Method and apparatus for compressing a gas

Abstract

In a method for compressing a gas (G), the gas is compressed in a compressor having an intermediate stage and a final stage, an intermediate cooler (R1) for cooling the gas downstream of the intermediate stage and a final cooler (R2) for cooling the gas downstream of the final compression stage, a refrigerant fluid, coming from a source (B) is divided into a first flow and a second flow, the first flow (21) is sent to cool the intermediate cooler and the second flow (11) is sent to cool the final cooler, the first and second reheated flows being at different temperatures, the first reheated flow is sent to supply heat to an element (A) producing a first cooled flow and the second reheated flow is mixed with the first cooled flow and the mixture (2) is sent to the source.

Description

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

[0002] An aim of the invention is to simplify the refrigerant fluid circuit (water or glycolated water in general) in the case of heat recovery only on at least one cooler of a compressor.

[0003] The invention consists of creating a single refrigerant fluid circuit, here similar to water, for the following two functions on the air compressor: The compressor is powered by a single cold water supply, which comes from a cooling system or network. Part of the water is used in the final cooling to conventionally cool the compressed gas. This part can also be used to cool the motor driving the compressor or another compressor, the oil sump, and possibly other auxiliaries on the compressor. This generates lukewarm water. Another part is used on the intercooler(s) for heat recovery and to manage hot water.

[0004] Hot water is sent to the heat-using system, then hot water that has been either completely cooled, partially cooled, or uncooled (i.e., not used) is mixed with the warm water. This mixture is then sent to the cooling system or network.

[0005] It is known from EP829691 to use two water flows from a common source to cool the aftercooler and an intercooler of a compressor. Both flows come from the same source and undergo essentially the same temperature increase.

[0006] FR2844863 shows that the water is sent in parallel to the two coolers to produce two flows of water at the same temperature, a temperature which is relatively low (35°C in the text).

[0007] In DE 1020120040480, we see the water flow divided in two. One flow cools the intercooler and the other cools the aftercooler. Thus, flow 12, 13, 14 heated by the intercooler is at 386K while flow 16 heated by the aftercooler is at 366K. The flow that was heated by the intercooler is also heated by an aftercooler.

[0008] The warmer flow is sent to a unit where it preheats water.

[0009] So the final cooler produces lukewarm water while the intercooler produces hot water and it is only the hot water that is sent to provide heat to the consumer element so that its temperature becomes compatible with the lukewarm water with which it must be mixed.

[0010] The invention is described for a two-stage compressor, but can easily be extrapolated to more than two stages. Similarly, the refrigerant is described as water, but can also be glycolated water or any other suitable refrigerant.

[0011] The compressor comprises at least two stages, including a final stage and at least one intermediate stage or a first stage, in the case of a two-stage compressor only.

[0012] The compressor includes a cooler with a temperature rise of the refrigerant, for example water) around 10°C (or 30°C for water at 20°C).

[0013] The compressor includes another chiller to make hot refrigerant, for example hot water, with a refrigerant temperature rise, for example water around 70°C (or 90°C for water at 20°C), with a very low refrigerant flow rate. The flow ratio between the flow sent to the chiller with a smaller refrigerant temperature rise and the flow sent to the chiller with a larger refrigerant temperature rise is between 5 and 15.

[0014] So the compressor produces a flow of warm refrigerant, for example warm water, and a flow of hot refrigerant, for example hot water.

[0015] Preferably, the hot refrigerant has been heated by an intercooler or first cooler and the warm refrigerant has been heated by an aftercooler. In some cases, the compressed gas in the last stage of the compressor may be at a higher temperature than the compressed gas in the intermediate stage or first stage.

[0016] A person skilled in the art would naturally choose to produce the hot refrigerant in the cooler after the final stage. Producing a large temperature rise implies that heat transfer is less efficient and that the compressor is less well cooled.

[0017] According to one aspect of the invention, the opposite is recommended. While the compressor's performance is not optimal in terms of energy, the use of the heat thus recovered largely compensates for the drop in machine performance, for an overall energy balance which is then improved.

[0018] According to an object of the invention, there is provided a method for compressing a gas in which the gas is compressed in a compressor having at least two stages, including an intermediate or first compression stage and a final compression stage for compressing the gas downstream of the intermediate or first compression stage, an intermediate cooler for cooling the gas downstream of the intermediate or first compression stage and a final cooler for cooling the gas downstream of the final compression stage, a refrigerant, for example water or glycolated water, coming from a source of the refrigerant or from a refrigerant cooling system is divided into a first flow and a second flow, the first flow is sent to cool only the intermediate cooler and the second flow is sent to cool only the final cooler,the first heated flow is removed from the intercooler and the second heated flow is removed from the final cooler, the first and second heated flows being at temperatures which differ by at least 30°C, preferably at least 40°C, or even at least 50°C, the first heated flow being hotter than the second heated flow, the first heated flow is sent at least occasionally to supply heat to a heat-consuming element producing a first flow cooled to a third temperature and the second heated flow, which has not been sent to supply heat to the heat-consuming element and has not been cooled, is mixed with the first flow at least occasionally cooled and the mixture is sent to the refrigerant source or to the refrigerant cooling system.

[0019] According to other optional aspects: the first heated flow has undergone a temperature rise of between 30°C and 80°C, or even between 50 and 80°C in the intercooler or first. the second heated flow has undergone a temperature rise of between 5 and 15°C in the final cooler. the first and second flows arrive respectively at the intercooler or first and at the final cooler at the same temperature, for example between 15 and 25°C. the first heated flow is sent to the heat-consuming element where at least occasionally it is not cooled or at least occasionally is not sent to the heat-consuming element. at least occasionally the second heated flow is mixed with the first cooled flow to the third temperature. at least occasionally the second heated flow is mixed with the first flow which has not been cooled.The second heated flow is mixed with the first heated flow, whether it has been cooled by the heat-consuming element or not. The first flow is smaller than the second flow. All refrigerants in the compressor are refrigerant flows, for example water, from the source or from a refrigerant cooling system. The first flow is smaller than the second flow, preferably the first flow is 5 to 15 times smaller than the second flow. The first flow is sent punctually to the heat-consuming element. The first flow is sent permanently to the heat-consuming element.

[0020] According to an object of the invention, there is provided a method for separating air by cryogenic distillation in which air is compressed according to one of the methods as described above, the compressed air is cooled, purified in a pressure and / or temperature swing adsorption purification unit and separated by distillation forming a fluid enriched in oxygen and / or nitrogen, the purification unit being regenerated by a regeneration gas.

[0021] According to an object of the invention, there is provided a method for separating air by cryogenic distillation in which air is compressed, the compressed air is cooled, purified in a purification unit by pressure and / or temperature swing adsorption, a part of the purified air is compressed according to one of the methods as described above and separated by distillation forming a fluid enriched in oxygen and / or nitrogen, the purification unit being regenerated by a regeneration gas.

[0022] According to other optional aspects: the heat-consuming element is a heater of at least a portion of the regeneration gas upstream of the purification unit and the first reheated flow provides all the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit. the heat-consuming element is a heater of at least a portion of the regeneration gas upstream of the purification unit and the first reheated flow provides only a portion of the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit, the remainder of the heat required being provided by an additional heater.

[0023] According to another aspect of the invention, there is provided an apparatus for compressing a gas, associated with a heat consuming element, comprising a compressor having at least two stages, including an intermediate or first compression stage and a final compression stage for compressing a gas downstream of the intermediate or first compression stage, an intermediate cooler for cooling the gas downstream of the intermediate or first compression stage and a final cooler for cooling the gas downstream of the final compression stage, means for dividing a refrigerant, for example water or glycolated water, coming from a source of the refrigerant or from a system for cooling the refrigerant into a first flow and a second flow, a conduit for sending the first flow to cool only the intermediate cooler and a conduit for sending the second flow to cool only the final cooler,a pipe for outputting the first heated flow from the intercooler or first and a pipe for outputting the second heated flow from the final cooler, the first and second heated flows being at temperatures which differ by at least 30°C, preferably at least 40°C, or even at least 50°C, the first heated flow being hotter than the second heated flow, means for sending at least occasionally the first heated flow to provide heat to the heat-consuming element producing a first flow at least occasionally cooled, means for sending the second heated flow to mix with the first flow at least occasionally cooled, directly without passing through the heat-consuming element or a cooling device and means for sending the mixture formed to the source of refrigerant fluid or to a system for cooling the refrigerant fluid.

[0024] The invention will be described in more detail with reference to the figures in which: [ FIG.1 ] represents a method according to the invention. [ FIG.2 ] represents a variant of a method according to the invention. [ FIG.3 ] represents another variant of a method according to the invention.

[0025] In the [ FIG.1 ], the gas G, for example air, is compressed in a compressor comprising at least two stages C1, C2. The gas compressed in stage C1 is then cooled in a cooler R1 by a refrigerant 21 to a temperature between 15 and 25°C which may be water or glycolated water. The refrigerant 21 is heated in the cooler R1 to 90°C.

[0026] The R1 cooler can be a cross-flow “shell and tube” exchanger with a multitude of passes.

[0027] Since the R1 cooler is generally integrated into the compressor, the maximum footprint is generally limited, which means that the cooling of the compressed gas may have to be slightly degraded in favor of maximum heating of the fluid to be heated. This implies a drop in performance for the next compression stage, with a slightly higher energy expenditure, but which is largely offset by the energy gain from heat recovery.

[0028] It is advantageous to only do heat recovery on the compressor intercooler(s) R1 by making a hot refrigerant, for example hot water, typically around 90°C and to keep a conventional refrigerant for the final refrigerant.

[0029] The gas cooled in R1 is compressed in the final stage C2 and then cooled by another flow 11 of the same refrigerant in a cooler R2, the other flow 11 arriving in the cooler at a temperature between 15 and 25°C

[0030] The R2 final cooler is typically a cross-flow shell and tube exchanger with a few passes. Its standard design allows for good gas cooling at the end of compression. If heat recovery had been used on this final refrigerant, the gas would have been poorly cooled, or a second refrigerant would have had to be added in series.

[0031] Flow 11 undergoes a moderate temperature rise in the final cooler R2, typically between 5°C and 15°C.

[0032] The heated flows 12,22 have temperatures which differ by at least 30°C, preferably at least 40°C, or even at least 50°C.

[0033] Preferably cooler R1 has more passes than cooler R2.

[0034] The compressed gas in stage C2 can undergo additional cooling after cooling in R2, for example against iced water or against a cold fluid. This is particularly the case in the context of an air separation device by cryogenic distillation: for the main wet air compressor, which is cooled against iced water in an exchanger or cooling tower before entering the overhead purification for the dry air booster, at the outlet of the overhead purification, which is cooled in the main cryogenic exchanger against a fluid resulting from the distillation of the air gases. The compressed gas is then sent elsewhere. It can, for example, be purified of water and CO2 in a purification unit operating by temperature and / or pressure switching. Then it can be separated in an air separation unit by cryogenic distillation. Part of the nitrogen produced by the distillation can be reheated in a heater to reach a temperature necessary to regenerate an adsorbent bed in the purification unit.

[0035] In the case where the heat available on the intermediate refrigerant(s) is sufficient for the intended use (for example the regeneration of an FEP of an ASU), this allows the gas to be cooled well at the end of compression, which is interesting for example when the compressed gas must then be cooled again either by being sent to a cold air gas separation box, or to a pre-cooling system upstream of an FEP.

[0036] Alternatively, compressed air can be purified and then only a portion of the purified air can be compressed in a compressor according to the invention, called a "supercharger" with several compression stages and coolers producing refrigerant flows from a common source but heated to different temperatures.

[0037] Thus, the compressor according to the invention can be a main air compressor or an air booster. It can also be a compressor of gaseous nitrogen or gaseous oxygen produced for example on an air separation device.

[0038] The heat recovered by refrigerant 22 can be used to heat all or part of the regeneration gas intended for TSA-type overhead purification, for example in an air separation unit. Alternatively, it can be used as a heat source for an absorption refrigeration unit.

[0039] Cooling system B provides a refrigerant, for example cold water 1. This system can be connected to a cooling network and / or to an atmospheric cooling tower (for example open, closed, air cooler, evaporative or adiabatic type) and / or an adsorption or absorption refrigeration unit. The cooling system is preferably a closed circuit to control the quality of the water and avoid problems of corrosion and / or deposits, which are accentuated by the high temperature at the outlet of the intermediate refrigerant. Depending on the cooling system B implemented, the refrigerant, for example cold water 1, preferably has a temperature close to the dry or wet bulb temperature of the ambient air.

[0040] A portion 11 of the refrigerant 1 , for example cold water 1 , goes to the final cooler R2 to cool the compressed gas G in the final stage C2 of the compressor. In the following, the refrigerant is described as water but it will be understood that it can be a mixture of water and glycol or ammonia.

[0041] The cold water is heated in the aftercooler R2 and exits as lukewarm water 12 with a moderate temperature rise, typically between 5°C and 15°C. This part 11 can also be used to cool the compressor motor, the compressor oil sump and possibly other auxiliaries on the compressor.

[0042] Another portion of the cold water 21 goes to the intercooler R1 to cool the compressed gas G in the stage C1 of the compressor. The cold water is heated in the final cooler R2 and leaves in the form of hot water 22, at a temperature typically between 50°C and 100°C above the temperature at which it arrives in the cooler R1, preferably around 90°C.

[0043] So, for example, if water 1 is at 20°C, flow rates 11, 21 are at 20°C, flow rate 12 will be heated to 30°C and flow rate 22 to 90°C.

[0044] The hot water 22, for example at 90°C, is sent to the heat user system A, which can use the heat intermittently. Then the water 23 leaves the heat user system A, water 23 which has been either completely cooled, partially cooled, or not cooled (i.e. not used) and is mixed with the warm water 12 forming a mixture 2. In the context of an air separation apparatus by cryogenic distillation, the user system can be a heater to heat all or part of the regeneration gas from the overhead purification. If the temperature reached is not sufficient, another heater can be added, for example electric or steam or gas to provide additional heating.

[0045] This mixture 2 is then sent to the cooling system B.

[0046] According to a variant of the invention, it is advantageous to manage the different phases of the regeneration of a TSA type adsorption system, in particular in the heating phase and the cooling phase, using the hot fluid 22 recovered from the compression heat of the compressor C1.

[0047] This variant consists of passing the hot fluid during the heating phase in an exchanger against the regeneration fluid and not passing the hot fluid during the cooling phase in this exchanger against the regeneration fluid, the regeneration fluid circulating in the exchanger during the heating and cooling phases.

[0048] Alternatively, another variant consists of passing the regeneration fluid during the heating phase through an exchanger against the hot fluid and not passing the regeneration fluid during the cooling phase through an exchanger against the hot fluid, the hot fluid circulating in the exchanger during the heating and cooling phases.

[0049] Furthermore, the regeneration fluid circuit has a second exchanger, typically an electric, steam or gas heater to provide either additional heating to reach a higher temperature and / or to enable the adsorption system to operate during operating phases where the compression heat is not available, for example during the start-up phase if the compressor is stopped.

[0050] According to the first variant, illustrated in the [ FIG.2 ], in a TSA type adsorption unit with two adsorbers, regeneration is composed of three main phases: Heating with a hot regeneration gas Cooling with a cold regeneration gas Reversal of the two adsorbers, generally including a phase of low pressure isolation, pressurization, paralleling of the two adsorbers, high pressure isolation and depressurization

[0051] This is the case, for example, with head purification on an air separation device. According to the first variant: In the heating phase, the hot fluid 22 passes through the three-way valve V to go as fluid 22a to the heat exchanger H1. The regeneration fluid 30 is heated against the fluid 22a in the exchanger H1. There is no flow 22b (non-passing valve to 22b). Valve V has an on-off operating mode.

[0052] Alternatively, the 3-way valve V can be a control valve which adjusts the flow rate in each outlet 22a and 22b so as to finely regulate the temperature of the fluid 31 at the outlet of the exchanger H1, in particular if the heater (and its associated temperature control regulation) is not used.

[0053] The three-way valve can be replaced by two two-way valves.

[0054] If necessary, the heated fluid 31 can be reheated in a heater H2, typically an electric heater or a heater heated by water vapor or gas. This can be done periodically if it is desired, for example, to increase the regeneration temperature (typically 120-150°C, or even 200°C) to better regenerate certain impurities that would be poorly regenerated with the temperature level obtained on the fluid 31 at the outlet of the exchanger H1 with the hot fluid 22 (typically 70 - 90°C).

[0055] In the operating phases where the fluid 22 is not hot (typically the compressor on which the heat recovery is carried out is not in operation), the regeneration fluid 30 is heated only using the heater H2.

[0056] In the cooling phase, the hot fluid 22 rotates through the three-way valve V to go as fluid 22b and bypass the heat exchanger H1. There is no flow 22a (non-passing valve towards 22a). The cold regeneration fluid 30 initially cools the heater H1 and H2 (thermal inertia). Fairly quickly (depending on the thermal inertia), the fluid 32 has the same cold temperature as the fluid 30. According to a second variant of the invention illustrated in the [ FIG.3 ] : In the heating phase, the hot fluid 22 passes through the heat exchanger H1. The regeneration fluid 30 (30a) is heated against the fluid 22 in the exchanger H1, with the valve V2 open and the valve V1 closed. It has no flow in 30b. The valves V1 and V2 have an on-off operating mode. Alternatively, both valves V1 and V2 may be control valves that adjust the flow in each branch 30a and 30b so as to finely regulate the temperature of the fluid 32, especially if the heater (and its associated temperature control regulation) is not used.

[0057] If necessary, the heated fluid 31 can be reheated in a heater H2, typically an electric heater or a heater heated by water vapor or gas. This can be done periodically if it is desired, for example, to increase the regeneration temperature (typically 120-150°C, or even 200°C) to better regenerate certain impurities that would be poorly regenerated with the temperature level obtained on the fluid 31 (typically 70 - 90°C) at the outlet of the exchanger H1 with the hot fluid 22.

[0058] In the operating phases where the fluid 22 is not hot (typically the compressor on which the heat recovery is carried out is not in operation), the regeneration fluid 30 is heated only using the heater H2.

[0059] In the cooling phase, the hot fluid 22 continues to pass through the heat exchanger H1. The fluid 30 (30b) bypasses the heat exchanger H1 and the heater H2, with the valve V2 closed and the valve V1 open. It has no flow in 30a. The cold regeneration fluid 30 passes directly into cold fluid 32, without thermal inertia.

[0060] So we see that the H2 heater is: used as a supplement, used in phases where the heat source is not available.

Claims

1. A method of compressing a gas (G) in which the gas is compressed in a compressor having at least two stages (C1, C2), including an intermediate or first compression stage and a final compression stage for compressing the gas downstream of the intermediate or first compression stage, an intermediate cooler (R1) for cooling the gas downstream of the intermediate or first compression stage and a final cooler (R2) for cooling the gas downstream of the final compression stage, a refrigerant, for example water or glycolated water, from a source of the refrigerant (B) or from a refrigerant cooling system is divided into a first flow and a second flow, the first flow (21) is sent to cool only the intermediate cooler and the second flow (11) is sent to cool only the final cooler,the first heated flow (22) is removed from the intercooler and the second heated flow (12) is removed from the final cooler, the first and second heated flows being at temperatures which differ by at least 30°C, preferably at least 40°C, or even at least 50°C, the first heated flow being hotter than the second heated flow, the first heated flow is sent at least occasionally to supply heat to a heat-consuming element (A) producing a first flow cooled to a third temperature and the second heated flow, which has not been sent to supply heat to the heat-consuming element and has not been cooled, is mixed with the first flow at least occasionally cooled and the mixture (2) is sent to the refrigerant source or to the refrigerant cooling system.

2. Method according to claim 1 or 2 in which the first heated flow (22) has undergone a temperature increase of between 30°C and 80°C, or even between 50 and 80°C in the intermediate or first cooler (R1).

3. Method according to claim 1 or 2 in which the second reheated flow (12) has undergone a temperature increase of between 5 and 15°C in the final cooler (R2).

4. Method according to claim 1 or 2 in which the first and second flows (11, 21) arrive respectively at the intermediate or first cooler (R1) and at the final cooler (R2) at the same temperature, for example between 15 and 25°C.

5. Method according to one of the preceding claims in which the first heated flow (22) is sent to the heat consuming element (A) where at least occasionally it is not cooled or at least occasionally is not sent to the heat consuming element.

6. Method according to claim 1 in which at least occasionally the second heated flow (12) is mixed with the first flow cooled to the third temperature (23).

7. Method according to claim 5 in which at least occasionally the second heated flow (12) is mixed with the first flow which has not been cooled.

8. Method according to one of claims 1 or 5 to 7 in which the second heated flow (12) is mixed with the first heated flow (22, 23), whether it has been cooled by the heat-consuming element or not.

9. Method according to one of the preceding claims in which the first flow rate (21) is smaller than the second flow rate (11).

10. Method according to one of the preceding claims in which all the refrigerant fluids of the compressor are refrigerant fluid flows (11, 21), for example water, coming from the source (A) or from a refrigerant fluid cooling system.

11. Method according to one of the preceding claims in which the first flow rate (21) is 5 to 15 times smaller than the second flow rate (11).

12. Method according to one of the preceding claims in which the first flow (22) is sent punctually to the heat consuming element (A).

13. Method according to one of the preceding claims 1 to 11 in which the first flow (22) is sent permanently to the heat consuming element (A).

14. Process for separating air by cryogenic distillation in which air (G) is compressed according to one of the processes of the preceding claims, the compressed air is cooled, purified in a pressure and / or temperature swing adsorption purification unit and separated by distillation forming a fluid enriched in oxygen and / or nitrogen, the purification unit being regenerated by a regeneration gas.

15. Process for separating air by cryogenic distillation in which air (G) is compressed, the compressed air is cooled, purified in a pressure and / or temperature swing adsorption purification unit, a portion of the purified air is compressed according to one of the processes of claims 1 to 11 and separated by distillation forming a fluid enriched in oxygen and / or nitrogen, the purification unit being regenerated by a regeneration gas.

16. Method according to claim 14 or 15 in which the heat consuming element (A) is a heater (H1) of at least a portion (30) of the regeneration gas upstream of the purification unit and the first reheated flow provides all the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit.

17. Method according to claim 14 or 15 in which the heat consuming element is a heater (H1) of at least a portion of the regeneration gas upstream of the purification unit and the first reheated flow provides only a portion of the heat necessary to bring the regeneration gas (30, 31, 32) to a temperature suitable for regenerating the purification unit, the remainder of the heat necessary being provided by an additional heater (H2).

18. Apparatus for compressing a gas associated with a heat-consuming element comprising a compressor having at least two stages (C1, C2), including an intermediate or first compression stage and a final compression stage for compressing a gas downstream of the intermediate or first compression stage, an intermediate cooler (R1) for cooling the gas downstream of the intermediate or first compression stage and a final cooler (R2) for cooling the gas downstream of the final compression stage, means for dividing a refrigerant, for example water or glycolated water, coming from a source of the refrigerant or from a refrigerant cooling system into a first flow (21) and a second flow (11), a pipe for sending the first flow to cool only the intermediate or first cooler and a pipe for sending the second flow to cool only the final cooler,a pipe for outputting the first heated flow (22) from the intercooler or first and a pipe for outputting the second heated flow (12) from the final cooler, the first and second heated flows being at temperatures which differ by at least 30°C, preferably at least 40°C, or even at least 50°C, the first heated flow being hotter than the second heated flow, means for sending at least punctually the first heated flow to provide heat to the heat-consuming element (A) producing a first flow at least punctually cooled (23), means for sending the second heated flow to mix with the first flow at least punctually cooled, directly without passing through the heat-consuming element or a cooling device and means for sending the mixture (2) formed to the source of refrigerant fluid or to a system for cooling the refrigerant fluid.

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