WO2016082269A1

WO2016082269A1 - Method for preparing bio-methane by purifying biogas

Info

Publication number: WO2016082269A1
Application number: PCT/CN2014/094784
Authority: WO
Inventors: 杨祝红; 丁键; 陈义峰; 李峥; 马春燕; 刘畅; 陆小华; 谢瑞杰; 袁圣娟
Original assignee: 南京工业大学
Priority date: 2014-11-28
Filing date: 2014-12-24
Publication date: 2016-06-02
Also published as: CN104437008A

Abstract

Provided is a method for preparing bio-methane by purifying biogas. The method comprises: pressurizing the biogas, introducing the pressurized biogas into an absorption tower from the lower part of the absorption tower till the pressure in the tower reaches 0.3 MPa to 20 MPa, continuously introducing the biogas, spraying an absorbent into the tower by means of a nozzle on the upper part of the absorption tower, and enabling the biogas and the absorbent to be in sufficient contact to remove carbon dioxide in the biogas, wherein the pressure in the absorption tower is 0.3 MPa to 20 MPa, and the flow ratio of the absorbent to the biogas is 8-100 kg/h:1 Nm³/h; the absorbent is an aqueous solution which takes at least one of choline-based deep eutectic solvents or imidazole ionic liquids as an active ingredient, and the mass fraction of the active ingredient is 5% to 90%.

Description

Method for purifying and purifying biogas to prepare biomethane

Technical field

The invention belongs to the field of gas separation, and relates to a method for purifying and purifying biogas to prepare biomethane, in particular to using a choline eutectic solvent or at least one of an imidazole ionic liquid as an active ingredient to purify and purify biogas to prepare a living organism. The method of methane.

Background technique

Biogas is a safe, clean and renewable energy source. Its main component is methane, about 45-60%, carbon dioxide, about 40-55%, and a small amount of water, hydrogen sulfide, nitrogen, oxygen and other trace gases. Biogas can be obtained by anaerobic fermentation of poor biomass (straw, human and animal waste, domestic garbage, etc.). Biogas can be obtained by purifying and purifying biogas (methane content is more than 97%), which can be widely used in vehicles. The use of energy, chemical raw materials, etc., is an important means to improve China's energy structure and solve environmental problems.

The biogas purification technologies widely used at present are mainly water washing method, alcohol amine method and membrane separation. The equipment cost of the water washing method is too high, and the microorganisms in the absorption tower are easy to breed microorganisms; the energy consumption of the absorbent of the alcohol amine method is higher, and the corrosion of the equipment is also serious; the methane loss of the membrane separation method is relatively large, and the requirements for the preliminary treatment are required. High and large-scale have certain technical difficulties.

Chinese patent application CN104083989 A discloses a method for purifying and purifying biogas pressure water, the main equipments are: a pressurizing device, a buffer tank, a water washing tower, a analytical tower, a dryer, and the method utilizes the solubility of carbon dioxide, hydrogen sulfide and methane in water. Differently, a water washing tower is constructed according to a physical adsorption process, and carbon dioxide and hydrogen sulfide gas in the biogas are removed by pressure water washing. The absorption efficiency is not high, and the investment in equipment after industrial amplification is large.

Chinese patent application CN102059037 A discloses a process for purifying carbon dioxide from natural gas tail gas, using MEA (ethanolamine) lean liquid to absorb carbon dioxide, and then releasing carbon dioxide, converting carbon dioxide in tail gas into liquid carbon dioxide for industrial production. . However, the regeneration energy consumption of the absorbent in the method is high.

Summary of the invention

The object of the present invention is to provide a method for purifying and purifying biogas to produce biomethane, which has the advantages of high cost of the water washing method and high energy consumption of the alcohol amine method absorbent regeneration in the prior art, and the method can improve the absorption effect while improving the absorption effect. Reduce the regeneration energy consumption of the absorbent, thereby reducing the overall biomethane production cost.

The object of the invention is achieved by the following technical solutions:

A method for purifying and purifying biogas to prepare biomethane comprises the following steps:

(1) The biogas is pressurized to 0.3 MPa to 20 MPa;

(2) The pressure of the pressurized biogas from the lower part of the absorption tower into the absorption tower to the absorption tower reaches 0.3 MPa. 20MPa, and then continue to pass the biogas, while spraying the absorbent into the tower through the nozzle at the upper part of the absorption tower, so that the biogas and the absorbent are in full contact to remove carbon dioxide in the biogas, and the carbon dioxide-removing gas is dried to obtain the bio-methane product gas;

Wherein, the pressure in the absorption tower is 0.3 MPa to 20 MPa, and the ratio of the flow rate of the absorbent to the biogas is 8 to 100 kg/h: 1 Nm ³ /h; the absorbent is a choline eutectic solvent Or an aqueous solution containing at least one of an imidazole-based ionic liquid as an active ingredient, wherein the mass fraction of the active ingredient in the absorbent is from 5 to 90%.

As a further aspect of the method for purifying and purifying biogas to prepare biomethane according to the present invention, the absorbent which absorbs carbon dioxide in step (2) enters a flash tank for regeneration treatment, and the pressure in the flash tank is 0.2-0.5 MPa, and the temperature is normal temperature (15). ～30°C); when the pressure difference between the absorption tower pressure and the flash tank is ≥0.5MPa, the absorbent that absorbs carbon dioxide is regenerated in a flash tank to remove carbon dioxide, and the regeneration efficiency of the absorbent reaches 95% or more; or when the absorption tower When the pressure difference between the pressure and the flash tank is <0.5 MPa, the absorbent which absorbs carbon dioxide is regenerated in the flash tank, and then enters the analytical tower for thermal regeneration treatment to remove carbon dioxide, wherein the pressure in the analytical column is 0.1 MPa and the temperature is 50. At ~95 ° C, the regeneration efficiency of the absorbent reaches 95% or more.

In the step (1), according to the content of hydrogen sulfide in the biogas, it is determined whether the hydrogen sulfide removal treatment needs to be performed first. When the content of hydrogen sulfide in the biogas is ≥80 ppm, the biogas is removed after the hydrogen sulfide treatment in the desulfurization tower. The pressurization system is pressurized; when the content of hydrogen sulfide in the biogas is <80 ppm, the biogas is directly pressurized by the pressurization system.

In the step (2), the temperature in the absorption tower is normal temperature (15 to 30 ° C); the pressure in the absorption tower is preferably 0.6 MPa to 2 MPa, further preferably 1.2 MPa to 2 MPa; The ratio of the flow rate of the agent to the biogas is preferably 15 to 40 kg/h: 1 Nm ³ /h, and more preferably 15 to 30 kg/h: 1 Nm ³ /h.

The mass fraction of the active ingredient in the absorbent is preferably from 15% to 50%. The active ingredient of the absorbent is at least one of a choline eutectic solvent or an imidazole ionic liquid; the mass ratio of the choline eutectic solvent to the imidazole ionic liquid in the absorbent is 1: 0 to 4.

The imidazole ionic liquid is in the form of [C _n mim][X], C _n represents a linear alkane (n=1, 2, 3), and X is F (fluorine), Cl (chlorine), Br (bromine ), I (iodine), BF ₄ (tetrafluoroborate), PF ₆ (hexafluorophosphate) or Tf ₂ N (bistrifluoromethylimidazolium); the choline eutectic solvent is A Formed after mixing with B, A is ChCl (choline chloride), [Choline] [Pro] (choline valine), [Choline] [Gly] (choline glycine), [Choline] [Ala] (biliary One of [alkaline alanine), [Choline] [Lys] (choline lysine), and B is at least one of urea (urea), EG (ethylene glycol) or PEG (polyethylene glycol) The molar ratio of A and B is from 0.1 to 5:1.

The methane finished gas has CH ₄ ≥ 95%, CO ₂ ≤ 4%, and H ₂ S ≤ 40 ppm.

The invention also provides a system for purifying and purifying biogas to prepare biomethane, comprising: desulfurization tank, gas-liquid separation tank I, pressurization system, buffer tank, absorption tower, flash tank, analytical tower, absorbent circulating pump , absorbent tank, gas and liquid The tank I and the drying tank are connected; the outlet of the desulfurization tank is connected to the inlet of the gas-liquid separation tank I, and the outlet of the gas-liquid separation tank I is connected to the inlet of the lower portion of the buffer tank via a pressurization system, the buffer The outlet of the upper part of the tank is connected with the inlet of the lower part of the absorption tower, and the upper part of the absorption tower is provided with at least one layer of nozzles, and the outlet of the top of the absorption tower is connected with the methane collecting device through the gas-liquid separation tank I and the drying tank; the absorption The liquid outlet at the bottom of the tower is connected to the absorbent inlet of the flash tank, the liquid outlet at the bottom of the flash tank is connected to the absorbent tank, and the other liquid outlet in the lower part of the flash tank is connected to the inlet of the upper portion of the analytical tower. The top of the tower is provided with an exhaust port, and the liquid outlet at the bottom of the analytical tower is connected to the absorbent tank; the absorbent tank is connected to the nozzle of the absorption tower via an absorbent circulation pump.

The system for purifying and purifying biogas to produce biomethane has at least two parallel dryers.

The upper part of the absorption tower is provided with at least one layer of nozzle for spraying the absorbent; the top of the absorption tower is provided with a mist eliminator; and the biogas inlet line of the absorption tower section is provided with a check valve, and the absorption liquid in the absorption tower is introduced into the liquid A fine adjustment valve is arranged on the pipeline; a liquid outlet at the bottom of the absorption tower is provided with a regulating valve; and an exhaust valve is arranged at an air outlet of the absorption tower.

The top of the flash tank is provided with an air outlet and an exhaust port, and the flash tank is connected to the inlet of the gas-liquid separation tank I through an air outlet, and a check valve is arranged on the air outlet of the flash tank, and the flash tank is provided. The exhaust port is provided with an exhaust valve for exhausting the air. According to the content of the component of the gas generated by the regeneration of the absorbent in the flash tank, it is determined whether it is necessary to mix the regenerated gas and the raw material biogas for purification and purification.

The liquid outlet line at the bottom of the flash tank and the other liquid outlet line at the lower part of the flash tank are each provided with a one-way valve.

The advantages of the present invention compared to the prior art:

The invention adopts a method for purifying and purifying biomethane by purifying biogas, and uses an ionic liquid (choline eutectic solvent, imidazole ionic liquid) aqueous solution as an absorbent, and the ionic liquid has good stability and greatly dissolves the gas. It can effectively remove carbon dioxide and hydrogen sulfide gas from biogas, and the purity of methane in the obtained product gas can reach 95%. The absorbent can be regenerated, the regeneration efficiency is over 95%, the energy consumption of the absorbent is low, the equipment is easy to operate, and the investment is low.

DRAWINGS

Figure 1 is a system for purifying and purifying biogas to prepare biomethane;

Figure 1, 1-desulfurization tower, 2-gas liquid separation tank I, 3-pressurization system, 4-buffer tank, 5-absorption tower, 6-flash tank, 7-analysis tower, 8-absorption and circulation pump , 9-absorbent storage tank, 10-gas liquid separation tank II, 11 - drying tank I, 12 - drying tank II.

Figure 2 shows the effect of the pressure in the absorption tower and the content of the active ingredient in the absorbent on the preparation of biomethane.

Figure 3 is a graph showing the effect of the ratio of the flow rate of the absorbent to the biogas on the preparation of biomethane.

Detailed ways

The invention will now be further described with reference to the accompanying drawings and embodiments.

As shown in FIG. 1 , a system for purifying and purifying biogas to prepare biomethane includes: desulfurization tank 1, gas-liquid separation tank I2, pressurization system 3, buffer tank 4, absorption tower 5, flash tank 6, and analysis a tower 7, an absorbent circulation pump 8, an absorbent tank 9, a gas-liquid separation tank I10, and a drying tank; the outlet of the desulfurization tank 1 is connected to the inlet of the gas-liquid separation tank I2, and the gas-liquid separation tank I2 The outlet is connected to the inlet of the lower portion of the buffer tank 4 via the pressurization system 3, the outlet of the upper portion of the buffer tank 4 is connected to the inlet of the lower portion of the absorption tower 5, and the upper portion of the absorption tower is provided with at least one layer of nozzles, and the absorption tower 5 The gas outlet of the top is connected by a gas-liquid separation tank I10, two parallel drying tanks I11, a drying tank II12 and a methane collecting device; the liquid outlet at the bottom of the absorption tower 5 is connected with the absorbent inlet of the flash tank 6 The liquid outlet at the bottom of the flash tank 6 is connected to the absorbent tank 9, and the other liquid outlet at the lower portion of the flash tank 6 is connected to the inlet of the upper portion of the analytical tower 7. The top of the analytical tower 7 is provided with an outlet, and the bottom of the analytical tower 7 Liquid outlet is connected to the absorbent tank 9; Collector tank 9 via the circulation pump 8 is connected to the absorber tower nozzles.

The upper part of the absorption tower 5 is provided with at least one layer of nozzles for spraying the absorbent; the top of the absorption tower 5 is provided with a mist eliminator; and the biogas inlet line of the absorption tower 5 is provided with a check valve for absorption in the absorption tower 5 A liquid regulating valve is provided on the liquid inlet pipe; a liquid outlet at the bottom of the absorption tower 5 is provided with a regulating valve; and an exhaust valve is arranged at an air outlet of the absorption tower 5.

The liquid outlet line at the bottom of the flash tank 6 and the other liquid outlet line at the lower portion of the flash tank 6 are each provided with a check valve.

The top of the flash tank 6 is provided with an air outlet and an exhaust port, and the flash tank 6 is connected to the inlet of the gas-liquid separation tank I2 via an air outlet, and a check valve is arranged on the air outlet of the flash tank 6. The exhaust port of the flash tank 6 is provided with an exhaust valve for exhausting the air.

During operation, the biogas output from the biogas storage tank determines whether it needs to be removed from the desulfurization tank 1 according to the hydrogen sulfide content, and the biogas is pressurized to 0.3 MPa to 20 MPa by the pressurization system 3, and then passed through the buffer tank 4 and the self-absorption tower 5 The lower part of the inlet into the absorption tower 5 to the pressure in the tower reaches 0.3 MPa to 20 MPa, and then the biogas is continuously introduced, and the absorbent is sprayed into the tower through the nozzle at the upper part of the absorption tower 5, in which the pressure in the tower is maintained. 0.3MPa～20MPa, temperature 15～30°C, the biogas is fully contacted with the absorbent to remove carbon dioxide in the biogas, and the carbon dioxide-removing gas is taken from the gas outlet of the top of the absorption tower 5 through the gas-liquid separation tank I10 and two parallel drying tanks. I11, drying tank II12, finally sent to the methane collecting device as methane product gas; the absorbent that absorbs carbon dioxide is sent from the liquid outlet at the bottom of the absorption tower 5 to the flash tank 6 (pressure is 0.2-0.5 MPa, temperature is 15-30 °C) performing regeneration treatment, when the pressure difference between the pressure of the absorption tower 5 and the flash tank 6 is ≥0.5 MPa, the absorbent which absorbs carbon dioxide is regenerated in the flash tank 6 to remove carbon dioxide; when the pressure and flash of the absorption tower 5 When the pressure difference of the tank 6 is <0.5 MPa, the absorbent which has absorbed carbon dioxide is regenerated in the flash tank 6, and then enters the analysis tower 7 for thermal regeneration treatment to remove carbon dioxide, wherein the pressure in the analytical column 7 is 0.1 MPa, and the temperature is 50. ~95 ° C. The regenerated treatment absorbent is sent to the absorbent tank 9 and sent to the absorption tower 5 by the absorbent circulation pump 8.

Example 1

Biogas (methane 55.1%, carbon dioxide 44.6%, hydrogen sulfide 2547ppm) was removed from the sulfurization tank 1 by hydrogen sulfide, and the hydrogen sulfide-removing biogas (methane 55.1%, carbon dioxide 44.6%, hydrogen sulfide 83 ppm) was pressurized by the pressurization system 3 to 0.8MPa, the pressurized biogas is passed into the absorption tower 5 from the lower part of the absorption tower 5 through the buffer tank 4 at a flow rate of 5Nm ³ /h until the pressure in the tower reaches 0.8 MPa, and then the biogas is continuously introduced at the same flow rate, and at the same time The absorbent (5% by weight of choline chloride and urea solution, choline chloride and urea in a molar ratio of 1:2) is delivered to the absorption tower 5 at a flow rate of 100 kg/h, and is sprayed from the nozzle in the upper part of the column. In the tower, in the process, the pressure in the tower is maintained at 0.8 MPa, the temperature is 25 to 30 ° C, the biogas is sufficiently contacted with the absorbent to remove carbon dioxide in the biogas, and the carbon dioxide-removing gas is dried to obtain the bio-methane product gas, to the living organism. Component analysis of methane product gas.

The absorbent from the bottom of the absorption tower 5 is analyzed and regenerated by a flash tank 6 (pressure: 0.4 MPa, temperature: 25 to 30 ° C), and an analytical tower 7 (pressure: 0.1 MPa, temperature: 70 ° C), and the regenerated absorbent is transported to the absorption. The agent tank 9 is reused, and the absorbent regeneration efficiency is 95% or more.

Example 2

The effect of the pressure in the absorption tower and the content of the active ingredient in the absorbent on the preparation of biomethane was investigated.

1. As shown in Table 1, when using a mass fraction of 5% absorbent (choline chloride and urea aqueous solution, the molar ratio of choline chloride to urea is 1:2), the pressure in the absorption tower is used to prepare biomethane. The other conditions are the same as those in the first embodiment.

Table 1 Effect of 5% mass fraction of absorbent on the preparation of biomethane under different pressure conditions in the absorption tower

2. As shown in Table 2, when using a mass fraction of 15% absorbent (choline chloride and urea solution, the molar ratio of choline chloride to urea is 1:2), the pressure in the absorption tower is used to prepare biomethane. The other conditions are the same as those in the first embodiment.

Table 2 Effect of 15% mass fraction of absorbent on the preparation of biomethane under different pressure conditions in the absorption tower

3. As shown in Table 3, when using a mass fraction of 30% absorbent (choline chloride and urea solution, the molar ratio of choline chloride to urea is 1:2), the pressure in the absorption tower is used to prepare biomethane. The other conditions are the same as those in the first embodiment.

Table 3 Effect of 30% mass fraction of absorbent on the preparation of biomethane under different pressure conditions in the absorption tower

4. As shown in Table 4, when using a mass fraction of 50% absorbent (choline chloride and urea solution, the molar ratio of choline chloride to urea is 1:2), the pressure in the absorption tower is used to prepare biomethane. The other conditions are the same as those in the first embodiment.

Table 4 Effect of 50% mass fraction of absorbent on the preparation of biomethane under different pressure conditions in the absorption tower

According to Table 1-4 and Figure 2, when the pressure in the absorption tower is constant, the methane content in the methane product gas increases first and then decreases as the content of the active ingredient in the absorbent (5% to 50% by mass) increases. The trend is better in the mass fraction of 15% to 50%. When the mass fraction is 15%, the methane content is the highest, indicating that the absorption of carbon dioxide is better when the mass fraction of the active ingredient in the absorbent is 15% to 50%; When the content of the active ingredient in the absorbent is constant, as the pressure increases, the methane content in the methane product gas increases with the increase of the pressure. In combination with the device provided by the present invention, when the pressure reaches a certain amount, the absorption tower is enlarged. The internal pressure has little effect on the methane content. In summary, when the pressure in the absorption tower is 0.8-2.0 MPa, especially 1.2 MPa-2.0 MPa, the biogas is purified and purified by using an absorbent having a mass fraction of 15% to 50%, and CH ₄ ≥ 95 can be obtained. %, CO ₂ ≤ 4%, H ₂ S ≤ 40 ppm of methane product gas.

Example 3

The biogas flow rate is 4Nm ³ /h, the absorption pressure in the absorption tower is 1MPa, the mass fraction is 30% of the absorbent (choline chloride and urea aqueous solution, the molar ratio of choline chloride to urea is 1:2), other conditions and In the same manner as in Example 1, the effects of the absorbent flow rates of 40 kg/h, 60 kg/h, 80 kg/h, 100 kg/h, 120 kg/h, 150 kg/h, and 160 kg/h on the preparation of biomethane were examined.

Table 5 Effect of different absorbent flow conditions on the preparation of biomethane

According to Table 5 and Figure 3, when the biogas flow rate and the pressure in the absorption tower are constant, the biogas is purified by using an absorbent with a mass fraction of 30%, when the flow rate of the absorbent is 40-160 kg/h, along with the flow rate of the absorbent. Increasing, the methane content in the methane product gas increases accordingly, and when the absorbent flow rate is 60-160 kg/h (the ratio of the absorbent flow rate to the biogas flow rate is 15 to 40 kg/h: 1 Nm ³ /h), the methane content is Above 95%, but when the absorbent flow rate reaches 120 kg / h (the ratio of the absorbent flow rate to the biogas flow rate is 30 kg / h: 1 Nm ³ / h), the methane content does not change much as the flow rate of the absorbent increases.

Example 4

Biogas (methane 55.1%, carbon dioxide 44.6%, hydrogen sulfide 2396ppm) was removed from the sulfurization tank 1 by hydrogen sulfide, and the hydrogen sulfide-removing biogas (methane 55.1%, carbon dioxide 44.6%, hydrogen sulfide 76 ppm) was pressurized by the pressurization system 3 to 0.8MPa, the pressurized biogas is passed into the absorption tower 5 from the lower part of the absorption tower 5 through the buffer tank 4 at a flow rate of 3Nm ³ /h until the pressure in the tower reaches 0.8 MPa, and then the biogas is continuously introduced at the same flow rate, and at the same time Absorbent (25% by mass of ChCl+urea+[Cmim][Br], the molar ratio of ChCl to urea is 1:1.5, [Cmim][Br] is 20% of the absorbent) to 50kg/h The flow rate is sent to the absorption tower 5, and is sprayed into the tower by a nozzle in the upper part of the tower. In the process, the pressure in the tower is maintained at 0.8 MPa, and the temperature is 25 to 30 ° C, so that the biogas is sufficiently contacted with the absorbent to remove the biogas. Carbon dioxide, the carbon dioxide-removing gas is dried to obtain a bio-methane product gas, and the bio-methane product gas is subjected to component analysis, and the methane content is 95.7%, carbon dioxide is 3.4%, and hydrogen sulfide is 34 ppm.

The absorbent from the bottom of the absorption tower 5 is regenerated and regenerated by a flash tank 6 (pressure 0.35 MPa, temperature 25 to 30 ° C), analytical column 7 (pressure 0.1 MPa, temperature 80 ° C), and the regenerated absorbent is transported to the absorption. The agent tank 9 is reused, and the absorbent regeneration efficiency is 95.5%.

Example 5

Biogas (55.3% of methane, 44.7% of carbon dioxide, 2254ppm of hydrogen sulfide) is desulfurized by desulfurization tank 1 to remove hydrogen sulfide. The biogas from which hydrogen sulfide is removed (55.3% of methane, 44.7% of carbon dioxide, 84ppm of hydrogen sulfide) is pressurized by the pressurization system 3. 1.2MPa, the pressurized biogas is passed into the absorption tower 5 from the lower part of the absorption tower 5 through the buffer tank 4 at a flow rate of 6Nm ³ /h until the pressure in the tower reaches 1.2 MPa, and then the biogas is continuously introduced at the same flow rate, and at the same time Absorbent (20% by mass of ChCl+urea+[Cmim][BF ₄ ] aqueous solution, the molar ratio of ChCl to urea is 1:2, [Cmim][BF ₄ ] accounts for 15% of the absorbent mass) to 90kg The flow rate of /h is sent to the absorption tower 5, and is sprayed into the tower from the nozzle in the upper part of the tower. In the process, the pressure in the tower is maintained at 1.2 MPa, the temperature is 15-20 ° C, and the biogas is sufficiently contacted with the absorbent to remove the biogas. The carbon dioxide in the carbon dioxide gas is dried to obtain the biomethane product gas, and the biomethane product gas is subjected to component analysis, and the methane content is 95.3%, the carbon dioxide is 3.8%, and the hydrogen sulfide is 35 ppm.

The absorbent from the bottom of the absorption tower 5 is regenerated by a flash tank 6 (pressure: 0.4 MPa, temperature: 15 to 20 ° C), and the regenerated absorbent is sent to the absorbent tank 9 for reuse, and the absorbent regeneration efficiency is 95.6%.

Example 6

Biogas (methane 55.4%, carbon dioxide 44.2%, hydrogen sulfide 2365ppm) is removed from the sulfurization tank 1 by hydrogen sulfide, and the hydrogen sulfide-removing biogas (methane 55.4%, carbon dioxide 44.2%, hydrogen sulfide 79ppm) is pressurized by the pressurization system 3 to 1.2MPa, the pressurized biogas is passed into the absorption tower 5 from the lower part of the absorption tower 5 through the buffer tank 4 at a flow rate of 5Nm ³ /h until the pressure in the tower reaches 1.2 MPa, and then the biogas is continuously introduced at the same flow rate, and at the same time The absorbent (30% by mass of ChCl+urea+EG aqueous solution, ChCl, urea and EG molar ratio of 1:1.5:0.5) is sent to the absorption tower 5 at a flow rate of 100 kg/h, and sprayed on the tower from the nozzle in the upper part of the tower. In the process, the pressure in the tower is maintained at 1.2 MPa, the temperature is 20-25 ° C, the biogas is sufficiently contacted with the absorbent to remove carbon dioxide in the biogas, and the carbon dioxide-removed gas is dried to obtain the bio-methane product gas, and the bio-methane is produced. The finished gas was analyzed for composition, with a methane content of 95.5%, a carbon dioxide content of 3.9%, and a hydrogen sulfide content of 36 ppm.

The absorbent from the bottom of the absorption tower 5 is regenerated by the flash tank 6 (pressure 0.4 Mpa, temperature 20-25 ° C), and the regenerated absorbent is transferred to the absorbent tank 9 for reuse. The absorbent regeneration efficiency is 96.1. %.

Example 7

Biogas (55.6% of methane, 44.5% of carbon dioxide, 2459ppm of hydrogen sulfide) is removed from the hydrogen sulfide by the desulfurization tank 1, and the biogas from which hydrogen sulfide is removed (55.6% of methane, 44.5% of carbon dioxide, and 85 ppm of hydrogen sulfide) is pressurized by the pressurization system 3. 1.2MPa, the pressurized biogas is passed into the absorption tower 5 from the lower part of the absorption tower 5 through the buffer tank 4 at a flow rate of 5Nm ³ /h until the pressure in the tower reaches 1.2 MPa, and then the biogas is continuously introduced at the same flow rate, and at the same time The absorbent regenerated in Example 6 was sent to the absorption tower 5 at a flow rate of 100 kg/h, and was sprayed into the tower from a nozzle in the upper portion of the column. In the process, the pressure inside the column was maintained at 1.2 MPa, and the temperature was 20 to 25 ° C. The biogas is sufficiently contacted with the absorbent to remove carbon dioxide in the biogas, and the carbon dioxide-removing gas is dried to obtain a biomethane product gas, and the biomethane product gas is subjected to component analysis, and the methane content is 95.6%, the carbon dioxide is 3.7%, and the hydrogen sulfide is 34 ppm.

Claims

A method for purifying and purifying biogas to produce biomethane, characterized in that it comprises the following steps:

(1) The biogas is pressurized to 0.3 MPa to 20 MPa;

(2) After the pressurized biogas is introduced into the absorption tower from the lower part of the absorption tower to the absorption tower to a pressure of 0.3 MPa to 20 MPa, the biogas is continuously introduced, and the absorbent is sprayed through the nozzle at the upper part of the absorption tower. In the tower, the biogas is sufficiently contacted with the absorbent to remove carbon dioxide in the biogas, and the carbon dioxide-removed gas is dried to obtain a bio-methane product gas;

Wherein, the pressure in the absorption tower is 0.3 MPa to 20 MPa, and the ratio of the flow rate of the absorbent to the biogas is 8 to 100 kg/h: 1 Nm 3 /h; the absorbent is a choline eutectic solvent Or an aqueous solution containing at least one of an imidazole-based ionic liquid as an active ingredient, wherein the mass fraction of the active ingredient in the absorbent is from 5 to 90%.
The method for preparing biomethane by purifying and purifying biogas according to claim 1, wherein the absorbent which absorbs carbon dioxide in step (2) enters a flash tank for regeneration treatment, and the pressure in the flash tank is 0.2 to 0.5 MPa, and the temperature is 15 to 30 ° C; when the pressure difference between the absorption tower pressure and the flash tank is ≥ 0.5 MPa, the absorbent that absorbs carbon dioxide is regenerated in a flash tank to remove carbon dioxide; when the pressure difference between the absorption tower pressure and the flash tank is < At 0.5 MPa, the absorbent which has absorbed carbon dioxide is regenerated in a flash tank, and then enters an analytical column for thermal regeneration treatment to remove carbon dioxide, wherein the pressure in the analytical column is 0.1 MPa and the temperature is 50 to 95 °C.
The method for preparing biomethane by purifying and purifying biogas according to claim 1, wherein in the step (1), when the content of hydrogen sulfide in the biogas is ≥80 ppm, the biogas is removed from the desulfurization tower after the treatment of removing hydrogen sulfide. Pressurized by the pressurization system; when the content of hydrogen sulfide in the biogas is <80 ppm, the biogas is directly pressurized by the pressurization system.
The method for preparing biomethane by purifying and purifying biogas according to claim 1, wherein in the step (2), the temperature in the absorption tower is 15 to 30 ° C; and the pressure in the absorption tower is 0.6 MPa. ～2 MPa; the ratio of the flow rate of the absorbent to the biogas is 15 to 40 kg/h: 1 Nm 3 /h.
The method for preparing biomethane by purifying and purifying biogas according to claim 4, wherein the pressure in the absorption tower is 1.2 MPa to 2 MPa; and the ratio of the flow rate of the absorbent to the biogas is 15 to 30 kg/h. : 1Nm 3 /h.
The method for preparing biomethane by purifying and purifying biogas according to claim 1, wherein the mass fraction of the active ingredient in the absorbent is 15% to 50%.
The method for preparing biomethane by purifying and purifying biogas according to claim 1 or 6, wherein the mass ratio of the choline eutectic solvent to the imidazole ionic liquid in the absorbent is 1:0 to 4.
The method for preparing biomethane by purifying and purifying biogas according to claim 7, wherein the imidazole-based ionic liquid is in the form of [C n mim][X], and C n represents a linear alkane, n=1, 2 And 3, X is one of fluorine, chlorine, bromine, iodine, tetrafluoroborate, hexafluorophosphate, and bistrifluoromethyleneimide;

The choline eutectic solvent is formed by mixing A and B, wherein A is choline chloride, choline valine, choline One of glycine, choline alanine and choline lysine, B is at least one of urea, ethylene glycol or polyethylene glycol, and the molar ratio of A and B is 0.1 to 5: 1.
A system for preparing biomethane by purifying and purifying biogas according to claim 1, comprising: a desulfurization tank, a gas-liquid separation tank I, a pressurization system, a buffer tank, an absorption tower, a flash tank, an analytical tower, An absorbent circulation pump, an absorbent tank, a gas-liquid separation tank I, and a drying tank; the outlet of the desulfurization tank is connected to an inlet of the gas-liquid separation tank I, and the outlet of the gas-liquid separation tank I is pressurized Connected to the inlet of the lower part of the buffer tank, the outlet of the upper part of the buffer tank is connected with the inlet of the lower part of the absorption tower, and the upper part of the absorption tower is provided with at least one layer of nozzle, and the outlet of the top of the absorption tower passes through the gas-liquid separation tank I and The drying tank is connected to the methane collecting device; the liquid outlet at the bottom of the absorption tower is connected to the absorbent inlet of the flash tank, the liquid outlet at the bottom of the flash tank is connected to the absorbent tank, and the lower part of the flash tank is A liquid outlet is connected to the inlet of the upper part of the analytical tower, and an exhaust port is arranged at the top of the analytical tower, and the liquid outlet at the bottom of the analytical tower is connected with the absorbent tank; the absorbent tank is passed through an absorbent circulating pump and an absorption tower. The nozzle is connected.