Method and device for purifying gas by cold adsorption of carbon dioxide, and liquification process and device

Abstract

The method (100) for purifying gas by cold adsorption of carbon dioxide (CO2) in at least one column having a molecular sieve configured to adsorb the carbon dioxide at a first adsorption temperature of between -20°C and -80°C and at a first adsorption pressure comprises a step (105) of purifying the gas to be purified by injection, at a first flow rate, into the column at the first temperature and at the first pressure.

Description

[0001] METHOD AND DEVICE FOR PURIFICATION OF GAS BY COLD ADSORPTION OF CARBON DIOXIDE AND METHOD AND DEVICE FOR LIQUEFACTION

[0002] Technical field of the invention

[0003] The present invention relates to a method and a device for gas purification by cold adsorption of carbon dioxide (CO2) and a method and a liquefaction device implementing this purification. The present invention applies, in particular to the liquefaction without crystallization of a flow composed of a major compound whose dew point temperature is lower than -80°C for pressures lower than 25 bara, this major compound being, for example, methane, air, oxygen or nitrogen, and CO2 with a rate lower than 5 mol%.

[0004] State of the art

[0005] The quality of liquefied biomethane is directly linked to the quality of gaseous biomethane. Regarding CO2, the lower the pressure at which liquefaction is carried out, the lower the CO2 content of the gaseous biomethane must be, and therefore the more efficient the upstream biogas purification process must be. The solubility of CO2 in liquefied biomethane decreases proportionally to the temperature and pressure of the liquefied biomethane. The presence of CO2 leads to the formation of crystals that hinder the transfer and implementation of liquefied biomethane. Regarding the water content (H2O), the dew point must be below -70°C and the associated risks are similar to the presence of CO2.

[0006] The advanced purification of biomethane or natural gas (an operation also called "polishing") with a view to its liquefaction, therefore concretely in a flow containing a very large majority of methane (at least 70% mol), aims to reduce the CO2 from a rate of between 5 and 0.5% mol to a rate of between 2.5% mol, or even 1% mol, and 50 ppm.

[0007] We want to achieve this degree of CO2 purification because the main methane flow can only be liquefied and then stored at pressures between 1 bara and 25 bara at very low temperatures (between -100°C and -160°C depending on the storage pressure). This means that, to avoid any risk of CO2 crystallization (and therefore blockage and clogging in equipment such as cryogenic exchangers or pipes connected to liquid storage), the CO2 level must be sufficiently low.

[0008] To solve this technical problem, three types of techniques are known: washing, with water, amines or with a specific solvent, the use of a molecular sieve regenerated by heat (TSA) or pressure (PSAA / PSA) and cryogenic purification.

[0009] Washing works with the following elements: a specific washing column which actually carries out the purification, a pump system, a specific regeneration column, and possibly, a heat production system, particularly in the case of amine washing.

[0010] Among the disadvantages of a scrubbing system, it requires technically complex equipment and, in particular, an adsorption column with a specific dimension for the gas being treated and whose manufacture is complex. In addition, "active" systems consuming either mechanical energy (pumps, for example) or thermal energy (heating system) at temperatures often above 150°C are required and require specific maintenance.

[0011] Regarding adsorption solutions, it is recalled that adsorption is a surface phenomenon by which atoms, ions or molecules (adsorbates) are fixed on a solid surface (adsorbent) from a gaseous, liquid phase or a solid solution. Industrially, adsorption takes place inside adsorbent grains or "molecular sieves", on the surface developed by the pores of the grains, in order to obtain a large quantity fixed in a minimum volume. CO2 adsorption is thus carried out on a molecular sieve whose material has the property of preferentially binding to CO2. Once the sieve is loaded with CO2, it must be regenerated. Different regeneration methods are used:

[0012] TSA (for “Temperature Swing Adsorption”), in which a high temperature flow (relative to the adsorption temperature) is used to regenerate the sieves,

[0013] PSA (for "Pressure Swing Adsorption"), in which a low pressure flow (relative to the adsorption pressure) is used to regenerate the sieves, and

[0014] VPSA (for Void Pressure Adsorption), in which the pressure is lowered below atmospheric pressure using a vacuum pump to regenerate the sieves.

[0015] Among the disadvantages of TSA systems, there is mainly the use of a significant heat source (above 150°C). PSA and VPSA systems require, in their regeneration phase, a rotating machine system: vacuum pump, boiler or dedicated compressor, which generates significant energy costs and significant maintenance costs.

[0016] Cryogenic cleaning, in which a complete cooling cycle dedicated to cleaning is used to separate CO2 from methane, has the disadvantage that, to achieve a very low impurity level, the treated gas must be cooled to very low (cryogenic) temperatures. Cryogenic cleaning therefore requires a very expensive low-temperature cooling system.

[0017] Presentation of the invention

[0018] The present invention aims to remedy all or part of these drawbacks.

[0019] To this end, according to a first aspect, the present invention relates to a device for purifying gas by cold adsorption of carbon dioxide (CO2) according to claim 1. Thus, in the device which is the subject of the invention, the adsorption temperature is lower than what was known in the prior art. This increases the CO2 adsorption capacity of the molecular sieve and it is therefore possible to reduce the size of the column and the quantity of molecular sieve it contains. In addition, the regeneration of this sieve is facilitated because the heat temperature level required for regeneration is lowered.

[0020] In the device of the invention, the adsorption temperature is lower than what was known in the prior art and the regeneration of the molecular sieve is carried out by TSA at a regeneration temperature lower than in the prior art. This increases the CO2 adsorption capacity of the molecular sieve and therefore makes it possible to reduce the size of the column and the quantity of molecular sieve it contains. In addition, the regeneration of this sieve is facilitated because the heat temperature level required for regeneration is lowered.

[0021] Improvements in these embodiments include: reducing the need for heat and facilitating heat recovery on related conventional systems, improved compactness of the installation and, in particular, of the adsorption column, and simplification of the shape of the column, which can be cylindrical, which reduces its cost, operability and maintenance.

[0022] In embodiments, the device comprises at least two columns configured to operate in staggered stages, one column operating in purification while another column operates in regeneration. Thanks to these arrangements, a more regular supply of purified gas (i.e. the duty cycle of supply of purified gas is higher), or even perfectly continuous, can be obtained at the outlet of the device.

[0023] In embodiments, the device that is the subject of the invention comprises: four columns mounted in parallel, an inlet pipe for the gas to be purified, a pre-cooling gas discharge pipe, a preheating and depressurization gas discharge pipe, a regeneration gas discharge pipe, a regeneration gas inlet pipe, a preheating gas inlet pipe, a pre-cooling gas inlet pipe, a purified gas outlet pipe, a first set of solenoid valves between each of the inlet pipes and one end of each of the columns, a second set of solenoid valves between each of the discharge or outlet pipes and another end of each of the columns, and a control unit configured to control the solenoid valves so that, at all times,one and only one of the columns is in the adsorption phase of a gas circulating between the inlet pipe for the gas to be purified and the outlet pipe for the purified gas, another column being in the pre-cooling phase by a gas circulating between the pre-cooling inlet pipe and the pre-cooling gas discharge pipe, yet another column is in the regeneration phase of a gas circulating between the regeneration gas inlet pipe and the regeneration gas discharge pipe, and the last column is in the preheating phase with a preheating gas circulating between the preheating gas inlet pipe and the preheating gas discharge pipe.,

[0024] Thanks to these provisions, a continuous supply of purified gas is obtained at the outlet of the device.

[0025] In embodiments, the device comprises, at the inlet of the gas purification means, a source of gas whose main components condense in liquid form at temperatures below -80°C at the final storage pressure.

[0026] In embodiments, the device comprises, at the inlet of the gas purification means, a gas source whose main components are biomethane, methane, ethane, nitrogen, oxygen and / or ethylene.

[0027] In embodiments, the first, adsorption pressure is greater than 15 bara.

[0028] In embodiments, the third, regeneration, pressure is lower than the first, adsorption, pressure.

[0029] In embodiments, the third, regeneration temperature is greater than 10°C and less than 30°C.

[0030] The inventor has found that the efficiency of the device is improved by respecting one or the other and, preferably, at least two, or even all, of these constraints relating to the adsorption and regeneration temperatures and pressures.

[0031] In embodiments, the regeneration means and the purification means are jointly configured such that the regeneration time is less than the adsorption time.

[0032] In embodiments, the third temperature, of regeneration, is greater than 60°C and the normal volume flow rate, at the temperature of 0°C and at the pressure of 1.013 bara, of regeneration is less than half of the normal volume flow rate of adsorption.

[0033] In embodiments, the regeneration temperature is greater than 10°C and less than 80°C and the normal volume flow rate, at the temperature of 0°C and the pressure of 1.013 bara, of regeneration is greater than the normal volume flow rate of adsorption.

[0034] The inventor has found that the efficiency of the device is further improved by respecting at least one of these two constraints, or even both of these constraints, relating to the adsorption and regeneration durations and flow rates.

[0035] According to a second aspect, the present invention relates to a device for liquefying a gas which comprises: a purification device which is the subject of the present invention, a compressor of the gas to be liquefied, a heat exchanger bringing the compressed gas to the second temperature and supplying the preheating gas to each preheating means of a purification column of the purification device, a heat exchanger configured to receive the preheating gas having passed through the purification device, configured to carry out a first precooling of this gas and to supply it to each purification means of a purification column of the purification device, a heat exchanger configured to receive the purified gas having passed through the purification column, configured to carry out a second cooling or precooling of the purified gas, a means of liquefying the purified gas after its second cooling,and a heat exchanger configured to subcool the liquefied gas and supply it to at least one liquefied gas tank.,

[0036] Thanks to these provisions, the gas to be liquefied performs the preheating function of each of the columns of the purification device.

[0037] In embodiments, the liquefaction device further comprises a final flash gas recovery circuit from at least one liquefied gas tank, configured to supply this final flash gas to each pre-cooling means of a column of the purification device.

[0038] Thanks to these provisions, the gas to be liquefied also performs the pre-cooling function of each of the columns of the purification device.

[0039] In embodiments, the liquefaction device further comprises a circuit for recovering final flash gas from at least one liquefied gas tank configured to, once this final flash gas has been reheated to the third temperature, supply this recovered final flash gas to each means of regeneration of a column of the purification device.

[0040] Thanks to these provisions, the gas to be liquefied also performs the function of regenerating the molecular sieve of each of the columns of the purification device.

[0041] According to a third aspect, the present invention relates to a method for purifying gas by cold adsorption of carbon dioxide (CO2), in at least one column provided with a molecular sieve configured to adsorb carbon dioxide at a first adsorption temperature of between -20°C and -80°C and at a first adsorption pressure, a method which comprises a step of purifying the gas to be purified by injection, with a first flow rate, into the column at the first temperature and at the first pressure.

[0042] In embodiments, the purification method which is the subject of the invention further comprises: a step of placing the column under a second pressure greater than one bara, a step of preheating the column under the second pressure to a second temperature greater than 10°C, a step of depressurizing the preheated column to a third pressure, a step of regenerating the screen by passing a regeneration gas at the third pressure through this screen at a third temperature, a step of pre-cooling the column to a fourth temperature and a step of re-pressurizing the column to the first temperature and to the first pressure.According to a fourth aspect, the present invention relates to a method for liquefying a gas which comprises: the steps of the purification method which is the subject of the invention, a step of compressing the gas to be liquefied, a step of bringing the compressed gas to the second temperature to provide the preheating gas for the preheating step of the purification method, a step of first cooling precooling the preheating gas having carried out the preheating step to carry out, on this gas, the steps of the purification method, a step of second cooling precooling the purified gas, a step of liquefying the gas after its second cooling, a step of subcooling the liquefied gas and storing the subcooled liquefied gas in a liquefied gas tank, and a step of recycling the gas used during a precooling step upstream of the compression step.

[0043] The advantages, aims and particular characteristics of this purification process and this liquefaction process being similar to those of the purification device and the liquefaction device, they are not recalled here.

[0044] Brief description of the figures

[0045] Other advantages, aims and particular characteristics of the invention will emerge from the following non-limiting description of at least one particular embodiment of the method and device which are the subject of the present invention, with reference to the appended drawings, in which:

[0046] Figure 1 represents, in the form of a flowchart, steps of a particular embodiment of the purification method which is the subject of the invention,

[0047] Figure 2 schematically represents a particular embodiment of a gas purification device which is the subject of the invention,

[0048] Figure 3 schematically represents a particular embodiment of a gas liquefaction device which is the subject of the invention, and

[0049] Figure 4 represents, in the form of a flowchart, steps of a particular embodiment of a gas liquefaction method which is the subject of the invention.

[0050] Description of the embodiments

[0051] This description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment in an advantageous manner.

[0052] As understood from the present description, various inventive concepts may be implemented by one or more methods or devices described below, several examples of which are provided herein. The actions or steps performed in carrying out the method or device may be ordered in any suitable manner. Accordingly, it is possible to construct embodiments in which the actions or steps are performed in a different order than illustrated, which may include performing certain acts simultaneously, even if they are presented as sequential acts in the illustrated embodiments.

[0053] The indefinite articles "a" and "an", as used in the description and claims, are to be understood as meaning "at least one", unless otherwise clearly indicated.

[0054] The expression "and / or", as used herein and in the claims, is to be understood to mean "either or both" of the elements so conjoined, i.e., elements which are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" are to be interpreted in the same way, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present, other than the elements specifically identified by the "and / or" clause, whether or not they are related to these specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with open language such as "comprising" may refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0055] As used herein in the description and in the claims, "or" is to be understood as having the same meaning as "and / or" as defined above. For example, when separating elements in a list, "or" or "and / or" is to be interpreted as inclusive, i.e., the inclusion of at least one, but also more than one, number or list of elements, and, optionally, additional elements not listed. Only terms clearly indicating the contrary, such as "only one of" or "exactly one of", or, when used in the claims, "consisting of", refer to the inclusion of only one element of a number or list of elements. In general, the term "or" as used herein should only be construed as indicating exclusive alternatives (i.e., 'either but not both') when preceded by terms of exclusivity, such as "either," 'one of," "only one of," or "exactly one of."

[0056] As used in this specification and in the claims, the expression "at least one", with reference to a list of one or more elements, is to be understood to mean at least one element selected from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding every combination of elements in the list of elements. This definition also allows for the optional presence of elements other than the specifically identified elements in the list of elements to which the expression "at least one" refers, whether or not related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, optionally including more than one, A, without B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, without A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0057] In the claims, as well as in the description below, all transitional expressions such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", "consisting of", and the like, are to be understood as open, i.e., as meaning including but not limited to. Only the transitional expressions "consisting of" and "consisting essentially of" are to be understood as closed or semi-closed transitional expressions, respectively.

[0058] The purpose of the invention is the advanced purification (called "polishing") of a gas, for example biomethane or natural gas with a view to its liquefaction. The steps of an embodiment 100 of the purification method which is the subject of the invention are represented in figure 1. These steps are carried out successively. Examples 1 to 3, which follow the description given with regard to figure 1, illustrate possible values ​​of pressures, temperatures, flow rates and durations in the adsorption column during the different steps.

[0059] During a step 105, the gas is purified in an adsorption column equipped with a molecular sieve, by injecting this gas at a first adsorption temperature T1, at a first pressure P1, with a first flow rate D1. Preferably, the direction of passage of the gas to be purified in the adsorption column goes from top to bottom.

[0060] The molecular sieve is determined to be loaded with CO2 when the volume of purified gas to the volume of the molecular sieve reaches a predetermined ratio. Alternatively, a sensor is used to measure the CO2 loading of the molecular sieve or the efficiency of the purification. Once the molecular sieve is loaded with CO2 and the passage of the gas to be purified has stopped, the loaded molecular sieve can be extracted and replaced with a regenerated molecular sieve and then step 105 can be repeated.

[0061] However, preferably and as shown in Figure 1, during a step 110, a pressure adaptation is carried out inside the column to a second pressure P2 greater than one bara. It is noted that this second pressure P2 will be, during step 115, the preheating pressure. For this purpose, if the first adsorption pressure P1 implemented during step 105 is greater than the second pressure P2, during step 115, a partial emptying of the column is carried out until the pressure in the column is equal to the second pressure P2. On the contrary, if the first pressure P1 implemented during step 105 is lower than the second pressure P2, during step 115, preheating gas is injected into the column at a pressure greater than or equal to the second pressure P2, until the pressure in the column is equal to the second pressure P2.

[0062] During step 115, the molecular sieve and the adsorption column are preheated by circulating, at a second flow rate D2, a preheating gas at the second pressure P2 and at a second temperature T2. It is noted that the second temperature T2 is higher than the first temperature T1 and corresponds to the regeneration temperature implemented during the regeneration step 125. The second flow rate D2 is preferably higher than or equal to the first flow rate D1. Preferably, the direction of circulation of this preheating gas during step 115 and, where appropriate, during step 110, is opposite to the direction of circulation of the gas to be purified during step 105. It is noted that the preheating gas preferably has a CO2 content of less than 40 mol%.

[0063] During a depressurization step 120, the pressure inside the column is reduced to a third pressure P3 lower than the second pressure P2 and preferably higher than one bara. In variants, step 120 is optional, the values ​​of P2 and P3 being equal. However, equality of the regeneration pressure P3 with the adsorption pressure P1 is preferential and the pressure P2 is lower than the pressures P1 and P3, for example equal to the pressure of the final flash gas, for example of the order of two bara. For this purpose, a partial emptying of the column is carried out, preferably by evacuation of preheating gas in the opposite direction to the direction of passage of the gas to be purified during the adsorption step.

[0064] During a step 125 of regeneration of the molecular sieve, a regeneration gas is passed through the column at a third temperature T3 under the third pressure P3, with a third flow rate D3. The regeneration gas has a CO2 level preferably less than 100 ppm. Preferably, the direction of passage of the regeneration gas, during step 125 is opposite to the direction of passage of the gas to be purified during step 105.

[0065] The molecular sieve is determined to be regenerated when the volume of regeneration gas to the volume of the molecular sieve reaches a predetermined ratio. Alternatively, a sensor is implemented that measures the CO2 loading of the molecular sieve or the regeneration efficiency.

[0066] For example, the duration of the adsorption phase is less than 50 minutes and the duration of regeneration is less than 40 minutes, with the following process characteristics:

[0067] Flow rate D1 of biomethane (e.g. biogas having undergone mass purification) to be purified, 250 Nm 3 / h with 2.5%mol of CO2;

[0068] T1, adsorption temperature after cooling = -50°C; mass of 13X molecular sieve of 27 kg;

[0069] T3, regeneration temperature, equal to 20°C;

[0070] D3 flow rate, regeneration, 400 Nm 3 / h ;

[0071] D2 flow, preheating, 400 Nm 3 / h (40%mol of CO2 and 60%mol of CH4);

[0072] T2, preheating temperature of 20°C;

[0073] D4 flow, pre-cooling 50 Nm 3 / h ; and

[0074] T4, pre-cooling temperature, -80°C.

[0075] Once the molecular sieve has been regenerated, during a pre-cooling step 130, a pre-cooling gas is passed through the column, at a temperature preferably lower than or equal to the first adsorption temperature T1, and, even more preferably, at least 30°C lower than the temperature T1. For example, if the adsorption takes place at -20°C, the temperature of the pre-cooling gas is preferably lower than or equal to -20°C and, even more preferably, lower than or equal to -50°C.

[0076] Preferably: the pre-cooling gas is identical to the regeneration gas, the direction of passage of the pre-cooling gas is opposite to the direction of passage of the gas to be purified during step 105, and / or the fourth flow rate D4 of pre-cooling gas is greater than a quarter of the first flow rate D1 of the gas to be purified during step 105.

[0077] During a re-pressurization step 135, gas to be purified is injected into the column at the first temperature T 1 , with a fifth inlet flow rate D5, until the first pressure P1 is reached. Then we return to step 105.

[0078] The values ​​of the operating parameters (temperatures, pressures, flow rates and durations) of three examples of implementation of the purification process which is the subject of the present invention are detailed below. The flow rates considered are standardized volume flow rates, at a temperature of 0°C and a pressure of 1.013 bara.

[0079] Example 1: “hot regeneration” of a gas that can contain up to 5%mol of CO2.

[0080] In this example 1: the first pressure P1, of adsorption, is greater than 15 bara and preferably less than 80 bara, the first temperature T1, of adsorption, is between -80°C and -20°C, the first flow rate D1, of adsorption, is, for example, a flow rate of biomethane of 250 Nm 3 / h with 2.5%mol of CO2 for an adsorption temperature T1 after cooling of - 50°C, a mass of 13X molecular sieve of 27 kg; a regeneration temperature T3 of 60°C and a regeneration flow rate D3 of 50 Nm 3 / h; a D2 flow rate, preheating, of 400 Nm 3 / h (40%mol of CO2 and 60%mol of CH4), a preheating temperature T2 of 60°C; a pre-cooling flow rate D4 of 50 Nm3 / h and a pre-cooling temperature T4 of -80°C, the pre-heating gas has a CO2 content of less than 50%mol, the second pre-heating pressure P2 is greater than one bara and, preferably, less than 80 bara, the second pre-heating temperature T2 is greater than 60°C and, preferably, less than 120°C, the second pre-heating flow rate D2 is greater than or equal to the flow rate D1, the regeneration gas has a CO2 content of less than 150 ppm, the third regeneration pressure P3 is greater than one bara (in all cases of hot regeneration, examples 1 and 2, the regeneration pressure is less than or equal to the adsorption pressure), the third regeneration temperature T3 is greater than 60°C and, preferably, less than 120°C, the third flow D3, regeneration,is preferably greater than or equal to 20% of the first flow rate D1, the pre-cooling gas has a CO2 level of less than 150 ppm, the fourth pre-cooling pressure P4 is greater than one bara, the fourth pre-cooling temperature T4 is preferably less than or equal to the first temperature T1 and, even more preferably, at least 30°C lower than the first temperature T1, the fourth pre-cooling flow rate D4 is greater than or equal to 25% of the first flow rate D1, the re-pressurization is carried out, at the inlet of the column, under the conditions of adsorption, except that the outlet of the column is closed and the flow rate D5, initially equal to D1, decreases as the pressure increases.,

[0081] In terms of durations, the duration of the adsorption step 105 serves as a reference unit: to determine the duration of the preheating step 115, for example greater than or equal to 48% of the duration of the step 105, to determine the duration of the regeneration step 125, for example greater than or equal to 75% of the duration of the step 105, and to determine the duration of the pre-cooling step 130, for example greater than or equal to 50% of the duration of the step 105.

[0082] The durations of steps 110, 120 and 135 are preferably greater than two minutes. Monitoring of the operation of the column is carried out, during steps 110, 120 and 135, by a sensor for measuring the internal pressure of the column.

[0083] Under these conditions, if the gas to be purified has, at the column inlet, a CO2 concentration of between 2.5 mol% and 5 mol%, the CO2 content of the purified gas at the column outlet is substantially equal to 0.398 times the CO2 content in the gas to be purified plus 0.99. If the gas to be purified has, at the column inlet, a CO2 content of less than 2.5 mol%, the CO2 content of the purified gas at the column outlet is less than 50 ppm.

[0084] Example 2 “hot regeneration” of a gas with a CO2 content of less than 2.5% mol.

[0085] In this example 2: the first adsorption pressure P1 is 40 bara, the first adsorption temperature T1 is -50°C, the first adsorption flow rate D1 is similar to that of example 1, the preheating gas has a CO2 content of less than 40%mol, the second preheating pressure P2 is greater than or equal to one bara, the second preheating temperature T2 is 80°C, the second preheating flow rate D2 is equal to 1.6 times D1, the regeneration gas has a CO2 content of 100 ppm, the third regeneration pressure P3 is equal to two bara, the third regeneration temperature T3 is equal to 80°C, the third regeneration flow rate D3 is equal to 30% of the first flow rate D1, the precool ...1 is greater than or equal to of CO2 equal to 100 ppm, the fourth pressure P4, of pre-cooling, is equal to two bara, the fourth temperature T4, of pre-cooling, is equal to -90°C, the fourth flow rate D4,of pre-cooling, is equal to 33% of the first flow rate D1, the re-pressurization takes place, at the inlet of the column, under the conditions of adsorption, except that the outlet of the column is closed and the flow rate D5, initially equal to D1, decreases as the pressure increases.,

[0086] In terms of durations, the duration of the adsorption step 105 serves as a reference unit: to determine the duration of step 110, equal to 6% of the duration of step 105, if this value is greater than three minutes and, otherwise, three minutes, to determine the duration of step 115, of preheating, equal to half the duration of step 105, to determine the duration of step 120, equal to 6% of the duration of step 105, if this value is greater than three minutes and, otherwise, three minutes, to determine the duration of step 125 of regeneration, equal to 80% of the duration of step 105, to determine the duration of step 130 of pre-cooling, equal to 55% of the duration of step 105 and to determine the duration of step 135, equal to 6% of the duration of step 105, if this value is greater than three minutes and, otherwise, three minutes.

[0087] The circulation of the gas is done, during step 105, from the top to the bottom of the column. The circulation of preheating gas, during step 115 and of regeneration gas, during step 125, is done from the bottom to the top of the column.

[0088] Under these conditions, the CO2 level of the purified gas leaving the column is less than 50 ppm.

[0089] Example 3 “warm regeneration” of a gas with a CO2 level of less than 5%mol.

[0090] In this example 3: the first pressure P1, of adsorption, is greater than one bara, and, preferably, less than 80 bara, the first temperature T1, of adsorption, is between -80°C and -20°C, the first flow rate D1, of adsorption, is a flow rate of biomethane of 250 Nm 3 / h with 2.5%mol of CO2; for a first temperature, T1, of adsorption after cooling of - 50°C; a mass of 13X sieve of 27 kg; A temperature T3, of regeneration, of 20°C; a flow rate D3, of regeneration, of 400 Nm 3 / h; a D2 flow rate, preheating, of 400 Nm 3 / h (40%mol of CO2 and 60%mol of CH4); a temperature T2, for preheating = 20°C; a flow rate D4, for precooling, of 50 Nm 3 / h, a pre-cooling temperature T4 of -80°C; a duration of the adsorption phase, less than 50 min and a duration of the regeneration phase less than 40 min, the preheating gas has a CO2 level less than 50% mol, the second preheating pressure P2 is greater than one bara, the second preheating temperature T2 is greater than 10°C, preferably less than 80°C, and even more preferably less than 30°C, the second preheating flow rate D2 is greater than or equal to the flow rate D1, the regeneration gas has a CO2 level less than 150 ppm, the third regeneration pressure P3 is greater than one bara, and preferably less than 80 bara, the third regeneration temperature T3 is greater than 10°C, preferably less than 60°C and even more preferably less than 30°C, the third regeneration flow rate D3 is greater than or equal at one and a half times the first flow rate D1,the pre-cooling gas has a CO2 level of less than 150 ppm, the fourth pre-cooling pressure P4 is greater than one bara, the fourth pre-cooling temperature T4 is less than or equal to the first temperature T1 and, preferably, at least 30°C lower than the first temperature T1, the fourth pre-cooling flow rate D4 is, preferably, greater than or equal to 20% of the first flow rate D1, the re-pressurization is carried out, at the inlet of the column, under the conditions of adsorption, except that the outlet of the column is closed and the flow rate D5, initially equal to D1, decreases as the pressure increases. The repressurization pressure P4 is, preferably, equal to the adsorption pressure P1.,

[0091] In terms of durations, the duration of the adsorption step 105 serves as a reference unit: to determine the duration of the preheating step 115, for example greater than or equal to 40% of the duration of the step 105, to determine the duration of the regeneration step 125, for example greater than or equal to 75% of the duration of the step 105, and to determine the duration of the pre-cooling step 130, for example greater than or equal to 40% of the duration of the step 105.

[0092] The durations of steps 110, 120 and 135 are preferably greater than two minutes. Monitoring of the operation of the column is carried out, during steps 110, 120 and 135, by a sensor for measuring the internal pressure of the column.

[0093] Under these conditions, if the gas to be purified has, at the column inlet, a CO2 concentration of between 2.5 mol% and 5 mol%, the CO2 content of the purified gas at the column outlet is substantially equal to 0.398 times the CO2 content in the gas to be purified plus 0.99. If the gas to be purified has, at the column inlet, a CO2 content of less than 2.5 mol%, the CO2 content of the purified gas at the column outlet is less than 50 ppm.

[0094] It is noted that the regeneration flow rate D3 is reduced: in hot regeneration (T> 60°C), the regeneration flow rate D3 is greater than or equal to a quarter, for example a third in example 2, of the adsorption flow rate D1 (flow rates expressed in Nm 3 / h), in warm regeneration (60°C > T > 10°C), the regeneration flow rate D3 is greater than or equal to 1.5 times the adsorption flow rate (flow rates expressed in Nm 3 / h).

[0095] In the latter case, since the regeneration time is greater than 0.75 times the adsorption time, the quantity of gas (time x flow rate) is greater for regeneration (0.75 * 1.5 = 1.125) than for adsorption (1 x 1 = 1). The regeneration gas cannot therefore be the gas to be purified. Another gas is therefore used for regeneration, for example nitrogen.

[0096] In embodiments, the device comprises at least two columns configured to operate in a step-shifted manner, one column operating in purification while another column operates in regeneration. Preferably, at any time, one of these columns operates in purification. For example, Figure 2 illustrates an embodiment comprising four columns operating in a step-shifted manner, such that at any time at least one column is in the adsorption phase.

[0097] Figure 2 thus illustrates a preferred embodiment of a device which is the subject of the invention applied to the advanced CO2 purification (polishing step) of a gas, for example with a view to its liquefaction. In this device 200, four columns 205, 215, 225 and 235 are mounted in parallel. These columns are thermally insulated to reduce the flow of lost heat to less than 120 W / m 2 on average.

[0098] A pipe 241 is dedicated to the inlet of gas to be purified. A pipe 242 is dedicated to the evacuation of pre-cooling gas.

[0099] A pipe 243 is dedicated to the evacuation of preheating and depressurization gases. A pipe 244 is dedicated to the evacuation of regeneration gases. A pipe 245 is dedicated to the inlet of regeneration gases. A pipe 246 is dedicated to the inlet of preheating gases. A pipe 247 is dedicated to the inlet of pre-cooling gases. A pipe 248 is dedicated to the outlet of purified gases.

[0100] This device 200 also comprises a first set of solenoid valves 201, 211, 221, 231, 205, 215, 225, 235, 206, 216, 226, 236, 207, 217, 227, and 237, between each of the inlet pipes 241, 245, 246, and 247 and one end of each of the columns (the upper end for the valves 201, 211, 221, 231 and the lower end for the others).

[0101] This device 200 also comprises a second set of solenoid valves 202, 212, 222, 232, 203, 213, 223, 233, 204, 214, 224, 234, 208, 218, 228, and 238, between each of the discharge or outlet pipes 242, 243, 244, and 248 and the other end of each of the columns (the lower end for the valves 208, 218, 228, 238 and the upper end for the others).

[0102] A control unit 250, for example a computer or a server, configured to control the solenoid valves so that, at all times, one and only one of the columns is in the adsorption phase of a gas circulating between the inlet pipe for the gas to be purified and the outlet pipe for the purified gas.

[0103] Simultaneously, apart from the switching phases: another column being in the pre-cooling phase by a gas circulating between the pre-cooling inlet pipe and the pre-cooling gas discharge pipe, yet another column is in the regeneration phase of a gas circulating between the regeneration gas inlet pipe and the regeneration gas discharge pipe, and the last column is in the pre-heating phase with a pre-heating gas circulating between the pre-heating gas inlet pipe and the pre-heating gas discharge pipe.

[0104] The sets of solenoid valves 201 to 204, 206 to 209, 211 to 214, 216 to 219, 221 to 224, 226 to 229, 231 to 234 and 236 to 239 allow the gas flows to be directed from any inlet pipe to any column 205, 215, 225 or 235, and from any column 205, 215, 225 or 235, to any outlet pipe. Thanks to this set of valves, each column 205, 215, 225 or 235 passes through the different phases described in figure 1, which makes it possible to ensure continuous purification, since one of the columns 205, 215, 225 or 235 is always in the adsorption phase.

[0105] In the case of biogas or biomethane purification: the preheating gas is the pretreated biogas, after purification of water H2O, tetrahydrothiophene THT, hydrogen sulfide H2S, preheated by a heating means, for example by heat recovery and / or dedicated auxiliary heating; the regeneration gas is, for example, the "end-flash gas" (or final flash gas) resulting from the final expansion of liquefied natural gas (LNG) after a subcooling step. It should be remembered that, in refrigeration, the final flash gas is a refrigerant in the form of a gas produced spontaneously when the condensed liquid is subjected to boiling. This final flash gas is reheated to the third temperature before participating in the regeneration of the molecular sieve; and the precooling fluid is, for example, the end-flash gas flow and / or an LNG top-up.

[0106] By implementing the invention, the TSA process is improved because the heat used to regenerate the sieves is limited and medium cooling is used (between -20°C and -80°C) to: increase the CO2 adsorption capacity of conventional molecular sieves, for example a 13X zeolite, reduce the size of the column and the quantity of sieve associated with it, and facilitate the regeneration of these sieves: in fact, the heat temperature level required for regeneration is lowered, for example to only 60°C, or even 10°C for warm regeneration (example 3).

[0107] The advantages of this process include: reduction of the need for heat and facilitation of heat recovery on related conventional systems, for example, recovery of the heat released by the compressor of the gas to be purified, better compactness: the size of the column and the quantity of associated zeolites are reduced compared to the non-cryogenic situation, and a simple column geometry because the gas passage section can be constant (at the inlets / outlets) and there is therefore no external envelope to be designed specifically for the column.With the device 200 illustrated in FIG. 2, the gas is purified of CO2 continuously for a continuous incoming gas flow having a CO2 level of less than 5 mol% down to a CO2 level of less than 3 mol% at the purification outlet and preferably, an incoming gas flow with a CO2 level of less than 2.5 mol% is purified of CO2 continuously down to a CO2 level of less than 50 ppm at the purification outlet.

[0108] Of course, it is possible, at the cost of greater complexity, to put two purification columns in series to obtain successive purifications leading to less than 50 ppm of CO2.

[0109] Figure 3 shows a particular embodiment of a gas liquefaction device 300 which is the subject of the invention, in the form of a block diagram. The biogas to be purified passes through a pretreatment means 305 which removes water, THT and hydrogen sulfide therefrom. Then, a compressor 310 compresses the gas to be purified to pressure P2 and a heat exchanger 315 heats the compressed gas so that it reaches temperature T2 at pressure P2. The gas to be purified is injected into the purification device 320. For example, if the device 320 includes the device 200 illustrated in Figure 2, the gas to be purified is injected via the pipe 246. The pipe 243 is connected to a mass CO2 purification means 325. Mass CO2 purification is the purification of biogas, that is, the purification that reduces the CO2 level from 40% mol to 2.5% mol typically. This is, for example, a membrane or washing system, with water, amines or with a specific solvent.The outlet of this means 325 passes through a first cooling heat exchanger, or precooling, 330 which brings the gas to be purified to the temperature T1 under the pressure P1, before it is injected into the device 320 via the pipe 241 and comes out, purified, via the pipe 248. The purified gas then passes into a second cooling heat exchanger, or precooling, 335, through a liquefaction means 340 and through a subcooling heat exchanger, or subcooling, 345. A valve 350 leads the liquefied gas to an intermediate tank 355 which feeds a storage tank 360, on the one hand, and, via a heat exchanger 370 and a solenoid valve 375, to the regeneration gas inlet pipe 245 of the purification device 320, on the other hand. The end-flash gas from the storage tank 360 feeds the pipe 247 of the purification device 320.Alternatively, using a solenoid valve 365, the end-flash gas from the intermediate tank 355 feeds the pipe 247 of the purification device.

[0110] The regeneration and pre-cooling fluids are injected upstream of the biogas compressor. In particular, the regeneration gas, once loaded with CO2, leaves upstream of the compressor because it is at low pressure. The regeneration and pre-cooling fluids do not pollute the biogas because their CO2 content is lower than that of the biogas, which is partially purified by the CO2 mass purification, which prevents any accumulation of CO2 in the biomethane at the polishing or pre-cooling inlet 1.

[0111] For example, the gas purification means is an adsorption column, preferably equipped with a molecular sieve. A means for placing the column under a pressure described above, a depressurization means and / or a re-pressurization means, may be a pump, a compressor, or a turbine, for example. Figure 4 shows steps of a particular embodiment of a gas liquefaction method 400 that is the subject of the invention. During a step 405, the gas to be liquefied undergoes a purification pretreatment, in particular by removing water, THT and H2S. During a step 410, the gas to be liquefied is compressed. During a step 415, the gas to be liquefied is brought to a preheating temperature and pressure. During a step 420, the gas to be liquefied preheats the purification column. During a step 425, the gas to be liquefied undergoes mass CO2 purification.During a step 430, the gas to be liquefied undergoes a first cooling, or “precooling”. During a step 435, the gas to be liquefied is purified in the purification column. During a step 440, the gas to be liquefied undergoes a second cooling, or “precooling”. During a step 445, the gas is liquefied. During a step 450, the liquefied gas undergoes subcooling, or “subcooling”. During a step 455, the liquefied gas undergoes expansion.

[0112] In a first embodiment, the majority of the gas leaving step 455 is stored during a step 460. A small portion of the gas from step 455 is used for the regeneration of the molecular sieve during a step 465, after a step 470 of pre-cooling the adsorption column and a step 475 of heating, for example via heat recovery. The cooling gas is then returned to step 410.

[0113] In a second embodiment, the end-flash gas from storage is used to pre-cool the purification column, during a step 480. The cooling gas is then returned to step 410.

[0114] Thus, in the embodiment illustrated in Figure 3, the liquefaction device 300 comprises a circuit for recovering final flash gas from at least one liquefied gas tank, configured to supply this final flash gas to each pre-cooling means of a column of the purification device.

[0115] In addition, in the embodiment illustrated in FIG. 3, the liquefaction device 300 comprises a circuit for recovering final flash gas from at least one liquefied gas tank configured to, once this final flash gas has been reheated to the third temperature, supply this recovered final flash gas to each means of regeneration of a column of the purification device.

[0116] It is noted that the present invention applies particularly to small production units, i.e. for gas flow rates to be treated of less than 2000 Nm 3 / h.

[0117] The invention is particularly suitable for the advanced purification of biomethane (typically an inlet gas mixture of 96% mol CH4; 0.2% mol O2, 0.8% N2 and 3% mol CO2) but it can be applied for any gas stream whose main components condense in liquid form at temperatures below -80°C at the final storage pressure (typically at less than 25 bara pressure). These main components are, for example, methane, ethane, nitrogen, oxygen, ethane or ethylene.

Claims

CLAIMS 1. Device (200) for gas purification by cold adsorption of carbon dioxide (CO2), characterized in that it comprises: at least one column (205, 215, 225, 235) provided with a molecular sieve configured to adsorb carbon dioxide at a first adsorption temperature (T1) between -20°C and -80°C and at a first adsorption pressure (P1), and - a means (241, 248, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239) for purifying the gas to be purified by injection, with a first flow rate (D1), into the column at the first temperature and at the first pressure, which further comprises: a means for placing the column under a second pressure (P2) greater than one bara, - a means (243, 246, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239) for preheating the column under the second pressure to a second temperature (T2) greater than 10°C, a means for depressurizing the preheated column to a third pressure (P3), - a means (244, 245, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239) for regenerating the sieve by passing through this sieve a regeneration gas at the third pressure at a third temperature (T3), - a means (242, 247, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239) for pre-cooling the column to a fourth temperature (T4) and a means for re-pressurizing the column to the first temperature and to the first pressure.

2. Device (200) according to claim 1, which comprises at least two columns (205, 215, 225, 235) configured to operate in step shift, one column operating in purification while another column operates in regeneration.

3. Device (200) according to claim 2, which comprises: four columns (205, 215, 225, 235) mounted in parallel, a pipe (241) for inlet of gas to be purified, a pipe (242) for evacuating pre-cooling gas, a pipe (243) for evacuating preheating and depressurization gas, a pipe (244) for evacuating regeneration gas, a pipe (245) for inlet of regeneration gas, a pipe (246) for inlet of preheating gas, a pipe (247) for inlet of pre-cooling gas, a pipe (248) for outlet of purified gas, a first set of solenoid valves (201, 211, 221, 231, 205, 215, 225, 235, 206, 216, 226, 236, 207, 217, 227, 237) between each of the inlet pipes (241, 245, 246, 247) and one end of each of the columns, a second set of solenoid valves (202, 212, 222, 232, 203, 213, 223, 233, 204, 214, 224, 234, 208, 218, 228, 238) between each of the discharge or outlet pipes (242, 243, 244, 248) and another end of each of the columns, and a control unit (250) configured to control the solenoid valves so that, permanently, one and only one of the columns is in the adsorption phase of a gas circulating between the inlet pipe for the gas to be purified and the outlet pipe for the purified gas, another column being in the pre-cooling phase by a gas circulating between the pre-cooling inlet pipe and the pre-cooling gas discharge pipe,yet another column is in the regeneration phase of a gas circulating between the regeneration gas inlet pipe and the regeneration gas outlet pipe, and the last column is in the preheating phase with a preheating gas circulating between the preheating gas inlet pipe and the preheating gas outlet pipe., 4. Device (200) according to one of claims 1 to 3, which comprises, at the inlet of the gas purification means (241, 248, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239), a source of gas whose main components condense in liquid form at temperatures below -80°C at the final storage pressure.

5. Device (200) according to one of claims 1 to 4, which comprises, at the inlet of the gas purification means (241, 248, 201 to 204, 211 to 214, 221 to 224, 231 to 234, 206 to 209, 216 to 219, 226 to 229, 236 to 239), a source of gas whose main components are biomethane, methane, ethane, nitrogen, oxygen and / or ethylene.

6. Device (200) according to one of claims 1 to 5, in which the first adsorption pressure (P1) is greater than 15 bara.

7. Device (200) according to one of claims 1 to 6, in which the third regeneration pressure (P3) is lower than the first adsorption pressure (P1).

8. Device (200) according to one of claims 1 to 7, in which the third regeneration temperature (T3) is greater than 10°C and less than 30°C.

9. Device (200) according to one of claims 1 to 8, in which the regeneration means and the purification means are jointly configured so that the regeneration duration is less than the adsorption duration.

10. Device (200) according to one of claims 1 to 9, in which the third temperature (T3), of regeneration, is greater than 60°C and the normal volume flow rate, at the temperature of 0°C and at the pressure of 1.013 bara, of regeneration is less than half of the normal volume flow rate of adsorption.

11. Device (200) according to one of claims 1 to 10, in which the third temperature (T3), of regeneration, is greater than 10°C and less than 60°C and the normal volume flow rate, at the temperature of 0°C and at the pressure of 1.013 bara, of regeneration is greater than the normal volume flow rate of adsorption.

12. Device (300) for liquefying a gas, which comprises: a purification device (200) according to one of claims 1 to 11, a compressor (310) of the gas to be liquefied, a heat exchanger (315) bringing the compressed gas to the second temperature (T2) and supplying the preheating gas to each means (246) for preheating a purification column (205, 215, 225, 235) of the purification device, a heat exchanger (330) configured to receive the preheating gas having passed through the purification column, configured to carry out a first precooling of this gas and to supply it to each means for purifying a purification column of the purification device, a heat exchanger (335) configured to receive the purified gas having passed through the purification device, configured to carry out a second precooling purified gas, a means (340) of liquefying the purified gas after the second cooling,and a heat exchanger (345) configured to subcool the liquefied gas and supply it to at least one liquefied gas tank.

13. Liquefaction device (300) according to claim 12, which further comprises a circuit for recovering final flash gas from at least one liquefied gas tank (360), configured to supply this final flash gas to each pre-cooling means (247) of a column (205, 215, 225, 235) of the purification device (200).

14. Liquefaction device (300) according to one of claims 12 or 13, which further comprises a circuit for recovering final flash gas from at least one liquefied gas tank (360) configured to, once this final flash gas has been reheated to the third temperature (T3), supply this recovered final flash gas to each means (245) for regenerating a column (205, 215, 225, 235) of the purification device (200).

15. Method (100) for purifying gas by cold adsorption of carbon dioxide (CO2), in at least one column (205, 215, 225, 235) provided with a molecular sieve configured to adsorb carbon dioxide at a first adsorption temperature (T1) between -20°C and -80°C and at a first adsorption pressure (P1), a method characterized in that it comprises a step (105) of purifying the gas to be purified by injection, with a first flow rate (D1), into the column at the first temperature and at the first pressure, which further comprises: a step (110) of placing the column (205, 215, 225, 235) under a second pressure (P2) greater than one bara, a step (115) of preheating the column under the second pressure to a second temperature greater than 10°C, a step (120) of depressurizing the preheated column to a third pressure (P3), a step (125) of regenerating the sieve by passing through this sieve a regeneration gas at the third pressure at a third temperature (T3), a step (130) of pre-cooling the column to a fourth temperature (T4) and a step (135) of re-pressurization of the column to the first temperature and pressure.

16. A method (400) for liquefying a gas which comprises: the purification method (100) according to claim 15, a step (410) of compressing the gas to be liquefied, a step (415) of bringing the compressed gas to the second temperature (T2) to provide the preheating gas for the preheating step (115) of the purification method, a step (430) of first cooling of the preheating gas having carried out the preheating step to carry out, on this gas, the steps of the purification method, a step (440) of second cooling of the purified gas, a step (445) of liquefying the gas after its second cooling, a step (450 to 460) of subcooling the liquefied gas and storing the subcooled liquefied gas in a liquefied gas tank, and a step recycling of gas used during a pre-cooling stage upstream of the compression stage.

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