PL243099B1 - Set of devices for cryogenic separation and method for cryogenic separation of carbon dioxide from waste gases - Google Patents

Abstract

A set of devices for the separation of carbon dioxide from waste gases, in particular from biogas, equipped with a compressor (1), an initial heat exchanger (2), a pipeline with a three-way valve (3) supplying gas alternately to cryogenic exchangers (6, 17), and an installation discharging the obtained liquid carbon dioxide in the form of a pipeline (10) and a parallel pipeline (9) discharging liquid biomethane, characterized in that at least two parallel cryogenic exchangers (6, 17) operating alternately are provided with at least one exchanger (5, 16) each ) of a thermosiphon installation and at least one evaporator (7, 18) of an auto-cascade refrigerant circuit system, said thermosyphon system exchangers (5, 16) in a closed system are connected in series with the thermosiphon system exchanger (12) located in the preliminary heat exchanger (2), while the auto-cascade refrigerant circulation system is powered by a compressor (24) connected on the discharge side with a condenser (25) powered by an absorption refrigeration system (29) and a phase separator (26), whose steam connector is connected through a regenerative exchanger (23) with an expansion valve (28) and a three-way valve (30) with evaporators (7, 18) of the auto-cascade refrigerant circulation system, while the liquid connector is connected through an expansion valve (27) with the regenerative exchanger (23) and a three-way valve (22) with evaporators (7, 18) auto-cascade refrigerant circulation system. The subject of the application is also a method of separating carbon dioxide from waste gases, in particular from biogas.

Description

Description of the invention

The subject of the invention is a set of devices and a method of cryogenic separation of carbon dioxide from waste gases, applicable in the purification of biogas and gases produced in the process of hydrocarbon combustion.

The development of biogas upgrading technology to the quality of natural gas can bring measurable benefits to the energy sector. The implementation of improved solutions for biogas purification leads to an increase in the use of organic waste as an important source of renewable energy. Biomethane formed after biogas treatment is a full-fledged RES gas fuel. As an effective and ecological energy carrier, it can replace conventional fuels in the production of heat and electricity. Reducing dependence on fossil fuels and reducing greenhouse gas emissions into the atmosphere are important aspects of today, and all actions should be aimed at securing the energy sector.

Biogas is obtained as a result of the decomposition of organic matter under anaerobic conditions and, depending on the conditions of fermentation and the substrates used, contains: 45-60% methane, 35-55% carbon dioxide and 1-5% water vapor, hydrogen sulfide, nitrogen, oxygen and hydrogen . The parameters of raw biogas and the impurities contained in it vary depending on the origin of the biological gas. There are three main sources of its origin: fermentation of agricultural waste, fermentation of sewage sludge and landfill gas. Due to the high concentration of carbon dioxide in the mixture, the calorific value of untreated biogas is low. It is crucial, in addition to cleaning the biogas of any other impurities, to remove carbon dioxide as it is an energy burden for the raw biogas. Increasing the share of methane increases the calorific value of the fuel. Impurities present in biogas prevent its direct use without prior treatment. Currently, biogas is mainly used in cogeneration by burning the obtained gaseous fuel at the production site. Treatment is then limited to the elimination of hydrogen sulphide and water vapour. Removal of carbon dioxide from biomethane, so that the methane content in the final product reaches 95%, allows for obtaining quality parameters that allow for the injection of the biomethane produced into the gas distribution network. Refined biogas to the parameters of high-methane gas, after liquefaction, can also be stored for further transport and sale.

The currently used biogas purification technologies are divided into the following types: membrane separation, methods using adsorption and absorption processes and cryogenic separation.

There is a known method of treating biogas from undesirable impurities using a membrane separator. The method consists in passing a mixture of gases through a layer made of a special composite. The membrane material is selectively permeable to certain gases. The separation of CH4 and CO2 occurs as a result of the difference in molecular size or by the affinity of the components of the mixture with the membrane material. The process uses the chemical potential difference on both sides of the partition. The degree of biogas purification depends on the type of membrane used. In this technology, there is a low methane recovery, and large amounts of contaminated CH4 remain in the waste stream of the installation.

A method of biogas treatment by absorption is known. In physical absorption, CO2 is absorbed by a solvent using a water scrubber using the difference in solubility according to Henry's Law. Carbon dioxide is many times more soluble in water than methane. The process is carried out by cooling and compressing the biogas, and then introducing the gas into a column with a countercurrent solvent stream. Increasing the biogas pressure implies an increase in its solubility in order to achieve high efficiency of the process. The washing water is regenerated in the stripping column. Most of the CO2 and H2S formed in the stripper goes into the gas phase and is stripped off with air. In the process of physical absorption, two waste streams are generated - exhaust air containing CO2 and H2S and a solvent stream. Processes in this technology require the use of a large amount of solvent, the consumption of which can be reduced by carrying out the process at higher pressure or using other absorbents in which the solubility of the adsorbed compounds is higher. In addition to water, other organic or inorganic chemical compounds can also be used as solvents. The process using organic solvents proceeds with solvent recirculation. As a result of the process, the methane content of the overhead stream is up to 94%.

In the chemical absorption technology, contact with the absorbing liquid occurs. The gases are passed through the absorption column in countercurrent. Carbon dioxide absorption takes place in aqueous amine solutions. In addition to the treated biogas stream, an amine solution leaves the column. After leaving the column, the carbon dioxide-rich solvent is passed through a desorber and the CO2 released in the process is emitted to the atmosphere. Regeneration of the solution requires a large amount of heat (maintaining the process temperature above 120°C). The concentration of methane in the obtained gas is of the order of 90%.

There is a known method of biogas treatment by adsorption, which consists in the separation of methane and carbon dioxide, using the physical attraction and binding of particles on the surface or in the micropores of the solid body. Adsorption processes are divided into physical and chemical. The selection of appropriate conditions and the type of adsorbent implies the adsorption of a given type of molecules on the surface of a solid. In order to run the process efficiently, methane is adsorbed under low temperature and high pressure conditions. The process is carried out in the cycles of particle adsorption and the reverse process - desorption, in which the retained particles are released and their transition to the gas phase takes place. The gas fed into the fixed bed is selectively retained. The carbon dioxide remains in the solid layer and the remaining gases are passed through. The continuity of operation is ensured by an installation based on a system of several adsorbers - columns operating in parallel in a specific sequence. In this technology, high porosity adsorbents such as charcoal, activated clays, silica gel, activated alumina and crystalline aluminosilicate zeolites are indicated. The most common method of removing CO2 from biogas is adsorption with PSA (Pressure Swing Adsorption) regeneration. Based on the pressure swing technique, a product with a methane content of 96-97% is obtained. In the TSA (Temperature Swing Adsorption) method, the adsorbent is regenerated by changing the temperature by heating the bed. Due to the need to supply a large amount of heat for desorption to occur, the method requires a large energy input. Regeneration of the adsorbent can also take place as a result of passing low-voltage electric current ESA (Electric Swing Adsorption), in the process the temperature of the adsorbent is increased using Joule's law. Heating the bed is faster and more effective than in the TSA (Temperaure Swing Adsorption) method, where the selection of a bed with good conductive properties and, at the same time, high CO2 adsorption capacity at low partial pressure is impossible. The method using the adsorption process is not suitable for use with high concentrations of gas in the mixture.

There is known a cryogenic method of cleaning biogas from carbon dioxide, using the phenomenon of phase separation between gases under given temperature and pressure conditions. Carbon dioxide is precipitated from the gas mixture in liquid or solid form, depending on the process technology used. CO2 liquefaction requires a significant reduction of the gas temperature or simultaneous reduction of the temperature and compression of the gas to a high pressure of several dozen bars. However, the implementation of the process of precipitation of CO2 in a solid form requires a much lower gas temperature. The triple point temperature of pure CO2 is -56.5°C, with a corresponding pressure of 5.2 bar. At lower pressure, carbon dioxide changes state directly from a gas to a solid. In the case of a solution, the achievement of the solidification (resublimation) process is closely related to the percentage of CO2 in the mixture. Resublimation of CO2 from a solution of CH4 and CO2 occurs below the phase equilibrium temperature of about -60°C.

Among the biogas purification technologies available on the market, cryogenic separation remains in the research and development phase.

A cryogenic method of purification is known, where the Joule-Thomson phenomenon is used, compressing biogas to high pressure, so that when it is expanded, the temperature of the gas reaches the phase change point. The process takes place at very low temperatures, down to -100°C, and at high pressures up to 40 bar. Dioxide contained in biogas is liquefied or resublimated, while methane remains in the gas phase. The cryogenic separation process is carried out in several stages. The raw gas passes through a pre-heat exchanger which cools the gas down to -70°C using heat exchange with the low temperature already treated gas. In the next stage, the gas flows through a series of compressors and heat exchangers. The transition process lowers the temperature of the gas to a pressure of about 40 bar just before entering the distillation column. Expansion of the gas in the distillation column results in a significant decrease in the temperature of the gas and sublimation of carbon dioxide. The system is characterized by the complexity of the process, the need to use a large number of devices and high inputs of electricity to operate the compressors. The cryogenic method makes it possible to achieve a high methane content of up to 99%.

A solution based on cryogenic purification of biogas from carbon dioxide, using phase separation when cooled to the appropriate temperature, is presented in the patent description PL225854 B1. The patent description proposes a method and installation in which the removal of carbon dioxide takes place by cooling biogas in a gas - liquid nitrogen exchanger. The multi-stage process consists of initially pressurizing the untreated biogas to a pressure above 1.5 MPa. Then the gas is directed to the pre-exchanger where it is cooled down, the heat exchange takes place with the output gas from the installation. The gas passes through a pre-treatment column using biogas chemistry from water and hydrogen sulphide. The upper part of the column is connected to the gas-liquid nitrogen exchanger, where the proper phase of the CO2 purification process takes place and the biogas temperature is lowered to the parameters from -62°C to -72°C. At the temperature conditions reached, carbon dioxide and other pollutants are condensed. Liquid nitrogen used for the process is supplied from a tank (dewar). Then the biogas passes through a phase separator, the separation is carried out using sieves or internal filters that prevent the flow of the liquid phase, the liquefied carbon dioxide remains in its lower part. In the exchanger, using the inlet gas from the initial phase of the process, the purified outlet gas is heated to a temperature above 10°C. The gas product is subjected to composition control and enriched with propane-butane gas fed by injection from the LPG tank. At the end of the process, the gas is compressed to prepare it for the required discharge pressure.

The patent description EP 1931612 B1 proposes a system that uses the cooling of the gas stream to a temperature ensuring CO2 condensation. In the first stage, biogas is compressed to a pressure of 10 bar and then cooled to -25°C. After removing water, siloxanes and other impurities from the biogas, the gas is passed through a coalescing filter and through a catalyst which removes any remaining impurities. The actual removal of carbon dioxide takes place in the next two steps. The first stage of gas cooling takes place to a temperature of about -60°C, ensuring partial CO2 liquefaction from biogas, reducing the carbon dioxide content by 50%. The temperature is then lowered to -65°C, reaching a value at which solidification of carbon dioxide from the treated biogas stream occurs. The second stage of purification consists in the removal of carbon dioxide in the form of a solid. The cooling process is carried out using two parallel triple coil exchangers. Due to the solidification of carbon dioxide occurring in the process, it is necessary to use two columns that operate alternately. During the thawing of one of the columns, the solidified carbon dioxide melts, while the actual process takes place in the other. The solid CO2 discharged in this stage is heated in the pre-process exchanger, where the heat exchange takes place with the gas flowing in at the beginning of the process. Both streams of carbon dioxide precipitated in two stages of purification go to the liquid CO2 tank. The final biogas temperature ranges from -65°C to -80°C, depending on the composition of the gas.

The technology that uses the phenomenon of changing the state of aggregation of carbon dioxide from vapor to solid, and thus its separation from the mixture of exhaust gases from the combustion process, is known from the patent description US007073348B2. The gas is cooled using a refrigeration system with an internal cascade. The carbon dioxide resublimes from the gas mixture and is then discharged and stored in liquid form. The first stage of the process is the pre-cooling of the hot exhaust gases in a water exchanger driving the generator's steam turbine, from the temperature of 600°C to 50°C. Then the flue gases pass through the exchanger, which lowers the temperature of the mixture to 40°C, where partial condensation of the water takes place. The next stage is a three-stage gas cooling process, which takes place in the evaporators of the cooling device. In the first evaporator, the temperature of the refrigerant in the refrigeration cycle is -5°C, and the gas is cooled to 36.5°C, then passes through a dehydrator to ensure complete drying of the mixture. In the second condenser, the gas is cooled down to -20°C, where heat is removed through the refrigeration circuit at -30°C. Between successive stages, additional cooling takes place in counter-current between the third exchanger supply pipeline and the nitrogen gas product outlet pipeline, the temperature of the gas reaches -72°C. The last stage is passing through the third heat exchanger and the temperature of the mixture is -80°C at a pressure of 0.85 bar, or -78.6°C at a pressure of 1 bar (depending on the technology selected for pumping exhaust gases through the system). CO2 resublimation takes place on the walls of the exchanger at a temperature in the evaporator of -90°C. Two parallel exchangers operate sequentially. The flow of the refrigerant through the exchanger is controlled by a three-way valve and directed to the active exchanger, while the second one is used to defrost the exchanger from solidified carbon dioxide. Before the refrigerant flows through the expansion valve to the active evaporator, the flow passes through the inactive evaporator to recover the heat of fusion in the defrosting exchanger. Before the process is switched through the second exchanger, the liquid carbon dioxide accumulated at the bottom of the chamber is pumped to the factor storage. The nitrogen remaining in the upper part of the exchanger after separation of the mixture is released to the atmosphere through the discharge pipeline. The refrigeration circuit serving the system consists of one compressor, a system of two condensers, two liquid-steam exchangers, a separator tank, a partial condenser and three evaporators, in which a three-stage purified gas cooling process takes place.

The patent claim US006082133A presents a solution for separating carbon dioxide from a gas mixture containing methane. Biogas is purified from carbon dioxide by resublimation. Initial cooling of the untreated gas takes place in a recuperative exchanger, heat exchange takes place between the inlet biogas and two outlet streams: sublimating CO2 and purified methane. The gas then passes through a switching valve which directs the gas to an active exchanger to purify the CO2 mixture by resublimating it on the surface of the exchanger. The system consists of two heat exchangers: active and regenerative. Switching between coils occurs when one of the coils has completed a defrost cycle. In the active chamber, after separating the two components of the mixture, methane is partially condensed at a pressure of about 14 bar, which then flows into the exchanger, where it changes its state of aggregation into gas in heat exchange with the cooling circuit. Before the finished gas product is released from the system, the gas is heated in the recuperative exchanger to conditions similar to those of the environment, so that the gas stream does not contain solid fractions. In the exchanger undergoing defrosting, sublimation of solidified carbon dioxide accumulated on the surface of the exchanger takes place. The process takes place under atmospheric pressure and a temperature of -78°C. The cooling circuit of the exchanger provides heat, accelerating the sublimation process. Gaseous carbon dioxide leaves the exchanger after passing through the regenerative exchanger. The concentration of methane in the obtained gas is about 98%.

An important problem not addressed in the existing solutions is the efficiency of the systems, the mutual interaction of its elements and the purity of obtaining separated gases. The application of the solution according to the invention makes it possible to increase the energy efficiency of the technology of cryogenic separation of carbon dioxide from waste gases through the use of a gravitational thermosyphon in the heat exchanger defrosting process and the use of waste heat as an energy source for the separation process.

The set of devices for the separation of carbon dioxide from waste gases, in particular from biogas, is equipped with a compressor, a preliminary heat exchanger, a pipeline with a three-way valve supplying gas alternately to cryogenic exchangers, and an installation for discharging the obtained liquid carbon dioxide in the form of a pipeline and a parallel pipeline discharging liquid biomethane. This assembly is characterized by the fact that at least two parallel cryogenic exchangers operating alternately are equipped with at least one heat exchanger of the thermosyphon system and at least one evaporator of the auto-cascade refrigerant circulation system. Said exchangers of the thermosyphon system in a closed system are connected in series with the heat exchanger of the thermosyphon system located in the primary heat exchanger. The auto-cascade refrigerant circulation system is powered by a compressor connected on the discharge side with a condenser powered by an absorption refrigeration system and a phase separator, whose steam connector is connected through a regenerative exchanger with an expansion valve and a three-way valve with the evaporators of the auto-cascade refrigerant circulation system, while the liquid connector is connected through expansion valve with regenerative exchanger and three-way valve with evaporators of auto-cascade refrigerant circulation system.

Preferably, the pipeline downstream of the heat exchanger of the thermosyphon system located in the preliminary heat exchanger is equipped with a dividing three-way valve connected to the pipelines supplying the medium to the exchangers of the thermosyphon system of cryogenic exchangers.

Preferably, the pipeline downstream of one of the heat exchangers of the thermosyphon system of cryogenic exchangers is provided with a three-way diverting valve connected to the pipelines draining the medium from one of said oppositely connected heat exchangers of the thermosyphon system of cryogenic exchangers and supplying the medium to the heat exchanger of the thermosyphon system located in the preliminary heat exchanger.

Preferably, the condenser is powered by an external compressor or absorption refrigeration system.

The method of separating carbon dioxide from waste gases, in particular from biogas, is characterized in that the gas is compressed to a pressure of 15 bar by means of a compressor, then the gas is preferably cooled down to -50°C in the preliminary exchanger with the participation of the siphon installation exchanger. The primary exchanger is fed with a factor with a lower thermodynamic potential transferred from the regenerated exchanger. The cooled gas is directed through a three-way valve to the active cryogenic exchanger where it is cooled down to a temperature of about -120°C at a favorable pressure of 15 bar. By means of the autocascade evaporator of the refrigerant circuit system, carbon dioxide in contact with the heat exchange surface is resublimated on the surface of said evaporator after reaching the phase equilibrium temperature. Separation of carbon dioxide in the cryogenic exchanger is carried out continuously until the accumulation of solidified carbon dioxide is achieved, causing a drop in the pressure of the gas flowing through the cryogenic exchanger and a drop in the suction pressure in the auto-cascade refrigerant circuit system. Then, using a three-way valve, the gas stream is directed to a cryogenic exchanger where it is cooled down to a temperature of about -120°C at a favorable pressure of about 15 bar. By means of the autocascade evaporator of the refrigerant circuit system, carbon dioxide in contact with the heat exchange surface is resublimated on the surface of said evaporator after reaching the phase equilibrium temperature. The separation of carbon dioxide and methane in the cryogenic exchanger is carried out continuously until the accumulation of solidified carbon dioxide is achieved, causing a drop in gas pressure in the cryogenic exchanger and a drop in suction pressure in the auto-cascade refrigerant circuit system. Cryogenic exchangers are cooled using an auto-cascade refrigerant system, in which the refrigerant is compressed by a compressor, then part of the mixture is condensed in a condenser before being discharged to a phase separator, where the gaseous fraction is separated from the liquid fraction, and the gaseous fraction is directed to the regenerative exchanger, where the condensation process continues, while the liquid fraction from the phase separator is expanded and the liquid fraction of the refrigerant mixed with the fraction partially evaporated in the cryogenic exchanger is directed to the regenerative exchanger, and the liquid fraction condensed in the regenerative exchanger is directed after expansion in the valve through a 3-way diverter valve to one of the cryogenic exchangers.

Preferably, a prerequisite for switching the three-way valve to isolate the cryogenic exchanger and direct the flow of gas into the cryogenic exchanger is the completion of the defrost cycle in the connected cryogenic exchanger, discharge of liquefied carbon dioxide at -56°C and 5.2 bar pressure from the system, and methane at -120°C and 15 bar pressure.

Preferably, the defrosting of the cryogenic exchangers is carried out by means of a gravity thermosyphon.

Preferably, the defrosting of the exchangers is carried out by means of a gravitational thermosyphon supplying the exchanger with a medium with a higher thermodynamic potential transferred from the primary exchanger system, and the circulation of the medium in the system takes place without a compressor forcing the circulation.

Preferably, the pre-cooling in the pre-exchanger is done by means of a gravitational thermosiphon supplying this exchanger with a medium with a lower thermodynamic potential transferred from the recovered CO2 melting heat of the regenerated cryogenic exchanger's defrosting process and that the refrigerant is circulated in the system without a compressor forcing the circulation.

Preferably, the cryogenic exchangers operate alternately, where the gas supply is controlled by the suction pressure signal on the side of the refrigeration system or by the value of the pressure drop of the gas flowing through the cryogenic exchanger.

Preferably, the compressor of the autocascading refrigerant system is powered at least in part by electrical energy obtained in an organic Rankine cycle supplied with low temperature waste heat, including heat given off in the condenser of the autocascading refrigeration device.

Preferably, the absorption system is supplied with medium-temperature waste heat.

The subject of the invention has been presented in an embodiment in a drawing showing a schematic diagram of a system for purifying waste gases, biogas from carbon dioxide in the resublimation process, together with an autocascade refrigeration system supplying it.

Thanks to the application of the solution according to the invention, it is possible to obtain a final gas product with the parameters of high-methane gas, allowing the biomethane produced to be injected into the gas distribution network or stored in liquefied form for its transport and sale. The proposed system may contribute to the development of the biogas production market, the increase in the number of biogas plants and the increase in the use of gaseous fuels from RES in the energy sector. In addition, the system allows for highly effective CO2 capture, and to obtain a final product in the form of liquefied carbon dioxide, which can be stored and used in refrigeration applications instead of removing it to the atmosphere. In addition, the system uses a thermosyphon plant for the defrosting process, reducing energy consumption and improving the energy efficiency of the cryogenic separation technology. In addition, the use of an external cooling system results in the use of waste heat, significantly reducing the consumption of electricity needed to reach the temperature of the cryogenic process in the system.

The set of devices for separating carbon dioxide from waste gases, in particular from biogas, is equipped with a compressor 1, an initial heat exchanger 2, a pipeline with a three-way valve 3 supplying gas alternately to cryogenic exchangers 6, 17, and an installation discharging the obtained liquid carbon dioxide in the form pipeline 10 and a parallel pipeline 9 discharging liquid biomethane. Alternately, at least two parallel cryogenic exchangers 6, 17 are provided with at least one exchanger 5, 16 of the thermosyphon system and at least one evaporator 7, 18 of the auto-cascade refrigerant circulation system. Said exchangers of the thermosiphon system 5, 16 in a closed system are connected in series with the exchanger 12 of the thermosyphon system located in the primary heat exchanger 2. The auto-cascade refrigerant circulation system is powered by a compressor 24 connected on the discharge side with a condenser 25 powered by an absorption refrigeration system 29 and a phase separator 26, whose steam port is connected through a regenerative exchanger 23 with an expansion valve 28 and a three-way valve 30 with evaporators 7, 18 of the auto-cascade refrigerant circulation system, while the liquid port is connected via an expansion valve 27 with the regenerative exchanger 23 and a three-way valve 22 with evaporators 7 , 18 auto-cascade refrigerant circulation system. The pipeline 13, downstream of the heat exchanger 12 of the thermosyphon system located in the preliminary heat exchanger 2, is equipped with a dividing three-way valve 14 connected to pipelines 15, 4 supplying the medium to heat exchangers 5, 16 of the thermosyphon system of cryogenic exchangers 6, 17. Pipeline 21 and pipeline 8 behind one of exchangers 5, 16 of the thermosyphon installation of cryogenic exchangers 6, 17 is provided with a three-way distribution valve 11 connected to pipelines draining the medium from one of said oppositely connected exchangers 5, 16 of the thermosyphon installation of cryogenic exchangers 6, 17 and supplying the medium to the exchanger 12 of the thermosyphon installation located in in the primary heat exchanger 2. The condenser 25 is fed by an external compressor or absorption refrigeration system 29.

The method of separating carbon dioxide from waste gases, in particular from biogas, is characterized in that the gas is compressed to a pressure of 15 bar by means of the compressor 1, then in the preliminary exchanger 2 with the participation of the exchanger 12 of the thermosiphon installation, the gas is preferably cooled down to -50° c The primary exchanger 2 is fed with a medium with a lower thermodynamic potential transferred from the regenerated exchanger 17, the cooled gas is directed through the three-way valve 3 to the active cryogenic exchanger 6 where it is cooled down to a temperature of about -120°C at a pressure of 15 bar by means of an evaporator 7 of the auto-cascade refrigerant circulation system, carbon dioxide in contact with the heat exchange surface, after reaching the phase equilibrium temperature, is resublimated on the surface of said evaporator 7. Separation of carbon dioxide in the cryogenic exchanger 6 is carried out continuously until accumulation of solidified carbon dioxide is achieved, causing a pressure drop gas flowing through the cryogenic exchanger 6 and the suction pressure drop in the auto-cascade refrigerant circulation system, then, by means of the three-way valve 3, the gas stream is directed to the cryogenic exchanger 17 where it is cooled to a temperature of about -120°C at a preferred pressure of about 15 bar, by means of the evaporator 18 of the auto-cascade refrigerant circuit system, the carbon dioxide in contact with the heat exchange surface is resublimated on the surface of said evaporator 18 after reaching the phase equilibrium temperature. Separation of carbon dioxide and methane in the cryogenic exchanger 17 is carried out continuously until accumulation of solidified carbon dioxide is achieved , causing a gas pressure drop in the cryogenic exchanger 17 and a suction pressure drop in the auto-cascade refrigerant circulation system, furthermore the cryogenic exchangers 6, 17 are cooled by an auto-cascade refrigerant system in which the refrigerant is compressed by the compressor 24 then in the condenser 25 part of the mixture is condensed before discharge to the phase separator 26, where the gaseous fraction is separated from the liquid fraction. The gaseous fraction is directed to the regenerative exchanger 23, where the liquefaction process is continued, while the liquid fraction from the phase separator 26 is expanded and the liquid fraction of the refrigerant mixed with the fraction partially evaporated in the cryogenic exchanger 6, 17 is directed to the regenerative exchanger 23, and the liquid fraction is condensed in the regenerative exchanger, after being decompressed in the expansion valve 28, through the three-way distribution valve 30, it is directed to one of the cryogenic exchangers 6, 17, where the proper cooling effect takes place. The necessary condition for switching the three-way valve 3 to shut off the cryogenic exchanger 6 and direct the gas stream to the cryogenic exchanger 17 is the completion of the defrost cycle in the connected cryogenic exchanger 17, the discharge of liquefied carbon dioxide at a temperature of -56°C and a pressure of 5.2 bar from the system , and methane at a temperature of -120°C and a pressure of 15 bar. Defrosting of the cryogenic exchangers 6, 17 is carried out by means of a gravity thermosyphon. Heat exchangers are defrosted by means of a gravitational thermosiphon supplying the exchanger with a medium with a higher thermodynamic potential transferred from the primary exchanger system, and the medium is circulated in the system without a compressor forcing circulation. Pre-cooling in the pre-exchanger 2 is carried out by means of a gravitational thermosiphon supplying this exchanger with a medium with a lower thermodynamic potential transferred from the recovered CO2 melting heat of the defrosting process of the regenerated cryogenic exchanger 6, 17, and that the refrigerant is circulated in the system without a compressor forcing the circulation. The cryogenic exchangers 6, 17 operate alternately by gas supply, controlled by the suction pressure signal on the side of the refrigeration system or by the pressure drop value of the gas flowing through the cryogenic exchanger. The compressor 24 of the autocascading refrigerant system is powered at least in part by electrical energy obtained from the organic Rankine cycle fed by low temperature waste heat, including the heat released in the condenser 25 of the autocascading refrigeration unit, and the absorption system 29 is powered by medium temperature waste heat.

Claims (11)

1. A set of devices for the separation of carbon dioxide from waste gases, in particular from biogas, equipped with a compressor (1), a preliminary heat exchanger (2), a pipeline with a three-way valve (3) supplying gas alternately to cryogenic exchangers (6, 17), and an installation for discharging the obtained liquid carbon dioxide in the form of a pipeline (10) and a parallel pipeline (9) for discharging liquid biomethane, characterized in that at least two parallel cryogenic exchangers (6, 17) operating alternately are provided with at least one exchanger (5) each , 16) of the thermosiphon installation and at least one evaporator (7, 18) of the auto-cascade refrigerant circuit system, said thermosiphon system exchangers (5, 16) in a closed system are connected in series with the thermosiphon system exchanger (12) located in the preliminary heat exchanger (2), while the auto-cascade refrigerant circulation system is powered by a compressor (24) connected on the discharge side with a condenser (25) powered by an absorption refrigeration system (29) and a phase separator (26), whose steam connector is connected through a regenerative exchanger ( 23) with an expansion valve (28) and a three-way valve (30) with evaporators (7, 18) of the auto-cascade refrigerant circulation system, while the liquid connector is connected through an expansion valve (27) with the regenerative exchanger (23) and the three-way valve (22) with evaporators (7, 18) of the auto-cascade refrigerant circulation system. 2. The assembly according to claim 1, characterized in that the pipeline (13) behind the exchanger (12) of the thermosyphon system located in the preliminary heat exchanger (2) is equipped with a three-way dividing valve (14) connected to pipelines (15, 4) supplying the medium to the exchangers (5, 16) thermosyphon installation of cryogenic exchangers (6, 17). 3. The assembly according to claim 1, characterized in that the pipeline (21) and the pipeline (8) behind one of the exchangers (5, 16) of the thermosyphon system of cryogenic exchangers (6, 17) is provided with a three-way diverting valve (11) connected to pipelines draining the medium from one of the said oppositely connected exchangers (5, 16) of the thermosyphon system of the cryogenic exchangers (6, 17) and supplying medium to the heat exchanger (12) of the thermosyphon system located in the primary heat exchanger (2). 4. The assembly according to claim The condenser (25) is powered by an external compressor or absorption refrigeration system (29). 5. A method of separating carbon dioxide from waste gases, in particular from biogas, characterized in that by means of a compressor (1) the gas is preferably compressed to a pressure of 15 bar, then in the preliminary exchanger (2) with the participation of the exchanger (12) of the siphon installation it is preferably cooled down to -50°C, the primary exchanger (2) is supplied with a medium with a lower thermodynamic potential transferred from the regenerated exchanger (17), the cooled gas is directed through the three-way valve (3) to the active cryogenic exchanger (6) ) where it is cooled to a temperature of about -120°C at a favorable pressure of 15 bar, by means of the evaporator (7) of the auto-cascade refrigerant circulation system, carbon dioxide in contact with the heat exchange surface, after reaching the phase equilibrium temperature, is resublimated on the surface of said evaporator (7 ), wherein the separation of carbon dioxide in the cryogenic exchanger (6) is carried out continuously until the accumulation of solidified carbon dioxide is achieved, causing a drop in the pressure of the gas flowing through the cryogenic exchanger (6) and a drop in the suction pressure in the auto-cascade refrigerant circulation system, then using the three-way valve (3), the gas stream is directed to the cryogenic exchanger (17) where it is cooled down to a temperature of about -120°C at a favorable pressure of about 15 bar, using the evaporator (18) of the auto-cascade refrigerant circulation system carbon dioxide in contact with heat exchange surface, after reaching the phase equilibrium temperature, is resublimated on the surface of said evaporator (18), while the separation of carbon dioxide and methane in the cryogenic exchanger (17) is carried out continuously until the accumulation of solidified carbon dioxide is achieved, causing the gas pressure in the cryogenic exchanger (17) and the suction pressure drop in the auto-cascade refrigerant circulation system, moreover, the cryogenic exchangers (6, 17) are fed by means of the auto-cascade refrigerant system, in which the refrigerant is compressed by means of the compressor (24) and then in the condenser (25 ) part of the mixture is condensed before the outlet to the phase separator (26), where the gaseous fraction is separated from the liquid fraction, with the gaseous fraction directed to the regenerative exchanger (23), where the liquefaction process is continued, while the liquid fraction from the phase separator (26) is expanded and the liquid fraction of the refrigerant mixed with the fraction partially evaporated in the cryogenic exchanger (6, 17) is directed to the regenerative exchanger (23), and the liquid fraction condensed in the regenerative exchanger is directed after expansion in the expansion valve (28) through the distribution three-way valve (30) to one of the cryogenic exchangers (6, 17) where the proper cooling effect takes place. 6. The method according to claim 5, characterized in that the necessary condition for switching the three-way valve (3) in order to shut off the cryogenic exchanger (6) and direct the flow of gas to the cryogenic exchanger (17) is the completion of the defrosting cycle in the connected cryogenic exchanger (17), discharge from the liquefied system carbon dioxide at -56°C and 5.2 bar pressure, and methane at -120°C and 15 bar pressure. 7. The method according to claim 5, characterized in that the defrosting of the cryogenic exchangers (6, 17) is carried out by means of a gravitational thermosyphon. PL 243099 B1 8. The method according to claim 5 and 7, characterized in that the process of defrosting the exchangers is carried out by means of a gravitational thermosyphon supplying the exchanger with a medium with a higher thermodynamic potential transferred from the primary exchanger system, and the circulation of the medium in the system takes place without a compressor forcing the circulation. 9. The method of claim 5, characterized in that the pre-cooling in the initial exchanger (2) is carried out by means of a gravitational thermosyphon supplying this exchanger with a medium with a lower thermodynamic potential transferred from the recovered CO2 melting heat of the defrosting process of the regenerated cryogenic exchanger (6, 17), and that the circulation of the medium in system is performed without a compressor forcing the circulation. 10. The method of claim 5, characterized in that the cryogenic exchangers (6, 17) operate alternately, where the gas supply is controlled by the suction pressure signal on the side of the refrigeration system or by the pressure drop value of the gas flowing through the cryogenic exchanger. 11. The method of claim 5, characterized in that the compressor (24) of the autocascading refrigerant system is powered at least partly by electric energy obtained in the organic Rankine cycle supplied with low-temperature waste heat, including the heat given off in the condenser (25) of the autocascading refrigeration device and the absorption system (29) is powered by medium-temperature waste heat.