Method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification

Abstract

Title: Method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification Method for starting a CO2 capture process by partial condensation of an input mixture (F) containing carbon dioxide, the CO2 capture process being carried out in a CO2 capture unit, the CO2 capture process comprising cooling (E) the mixture, separating the cooled mixture by partial condensation (B), the start-up method comprising the steps of treating the input mixture in at least one part of the CO2 capture process comprising at least one of the following steps: compression (C, C1), drying (TSA), cooling (E) and expansion (T) and recycling at least a part (P, G, L) of the treated gases at the inlet of the CO2 capture unit. Abstract figure: 2

Description

Title of the invention: Method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification

[0001] The present invention relates to a method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification.

[0002] The capture of carbon dioxide (CO2) by cryogenic means is a process that starts gradually, the time to start all the equipment successively and especially to cool the cryogenic part to its set temperature. During this start-up, the operating conditions of the fluids in the different equipment are not necessarily those of the normal operating case. Thus the equipment does not fulfill its performance, which can lead to risks of damaging certain parts of the process. In addition, during start-up, the treated gas cannot be recovered due to uncertainties about its composition.

[0003] STATE OF THE ART

[0004] Today, CO2 capture units are started in an open loop. The inlet fluid containing CO2 is sent gradually to all the equipment being started up, then it is sent to the stack or flare until it reaches the specifications of the final product. It is therefore neither recovered nor recycled in the process. The invention completes the fold xxx on the operation of the turbines up to an intermediate pressure to avoid any risk of impurity freezing during start-up.

[0005] PROBLEM SOLVED BY THE INVENTION

[0006] The invention proposes an improvement to the start-up procedure for cryogenic CO2 capture units. This invention consists of starting the unit by recycling at least part of the specially treated gas to facilitate the start-up of the unit. Start-up in a closed or semi-closed loop has the following two advantages. Firstly, the quantity of gas passing through the unit during this phase is reduced and therefore the quantity of impurities. The risk of these impurities damaging the process is therefore considerably reduced. Furthermore, recycling the treated gas also makes it possible to continue to recover all or part of the input gas if it has an economic value.

[0007] INVENTION

[0008] According to an object of the invention, there is provided a method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification of an input mixture containing carbon dioxide and at least one of the compounds following: nitrogen, oxygen, argon, hydrogen, helium, methane, water, carbon monoxide, nitrogen monoxide, nitrogen dioxide, the CO2 capture process being carried out in a CO2 capture unit, the CO2 capture process comprising cooling the mixture, separating the cooled mixture by partial condensation and / or distillation and / or solidification, optionally compressing the mixture to be cooled, optionally drying the mixture to be cooled, optionally expanding a fluid produced by the separation, the start-up process comprising the following steps: i. Processing the input mixture in at least one part of the CO2 capture process comprising at least one of the following steps: compression, drying, cooling and expansion. ii. Recycling of at least part of the gases treated by step i) at the inlet of the CO2 capture unit or at least upstream in the separation process and iii. Reduction of the flow rate of the mixture at the inlet of the CO2 capture process by using the gases recycled by step ii).

[0009] According to a variant, there is provided a method for starting a CO2 capture method as described above treating an input mixture coming from a hydrogen production unit, the input mixture containing carbon dioxide, water and at least one of the following compounds: hydrogen, methane, carbon monoxide, comprising the following steps: i. Reducing the flow rate of the inlet mixture at the inlet of the CO2 capture process by using the gases recycled by stage 2 in order to reduce the quantity of water in the CO2 capture process to limit the risks of condensation or freezing of the water and ii. Valorization of the part of the untreated input mixture in the CO2 capture process within the hydrogen production unit.

[0010] DESCRIPTION OF THE INVENTION

[0011] The invention consists in recycling at least part of the gases treated from a CO2 capture unit by cryogenic separation at the inlet of the process or at least upstream of the cryogenic separation step in order to facilitate start-up while reducing the flow rate of the inlet gas necessary for start-up, which reduces the presence of impurities.

[0012] Preferably, at least some of these gases are not recycled in the event of normal operation (after start-up) at the inlet of the CO2 capture unit.

[0013] The invention will be described in more detail with reference to the figures where:

[0014] [Fig.l] represents a method according to the prior art.

[0015] [Fig.2] represents a method according to the invention.

[0016] [Fig.3] represents a method according to the prior art.

[0017] [Fig.4] represents a method according to the invention.

[0018] [Fig. 1] represents a method according to the prior art in which a gas mixture F is compressed in a compressor C, dried in a TSA dryer, compressed in a compressor C1, cooled in a heat exchanger E where it partially condenses forming a liquid L and a gas G in a phase separator B. During steady-state operation, the liquid L can be separated by partial condensation and / or distillation and / or solidification and the gas G is reheated in the heat exchanger E and expanded in a turbine T.

[0019] During start-up, the liquid L is vaporized in the heat exchanger and the expanded gas G is heated in the exchanger and the two gases formed G, L are sent to a location S where they do not pose a safety risk.

[0020] [Fig.2] represents a method according to the invention which is a variant of [Fig.l]. Here during start-up, the expanded gas G, the vaporized liquid L and a part P of the gas mixture dried in the dryer are sent upstream of the compressor C.

[0021] Valves allow the G, L, P gases to be regulated and / or expanded.

[0022] [Fig.3] represents a process according to the prior art in which a gas mixture F is compressed in a compressor C, dried in a TSA dryer, compressed in a compressor C1, cooled in a heat exchanger E where it partially condenses forming a liquid L and a gas G in a phase separator B. During the stable operation, the liquid L can be separated by partial condensation and / or distillation and / or solidification.

[0023] During start-up, the liquid L is vaporized in the heat exchanger and the gas G is heated in the exchanger and the two gases formed are sent to a location S where they do not pose a safety risk.

[0024] [Fig.4] represents a method according to the invention which is a variant of [Fig.l]. Here during start-up, the gas G, the vaporized liquid L and a part P of the gas mixture dried in the dryer are sent upstream of the compressor C.

[0025] Valves allow the gases G, L, P to be regulated and / or expanded.

[0026] The gas F may be an input mixture containing carbon dioxide and at least one of the following compounds: nitrogen, oxygen, argon, hydrogen, helium, methane, water, carbon monoxide, nitrogen monoxide, nitrogen dioxide

[0027] The gas F may be an input mixture from a hydrogen production unit. In this case, the gas F contains carbon dioxide, water and at least one of the following compounds: hydrogen, methane, carbon monoxide

Claims

Claims

1. A method for starting a CO2 capture process by partial condensation and / or distillation and / or solidification of an input mixture (F) containing carbon dioxide and at least one of the following compounds: nitrogen, oxygen, argon, hydrogen, helium, methane, water, carbon monoxide, nitrogen monoxide, nitrogen dioxide, the CO2 capture process being carried out in a CO2 capture unit, the CO2 capture process comprising cooling (E) the mixture, separating the cooled mixture by partial condensation and / or distillation and / or solidification (B), optionally compressing the mixture to be cooled, optionally drying the mixture to be cooled, optionally expanding a fluid produced by the separation, the start-up method comprising the following steps: i. Treatment of the input mixture in at least one part of the CO2 capture process comprising at least one of the following steps: compression (C, Cl), drying (TSA), cooling (E) and expansion (T). ii. Recycling of at least a portion (P,G,L) of the gases treated by step i) at the inlet of the CO2 capture unit or at least upstream in the separation process and iii. Reduction of the flow rate of the mixture at the inlet of the CO2 capture process by using the gases recycled by step ii).

Images