Process and apparatus for liquefaction and optionally separation of co2 by distillation

Abstract

A process for liquefying a CO2-rich feed stream comprises the following steps: a) compressing (C1,C2) the feed stream (1) from an initial pressure to a first pressure greater than 30 bara to obtain a feed stream (7) at a first temperature, b) cooling the feed stream at the first temperature by a water stream at a second temperature lower than the first temperature to form a feed stream at a third temperature, c) cooling the feed stream at the third temperature to form a feed stream at a fourth temperature by heat exchange with at least one stream (13, 14, 17, 19, 21) derived from the feed stream, d) cooling (R2) the feed stream at the fourth temperature by heat exchange with a fluid stream at a temperature between 5 and 40°C, which is air or water, to form a stream at a fifth temperature,and at least part of the feed flow at the fifth temperature is liquefied (11, 13, 23).

Description

[0001] The present invention relates to a method and apparatus for liquefying CO2 and optionally separating CO2 by distillation and / or washing and / or partial condensation.

[0002] The CO2 stream that is liquefied and eventually separated may contain more than 95% CO2 but also other impurities such as water, oxygen, nitrogen, argon, methane, carbon monoxide, hydrogen, helium etc.

[0003] CO2 liquefiers using CO2 as a refrigerant involve the use of a cycle compressor followed by liquefaction, or densification in the case of operation above the critical pressure of CO2. A significant amount of heat is generated during CO2 compression which is typically dissipated in the compressor's intermediate heat exchangers as well as during condensation / densification by being transferred to the cooling fluid, typically water or air. It is therefore dissipated without being used.

[0004] However, these dissipated calories can have value in certain cases. For example, they could be used to heat a fluid, for example water for district heating, to preheat boiler water, etc. The invention presents heat recovery solutions with a moderate impact on the liquefier's electricity consumption.

[0005] It is known to those skilled in the art that heat recovery in a multi-stage compressor can be achieved by avoiding certain intermediate coolings in order to allow the temperature of the compressed gas to increase. When the gas is sufficiently hot, it can be cooled against the fluid to be heated, such as boiler water or district heating water.

[0006] In FR2974167, the CO2 is compressed in a multi-stage compressor, with intermediate inlets corresponding to the different cooling levels of the cold process. Between each stage, there is a water cooler. At the compressor outlet, the CO2 increases in density in a water or air cooler and then in another exchanger whose cold fluid is a portion of the liquid CO2 obtained by expansion of the densified CO2. The remaining CO2, liquid and therefore partially cooled, is sent to the cold process for subcooling against the different CO2 flows at different pressures that are integrated into the compressor. These flows are therefore also partially cold because they come from the heat exchange with the partially cooled liquid CO2.Thus, they cool by direct contact the compressed CO2 in the compressor with which they are mixed, limiting the temperature rise in the intermediate stages of compression, which makes heat recovery unsuitable. Problem solved by the invention

[0007] The invention allows for optimizing heat exchanges to increase the temperature of the fluids returned to the compressor from the coldest part of the process, in order to be able to recover more calories from their compression and from the condensation / densification of CO2, while having a moderate impact on the compression energy of the CO2. It may be considered counter-intuitive to heat before compression, but the impact on compression energy is minimized since the recycled flow rates are reduced because more cold is transferred to the CO2 being densified.

[0008] The fluids are heated against the CO2 which is itself cooled by a fluid (for example district heating water) which is at room temperature or which is slightly warm (for example at most 40°C). Therefore, taking into account the approach temperatures, the recycled gases are between 20 and 50°C where recycling was between 0°C and 20°C before the invention was implemented.

[0009] In particular, it is a question of making the most possible use of the heat recoverable during cooling at the compressor outlet.

[0010] This also makes it possible to significantly reduce the demand for water or ambient air to between 5 and 40°C for the condensation / densification of CO2, which is particularly important when it comes to water (its production system being smaller). Description of the invention

[0011] According to an object of the invention, there is provided a method of liquefaction and optionally separation of a feed flow rich in CO2 comprising the following steps: a) compressing the feed flow from an initial pressure to a first pressure greater than 30 bara to obtain a feed flow at the first pressure and at a first temperature, b) cooling the feed flow at the first pressure and the first temperature by a flow of water or oil at a second temperature lower than the first temperature to form a feed flow at the first pressure and at a third temperature, c) cooling the feed flow at the first pressure and the third temperature to form a feed flow at the first pressure and at a fourth temperature by heat exchange with at least one stream which is produced by heating a liquid,this liquid resulting from the liquefaction and possibly the separation of the feed flow d) cooling the feed flow at the first pressure and at the fourth temperature by heat exchange with a fluid flow at a temperature between 5 and 40°C which is air or water to form a feed flow at the first pressure and at a fifth temperature, and at least a portion of the feed flow at the first pressure and fifth temperature being liquefied and optionally separated by partial condensation and / or distillation to form a liquid product, optionally a portion of the liquid portion also being separated by partial condensation and / or distillation.

[0012] According to other optional features: the water or oil flow of step b) is heated from the second temperature to a temperature above 40°C, preferably above 80°C, or even above 90°C in step b).the method comprising the steps of: e) cooling the feed flow at the first pressure and at the fifth temperature to a sixth temperature, f) the feed flow at the sixth temperature is expanded to a second pressure above 5.1 bar and a seventh temperature below the sixth temperature but above -56.6°C, forming a two-phase fluid which is separated into a gaseous part and a liquid part, g) at least a portion of the liquid part exchanging heat with the feed flow to effect the cooling of steps c) and / or e) and h) at least a portion of the gaseous part being liquefied and optionally separated by partial condensation and / or by distillation to form the liquid product, optionally a portion of the liquid part also being separated by partial condensation and / or by distillation.the cooling of step c) takes place in a first heat exchanger and the cooling of step e) takes place in a second heat exchanger. the cooling of step c) and step e) takes place in a single heat exchanger. cooling the feed flow to the first pressure and the third temperature to form a feed flow at the first pressure and a fourth temperature by heat exchange with at least one stream which is produced by vaporization of a liquid resulting from the liquefaction and optionally the separation of the feed flow the liquid, resulting from the liquefaction and optionally the separation of the flow, is sent to exchange heat with the feed flow and forms a stream which heats up during step c) and optionally step e).the flow heated during the cooling of steps c) and optionally e) is sent to the inlet of a compression stage where the feed flow is compressed. the flow is sent to the inlet of a compression stage at a pressure equal to or greater than the initial pressure but preferably lower than the first pressure. at least one gaseous flow produced during the liquefaction and optionally the separation of the feed flow is sent at a temperature above 0°C to heat up by heat exchange with the feed flow which cools during steps c) and optionally e), the at least one gaseous flow being compressed from a pressure at most equal to the initial pressure and then mixed with the feed flow at the initial pressure.the at least one gas stream produced during liquefaction and optionally separation of the feed stream is produced by vaporization of a liquid produced during liquefaction or separation of the feed stream. at least one compression step of the feed stream or at least one compression step of the at least one gas stream is adiabatic. the water or oil stream at the second temperature is heated to at least 60°C and optionally less than 150°C during step b). the second temperature is between 5 and 50°C. the third temperature is between 40°C and 60°C, or even 50°C. the density of the feed stream at the fifth temperature is above 400kg / m3, or even above 600kg / m3. the fluid flow at a temperature between 5 and 40°C which is water heated by cooling the feed flow at the first pressure and the fourth temperature is sent to a boiler and / or a heating system.

[0013] According to another object of the invention, there is provided an apparatus for liquefying and optionally separating a CO2-rich feed flow comprising a compressor for compressing the feed flow from an initial pressure to a first pressure greater than 30 bara to obtain a feed flow at the first pressure and at a first temperature, a first heat exchanger, fluidically connected to the compressor, for cooling the feed flow at the first pressure and the first temperature by indirect heat exchange with a water or oil flow at a second temperature lower than the first temperature which heats up, to form a feed flow at the first pressure and at a third temperature,a second heat exchanger fluidly connected to the first heat exchanger for cooling the feed flow at the first pressure and third temperature to form a feed flow at the first pressure and a fourth temperature by heat exchange with at least one stream that is produced by heating a liquid resulting from liquefaction and optionally separation of the feed flow,a third heat exchanger fluidly connected to the second heat exchanger for cooling the feed flow at the first pressure and the fourth temperature by heat exchange with a fluid flow which is air or water at a temperature between 5 and 40°C to form a feed flow at the first pressure and a fifth temperature and means for liquefying and optionally separating by partial condensation and / or distillation at least a portion of the feed flow at the first pressure and the fifth temperature to form a liquid product, these means being fluidly connected to the third heat exchanger.,

[0014] According to other optional aspects: the apparatus comprises an n-stage CO2 compressor with at most n-2 intercoolers. the apparatus comprises an n-stage compressor with at most n-2 intercoolers cooled by water. the apparatus comprises an n-stage CO2 compressor with only one intercooler in which water is heated, the apparatus comprises another cooler for cooling the CO2 at the outlet of the compressor in which water or oil is heated, to an intermediate temperature for the CO2, for example between 40°C and 60°C, or even 50°C. Several variants are possible, in order of interest: Continue the densification in an exchanger against a readily available fluid, for example water or oil at between 0°C and 40°C or air at between 0°C and 40°C.Cooling of the cooled CO2 against the fluid which is water at between 0°C and 40°C or air at between 0°C and 40°C in a heat exchanger (called "economizer") where the CO2 is partially condensed producing a cooled liquid which is sent to the heat exchanger to partially condense the CO2. Sharing the economizer with the densifier which follows the ambient media exchanger in order to better integrate the heat exchange and minimize the number of equipment. Increasing the compressor outlet pressure beyond what is necessary in terms of density obtained after cooling in order to recover more heat at the outlet, potentially supplemented by a liquid turbine for expansion before the densifier. In doing so, the electrical consumption of the compressor is slightly increased. On the other hand, the recovered energy increases significantly for a low impact on electrical consumption.Preheating of the inlet CO2 in the economizer in order to compress hotter CO2 and therefore achieve higher temperatures and / or more calories transferred to the heated fluid. Integration of the heat recovery exchangers in a common exchanger, or even in the economizer / densifier of the first point.

[0015] The invention will be described in more detail with reference to the figures. [ FIG.1 ] shows a method according to the invention in which a feed stream 1 which is gaseous CO2 is liquefied to form liquid CO2 23. [ FIG.2 ] shows a method according to the invention in which a feed stream 1 which is gaseous CO2 is liquefied to form liquid CO2 23. [ FIG.3 ] shows a method according to the invention in which a feed stream 1 which is gaseous CO2 is liquefied to form liquid CO2 23. [ FIG.4 ] shows a method according to the invention in which a feed stream 1 which is gaseous CO2 is liquefied to form liquid CO2 23.

[0016] In the Figure 1 , the feed flow 1 is sent to the inlet of a stage C2 of a compressor. The gas 1 is mixed with a gas 13 to form a gas which is compressed in stage C2 to form the flow 7. The flow 7 compressed to a first pressure above 30 bara is cooled from a first temperature T1 to a third temperature T3 and cools in a cooler R1 by indirect contact with a fluid at a second temperature T2, for example water to an intermediate temperature of at least 40°C (for example between 40 and 60°C, for example 48-52°C) such that the density of the CO2 7 remains relatively low, below 400kg / m 3< , the CO2 being cooled to a third temperature T3. The fluid in the cooler R1 is oil, district heating water or boiler water. The fluid, for example water, in cooler R1 therefore recovers the heat of compression of the CO2.

[0017] The CO2 partially cooled by the cooler R1 to the third temperature T3 is sent to a heat exchanger E1, for example of the plate and fin type. It cools from the third temperature T » to a fourth temperature T4 which is an intermediate temperature of this exchanger E1, lower than the first temperature and then leaves the exchanger to be cooled by a cooler R2 cooled by a fluid at an ambient temperature which is air or water. This ambient temperature is between 5 and 40°C.

[0018] Because the CO2 has already been cooled by cooler R1, cooler R2 can be smaller and consume less fluid at room temperature.

[0019] The CO2 cooled to a fifth temperature T5 and condensed or partially densified by the cooler R2 is subcooled in the heat exchanger E1 or in another heat exchanger and then is expanded in a valve V1 to form a two-phase fluid which separates in a liquefaction and separation unit comprising a phase separator S. This separator S produces a gas 9 which is sent to a section B of the liquefaction unit and possibly separation by partial condensation and / or washing and / or distillation. The separator S also produces a liquid of which a part 11 is sent to section B of the liquefaction unit and the remainder 13 vaporizes and heats up in the heat exchanger E1 at a pressure substantially equal to the inlet pressure of the stage C2. The liquid 13 can vaporize in the exchanger E1 upstream or downstream of the cooler R2. The vaporized liquid 13 is mixed with the gas 1 as mentioned.

[0020] Section B produces an end product 23 which is liquid carbon dioxide, generally purer in carbon dioxide than stream 1.

[0021] It optionally produces at least one fluid 15 containing at least one light or heavy impurity present in the flow 1.

[0022] In the Figure 2 , the feed flow 1 is sent to the inlet of a stage C1 of a common compressor comprising n, here four, stages, including two stages CR1, CR2 upstream of stage C1. The gas 1 is mixed with a gas 17 to form a gas 3 which is compressed in stage C1 to form the flow 5. The flow 5 is mixed with the flow 13 and is then sent directly to the final stage C2 without having been cooled. The flow 7 compressed in the two stages up to a first pressure greater than 30 bara, or even greater than 60 bara, is cooled from a first temperature T1 to a third temperature T3 and cools in a cooler R1 by indirect contact with a fluid at a second temperature T2, for example water up to an intermediate temperature of at least 40°C (for example between 40 and 60°C, for example 48-52°C) so that the density of the CO2 7 remains relatively low, less than 400kg / m 3< , the CO2 being cooled down to a first temperature.The fluid in cooler R1 can be oil, district heating water, or boiler water. The fluid, e.g., water, in cooler R1 therefore recovers the heat of compression from the CO2.

[0023] The CO2 partially cooled by the cooler R1 to the third temperature is sent to a heat exchanger, for example a plate and fin heat exchanger. It cools from the third temperature T3 to a fourth temperature T4 which is an intermediate temperature of this exchanger E1, lower than the first temperature and then leaves the exchanger to be cooled by a cooler R2 cooled by a fluid at an ambient temperature which is air or water. This ambient temperature is between 5 and 40°C.

[0024] Because the CO2 has already been cooled by cooler R1, cooler R2 can be smaller and consume less fluid at room temperature.

[0025] The CO2 cooled to a fifth temperature T5 and condensed or partially densified by the cooler R2 is subcooled in the heat exchanger E1 or in another heat exchanger and then is expanded in a valve V1 to form a two-phase fluid which separates in a liquefaction and separation unit comprising a phase separator S. This separator S produces a gas 9 which is sent to a section B of the liquefaction unit and possibly separation by partial condensation and / or washing and / or distillation. The separator S also produces a liquid of which a part 11 is sent to section B of the liquefaction unit and the remainder 13 vaporizes and heats up in the heat exchanger E1 at a pressure substantially equal to the outlet pressure of stage C1. The liquid 13 can vaporize in the exchanger E1 upstream or downstream of the cooler R2. The vaporized liquid 13 is mixed with the gas 5 as mentioned.Three other gaseous CO2 flows 21, 19, 17, at the inlet pressures of stages CR1, CR2 and C1 respectively, coming from section B are heated in exchanger E1 and are sent to the inlet of stages CR1, CR2 and C1 respectively. The pressure of flow 19 is lower than that of 17. The pressure of flow 21 is lower than that of 19. These gaseous flows 17, 19, 21 are produced during the liquefaction and / or separation by washing and / or distillation and / or partial condensation process which takes place in section B. At least one of the flows 17, 19, 21 can be produced in liquid form, vaporized in section B and sent as gas to exchanger E1.

[0026] Section B produces an end product 23 which is liquid carbon dioxide, generally purer in carbon dioxide than stream 1.

[0027] It optionally produces at least one fluid 15 containing at least one light or heavy impurity present in the flow 1.

[0028] Gas 21 is compressed in stage CR1 and then mixed with gas 19 and sent to the next stage CR2 without intermediate cooling. The compressed gas in stage CR2 is cooled by a cooler RR1 and then mixed with feed stream 1 and gas 17.

[0029] Thus the common compressor CR1, CR2, C1, C2 comprises n, here four, stages on the same axis and only n-2, here two, coolers, including an intermediate cooler RR1 between stages CR2 and C1 and a final cooler R1 downstream of the last stage C2.

[0030] [ FIG.3 ] shows an alternative process to that of the Figure 1 in which only flow 13 is used to cool the gas coming from cooler R2 upstream of valve V1 in exchanger E2. Gases 17, 19, 21 do not pass into exchanger E2 but are heated in heat exchanger E1 and are sent respectively upstream of stage C1, upstream of stage CR2 and upstream of stage CR1. Here again at least one of the flows 17, 19, 21 can be produced in liquid form, vaporized in section B and sent as gas to exchanger E1.

[0031] This allows to reduce the overall price for the heat exchange since the E2 exchanger can be of a type allowing the exchange of heat between only two fluids, for example a shell and tube exchanger.

[0032] [ FIG.4 ] still shows an alternative method of the Figure 1in which the separation unit does not include a phase separator S or a valve V1. Unit B is a liquefaction or separation unit by distillation and / or washing and / or partial condensation.

[0033] In this figure, the entire feed flow leaving the cooling in R2 at the fourth temperature T4 is sent to the liquefaction or separation unit B. This unit produces a final product 21 having a CO2 content equal to or greater than that of flow 1.

[0034] The unit also produces CO2-rich gases 14, 17, 19, 21 respectively at the pressures between stages C1 and C2, between stages CR2 and C1, between stages CR1 and CR2 and upstream of stage CR1. At least one of the flows 14, 17, 19, 21 is produced in liquid form, vaporized in section B and sent as gas to exchanger E1.

[0035] In all examples, the coolers between stages CR1 and CR2 and between stages C1 and C2 are absent, while cooler RR1 and cooler R1 are present. The presence of cooler RR1 is also optional.

[0036] In these examples, the number of gases reheated and recycled, each at a different pressure, is strictly equal to the number of compressor stages. It will be understood that the number of compressor stages can vary.

[0037] In addition, the number of reheated gases, each at its own pressure, may be less than the number of stages, for example equal to n-1, so that for certain stages, no flow is recycled directly upstream of the stage.

[0038] The outlet pressure of the last stage of compressor C2 may be supercritical. In this document, the term "liquefaction" will include the densification of a supercritical gas or partial liquefaction.

Claims

1. A process for liquefying and optionally separating a CO2-rich feed stream comprising the following steps: a) compression (C1, C2) of the supply flow (1) from an initial pressure to a first pressure greater than 30 bara to obtain a supply flow (7) at the first pressure and at a first temperature, b) cooling the feed flow at the first pressure and the first temperature by a flow water or oil at a second temperature lower the first temperature to form a feed flow at the first pressure and a third temperature, c) cooling of the feed flow at the first pressure and third temperature to form a feed flow at the first pressure and at a fourth temperature by heat exchange with at least one stream (13, 14, 17, 19, 21) which is produced by heating a liquid, this liquid resulting from the liquefaction and possibly the separation of the feed flow d) cooling (R2) of the supply flow at the first pressure and at the fourth temperature 20 by heat exchange with a flow of fluid at a temperature between 5 and 40°C which is air or water to form a feed flow at the first pressure and at a fifth temperature and at least part of the feed flow at the first pressure and fifth temperature being liquefied and optionally separated by partial condensation and / or by distillation to form a liquid product (11, 13, 23), optionally a portion of the liquid part also being separated by partial condensation and / or by distillation.

2. A process according to claim 1 in which the flow of water or oil in step b) is heated from the second temperature to a temperature of higher than 40°C, preferably higher than 80°C, or even higher than 90°C in step b).

3. A method according to one of claims 1 and 2 comprising the steps of e) cooling of the supply flow at the first pressure and at fifth temperature to a sixth temperature, f) the feed rate at the sixth temperature is expanded to a second pressure higher than 5.1 bar and a seventh temperature lower than the sixth temperature but above - 56.6°C, forming a two-phase fluid which is separated into a gaseous part (9) and a liquid part (11, 13), g) at least one portion (13) of the liquid part exchanging heat with the feed flow to effect cooling in steps c) and / or e) and h) at least part of the gaseous part being liquefied and optionally separated by partial condensation and / or distillation to form the product liquid (23), possibly a portion of the liquid part also being separated by partial condensation and / or distillation.

4. Process according to claim 3 in which the cooling of step c) takes place in a first heat exchanger (E1) and the cooling of step e) takes place in a second heat exchanger (E2).

5. Process according to claim 3 in the cooling in step c) and step e) takes place in a single heat exchanger (E1).

6. Process according to one of the preceding claims in which the liquid resulting from the liquefaction and possible separation of the feed flow is sent to exchange heat with the feed flow and form a stream which heats up during step c) and possibly step e).

7. Process according to one of the preceding claims in which the flow heated (13, 14, 17, 19, 21) during the cooling of steps c) and optionally e) is sent to the inlet a compression stage (C1, C2) where the feed flow (1) is compressed.

8. Method according to claim 7 in which the stream (13, 14, 17, 19, 21) is sent to the inlet of a compression stage (CR1, C2) at a pressure equal to or greater than the initial pressure but preferably less than the first pressure.

9. Process according to one of the preceding claims 3 to 5 and 6 to 8 when claims 6 to 8 depend on claim 3, in which at least one gas stream (14, 17, 19, 21) produced during liquefaction and optionally separation of the feed flow is sent at a temperature above 0°C to be heated by heat exchange with the feed flow (1) which cools during steps c) and possibly e), the at least one gas stream being compressed (CR1, CR2) from a pressure at most equal to the initial pressure and then mixed with the supply flow (1) at the initial pressure.

10. A method according to claim 9 in which the at least one gas stream (14, 17, 19, 21) produced during liquefaction and optionally separation of the feed flow is produced by vaporisation of a liquid produced during liquefaction or separation of the feed flow.

11. Method according to at least one of the preceding claims in which at least at least one compression step (C1, C2) of the feed flow (1) or according to claim 9 or 10 in which at least one compression step (CR1, CR2) of the at least one gas flow (14, 17, 19, 21) is adiabatic.

12. A process according to at least one of the preceding claims in which the flow of water or oil at the second temperature is heated to at least 60°C. and possibly less than 150°C during step b).

13. A process according to at least one of the preceding claims in which the second temperature is between 5 and 50°C.

14. Process according to at least one of the preceding claims in which the third temperature is between 40°C and 60°C, or even 50°C.

15. Process according to at least one of the preceding claims in which the density of the feed flow at the fifth temperature is above 400 kg / m3, or even above 600 kg / m3.

16. Apparatus for liquefaction and optionally separation of a CO2-rich feed stream comprising a compressor (C1, C2) for compressing the feed from an initial pressure to a first pressure greater than 30 bara to obtain feed (7) at the first pressure and at a first temperature, a first heat exchanger (R1), fluidically connected to the compressor, for cooling the feed at the first pressure and the first temperature by indirect heat exchange with a flow of of water or oil at a second temperature lower than the first temperature, which heats up to form a feed flow at the first pressure and at a third temperature higher than the first temperature, a second heat exchanger (E1) fluidically connected to the first heat exchanger for cooling the feed at the first pressure and the third temperature to form a feed flow at the first pressure and a fourth temperature by heat exchange with at least one flow (13, 14, 17, 19, 21) which is produced by heating a liquid resulting from liquefaction and possible separation of the feed flow, a third heat exchanger (R2) fluidically connected to the second heat exchanger to cool the feed at the first pressure and at the fourth temperature by heat exchange with a flow of fluid which air or water at a temperature between 5 and 40°C to form a feed flow at the first pressure and at a fifth temperature and means (V1, B) for liquefying and optionally separating by partial condensation and / or distillation at least part of the feed at the first pressure and at the fifth temperature to form a liquid product (11, 23), these means being fluidically connected to the third heat exchanger.

Images