NL2010791C2 - Energy saving method and apparatus for removing harmful compounds from a gas mixture. - Google Patents
Energy saving method and apparatus for removing harmful compounds from a gas mixture. Download PDFInfo
- Publication number
- NL2010791C2 NL2010791C2 NL2010791A NL2010791A NL2010791C2 NL 2010791 C2 NL2010791 C2 NL 2010791C2 NL 2010791 A NL2010791 A NL 2010791A NL 2010791 A NL2010791 A NL 2010791A NL 2010791 C2 NL2010791 C2 NL 2010791C2
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- Prior art keywords
- gaseous stream
- heat
- heat exchanging
- main line
- condenser
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- 150000001875 compounds Chemical class 0.000 title claims description 123
- 238000000034 method Methods 0.000 title claims description 42
- 239000000203 mixture Substances 0.000 title claims description 42
- 238000001816 cooling Methods 0.000 claims description 83
- 239000007789 gas Substances 0.000 claims description 52
- 238000009833 condensation Methods 0.000 claims description 32
- 230000005494 condensation Effects 0.000 claims description 32
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 238000011144 upstream manufacturing Methods 0.000 claims description 20
- 238000007711 solidification Methods 0.000 claims description 19
- 230000008023 solidification Effects 0.000 claims description 19
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 239000007788 liquid Substances 0.000 claims description 12
- 238000003860 storage Methods 0.000 claims description 9
- 238000009434 installation Methods 0.000 claims description 4
- 238000009825 accumulation Methods 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 230000000694 effects Effects 0.000 claims description 2
- 238000000605 extraction Methods 0.000 claims 1
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 66
- 230000008014 freezing Effects 0.000 description 7
- 238000007710 freezing Methods 0.000 description 7
- 231100001261 hazardous Toxicity 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000011084 recovery Methods 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 238000004880 explosion Methods 0.000 description 3
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical compound C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 description 2
- -1 benzene Chemical class 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000003915 liquefied petroleum gas Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 238000010792 warming Methods 0.000 description 2
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000013056 hazardous product Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/30—Sulfur compounds
- B01D2257/304—Hydrogen sulfide
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
- B01D2257/702—Hydrocarbons
- B01D2257/7027—Aromatic hydrocarbons
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/01—Engine exhaust gases
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/45—Gas separation or purification devices adapted for specific applications
- B01D2259/455—Gas separation or purification devices adapted for specific applications for transportable use
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/65—Employing advanced heat integration, e.g. Pinch technology
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/26—Drying gases or vapours
- B01D53/265—Drying gases or vapours by refrigeration (condensation)
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Description
NLP193361
Energy saving method and apparatus for removing harmful compounds from a gas mixture
Field of the invention
The invention relates to a method and apparatus for removal of harmful compounds from a gas mixture wherein harmful compounds are removed from a gaseous stream comprising a gas mixture containing harmful compounds in a series of temperature lowering steps, wherein the resulting cold clean gaseous stream is applied to provide a source of cooling. The invention relates in particular to a method and apparatus for removal of harmful compounds gases present in storage tanks and ship's tanks. The invention may also be applied in removal of exhaust gases and gases that are released during shale gas recovery.
Background of the invention
Usually tanks are ventilated, especially if hazardous compounds, such as benzene, have been present in the tank. Ventilating is a time-consuming procedure and produces vapours that are potentially dangerous to the environment. When emitted these vapours are combusted in an incinerator or discharged into the outside air. These methods are both expensive and detrimental to the environment and therefore not desired and often even not allowed.
PCT application publication number W02010/052020 A1 describes an alternative method for removing vapours of hazardous compounds from a tank. In said method vapour present in a tank is heated. Subsequently the vapour is sucked out of the tank using a pump. The vapour is subsequently cooled by means of a cooling system. The compounds condensed as a result of this cooling down are collected in a reservoir for liquids and the residual vapour is passed back again into the tank. This cycle is then repeated until an acceptable or desired residual level of hazardous material in the tank has been reached. The method described in W02010/052020 A1 seeks to improve previous methods of cleaning and ventilating tanks but nonetheless it has its limitations, because many of the hazardous compounds transported in tanks are highly flammable. As a result heating the tank often is impossible and/or not allowed by authorities because of safety rules. Heating the vapours present in the tank entails the risk of ignition and thus an increased risk of explosion. Moreover this method uses relatively much external energy when heating the tank.
A further improvement is described in W02013/002637 Al, wherein residual material is passed out of a tank in the form of vapour. The vapour is subsequently cooled down. Due to cooling down, a part of the vapour condenses. The liquid components are then collected. An inertising system supplies an inert gas or inert gas mixture to the residual vapour and the overall gas mixture is heated and passed back into the tank. The cycle is repeated until an acceptable or desired residual level of material in the tank has been reached. This way the risk of ignition is avoided and the external energy required for cleaning tanks is reduced.
However, the present inventors found that there is still a need for improvement. The abovementioned methods and apparatuses are in particular designed to remove harmful residues having a condensation temperature of preferably between -10 °C and 10 °C. However, many harmful compounds have a condensation temperature at atmospheric pressure which is lower than -10 °C. For instance CO2 sublimes (solid-gas phase change) at 1.0 bar, normal pressure, at -78 °C. At atmospheric pressure, SO2 will begin to condense at -10.1 °C. By-products of fracking during shale gas recovery such as methane gas or H2S will only condense at atmospheric pressure at temperatures up to -161 °C and -60.7 °C respectively.
Cooling of compounds to very low temperatures by means of a conventional cooling system requires an undesirably large amount of energy. It is also time consuming to cool down these compounds to a level where condensation or solidification takes place. Although it would be possible to cause condensation of the abovementioned harmful compounds at a lower temperature by increasing the pressure, this is not a favourable option. The energy required to increase the pressure would be high and thus lead to high costs. In addition, increasing pressure in areas with inflammable materials may increase the risk of explosions. Increasing the pressure in the tank may also increase the risk of explosions.
Therefore, there is a strong need for a technique that can be applied to remove harmful compounds having a wide range of condensation temperatures, including temperatures as low as -250 °C, from gas mixtures in a fast, safe and energy saving manner .
Summary of the invention
In the method and apparatus of the invention harmful compounds are removed from a gaseous stream in a series of temperature lowering steps, wherein the resulting cold clean gaseous stream is used to provide a source of cooling. The cold clean gaseous stream is thus reused to cool down a gaseous stream comprising harmful compounds before entering a heat exchanging condenser, thereby lowering the energy required to condense or freeze harmful compounds in that heat exchanging condenser .
The invention relates to a method for removing harmful compounds from a gas mixture, comprising the steps of: a) passing a gaseous stream comprising a gas mixture containing harmful compounds from a gas source into a heat exchanging condenser cooled by a cold source; b) cooling the gaseous stream in the heat exchanging condenser to a predetermined temperature suitable to condense or solidify at least one predetermined harmful compound; c) passing the gaseous stream from said heat exchanging condenser to a further heat exchanging condenser cooled by a cold source; d) cooling the gaseous stream in the further heat exchanging condenser to a predetermined temperature suitable to condense or solidify at least one predetermined harmful compound; e) optionally repeating steps c and d one or more time, wherein the total number of heat exchanging condensers is sufficient to reach a desired level of the harmful compounds in the gas mixture contained in the gaseous stream and a clean gaseous stream is formed; and, f) when a desired level of the harmful compounds in the gas mixture contained in the gaseous stream has been reached and a clean gaseous stream is formed, passing the clean gaseous stream from the last heat exchanging condenser to at least one heat exchanger wherein the or each of the at least one heat exchanger is arranged such that it brings the clean gaseous stream in heat exchanging contact with the gaseous stream comprising harmful compounds flowing upstream of a heat exchanging condenser; thereby cooling down the gaseous stream comprising harmful compounds passing into said heat exchanging condenser and lowering the amount of energy required to effect condensation or solidification of the harmful compounds in the respective heat exchanging condenser; g) passing the clean gaseous stream from the at least one heat exchanger; h) removing the condensed or solidified harmful compounds from the heat exchanging condensers.
In another aspect the invention relates to an apparatus for removing harmful compounds from a gas mixture, comprising: a main conduit (1) provided with a pump (2) for passing a gaseous stream comprising a gas mixture containing harmful compounds from a main inlet (3) of said main conduit to a main outlet (4) of said main conduit; a first heat exchanging condenser (5) incorporated in said main conduit, the first heat exchanging condenser comprising a first compartment (6) having an inlet (7) to receive said gaseous stream from the main conduit, an outlet (8) for removal of condensed or solidified harmful compounds, and an outlet (9) for passing the gaseous stream further into the main conduit, and a second compartment (10) comprising an inlet (11) to receive a cold medium from a cooling source (12) and an outlet (13) for the exit of said cold medium; one or more further heat exchanging condenser (5', 5x) incorporated in said main conduit and placed in serial arrangement with said first heat exchanging condenser (5) and with each other, each of the one or more further heat exchanging condenser comprising a first compartment (6', 6x) having an first inlet (7', 7x) to receive said gaseous stream, an outlet (8', 8x) for removal of condensed or solidified harmful compounds, and an outlet (9, 9x) for passing the gaseous stream further into the main conduit, and a second compartment (10', lOx) comprising an inlet (11', llx) to receive a cold medium from a cooling source (12', 12x) and an outlet (13', 13x) for the exit of said cold medium; the apparatus further comprising one or more heat exchanger (14, 14x) , the or each heat exchanger being incorporated in the main conduit in heat exchanging contact with the main conduit at a position directly upstream of a heat exchanging condenser (5, 5', 5x) , said one or more heat exchanger (14, 14x) having a first compartment (15, 15x) having an inlet (16, 16x) to receive a clean gaseous stream, an outlet (17, 17x) for passing on said clean gaseous stream further into the main conduit, and a second compartment (18, 18x) comprising an inlet (19, 19x) to receive the gaseous stream comprising a gas mixture containing harmful compounds from the main conduit, and an outlet (20, 20x) for passing the gaseous stream further into the main conduit, wherein the first of the one or more heat exchanger (14) is connected via the main conduit with the last of the one or more heat exchanging condenser (5x).
The present invention provides a method and apparatus for removing harmful compounds from a gas mixture that enable cooling down gaseous streams to temperatures in a range of -250 °C to 250 °C in an energy saving manner. The apparatus is suitable to perform the method of the invention. The invention provides a technique that is applicable to remove a broad range harmful compounds having a wide range of condensation or freezing temperatures from gas mixtures in a fast, safe and energy saving manner. The invention thus provides a technique that enables a gaseous stream to cool down from 25 °C or higher to -200 °C or lower by using the cooled clean gaseous stream to reduce the amount of energy required to perform the cooling steps. The method and apparatus of the invention may be used in the removal of harmful compounds such benzene, ethanol, methanol, methane, gasoline, crude oil, diesel, liquefied petroleum gas (LPG) , toluene, acrylonitrile, styrene, xylene, NOx, H2S, S02, C02. By recovering these compounds the invention also allows for easy recycling of expensive materials. The invention provides a technology which is applicable to remove a broad range of harmful compounds in separate steps for each particular harmful compound. The invention is however also applicable to remove one particular compound in a very efficient way by cooling a harmful compound to far below its condensation temperature. With the technology of the invention this results in very fast condensation or freezing/ solidification without the burden of high energy use .
Short description of the drawings
Figure 1: Schematic representation of an exemplary embodiment of the apparatus of the invention. The solid line through the main conduit represents a gaseous stream containing a gas mixture containing harmful compounds, the dotted line represents a clean gaseous stream.
Figure 2: A: Schematic representation of removal of benzene according to an exemplary embodiment of the method of the invention; B: scheme for removal of H2S according to the method of the invention. The solid line through the main conduit represents a gaseous stream containing a gas mixture containing harmful compounds, the dotted line represents a clean gaseous stream.
Detailed description of the invention
In the method of the invention harmful compounds are removed from a gaseous stream in a series of temperature lowering steps, wherein the resulting cold clean gaseous stream is used to provide a source of cooling for these temperature lowering steps .
In the method of the invention, a gaseous stream comprising a gas mixture containing harmful compounds is led through two stages, wherein in the first stage harmful compounds are condensed or solidified in two or more heat exchanging condensers wherein each subsequent heat exchanging condenser cools the gaseous stream to a lower temperature than the previous heat exchanging condenser. In the second stage the resulting cold and clean gaseous flow is then used to provide additional cooling for the condensation or solidification steps of the first stage.
In the first stage a gaseous stream comprising a gas mixture containing harmful compounds is passed through a conduit through a series of heat exchanging condensers. During passing the gaseous stream is cooled down in a series of multiple cooling steps using these heat exchanging condensers. During these cooling steps harmful compounds are condensed or solidified in the heat exchanging condensers. Whether a heat exchanging condenser causes condensation or solidification depends on the harmful compound to be removed and how of the heat exchanging condenser is designed. For purposes of the invention a particular harmful compound may be either solidified or condensed because both phases allow easy removal of the harmful compound from a heat exchanging condenser. The number of heat exchanging condensers a gaseous stream comprising a gas mixture containing harmful compounds passes in the first stage is at least two, but any suitable number of heat exchanging condenser assisted cooling steps required to obtain a desirable level of harmful compounds may be applied. In order to realize cooling of the gaseous stream, heat exchanging condensers are used that are cooled by a cold source. In an exemplary embodiment of the invention three heat exchanging condenser assisted condensation or solidification steps may be applied. The first condensation or solidification step may for instance serve to cool down a gaseous stream to a temperature of -25 °C, a second condensation or solidification step may for instance cool down the gaseous stream to -60 °C and a third condensation or solidification step may for instance cool down the gaseous stream to -200 °C.
The heat exchanging condensers enabling condensation or solidification of harmful compounds may be cooled by separate cooling sources. The cooling source connected to the heat exchanging condensers may be a separate cooling system for each heat exchanging condenser. Such cooling systems may be provided by a Stirling engine. Alternatively, the heat exchanging condensers may be connected to a cold source that serves to cool down also other heat exchanging condensers in the first stage.
The heat exchanging condenser(s) in the first method step(s) of condensation or solidification (with cooling down to approximately -70 °C) may be cooled using conventional cooling systems, for instance using a Stirling engine or a cooling installation with turbine expansion. Later method steps may require rather deep cooling (with cooling down to -250 °C) . Therefore a cryogenic cooling installation may more suitable for these deep cooling steps, for instance a Stirling cryo-cooler. The cryogenic cooling system may also be applied to serve as a cooling device for the condensation or solidification steps until approximately -70 °C. The deep cooling steps may require that the rate of flow of the gaseous stream passing through the heat exchanging condenser for deep cooling is decreased in order to create a longer residence time which is sufficient to freeze or condense compounds with low condensation and/ or melt temperatures. An attractive alternative is to use liquid nitrogen as a cooling source for the cryogenic cooling step. The source of liquid nitrogen may be a liquid nitrogen tank. Such tanks are commercially available. Alternatively the apparatus of the invention may be connected to a system that is capable of producing liquid nitrogen. In such a system liquid nitrogen may be produced by means of a Stirling cryo-cooler or by using pressure swing adsorption technology. The cooling source thus may be one or more selected from the group of a Stirling engine, a cooling installation with turbine expansion, a Stirling cryo-cooler and a liquid nitrogen tank.
Use of liquid nitrogen for cooling purposes is preferred because nitrogen may also be used to be injected into the gaseous stream to inertise the gas mixture contained therein. This way the nitrogen serves two purposes: cooling the gaseous stream and increasing safety by inertising it.
After the final condensation or solidification step, when the level of harmful compounds has reached an acceptable level, the resulting clean gaseous stream goes through a second stage of one or more heating step wherein heat exchange of the clean gaseous stream with the gaseous stream comprising a gas mixture containing harmful compounds takes place. The heating results from the heat transfer that is effected by means of one or more heat exchangers which are each incorporated in the main conduit directly upstream of one of the two or more heat exchanging condensers through which the gaseous stream comprising a gas mixture containing harmful compounds passes in the first stage. In the exemplary embodiment described above, which comprises up to three heat exchanging condenser assisted cooling steps, three of these heat exchangers may be applied. The cold clean gaseous stream flowing through the heat exchangers serves to cool the gaseous stream before it enters a heat exchanging condenser. Because of this cooling, the amount of energy required to realise condensation by the heat exchanging condensers of the first stage is significantly lowered.
In a preferred embodiment, the clean gaseous stream is brought in heat exchanging contact with the gaseous stream comprising harmful compounds directly upstream of any heat exchanging condenser; thereby cooling down the gaseous stream comprising harmful compounds passing into said heat exchanging condenser. For example, when three heat exchanging condenser assisted cooling steps are performed in the first stage, it is preferred that also three heat exchanger assisted heat exchange steps take place, because this way the energy required for each condensation step in a heat exchanging condenser is lower.
Alternatively, the clean gaseous stream is brought in heat exchanging contact with the gaseous stream comprising harmful compounds directly upstream of any heat exchanging condenser that cools the gaseous stream comprising harmful compounds down to a temperature below -7 0 °C; thereby cooling down the gaseous stream comprising harmful compounds passing into said heat exchanging condenser.
In case the invention is applied to cool down high temperature gases (for instance having a temperature of between 200 and 600 °C) , it is preferred to perform an additional precooling step before the gaseous stream enters the first heat exchanger assisted or heat exchanging condenser assisted cooling step. Such a "precooling" step may be performed by using a cooling jacket around the main conduit. In case exhaust gases of a ship are passed through the apparatus of the invention a "precooling" step may be conveniently performed by means of (sea)water .
If desired, a first heat exchanging condenser assisted solidification or condensing step may be applied to remove moisture or water from the gaseous stream. This may be beneficial if harmful compounds are to be removed from the gaseous stream in a pure form, allowing easy recycling of the harmful compounds .
The method and apparatus of the invention can be conveniently controlled by means of computer implemented software and parameters such as rate of flow, pressure, temperature and concentration of compounds may be continuously measured in order to determine the optimal condensation or solidification temperature in the heat exchanging condensers.
Upon beginning the method of the invention, the conduits, heat exchanging condensers and heat exchangers need to have a predetermined sufficient low temperature. Therefore, before passing a gaseous stream containing a gas mixture comprising harmful residues through the apparatus of the invention the apparatus is precooled. For precooling of the apparatus, preferably clean air is used instead of the gas mixture from which harmful compounds are to be removed.
Precooling of the components of the apparatus may be performed in loops using the cooling sources for the heat exchanging condensers. These cooling sources may be incorporated in separate loops wherein circulation of cold air between a particular heat exchanging condenser and a heat exchanger placed immediately upstream of that respective heat exchanging condenser takes place.
An alternative and preferred way of precooling the conduits is to use the cooling source used for the deep cooling steps, i.e. the cryogenic or cry-cooling steps. The apparatus of the invention therefore may be precooled by injection of liquid nitrogen. It is important that the liquid nitrogen is injected between the last heat exchanging condenser and the first heat exchanger warming up the clean gaseous stream passing from said last heat exchanging condenser. This allows deep precooling of the heat exchanging condensers for condensation of harmful compounds with very low condensation temperatures (e.g. < -70 °C) while more upstream heat exchanging condensers are precooled to a higher temperature. If said upstream heat exchanging condensers would be precooled to a very low temperature, there would be a risk that harmful compounds having a melting point above this temperature would solidify in the main conduit and block the circulation.
After the apparatus is precooled the gaseous stream comprising harmful compound is passed into the apparatus.
The outlet for removal of condensed harmful compounds and the outlet for passing the gaseous stream further into the main conduit may be one outlet, leading to the main conduit, wherein the main conduit is connected via a valve with a tank or reservoir wherein hazardous compounds can be stored. In this case an outlet for removal of condensed harmful compounds and an outlet for passing the gaseous stream further into the main conduit are the same. Alternatively the heat exchanging condenser is equipped with two outlets, one outlet for removal of condensed harmful compounds and another outlet for passing the gaseous stream further into the main conduit.
In case the invention is applied to remove harmful compounds from a gas mixture from a tank, condensed or solidified harmful compounds may be removed from the heat exchanging condensers at the moment that harmful compounds are removed from the tank to a desired level. For this purpose the heat exchanging condensers may be warmed up or cooling may be switched off in order to render the harmful compounds removable. Any number of valves, further conduits and other means for removing the condensed or solidified harmful compound from the heat exchanging condensers may be applied.
In particular when harmful compounds are to be removed from a continuous gaseous stream, for instance when the invention is applied to remove harmful compounds from exhaust gases of an engine, it may be more preferable to position for each heat exchanger designed for condensation or solidification of a particular harmful compound a bypass to a second or further heat exchanging condenser that is suitable for condensation or solidification of the same compound and/or cooling down to the same temperature. In case a heat exchanging condenser has reached a certain limit of capacity, the gaseous stream may be passed to this second or further heat exchanging condenser. The connection of the heat exchanging condenser that has reached the limit of capacity to the main conduit can then be closed, the heat exchanging condenser can be warmed up and the harmful compound can be drained to a storage reservoir.
In the storage reservoir for harmful compounds it is likely that apart from being condensed or solidified, said harmful compounds will not be fully condensed or solidified, but will be to a certain extent in a gaseous form. These gaseous harmful compounds may be passed back to the gaseous stream passing through the main conduit via a conduit connected between the reservoir and the main conduit. The vapour may then be further condensed or solidified in the next heat exchanging condenser. This way it is prevented that harmful compounds are emitted from the storage reservoirs.
The principle of the invention is further explained Figure 1. Figure 1 shows a schematic representation of an embodiment of the apparatus of the invention. In the apparatus shown in Figure 1 a gaseous stream is passed via a main conduit (1) from a main inlet (3) of said main conduit to a main outlet (4) of said main conduit. The main conduit is provided with a pump (2) to provide a stream. The pump may be incorporated at any suitable place in the main conduit, thereby performing a sucking and/or pressing action. The gaseous stream is passed via the main conduit through a first heat exchanging condenser (5) . The first heat exchanging condenser comprises a first compartment (6) having an inlet (7) to receive said gaseous stream, an outlet (8) for removal of condensed harmful compounds, and an outlet (9) for passing the gaseous stream further into the main conduit. The heat exchanging condenser also comprises a second compartment (10) comprising an inlet (11) to receive a cold medium from a cooling source (12) and an outlet (13) for the exit of said cold medium, for instance back to the cold source.
In one embodiment each heat exchanging condenser is cooled by a separate cooling source.
In another embodiment one cold source serves as a cooling source for all heat exchanging condensers, such as a cooling source that capable of cryo-cooling. To ensure that each heat exchanging condenser cools down to the desired predetermined temperature any means suitable to realise this can be applied, for instance heating jackets, isolation jackets.
In the heat exchanging condenser the gaseous stream is cooled to a predetermined temperature suitable to condense or freeze a predetermined harmful compound. After leaving the first heat exchanging condenser the gaseous flow is passed to one or more further heat exchanging condenser (5', 5x) incorporated in said conduit and arranged in serial arrangement with said first heat exchanging condenser (5) and with each other. Each of this one or more further heat exchanging condenser comprises a first compartment (6', 6x) having an first inlet (7', 7X) to receive said gaseous stream, an outlet (8', 8x) for removal of condensed harmful compounds, and an outlet (9', 9x) for passing the gaseous stream further into the conduit, and a second compartment (10', lOx) comprising an inlet (11', llx) to receive a cold medium and an outlet (13', 13x) for exiting of said cold medium. In each of the heat exchanging condensers the gaseous stream is cooled further down to a further lower predetermined temperature.
The heat exchanging condensers (5, 5', 5x) are preferably connected via a further conduit (21, 21', 21x) with a reservoir (22x) for storage of harmful compounds.
As many heat exchanging condensers as desired may be incorporated into the apparatus. The apparatus of the invention comprises at least two heat exchanging condensers, but it is well possible to have more heat exchanging condensers arranged in serial arrangement with respect to each other, wherein a heat exchanging condenser which is positioned downstream to another heat exchanging condenser cools down the gaseous stream containing harmful compounds to a temperature which is lower than the temperature to which the adjacent upstream heat exchanging condenser cooled down the gaseous stream. This way a stepwise decrease in temperature is realized, each step cooling down to a temperature which is suitable to condense or freeze a particular harmful compound or particular harmful compounds. For instance, when it is desired to remove a large number of harmful compounds with different condensation or melting temperatures, also a large number of cooling steps and consequently heat exchanging condensers may be required.
After a desired level of harmful materials is obtained and the gaseous stream has passed the last heat exchanging condenser in the series the resulting clean cold gaseous stream is passed to one or more heat exchanger (14, 14x) , wherein each of the heat exchangers is incorporated in the main conduit in heat exchanging contact with a part of the main conduit at a position directly upstream of the first heat exchanging condenser (5) or between two heat exchanging condenser (5, 5', 5x) , the heat exchangers (14, 14x) having a first compartment (15, 15x) having an inlet (16, 16x) to receive said gaseous stream and an outlet (17, 17x) for passing said clean gaseous stream further into the conduit and a second compartment (18, 18x) comprising an inlet (19, 19x) to receive a gaseous stream containing a gas mixture containing harmful compounds and an outlet (20, 20x) for passing the gaseous stream containing a gas mixture containing harmful compounds further into the main conduit. The gaseous stream containing a gas mixture containing harmful compounds is then passed via the main conduit to a heat exchanging condenser. After passing the last heat exchanger for increasing the temperature of the clean gaseous flow, the clean gaseous flow is passed out of the main outlet (4) . The heat exchanging condensers (5, 5', 5x) are preferably connected via a further conduit (21, 21x) with a reservoir (22x) for storage of harmful compounds.
In one embodiment a heat exchanger is incorporated in the main conduit in heat exchanging contact with the main conduit at an position directly upstream of a heat exchanging condenser cooling the gaseous stream to a temperature below -70 °C. In another embodiment a heat exchanger is incorporated in the main conduit in heat exchanging contact with the main conduit at an position directly upstream of each heat exchanging condenser. In figure 1 each heat exchanger is incorporated in the main conduit in heat exchanging contact with the main conduit at an position directly upstream of each heat exchanging condenser. This is a preferred arrangement.
The invention may be applied as an end of pipe technology. Such a technique is called 'end-of-pipe' because it is normally implemented as a last stage of a process before compounds are disposed of or delivered. In this respect the clean gaseous stream obtained after removal of harmful compounds may be released in the open air via the outlet. In case the invention is applied as an end of pipe technology said gaseous stream is passed once only, without being circulated, through the main conduit.
The apparatus may also be designed as a closed system. This means that hazardous compounds cannot leave the apparatus, except when this is desirable, such as when hazardous compounds have to be removed from the reservoirs. A closed system should furthermore be understood to mean that in such a system supply and discharge of gasses or gas mixtures only takes place when this is desirable. In such a closed system all harmful compounds are removed from the gaseous stream to a desired level in one cycle. The clean gaseous stream or air may then circulate in the system after the first cycle. The person skilled in the art will recognize that each different harmful compound may require removal to a different desired level depending on local legal requirements.
For safety reasons, in a preferred embodiment the apparatus of the invention is placed in a refrigerated container, wherein the cold sources (12) of the apparatus are placed in a separate compartment of the container which is under continuous overpressure, the other components of the apparatus being placed in another separate compartment of the container, wherein said another separate compartment is a deep cooled compartment.
In another embodiment, the source of the gaseous stream may be a storage tank or a ship's tank, that was used for instance to transport benzene or ethanol. In this embodiment the inlet and the outlet of the main conduit may be connected to said storage tank or ship's tank. The source may also be an exhaust pipe of an engine or another industrial application. In this embodiment the inlet of the main conduit may be connected to an exhaust pipe, such as an exhaust pipe of an engine or another industrial application, and the outlet of the main conduit may be in open connection to the open air. The source of the gaseous stream may also be a buffer vessel or an accumulation tank of a shale gas recovery system. In this embodiment wherein the inlet of the main conduit is connected to a buffer vessel or an accumulation tank of a shale gas recovery system and the outlet of the main conduit is in open connection to the open air.
Examples
An exemplary embodiment of the apparatus comprising three heat exchanging condensers and three heat exchangers for warming up the clean gaseous stream, each of the latter being placed in connection with the main conduit directly upstream of one of the heat exchanging condensers, may be applied to remove benzene (Figure 2A) or H2S (Figure 2B) from a gaseous stream. Because the purpose of figure 2A and B is to illustrate the method of the invention rather than the apparatus of the invention the schemes of figures 2A and B represent a simplified and incomplete representation of the apparatus.
In these examples benzene has a concentration of > 100% LEL, Lower Explosive Limit, (100% LEL = 12000 ppm) and an initial temperature of 25 °C. In the H2S example H2S has a concentration of 11,5% by weight and an initial temperature of 25 °C. In these examples benzene or H2S are passed through the apparatus with a rate of flow of 1000 m3/h by means of a pump (2) .
For a first freezing/condensing step, the benzene or H2S containing gaseous stream is passed first through the second compartment of a first heat exchanger (14'') . After passing the first heat exchanger (14''), the temperature drops to -20 °C. The stream then passes through the heat exchanging condenser (5) placed directly downstream of heat exchanger (14''), which causes a temperature drop to -25 °C.
For a second freezing/condensing step, to remove remaining benzene or H2S in the gaseous stream left after the first freezing/condensing step the gaseous flow then passes the second compartment of another heat exchanger (14') . Here the temperature drops to -50 °C. The stream then passes through the heat exchanging condenser (5') placed directly downstream of heat exchanger (14'), which causes a temperature drop to -60 °C.
For a third freezing/condensing step, to remove further remaining benzene or H2S in the gaseous stream left after the second condensation step the gaseous flow then passes the second compartment of another heat exchanger (14), the temperature drops to -75 °C in case of benzene or -155 °C in case of H2S. The stream then passes through the heat exchanging condenser (5'') placed directly downstream of heat exchanger (14), which causes a temperature drop to -95 °C in case of benzene or -175 °C in case of H2S.
After this step a clean gaseous stream consisting of clean air or (injected) nitrogen is obtained with a benzene or H2S concentration of less than 2 ppm). The clean gaseous stream is then passed through a first compartment of heat exchanger (14), where the temperature of the clean gaseous flow increases to -70 °C (benzene and H2S), because of the warmer gaseous stream entering the second compartment of heat exchanger (14). Subsequently the clean gaseous stream is passed through a first compartment of heat exchanger (14'), where the temperature of the clean gaseous flow increases to -35 °C, because of the warmer gaseous stream entering the second compartment of heat exchanger (14') . Subsequently the clean gaseous stream is passed through a first compartment of heat exchanger (14''), where the temperature of the clean gaseous stream increases to 10 °C, because of the warmer gaseous stream entering the second compartment of heat exchanger (14') . After this the clean gaseous stream is discharged from the apparatus.
Under these circumstances cooling down from 25 °C to -25 °C a gaseous stream containing benzene or H2S requires a cooling capacity of approximately 67 kW (benzene and H2S) . It is estimated that heat exchanger (14'') has a cooling capacity of approximately 64 kW under these circumstances. Therefore only 3 kW is needed from an external cold source (12).
Cooling down from -25 °C to -60 °C a gaseous stream containing benzene or H2S requires a cooling capacity of approximately 13 kW. It is estimated that the heat exchanger (14') has a cooling capacity of approximately 9 kW under these circumstances. Therefore only 4 kW is needed from an external cold source (12').
Cooling down from -60 °C to -95 °C a gaseous stream containing benzene requires a cooling capacity of approximately 12 kW. It is estimated that the heat exchanger (14) has a cooling capacity of approximately 5 kW under these circumstances. Therefore only 7 kW is needed from an external cold source (12'') . Cooling down from -60 °C to -175 °C a gaseous stream containing H2S requires a cooling capacity of approximately 67 kW. It is estimated that the heat exchanger (14) has a cooling capacity of approximately 60 kW under these circumstances.
Therefore only 7 kW is needed from an external cold source (12" ) .
From this example follows that if the cold clean gaseous stream would not be applied to cool down the gaseous stream containing benzene before entering the heat exchanging condensers an external energy source providing a cooling capacity of 92 kW (benzene) or 147 kW (H2S) would be required. These examples show that by applying the method of the invention only an external energy source providing a cooling capacity of 14 kW (benzene and H2S) would be required. This means a reduction in required energy to operate the cooling systems (12, 12' 12") by 85% in case of benzene or even 90 % in case of H2S. The method and apparatus of the invention thus provide fast condensation or freezing of harmful compounds without the burden of high energy use.
Claims (19)
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| NL2010791A NL2010791C2 (en) | 2013-05-13 | 2013-05-13 | Energy saving method and apparatus for removing harmful compounds from a gas mixture. |
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| NL2010791A NL2010791C2 (en) | 2013-05-13 | 2013-05-13 | Energy saving method and apparatus for removing harmful compounds from a gas mixture. |
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