Biogas fermentation purification liquefaction and carbon capture process

Abstract

The invention discloses a biogas fermentation purification liquefaction and carbon capture process. The process comprises a biogas fermentation system for performing high-temperature fermentation on biomass; the biogas purification and liquefaction system, the CO2 purification and liquefaction system and the organic fertilizer production system are arranged at the biogas residue output end of the biogas fermentation system to produce organic fertilizer; a thermal energy recovery system; according to the invention, a high-temperature facultative anaerobic hydrolysis and high-temperature anaerobic fermentation process is provided, so that high-concentration biomass biogas is produced; cH4, H2S and CO2 in the biogas are separated and liquefied by adopting a process of'wet process and dry process serial desulfurization, PSA (Pressure Swing Adsorption) + MDEA (Methyl Methanol Ether Alcohol) decarburization, molecular sieve dehydration, single-order two-stage mixed refrigerant compression and propane refrigeration compression ', and produced liquid CH4 and CO2 are recycled; meanwhile, the biogas residues are subjected to a secondary fermentation technology under the action of microorganisms to obtain a solid organic fertilizer; in addition, the solar heat collection and heat pump technology is utilized, and the whole-field heat energy is recycled to supply heat to the biogas fermentation system.

Description

Technical Field

[0001] The present invention specifically relates to a biogas fermentation, purification, liquefaction and carbon capture process. Background Art

[0002] Biogas projects are gradually developing towards large and medium-sized ones. The abundant biogas resources are facing the problem of subsequent consumption, especially when it is difficult to integrate into the natural gas pipeline network and power generation grid. This problem is more prominent.

[0003] An existing patent, patent number CN110078561A, discloses a method for comprehensive utilization of feces and crop straw by combined fermentation. First, hydrogen peroxide and urea are added to the straw for pretreatment, and then biogas is added for pyrolysis. The pyrolyzed straw is mixed with livestock and poultry manure, sprayed with biogas mist, and then anaerobic fermentation is carried out. Part of the biogas produced by the fermentation enters the boiler to generate steam, and the steam is returned to the fermentation system as a heat source or for heating in winter. The other part enters the gas pipeline as fuel gas. The biogas after solid-liquid separation is used as organic fertilizer, and the biogas residue is further pyrolyzed to produce gas; the second prior art patent No. CN111256431B discloses a mixed refrigerant biogas pressurized liquefaction system and its working method, the biogas is desulfurized, dehydrated, filtered and then pressurized by a biogas pretreatment unit, and a high-purity CH4 flow and CO2-rich biogas flow are obtained by a secondary membrane separation unit, and pressurized liquid CH4 and food-grade liquid CO2 are obtained by pressurized liquefaction and rectification; the third prior art patent No. CN111912168A discloses a biogas purification and liquefaction system, which consists of a carbon dioxide separation system, a refrigeration cycle loop and a biogas liquefaction loop. The carbon dioxide separation system uses a low-temperature liquefaction method to remove carbon dioxide. The water is first removed by a gas-liquid separator, and the gas enters the compressor. After being cooled by a heat exchanger, it enters the gas-liquid separator again to separate the liquid carbon dioxide.

[0004] However, the above patent has some shortcomings in practical application:

[0005] The existing patent is a process of "using feces and crop straw as raw materials and high-temperature anaerobic fermentation". The above process has the following problems: the fermentation temperature range is wide (50°C ~ 55°C), which can easily cause unstable gas generation, complex process flow, large consumption of chemical agents and high energy consumption.

[0006] The second existing technology uses the "dry desulfurization + two-stage membrane separation" process to separate CH4, CO2 and H2S from biogas, and combines the "mixed refrigerant four-stage compression + cryogenic distillation" process to obtain the product LNG + LCO2. The above process has the following problems: dry desulfurization and two-stage membrane separation of CO2 cannot meet the requirements of natural gas liquefaction; the four-stage compression process of mixed refrigerant is complex, energy-intensive, and has high investment and operating costs. At the same time, CH4, CO2, H2S and biogas residues in biogas are not recovered to the maximum extent, resulting in a waste of resources.

[0007] The third existing technology adopts low-temperature liquefaction to obtain LCO2 products and separate CH4, and combines the mixed refrigerant two-stage compression "pre-cooling + main cooling" process to obtain LNG products. The above process has the following problems: H2S in biogas is not removed, which cannot meet the requirements of NG and CO2 liquefaction, and there are safety hazards; CO2 liquefaction is not deeply dehydrated first, which is easy to cause equipment freezing and blocking. At the same time, the pre-cooling + main cooling process of natural gas liquefaction is complicated to operate. For this reason, we propose a biogas fermentation purification liquefaction and carbon capture process. Summary of the invention

[0008] The purpose of the present invention is to provide a biogas fermentation purification liquefaction and carbon capture process to solve the problems raised in the above background technology that the existing biogas fermentation cycle is long, the gas production is unstable, the fermentation heat source energy consumption is high, the mixed refrigerant in the biogas purification liquefaction system needs four-stage compression, and the investment and operating costs are high; at the same time, H2S cannot be removed well during biogas purification, and CO2, H2S and biogas residue cannot be recovered to the maximum in the later stage.

[0009] To achieve the above object, the present invention provides the following technical solution: a biogas fermentation, purification, liquefaction and carbon capture process, comprising:

[0010] Biogas fermentation system for high temperature fermentation of biomass;

[0011] The biogas purification and liquefaction system is arranged at the biogas output end of the biogas fermentation system to process the biogas;

[0012] A CO2 purification and liquefaction system is connected to one end of the biogas purification and liquefaction system to purify and form CO2;

[0013] An organic fertilizer production system is arranged at the biogas residue output end of the biogas fermentation system to produce organic fertilizer;

[0014] The heat recovery system is connected to one end of the biogas fermentation system through a pipeline to circulate the hot water of the biogas fermentation system.

[0015] Preferably, the biogas fermentation system includes a crushing unit, a hydrolysis tank and a high-temperature anaerobic fermentation tank. The crushing unit is arranged at the input end of the hydrolysis tank to crush the crops. The high-temperature anaerobic fermentation tank is arranged at the output end of the hydrolysis tank. A double-membrane gas holder is provided at the output end of the high-temperature anaerobic fermentation tank. The biogas output port of the double-membrane gas holder is connected to the biogas purification and liquefaction system.

[0016] Preferably, the other input end of the hydrolysis tank is connected to a homogenization tank for mixing the feces.

[0017] Preferably, the biogas purification and liquefaction system includes a desulfurization unit, a decarbonization unit, a secondary boosting unit, a fine decarbonization unit, a liquefaction cold box unit and a loading unit. The desulfurization unit that performs desulfurization by dry and wet methods is connected to the biogas output port of the biogas fermentation system. The decarbonization unit is arranged at the output end of the desulfurization unit to capture CO2, and a primary boosting unit is provided between the decarbonization unit and the desulfurization unit. The secondary boosting unit is connected to the natural gas output port of the decarbonization unit, and a fine decarbonization unit is arranged at the output end of the secondary boosting unit. The output end of the fine decarbonization unit is connected to a dehydration and demercuration unit. The liquefaction cold box unit is arranged at the output end of the dehydration and demercuration unit to deep cool the natural gas, and the loading unit is arranged at the output end of the liquefaction cold box unit to load the generated gas.

[0018] Preferably, the cold input end of the liquefied cold box unit is connected to a secondary mixed refrigerant compression unit, and the input end of the mixed refrigerant compression unit is connected to a refrigerant storage and recovery unit.

[0019] Preferably, the organic fertilizer production system includes a fermentation tank unit, a secondary fermentation unit, a feeding unit, a crushing unit, a screening unit and a packaging unit. The fermentation tank unit is connected to the sludge output end of the biogas fermentation system, the output end of the fermentation tank unit is provided with a secondary fermentation unit, the output end of the secondary fermentation unit is connected to a crushing unit for crushing the fermented material through the feeding unit, and the output end of the crushing unit is connected to a screening unit and a packaging unit in sequence.

[0020] Preferably, the CO2 purification and liquefaction system includes a CO2 metering and filtration unit, a CO2 compression unit, a CO2 dehydration unit and a CO2 purification and liquefaction unit. The input port of the CO2 metering and filtration unit is connected to the CO2 analysis gas output port of the biogas purification and liquefaction system. The output end of the CO2 metering and filtration unit is provided with a CO2 dehydration unit, and a CO2 compression unit is provided between the CO2 dehydration unit and the CO2 metering and filtration unit. The output end of the CO2 dehydration unit is connected to the CO2 purification and liquefaction unit.

[0021] Preferably, the output end of the CO2 purification and liquefaction unit is connected to a CO2 storage tank for storing CO2, and the output end of the CO2 storage tank is provided with a CO2 loading unit.

[0022] Preferably, the input end of the CO2 purification and liquefaction unit is connected to a propane compression unit for providing cold energy thereto.

[0023] Preferably, the heat energy recovery system includes a solar collector, a solar hot water pump, a hot water tank, a hot water pump, an electric heater and a heat pump unit. The hot water tank is connected to one end of the biogas fermentation system through a hot water pipe. The input end of the hot water tank is provided with a solar hot water pump. One end of the solar hot water pump is provided with a solar collector. The output end of the hot water tank is provided with a hot water pump, an electric heater and a heat pump unit in sequence. The output end of the heat pump unit is connected to the biogas fermentation system.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention adopts the "biogas purification, liquefaction and carbon capture" process mode to separate and liquefy CH4, H2S and CO2 in biogas to produce liquid CH4 and CO2. During desulfurization, H2S is effectively removed by combining wet and dry methods in series. A mixed refrigerant compression unit with cold box precooling to provide cold capacity and two-stage compression can avoid the large energy consumption required for four-stage compression. Before CO2 is liquefied, it is deeply dehydrated and desulfurized first, which can effectively reduce the use of cold energy and reduce the occurrence of freezing and blockage of equipment. The process structure is simple.

[0026] (2) The “high temperature hydrolysis + aerobic bacteria” method is adopted to significantly improve the degradation rate of straw, improve the utilization rate of straw to a limited extent, avoid the use of chemical agents, and no chemical hazardous waste is generated. The high temperature constant temperature (51°C) anaerobic fermentation technology is adopted to significantly improve the killing rate of parasite eggs and shorten the fermentation time. By adjusting the ratio of straw and feces, the gas production rate and methane content per unit volume are significantly improved;

[0027] (3) The new process of "pressure swing adsorption + MDEA decarbonization" is adopted to solve the problems of the existing biogas purification processes, which mainly include water washing and membrane separation processes. The gas processing accuracy cannot meet the requirements for LNG production, the methane yield is low, and the membrane components are dependent on imports. At the same time, the new CO2 liquefaction model is combined to achieve 100% localization of technology and equipment, which is also conducive to ensuring that the methane yield is increased to more than 99%.

[0028] (4) Adopting the "solar collector + heat pump unit" process, the whole-field heat energy recovery is realized to provide heat for the biogas fermentation system, ensuring stable fermentation temperature and stable gas production;

[0029] (5) Under the action of microorganisms, the biogas residue is fermented into solid organic fertilizer using the "secondary fermentation" technology, thus maximizing the utilization of biogas residue. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the system flow of the present invention;

[0031] Figure 2 It is a schematic diagram of the biogas fermentation process of the present invention;

[0032] Figure 3 This is a schematic diagram of the biogas purification and liquefaction process of the present invention;

[0033] Figure 4 This is a schematic diagram of the CO2 purification and liquefaction process of the present invention;

[0034] Figure 5 It is a schematic diagram of the production process of organic fertilizer of the present invention;

[0035] Figure 6 This is a schematic diagram of the heat recovery system flow.

[0036] In the figure: 1. Biogas fermentation system; 2. Biomass biogas purification and liquefaction system; 3. CO2 purification and liquefaction system; 4. Organic fertilizer production system; 5. Heat recovery system; 1a. Crushing unit; 2a. Homogenization tank; 3a. Hydrolysis tank; 4a. High-temperature anaerobic fermentation tank; 5a. Double membrane gas holder; 1b. Desulfurization unit; 2b. Primary booster unit; 3b. PSA decarbonization unit; 4b. Secondary booster unit; 5b. MDEA fine decarbonization unit; 6b. Dehydration and mercury removal unit; 7b. Liquefaction cold box unit; 8b. LNG loading unit; 9b. Refrigerant storage and recovery unit; 10b, mixed refrigerant compression unit; 1c, CO2 metering and filtration unit; 2c, CO2 compression unit; 3c, CO2 dehydration unit; 4c, CO2 purification and liquefaction unit; 5c, LCO2 storage tank; 6c, LCO2 loading unit; 7c, propane compression unit; 1d, fermentation tank unit; 2d, secondary fermentation unit; 3d, feeding unit; 4d, crushing unit; 5d, screening unit; 6d, packaging unit; 1e, solar collector; 2e, solar hot water pump; 3e, hot water tank; 4e, hot water pump; 5e, electric heater; 6e, heat pump unit. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-Figure 6 The present invention provides a technical solution: a biogas fermentation, purification, liquefaction and carbon capture process, comprising:

[0039] Biogas fermentation system for high temperature fermentation of biomass 1;

[0040] The biogas purification and liquefaction system 2 is arranged at the biogas output end of the biogas fermentation system 1 to process the biogas to form LNG;

[0041] A CO2 purification and liquefaction system 3, connected to one end of the biogas purification and liquefaction system 2 to purify and form LCO2;

[0042] The organic fertilizer production system 4 is arranged at the biogas residue output end of the biogas fermentation system 1 to produce organic fertilizer;

[0043] The heat recovery system 5 is connected to one end of the biogas fermentation system 1 through a pipeline to circulate the hot water of the biogas fermentation system 1 .

[0044] Preferably, the biogas fermentation system 1 includes a crushing unit 1a, a hydrolysis tank 3a and a high-temperature anaerobic fermentation tank 4a, the crushing unit 1a is arranged at the input end of the hydrolysis tank 3a to crush the crops, the high-temperature anaerobic fermentation tank 4a is arranged at the output end of the hydrolysis tank 3a, and the output end of the high-temperature anaerobic fermentation tank 4a is provided with a double-membrane gas cabinet 5a, and the biogas output port of the double-membrane gas cabinet 5a is connected to the biogas purification and liquefaction system 2.

[0045] Preferably, the other input end of the hydrolysis tank 3a is connected to a homogenization tank 2a for mixing feces.

[0046] Preferably, the biogas purification and liquefaction system 2 includes a desulfurization unit 1b, a PSA decarbonization unit 3b, a secondary booster unit 4b, an MDEA fine decarbonization unit 5b, a liquefaction cold box unit 7b and an LNG loading unit 8b. The desulfurization unit 1b for desulfurization by dry and wet methods is connected to the biogas output port of the biogas fermentation system 1. The PSA decarbonization unit 3b is arranged at the output end of the desulfurization unit 1b to capture CO2, and there is a gap between the PSA decarbonization unit 3b and the desulfurization unit 1b. The first-stage boosting unit 2b, the second-stage boosting unit 4b is connected to the natural gas output port of the PSA decarbonization unit 3b, and the output end of the second-stage boosting unit 4b is provided with an MDEA fine decarbonization unit 5b, the output end of the MDEA fine decarbonization unit 5b is connected with a dehydration and demercuration unit 6b, the liquefaction cold box unit 7b is provided at the output end of the dehydration and demercuration unit 6b to deep cool the natural gas, and the LNG loading unit 8b is provided at the output end of the liquefaction cold box unit 7b to load the generated LNG.

[0047] Preferably, the cooling input end of the liquefied cold box unit 7b is connected to a secondary mixed refrigerant compression unit 10b, and the input end of the mixed refrigerant compression unit 10b is connected to a refrigerant storage and recovery unit 9b.

[0048] Preferably, the organic fertilizer production system 4 includes a fermentation tank unit 1d, a secondary fermentation unit 2d, a feeding unit 3d, a crushing unit 4d, a screening unit 5d and a packaging unit 6d, the fermentation tank unit 1d is connected to the sludge output end of the biogas fermentation system 1, the output end of the fermentation tank unit 1d is provided with a secondary fermentation unit 2d, the output end of the secondary fermentation unit 2d is connected to a crushing unit 4d for crushing the fermented material through the feeding unit 3d, and the output end of the crushing unit 4d is sequentially connected to the screening unit 5d and the packaging unit 6d.

[0049] Preferably, the CO2 purification and liquefaction system 3 includes a CO2 metering and filtration unit 1c, a CO2 compression unit 2c, a CO2 dehydration unit 3c and a CO2 purification and liquefaction unit 4c, the input port of the CO2 metering and filtration unit 1c is connected to the CO2 analysis gas output port of the biogas purification and liquefaction system 2, the output end of the CO2 metering and filtration unit 1c is provided with a CO2 dehydration unit 3c, and a CO2 compression unit 2c is provided between the CO2 dehydration unit 3c and the CO2 metering and filtration unit 1c, and the output end of the CO2 dehydration unit 3c is connected to the CO2 purification and liquefaction unit 4c.

[0050] Preferably, the output end of the CO2 purification and liquefaction unit 4c is connected to an LCO2 storage tank 5c for storing LCO2, and the output end of the LCO2 storage tank 5c is provided with an LCO2 loading unit 6c.

[0051] Preferably, the input end of the CO2 purification and liquefaction unit 4c is connected to a propane compression unit 7c for providing cold energy thereto.

[0052] Preferably, the heat energy recovery system 5 includes a solar collector 1e, a solar hot water pump 2e, a hot water tank 3e, a hot water pump 4e, an electric heater 5e and a heat pump unit 6e. The hot water tank 3e is connected to one end of the biogas fermentation system 1 through a hot water pipe. The input end of the hot water tank 3e is provided with a solar hot water pump 2e. One end of the solar hot water pump 2e is provided with a solar collector 1e. The output end of the hot water tank 3e is provided with a hot water pump 4e, an electric heater 5e and a heat pump unit 6e in sequence. The output end of the heat pump unit 6e is connected to the biogas fermentation system 1.

[0053] The process steps of the present invention are:

[0054] Step A: The straw crushed by the crushing unit 1a is mixed with the feces from the homogenization tank 2a and sent to the hydrolysis tank 3a. After being hydrolyzed by the bacteria at high temperature for a certain period of time under an aerobic environment, it is sent to the high-temperature anaerobic fermentation tank 4a. After the mixed materials are anaerobic fermented at high temperature of 51°C, the generated biogas is temporarily stored in the double-membrane gas cabinet 5a and then sent to the desulfurization unit 1b. The substrate sludge of the high-temperature anaerobic fermentation tank 4a is sent to the fermentation tank unit 1b of the organic fertilizer production system 4;

[0055] Step B: The biogas enters the desulfurization unit 1b and is first subjected to wet desulfurization and then dry desulfurization to remove H2S concentration to ≤6mg / Nm3, and then is pressurized and cooled by the first-stage booster unit 2b, and then enters the PSA decarbonization unit 3b together with the non-condensable gas from the CO2 purification and liquefaction unit 4c. After rough decarbonization by the PSA decarbonization unit 3b, biogas is obtained, and the CO2 content of the biogas is ≤3%;

[0056] Step C: After the biogas is pressurized and cooled by the secondary pressurization unit 4b, it is sent to the MDEA fine decarbonization unit 5b and the dehydration and mercury removal unit 6b to remove CO2, H2O and Hg in sequence (concentration index: CO2≤50ppm, H2O≤1ppm, Hg≤0.01μg / m 3 ), enters the liquefied cold box unit 7b to deep cool the biogas to -162°C (before throttling), and then is sent to the LNG loading unit 8b. After throttling, the gas phase refrigerant and the liquid phase refrigerant are respectively reheated by the liquefied cold box unit 7b and flow back to the entrance of the mixed refrigerant compressor unit 10b;

[0057] Step D: The CO2 analysis gas produced by the PSA decarbonization unit 3b is first metered and filtered by the CO2 metering and filtering unit 1c, and then sent to the CO2 compression unit 2c for pressurization and cooling, and then deeply dehydrated by the CO2 dehydration unit 3c, and sent to the CO2 purification and liquefaction unit 4c for purification and liquefaction to obtain the LCO2 product, which is sent to the LCO2 storage tank 5c, and finally loaded and transported by the LCO2 loading unit 6c, while the non-condensable gas produced by the CO2 purification and liquefaction unit 4c flows back to the PSA decarbonization unit 3b.

[0058] Step E: The substrate sludge from the high-temperature anaerobic fermentation tank 4a is proportioned with auxiliary materials such as plant straw and fermentation bacteria according to the formula requirements, and after mixing, it is evenly sent to the fermentation tank unit 1d by a forklift. After turning the pile 1-2 times, the oxygen provided by the contact between the material and the air during turning the pile is continuously aerobic fermented, so that the fermented material is quickly decomposed, sterilized, deodorized, dehydrated and dried. The fermentation cycle is 10-20 days. After the fermentation is completed, the material is sent to the secondary fermentation unit 2d for stacking and fermentation. After further decomposition and dehydration, it is sequentially passed through the feeding unit 3d, the crushing unit 4d, the screening unit 5d and the powder fertilizer packaging unit 6d to obtain a powdered finished organic fertilizer.

[0059] Step F: The hot water in the hot water tank 3e is transported to the solar collector 1e through the solar hot water pump 2e, and after being heated, it flows back to the hot water tank 3e, and then is transported to the electric heater 5e through the hot water pump 4e, and then transported to the heat pump unit 6e; using circulating water as a carrier, the waste heat of the biomass biogas purification and liquefaction system and the CO2 purification and liquefaction system is transported to the heat pump unit 6e. Under the action of the heat pump unit 6e, the hot water is heated to 65-75°C, and after being transported to the biogas fermentation system 1, it flows back to the hot water tank 3e.

[0060] The principle of biogas liquefaction and carbon capture of the present invention is described as follows:

[0061] Biogas desulfurization principle:

[0062] In desulfurization, the principle of wet desulfurization is to use Fe in the desulfurizer 3+ It undergoes redox reaction with H2S, and the chemical reaction equation is as follows:

[0063] H2S(g)+2Fe 3+ (aq)→2H + (aq)+$ + +Fe 2+ (aq)

[0064] The principle of desulfurization rich liquid regeneration is to use oxygen in the air to 2+ Oxidized to Fe 3+ , the chemical reaction equation is as follows:

[0065] 1 / 2O2(g)+H2O(I)+2Fe 2+ (aq)→2OH - (I)+2Fe 3+ (aq)

[0066] Dry desulfurization is to fill the desulfurizer in the filling tower. After the biogas and the desulfurizer come into contact, the H2S in it is removed. The reaction formula is as follows:

[0067] Fe2O3·4H2O+H2S→Fe2S3+4H2O

[0068] Fe2S3+3 / 2O2+3H2O→Fe2O3·H2O++2H2O+3S

[0069] PSA decarbonization principle:

[0070] Pressure swing adsorption (PSA) technology uses the property that the equilibrium adsorption capacity of the adsorbent increases with the increase of the partial pressure of the component to perform pressurized adsorption and reduced pressure desorption. The cyclic change of pressure is the driving force for separation, so that one or more components can be concentrated or purified.

[0071] MDEA decarbonization process principle:

[0072] MDEA is N-methyldiethanolamine, with the molecular formula CH3-N(CH2CH2OH)2, molecular weight 119.2, boiling point 246-248℃, flash point 260℃, freezing point -21℃, latent heat of vaporization 519.16KJ / Kg, miscible with water and alcohol, slightly soluble in ether. Under certain conditions, it has a strong absorption capacity for acidic gases such as CO2, and has low reaction heat, low desorption temperature, stable chemical properties, and no degradation. Pure MDEA solution does not react with CO2, but its aqueous solution can react with CO2 as follows:

[0073] CO2+H2O==H++HCO3 - (1b)

[0074] H++R2NCH3==R2NCH3H + (2b)

[0075] Formula (1b) is controlled by the liquid film, and the reaction rate is extremely slow. Formula (2b) is an instantaneous reversible reaction. Therefore, formula (1b) is the control step of MDEA absorbing CO2. In order to speed up the absorption rate, after adding 1-5% of the activator DEA (RNH) to the MDEA solution, the reaction proceeds as follows:

[0076] R2 / NH+CO2==R2 / NCOOH(3b)

[0077] R2 / NCOOH+R2NCH3+H2O==R2 / NH+R2CH3NH+HCO3 - (4b)

[0078] (3b)+(4b):

[0079] R2NCH3+CO2+H2O==R2CH3NH+HCO3 - (5b)

[0080] From formula (3b) to (5b), it can be seen that the activator absorbs CO2 and transfers CO2 to the liquid phase, which greatly accelerates the reaction rate, and MDEA is regenerated. The MDEA molecule contains a tertiary amine group, which generates bicarbonate after absorbing CO2. The heat required for heating regeneration is much lower than that of carbamate generated by primary and secondary amines.

[0081] Principles of natural gas dehydration and CO2 dehydration:

[0082] The principle of molecular sieve membrane dehydration is to use the regular pores of molecular sieve to achieve selective adsorption of water. Molecular sieve is a microporous crystal composed of a certain substance, and there are some pores and gaps in its structure. The size and shape of these pores and gaps are very regular, forming a molecular "screener" effect.

[0083] Principle of natural gas liquefaction:

[0084] The principle of natural gas liquefaction is to obtain cold energy by pressurizing and throttling the refrigerant to deep cool the gas phase natural gas. The MRC refrigeration process is adopted. The liquefied refrigerant mainly contains nitrogen, CH4, ethylene, isobutane and other components mixed in a certain proportion.

[0085] Principle of CO2 purification and liquefaction:

[0086] The CO2 liquefaction and purification system uses cryogenic distillation. This means that the difference in volatility and boiling point of each component in the liquid mixture is used to partially vaporize the liquid mixture multiple times and then partially condense it, so as to separate the components contained therein, thereby purifying the substance and finally obtaining a qualified product.

[0087] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A biogas fermentation, purification, liquefaction and carbon capture process, characterized in that: include: Biogas fermentation system for high temperature fermentation of biomass (1); A biogas purification and liquefaction system (2) is arranged at the biogas output end of the biogas fermentation system (1) to process the biogas to form LNG; A CO2 purification and liquefaction system (3) connected to one end of the biogas purification and liquefaction system (2) to purify and form LCO2; An organic fertilizer production system (4) is arranged at the biogas residue output end of the biogas fermentation system (1) to produce organic fertilizer; The heat energy recovery system (5) is connected to one end of the biogas fermentation system (1) through a pipeline to circulate the hot water of the biogas fermentation system (1).

2. A biogas fermentation, purification, liquefaction and carbon capture process according to claim 1, characterized in that: The biogas fermentation system (1) comprises a crushing unit (1a), a hydrolysis tank (3a) and a high-temperature anaerobic fermentation tank (4a), wherein the crushing unit (1a) is arranged at the input end of the hydrolysis tank (3a) to crush crops, the high-temperature anaerobic fermentation tank (4a) is arranged at the output end of the hydrolysis tank (3a), and a double-membrane gas cabinet (5a) is arranged at the output end of the high-temperature anaerobic fermentation tank (4a), and the biogas output port of the double-membrane gas cabinet (5a) is connected to the biogas purification and liquefaction system (2).

3. A biogas fermentation, purification, liquefaction and carbon capture process according to claim 2, characterized in that: The other input end of the hydrolysis tank (3a) is connected to a homogenization tank (2a) for mixing feces.

4. The biogas fermentation, purification, liquefaction and carbon capture process according to claim 1, characterized in that: The biogas purification and liquefaction system (2) comprises a desulfurization unit (1b), a PSA decarbonization unit (3b), a secondary booster unit (4b), an MDEA fine decarbonization unit (5b), a liquefaction cold box unit (7b) and an LNG loading unit (8b). The desulfurization unit (1b) for desulfurization by dry and wet methods is connected to the biogas output port of the biogas fermentation system (1). The PSA decarbonization unit (3b) is arranged at the output end of the desulfurization unit (1b) to capture CO2, and there is a gas exchanger between the PSA decarbonization unit (3b) and the desulfurization unit (1b). A primary boosting unit (2b), the secondary boosting unit (4b) is connected to the natural gas output port of the PSA decarbonization unit (3b), and the output end of the secondary boosting unit (4b) is provided with an MDEA fine decarbonization unit (5b), the output end of the MDEA fine decarbonization unit (5b) is connected to a dehydration and demercuration unit (6b), the liquefaction cold box unit (7b) is provided at the output end of the dehydration and demercuration unit (6b) to deep cool the natural gas, and the LNG loading unit (8b) is provided at the output end of the liquefaction cold box unit (7b) to load the generated LNG.

5. A biogas fermentation, purification, liquefaction and carbon capture process according to claim 4, characterized in that: The cold input end of the liquefied cold box unit (7b) is connected to a secondary mixed refrigerant compression unit (10b), and the input end of the mixed refrigerant compression unit (10b) is connected to a refrigerant storage and recovery unit (9b).

6. The biogas fermentation, purification, liquefaction and carbon capture process according to claim 1, characterized in that: The organic fertilizer production system (4) comprises a fermentation tank unit (1d), a secondary fermentation unit (2d), a feeding unit (3d), a crushing unit (4d), a screening unit (5d) and a packaging unit (6d); the fermentation tank unit (1d) is connected to the biogas residue output end of the biogas fermentation system (1); the output end of the fermentation tank unit (1d) is provided with a secondary fermentation unit (2d); the output end of the secondary fermentation unit (2d) is connected to a crushing unit (4d) for crushing the fermented product through the feeding unit (3d); and the output end of the crushing unit (4d) is connected to a screening unit (5d) and a packaging unit (6d) in sequence.

7. The biogas fermentation, purification, liquefaction and carbon capture process according to claim 1, characterized in that: The CO2 purification and liquefaction system (3) comprises a CO2 metering and filtering unit (1c), a CO2 compression unit (2c), a CO2 dehydration unit (3c) and a CO2 purification and liquefaction unit (4c); the input port of the CO2 metering and filtering unit (1c) is connected to the CO2 analysis gas output port of the biogas purification and liquefaction system (2); the output end of the CO2 metering and filtering unit (1c) is provided with a CO2 dehydration unit (3c); a CO2 compression unit (2c) is provided between the CO2 dehydration unit (3c) and the CO2 metering and filtering unit (1c); and the output end of the CO2 dehydration unit (3c) is connected to the CO2 purification and liquefaction unit (4c).

8. A biogas fermentation, purification, liquefaction and carbon capture process according to claim 7, characterized in that: The output end of the CO2 purification and liquefaction unit (4c) is connected to an LCO2 storage tank (5c) for storing LCO2, and the output end of the LCO2 storage tank (5c) is provided with an LCO2 loading unit (6c).

9. A biogas fermentation, purification, liquefaction and carbon capture process according to claim 8, characterized in that: The input end of the CO2 purification and liquefaction unit (4c) is connected to a propane compression unit (7c) for providing cold energy thereto.

10. The biogas fermentation, purification, liquefaction and carbon capture process according to claim 1, characterized in that: The heat energy recovery system (5) comprises a solar collector (1e), a solar hot water pump (2e), a hot water tank (3e), a hot water pump (4e), an electric heater (5e) and a heat pump unit (6e); the hot water tank (3e) is connected to one end of the biogas fermentation system (1) via a hot water pipe; the input end of the hot water tank (3e) is provided with a solar hot water pump (2e); one end of the solar hot water pump (2e) is provided with a solar collector (1e); the output end of the hot water tank (3e) is provided with a hot water pump (4e), an electric heater (5e) and a heat pump unit (6e) in sequence; the output end of the heat pump unit (6e) is connected to the biogas fermentation system (1).

Images