Method and apparatus for compressing a gas mixture

Abstract

Title: Method and apparatus for compressing a gas mixture In a method for compressing a gas mixture (120, 121), the gas mixture to be compressed (120) is cooled by indirect heat exchange (102) with at least one fluid (111, 112) from a method implementing an adsorption and desorption refrigeration cycle to form a gas mixture cooled to a first temperature lower than the wet bulb temperature of the air and then compressed to the first temperature in at least one compression stage (131) forming a compressed gas mixture (122), the heat used for desorption coming from a compression stage (130) upstream of the cooling. Abstract figure: Fig. 2

Description

Title of the invention: Method and apparatus for compressing a gas mixture

[0001] The present invention relates to a method and apparatus for compressing a gas mixture.

[0002] It relates to the compression of gas in association with an adsorption refrigeration system for use intended in particular for a process for separating a gas mixture, for example air, at a temperature lower than the wet bulb temperature of the air, or even cryogenic, or for a process for liquefying air gas, for example nitrogen, oxygen or argon.

[0003] To produce a gas from air, it is known to use the cryogenic route and to use in particular the following steps: compression of the ambient air, purification of the air from water and CO2 by adsorption, cooling of the air in a brazed aluminum exchanger to a temperature close to its dew point, separation by distillation in one or more columns of one or more fractions enriched in oxygen and one or more fractions enriched in nitrogen, heating of these fractions counter-current to the air in the brazed aluminum exchanger.

[0004] The percentages concerning purities in this document are molar percentages.

[0005] Adsorption refrigeration is based on the use of a solid adsorbent (e.g. silica gel) and a fluid (e.g. water). The fluid evaporates at a temperature below the wet bulb temperature of the air to cool the water. The fluid is adsorbed on a first bed of adsorbent cooled with water at a temperature close to the wet bulb temperature of the air. A second bed in parallel is regenerated by heating it with hot water. The fluid desorbs at a pressure higher than the evaporation pressure. It is recondensed with water at a temperature close to the wet bulb temperature of the air. The liquid fluid is returned to the evaporator. The beds are reversed cyclically. For more details, please refer to the Engineering Techniques "Solid Sorption Thermal Systems".

[0006] The present invention proposes to significantly increase the compression efficiency by using an adsorption refrigeration unit. In particular, one of the objects of the invention is to propose a hybrid compression system combining, for example, a multi-stage centrifugal compressor with a regenerative adsorption refrigeration system so as to increase the compression exergy efficiency by at least 3% preferably.

[0007] According to an object of the invention, there is provided a method of compressing a mixture gaseous, in which the gaseous mixture to be compressed is cooled by indirect heat exchange with at least one fluid from a process implementing an adsorption and desorption refrigeration cycle to form a gaseous mixture cooled to a first temperature lower than the wet bulb temperature of the air and then compressed to the first temperature in at least one compression stage forming a compressed gaseous mixture and in which the heat used for desorption comes from: i. a compression step upstream of cooling and / or ii. a compression step of the compressed gas mixture downstream of the cooling dissement and / or iii. of a process fed by at least a fraction of the compressed gas mixture.

[0008] According to other optional features: • the gas mixture is air, natural gas or a gas containing at least one of the following components: carbon dioxide, carbon monoxide, methane, nitrogen, oxygen, argon, hydrogen, helium. • the compressed gas mixture is then at least partially liquefied. • the compressed gas mixture is then separated by cryogenic distillation to produce a fluid. • the process supplied by the compressed gas mixture is a process comprising the separation of air and another step using a product of the air separation and generating heat according to variant iii) used for desorption. • the process fed by the compressed gas mixture is an air separation and chemical conversion or combustion process, the gaseous oxygen from the air separation process feeding the chemical conversion or combustion and the chemical conversion or combustion generating heat according to variant iii) used for desorption. • the fluid resulting from a process using an adsorption refrigeration cycle is water. • the fluid resulting from a process using an adsorption refrigeration cycle is ammonia which enters the heat exchanger at a temperature below 0°C. • the gas mixture is cooled by indirect heat exchange with at least two, or even at least three fluids from the process implementing an adsorption and desorption refrigeration cycle, at least two fluids exchanging heat with the gas mixture at at least two different temperatures. • the gas mixture, preferably at room temperature, is compressed in at least one compression stage and then cooled, being cooled first by a refrigerant flow and then by the at least one fluid from the process implementing an adsorption and desorption refrigeration cycle. • both coolings take place in the same heat exchanger. • the refrigerant flow heated by the gas mixture regenerates an adsorbent of the adsorption and desorption refrigeration cycle.

[0009] According to another object of the invention, there is provided an apparatus for compressing a gas mixture, comprising at least one compression stage and a refrigeration apparatus operating using an adsorption and desorption refrigeration cycle, an indirect heat exchanger allowing heat exchange between the gas mixture to be compressed and at least one fluid from the apparatus implementing an adsorption and desorption refrigeration cycle to form a gas mixture cooled to a first temperature lower than the wet bulb temperature of the air, a pipe for sending the cooled gas mixture in the heat exchanger to the at least one compression stage to be compressed forming a compressed gas mixture and means for transferring heat used for desorption from: i. a compression stage upstream of the cooling and / or ii. a compression stage of the compressed gas mixture downstream of the cooling dissement and / or iii. an apparatus supplied with at least a fraction of the compressed gas mixture.

[0010] According to another object of the invention, there is provided an apparatus for separating air by cryogenic distillation comprising a compression apparatus as described above for compressing the air, a purification unit for purifying the air into CO2 and water, a heat exchanger for cooling the purified air in the purification unit and a system of columns for separating the purified and cooled air.

[0011] The air separation apparatus may comprise an air booster for booster part of the purified air.

[0012] According to another object of the invention, there is provided an apparatus for separating air by cryogenic distillation comprising a compressor for compressing the air, a purification unit for purifying the air compressed in the compressor into CO2 and water, a compression apparatus as described above for compressing a portion of the purified air into CO2 and water, a heat exchanger for cooling the purified air in the purification unit and a system of columns for separating the purified and cooled air.

[0013] The invention will be described in more detail with reference to the figures in which:

[0014] [Fig-1] shows the state of the art of compression on a gas separation plant the air.

[0015] [Fig.2] shows a method according to the invention.

[0016] [Fig.l] which is described in patent FR-2777641 illustrates an installation 1 for air distillation with argon production. This installation 1 essentially comprises a double air distillation column 2, a column 3 for producing impure argon called a mixture column, a column 4 for producing pure argon called a denitrogenation column, a main heat exchange line 5, a main compressor for air to be distilled 6 and an air purification apparatus for distillation 7.

[0017] The double column 2 comprises a medium pressure column 8, operating under a medium pressure for example of 5 bar absolute, a low pressure column 9, operating under a low pressure lower than the medium pressure, for example a pressure slightly higher than 1 bar absolute, and a main vaporizer-condenser 10.

[0018] The impure argon production column 3 comprises a head condenser 12 for partially condensing the impure argon at the head of the column 3.

[0019] The column 4 for producing pure argon comprises a head condenser 13 and a bottom vaporizer 14.

[0020] A gas pipe 16, called the argon tapping pipe, connects an intermediate point of the low pressure column 9 to the tank of the column 3 for producing impure argon, from the bottom of which a liquid return pipe 17 joins the column 9, at approximately the same level as the pipe 16.

[0021] A gas pipe 19 connects an outlet of the head condenser 12 of the column 3 to an intermediate level of the column 4 for producing approximately pure argon. This pipe withdraws the non-condensed part in the condenser 12 of the impure argon at the head of the column 3. This pipe 19 passes successively from the column 3, a heat exchanger 20, to condense the impure gaseous argon, and an expansion valve 21, to expand this condensed impure argon.

[0022] The gaseous air to be distilled is compressed by the compressor 6 in this example a 3-stage centrifugal compressor 6A, 6B and 6C, each followed by 3 water coolers 106A, 106B and 106C. The water (not shown) removes the heat of compression by heating up and is then cooled in an atmospheric tower (not shown) in direct contact with the ambient air to a temperature close to but typically 2 to 5°C higher than the wet bulb temperature of the ambient air. The wet bulb temperature of the air (in English "wet bulb temperature") corresponds to the temperature of the ambient air (unsaturated) when it is brought into contact with water to saturate it. The compressed gaseous air is then purified of water and CO2, for example by adsorption, in the apparatus 7, is divided into two primary flows.

[0023] The first primary air flow is cooled in the main exchange line thermal 5 then divided into two secondary flows. The first secondary flow is injected into the bottom of the medium pressure column near its dew point. The second secondary flow is sent to the bottom vaporizer 14 of the column 4 for producing pure argon, where this second secondary flow is liquefied by vaporizing the bottom argon of this column 4. The liquid thus produced is sent via a pipe 23 to the bottom of the medium pressure column 8.

[0024] The second primary stream of compressed and purified air is compressed by a compressor 230 in this example, a four-stage centrifugal compressor 230A, 230B, 230C and 230D, each followed by one of four water coolers 232A, 232B, 232C and 232D. The water (not shown) removes the heat of compression by heating up and is then cooled in an atmospheric tower (not shown) in direct contact with the ambient air to a temperature close to but typically 2 to 5°C higher than the wet bulb temperature of the ambient air. This second primary air flow is then liquefied upon crossing the main heat exchange line 5 and expanded in an expansion valve 231 substantially to the pressure prevailing in the medium pressure column 8. A first part of this flow is then injected at an intermediate level of the medium pressure column 8.The other part of this flow is sub-cooled upon passing through a heat exchanger 24, then expanded in an expansion valve 240 and injected at the intermediate level of the low pressure column 9.

[0025] The vaporizer-condenser 10 vaporizes liquid oxygen in the bottom of the low pressure column 9 by condensation of nitrogen from the top of the medium pressure column 8.

[0026] Rich liquid (enriched in oxygen) LR is withdrawn from the bottom of the medium pressure column 8, then subcooled in the heat exchanger 24 and finally divided into two streams. The first stream is sent, after expansion in an expansion valve 25, to an intermediate level of the low pressure column 9. The second stream is sent, after expansion in an expansion valve 26 to the condenser 12 at the top of the column 3 for producing impure argon, where this second stream is vaporized by condensation of impure argon at the top of the column 3. The gas thus produced is returned, via a pipe 27, to the low pressure column 9 at an intermediate level lower than that of injection of the first stream of rich liquid.

[0027] Lean liquid (nearly pure nitrogen) LP is taken from the upper part of the medium pressure column 8, then subcooled in the heat exchanger 24, and finally divided into three streams. The first stream is expanded in an expansion valve 30 then injected at the top of the low pressure column 9. The second stream is expanded in an expansion valve 31 then vaporized in the heat exchanger 20, condensing the impure argon channeled by the line 19, then this vaporized stream is expanded again in an expansion valve 32. This second stream is then returned by a waste line 33 to the heat exchanger 24, where this second stream is heated by cooling the LP and LR liquids passing through the exchanger 24. This second flow is finally sent to the main heat exchange line 5, where this second flow is heated by participating in the cooling of the air to be distilled. The third flow of lean liquid is expanded in an expansion valve 34 before being sent to the condenser 13 at the top of the column 4 for producing pure argon, where this third flow is vaporized by condensation of the impure nitrogen at the top of the column 4. The gas thus produced is sent, after expansion in an expansion valve 35, into the residual line 33 to be heated on the one hand in the heat exchanger 24 by ensuring the cooling of the LP and LR liquids and, on the other hand, in the main heat exchange line 5 by participating in the cooling of the air to be distilled.

[0028] Impure or residual nitrogen NR, withdrawn from the top of the low pressure column 9, is sent to the residual line 33, where this impure nitrogen is reheated upon passing through the heat exchanger 24, then the main heat exchange line 5.

[0029] Liquid oxygen OL, drawn off from the bottom of the low pressure column 9, is pumped by a pump 37 then sent via a pipe 38 to the main heat exchange line 5, where this liquid oxygen is vaporized, participating in the cooling of the air to be distilled.

[0030] Medium pressure nitrogen gas NGMP is taken from the top of the medium pressure column 8 and then sent via a pipe 39 to the heat exchange line 5 to participate in the cooling of the air to be distilled. In an intermediate region of this heat exchange line 5, the medium pressure nitrogen gas is divided into two streams. The first stream passes through the rest of the line 5 where it is reheated and then it is distributed via a production pipe 40, for example to supply a consumer installation 140. The second stream is expanded in a turbine 41 and then sent to the waste pipe 33 at the cold end of the heat exchange line 5, to participate again in the cooling of the air to be distilled.

[0031] Medium pressure liquid nitrogen NLMP is withdrawn at the top of the medium pressure column 8 and then sent via a pipe 43 to the heat exchanger 24, where this liquid nitrogen is sub-cooled by heating the residual gases channeled by the residual pipe 33. This liquid nitrogen is then distributed, for example by supplying, after expansion in an expansion valve 143, a storage tank 144.

[0032] Approximately pure liquid argon ArL is withdrawn from the bottom of column 4 and then distributed via a production line 45. Impure or residual nitrogen is taken from the top of column 4 and then evacuated via a line 46.

[0033] The installation 1 further comprises a bypass pipe 48 whose inlet 49 is connected to the pipe 19, between the heat exchanger 20 and the expansion valve 21, and whose outlet 50 opens into the waste pipe 33, just upstream of the heat exchanger 24.

[0034] [Fig. 2] shows a first embodiment of the invention. A gaseous fluid 119 at ambient temperature is compressed in an nth compressor stage 130 to give a compressed fluid 120 at a temperature above ambient temperature. The fluid 120 is cooled in a heat exchanger 102 to a temperature below the wet bulb temperature of the air to give a fluid 121 which is then compressed from the temperature below the wet bulb temperature of the air in an n+1th compression stage.

[0035] The fluid 114 is heated in the exchanger 102 by heat exchange with the compressed gas mixture 120, heated by compression in the stage 130. The heated fluid 14 leaves the hot end of the exchanger 102 as the fluid 113 (for example water at 90°C).

[0036] The fluid 119 may possibly be at the same temperature as the flow rate 121.

[0037] The refrigerant 111 of the exchanger 102 comes from a refrigeration system by adsorption which will now be described.

[0038] The adsorption refrigeration system 310 therefore operates by adsorption of a refrigerant, for example water or ammonia on the surface of a solid adsorbent, for example a zeolite. Two chambers 311, 312 filled with adsorbent serve, in turn, as adsorber and desorber. In the first period, the adsorbent of a first chamber 311 is used for the production of cold, while the other chamber 312 is passed through by hot water, and thus regenerated. In the second period, when the adsorbent of the first chamber is saturated, it is replaced by that of the second chamber for the production of cold, and is then itself regenerated.

[0039] The adsorption refrigeration system 310 comprises four chambers 311, 312, 313 and 314 cyclically connected by valves (or any other device which may have an open position and a closed position) 315, 316, 317 and 318. In the chamber 311, the refrigerant 112 (for example water) is cooled to a temperature below the wet bulb temperature of the ambient air (for example 7°C) by evaporation of water under vacuum (for example at 4°C). This water under vacuum passes through the device 316 to enter one of the two adsorption chambers 313. The adsorbent may be alumina, zeolite or silica gel.

[0040] The refrigerant 112 circulates in a closed circuit passing through the chamber 311 and the heat exchanger 102. The fluid 111 cools in the chamber 311 and is sent to the cold end of the heat exchanger 102 where it cools the gas mixture 120 to form the cooled gas mixture 121 which exits at the cold end of the heat exchanger 102. The refrigerant heated by this exchange exits as fluid 112 from the exchanger at an intermediate point thereof and is returned to the chamber 311.

[0041] In the other adsorption chamber 312, the water is desorbed by indirect heating by the hot fluid 113 (for example water at 90°C) to regenerate the adsorbent. The valves 300 and 305 are open and the valve 301 is closed. The desorbed water is then condensed using cooling water 115 at a temperature higher than (but close to) the wet bulb temperature of the ambient air (for example at 25°C). The condensed water is returned to the chamber 311 by a device not shown in [Fig. 2].

[0042] A portion of the cooling water 115 serves to cool the gas mixture in the exchanger 102 entering the exchanger 102 to a temperature higher than that to which the fluid 112 is heated there and leaving the exchanger 102 at a temperature lower than the temperature at which the refrigerant flow 114 enters there.

[0043] After desorption, the adsorbent in chamber 312 is cooled by indirect exchange with a fraction of the cooling water 115 which passes through valves 302 and 304.

[0044] When the adsorbent in chamber 313 is saturated with water, the system is reversed by reversing the positions of devices 315, 316, 317 and 318. Chamber 312 then switches to adsorption.

[0045] The water can be replaced by another fluid such as ammonia. It is then possible to generate a refrigerant fluid at a temperature below 0°C (especially in winter when the wet bulb temperature of the air is below 0°C) which can be used for cooling a dry gas as in the air compressor 230 of [Fig. 2] in the coolers 232A, 232B, 232C, 232D.

[0046] The compressor 130 is not essential to the invention.

[0047] The heat to generate the cold to cool the mixture to be compressed comes in this example from the compression upstream of the mixture to be compressed.

[0048] It is also possible to generate the refrigerant flow called “hot fluid” 113 on one or more stages of a compressor (for example the compressor 6 of [Fig.l]) and to use the refrigerant 111 on another compressor of the process (for example the air booster 230).

[0049] An installation using a product from an air separation device supplied by the compressed gas mixture, here air, can also generate at least one additional desorption heat to that generated by compression. The product can for example be gaseous oxygen coming from the device of [Fig.l] and a process using gaseous oxygen, such as combustion, chemical conversion, a blast furnace, can generate the heat for desorption.

[0050] Alternatively, a single refrigerant fluid can be used in the exchanger 102 (i.e., the flow 111 and the refrigerant flow 113 circulate in a common circuit). The hot flow 113 is first used to desorb the water by indirect heating and is then cooled to a temperature close to but higher than the wet bulb temperature of the air by a fraction of the flow 115 and then enters the water vaporization chamber 311 to be cooled there to a temperature lower than the wet bulb temperature of the air.

[0051] The following applications can be envisaged: • Air gas separation or liquefaction unit • Natural gas liquefaction unit • Unit for liquefaction or separation of a mixture containing CO2 (for example for the recovery of heat from fumes) • Use of the heat released by a process using oxygen (oxy-combustion, blast furnaces, chemistry, etc.) to cool the compressors of an air separation device producing the oxygen intended for the process.

Claims

Claims

1. A method of compressing a gas mixture (120, 121), in which the gas mixture to be compressed (120) is cooled by indirect heat exchange (102) with at least one fluid (111, 112) from a method implementing an adsorption and desorption refrigeration cycle to form a gas mixture cooled to a first temperature below the wet bulb temperature of the air and then compressed to the first temperature in at least one compression stage (131, 230A, 230B, 230C, 230D) forming a compressed gas mixture (122) and in which the heat used for desorption comes from: i. a compression step (130, 6A, 6B, 6C) upstream of the cooling and / or ii. a compression step of the compressed gas mixture downstream of the cooling and / or iii. of a process fed by at least a fraction of the compressed gas mixture (122).

2. The method of claim 1 wherein the gas mixture (119, 120, 121, 122) is air, natural gas or a gas containing at least one of the following components: carbon dioxide, carbon monoxide, methane, nitrogen, oxygen, argon, hydrogen, helium.

3. Method according to one of the preceding claims in which the compressed gas mixture (122) is then at least partially liquefied.

4. The method of claim 3 wherein the compressed gas mixture (122) is then separated by cryogenic distillation to produce a fluid.

5. Method according to one of the preceding claims in which the method supplied by the compressed gas mixture (122) is a method comprising the separation of air and a further step using a product (38, 40) of the air separation and generating heat according to variant iii) used for desorption.

6. The method of claim 5 wherein the process powered by the compressed gas mixture (122) is an air separation and chemical conversion or combustion process, the oxygen gas from the air separation process powering the chemical conversion or combustion. and chemical conversion or combustion generating heat according to variant iii) serving for desorption.

7. Method according to one of the preceding claims in which the fluid (111, 112) resulting from a method implementing an adsorption refrigeration cycle is water.

8. Method according to one of the preceding claims 1 to 6 in which the fluid (111, 112) resulting from a method implementing an adsorption refrigeration cycle is ammonia which enters the heat exchanger at a temperature below 0°C.

9. Method according to one of the preceding claims in which the gaseous mixture (121) is cooled by indirect heat exchange with at least two, or even at least three fluids (111, 115, 114) from the method implementing an adsorption and desorption refrigeration cycle, at least two fluids exchanging heat with the gaseous mixture at at least two different temperatures.

10. Method according to one of the preceding claims in which the gaseous mixture (119), preferably at ambient temperature, is compressed in at least one compression stage (130, 6) and then cooled, being cooled first by a refrigerant flow (114) and then by the at least one fluid (111, 112) resulting from the method implementing an adsorption and desorption refrigeration cycle.

11. A method according to claim 9 or 10 wherein both coolings take place in the same heat exchanger (102).

12. Method according to claim 10 or 11 in which the refrigerant flow (114, 113) heated by the gas mixture (120) regenerates an adsorbent of the refrigeration cycle by adsorption and desorption.

13. Apparatus for compressing a gas mixture (120, 121), comprising at least one compression stage (131, 230A, 230B, 230C, 230D) and a refrigeration apparatus operating using an adsorption and desorption refrigeration cycle, an indirect heat exchanger (102) allowing heat exchange between the gas mixture to be compressed (120) and at least one fluid (111, 112) coming from the apparatus implementing an adsorption and desorption refrigeration cycle to form a gas mixture cooled to a first temperature lower than the wet bulb temperature of the air, a pipe for sending the cooled gas mixture in the heat exchanger to the at least one compression stage to be compressed forming a compressed gas mixture (122) and means for transferring heat used for desorption Since: i. ii. iii. a compression stage (130, 6A, 6B, 6C) upstream of the cooling and / or a compression stage of the compressed gas mixture downstream of the cooling and / or a device supplied with at least a fraction of the compressed gas mixture (122).

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