Process and apparatus for the separation of CO2 by partial condensation and / or distillation

Abstract

Title: Process and Apparatus for CO2 Separation by Partial Condensation and / or Distillation In a CO2 separation process by partial condensation and / or distillation, a first gas (1) containing hydrogen, water, and carbon dioxide is compressed in a compressor (17), dried in an adsorption drying unit (19), and then separated by partial condensation and / or distillation to produce a CO2-enriched fluid (25). A second gas (3), containing carbon dioxide, hydrogen, and water, from an absorption separation process (A), is cooled to condense at least some (7) of the water it contains. The water is separated from the gas, forming a dried gas (9), and the dried gas is mixed with the first gas upstream of the adsorption drying unit and possibly upstream of the compressor. Abstract Figure: Fig. 4

Description

Title of the invention: Method and apparatus for separating CO2 by partial condensation and / or distillation

[0001] The present invention relates to a method and apparatus for separating CO2 by partial condensation and / or distillation. In particular, it relates to such a method supplied with a CO2-enriched gas originating from a CO2 absorption separation process.

[0002] CO2 removal is already widely deployed on an industrial scale, mainly with absorption processes. These processes, whether physical, chemical or physicochemical, all use a liquid solvent to remove one or more compounds (here CO2) from a gas stream.

[0003] The rich solvent is then regenerated and releases the captured compounds. This regeneration is generally done by expansion and the addition of heat.

[0004] Applied to CO2 removal, these processes all produce CO2 from near atmospheric pressure up to ~3 bara, depending on the process flowsheet. In addition, many absorption processes (amine scrubbing, hot potassium scrubbing, Purisol ®...) use aqueous solvents, and thus release wet CO2.

[0005] This low-pressure wet CO2 production is not problematic when CO2 removal is justified by the specifications of the downstream process (synthesis, cryogenic treatment, etc.). However, CCS (Carbon Capture and Sequestration) specifications generally require dry, pressurized, or liquefied CO2. CO2 from absorption processes must therefore be compressed, dried, and possibly liquefied to be integrated into CCS schemes. This requires additional equipment and operating expenses.

[0006] It is known to separate CO2 from a waste gas of a PSA producing hydrogen. The waste gas is compressed and separated by partial condensation and / or distillation. While the waste gas contains water, this is in a low-saturated state and therefore the waste gas can be compressed without the water condensing upstream of the separation by partial condensation and / or distillation. A dryer is therefore necessary upstream of the partial condensation and / or distillation.

[0007] It is also known from WO2015 / 075071 to mix a CO2-enriched gas from an amine wash with the waste gas from a H2 PSA and to separate the mixture by partial condensation and / or distillation.

[0008] It is also known from US2013 / 9156686 to use amine washing to produce a CO2-enriched fluid and a CO2-depleted fluid, to separate the CO2-depleted fluid by PSA producing hydrogen and another hydrogen-depleted gas, the other gas being separated at low temperature to recover the CO2 it contains.

[0009] The wet CO2 generated by the absorption processes can be directly integrated into the PSA H2 waste separation process by partial condensation and / or distillation. Being (in most cases) wet and available at low pressure, it is ideally injected into the separation process at the inlet of the PSA H2 waste compressor.

[0010] Since CO2-enriched gases from the absorption process are generally available at about 1.3 bara, a blower may be required to increase the pressure of the CO2-enriched gas from the absorption process to the correct pressure. Such a device might also be required if the two processes are not close to each other.

[0011] The injection of a wet stream from the absorption process into the PSA gaseous waste could be very detrimental to the partial condensation and / or distillation process, because it increases the dew point temperature of the PSA H2 gaseous waste, and therefore reduces the pressure achievable without condensation. Drying must then be carried out at lower pressure, which is expensive both in terms of investment and operating costs.

[0012] The most relevant solution is therefore to cool the wet flow enriched in CO2 coming from the absorption process to condense as much water as possible, before mixing it with the PSA H2 waste.

[0013] By cooling the wet stream to condense the water it contains, the water level can be desaturated to a level that allows the two gases to be compressed together.

[0014] Obviously the compressor and the partial condensation and / or distillation separation apparatus will be larger to be able to treat the two mixed gases.

[0015] According to an object of the invention, there is provided a process for separating CO2 by partial condensation and / or distillation in which i. a first gas containing hydrogen, water and carbon dioxide is compressed in a compressor, dried in an adsorption drying unit and then separated by partial condensation and / or distillation to produce a CO2-enriched fluid ii. a second gas, containing carbon dioxide, hydrogen and / or nitrogen as well as water and possibly carbon monoxide and / or methane, originating from an absorption separation process, is cooled to condense at least part of the water it contains, the water is separated from the gas forming a dried gas and the dried gas is mixed with the first gas upstream of the adsorption drying unit and possibly upstream of the compressor.

[0016] According to other optional features: • the dried gas is mixed with the first gas upstream of the adsorption drying unit and downstream of the compressor. • the second gas is compressed upstream of the cooling to a pressure which is that of the first gas upstream of the adsorption drying unit. • the second gas is compressed upstream of the cooling to a pressure which is that at the inlet of the adsorption drying unit. • the second gas is compressed upstream of the cooling to a pressure of at least 9 bars abs • the second gas is cooled by indirect heat exchange with water. • the second gas is cooled by indirect heat exchange with a fluid, possibly enriched with CO2, produced by partial condensation and / or distillation, possibly at a temperature below 0°C. • the second dried gas is heated by heat exchange with the second gas upstream of the cooling. • the first gas is a waste gas from an adsorption separation process producing a hydrogen-enriched gas and a hydrogen-depleted gas which is the waste gas. • the CO2 and / or water content of the first gas is lower than that of the second gas. • the CO2 content of the mixture formed by mixing the dried gas with the first gas is higher than that of the first gas. • the flow rate of the first gas is greater than that of the second gas. • the ratio between the flow rates of the first and second gases is at least equal to 10. • the second gas comes from an amine or potassium carbonate washing unit. • fumes are separated by the absorption process to produce the second gas. • a synthesis gas is separated by the absorption process to produce the second gas.

[0017] According to another object of the invention, there is provided an apparatus for separating CO2 by partial condensation and / or distillation comprising a compressor, an adsorption drying unit, a partial condensation and / or distillation separation unit, means for sending a first gas containing hydrogen, water and carbon dioxide to be compressed in the compressor, means for sending the first compressed gas to be dried in the adsorption drying unit and means for sending the first compressed and dried gas to be separated by partial condensation and / or distillation to produce a CO2-enriched fluid, a cooler, a phase separator, means for sending a second gas, containing carbon dioxide, hydrogen and / or nitrogen as well as water and possibly carbon monoxide and / or methane, from an absorption separation process to the cooler to be cooled to condense at least part of the water it contains, means for removing the water separated from the gas from the phase separator, means for removing a dried gas from the phase separator and means for sending the dried gas to mix with the first gas upstream of the adsorption drying unit and possibly upstream of the compressor.

[0018] The apparatus may comprise means for sending the dried gas to mix with the first gas upstream of the adsorption drying unit and downstream of the compressor.

[0019] The invention will be described in more detail with reference to the figures where:

[0020] [Fig-1] represents a method according to the invention.

[0021] [Fig.2] represents a method according to the invention.

[0022] [Fig.3] represents a method according to the invention.

[0023] [Fig.4] represents a method according to the invention.

[0024] In [Fig.l], a stream 3 from an absorption unit A contains carbon dioxide, water, hydrogen and / or nitrogen and possibly carbon monoxide and / or methane. The absorption unit may use amine washing, hot potassium carbonate washing, Purisol ® type washing with NMP washing) and produces stream 3 at substantially atmospheric pressure or higher pressures. In some cases, it is therefore necessary to boost stream 3 with a blower B in order to bring its pressure to about 1.5 bar abs or more. Stream 3 is then cooled by indirect heat exchange with water 11 in cooler K to condense at least a portion 7 of the water it contains. The dried gas 9 leaves the separator S used to remove the water 7 and is sent to mix with the waste gas 1 from a pressure swing adsorption hydrogen separation process P.This first gas 1 contains carbon dioxide, hydrogen and water and usually has a lower carbon dioxide content than flow 3. The first gas 1 usually has a lower water content than flow 3. The flow rate of the first gas 1 is preferably higher than that of the second gas 3.

[0025] The separation of such a flow is well known and is described for example in US8021464.

[0026] The mixture 15 is then treated in a separation unit C. It is compressed to a pressure above 9 bar abs, or even above 20 bar, dried by adsorption to remove the remaining water and then cooled and separated by partial condensation and / or distillation to obtain at least one gas and / or at least one liquid enriched in CO2 containing for example at least 90 mol%, or even at least 95 mol% CO2 and a hydrogen-enriched gas.

[0027] The blower B, if present, can compress the gas 9 to the pressure of the gas 1 or to the pressure at the inlet of the dryer 19 of [Fig.4].

[0028] In [Fig.2], the flow 3 is cooled in a cooler R upstream of the cooler K and downstream of the absorption unit A and possibly the blower B. This cooler R allows indirect heat exchange between the dried gas 9 coming from the separator S and the flow to be cooled 3. The gas cooled in the cooler R is mixed with the first gas 1 as for [Fig.l]. This allows the consumption of water 11 to be reduced.

[0029] In some cases, flow 3 is available at higher pressure than the first gas 1 and therefore flow 9 can be mixed with the residual 3 after compression of the residual 3 in at least one stage of the compressor of unit C.

[0030] In [Fig. 3], the flow 3 is cooled to condense the water at least from a liquid 15 enriched in CO2 relative to the mixture coming from at least one phase separator of the unit C where the mixture 13 separates. The liquid is sent to the cooler K at a temperature below 0°C and vaporizes in the cooler K. The liquid 15 can otherwise constitute a part of the bottom liquid of a distillation column, this liquid comprising at least 90 mol% CO2.

[0031] The use of such a flow rate makes it possible to reduce the consumption of water 11 and in addition achieves the vaporization necessary to produce the liquid 15 in gaseous form to be sent to the customer.

[0032] [Fig.4] shows a version of [Fig.l] with unit C illustrated in more detail. Unit C comprises a compressor 17, an adsorption drying unit (TSA) 19, an exchange line 21 for cooling the compressed and dried mixture and a separation part 23 by partial condensation and / or distillation producing at least one CO2-enriched fluid 25 relative to the mixture 13.

[0033] The invention is of greatest interest when the flow rate of gas 3 is lower than the flow rate of gas 1 because mixing the flow rates 1, 9 requires oversizing the unit C.

[0034] The invention applies particularly to the case where the ratio between the flow rate of gas 3 and that of flow rate 1 is less than 0.1, the exact ratio depending on economic factors.

[0035] Nevertheless, in terms of investment, the equipment for compressing and processing the flows 1, 3 together is less expensive than that for separating them separately.

[0036] Furthermore, as flow 3 is often richer in CO2 than flow 1, adding flow 9 to gas 1 increases the molecular weight of gas 1 and makes compression in unit C more efficient. Separation by partial condensation and / or distillation is also more efficient when the flow to be separated is richer in CO2.

[0037] On the other hand, the residual gas of PSA H2 undergoes fluctuations in composition of the due to the cyclicality of the PSA process. Mixing it with a fixed composition gas helps to mitigate the effect of these composition variations on the compressor and the downstream separation process.

[0038] Finally, unit C makes it possible to eliminate impurities remaining in flow 3, for example nitrogen and / or hydrogen, carbon monoxide and methane, whereas absorption does not make it possible to get rid of them. Thus, unit C makes it possible to produce good quality CO2 with the CO2-rich gas from an absorption unit.

Claims

Claims

1. A method for separating CO2 by partial condensation and / or distillation in which i) a first gas (1) containing hydrogen, water and carbon dioxide is compressed in a compressor (17), dried in an adsorption drying unit (19) and then separated by partial condensation and / or distillation to produce a CO2-enriched fluid (25), ii) a second gas (3), containing carbon dioxide, hydrogen and / or nitrogen as well as water and optionally carbon monoxide and / or methane, from an absorption separation process (A), is cooled to condense at least a portion (7) of the water it contains, the water is separated from the gas forming a dried gas (9) and the dried gas is mixed with the first gas upstream of the adsorption drying unit and optionally upstream of the compressor.

2. Method according to claim 1 in which the second gas (3) is compressed (B) upstream of the cooling to a pressure which is that of the first gas upstream of the adsorption drying unit (21).

3. Method according to one of the preceding claims in which the second gas (3) is cooled by indirect heat exchange with water (11).

4. Method according to one of the preceding claims in which the second gas (3) is cooled by indirect heat exchange with a fluid, optionally enriched in CO2 (15), produced by partial condensation and / or distillation, optionally at a temperature below 0°C.

5. Method according to one of the preceding claims in which the second dried gas (9) is heated by heat exchange with the second gas (3) upstream of the cooling (K).

6. A method according to any preceding claim wherein the first gas (1) is a waste gas from an adsorption separation process (P) producing a hydrogen-enriched gas and a hydrogen-depleted gas which is the waste gas.

7. Method according to one of the preceding claims in which the CO2 and / or water content of the first gas (1) is lower than that of the second gas (3).

8. Method according to one of the preceding claims in which the CO2 content of the mixture (13) formed by mixing the dried gas (9) with the first gas is greater than that of the first gas (1).

9. Method according to one of the preceding claims in which the ratio between the flow rates of the first and second gases is at least equal to 10.

10. Apparatus for separating CO2 by partial condensation and / or distillation comprising a compressor (17), an adsorption drying unit (19), a partial condensation and / or distillation separation unit (C), means for sending a first gas (1) containing hydrogen, water and carbon dioxide to be compressed in the compressor (17), means for sending the first compressed gas to be dried in the adsorption drying unit (19) and means for sending the first compressed and dried gas to be separated by partial condensation and / or distillation to produce a CO2-enriched fluid (25), a cooler (K), a phase separator, means for sending a second gas (3), containing carbon dioxide, hydrogen and / or nitrogen as well as water and optionally carbon monoxide and / or methane, from an absorption separation process (A),to the cooler to be cooled to condense at least a portion (7) of the water it contains, means for removing the water separated from the gas from the phase separator, means for removing a dried gas (9) from the phase separator and means for sending the dried gas to mix with the first gas upstream of the adsorption drying unit and possibly upstream of the compressor.,

Images