阅读说明：本技术 一种基于木质纤维素的沼气生产方法 (Biogas production method based on lignocellulose ) 是由 *** 梅雪 朱娜 郝艳萍 李旭源 陈秀玉 于 2019-12-17 设计创作，主要内容包括：本发明公开了一种基于木质纤维素的沼气生产方法,包括高温厌氧预处理和高温厌氧发酵两个阶段,前一阶段是将经过粉碎的木质纤维素原料加入到动物粪便培养液中形成预处理体系,在温度45～55℃、pH 6～8时进行厌氧发酵预处理,预处理的物料停留时间为24～72h,得料液；后一阶段是将料液导入厌氧发酵反应器进行厌氧发酵形成沼液并生产沼气,发酵温度45～55℃,物料停留时间在10～20天。两个阶段循环时,将动物粪便培养液替换成沼液。该方法将木质纤维素的水解酸化过程提前进行,不需要氧气辅助,无需添加化学品,且提高了水解效率,再联合后续的高温厌氧发酵生产沼气,具有高转化、高效、能耗低、工艺运行稳定的特点。(The invention discloses a lignocellulose-based biogas production method, which comprises two stages of high-temperature anaerobic pretreatment and high-temperature anaerobic fermentation, wherein in the former stage, crushed lignocellulose raw materials are added into an animal manure culture solution to form a pretreatment system, anaerobic fermentation pretreatment is carried out at the temperature of 45-55 ℃ and the pH of 6-8, and the retention time of the pretreated materials is 24-72 hours to obtain feed liquid; and in the latter stage, introducing the feed liquid into an anaerobic fermentation reactor for anaerobic fermentation to form biogas slurry and producing biogas, wherein the fermentation temperature is 45-55 ℃, and the retention time of the material is 10-20 days. And when the two stages are circulated, replacing the animal excrement culture solution into biogas slurry. The method advances the hydrolysis acidification process of the lignocellulose, does not need oxygen assistance, does not need to add chemicals, improves the hydrolysis efficiency, combines the subsequent high-temperature anaerobic fermentation to produce the biogas, and has the characteristics of high conversion, high efficiency, low energy consumption and stable process operation.)

1. A method for producing methane based on lignocellulose is characterized by comprising two stages of high-temperature anaerobic pretreatment and high-temperature anaerobic fermentation,

in the high-temperature anaerobic pretreatment stage, the crushed lignocellulose raw material is added into an animal manure culture solution to form a pretreatment system, anaerobic fermentation pretreatment is carried out at the temperature of 45-55 ℃ and under the condition of the pH value of 6-8, and the retention time of the pretreated material is 24-72 hours to obtain feed liquid;

in the high-temperature anaerobic fermentation stage, the feed liquid is introduced into an anaerobic fermentation reactor to carry out anaerobic fermentation to form biogas slurry and produce biogas, the fermentation temperature is 45-55 ℃, and the retention time of the material in the anaerobic fermentation reactor is 10-20 days;

when the two stages are circulated, the animal manure culture solution in the high-temperature anaerobic pretreatment stage is replaced by biogas slurry generated in the high-temperature anaerobic fermentation stage.

2. Biogas production process according to claim 1, characterized in that the total solids content in the animal manure culture fluid does not exceed 5 wt.%.

3. Biogas production process according to claim 1, characterized in that the anaerobic fermentation pretreatment is subjected to three successive temperature swing processes before a two-stage cycle: anaerobic fermentation is carried out for 2-3 days at the temperature of 30-35 ℃, for 1-3 days at the temperature of 40-45 ℃ and for 1-2 days at the temperature of 50-55 ℃.

4. The biogas production method as claimed in claim 3, wherein the lignocellulosic raw material is added in portions, the first addition is no more than 3 wt% of the pretreatment system, after the three temperature-changing processes are completed, the second addition is performed, the solid content in the pretreatment system after the addition accounts for 12-18 wt%, the anaerobic environment is maintained and the stirring is performed, and the anaerobic fermentation pretreatment is performed.

5. The biogas production method according to claim 1, wherein the fermentation temperature in the high temperature anaerobic pretreatment stage is 48-55 ℃.

6. The biogas production method according to claim 5, wherein the fermentation temperature in the high temperature anaerobic pretreatment stage is 51 to 54 ℃ and the pH value is 6.8 to 7.4.

7. The biogas production method according to claim 1, wherein the pretreatment system has a total solid content of 6 to 18 wt%.

8. The biogas production method according to claim 1, wherein the fermentation temperature of the high-temperature anaerobic fermentation stage is 50 to 55 ℃ and the pH value is 6.0 to 8.0.

9. The biogas production method according to claim 8, wherein the fermentation temperature in the high-temperature anaerobic fermentation stage is 52-54 ℃, the pH value is 7.0-7.4, and the material retention time in the anaerobic fermentation reactor is 12-15 days.

10. The biogas production method according to claim 1, wherein the particle size of the crushed lignocellulosic raw material is 1-5 cm.

Technical Field

The invention relates to the technical field of methane production, in particular to a methane production method based on lignocellulose.

Background

Biomass resources are large and varied, with lignocellulose being one of the most abundant renewable resources, produced by plants through photosynthesis. Lignocellulosic feedstocks can be converted into different types of energy fuels by various technical approaches. For lignocellulose raw materials, one way of utilization with high comprehensive value is to produce biogas by carrying out anaerobic fermentation process on crop straws, and the biogas can be used for power generation or purified into natural gas to be used as vehicle fuel gas or be merged into a natural gas pipe network.

The cellulose crystal structure formed by bonding three substances and pectin and the like together forms a dried barrier for anaerobic microbial flora, particularly the molecular chemical bond of the straw has stronger hydrophobicity, the microbial and enzyme enter the interior of the straw fiber to perform hydrolysis, and the cellulose and the lignin are not easy to degrade to a certain extent, so that the problem that the subsequent cellulose hydrolysis and methanation reaction cannot be easily caused is solved, and the problem that the subsequent cellulose hydrolysis and methanation reaction cannot be easily solved.

At present, the pretreatment measures for lignocellulose mainly comprise physical pretreatment, chemical pretreatment and biological pretreatment, but the pretreatment methods also have a series of problems while improving the characteristics of the lignocellulose raw material, improving the digestibility of the raw material and increasing the gas production, and each has different limitations. Mainly embodied in the following aspects:

no matter what pretreatment mode is adopted, the hydrolysis and acidification processes of lignocellulose are mainly realized by anaerobic fermentation, the conversion period is long, and a larger reactor volume is needed for keeping the continuous supply of biogas. The conversion rate of methane of single organic matters in the lignocellulose raw material is low, and especially the gas yield is lower for the straws. The straw is easy to form a floating layer in the reactor, so that a crust layer is formed, and in order to avoid a scum layer, longer stirring time and stirring energy consumption are needed, so that the investment and operation cost are very high. In addition, the difficulty of feeding and discharging and material conveying of the reaction system is high, pipeline valves are often easy to block, and some chemical modes are needed for pretreatment, so that the maintenance cost is high, and secondary pollution is easily caused.

Chinese patent CN105132469B discloses a method for pretreating lignocellulose by using a facultative manner, which can make the methane content in the biogas produced by crop straw raw materials reach 57%, and greatly shorten the biogas production time. The maintenance of facultative conditions requires intermittent aeration, and energy is continuously consumed; meanwhile, in order to maintain the biological activity of the facultative anaerobe, the system temperature cannot be higher than 45 ℃, so that the fermentation liquor of the high-temperature anaerobic fermentation system which is pretreated and is at 45-55 ℃ needs to be additionally cooled when flowing back to the facultative pretreatment system, thereby consuming energy and causing more remarkable heat loss.

Disclosure of Invention

The invention aims to solve the problems of low conversion rate of organic matters per unit, high energy consumption and large heat loss in the process of producing biogas by fermenting lignocellulose in the prior art, and provides a novel lignocellulose-based biogas production method with high efficiency and energy saving.

Lignocellulose, including cellulose, hemicellulose, and lignin. Lignocellulosic materials include straw from agricultural wastes and the like.

In the chinese patent CN105132469B, the hydrolysis and acidification of lignocellulose organic substances are promoted by using cellulose hydrolase, hemicellulose hydrolase and medium temperature anaerobic fermentation processes secreted by aerobic microorganisms in a manner of alternately performing aeration for 10-40 minutes and stopping aeration for 10-40 minutes. Various hydrolytic enzymes secreted by aerobic microorganisms can promote the hydrolysis of lignocellulose at the temperature of below 45 ℃, the hydrolysis needs to be carried out under the condition of aerating the system, and the aerobic microorganisms have additional requirements on the temperature of the system and cannot be higher than 45 ℃. There are also three aspects of the effect of aeration into the system: firstly, the operation of the aeration fan needs to consume energy; secondly, the oxygen input into the system can inhibit the breeding of anaerobic microorganism flora; thirdly, when the air input into the system leaves the system, organic matters in the system can be entrained, so that the yield of the biogas is reduced, and the environment is polluted.

Through a large number of researches, it is discovered that a large number of anaerobic hydrolytic acidification microorganisms can be screened and enriched from animal excrement culture solution under the specific anaerobic environment created by controlling the temperature, adjusting the pH value of a pretreatment system and controlling the extremely low oxygen content of the system, and at a higher temperature, the efficient hydrolysis of lignocellulose materials is realized by the anaerobic hydrolytic acidification microorganisms, so that the hydrolytic conversion efficiency is remarkably improved at a higher temperature, the overall reaction rate and the conversion rate of the lignocellulose to the methane are greatly improved, and the production efficiency is improved.

Based on the above, the invention provides a lignocellulose-based biogas production method, which comprises two stages of high-temperature anaerobic pretreatment and high-temperature anaerobic fermentation;

in the high-temperature anaerobic pretreatment stage, the crushed lignocellulose raw material is added into an animal manure culture solution to form a pretreatment system, anaerobic fermentation pretreatment is carried out at the temperature of 45-55 ℃ and under the condition of the pH value of 6-8, and the retention time of the pretreated material is 24-72 hours to obtain feed liquid;

in the high-temperature anaerobic fermentation stage, the feed liquid is introduced into an anaerobic fermentation reactor to carry out anaerobic fermentation to form biogas slurry and produce biogas, the fermentation temperature is 45-55 ℃, and the material retention time in the anaerobic fermentation reactor is 10-20 days.

When the two stages are circulated, the animal manure culture solution in the high-temperature anaerobic pretreatment stage is replaced by biogas slurry generated in the high-temperature anaerobic fermentation stage.

The active temperature of the anaerobic fermentation microorganisms is 10-60 ℃, wherein the temperature range of medium-temperature fermentation is 30-40 ℃, the optimal temperature range is 35-38 ℃, the temperature range of high-temperature fermentation generally exceeds 45 ℃, and the optimal fermentation temperature range is 50-55 ℃. The decomposition speed of the organic materials and the biogas production capacity can be greatly improved by increasing the fermentation temperature. For easily dispersed organic materials, the retention time of the materials in the medium-temperature fermentation process is generally 25-30 days, and the retention time of the materials in the high-temperature fermentation process is generally 10-15 days. The fermentation speed is increased by about 1 time from the medium-temperature fermentation to the high-temperature fermentation. When the lignocellulose is hydrolyzed by anaerobic microorganisms, the anaerobic hydrolysis temperature is increased to a high-temperature interval, the hydrolysis efficiency of the lignocellulose is greatly improved, and meanwhile, anaerobic microbial flora cannot be inhibited due to the existence of an intermittent aerobic process. Through a large amount of researches, the aim of pretreatment can be basically achieved only by prolonging the retention time of the material subjected to anaerobic pretreatment to more than 72 hours without intermittently supplying oxygen and increasing the pretreatment temperature, and the pretreatment time can be shortened to 24-48 hours by increasing the temperature of the anaerobic pretreatment, so that the hydrolysis acidification degree of lignocellulose equivalent to the facultative pretreatment can be achieved, and the condition that the anaerobic fermentation process at the downstream of the working procedure can generate sufficient biogas is ensured. The lignocellulose is hydrolyzed by using anaerobic conditions, and although the promotion effect of hydrolase generated by aerobic bacteria is lost, the pretreatment temperature can be increased to accelerate the hydrolysis acidification process; meanwhile, the hydrolysis conversion rate can be improved by 10-20% by increasing the pretreatment temperature. The hydrolysis conversion rate is a chemical equilibrium influenced by thermodynamics, and increasing the reaction temperature promotes the forward shift of the hydrolysis chemical equilibrium.

Preferably, in the above biogas production method, the total solid content in the animal waste culture solution is not more than 5 wt%. wt% means weight percentage.

Preferably, in the above biogas production method, the anaerobic fermentation pretreatment is subjected to three consecutive temperature-changing processes before the two-stage cycle: anaerobic fermentation is carried out for 2-3 days at the temperature of 30-35 ℃, for 1-3 days at the temperature of 40-45 ℃ and for 1-2 days at the temperature of 50-55 ℃. The fermentation is favorable for creating a mild environment for flora in the animal excrement at the temperature of 30-35 ℃, so that the flora is propagated in a large quantity, the temperature is raised to 40-45 ℃, part of strains which cannot tolerate high temperature are screened out, the surviving strains are propagated continuously, finally the temperature is raised to 50-55 ℃ for secondary screening, high-temperature resistant dominant flora is formed, and the lignocellulose is pretreated by anaerobic fermentation. After circulation, because the flora does not need to be screened and cultured again, the anaerobic fermentation can be directly continued at the temperature of 45-55 ℃, and the time is saved.

Preferably, in the biogas production method, the lignocellulose raw material is added in several times, the first addition is not more than 3 wt% of the pretreatment system, after the three temperature changing processes are completed, the second addition is carried out, the solid content in the added pretreatment system accounts for 12-18 wt%, the anaerobic environment is kept and the mixture is stirred, and anaerobic fermentation pretreatment is carried out. The addition method is convenient for the formation of primary flora culture solution and is suitable for the addition of lignocellulose raw material for the second time.

Preferably, in the biogas production method, the fermentation temperature in the high-temperature anaerobic pretreatment stage is 48-55 ℃. More preferably 52-54 ℃ and pH 6.8-7.4.

The high-temperature anaerobic pretreatment stage is mainly a hydrolysis acidification process of lignocellulose, when the temperature of a system is increased to be more than 50 ℃, the hydration of a lignocellulose structure can be obviously improved, and the hydrolysis acidification is realized through a physical and chemical process and a biochemical process. The temperature condition of anaerobic fermentation needs to be considered comprehensively, on one hand, the breeding of anaerobic microorganisms needs to be met, high biological activity is kept, and on the other hand, the processes of destruction of hydrogen bonds of lignocelluloses endophytes and water hydration can be realized. More preferably, the temperature is in the range of 52-54 deg.C, and both physicochemical and biochemical processes can be efficiently performed in this temperature range. The pretreatment temperature, the pH value and the biogas slurry flow returned by the subsequent anaerobic fermentation section are strictly controlled.

Preferably, in the biogas production method, the total solid content of the pretreatment system is 6-18 wt%.

The flow rate of the biogas slurry refluxed in the anaerobic fermentation section is determined according to the total solid content of the pretreatment system, the total solid content of the pretreatment system is preferably 6-18 wt%, and more preferably 10-15 wt%. The anaerobic pretreatment system environment should provide the most preferable suitable conditions for the reproduction and propagation of anaerobic hydrolytic acidification microorganisms so as to realize the optimal hydrolytic acidification process.

The total solid content of the pretreatment system is controlled by adding lignocellulose and refluxing anaerobic fermentation biogas slurry, the maintenance of the concentration of the total solid content is beneficial to the mass propagation and aggregation of beneficial microbial floras, the change of the concentration can impact microorganisms in the pretreatment system, the propagation of the microorganisms is a process, the increase or decrease of the concentration needs a time for buffering, the stability of the concentration of hydrolytic acidification substrates is maintained, and the optimal ecological environment can be provided for the microbial floras.

Preferably, in the above biogas production method, when continuously feeding, the high temperature anaerobic pretreatment process is maintained using a product of the high temperature anaerobic fermentation stage instead of the animal manure culture solution.

When the lignocellulose raw material is added into the animal manure culture solution for the first time, the temperature of the animal manure culture solution needs to be raised to a high-temperature range, necessary culture is carried out, and the biological activity of a pretreatment system can be maintained by relying on living microorganisms in the system and microorganisms introduced into anaerobic fermentation reflux liquid of a subsequent working section during continuous feeding after starting.

The moisture content in the straw lignin is very low, and the moisture needs to be supplemented into a pretreatment system while the feed is pretreated. In order to reduce heat consumption, biogas slurry reflowing from a subsequent high-temperature anaerobic fermentation section directly reflows into the high-temperature anaerobic pretreatment reactor without any temperature change measure. The biological characteristics of microbial flora are influenced by the environment remarkably, and anaerobic microorganisms which survive in reflux liquid flowing back into the pretreatment reactor have excellent promoting effect on a pretreatment system under the condition of reasonably controlling reaction conditions. The biogas slurry in the anaerobic fermentation section is refluxed, so that heat and moisture are provided for a pretreatment system, the biological activity of pretreatment anaerobic microorganisms is improved, and the anaerobic hydrolysis process of lignocellulose is promoted.

Preferably, in the biogas production method, the fermentation temperature in the high-temperature anaerobic fermentation stage is 50-55 ℃, and the pH value is 6.0-8.0. More preferably, the fermentation temperature in the high-temperature anaerobic fermentation stage is 52-54 ℃, the pH value is 7.0-7.4, and the material retention time in the anaerobic fermentation reactor is 12-15 days.

As mentioned before, the progress of anaerobic fermentation is significantly affected by temperature. Compared with medium-low temperature anaerobic fermentation, the feed liquid after hydrolytic acidification pretreatment has shorter fermentation period, higher fermentation efficiency and higher methane conversion rate under the condition of high-temperature anaerobic fermentation. The fermentation temperature has positive promoting effect on the aspects of fermentation kinetics and fermentation thermodynamics. Therefore, the fermentation efficiency is highest when the above preferable value is adopted.

Preferably, in the biogas production method, the particle size of the crushed lignocellulose raw material is 1-5 cm. Preferably 1.5 to 2.5 cm. The effect of hydrolytic acidification is influenced by the excessively large particle size, more mechanical energy needs to be additionally provided to realize the extremely small particle size, so that excessive energy consumption is caused, and the comprehensive economic benefit of the particle size range is optimal.

Compared with the prior art, the invention has the following beneficial effects:

(1) the hydrolysis acidification process of the lignocellulose is relatively independent from the anaerobic fermentation biogas production process, and the high-temperature anaerobic process is adopted, so that the biological activity of anaerobic microorganisms is optimal, and the hydrolysis acidification process of the lignocellulose is carried out efficiently.

(2) Because the acidification reaction is simultaneously carried out in the high-temperature anaerobic pretreatment reactor, the pH value in the feed liquid is in a slightly acidic state. Under the conditions of temperature and pH, carboxyl in the acidizing fluid can more easily perform decarboxylation process in the presence of anaerobic bacteria to release a certain amount of CO ₂Gas, and simultaneously, the pH value of the acidizing fluid is reduced. The process has two advantages, on one hand, the pH value of the pretreatment system is kept relatively constant, and the impact of the pretreated materials entering a high-temperature anaerobic fermentation gas production section on the pH value of the high-temperature anaerobic fermentation section system is greatly reduced; on the other hand, CO in the high-temperature anaerobic fermentation biogas can be reduced ₂The content is reduced by 10-20% compared with the content in the conventional process. In the presence of oxygen, the oxygen in the system oxidizes and converts part of the carbon in the biomass into CO ₂Thereby reducing the methane conversion rate and influencing the economic benefit of the whole device, but the anaerobic acidification hydrolysis process does not have the influence.

(3) The pretreatment and fermentation processes of the lignocellulose are biochemical processes, no chemicals are added in the technical process, no oxygen auxiliary pretreatment is introduced from the outside of the system, and the operation cost is low; the combination of high-temperature anaerobic pretreatment and high-temperature anaerobic fermentation shortens the material retention time in the process, greatly reduces the total volume of the reactor, and reduces the investment cost; higher temperature promotes the carboxyl of the system to react with CO in the hydrolysis acidification pretreatment of the lignocellulose ₂The form of the methane leaves the system, maintains the pH of the material system to be stable, and reduces CO in the product methane ₂The calorific value is increased.

(4) The process method is particularly suitable for the biological treatment process of the straw fiber raw materials, and has the characteristics of high conversion, high efficiency, low energy consumption and stable process operation.

Detailed Description

The present invention will be further described with reference to specific examples to assist understanding and practice of the present invention, which are not intended to limit the scope of the present invention.