阅读说明：本技术 一种利用秸秆厌氧发酵制取甲烷的方法 (Method for preparing methane by utilizing straw anaerobic fermentation ) 是由 孟祥汇 曲京博 刘昱英男 李楠 王智 曲斌 孙勇 于 2020-06-30 设计创作，主要内容包括：本发明提供了一种利用秸秆厌氧发酵制取甲烷的方法,涉及甲烷制备技术领域,所述利用秸秆厌氧发酵制取甲烷的方法包括以下步骤：将秸秆切割成2-3cm的小段后,将其放置在装有造纸废水的密封的发酵反应器中,在50-55℃的温度下混合,并保持密封状态3-4天后,向发酵反应器中加入沼液作为接种物,并继续向发酵反应器中加入酸性溶液,使混合溶液的pH值范围为6.8-7.5；继续向发酵反应器中通入氮气,进行厌氧发酵,获得甲烷。本发明用造纸废水预处理秸秆,对秸秆内部的木质素进行了破坏,在厌氧发酵的过程中使水分子进入秸秆内部,提高了秸秆的沉降性,解决了浮渣结壳层的问题,促进厌氧发酵的进程,增加甲烷气体的产量。(The invention provides a method for preparing methane by utilizing straw anaerobic fermentation, which relates to the technical field of methane preparation, and comprises the following steps: cutting straws into 2-3cm segments, placing the segments in a sealed fermentation reactor filled with papermaking wastewater, mixing at 50-55 ℃, keeping the sealed state for 3-4 days, adding biogas slurry serving as an inoculum into the fermentation reactor, and continuously adding an acidic solution into the fermentation reactor to ensure that the pH value of the mixed solution is within the range of 6.8-7.5; and continuously introducing nitrogen into the fermentation reactor for anaerobic fermentation to obtain methane. The invention pretreats the straws with the papermaking wastewater, destroys lignin in the straws, and enables water molecules to enter the straws in the anaerobic fermentation process, thereby improving the settleability of the straws, solving the problem of scum shell-forming layer, promoting the anaerobic fermentation process and increasing the yield of methane gas.)

1. A method for preparing methane by utilizing straw anaerobic fermentation is characterized by comprising the following steps:

cutting straws into small sections of 2-3cm, placing the straws in a sealed fermentation reactor filled with papermaking wastewater, mixing at the temperature of 50-55 ℃, and keeping the sealed state for 3-4 days to obtain a first mixed solution;

adding biogas slurry serving as an inoculum into the fermentation reactor to obtain a second mixed solution;

adding an acidic solution into the fermentation reactor to obtain a third mixed solution, wherein the pH value of the third mixed solution is 6.8-7.5;

and step four, introducing nitrogen into the fermentation reactor, and performing anaerobic fermentation to obtain methane.

2. The method for preparing methane by utilizing the anaerobic fermentation of straws as claimed in claim 1, wherein the mixing ratio of the straws and the papermaking wastewater in the step one is 2000-3000ml for every 100-150g of the straws.

3. The method for preparing methane by utilizing straw anaerobic fermentation as claimed in claim 2, wherein the mixing ratio of the straw and the paper-making wastewater in the step one is 2000ml of the paper-making wastewater per 100g of the straw.

4. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 1, wherein the mixing condition in the first step is that the fermentation reactor is shaken 2-3 times per day, and the duration time of each time is 4-6 minutes.

5. The method for preparing methane by utilizing straw anaerobic fermentation as claimed in claim 1, wherein in the second step, the biogas slurry is prepared by fermenting organic substances filtered by a 10-mesh filter screen.

6. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 1, wherein the total solid content of the second mixed solution in the second step is in the range of 6-8%.

7. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 1, wherein the acidic solution in the third step is selected from acetic acid, sulfuric acid or hydrochloric acid.

8. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 1, wherein the time for introducing the nitrogen in the fourth step is 3-5 min.

9. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 1, wherein the anaerobic fermentation in the fourth step is carried out under a constant temperature condition, and the temperature range of the anaerobic fermentation is 34-36 ℃.

10. The method for preparing methane by utilizing the anaerobic fermentation of the straws as claimed in claim 9, wherein the time of the anaerobic fermentation is 20-25 days.

Technical Field

The invention relates to the technical field of methane preparation, in particular to a method for preparing methane by utilizing straw anaerobic fermentation.

Background

China is a big agricultural country, and 8 hundred million tons of straws are produced every year in the process of growing and producing a large amount of agricultural products, wherein the yield of the corn straws accounts for more than 25 percent of the total yield of the straws. Since 2014, after the national promulgates the forbidden burning of straws, the comprehensive utilization rate of the straws is greatly improved, but a large amount of straws are not utilized, so that the serious environmental pollution and the great resource waste are caused.

Disclosure of Invention

The invention solves the technical problem of how to prepare high-yield methane by utilizing straw anaerobic fermentation.

In order to solve the problems, the invention provides a method for preparing methane by utilizing straw anaerobic fermentation, which comprises the following steps:

cutting straws into small sections of 2-3cm, placing the straws in a sealed fermentation reactor filled with papermaking wastewater, mixing at the temperature of 50-55 ℃, and keeping the sealed state for 3-4 days to obtain a first mixed solution;

adding biogas slurry serving as an inoculum into the fermentation reactor to obtain a second mixed solution;

adding an acidic solution into the fermentation reactor to obtain a third mixed solution, wherein the pH value of the third mixed solution is 6.8-7.5;

and step four, introducing nitrogen into the fermentation reactor, and performing anaerobic fermentation to obtain methane.

Optionally, the mixing ratio of the straw and the papermaking wastewater in the step one is that 3000ml of the papermaking wastewater is required for every 100-150g of the straw.

Optionally, in the step one, the mixing ratio of the straw to the papermaking wastewater is 2000ml for every 100g of the straw.

Optionally, the mixing in step one is performed under conditions such that the fermentation reactor is shaken 2-3 times per day for a duration of 4-6 minutes.

Optionally, in the second step, the biogas slurry is prepared by fermenting organic substances filtered by a 10-mesh filter screen.

Optionally, the total solids content of the second mixed solution in step two is in the range of 6-8%.

Optionally, the acidic solution in step three is acetic acid, sulfuric acid or hydrochloric acid.

Optionally, the time for introducing the nitrogen in the fourth step is 3-5 min.

Optionally, the anaerobic fermentation in step four is performed under constant temperature conditions, and the temperature range of the anaerobic fermentation is 34-36 ℃.

Optionally, the anaerobic fermentation is for a period of 20-25 days.

Compared with the prior art, the method for preparing methane by utilizing straw anaerobic fermentation has the following beneficial effects:

1) the straw pretreatment cost can be reduced by pretreating the straw with the papermaking wastewater, the pretreatment process is simple, the loss of equipment is low, and the time and the operation cost are saved.

2) Compared with the traditional method for preparing methane gas by anaerobic fermentation under the conditions of the same scale and the like, the total yield of the methane gas prepared by the method is improved by 20-30%, the thickness of the scum layer in the anaerobic fermentation process is reduced by 25-40%, the use cost is low, the method is environment-friendly, and the social and economic benefits are improved.

3) The method of the invention reduces the BOD and COD index of the papermaking wastewater by 30-40 percent, and reduces the subsequent pollution to the environment.

Drawings

FIG. 1 is a flow chart of a method for preparing methane by utilizing straw anaerobic fermentation in the embodiment of the invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the description of the present invention, it is to be understood that the terms "first", "second" and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of the feature. The description of the term "some embodiments" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. Throughout this specification, the schematic representations of the terms used above do not necessarily refer to the same implementation or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Most of the waste water in the paper making process in China is cooking waste liquid, is strong alkaline liquid with the pH value between 11 and 13, and can be discharged after being treated due to high BOD value, high COD value and strong pollution, so that the production cost of enterprises is greatly increased, and certain harm is caused to the environment. In the prior art, straws are widely used as raw materials of biogas engineering, clean energy biogas is obtained in an anaerobic fermentation mode, but at the production stage of biogas, lignin in the straws wraps cellulose and hemicellulose in the anaerobic fermentation process at present, so that water molecules are difficult to enter, the water absorption of the straws is poor, the settleability is reduced, the straws directly float on the upper layer of an anaerobic fermentation system, a scum layer is formed in an accumulated manner, the success of the anaerobic fermentation process is further influenced, and the yield of the biogas is finally reduced. Therefore, aiming at the characteristics of the papermaking wastewater and the straw, the method has the advantages of convenient treatment mode, low cost and capability of preparing high-quality clean energy methane, and is very necessary to obtain certain economic benefit.

As shown in figure 1, the embodiment of the invention provides a method for preparing methane by utilizing straw anaerobic fermentation, which comprises the following steps:

cutting straws into small sections of 2-3cm, placing the straws in a sealed fermentation reactor filled with papermaking wastewater, mixing at the temperature of 50-55 ℃, and keeping the sealed state for 3-4 days to obtain a first mixed solution;

adding biogas slurry serving as an inoculum into the fermentation reactor to obtain a second mixed solution;

adding an acidic solution into the fermentation reactor to obtain a third mixed solution, wherein the pH value of the third mixed solution is 6.8-7.5;

and step four, introducing nitrogen into the fermentation reactor, and performing anaerobic fermentation to obtain methane.

Preferably, the mixing ratio of the straws to the papermaking wastewater in the step one is that 3000ml of 2000-150 g of the papermaking wastewater is needed for every 100-150g of the straws, so that the straws can be completely soaked in the papermaking wastewater.

Preferably, the mixing ratio of the straws and the papermaking wastewater in the step one is that 2000ml of the papermaking wastewater is needed for every 100g of the straws. Therefore, raw materials are saved, the straw can be completely soaked in the papermaking wastewater, and the straw and the papermaking wastewater are mixed more fully.

Preferably, the condition of the intensive mixing in the first step is to shake the fermentation reactor 2-3 times per day for 4-6 minutes each time. Therefore, the papermaking wastewater can fully treat the straws, damage the internal structure of the straws, namely damage the structure of lignin in the straws, so that the straws are not wrapped by cellulose and hemicellulose, and the production of methane in the later period is facilitated.

Preferably, the biogas slurry in the second step is prepared by fermenting organic substances filtered by a 10-mesh filter screen. The preparation is simple, the raw materials are easily obtained, and the sources of the raw materials are rich.

Preferably, the total solid content of the second mixed solution in the second step is in the range of 6-8%, which can avoid the organic load from being too high, and is more beneficial to start the anaerobic reaction.

Preferably, the acidic solution in the third step is acetic acid, sulfuric acid or hydrochloric acid, which can neutralize the alkalinity of the papermaking wastewater, and is more favorable for constructing the environment for producing methane and the production of methane in the later period.

Preferably, the nitrogen is introduced in the fourth step for 3-5min, so as to ensure an anaerobic environment for producing methane.

Preferably, the anaerobic fermentation in the fourth step is carried out under constant temperature condition, and the temperature range of the anaerobic fermentation is 34-36 ℃, which is more suitable for the temperature of the anaerobic fermentation and has better economic performance.

Preferably, the time for anaerobic fermentation is 20-25 days, so as to ensure the complete anaerobic fermentation process.

In some specific embodiments, a method for producing methane by using straw anaerobic fermentation comprises the following steps:

cutting straws into small sections of 2-3cm, placing the straws in a sealed transparent fermentation reactor filled with papermaking wastewater according to the proportion that every 100-150g of the straws needs 2000-3000ml of the papermaking wastewater, mixing at the temperature of 50-55 ℃, and keeping the sealed state for 3-4 days to obtain a first mixed solution; and shaking the fermentation reactor for 2-3 times every day, wherein the duration of each time is 4-6 minutes, so that the papermaking wastewater can fully treat the straws; on one hand, the straws are pretreated by the papermaking wastewater, lignin in the straws is damaged, water molecules can enter the straws in the anaerobic fermentation process, the settleability of the straws is improved, so that the problem of scum shell layers is solved to a certain extent, the anaerobic fermentation process is promoted, the yield of methane gas is increased, and on the other hand, the fermentation reactor is sealed and transparent, so that the anaerobic fermentation is facilitated, and the reaction condition in the fermentation reactor can be observed constantly;

step two, adding biogas slurry serving as an inoculum into the fermentation reactor to obtain a second mixed solution, and ensuring that the total solid content range of the second mixed solution is 6-8%;

adding an acidic solution into the fermentation reactor to obtain a third mixed solution, wherein the pH value of the third mixed solution is 6.8-7.5;

and step four, introducing nitrogen into the fermentation reactor, continuing for 3-5min, and performing anaerobic fermentation for 20-25 days at the temperature of 34-36 ℃ to obtain methane.

The method for preparing methane by utilizing straw anaerobic fermentation in the embodiment pretreats the straw with the papermaking wastewater, destroys lignin in the straw, and enables water molecules to enter the straw in the anaerobic fermentation process, thereby improving the settleability of the straw, solving the problem of scum crusting layer to a certain extent, promoting the anaerobic fermentation process, increasing the yield of methane gas, compared with the traditional method for preparing methane gas by utilizing anaerobic fermentation under the conditions of the same scale and the like, the total yield of preparing methane gas by the method of the invention is improved by 20-30%, the thickness of the scum layer in the anaerobic fermentation process is reduced by 25-40%, the use cost is low, the method is environment-friendly, social and economic benefits are improved, meanwhile, the cost of straw pretreatment can be reduced, the pretreatment process is simple, and the loss of equipment is small, saving time and operating costs. In addition, the method of the embodiment reduces both BOD and COD of the papermaking wastewater by 30-40%, and reduces subsequent pollution to the environment.