Method for producing biogas through biomass fermentation

Abstract

The invention relates to the technical field of biomass energy utilization, in particular to a method for producing biogas by biomass fermentation, which comprises the following steps: pretreating raw materials, collecting agricultural wastes, forestry residues, organic household garbage and other biomass raw materials, sorting and crushing the biomass raw materials until the particle size is 1-3mm, putting the biomass raw materials into a soaking pool and adding biogas slurry for soaking, adding a compound enzyme preparation, and stirring and soaking for 12-24 hours at 30-40 DEG C; draining the pretreated raw materials, inoculating microbial flora, and transferring into an anaerobic fermentation tank; in the initial stage of fermentation, the temperature in the tank is 28-32 DEG C, the pH value is 6.5-7.0 and is kept anaerobic, after the gas production rate is increased, the temperature is adjusted to 35-38 DEG C, the pH value is 7.0-7.2, and a buffering agent is added in good time. According to the method, the biomass raw materials are subjected to fine pretreatment, so that complex organic components in the biomass raw materials can be fully decomposed, more organic matters which are originally difficult to utilize by microorganisms are converted into fermentable substrates, the gas production efficiency is remarkably improved, and compared with a traditional method, the biogas yield can be remarkably increased.

Description

Technical Field

[0001] The invention relates to the technical field of biomass energy utilization, and in particular to a method for producing biogas by biomass fermentation. Background Art

[0002] With the continuous growth of energy demand and the emphasis on environmental protection, the development of renewable energy has become an important issue. Biogas, as a clean and renewable energy source, can be produced by biomass fermentation. However, the traditional method of producing biogas by biomass fermentation has many shortcomings.

[0003] In terms of raw material processing, some methods do not pre-treat biomass in detail, resulting in the inability to fully decompose the complex organic components in the raw materials, reducing the gas production efficiency. In terms of fermentation condition control, many fermentation processes do not accurately control key parameters such as temperature and pH value, which can easily lead to reduced microbial activity, unstable fermentation, and large fluctuations in biogas production and quality. In addition, traditional methods also have problems such as low efficiency and incomplete purification in the biogas collection and purification process, which affects the subsequent use of biogas. Summary of the invention

[0004] The purpose of the present invention is to provide a method for producing biogas by biomass fermentation, which can solve the above technical problems.

[0005] The present invention provides a method for producing biogas by biomass fermentation, comprising the following steps:

[0006] Raw material pretreatment:

[0007] Sorting and crushing: Collect biomass raw materials, including but not limited to agricultural waste (such as wheat straw, rice straw, etc.), forestry residues (such as branches, wood chips, etc.) and organic household waste. Sorting the collected raw materials to remove non-biomass impurities such as plastics and metals. Then crush the sorted raw materials to control the particle size of the raw materials to 1-3 mm to increase the specific surface area of ​​the raw materials for subsequent fermentation;

[0008] Soaking and enzymatic hydrolysis: Put the crushed raw materials into the soaking pool, add biogas slurry to immerse them, soak for 12-24 hours, and add compound enzyme preparations, including cellulase, hemicellulase and ligninase, with the dosage of 0.5%-1.5% of the dry weight of the raw materials. During the soaking process, keep the temperature at 30-40℃ and stir moderately to promote the full contact between the enzyme and the raw materials, accelerate the hydrolysis of the raw materials, and make the macromolecular organic matter in the raw materials initially decompose into small molecular organic matter. The biogas slurry after solid-liquid separation can improve the degradation level and gas production rate. Since the biogas slurry provides additional microorganisms and nutrients, the fermentation start-up speed of biomass will be accelerated.

[0009] Microbial inoculation and fermentation conditions optimization:

[0010] Inoculation of special microbial flora: After the pretreated raw materials are drained, the microbial flora is inoculated, wherein the microbial flora includes Methanosarcina, Methanobacterium brucei, and Clostridium thermocellum, and the inoculation amount is 15%-25% of the dry weight of the raw materials to ensure that there is a sufficient number of microorganisms in the raw materials to start fermentation;

[0011] Adjust the fermentation environment parameters: transfer the inoculated raw materials to the anaerobic fermentation tank. In the early stage of fermentation, control the temperature in the fermentation tank at 28-32°C and maintain the pH value at 6.5-7.0 to maintain the anaerobic environment. When the gas production rate begins to rise, increase the temperature to 35-38°C, adjust the pH value to 7.0-7.2, and add buffers in time according to the changes in pH value; this is the main gas production stage of fermentation. During the entire fermentation process, add buffers (such as ammonium bicarbonate) in time according to the changes in pH value to stabilize the pH value within an appropriate range;

[0012] Stirring: A stirring device and an internal circulation system are set in the fermentation tank. The stirring device runs regularly every day, with a stirring speed of 20-30 rpm and a stirring time of 15-30 minutes each time, to further improve the contact efficiency between microorganisms and raw materials and promote uniform fermentation;

[0013] Biogas collection and purification:

[0014] Biogas collection: A biogas collection port is set on the top of the fermentation tank and connected to the biogas collection pipeline. A gas flow sensor and a pressure sensor are installed on the collection pipeline. The collected biogas is first passed into a gas-liquid separation device to separate the water and a small amount of solid particles entrained therein;

[0015] Biogas purification: After gas-liquid separation, the biogas passes through the desulfurization tower, decarbonization tower and dryer in turn. In the desulfurization tower, iron oxide desulfurizer is used to remove hydrogen sulfide gas, and in the decarbonization tower, chemical absorption is used to remove carbon dioxide. Finally, in the dryer, adsorbents (such as silica gel, molecular sieves, etc.) are used to remove the remaining trace moisture, so that the biogas reaches a higher purity and meets the requirements of subsequent utilization.

[0016] Preferably, the dosage of the complex enzyme preparation is 1% of the dry weight of the raw material.

[0017] Preferably, the microbial flora inoculation amount is 20% of the dry weight of the raw material.

[0018] Preferably, the initial fermentation temperature is 30°C and the pH value is 6.8.

[0019] Preferably, the stirring speed is 25 rpm, and each stirring time is 20 minutes.

[0020] Preferably, the chemical absorption method uses ethanolamine solution to remove carbon dioxide.

[0021] Advantageous Effects of the Invention

[0022] The present invention can fully decompose the complex organic components in the biomass raw materials by fine pretreatment, so that more organic matter that was originally difficult to be used by microorganisms can be converted into fermentable substrates, thereby significantly improving the gas production efficiency. Compared with traditional methods, the biogas output can be significantly improved. The key parameters such as temperature and pH value in the fermentation process are accurately controlled to maintain the optimal environment for microbial growth and metabolism. At the same time, the precise regulation of pH value ensures the stability of microbial activity, avoids microbial growth inhibition caused by environmental discomfort, and makes the entire fermentation process stable, and the biogas output and quality no longer fluctuate greatly. In the purification stage, impurities such as hydrogen sulfide and carbon dioxide are removed, so that the purity of biogas is greatly improved, and the methane content is significantly increased, meeting higher quality energy use standards, and providing high-quality biogas resources for subsequent energy utilization. DETAILED DESCRIPTION

[0023] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention.

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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.

[0025] Example 1

[0026] Raw material preparation: 1,000 kg of rice straw and 500 kg of organic household waste were collected as biomass raw materials. They were sorted to remove impurities such as plastic and glass, and then crushed into particles of about 2 mm using a crusher.

[0027] Pretreatment: Put the crushed raw materials into the soaking tank, add an appropriate amount of biogas slurry to completely immerse the raw materials. Add compound enzyme preparation to the soaking tank, the dosage is 1% of the dry weight of the raw materials, keep the temperature at 35℃, soak for 18 hours, and stir every 2 hours.

[0028] Inoculation and fermentation: After the pretreated raw materials are drained, the microbial flora is inoculated, including: Methanobacterium Bryantii (China Microbial Strain Query Network, No. bio-110583), Methanosarcina barkeri (China Microbial Strain Query Network, No. bio-72834), Clostridium thermocellum (China Microbial Strain Query Network, No. bio-83387), and the inoculation amount is 20% of the dry weight of the raw materials. The raw materials are transferred to an anaerobic fermentation tank with a volume of 3000 liters. At the beginning of fermentation, the temperature in the fermentation tank is controlled at 30°C, the pH value is maintained at 6.8, and nitrogen is introduced to maintain an anaerobic environment. When the gas production rate begins to rise, the temperature is raised to 36°C, the pH value is adjusted to 7.1, and the pH value is maintained stable by adding ammonium bicarbonate. The stirring device is operated 3 times a day, each stirring speed is 25 rpm, and the stirring time is 20 minutes. At the same time, start the internal circulation system to allow the material to circulate slowly.

[0029] Biogas collection and purification: Biogas is collected through the collection port on the top of the fermentation tank, and after passing through the gas-liquid separation device, it is passed into the desulfurization tower, decarbonization tower and dryer for purification. According to the test, the biogas production of this embodiment can reach 200 cubic meters per day during the fermentation stabilization period, the methane content in the biogas reaches 68%, the hydrogen sulfide content is less than 0.01%, the carbon dioxide content is less than 3%, and the moisture content is less than 0.5%.

[0030] Example 2

[0031] Raw material preparation: 800 kg of wheat straw and 200 kg of tree branches were collected as biomass raw materials, sorted and crushed to a particle size of 1.5 mm.

[0032] Pretreatment: Put the crushed raw materials into a soaking tank, add biogas slurry to immerse them, add complex enzyme preparation (the dosage is 0.8% of the dry weight of the raw materials), soak at 32°C for 20 hours, and stir every 3 hours.

[0033] Inoculation and fermentation: After draining the raw materials, inoculate the microbial flora, including: Methanobacterium Bryantii (China Microbial Strain Query Network, No. bio-110583), Methanosarcina barkeri (China Microbial Strain Query Network, No. bio-72834), Clostridium thermocellum (China Microbial Strain Query Network, No. bio-83387), the inoculation amount is 22% of the dry weight of the raw materials, and put into an anaerobic fermentation tank with a volume of 2500 liters. The initial fermentation temperature is 29°C and the pH value is 6.6. After the gas production rate increases, the temperature is adjusted to 37°C and the pH value is adjusted to 7.0. The stirring device runs 4 times a day, the speed is 22 rpm, the time is 25 minutes, and the internal circulation system is operated at the same time.

[0034] Biogas collection and purification: Biogas is collected and purified after gas-liquid separation. The daily gas production in the stable period is 180 cubic meters, with a methane content of 65%, a hydrogen sulfide content of less than 0.01%, a carbon dioxide content of less than 4%, and a moisture content of less than 0.5%.

[0035] It can be seen from the above examples that the method of the present invention can effectively improve the biogas yield and quality, and can operate stably under different biomass raw material combinations.

[0036] Comparative Example 1

[0037] Raw material preparation: 800 kg of rice straw and 700 kg of organic household waste were collected as biomass raw materials. The raw materials were simply sorted to remove large impurities such as plastic and glass, but no crushing was performed. The particle sizes of the raw materials varied, mostly between 5 and 20 mm.

[0038] Pretreatment: Put the sorted raw materials into a soaking tank, add appropriate amount of water to completely immerse the raw materials, do not add complex enzyme preparations, keep the temperature at 30°C, soak for 12 hours, and do not stir during the period.

[0039] Inoculation and fermentation: After draining the raw materials, the microbial flora was inoculated at a rate of 10% of the dry weight of the raw materials. The microbial flora included Methanosarcina barkeri, Bacteroides thetaiotaomicron, and Clostridium aceticum. The raw materials were transferred to an anaerobic fermentation tank with a capacity of 3,000 liters. During the fermentation process, the temperature was maintained at 32°C, the pH value was not controlled, and nitrogen was not introduced into the fermentation tank. No stirring device or internal circulation system was set.

[0040] Biogas collection and purification: Biogas is collected through the collection port on the top of the fermentation tank. After collection, it is purified only by simple water washing, without going through the complete purification process of gas-liquid separation device, desulfurization tower, decarbonization tower and dryer. According to the test, the daily biogas production during the stable fermentation period is only 80 cubic meters, the methane content in the biogas is 45%, the hydrogen sulfide content is about 0.05%, the carbon dioxide content is about 10%, and the water content is about 3%.

[0041] By comparison with Example 1, it can be seen that the various treatment measures in Example 1 (such as raw material crushing, enzyme preparation addition, appropriate inoculation amount and multiple microorganisms synergy, precise fermentation condition control and perfect biogas purification process) have significant effects on improving biogas production and quality. The deficiencies in raw material treatment, microbial inoculation, fermentation condition control and biogas purification in Comparative Example 1 led to poor gas production results.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing biogas by biomass fermentation, characterized in that: The following steps are involved: Raw material pretreatment: Sorting and crushing: Collect biomass raw materials, sort and remove non-biomass impurities, and then crush them into particles of 1-3 mm in size; Soaking and enzymatic hydrolysis: Put the crushed raw materials into the soaking tank, add biogas slurry to immerse them, soak for 12-24 hours, and add compound enzyme preparations, which include cellulase, hemicellulase and ligninase, and the dosage is 0.5%-1.5% of the dry weight of the raw materials. Keep the temperature at 30-40℃ and stir during the soaking process; Microbial inoculation and fermentation conditions optimization: Inoculation of microbial flora: After the pretreated raw materials are drained, inoculation of microbial flora is carried out, and the inoculation amount is 15%-25% of the dry weight of the raw materials; Adjust the fermentation environment parameters: transfer the inoculated raw materials to the anaerobic fermentation tank. In the early stage of fermentation, control the temperature in the fermentation tank at 28-32°C and maintain the pH value at 6.5-7.0 to maintain the anaerobic environment. When the gas production rate begins to rise, increase the temperature to 35-38°C, adjust the pH value to 7.0-7.2, and add buffers in time according to the pH change; Stirring: A stirring device is installed in the fermentation tank. The stirring device is operated regularly every day. The stirring speed is 20-30 rpm and the stirring time is 15-30 minutes each time. Biogas collection and purification: Biogas collection: A biogas collection port is set on the top of the fermentation tank and connected to the biogas collection pipeline. A gas flow sensor and a pressure sensor are installed on the collection pipeline. The collected biogas is first passed into the gas-liquid separation device; Biogas purification: After gas-liquid separation, the biogas passes through the desulfurization tower, decarbonization tower and dryer in turn. In the desulfurization tower, iron oxide desulfurizer is used to remove hydrogen sulfide gas, in the decarbonization tower, chemical absorption method is used to remove carbon dioxide, and in the dryer, adsorbent is used to remove trace moisture.

2. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The biomass raw materials include one or more of agricultural waste, forestry residues and organic household waste.

3. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The dosage of the composite enzyme preparation is 1% of the dry weight of the raw material.

4. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The inoculation amount of the microbial flora is 20% of the dry weight of the raw material.

5. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The initial fermentation temperature was 30° C. and the pH value was 6.

8.

6. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The stirring speed is 25 rpm, and each stirring time is 20 minutes.

7. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The buffer is ammonium bicarbonate.

8. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The chemical absorption method uses ethanolamine solution to remove carbon dioxide.

9. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The adsorbent includes silica gel and molecular sieve.

10. The method for producing biogas by biomass fermentation according to claim 1, characterized in that: The microbial flora comprises Methanosarcina, Methanobacterium brasiliensis, and Clostridium thermocellum.