Patent Application
20250237431
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French patent application No. FR2400582, filed Jan. 22, 2024, which is herein incorporated by reference in its entirety.
The present invention relates to a method and to an apparatus for compressing a gas.
EP829691 discloses the use of two water flows from a common source for cooling the final cooler and an intermediate cooler of a compressor. The two flows come from the same source and undergo essentially the same temperature increase.
FR2844863 discloses that water is sent in parallel to two coolers in order to produce two water flows at the same temperature, which temperature is relatively low (35° C. in said document).
In DE1020120040480, the water flow is divided into two. One of the flows cools the intermediate cooler and the other cools the final cooler. The flow 12, 13, 14 heated by the intermediate cooler is thus at 386 K, whereas the flow 16 heated by the final cooler is at 366 K. The flow that has been heated by the intermediate cooler is also heated by a final cooler.
The hottest flow is sent to a unit where it preheats water.
The final cooler thus produces warm water whereas the intermediate cooler produces hot water, and it is the hot water only that is sent to provide heat to the consuming element so that its temperature becomes compatible with the warm water with which it is to be mixed.
One aim of the invention is to simplify the circuit for the refrigerant (generally water or glycol water) in the case of heat recovery only in at least one cooler of a compressor.
In certain embodiments, the invention may include creating a single circuit of refrigerant, likened to water here, for the following two functions in the air compressor.
The hot water is sent to the system using the heat, and the hot water that has been either completely cooled, partially cooled, or not cooled (that is, not used) is then mixed with the warm water. This mixture is then sent to the cooling system or network.
The invention is described with respect to a two-stage compressor, but it can easily be extrapolated to more than two stages. Likewise, the refrigerant is described as water, but it can also be glycol water or any other suitable refrigerant.
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 compressor with only two stages.
The compressor comprises a cooler with a temperature increase of the refrigerant (for example water) of around 10° C. (i.e. 30° C. for water at 20° C.).
The compressor comprises another cooler for making hot refrigerant, for example hot water, with a temperature increase of the refrigerant (for example water) of around 70° C. (i.e. 90° C. for water at 20° C.), with a greatly reduced refrigerant flow. The ratio between the flow sent to the cooler with a smaller refrigerant temperature increase and the flow sent to the cooler with a greater refrigerant temperature increase is between 5 and 15.
The compressor thus produces a flow of warm refrigerant, for example warm water, and a flow of hot refrigerant, for example hot water.
Preferably, the hot refrigerant has been heated by an intermediate cooler or a first cooler and the warm refrigerant has been heated by a final cooler.
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.
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 increase implies that the heat transfer is less efficient and that the compressor is less well cooled.
According to one aspect of the invention, the opposite is recommended. While the performance of the compressor is not optimal in terms of energy, the use of the heat thus recovered greatly compensates for the reduced performance of the machine, for an improved overall energy balance.
According to one object of the invention, a method for compressing a gas is provided wherein 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 glycol water, coming from a refrigerant source or a refrigerant cooling system, is divided into a first flow and a second flow, the first flow is sent to cool the intermediate cooler only and the second flow is sent to cool the final cooler only, the first heated flow is removed from the intermediate cooler and the second heated flow is removed from the final cooler, the first and second heated flows being at temperatures that differ by at least 30° C., preferably at least 40°, or even at least 50°, the first heated flow being hotter than the second heated flow, the first heated flow is sent at least periodically to provide 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 provide heat to the heat consuming element and has not been cooled, is mixed with the first at least periodically cooled flow, and the mixture is sent to the refrigerant source or to the refrigerant cooling system.
According to other optional aspects:
According to one object of the invention, a method is provided for separating air by cryogenic distillation, wherein air is compressed according to one of the methods as described above, and the compressed air is cooled, purified in a purification unit by pressure and/or temperature swing adsorption and separated by distillation, forming an oxygen- and/or nitrogen-enriched fluid, the purification unit being regenerated by a regeneration gas.
According to one object of the invention, a method is provided for separating air by cryogenic distillation, wherein air is compressed, the compressed air is cooled and purified in a purification unit by pressure and/or temperature swing adsorption, and one portion of the purified air is compressed according to one of the methods described above and separated by distillation, forming an oxygen- and/or nitrogen-enriched fluid, the purification unit being regenerated by a regeneration gas.
According to other optional aspects:
According to another aspect of the invention, an apparatus for compressing a gas is provided, 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 glycol water, coming from a refrigerant source or a refrigerant cooling system, into a first flow and a second flow, a duct for sending the first flow to cool the intermediate cooler only and a duct for sending the second flow to cool the final cooler only, a duct for removing the first heated flow from the intermediate or first cooler and a duct for removing the second heated flow from the final cooler, the first and second heated flows being at temperatures that differ by at least 30° C., preferably at least 40°, or even at least 50°, the first heated flow being hotter than the second heated flow, means for at least periodically sending the first heated flow to provide heat to the heat consuming element producing a first at least periodically cooled flow, means for sending the second heated flow to mix with the first at least periodically cooled flow, directly without passing through the heat consuming element or a cooling apparatus, and means for sending the mixture formed to the refrigerant source or to a refrigerant cooling system.
The invention will be understood better from reading the following description and from studying the accompanying figures. These figures are given only by way of illustration and do not in any way limit the invention.
The invention will be described in greater detail with reference to the figures, in which:
In [
The cooler R1 can be a cross-current shell and tube heat exchanger with multiple passes.
As the cooler R1 is generally incorporated into the compressor, the maximum footprint is generally restricted, which makes it necessary to potentially slightly degrade the cooling of the compressed gas in favour of maximum heating of the fluid to be heated. This implies reduced performance for the next compression stage, with slightly higher energy expenditure, which is however largely counterbalanced by the energy saving from the heat recovery.
It is advantageous to recover heat only in the intermediate cooler(s) R1 of the compressor by producing a hot refrigerant, for example hot water, typically at around 90° C., and retaining a conventional refrigerant for the final refrigerant.
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 of between 15° C. and 25° C.
The final cooler R2 is conventionally a cross-current shell and tube heat exchanger with a few passes. The standard design thereof makes it possible to cool the gas satisfactorily at the end of compression. If heat were recovered in this final refrigerant, this would result in poorly cooled gas, or a second refrigerant would have to be added in series.
The flow 11 undergoes a moderate temperature increase in the final cooler R2, typically between 5° C. and 15° C.
The heated flows 12, 22 have temperatures that differ by at least 30° C., preferably at least 40° C., or even at least 50° C.
Preferably, the cooler R1 comprises more passes than the cooler R2.
The gas compressed in stage C2 can undergo additional cooling after cooling in R2, for example against iced water or against a cold fluid. This is in particular the case with respect to a apparatus for separating air by cryogenic distillation:
The compressed gas is then sent elsewhere. It can for example be purified into water and CO2 in a purification unit operating by means of temperature and/or pressure swing. It can then be separated in a unit for separating air by cryogenic distillation. One portion of the nitrogen produced by distillation can be heated in a heater in order to reach the temperature necessary for regenerating an adsorbent bed of the purification unit.
If the heat available in the intermediate refrigerant(s) is sufficient for the envisaged use (for example regenerating the FEP unit of an ASU), this makes it possible to cool the gas satisfactorily at the end of compression, which is beneficial for example when the compressed gas must then be cooled again, either by being sent to a cold box for separating the gases of air, or in a pre-cooling system upstream of an FEP unit.
As an alternative, compressed air can be purified and then just one portion of the purified air can be compressed in a compressor according to the invention, known as a booster compressor, with a plurality of compression stages and coolers producing refrigerant flows coming from a common source but heated to different temperatures.
The compressor according to the invention can thus be a main air compressor or a booster air compressor. It can also be a compressor for nitrogen gas or gaseous oxygen produced for example in an air separation apparatus.
The heat recovered by the refrigerant 22 can make it possible to heat all or some of the regeneration gas intended for a TSA front-end purification unit, for example in an air separation apparatus. Otherwise, it can be used as a heat source for an absorption refrigeration unit.
The cooling system B supplies 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, dry cooling, evaporative or adiabatic) and/or an adsorption or absorption refrigeration unit. The cooling system is preferably a closed circuit in order to control the water quality and avoid problems of corrosion and/or deposits, which are accentuated by the high temperature at the intermediate refrigerant outlet. Depending on the cooling system B implemented, the refrigerant, for example cold water 1, preferably has a temperature close to the dry or wet temperature of the ambient air.
One portion 11 of the refrigerant 1, for example cold water 1, goes to the final cooler R2 to cool the gas G compressed in the final stage C2 of the compressor.
Hereinafter, the refrigerant is described as being water but it will be understood that it can be a mixture of water and glycol or ammonia.
The cold water is heated in the final cooler R2 and exits in the form of warm water 12 with a moderate temperature increase, typically between 5° C. and 15° C. This portion 11 can also be used to cool the motor of the compressor, the oil sump of the compressor, and optionally other auxiliary equipment on the compressor.
Another portion of the cold water 21 goes to the intermediate cooler RI to cool the gas G compressed in stage C1 of the compressor. The cold water is heated in the final cooler R2 and exits 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.
According to one example, if the water 1 is at 20° C., the flows 11, 21 are at 20° C., and the flow 12 will thus be heated to 30° C. and the flow 22 to 90° C.
The hot water 22, for example at 90° C., is sent to the system using the heat A, which can use the heat intermittently. The water 23 then exits the system using the heat A, which water 23 has been either completely cooled, partially cooled, or not cooled (that is, not used), and is mixed with the warm water 12, forming a mixture 2. With respect to a apparatus for separating air by cryogenic distillation, the using system can be a heater for heating all or some of the front-end purification regeneration gas. If the temperature reached is insufficient, another heater can be added, for example an electric, steam or gas heater, to provide supplementary heating.
This mixture 2 is then sent to the cooling system B.
According to one variant of the invention, it is beneficial to manage the different phases of the regeneration of a TSA system, in particular in the heating phase and the cooling phase, by using the hot fluid 22 recovered from the compression heat of the compressor C1.
This variant consists in passing the hot fluid into an exchanger against the regeneration fluid during the heating phase, and not passing the hot fluid into this exchanger against the regeneration fluid in the cooling phase, with the regeneration fluid circulating in the exchanger during the heating and cooling phases.
Alternatively, another variant consists in passing the regeneration fluid into an exchanger against the hot fluid during the heating phase, and not passing the regeneration fluid into this exchanger against the hot fluid in the cooling phase, with the hot fluid circulating in the exchanger during the heating and cooling phases.
In addition, the regeneration fluid circuit is provided with a second exchanger, typically an electric or steam or gas heater to either provide supplementary heating to reach a higher temperature and/or to allow the operation of the adsorption system during operating phases in which the compression heat is not available, for example in the start-up phase if the compressor is shut down.
According to the first variant, illustrated in [
This is for example the case on a front-end purification unit on an air separation apparatus.
According to the first variant:
Alternatively, the three-way valve V can be a control valve that adjusts the flow in each outlet 22a and 22b so as to finely adjust the temperature of the fluid 31 at the outlet of the exchanger H1, in particular if the heater (and its associated temperature control adjustment) is not used.
The three-way valve can be replaced by 2 two-way valves.
If necessary, the heated fluid 31 can be heated again in a heater H2, typically an electric heater or a heater heated by water vapour or gas. This can be done periodically if the regeneration temperature (typically 120° C.-150° C., or even 200° C.) is to be increased for example in order to improve the regeneration of certain impurities that would be poorly regenerated with the temperature level obtained in the fluid 31 at the outlet of the exchanger H1 with the hot fluid 22 (typically 70° C.-90° C.).
In the operating phases in which the fluid 22 is not hot (typically, the compressor on which heat is recovered is not operating), the regeneration fluid 30 is heated using the heater H2 only.
In the cooling phase, the hot fluid 22 turns through the three-way valve V to go as fluid 22b and bypass the heat exchanger H1. There is no flow 22a (the valve is closed towards 22a). The cold regeneration fluid 30 initially cools the heater H1 and H2 (thermal inertia). The fluid 32 reaches the same cold temperature as the fluid 30 quite quickly (depending on the thermal inertia).
According to a second variant of the invention illustrated in [
Alternatively, the two valves V1 and V2 can be control valves that adjust the flow in each branch 30a and 30b so as to finely adjust the temperature of the fluid 32, in particular if the heater (and its associated temperature control adjustment) is not used.
If necessary, the heated fluid 31 can be heated again in a heater H2, typically an electric heater or a heater heated by water vapour or gas. This can be done periodically if the regeneration temperature (typically 120° C.-150° C., or even 200° C.) is to be increased for example in order to improve the regeneration of certain impurities that would be poorly regenerated with the temperature level obtained in the fluid 31 (typically 70° C.-90° C.) at the outlet of the exchanger H1 with the hot fluid 22.
In the operating phases in which the fluid 22 is not hot (typically, the compressor on which heat is recovered is not operating), the regeneration fluid 30 is heated using the heater H2 only.
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, the valve V2 being closed and the valve V1 open. There is no flow in 30a. The cold regeneration fluid 30 passes directly as cold fluid 32, without thermal inertia.
It can thus be seen that the heater H2 is:
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2400582 | Jan 2024 | FR | national |
