FR2872890A1 - Integrated process for adsorption and cryogenic separation for the production of carbon dioxide from sources containing low percentages of carbon dioxide - Google Patents

Abstract

The process involves the optimisation of a separation unit by combining an adsorption technique, VPSA, VSA or PSA, and a cryogenic unit, both operating in their preferred modes. The process uses an adsorption unit a cryogenic unit, whereby the gas is conveyed to an adsorption unit to be separated into a flow enriched in CO2 and one depleted in CO2 ; the enriched fraction is sent to a cryogenic unit whence it is separated into a CO2-rich flow and a CO2-depleted flow.The initial enriched fraction has a CO2 content of 50 - 95%, preferably 70 - 90%, and the CO2-rich fraction from the cryogenic unit has a CO2 content greater than 80%, preferably greater than 99%. The adsorption section may comprise one or more units operated in parallel.

Description

1 2872890

  The present invention relates to an integrated cryogenic adsorption and separation process for producing 002 and to an installation for carrying out the process.

  The recovery of 002 will develop more and more because of the devices put in place to limit the emission of greenhouse gases and current developments on recycling processes.

  The predominantly dominant technology for recovering 002 in a low pressure source (typically <10 bar) and low concentration in 002 (typically less than 50%, or even 20% most often) is the chemical absorption, and more particularly the washes with amines (MDEA, MEA ...) which make it possible to produce pure low pressure 002 (typically> 99% on a dry basis). However, the washing processes have several limitations: - large amount of steam required - sensitivity to oxygen - corrosion - high operating cost - solvent entrainment, and in general, releases of chemicals, which are not negligible on large capacities (amines, ammonia, salts from the amine regenerator, amine degradation products ...).

  Another possible technology that does not have these disadvantages is pressure swing adsorption such as VPSA (Vacuum Pressure Swing Adsorption), VSA (Vacuum Swing Adsorption) or PSA (Pressure Swing Adsorption). However, the defect of these adsorption units is that they produce impure 002 (typically between 50% and 90% 002).

  For their part cryogenic separation units of 002 (including liquefiers) are only used to treat gases whose concentration is greater than 50% (preferably greater than 70% and greater than 90%) because the performance of these units collapses and / or the energy consumption rises sharply when the share of gases other than 002 increases, due to: - the physical characteristics of the 002 mixtures with nitrogen, carbon monoxide, hydrogen , oxygen, methane ..., 2 2872890 - the triple point of CO2 that prevents descending to temperatures below 50 C.

  The invention proposes to optimize a CO2 separation unit by coupling a VPSA (or VSA or PSA) and a cryogenic unit, both operating in their preferred operating domain. An additional advantage of this coupling is that the CO2 can be directly produced under pressure (in liquid, gaseous or supercritical form) and is thus directly available for subsequent transport in large quantities, for sale in liquid form, ultimate sequestration or valuation in EOR or ECBM for example.

  The object of the invention is i) The coupling of a CO2 separation unit by adsorption with a cryogenic unit to produce a fluid very rich in CO2 (under pressure), the idea being to make a prepurification with adsorption unit and final purification by the cryogenic unit; ii) various integration devices between the adsorption unit and the cryogenic unit.

  The term "cryogenic unit" means a unit in which at least one fluid of the process descends to a temperature below -10 ° C. and undergoes at least one partial condensation step. This unit can produce CO2 in gaseous, liquid or supercritical form; a unit producing liquid as a product is designated a liquefier; - VPSA unit (Vacuum Pressure Swing Adsorption Unit), a unit based on a cyclic process comprising at least one adsorption phase on an adsorbent solid at a pressure greater than 1.5 bar abs., and a phase of regeneration during which the pressure is lower than the atmospheric pressure; unit VSA (vacuum swing adsorption unit), unit based on a cyclic process comprising at least one adsorption phase on an adsorbent solid at a pressure lower than 1.5 bar abs, and a regeneration phase during which the pressure is below atmospheric pressure; 3 2872890 - pressure swing adsorption unit (PSA), unit based on a cyclic process comprising at least one phase adsorption on an adsorbent solid at a pressure greater than 1.5 bar abs., and a regeneration phase. during which the pressure is above atmospheric pressure; the VPSA, VSA and PSA units will be referred to below as adsorption units.

  All percentages mentioned are molar percentages.

  In the current state of the art, an adsorption unit does not make it possible to economically produce CO2 at 95% purity, and even less at 99% purity, from poor sources (ie that is, typically containing less than 45% CO2). It can not therefore be used as such for the concentration of CO2 for recovery as merchantable CO2 or for re-injection into a geological formation, where CO2 purities greater than 95% are generally required.

  Currently, the adsorption process is used in the iron and steel industry for the deballasting of Direct Reduced Iron or COREX gas. In this case, the purge gas of the adsorption process, rich in CO2 (typically 80% CO 2, 25% CO, 5% N 2), leaving this unit, is then used as fuel because it still contains a sufficient amount of CO. Fumes from combustion are released into the atmosphere. The decarbonation of the flows of a DRI unit is preferably done by a VPSA unit as described in US 5,858,057 and US 5,676,732. The disadvantage of the schemes described in these patents is that CO2 is not valorised as a merchantable product or sequestered durably and is simply rejected to the atmosphere.

  In order to improve the operation of the VPSA CO2, US Pat. No. 5,582,029 and US Pat. No. 6,562,103, disclose the use of an external bleed gas, low in CO2, in order to elute the adsorbent bed. US 5582029 proposes to use nitrogen produced by an air separation unit and US6562103 proposes to use a stream of natural gas. The disadvantage of these two solutions is that the CO2 at the purge outlet is diluted in these purge gases.

  The coupling of a cryogenic unit for producing CO2 from the waste gas of an H2 PSA is described in US 2002/0073845 and WO 99/35455. The waste gas of PSA H2 typically contains 50 mol%. CO2.

  The difference with respect to the subject of the invention is: the PSA H2 is optimized for the purification of hydrogen, so the whole is not optimized for the production of CO2 at lower cost (or maximum production) . In addition, the PSA H2 operates between 20 bar high pressure and between 1 and 2 bar low pressure and separates hydrogen on one side and carbon monoxide and carbon dioxide on the other. It is therefore not a VPSA, VSA or PSA CO2 technology as envisaged here; - The main goal of the cryogenic unit is to separate mainly H2 vs CO2 (CO2 vs. H2 separation is easier than CO2 vs. CO or CO2 vs. N2); the flows concerned are well below the flows of the iron and steel gases considered.

  The coupling of a PSA and a liquefaction unit is also described in Takamura et al. The Canadian Journal of Chemical Engineering, 79 (5), 812-816: Application of high pressure swing adsorption process for improvement of CO2 recovery system from flue gas (2001). An ultra-cold separator is placed on the waste gas of a PSA treating the effluents of a boiler. The incondensables of the liquefier are introduced into a high pressure PSA and the purge of this PSA is reintroduced to the feed of the liquefier to improve its performance. However, in this case, it is rather sought to optimize the efficiency of the liquefier through recycle through the PSA, the object of the present invention is to optimize the entire adsorption unit and the liquefier by operating the adsorption unit at a moderate CO2 purity.

  EP-A-0341879 discloses a process for producing CO2 in which a waste gas is sent to a first PSA which produces a flow rate containing about 50% CO2. This flow is sent to a second PSA that produces a flow containing at least 98% CO2. This flow from the second PSA is sent to a cryogenic separation apparatus which produces a liquid containing at least 99.9% CO2.

  The present invention makes it possible to overcome the defects of the prior art.

  According to one object of the invention, there is provided an integrated process using an adsorption unit and a cryogenic unit, in which a gas is sent to the adsorption unit where it separates into a flow enriched in 002 and a flow depleted in 002, the flow enriched in 002 being sent to the cryogenic unit where it is separated into a flow rich in 002 and a low flow rate in 002 characterized in that: a. The 002 enriched flow leaving the adsorption unit has a 002 content of between 50% and 95% (preferably 70% to 90%).

  b. The 002-rich flow leaving the cryogenic distillation unit has a 002 content greater than 80% (preferably> 99%) c. There is only one adsorption unit or several adsorption units operated in parallel.

  According to other optional aspects: the flow enriched in 002 is sent directly from the adsorption unit to the cryogenic unit, without undergoing further separation steps between the two units; the flow rate depleted in 002 produced by the adsorption unit is expanded in a turbine which brings cooling capacity to the cryogenic unit; - The 002 poor gas produced by the adsorption unit is first cooled before being expanded in a turbine which brings cooling capacity to the cryogenic unit; at least part of the 002-poor gas leaving the cryogenic unit is returned to the adsorption unit, particularly a. the suction compressor of the adsorption unit (if it exists) b. just before adsorbers c. either in adsorbers during a repressurization step (co-current or countercurrent) d. either in the adsorbers during an adsorption stage - at least part of the 002 poor gas leaving the cryogenic unit is expanded in a turbine whose inlet temperature is greater than 10 C and then recycled to the adsorption unit at. at the intake of the VPSA (or VSA or PSA) supply compressor (if it exists) 6 2872890 b. just before adsorbers c. either in adsorbers during a repressurization step (co-current or countercurrent) d. either in the adsorbers during an adsorption step.

  - before entering the turbine, the recycled gas is first heated a. by direct combustion of this gas (injection of air or enriched air) and / or b. by heating in a boiler preferably burning blast furnace gas and / or c. by exchange with a fluid of the steelworks whose temperature is higher than 150 C and / or d. by heat exchange with the enriched 002 gas produced by the adsorption unit upstream of the cryogenic unit.

  at least a portion of the oxygen-poor gas leaving the cryogenic unit is used as a fuel to heat the gas of the cryogenic unit to heat the regeneration heater of the cryogenic unit and / or to heat the poor gas in 002 VPSA (or VSA or PSA) (before or after expansion in a possible turbine) and / or heating a regeneration heater of an air separation unit and / or producing steam suitable for use in the installation by the regeneration heater of the cryogenic unit and / or, a machine driving turbine (s) and / or an absorption refrigerating unit (for example for cooling the gas before the unit purifiers) cryogenic) and / or a heat exchanger heating the oxygen-poor gas leaving the adsorption unit - at least a portion of the oxygen-poor gas leaving the adsorption unit is used as a fuel to heat the heating element. regenerating the cryogenic unit and / or producing steam for use in the plant by the regeneration heater and / or the machine driving turbine (s) and / or refrigerating unit by absorption (used for example to cool the gas before the purifiers of the cryogenic unit) - the refrigeration unit of the cryogenic unit also serves to cool the inlet gas of the adsorption unit; the gas enriched in 002 is compressed only by a compressor before sending it to the cryogenic unit; the gas enriched in 002 leaving the adsorption unit is sent to a mixing capacity before being introduced into the cryogenic unit.

  According to another aspect of the invention, there is provided an integrated plant comprising an adsorption unit, a cryogenic unit, means for sending a gas to the adsorption unit where it separates into a flow enriched in 002 and a flow rate depleted in 002, means for sending the flow enriched in 002 to the cryogenic unit where it is separated into a flow rich in 002 and a low flow rate in 002 characterized in that: a) the flow enriched in 002 leaving the adsorption unit has a content of 002 between 50% and 95% (preferably between 70% and 90%).

  b) The 002-rich flow leaving the cryogenic distillation unit has a content of 002 greater than 80% (preferably> 99%). c) There is a single adsorption unit or several adsorption units operated in parallel.

  According to other aspects of the invention, provision is made for: means for sending the enriched flow in 002 directly from the adsorption unit to the cryogenic unit; a mixing capacity downstream of the adsorption unit and upstream of the cryogenic unit.

  The invention will be described in more detail with reference to the figures. Figures 1 to 5 are schematic drawings illustrating examples of methods according to the invention and Figure 6 is a schematic drawing of a cryogenic unit adapted for use in a method according to the invention.

  FIG. 1 shows a VPSA (or VSA or PSA) adsorption unit 3 supplied with a gas to be treated 1. The gas to be treated contains between 10 and 60% of 002, mixed with at least one other gas which may be nitrogen, carbon monoxide, hydrogen, oxygen, methane, argon, water vapor ... The gas to be treated by the adsorption unit is at a pressure between 1 and 10 bar abs. This pressure is reached possibly by adding a compressor upstream of the adsorbers.

  An adsorption unit operates cyclically. At least one of the stages of the cycle consists in supplying at least one adsorber with the feed gas, and withdrawing a CO2-depleted gas at the outlet of said at least one adsorber. This step is called the adsorption step. At least one other stage of the cycle consists in depressurizing at least one adsorber, and recovering during this depressurization, a gas enriched in CO2, called purge gas. At least one further stage of the cycle consists in repressurizing at least one adsorber so as to reduce the pressure to the adsorption pressure. This step is called the repressurization step.

  Unit 3 produces a CO2 depleted gas 5 and a CO2 enriched gas 7. The CO2 enriched gas 7 contains on average between 50 and 95% of CO2, but this CO2 content in the purge gas varies cyclically. . In order to homogenize the CO2 content of this gas, it is sent to a mixing capacity 4. The homogenized mixture is then sent to a cryogenic unit 9 where it condenses at least partially at least once. Before being partially condensed, the flow enriched in CO2 is compressed at a pressure greater than 6 bar abs, preferably greater than 20 bar abs. This unit 9 can be a liquefier or a distillation unit. The cryogenic unit produces a CO2-poor gas 13 and a CO2-rich gas containing at least 80% CO2 and preferably more than 99% CO2.

  The CO2 can then be purified to produce an even more pure CO2-containing gas, for example in a depletion column.

  In Figure 1, the adsorption unit VPSA type (or VSA or PSA) 3 comprises among others: - adsorbers - a valve system as well as possibly - vacuum pumps (if it is a question of VPSA or VSA) - a gas compressor to be treated 1 - a CO2 enriched gas capacity 4 - a CO2 depleted gas capacity 2872890 In the example above, the cryogenic unit 9 can comprise inter alia: - a feed gas compressor which compresses the gas to at least 6 bar abs, preferably up to at least 20 bar abs - purifiers (typically containing alumina or molecular sieve) and their regeneration heater - a cold exchanger - as well as possibly - one or more condenser / reboiler - one or more distillation columns - a recycle compressor - a device for the removal of CO and hydrogen (catalytic or not) - a refrigeration unit (mechanical or by absorption) - a pre-cooling device Figure 2 differs from Figure 1 only in that the CO2-depleted gas is expanded in a turbine 15. The energy recovered on the turbine 15 may be used to drive a compressor of the cryogenic unit 9 (even partially with an auxiliary motor), or be used to produce electricity. The turbine 15 brings at least a portion of its cooling capacity to the cryogenic unit 9.

  FIG. 3 shows the use of a cooler upstream of the turbine 15 of FIG. 2, this cooler serving to bring additional cooling capacity to the cryogenic unit 9 by sending the gas expanded in the turbine 15 to a heat exchanger of the cryogenic unit. In the case where liquid CO2 vaporizes in the cryogenic unit, most of the intake of frigories comes from this latent heat but a small contribution to compensate for heat losses can be provided by the expanded gas.

  If the purpose of the relaxation is to produce energy rather than supplying cold units to the cryogenic unit, then it will be more interesting to heat the flow to relax.

  In Figure 4, the low CO2 flow 13 is divided in two. A portion 13A serves as a purge while the flow 13B is expanded in a turbine 19 which is recycled upstream of the adsorption unit 3. The gas can optionally be sent to the adsorbers during a repressurization step or 2872890 during a step adsorption. Alternatively the purge 13A can be separated from the flow 13 downstream of the turbine 19 to increase energy production.

  The energy recovered at the shaft of the turbine 19 may be used to produce electricity or to drive a compressor.

  It is advantageous, as can be seen in FIG. 5, to heat the gas 13B upstream of the turbine 19 with a heater 21. The gas can be heated by direct combustion, by heating in a boiler or by heat exchange with a fluid available on the site, for example the smoke of a Cowpers.

  Figure 6 shows a cryogenic unit that allows to liquefy a gas containing 002. A flow 7 having a content of 002 between 50% and 95% (preferably between 70% or 90%) is compressed and sent to a purifier 33 operating by radial or axial bed scrubbing in order to purify the gas before cooling it below -10 C. This purifier will be periodically regenerated by a gas heated in a regeneration heater.

  The purified gas is cooled in a heat exchanger where it is partially condensed. The condensed phase is separated from the gas phase in a phase separator 45. The liquid part 51 is sent to a storage 49 after expansion in a valve. The gaseous portion 53 is sent to a second heat exchanger 43 where it partially condenses. The partially condensed phase 53 is separated from the gas phase in a phase separator. The liquid flow 57 withdrawn from the phase separator 47 is sent to the storage 49 after expansion in a valve. The gas flow 61 is returned to the exchangers 43, 37 and returned to the compressor.

  The product 63 containing at least 80% of 002 is withdrawn from the storage 49. The gaseous part 59 is heated in the exchangers 43, 37 and returned to the adsorption unit 2.

  The frigories for liquefaction are provided by two refrigerant cycles 39, 41, possibly coupled.

Claims (2)

11 2872890 Claims   An integrated process using an adsorption unit (3) and a cryogenic unit (9), wherein a gas is sent to the adsorption unit where it separates at a rate enriched in 002 (7) and a flow rate depleted in 002 (5), the flow enriched in 002 being sent to the cryogenic unit where it is separated into a flow rich in 002 (11) and a low flow rate in 002 (13) characterized in that: a) The flow rate enriched in 002 (7) leaving the adsorption unit has a content of 002 between 50% and 95% (preferably between 70% and 90%).   b) The 002-rich flow (11) leaving the cryogenic distillation unit has an 002 content greater than 80% (preferably> 99%).   c) There is only one adsorption unit (3) or several adsorption units operated in parallel.   2. The method of claim 1 wherein the flow enriched in 002 (7) is sent directly from the adsorption unit (3) to the cryogenic unit (9) without undergoing further separation steps between the two. units.   Process according to Claim 1 or 2, in which the 002 depleted flow rate (5) produced by the adsorption unit (3) is expanded in a turbine (15) which supplies cooling capacity to the cryogenic unit ( 9).   4. The method of claim 3 wherein the 002 depleted gas (5) produced by the adsorption unit is first cooled before being expanded in the turbine (15) which brings cooling capacity to the cryogenic unit.   5. Method according to one of the preceding claims wherein at least a portion of the 002 lean gas (13) leaving the cryogenic unit is returned to the adsorption unit (3), particularly a) or to the suction a compressor of supply of the adsorption unit b) is just before adsorbers of the adsorption unit 12 2872890 c) or in the adsorbers of the adsorption unit during a step of repressurization (to co-current or countercurrent) d) in the adsorbers of the adsorption unit during an adsorption step.   6. Method according to one of the preceding claims wherein at least a portion (13B) of 002 poor gas (13) leaving the cryogenic unit (9) is expanded in a turbine (19) whose inlet temperature is greater than -10 C and then recycled to the adsorption unit a) either to the suction of a supply compressor of the adsorption unit b) or just before the adsorbers of the adsorption unit c or) in the adsorbers during a repressurization step (cocurrent or countercurrent) d) or in the adsorbers during an adsorption step.   7. The method of claim 6 wherein before entering the turbine, the recycled gas is first heated a) by direct combustion of the gas (injection of air or enriched air) and / or b) by heating in a boiler preferably burning blast furnace gas and / or c) by exchange with a fluid of the ironworks whose temperature is higher than 150 C and / or d) by heat exchange with the gas enriched in 002 (7 ) produced by the adsorption unit (3) upstream of the cryogenic unit.   8. A method according to one of the preceding claims wherein at least a portion of the 002 poor gas (13) leaving the cryogenic unit is used as fuel for - heating a gas of the cryogenic unit and / or - heating a heater regenerating the cryogenic unit (9) and / or 13 2872890 - heating the poor gas in 002 (5) of the adsorption unit (3) (before or after expansion in a possible turbine) and / or - heating a regeneration heater of an air separation unit and / or - producing steam suitable for use in the installation by the regeneration heater of the cryogenic unit and / or, a turbine or turbine driving the machines and / or an absorption refrigerating unit (for example for cooling the gas before the purifiers of the cryogenic unit) and / or E a heat exchanger heating the poor gas in 002 (5) leaving the unit d 9. Process according to one of the preceding claim wherein at least a portion of the 002-poor gas (5) leaving the adsorption unit is used as a fuel for - heating the regeneration heater of the cryogenic unit and / or - producing steam that can be used in the installation by E the regeneration heater and / or, E a machine drive turbine (s) and / or an absorption refrigeration unit (for example for cooling the gas before the cryogenic unit purifiers) 10. Process according to one of the preceding claims wherein a refrigeration unit of the cryogenic unit (9) is also used to cool the gas (1) at the inlet of the adsorption unit (3).   11. A method according to one of the preceding claims wherein the enriched gas 002 (7) is compressed by a single compressor before sending it to the cryogenic unit (9).   The method according to one of the preceding claims wherein the 002 enriched gas (7) leaving the adsorption unit is sent into a mixing capacity (4) before being introduced into the cryogenic unit. (9).   13. Integrated plant comprising an adsorption unit (3), a cryogenic unit (9), means for sending a gas to the adsorption unit where it separates into a flow enriched in 002 (7) and a flow rate depleted in 002 (5), means for sending the enriched flow 002 to the cryogenic unit where it is separated into a rich flow 002 (11) and a poor flow 002 (13) characterized in that: a) The 002 enriched flow leaving the adsorption unit has a 002 content of between 50% and 95% (preferably 70% to 90%).   b) The 002-rich flow leaving the cryogenic distillation unit has a 002 content greater than 80% (preferably> 99%).   c) There is only one adsorption unit or several adsorption units operated in parallel.   14. Installation according to claim 13 wherein there are means for sending the enriched flow 002 directly from the adsorption unit to the cryogenic unit.   15. Installation according to claim 13 or 14 comprising a mixing capacity (4) downstream of the adsorption unit (3) and upstream of the cryogenic unit (9).