Method and apparatus for compressing gas

Abstract

A method for compressing a gas, the gas being compressed in a compressor, the compressor having: at least two stages; an intercooler; and a final cooler, refrigerant from a refrigerant source being divided into a first stream and a second stream, the first stream being sent only to cool the intercooler, the second stream being sent only to cool the final cooler, a first heated stream being discharged from the intercooler, a second heated stream being discharged from the final cooler, the temperature of the first heated stream differs from the temperature of the second heated stream by at least 30 DEG C. The first heated stream is delivered at least periodically to provide heat to the heat consuming element to produce a first cooled stream. A second heated stream that is not delivered to provide heat to the heat consuming element and that is not cooled is mixed with the first cooled stream that is at least periodically cooled, the mixture being delivered to the refrigerant source. The invention also relates to a method for separating air by cryogenic distillation and to a device for compressing gas.

Description

TECHNICAL FIELD

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

[0002] An object of the present invention is to simplify the circuit of a refrigerant (usually water or an aqueous solution of ethylene glycol) in the case where heat is recovered only in at least one cooler of a compressor.

[0003] The present invention consists in creating a single refrigerant (here compared to water) circuit in an air compressor for the following two functions:

[0004] · The compressor is supplied by a single cold water supply device from a cooling system or network.

[0005] · A part of the water is used for final cooling in order to cool the compressed gas in a conventional manner. This part can also be used to cool the motor driving the compressor or another compressor, the oil sump, and optionally other auxiliary devices on the compressor. This produces warm water.

[0006] · Another part is used for intermediate cooling for heat recovery in order to produce hot water.

[0007] The hot water is transported to the system using the heat, and then the fully cooled, partially cooled, or uncooled (i.e., unused) hot water is mixed with the warm water. This mixture is then sent to the cooling system or network. BACKGROUND ART

[0008] EP829691 discloses using two water streams from a common source to cool the final cooler and the intermediate cooler of a compressor. These two streams come from the same source and undergo substantially the same temperature increase.

[0009] FR2844863 discloses that water is transported in parallel to two coolers to produce two water streams at the same temperature, which is relatively low (35°C in the said document).

[0010] In DE1020120040480, the water stream is divided into two. One cools the intermediate cooler and the other cools the final cooler. Thus, the streams 12, 13, 14 heated by the intermediate cooler are at 386K, while the stream 16 heated by the final cooler is at 366K. The stream that has been heated by the intermediate cooler is also heated by the final cooler.

[0011] The hottest stream is sent to a unit where the water is preheated.

[0012] Therefore, the final cooler produces warm water, while the intermediate cooler produces hot water, and only the hot water is transported to supply heat to the consumption element so that its temperature becomes compatible with the warm water to be mixed with it. SUMMARY OF THE INVENTION

[0013] The present invention is described for a two-stage compressor, but can be easily extended to more than two stages. Similarly, the refrigerant is described as water, but can also be an aqueous solution of ethylene glycol or any other suitable refrigerant.

[0014] The compressor includes at least two stages. In the case where the compressor has only two stages, it includes a final stage and at least one intermediate stage or a first stage.

[0015] The compressor includes a cooler in which the temperature of the refrigerant (e.g., water) increases by about 10 °C (i.e., water at 20 °C is increased to 30 °C).

[0016] The compressor includes another cooler for generating hot refrigerant, such as hot water, in which the temperature of the refrigerant (e.g., water) increases by about 70 °C (i.e., water at 20 °C is increased to 90 °C) and the refrigerant flow rate is greatly reduced. The ratio between the flow rate sent to the cooler where the refrigerant temperature increase is smaller and the flow rate sent to the cooler where the refrigerant temperature increase is larger is in the range of 5 to 15.

[0017] Thus, the compressor generates a warm refrigerant stream, such as warm water, and a hot refrigerant stream, such as hot water.

[0018] Preferably, the hot refrigerant has been heated by an intercooler or a first cooler, and the warm refrigerant has been heated by a final cooler.

[0019] In some cases, the gas compressed in the last stage of the compressor can be at a higher temperature than the gas compressed in the intermediate stage or the first stage.

[0020] Those skilled in the art will naturally choose to generate hot refrigerant in a cooler after the last stage. Generating a large temperature increase means lower heat transfer efficiency and less good cooling of the compressor.

[0021] According to one aspect of the present invention, the opposite situation is recommended. Although the performance of the compressor is not optimal in terms of energy, the use of the heat recovered in this way greatly compensates for the reduction in the performance of the machine, thus improving the overall energy balance.

[0022] According to an object of the present invention, there is provided a method for compressing a gas, wherein the gas is compressed in a compressor having: at least two stages including an intermediate stage or a first compression stage and a final compression stage for compressing the gas downstream of the intermediate stage or the first compression stage; an intercooler for cooling the gas downstream of the intermediate stage or the first compression stage; and a final cooler for cooling the gas downstream of the final compression stage. Refrigerant from a refrigerant source or a refrigerant cooling system, such as water or an aqueous ethylene glycol solution, is divided into a first stream and a second stream. The first stream is only sent to cool the intercooler, and the second stream is only sent to cool the final cooler. A first heated stream is discharged from the intercooler, and a second heated stream is discharged from the final cooler. The temperature difference between the first heated stream and the second heated stream is at least 30°C, preferably at least 40°C, or even at least 50°C. The first heated stream is hotter than the second heated stream. The first heated stream is at least periodically conveyed to provide heat to a heat-consuming element, thereby generating a first stream cooled to a third temperature. The second heated stream that is not conveyed to provide heat to the heat-consuming element and is not cooled is mixed with the at least periodically cooled first stream, and the mixture is conveyed to the refrigerant source or the refrigerant cooling system.

[0023] According to other alternative aspects:

[0024] · In the intercooler or the first cooler, the first heated stream has experienced a temperature increase of 30°C to 80°C,

[0025] or even 50°C to 80°C.

[0026] · In the final cooler, the second heated stream has experienced a temperature increase of 5°C to 15°C.

[0027] · The first stream and the second stream reach the intercooler or the first cooler and the final cooler at the same temperature, which is, for example, in the range of 15°C to 25°C.

[0028] · The first heated stream is conveyed to the heat-consuming element, and the first heated stream is at least periodically not cooled at the heat-consuming element, or the first heated stream is at least periodically not conveyed to the heat-consuming element.

[0029] · The second heated stream is at least periodically mixed with the first stream cooled to the third temperature.

[0030] · The second heated stream is at least periodically mixed with the non-cooled first stream.

[0031] · The second heated stream is mixed with the first heated stream regardless of whether the first stream has been cooled by the heat-consuming element.

[0032] ● The first stream is less than the second stream.

[0033] ● All the refrigerant of the compressor is the refrigerant flow from a refrigerant source or a refrigerant cooling system such as water.

[0034] · The first flow is less than the second flow. Preferably, the first flow is 1 / 5 to 1 / 15 times the second flow.

[0035] ● The first flow is periodically delivered to the heat-consuming element.

[0036] ● The first flow is continuously delivered to the heat-consuming element.

[0037] According to an object of the present invention, there is provided a method for separating air by cryogenic distillation, wherein air is compressed according to one of the above methods, and the compressed air is cooled, purified by pressure swing and / or temperature swing adsorption in a purification unit, and separated by distillation to form an oxygen-enriched and / or nitrogen-enriched fluid, and the purification unit is regenerated by a regeneration gas.

[0038] According to an object of the present invention, there is provided a method for separating air by cryogenic distillation, wherein air is compressed, the compressed air is cooled, purified by pressure swing and / or temperature swing adsorption in a purification unit, and a part of the purified air is compressed and separated by distillation according to one of the above methods to form an oxygen-enriched and / or nitrogen-enriched fluid, and the purification unit is regenerated by a regeneration gas.

[0039] According to other alternative aspects:

[0040] · The heat-consuming element is a heater for heating at least a part of the regeneration gas upstream of the purification unit, and the first heated flow provides all the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit.

[0041] · The heat-consuming element is a heater for heating at least a part of the regeneration gas upstream of the purification unit. The first heated flow only provides a part of the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit, and the remaining required heat is provided by an additional heater.

[0042] According to another aspect of the present invention, there is provided a device for compressing a gas, which is associated with a heat-consuming element. The device includes: a compressor having at least two stages including an intermediate compression stage or a first compression stage and a final compression stage for compressing the gas downstream of the intermediate compression stage or the first compression stage, an intermediate cooler or a first cooler for cooling the gas downstream of the intermediate compression stage or the first compression stage, and a final cooler for cooling the gas downstream of the final compression stage; means for dividing a refrigerant, such as water or an aqueous ethylene glycol solution, from a refrigerant source or a refrigerant cooling system into a first stream and a second stream; a pipe for conveying the first stream to cool only the intermediate cooler and a pipe for conveying the second stream to cool only the final cooler; a pipe for discharging a first heated stream from the intermediate cooler or the first cooler and a pipe for discharging a second heated stream from the final cooler, the temperature difference between the first heated stream and the second heated stream being at least 30 °C, preferably at least 40 °C, or even at least 50 °C, and the first heated stream being hotter than the second heated stream; means for at least periodically conveying the first heated stream to supply heat to the heat-consuming element to generate a first cooled stream that is at least periodically cooled; means for conveying the second heated stream without passing it through the heat-consuming element or the cooling device to directly mix it with the first cooled stream that has been at least periodically cooled; and means for conveying the formed mixture to the refrigerant source or the refrigerant cooling system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be described in more detail with reference to the accompanying drawings, in which:

[0044] Figure 1 A method according to the present invention is shown.

[0045] Figure 2 A variant of the method according to the present invention is shown.

[0046] Figure 3 Another variant of the method according to the present invention is shown. DETAILED DESCRIPTION OF THE INVENTION

[0047] In Figure 1 a gas G, such as air, is compressed in a compressor including at least two stages C1, C2. The gas compressed in stage C1 is then cooled by a refrigerant 21 in a cooler R1, the temperature of the refrigerant 21 being in the range of 15 °C to 25 °C, which may be water or an aqueous ethylene glycol solution. The refrigerant 21 is heated to 90 °C in the cooler R1.

[0048] The cooler R1 may be a crossflow / counterflow shell-and-tube heat exchanger with multiple channels.

[0049] Since the cooler R1 is usually integrated into the compressor, the maximum occupied area is typically limited, which makes it necessary to potentially slightly degrade the cooling of the compressed gas in favor of the maximum heating of the fluid to be heated. This means a reduced performance of the next compression stage and a slightly higher energy consumption, but this is largely offset by the energy saved through heat recovery.

[0050] It is advantageous to recover heat only in the intermediate cooler R1 of the compressor by generating a hot refrigerant (e.g., hot water, typically around 90 °C) and retaining the conventional refrigerant as the final refrigerant.

[0051] The gas cooled in R1 is compressed in the final stage C2 and then cooled in the cooler R2 by another stream 11 of the same refrigerant, which reaches the cooler at a temperature in the range of 15 °C to 25 °C.

[0052] The final cooler R2 is typically a cross-flow shell-and-tube heat exchanger with a small number of channels. Its standard design makes it possible to satisfactorily cool the gas at the end of compression. If heat is recovered in this final refrigerant, this would result in poor gas cooling or a second refrigerant would have to be added in series.

[0053] Stream 11 undergoes a moderate temperature increase in the final cooler R2, typically in the range of 5 °C to 15 °C.

[0054] The temperatures of the heated streams 12, 22 differ by at least 30 °C, preferably at least 40 °C, or even at least 50 °C.

[0055] Preferably, the cooler R1 includes more channels than the cooler R2.

[0056] The gas compressed in stage C2 can undergo additional cooling after being cooled in R2, for example, by cooling with ice water or a cold fluid. This is especially the case for equipment for separating air by cryogenic distillation:

[0057] ● For the main humid air compressor, the air is cooled with ice water in an exchanger or cooling tower before entering the front-end purification device;

[0058] · For the dry air booster, at the outlet of the front-end purification device, it is cooled by the fluid generated by the gas distillation in air in the main cryogenic exchanger.

[0059] The compressed gas is then sent elsewhere. For example, it can be purified of water and CO2 in a purification unit by a temperature-changing and / or pressure-changing operation. Then it can be separated in a unit for separating air by cryogenic distillation. A part of the nitrogen produced by distillation can be heated in a heater to reach the temperature required for regenerating the adsorption bed of the purification unit.

[0060] If the heat available in the intermediate refrigerant is sufficient for the intended use (e.g., regeneration of the FEP unit of the ASU), this makes it possible to satisfactorily cool the gas at the end of compression, which is beneficial, for example, when the compressed gas then has to be cooled again, and this re-cooling is achieved either by sending it to the cold box of the gas used for air separation or in a pre-cooling system upstream of the FEP unit.

[0061] As an alternative, the compressed air can be purified and then only a part of the purified air can be compressed in the compressor according to the invention, which is known as a booster compressor and has a plurality of compression stages and coolers that produce refrigerant flows from a common source but heated to different temperatures.

[0062] Thus, the compressor according to the invention can be a main air compressor or a booster air compressor. It can also be, for example, a compressor for nitrogen or gaseous oxygen produced in an air separation plant.

[0063] The heat recovered by refrigerant 22 can make it possible to heat all or part of the regeneration gas for, for example, the TSA front-end purification unit in an air separation plant. Additionally, it can be used as a heat source for an absorption refrigeration unit.

[0064] Cooling system B supplies a refrigerant, such as chilled water 1. This system can be connected to a cooling network and / or an atmospheric cooling tower (e.g., open, closed, dry cooling, evaporative or adiabatic) and / or an adsorption or absorption refrigeration unit. The cooling system is preferably a closed loop to control the water quality and avoid corrosion and / or deposition problems, which are exacerbated by the high temperature at the intermediate refrigerant outlet. Depending on the cooling system B implemented, the refrigerant, such as chilled water 1, preferably has a temperature close to the dry or wet temperature of the ambient air.

[0065] A part 11 of refrigerant 1, such as chilled water 1, enters the final cooler R2 to cool the gas G compressed in the final stage C2 of the compressor.

[0066] Hereinafter, the refrigerant is described as water, but it should be understood that the refrigerant can be a mixture of water and ethylene glycol or ammonia.

[0067] The chilled water is heated in the final cooler R2 and discharged in the form of warm water 12, where the warm water 12 has a moderate temperature increase, typically in the range of 5°C to 15°C. This part 11 can also be used to cool the motor of the compressor, the oil sump of the compressor, and optionally other auxiliary devices on the compressor.

[0068] Another part of the cold water 21 enters the intercooler R1 to cool the gas G compressed in the C1 stage of the compressor. The cold water is heated in the final cooler R2 / intercooler R1 and discharged in the form of hot water 22, whose temperature is generally 50°C to 100°C higher than the temperature when it reaches the cooler R1, and this temperature is preferably about 90°C.

[0069] According to an example, if the water 1 is at 20°C, then the streams 11, 21 are at 20°C, so the stream 12 will be heated to 30°C and the stream 22 will be heated to 90°C.

[0070] The hot water 22 (which is, for example, at 90°C) is conveyed to the heat-using system A, which can use heat intermittently. Then, the water 23 leaves the heat-using system A (this water 23 has been fully cooled, partially cooled, or not cooled (i.e., not used)) and is mixed with the warm water 12, thus forming the mixture 2. Regarding the equipment for separating air by low-temperature distillation, this using system can be a heater for heating all or part of the front-end purification regeneration gas. If the temperature reached is not sufficient, another heater (such as an electric heater, a steam heater, or a gas heater) can be added to provide supplementary heating.

[0071] This mixture 2 is then sent to the cooling system B.

[0072] According to a variant of the present invention, it is beneficial to manage the different stages of the TSA system regeneration, especially the heating stage and the cooling stage, by using the hot fluid 22 recovered from the compression heat of the compressor C1.

[0073] This variant includes passing the hot fluid against the regeneration fluid into the exchanger during the heating stage and not passing the hot fluid against the regeneration fluid into this exchanger during the cooling stage, where the regeneration fluid circulates in the exchanger during the heating stage and the cooling stage.

[0074] Alternatively, another variant includes passing the regeneration fluid against the hot fluid into the exchanger during the heating stage and not passing the regeneration fluid against the hot fluid into this exchanger during the cooling stage, where the hot fluid circulates in the exchanger during the heating stage and the cooling stage.

[0075] In addition, the regeneration fluid circuit is provided with a second exchanger (which is generally an electric heater or a steam heater or a gas heater) to provide auxiliary heating to reach a higher temperature and / or allow the adsorption system to operate during the operating stages where the compression heat is not available, such as during the start-up stage when the compressor is shut down.

[0076] According to the first variant, as Figure 2 shown, in a TSA unit with two adsorbers, the regeneration consists of three main stages:

[0077] ·Heated with hot regeneration gas;

[0078] ·Cooled with cold regeneration gas;

[0079] ·Switching of two adsorbers, usually including a low-pressure isolation stage, a pressurization stage, a stage of placing two adsorbers in parallel, a high-pressure isolation stage, and a depressurization stage.

[0080] This is the case for the front-end purification unit of an air separation device, for example.

[0081] According to the first variant:

[0082] ● In the heating stage, the hot fluid 22 flows through the three-way valve V and flows to the heat exchanger H1 as the fluid 22a. The regeneration fluid 30 is heated by the fluid 22a in the exchanger H1. There is no flow 22b (the valve is closed towards 22b). The valve V has an all-or-nothing operation mode.

[0083] Alternatively, the three-way valve V can be a control valve that regulates the flow rate in each outlet 22a and 22b in order to finely adjust the temperature of the fluid 31 at the outlet of the exchanger H1, especially if no heater (and its associated temperature control regulation) is used.

[0084] The three-way valve can be replaced by two two-way valves.

[0085] If necessary, the heated fluid 31 can be reheated in the heater H2, which is usually an electric heater or a heater heated by steam or gas. This can be done periodically in the following cases: to increase the regeneration temperature (usually 120°C - 150°C, or even 200°C) in order to improve the regeneration of certain impurities, for example, which will regenerate poorly at the temperature level (usually 70°C - 90°C) of the fluid 31 at the outlet of the heat exchanger H1 obtained by using the hot fluid 22.

[0086] In the operating stage where the fluid 22 is not hot (usually, the compressor on which heat is recovered does not operate), only the heater H2 is used to heat the regeneration fluid 30.

[0087] In the cooling stage, the hot fluid 22 flows in the form of the fluid 22b through the three-way valve V and bypasses the heat exchanger H1. There is no flow 22a (the valve is closed towards 22a). The cold regeneration fluid 30 initially cools the heaters H1 and H2 (thermal inertia). The fluid 32 very quickly reaches the same low temperature as the fluid 30 (depending on the thermal inertia).

[0088] According to Figure 3 the second variant of the present invention shown:

[0089] ● During the heating phase, the hot fluid 22 passes through the heat exchanger H1. The regeneration fluid 30 (30a) is heated by the fluid 22 in the exchanger H1, the valve V2 is open, and the valve V1 is closed. There is no flow in 30b. The valves V1 and V2 have an all-or-nothing operation mode.

[0090] Alternatively, the two valves V1 and V2 can be control valves that regulate the flow rate in each branch 30a and 30b in order to finely adjust the temperature of the fluid 32, especially in the case where the heater (and its associated temperature control regulation) is not used.

[0091] If necessary, the heated fluid 31 can be reheated in the heater H2, which is typically an electric heater or a heater heated by steam or gas. This can be done periodically in the following cases: to increase the regeneration temperature (usually 120°C - 150°C, or even 200°C) in order to, for example, improve the regeneration of certain impurities that would regenerate poorly at the temperature level (usually 70°C - 90°C) of the fluid 31 at the outlet of the heat exchanger H1 using the hot fluid 22.

[0092] During the operating phase in which the fluid 22 is not hot (usually, the compressor on which heat is recovered is not running), only the heater H2 is used to heat the regeneration fluid 30.

[0093] During 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, the valve V2 is closed, and the valve V1 is open. There is no flow in 30a. The cold regeneration fluid 30 passes directly as the cold fluid 32 without / without using thermal inertia.

[0094] Thus, it can be seen that the heater H2 is:

[0095] ● For auxiliary heating;

[0096] ● For the phase in which the heat source is not available.

Claims

1. A method for compressing a gas (G), wherein, The gas is compressed in a compressor having: at least two stages (C1, C2), the at least two stages including an intermediate stage or a first compression stage and a final compression stage for compressing the gas downstream of the intermediate stage or the first compression stage; an intercooler (R1) for cooling the gas downstream of the intermediate stage or the first compression stage; and a final cooler (R2) for cooling the gas downstream of the final compression stage. Refrigerant, such as water or an aqueous solution of ethylene glycol, from a refrigerant source (B) or a refrigerant cooling system is divided into a first stream and a second stream. The first stream (21) is sent only to cool the intercooler, and the second stream (11) is sent only to cool the final cooler. A first heated stream (22) is discharged from the intercooler, and a second heated stream (12) is discharged from the final cooler. The temperature difference between the first heated stream and the second heated stream is at least 30 °C, preferably at least 40 °C, or even at least 50 °C. The first heated stream is hotter than the second heated stream. The first heated stream is at least periodically conveyed to provide heat to a heat-consuming element (A), thereby generating a first cooled stream cooled to a third temperature. The second heated stream that is not conveyed to provide heat to the heat-consuming element and is not cooled is mixed with the first cooled stream that is at least periodically cooled, and the mixture (2) is conveyed to the refrigerant source or the refrigerant cooling system.

2. The method according to claim 1, wherein, In the intercooler or the first cooler (R1), the first heated stream (22) has experienced a temperature increase of 30 °C to 80 °C, or even 50 °C to 80 °C.

3. The method according to claim 1 or 2, wherein In the final cooler (R2), the second heated stream (12) has experienced a temperature increase of 5 °C to 15 °C.

4. The method according to claim 1 or 2, wherein The first stream (21) and the second stream (11) reach the intercooler or the first cooler (R1) and the final cooler (R2) respectively at the same temperature, which is, for example, in the range of 15 °C to 25 °C.

5. The method according to any one of the preceding claims, wherein, The first heated stream (22) is conveyed to the heat-consuming element (A), and the first heated stream is at least periodically not cooled at the heat-consuming element, or the first heated stream is at least periodically not conveyed to the heat-consuming element.

6. The method according to claim 1, wherein The second heated stream (12) is at least periodically mixed with the first cooled stream (23) cooled to the third temperature.

7. The method according to claim 5, wherein The second heated stream (12) is at least periodically mixed with the uncooled first stream.

8. The method according to any one of claims 1 and 5 to 7, wherein The second heated stream (12) is mixed with the first heated stream regardless of whether the first heated stream has been cooled by the heat-consuming element.

9. The method according to any one of the preceding claims, wherein, The first stream (21) is less than the second stream (11).

10. The method according to any one of the preceding claims, wherein, All the refrigerant of the compressor is a stream of refrigerant, such as water, from the refrigerant source (B) or the refrigerant cooling system.

11. The method according to any one of the preceding claims, wherein, The first stream (21) is 1 / 5 to 1 / 15 times that of the second stream (11).

12. The method according to any one of the preceding claims, wherein, The first stream (22) is periodically conveyed to the heat-consuming element (A).

13. The method according to any one of claims 1 to 11, wherein The first stream (22) is continuously conveyed to the heat-consuming element (A).

14. A method for separating air by cryogenic distillation, wherein, Air (G) is compressed according to the method of any one of the preceding claims, and the compressed air is cooled, purified in a purification unit by pressure swing and / or temperature swing adsorption, and separated by distillation to form an oxygen-enriched and / or nitrogen-enriched fluid, and the purification unit is regenerated by a regeneration gas.

15. A method for separating air by cryogenic distillation, wherein, Air (G) is compressed, the compressed air is cooled, purified in a purification unit by pressure swing and / or temperature swing adsorption, and a part of the purified air is compressed and separated by distillation according to the method of any one of claims 1 to 11 to form an oxygen-enriched and / or nitrogen-enriched fluid, and the purification unit is regenerated by a regeneration gas.

16. The method according to claim 14 or 15, wherein, The heat-consuming element (A) is a heater (H1) for heating at least a part (30) of the regeneration gas upstream of the purification unit, and the first heated stream provides all the heat necessary to bring the regeneration gas to a temperature suitable for regenerating the purification unit.

17. The method according to claim 14 or 15, wherein The heat-consuming element is a heater (H1) for heating at least a part of the regeneration gas upstream of the purification unit, and the first heated stream provides only a part of the heat necessary to bring the regeneration gas (30, 31, 32) to a temperature suitable for regenerating the purification unit, and the remaining required heat is provided by an additional heater (H2).

18. An apparatus for compressing a gas, the apparatus being associated with a heat consuming element, the apparatus comprising: A compressor having: at least two stages (C1, C2) including an intermediate compression stage or a first compression stage and a final compression stage for compressing the gas downstream of the intermediate compression stage or the first compression stage, an intercooler (R1) for cooling the gas downstream of the intermediate compression stage or the first compression stage, and a final cooler (R2) for cooling the gas downstream of the final compression stage; means for dividing a refrigerant, such as water or an aqueous solution of ethylene glycol, from a refrigerant source or a refrigerant cooling system into a first stream (21) and a second stream (11); pipes for conveying the first stream to cool only the intercooler or the first cooler and pipes for conveying the second stream to cool only the final cooler; pipes for discharging a first heated stream (22) from the intercooler or the first cooler and pipes for discharging a second heated stream (12) from the final cooler, the temperature difference between the first heated stream and the second heated stream being at least 30 °C, preferably at least 40 °C, or even at least 50 °C, and the first heated stream being hotter than the second heated stream; Means for at least periodically conveying the first heated stream to supply heat to the heat-consuming element (A) to produce a first cooled stream (23) that is at least periodically cooled; Means for conveying the second heated stream without passing the second heated stream through the heat-consuming element or the cooling device to directly mix with the at least periodically cooled first cooled stream; and means for conveying the formed mixture (2) to the refrigerant source or the refrigerant cooling system.

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