash for dust control in handling, for example raising the hot ash water content from essentially zero to 5 wt%. Some of the water evaporates and this steam may also be as a low temperature heat source with the condensate reused as process water, be vented, be sent to a flare, or condensed and reused as process water after removal of any entrained ash.

[0083] In another embodiment, the method of the present invention places the salts and suspended solids from the wastewater into the ash product from the gasifier, reduces plant water consumption, and wholly or in part eliminates wastewater treatment for the gasification process. The high pressure steam generated from the direct injection of waste water to the hot ash can be directly connected to the gasifier, without having been cleaned to remove any entrained ash particles, thereby reducing the need for high pressure clean steam, and resulting in significant increase in heat energy efficiency, yet only minimal increase in capital costs.

[0084] It is understood that examples and embodiments described herein are for illustrative purpose only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents and patent applications cited in this patent are hereby incorporated by reference for all purposes.

[0085] One or more features from any embodiment maybe combined with one or more features of any other embodiment without departing from the scope of the disclosure. The above description is illustrative and is not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of the disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the claims along with their full scope or equivalents.

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2014240146 07 Aug 2018 [0086] Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises or comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0087] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

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Claims

The claims defining the invention are as follows:

1. A gasification system comprising:

a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable hot ash under pressure are discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and a high temperature ash cooler connected to the gasifier and into which the flowable hot ash under pressure is discharged, wherein the high temperature ash cooler comprises a water supplying apparatus that provides atomized water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized water completely and instantaneously vaporized upon contact with the flowable hot ash.
2. The gasification system of claim 1, wherein the atomized water is vaporized to generate steam having a pressure sufficient to replace the fluidizing and reacting steam needed for the gasifier.
3. The gasification system of claim 1 or claim 2, wherein the water-supplying apparatus further supplies water to the high temperature ash cooler to cool the ash via indirect heat transfer.
4. The gasification system of claim 3, wherein the high temperature ash cooler comprises a cooling jacket, or cooling coils, or a cooling panel through which the cooling water flows and absorbs heat indirectly from the hot ash.
5. The gasification system of claim 3 or claim 4, further comprising a connection between the high temperature ash cooler and the gasifier, wherein steam generated from the water for indirect heat transfer is supplied to the gasifier.
6. The gasification system of any one of claims 1 to 5, further comprising:

a depressurizing device which is connected to the high temperature ash cooler to receive the cooled high pressure ash from the high temperature ash cooler, and which is able to reduce the pressure of the ash to ambient pressure.

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7. The gasification system of claim 6, wherein the depressurizing device comprises a double sealed lock hopper.
8. The gasification system of claim 1, further comprising:

a second ash cooler device which is connected to the high temperature ash cooler to receive the cooled high pressure ash from the high temperature ash cooler, and which is able to further lower the temperature of the ash to ambient temperature.
9. The gasification system of claim 6 or 7, further comprising:

a second ash cooler device which is connected to the depressurizing device to receive the ash from the high temperature ash cooler, and which is able to further lower the temperature of the ash to ambient temperature.
10. The gasification system of claim 8, further comprising:

a depressurizing device which is connected to the second ash cooling device to receive the ash from the second ash cooling device, and which is able to reduce the pressure of the ash to ambient pressure.
11. The gasification system of any of claims 1 to 10, wherein the high temperature ash cooler comprises a fluidized bed or a moving bed wherein the high pressure ash makes direct contact with the atomized water from the water supplying apparatus.
12. The gasification system of any of claims 1 to 11, wherein the water supply apparatus comprises means to disperse the liquid into the ash, selected from the group consisting of spray nozzles, atomizing spray nozzles and microporous pipes.
13. A gasification system comprising:

a fluidized bed gasifier into which a carbonaceous feed material is fed, and out of which a product gas stream and a flowable hot ash under pressure are discharged, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants,

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2014240146 07 Aug 2018 a wet scrubber for removing the pollutants from the product gas stream and producing a waste water stream, a high temperature ash cooler connected with the gasifier to receive the flowable hot ash from the gasifier; and a connection to deliver at least a portion of the waste water stream to the high temperature ash cooler, wherein the high temperature ash cooler comprises a water supplying apparatus that atomizes the waste water stream from the wet scrubber and provides the atomized waste water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized waste water completely and instantaneously vaporized upon contact with the flowable hot ash.
14. The gasification system of claim 13, wherein he atomized waste water is vaporized to generate steam having a pressure sufficient to replace the fluidizing and reacting steam needed for the gasifier.
15. The gasification system of claim 13 or 14, further comprising a low temperature ash cooler, and wherein at least a portion of the waste water is delivered to the low temperature ash cooler.
16. A method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable hot ash under pressure are discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, the method comprising:

providing atomized water to be in direct contact with the flowable hot ash in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment in a high temperature ash cooler which is connected to the gasifier and into which the hot ash under pressure is discharged, with the atomized water completely and instantaneously vaporized upon contact with the flowable hot ash.
17. The method according to claim 16, wherein the atomized water is vaporized to

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2014240146 07 Aug 2018 generate steam having a pressure sufficient to replace the fluidizing and reacting steam needed for the gasifier.
18. The method according to claim 16 or 17, further comprising:

receiving the cooled high pressure ash from the high temperature ash cooler, and reducing the pressure of the ash to ambient pressure with a depressurizing device which is connected to the high temperature ash cooler.
19. The method according to claim 18, further comprising:

receiving the cooled ambient pressure ash from the depressurizing device, and further lowering the temperature of the ash to ambient temperature with a second ash cooler device which is connected to the depressurizing device.
20. A method for cooling ash discharged from a fluidized bed gasifier, wherein a fluidized bed gasifier is fed with a carbonaceous feed material, and a product gas stream and a flowable ash under pressure are discharged out of the gasifier, wherein the gasifier is operated at a temperature just under a melting point of the ash and under a pressure not less than 6 bar gauge, and wherein the product gas stream comprises gaseous and particulate pollutants, the method comprising:

removing the pollutants from the product gas stream and producing a waste water stream with a wet scrubber, delivering at least a portion of the waste water stream from the wet scrubber to a high temperature ash cooler connected with the gasifier which receives the flowable hot ash from the gasifier, and atomizing the waste water and providing the atomized waste water to be in direct contact with the flowable hot ash in the high temperature ash cooler in an amount for cooling the flowable hot ash to a temperature suitable for the ash to be handled with conventional carbon steel equipment, with the atomized wastewater completely and instantaneously vaporized upon contact with the flowable hot ash.
21. The method according to claim 20, further comprising delivering at least a portion of the waste water to a low temperature ash cooler.

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22. The method according to claim 20 or 21, wherein the atomized waste water is vaporized to generate steam having a pressure sufficient to replace the fluidizing and reacting steam needed for the gasifier.

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1/3 syngas

Figure 1

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2/3

Figure 2

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3/3

Steam/Oxygen