Exogenous hydrogen driven anaerobic fermentation methanation device and methane production process

Abstract

The invention belongs to the technical field of agricultural waste biomass biogas fermentation, and particularly relates to an exogenous hydrogen driven anaerobic fermentation methanation device and a methane production process. The exogenous hydrogen driven anaerobic fermentation methanation device comprises a plurality of acid production tanks, a main fermentation tank, a fermentation liquor return tank, a water circulation mechanism and a mixed gas circulation mechanism. The two-phase anaerobic fermentation mode is set, acid production and methane production are carried out in different tanks respectively, and hydrogen, CO2 and the like produced in the acid production process are separated and purified through the mixed gas circulation mechanism and used for subsequent methane production anaerobic fermentation. In the methane production process, exogenous high-purity and high-quality hydrogen and CO2 are introduced into the main fermentation tank together, and the fermentation efficiency is improved by adjusting the introduction amount of hydrogen and CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of anaerobic fermentation of agricultural waste biomass, and particularly relates to an exogenous hydrogen-driven anaerobic fermentation methanation device and a methane production process. Background Art

[0002] Anaerobic fermentation using agricultural waste biomass as raw material can obtain two products, biogas and biogas fertilizer. Biogas is a gaseous fuel containing about 60% methane (CH4) and 40% carbon dioxide (CO2). As is well known, it is methane that plays the role of fuel. When the methane content reaches over 90%, its combustion performance is comparable to that of natural gas, so it is also called biomethane. However, no matter what fermentation technology and process are adopted, it is very difficult to obtain biogas with a relatively high methane ratio through direct fermentation, because the methane proportion in biogas is determined by the characteristics of the raw materials. Taking straw as an example, its main components are cellulose, hemicellulose and lignin. It is cellulose and hemicellulose that participate in fermentation and produce methane and carbon dioxide. Cellulose is a macromolecular polysaccharide composed of glucose units (C6H 10 O5)n, while hemicellulose is a heterogeneous polymer composed of several different types of pentose (C5H8O4)n and hexose. It is not difficult to see from the molecular structures of cellulose or hemicellulose that in the process of their conversion into methane, obviously hydrogen is insufficient, and a considerable proportion of carbon dioxide will inevitably be produced. Agricultural waste biomass is scattered in nature, and the same proportion of carbon dioxide will also be produced under anoxic conditions.

[0003] To increase the methane content in biogas, hydrogen addition is crucial during the anaerobic fermentation process. It is not difficult to introduce hydrogen gas into the feed liquid of anaerobic fermentation. The challenge lies in how to enable the added hydrogen to participate in biochemical reactions to the greatest extent, that is, to convert more hydrogen molecules into hydrogen ions and dissolve them into the fermentation broth and participate in the methanation reaction, rather than overflowing from the liquid surface. An excessive supply of hydrogen not only causes waste and dilutes the methane content but also leads to too high a hydrogen partial pressure within the system, thereby inhibiting the activity of methanogenic microorganisms. There are mainly two ways for exogenous hydrogen to react with carbon dioxide to drive methanation: one is to use hydrogen as an electron donor, and under the action of hydrogenotrophic methanogens and various enzymes, through a series of enzymatic reactions, electrons are transferred to carbon dioxide, reducing carbon dioxide step by step; the other is that hydrogen and carbon dioxide react under the action of homoacetogens to form acetic acid, which is then converted into methane. Due to the low solubility of hydrogen in liquids, it is not easy for exogenous hydrogen addition to be utilized by the microorganisms in the fermentation system. The applicant found through previous research that by increasing the gas-liquid contact area and prolonging the gas residence time, the ionic conversion rate of hydrogen molecules can be increased. In addition, the timing of hydrogen addition also needs to be considered. During the anaerobic fermentation process, hydrogen-producing and acetate-producing metabolism requires reducing the hydrogen partial pressure in the system, while homoacetogenic metabolism requires a relatively high hydrogen partial pressure. Therefore, exogenous hydrogen added after the hydrogen-producing and acetate-producing stage and before the homoacetogenic stage can achieve its highest efficiency. However, the limiting factors for the ionization rate of hydrogen in the fermentation broth in a complex ecological environment, the influence mechanism on the electron transfer of microorganisms in the fermentation broth in the presence of a certain proportion of hydrogen ions, and the efficient path of hydrogen carbon fixation are not very clear, which to a certain extent restricts the improvement of carbon fixation efficiency. To achieve efficient hydrogen-driven anaerobic fermentation methanation, the kinetic characteristics of the hydrogen molecule ionic conversion rate and the carbon fixation mechanism of carbon dioxide reduction need to be further studied.

[0004] Due to its simple and efficient characteristics, the technology of driving anaerobic fermentation methanation by hydrogen addition has gradually become a sustainable, environmentally friendly, and scientific and reasonable energy upgrade solution. However, there are still problems that need to be solved urgently, such as the lack of unified hydrogen addition system technology, the low dissolution rate of hydrogen in the fermentation broth, and the unclear hydrogen-driven methanation path. Therefore, it is necessary to construct a new type of anaerobic fermentation biogas production system for hydrogen carbon fixation. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention designs an exogenous hydrogen-driven anaerobic fermentation methanation device and a methanation process. By setting a two-phase anaerobic fermentation method, acid production and methanation are carried out in different tanks respectively. Through a mixed gas circulation mechanism, hydrogen, CO2, etc. produced during the acid production process are separated and purified for subsequent anaerobic fermentation of methanation.

[0006] During the methane production process of the external hydrogen-driven anaerobic fermentation methanation device of the present invention, high-purity and high-quality external hydrogen and CO2 are introduced into the main fermentation tank together, and the fermentation efficiency is improved by adjusting the input amounts of hydrogen and CO2.

[0007] Based on the above purposes, the present invention adopts the following technical solutions:

[0008] An external hydrogen-driven anaerobic fermentation methanation device includes several acid-producing tanks, a main fermentation tank, a fermentation liquid reflux tank, and a water circulation mechanism and a mixed gas circulation mechanism;

[0009] The main fermentation tank includes a tank body and an upper cover; the tank body of the main fermentation tank is provided with a feed end, an air inlet end, a discharge end, and a first sewage discharge end;

[0010] The feed end of the main fermentation tank is connected with a main feed pipe; the discharge ends of several acid-producing tanks are all connected to the main feed pipe through a first discharge pipe;

[0011] The discharge end of the main fermentation tank is connected to the feed end of the fermentation liquid reflux tank through a second discharge pipe;

[0012] The discharge end of the fermentation liquid reflux tank is connected to the main feed pipe through a reflux pipe;

[0013] The mixed gas circulation mechanism includes a main gas collecting pipe, a solid-liquid impurity separator, a membrane separator, an external hydrogen addition pipe, and several first hydrogen collecting pipes;

[0014] Second exhaust ends are provided at the tops of several acid-producing tanks, and the second exhaust ends of several acid-producing tanks are all connected to the main gas collecting pipe through the first hydrogen collecting pipes;

[0015] The main gas collecting pipe is connected to the input end of the solid-liquid impurity separator. The solid-liquid impurity separator is provided with a gas output end and a solid-liquid separation end. The gas output end of the solid-liquid impurity separator is connected to the input end of the membrane separator through a pipeline; the membrane separator is provided with a hydrogen output end and a CO2 output end;

[0016] The CO2 output end of the membrane separator is connected to the air inlet end of the main fermentation tank through a first air inlet pipeline;

[0017] The external hydrogen addition pipe is connected to the first air inlet pipeline; the external hydrogen addition pipe accesses external high-purity and high-quality hydrogen.

[0018] Furthermore, there are three acid-producing tanks.

[0019] Furthermore, the top of the tank body is open, and the upper cover is detachably installed at the top of the tank body. After the upper cover is installed at the top of the tank body, structural sealing can be achieved.

[0020] Furthermore, first discharge pumps and first valves are provided on the first discharge pipes.

[0021] Further, a second valve is provided at a position on the main feed pipe close to the main fermentation tank.

[0022] Further, a stirring paddle is provided in the main fermentation tank. The shaft end of the stirring paddle extends upward out of the upper cover of the main fermentation tank, and a stirring motor is provided at the top end of the main fermentation tank. The output shaft of the stirring motor is connected to the shaft end of the stirring paddle.

[0023] Further, a first exhaust end is also provided on the upper cover of the main fermentation tank. The first exhaust end is connected to a methane gas collection pipe; an inspection end is also provided on the side wall of the main fermentation tank.

[0024] Further, a third valve and a second discharge pump are provided on the second discharge pipe.

[0025] Further, a reflux pump and a fourth valve are provided on the reflux pipe; a second sewage discharge end is also provided at the bottom end of the fermentation liquid reflux tank.

[0026] Further, a main header pipe pump and a fifth valve are provided at the connection between the main header pipe and the solid-liquid impurity separator.

[0027] Further, an air supply pipe is also provided in the main fermentation tank. The air supply pipe extends horizontally left and right along the water direction. One end of the air supply pipe is connected to the air inlet end of the main fermentation tank, and the other end of the air supply pipe bends upward and is provided with an aerator.

[0028] Further, a first air inlet pump and a sixth valve are provided on the first air inlet pipeline; a gas flow meter is also provided near the connection of the first air inlet pipeline to the main fermentation tank.

[0029] Further, the mixed gas circulation mechanism further includes a hydrogen storage tank;

[0030] The hydrogen output end of the membrane separator is communicated with the hydrogen storage tank through a hydrogen collection pipe. The output end of the hydrogen storage tank is also communicated with the first air inlet pipeline through a hydrogen reflux pipe, and a seventh valve is provided on the hydrogen reflux pipe.

[0031] Further, an eighth valve is provided on the external hydrogen addition pipe.

[0032] Further, the water circulation mechanism includes a heat preservation water tank, a first water outlet pipe, a first water inlet pipe, a second water outlet pipe and a second water inlet pipe;

[0033] A jacket layer is further provided outside the main fermentation tank. The bottom end of the jacket layer is provided with a water inlet end, and the top end of the jacket layer is provided with a water outlet end;

[0034] The bottom of the heat preservation water tank is communicated with the water inlet end of the jacket layer through the first water outlet pipe, and the water outlet end of the jacket layer is communicated with the bottom of the heat preservation water tank through the first water inlet pipe.

[0035] Further, the top of the heat preservation water tank is discharged externally through the second water outlet pipe, and the externally connected hot water can be introduced into the heat preservation water tank through the second water inlet pipe; at the same time, part of the water in the heat preservation water tank is discharged and hot water is introduced through the second water outlet pipe and the second water inlet pipe, so as to keep the water in the heat preservation water tank at a certain temperature;

[0036] Valves are provided on the first water outlet pipe, the first water inlet pipe, the second water outlet pipe and the second water inlet pipe to control the inflow and outflow of water in the heat preservation water tank. They are all conventional settings in the prior art and are not the inventive points of the present invention, so they will not be elaborated here.

[0037] Further, based on a general inventive concept, the present invention also provides a methane production process using an anaerobic fermentation methanation device driven by exogenous hydrogen, including the following steps:

[0038] 1) Anaerobic fermentation to produce acid:

[0039] First, place the fermentation raw material (corn straw) and the inoculum (activated sludge) containing methanogens (including hydrogenotrophic methanogenic bacteria) in the acid production tank. During the acid production process, the methanogens (including hydrogenotrophic methanogenic bacteria) convert the fermentation raw material (corn straw) into acetic acid, forming a fermentation broth, and at the same time producing part of hydrogen and part of CO2;

[0040] 2) Collection and purification of the mixed gas:

[0041] Part of the hydrogen and part of the CO2 obtained during the acid production process in the acid production tank are used as the primary mixed gas and collected into the main gas collecting pipe through the first hydrogen collecting pipe;

[0042] At this time, open the main gas collecting pipe pump and the fifth valve, and introduce the primary mixed gas in the main gas collecting pipe into the solid-liquid impurity separator to remove the solid / liquid impurities mixed in the mixed gas for preliminary purification. The preliminarily purified mixed gas enters the membrane separator and is separated into hydrogen and CO2 in the membrane separator. The separated pure hydrogen flows to the hydrogen storage tank through the hydrogen collecting pipe;

[0043] 3) Anaerobic fermentation to produce methane:

[0044] Open the valves on the first water outlet pipe and the first water inlet pipe, and introduce the water with a certain temperature in the heat preservation water tank into the jacket layer and circulate between the jacket layer and the heat preservation water tank, so as to make the main fermentation tank reach a certain fermentation temperature;

[0045] Open the first discharge pump, the first valve, and the second valve, and introduce the materials (including the fermentation broth) after acid production in the three acid production tanks into the main fermentation tank. Then, open the first air inlet pump and the sixth valve, and under the action of the first air inlet pump, the carbon dioxide separated by the membrane separator enters the main fermentation tank through the first air inlet pipeline, the aeration pipe, and the aerator. At the same time, open the eighth valve on the external hydrogen addition pipe, and introduce the external hydrogen into the main fermentation tank through the first air inlet pipeline. The separated CO2 and the external hydrogen in the first air inlet pipeline form a secondary mixed gas.

[0046] When the secondary mixed gas in the first air inlet pipeline enters the main fermentation tank, it first passes through the aeration of the aerator, and then the stirring motor is turned on, and methane fermentation is carried out under the condition of the secondary mixed gas.

[0047] Specifically, in step 2), the gas separation membrane in the membrane separator uses a graphene-like carbon nitride separation membrane with a thickness of 0.51 nm, and the temperature during the operation of the membrane separator is maintained at 25 - 30 °C.

[0048] Specifically, in step 3), the fermentation temperature in the main fermentation tank is maintained at 30 - 32 °C.

[0049] Specifically, as another preferred technical solution, in step 3), the low-quality hydrogen collected in the hydrogen storage tank can also be mixed with the CO2 separated by the membrane separator and introduced into the main fermentation tank.

[0050] Specifically, in step 3), during methane fermentation, hydrogenotrophic methanogenic bacteria convert carbon dioxide and hydrogen into methane, which is discharged through the methane gas collection pipe. At the same time, a methane gas collection tank can be set to collect the methane gas discharged from the methane gas collection pipe, and the collected methane gas can be purified subsequently.

[0051] Specifically, in step 3), after fermentation, open the second discharge pump and the third valve, and introduce the remaining materials after fermentation into the fermentation broth reflux tank for static settlement and temporary storage. Then, open the fourth valve and the reflux pump, and pump the fermentation broth rich in microorganisms in the fermentation broth reflux tank back to the main fermentation tank for recycling, so as to improve the activity of hydrogenotrophic methanogenic bacteria in the main fermentation tank.

[0052] Specifically, in step 1), the dosage of the fermentation raw material is 20 - 40 grams per liter of fermentation broth.

[0053] Specifically, in step 1), the inoculation amount of the inoculum (activated sludge) is 10 - 30% (volume fraction).

[0054] Specifically, anaerobic acid production starts from the 1st - 2nd day of fermentation and ends on the 3rd - 4th day, and the acid production time is about 3 days.

[0055] Specifically, methane production by anaerobic fermentation starts on the 4th - 5th day and ends on the 28th day, and the methane production time is about 20 - 23 days.

[0056] Specifically, in step 3), during methane-producing fermentation, the daily hydrogen addition amount is 100 - 400 mL.

[0057] Preferably, in step 3), during methane-producing fermentation, the daily hydrogen addition amount is 100, 200, 300, or 400 mL.

[0058] Specifically, in step 3), during methane-producing fermentation, the volume ratio of hydrogen to carbon dioxide is (1 - 5):1.

[0059] Preferably, in step 3), during methane-producing fermentation, the volume ratio of hydrogen to carbon dioxide is 1:1, 3:2, or 4:1.

[0060] Compared with the prior art, the advantages of this application are as follows:

[0061] The exogenous hydrogen-driven anaerobic fermentation methanation device of the present invention includes several acid-producing tanks, a main fermentation tank, a fermentation liquid reflux tank, as well as a water circulation mechanism and a mixed gas circulation mechanism. By setting a two-phase anaerobic fermentation method, acid production and methane production are carried out in different tanks respectively. Through the setting of the mixed gas circulation mechanism, hydrogen, CO2, etc. produced during the acid production process are separated and purified for subsequent methane-producing anaerobic fermentation.

[0062] During the methane production process of the exogenous hydrogen-driven anaerobic fermentation methanation device of the present invention, high-purity and high-quality exogenous hydrogen and CO2 are introduced into the main fermentation tank together, and the fermentation efficiency is improved by adjusting the introduction amounts of hydrogen and CO2.

[0063] Compared with the conventional treatment scheme, by introducing exogenous high-purity and high-quality hydrogen during the methane-producing fermentation process, the present invention can also improve the carbon fixation efficiency, thereby increasing the methane production amount of anaerobic fermentation, and has good application prospects. Description of the Drawings

[0064] Figure 1 is the structural diagram of the exogenous hydrogen-driven anaerobic fermentation methanation device described in Example 1;

[0065] Figure 2 is the cumulative methane production amount under different hydrogen addition amounts;

[0066] Figure 3 is the methane concentration under different hydrogen addition amounts;

[0067] Figure 4 is the cumulative methane production amount under different ratios of added hydrogen to carbon dioxide;

[0068] Figure 5is the methane concentration under different ratios of added hydrogen to carbon dioxide;

[0069] Figure 6 is the cumulative methane production under different hydrogenation times;

[0070] Figure 7 is the methane concentration under different hydrogenation times. Detailed implementation manners

[0071] To make the above objects, features and advantages of the present invention more obvious and understandable, the following will describe in detail the specific implementation manners of the present invention with reference to the accompanying drawings. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field. Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art.

[0072] Example 1

[0073] As Figure 1 shown, an anaerobic fermentation methanation device driven by exogenous hydrogen includes three acid-producing tanks (each with a volume of 3 L) 1, a main fermentation tank (with a volume of 10 L) 2, a fermentation liquid reflux tank (with a volume of 15 L) 3, as well as a mixed gas circulation mechanism and a water circulation mechanism;

[0074] The main fermentation tank 2 includes a tank body and an upper cover. The tank body has an opening at the top, and the upper cover is detachably installed at the top of the tank body. After the upper cover is installed at the top of the tank body, structural sealing can be achieved; the tank body of the main fermentation tank 2 is provided with a feed end, an air inlet end, a discharge end and a first sewage discharge end 26;

[0075] The feed end of the main fermentation tank 2 is connected with a main feed pipe 11; the discharge ends of the three acid-producing tanks 1 are all connected to the main feed pipe 11 through first discharge pipes; first discharge pumps 12 and first valves 13 are provided on all three first discharge pipes;

[0076] A second valve 14 is provided on the main feed pipe 11 near the main fermentation tank 2;

[0077] A stirring paddle is provided in the main fermentation tank 2. The shaft end of the stirring paddle extends upward out of the upper cover of the main fermentation tank 2, and a stirring motor 21 is provided at the top of the main fermentation tank 2. The output shaft of the stirring motor 21 is connected to the shaft end of the stirring paddle;

[0078] The upper cover of the main fermentation tank 2 is also provided with a first exhaust end 22, and the first exhaust end 22 is connected with a methane gas collection pipe 28; an inspection end 23 is also provided on the side wall of the main fermentation tank 2;

[0079] The discharge end of the main fermentation tank 2 is connected to the feed end of the fermentation liquid reflux tank 3 through a second discharge pipe 31. A third valve 32 and a second discharge pump 38 are provided on the second discharge pipe 31;

[0080] The discharge end of the fermentation broth reflux tank 3 is connected to the main feed pipe 11 through a reflux pipe 35; a reflux pump 37 and a fourth valve 36 are provided on the reflux pipe 35; a second sewage discharge end 33 is also provided at the bottom end of the fermentation broth reflux tank 3;

[0081] The mixed gas circulation mechanism includes three first hydrogen collection pipes 15, a total gas collection pipe 51, a solid-liquid impurity separator 5, a membrane separator 6, a hydrogen storage tank 4, and an external hydrogen addition pipe 81;

[0082] Second exhaust ends are provided at the tops of the three acid-producing tanks 1, and the second exhaust ends of the three acid-producing tanks 1 are all connected to the total gas collection pipe 51 through the first hydrogen collection pipes 15;

[0083] The total gas collection pipe 51 is connected to the input end of the solid-liquid impurity separator 5, and a total gas collection pipe pump 52 and a fifth valve 53 are provided at the connection between the total gas collection pipe 51 and the solid-liquid impurity separator 5;

[0084] The solid-liquid impurity separator 5 is provided with a gas output end and a solid-liquid separation end, and the gas output end of the solid-liquid impurity separator 5 is connected to the input end of the membrane separator 6 through a pipeline; the membrane separator 6 is provided with a hydrogen output end and a CO2 output end;

[0085] The CO2 output end of the membrane separator 6 is connected to the intake end of the main fermentation tank 2 through a first intake pipeline 61. An aeration pipe 25 is also provided in the main fermentation tank 2. The aeration pipe 25 extends horizontally left and right. One end of the aeration pipe 25 is connected to the intake end of the main fermentation tank 2, and the other end of the aeration pipe 25 bends upward and is provided with an aerator 24; a first intake pump 62 and a sixth valve 63 are provided on the first intake pipeline 61; a gas flow meter 64 is also provided near the connection between the first intake pipeline 61 and the main fermentation tank 2 for monitoring the intake volume;

[0086] The hydrogen output end of the membrane separator 6 is connected to the hydrogen storage tank 4 through a hydrogen collection pipe 41, and the output end of the hydrogen storage tank 4 is also connected to the first intake pipeline 61 through a hydrogen reflux pipe 42. A seventh valve 43 is provided on the hydrogen reflux pipe 42;

[0087] The external hydrogen addition pipe 81 is connected to the first intake pipeline 61, and an eighth valve 82 is provided on the external hydrogen addition pipe 81; the external hydrogen addition pipe 81 accesses external high-purity and high-quality hydrogen.

[0088] The mixed gas collected by the main gas collecting pipe 51 passes through the solid-liquid impurity separator 5 to remove the solid / liquid impurities mixed in the mixed gas and conduct preliminary purification. The preliminarily purified mixed gas enters the membrane separator 6. The gas separation membrane in the membrane separator 6 is a graphene-like carbon nitride separation membrane with a thickness of 0.51 nm (purchased from Haining Kelo Membrane Filtration Equipment Co., Ltd.). When the membrane separator 6 operates, the temperature is maintained at 27 °C. The separated pure hydrogen flows through the hydrogen collecting pipe 41 to the hydrogen storage tank 4. The separated carbon dioxide enters the main fermentation tank 2 through the first intake pipe 61, the aeration pipe 25, and the aerator 24 under the action of the first intake pump 62;

[0089] Meanwhile, exogenous hydrogen (high-purity and high-quality hydrogen) can also enter the main fermentation tank 2 through the first intake pipe 61, the aeration pipe 25, and the aerator 24. The secondary mixed gas after passing through the aerator 24 increases the contact probability between carbon dioxide and methanogens, thereby enhancing the probability of carbon dioxide being fixed.

[0090] In addition, the low-quality hydrogen collected in the hydrogen storage tank 4 can also enter the main fermentation tank 2 through the first intake pipe 61, the aeration pipe 25, and the aerator 24. After passing through the aerator 24, the contact probability between the gas and methanogens is increased.

[0091] The water circulation mechanism includes a heat preservation water tank 71, a first water outlet pipe 73, a first water inlet pipe 74, a second water outlet pipe 75, and a second water inlet pipe 76;

[0092] A jacket layer 27 is also provided outside the main fermentation tank 2. The bottom end of the jacket layer 27 is provided with a water inlet end, and the top end of the jacket layer 27 is provided with a water outlet end;

[0093] The bottom of the heat preservation water tank 71 is connected to the water inlet end of the jacket layer 27 through the first water outlet pipe 73, and the water outlet end of the jacket layer 27 is connected to the bottom of the heat preservation water tank 71 through the first water inlet pipe 74;

[0094] The top of the heat preservation water tank 71 is externally drained through the second water outlet pipe 75, and the externally connected hot water can be introduced into the heat preservation water tank 71 through the second water inlet pipe 76; at the same time, part of the water in the heat preservation water tank 71 is discharged and hot water is introduced through the second water outlet pipe 75 and the second water inlet pipe 76, so as to keep the water in the heat preservation water tank 71 at a certain temperature.

[0095] Valves (not marked in the figure) are provided on the first water outlet pipe 73, the first water inlet pipe 74, the second water outlet pipe 75, and the second water inlet pipe 76 to control the inflow and outflow of water in the heat preservation water tank 71. They are all conventional settings in the prior art and are not the inventive points of the present invention, so they will not be described in detail.

[0096] The external hydrogen-driven anaerobic fermentation methanation device of the present invention is a two-phase anaerobic fermentation, where acid production and methane production are carried out in different tanks. Specifically, acid production is carried out in three acid-producing tanks 1, and methane production is carried out in the main fermentation tank 2.

[0097] The operating principle of the external hydrogen-driven anaerobic fermentation methanation device of the present invention is as follows:

[0098] Before operation, first place the fermentation raw material (corn straw) and the inoculum (activated sludge) containing methanogens (including hydrogenotrophic methanogenic bacteria) in the three acid-producing tanks 1. The inoculation amount of activated sludge is 30% (volume fraction). During the acid production process, methanogens (including hydrogenotrophic methanogenic bacteria) convert the fermentation raw material (corn straw) into acetic acid, forming a fermentation broth, and at the same time producing some hydrogen and some CO2, that is, obtaining a primary mixed gas, which is collected into the main gas collecting pipe 51 through the first hydrogen collecting pipe 15;

[0099] Among them, the reference for the activated sludge is: Zhang Yupeng, Li Jianzheng, Liu Fengqin, etc. Influence mechanism of bicarbonate on hydrogenotrophic and aceticlastic methanogenic bacteria [J]. China Environmental Science, 2017, 37(05): 1937-1944.

[0100] Among them, the reference for the methanogens used in the present invention is (Gong Weijia, Li Wenzhe, Liu Jianyu. Research progress of methanogens in anaerobic digestion [J]. Journal of Northeast Agricultural University, 2006, (06): 838-841.).

[0101] Then open the valves on the first water outlet pipe 73 and the first water inlet pipe 74, and introduce the water with a certain temperature in the heat preservation water tank 71 into the jacket layer 27 and circulate between the jacket layer 27 and the heat preservation water tank 71, so as to make the main fermentation tank 2 reach a certain fermentation temperature (specifically, in this embodiment, keep the fermentation temperature in the main fermentation tank 2 at 30 °C);

[0102] Then open the first discharge pump 12, the first valve 13, and the second valve 14, and introduce the acid-produced materials (including the fermentation broth) in the three acid-producing tanks 1 into the main fermentation tank 2. At this time, open the main gas collecting pipe pump 52 and the fifth valve 53, and introduce the primary mixed gas in the main gas collecting pipe 51 into the solid-liquid impurity separator 5 and the membrane separator 6 in sequence, and separate it into hydrogen and CO2 in the membrane separator 6. Then open the first intake pump 62 and the sixth valve 63, and introduce the separated CO2 into the main fermentation tank 2 through the first intake pipeline 61. At the same time, open the eighth valve 82 on the external hydrogen addition pipe 81, and introduce the external hydrogen into the main fermentation tank 2 through the first intake pipeline 61. In the first intake pipeline 61, the separated CO2 and the external hydrogen form a secondary mixed gas (or the low-quality hydrogen collected in the hydrogen storage tank 4 can also be mixed with the CO2 separated by the membrane separator 6 and introduced into the main fermentation tank 2);

[0103] When the secondary mixed gas in the first intake pipe 61 enters the main fermentation tank 2, it first passes through the aeration of the aerator 24, and then the stirring motor 21 is turned on to improve the reaction efficiency, and methane fermentation is carried out under the condition of the secondary mixed gas. Specifically, hydrogenotrophic methanogenic bacteria convert carbon dioxide and hydrogen into methane, which is discharged through the methane gas collection pipe 28. At the same time, a methane gas collection tank can be set to collect the methane gas discharged from the methane gas collection pipe 28, and the collected methane gas can be purified subsequently;

[0104] After fermentation, the second discharge pump 38 and the third valve 32 are opened, and the remaining materials after fermentation are introduced into the fermentation liquid reflux tank 3 for standing and temporary storage. Then, the fourth valve 36 and the reflux pump 37 are opened, and the fermentation liquid rich in microorganisms in the fermentation liquid reflux tank 3 is pumped back into the main fermentation tank 2 for recycling, so as to improve the activity of hydrogenotrophic methanogenic bacteria in the main fermentation tank 2.

[0105] Example 2

[0106] The methane production process using the anaerobic fermentation methanation device driven by exogenous hydrogen described in Example 1 is as follows:

[0107] 1) Anaerobic fermentation to produce acid:

[0108] First, place the fermentation raw material (corn straw) and the inoculum (activated sludge) containing methanogenic bacteria (including hydrogenotrophic methanogenic bacteria) in three acid production tanks 1. The inoculation amount of activated sludge is 30% (volume fraction). During the acid production process, methanogenic bacteria (including hydrogenotrophic methanogenic bacteria) convert the fermentation raw material (corn straw) into acetic acid, forming a fermentation liquid, and at the same time producing some hydrogen and some CO2; among them, the dosage of the fermentation raw material is 30 grams of corn straw per liter of fermentation liquid;

[0109] Among them, the methanogenic bacteria used in the present invention refer to the reference (Gong Weijia, Li Wenzhe, Liu Jianyu. Research progress of methanogenic bacteria in anaerobic digestion [J]. Journal of Northeast Agricultural University, 2006, (06): 838-841.);

[0110] The temperature of the acid production fermentation is 30 °C, the initial pH is 7, and the acid production fermentation time is about 3-4 days;

[0111] 2) Collection and purification of the mixed gas:

[0112] Part of the hydrogen and part of the CO2 obtained during the acid production process in the three acid production tanks 1 are used as the primary mixed gas and collected into the main gas collection pipe 51 through the first hydrogen collection pipe 15;

[0113] At this time, turn on the main header pipe pump 52 and the fifth valve 53, and introduce the primary mixed gas in the main header pipe 51 into the solid-liquid impurity separator 5 to remove the solid / liquid impurities mixed in the mixed gas and conduct preliminary purification. The preliminarily purified mixed gas enters the membrane separator 6, where it is separated into hydrogen and CO2. The gas separation membrane in the membrane separator 6 uses a graphene-like carbon nitride separation membrane with a thickness of 0.51 nm (purchased from Haining Kelo Membrane Filtration Equipment Co., Ltd.). When the membrane separator 6 operates, the temperature is maintained at 27°C. The separated pure hydrogen flows through the hydrogen collection pipe 41 to the hydrogen storage tank 4;

[0114] 3) Anaerobic fermentation to produce methane:

[0115] Open the valves on the first water outlet pipe 73 and the first water inlet pipe 74, and introduce the water with a certain temperature in the heat preservation water tank 71 into the jacket layer 27 and circulate between the jacket layer 27 and the heat preservation water tank 71, so that the main fermentation tank 2 reaches a certain fermentation temperature (specifically, in this embodiment, the fermentation temperature in the main fermentation tank 2 is maintained at 30°C);

[0116] Open the first discharge pump 12, the first valve 13, and the second valve 14, and introduce the acid-producing materials (including fermentation broth) in the three acid-producing tanks 1 into the main fermentation tank 2. Then open the first air inlet pump 62 and the sixth valve 63, and under the action of the first air inlet pump 62, the carbon dioxide separated by the membrane separator 6 enters the main fermentation tank 2 through the first air inlet pipeline 61, the aeration pipe 25, and the aerator 24. At the same time, open the eighth valve 82 on the external hydrogen addition pipe 81, and introduce the external hydrogen into the main fermentation tank 2 through the first air inlet pipeline 61. The separated CO2 and the external hydrogen in the first air inlet pipeline 61 form a secondary mixed gas (or the low-quality hydrogen collected in the hydrogen storage tank 4 can also be mixed with the CO2 separated by the membrane separator 6 and introduced into the main fermentation tank 2);

[0117] When the secondary mixed gas in the first air inlet pipeline 61 enters the main fermentation tank 2, it first passes through the aeration of the aerator 24, and then turn on the stirring motor 21 to improve the reaction efficiency, and carry out methane-producing fermentation under the condition of the secondary mixed gas (the temperature of methane-producing fermentation is 30°C, the pH is about 6.5 - 7, and the overall methane-producing time is about 20 - 23 days). Specifically, hydrogenotrophic methanogenic bacteria convert carbon dioxide and hydrogen into methane, which is discharged externally through the methane gas collection pipe 28. At the same time, a methane gas collection tank can also be set to collect the methane gas discharged from the methane gas collection pipe 28, and the collected methane gas can be purified subsequently;

[0118] After fermentation, open the second discharge pump 38 and the third valve 32, and introduce the remaining materials after fermentation into the fermentation liquid reflux tank 3 for static settlement and temporary storage. Then open the fourth valve 36 and the reflux pump 37, and pump the fermentation liquid rich in microorganisms in the fermentation liquid reflux tank 3 back to the main fermentation tank 2 for recycling, so as to improve the activity of hydrogenotrophic methanogenic bacteria in the main fermentation tank 2.

[0119] Experimental results

[0120] In the following experiments, the methods for collecting and detecting methane gas are referenced from: Li Jingyu, Zhang Yingwei, Li Wenzhe, etc. Research on the Determination of Biogas Gas Composition and Content by Gas Chromatography [J]. Journal of Agricultural Mechanization Research, 2015, 37(06): 255-257.

[0121] 1. Influence of different hydrogen addition amounts on methane production by anaerobic fermentation

[0122] In order to obtain the optimal process for exogenous hydrogen-driven anaerobic fermentation methanation, different factors need to be changed, and the influence on indicators such as methane content and production can be obtained through experiments. First, experiments with different hydrogen addition amounts were carried out. When anaerobic methanogenic fermentation was carried out in the main fermentation tank 2, the daily hydrogen addition amounts were 100, 200, 300, and 400 mL respectively. At the same time, a control group without hydrogen addition was set up. At this time, pure hydrogen was introduced and no carbon dioxide was added. The addition method was as in step 3) of Example 2. Through the external hydrogen addition pipe 81, high-purity and high-quality external hydrogen was introduced into the main fermentation tank 2 through the first intake pipeline 61, and at the same time, the first intake pump 62 and the sixth valve 63 were closed.

[0123] The changes in cumulative methane production and methane concentration are as Figure 2 、 3 shown. Through experiments, it can be obtained that when the hydrogen addition amount is 300 mL / d, the maximum cumulative methane production is 350.3 mL / g VS (mL / g VS refers to the amount of methane that can be produced by the organic solids contained in each gram of corn straw). Compared with the control group, the production increased by 20.86%. At this time, the methane concentration can also reach the maximum value of 78%, and the average methane concentration increased by 15% compared with the control group. The methane production increases with the increase of the hydrogen addition amount, but when the hydrogen addition amount is too large at 400 mL / d, the methane production will instead decrease.

[0124] 2. Influence of different ratios of hydrogen and carbon dioxide addition on methane production by anaerobic fermentation

[0125] When adding external hydrogen, the influence of different ratios of hydrogen and carbon dioxide on cumulative methane production and methane concentration is as Figure 4 、 5As shown, the experimental conditions are the same as above. The volume ratios of hydrogen to carbon dioxide are set to 1:1, 3:2, 4:1, and pure hydrogen respectively. The addition method is as follows: in step 3) of Example 2, high-purity and high-quality hydrogen from outside is introduced into the main fermentation tank 2 through the first air inlet pipeline 61 via the external hydrogen addition pipe 81. At the same time, the carbon dioxide separated by the membrane separator 6 enters the main fermentation tank 2 through the first air inlet pipeline 61, the aeration pipe 25, and the aerator 24 under the action of the first air inlet pump 62.

[0126] According to the experimental results, when the volume ratio of hydrogen to carbon dioxide gas is 1:1, it will have an inhibitory effect on anaerobic fermentation. When the volume ratio is 4:1, the methane production is slightly higher than that of pure hydrogen. This may be because at the initial stage of anaerobic fermentation, a higher hydrogen partial pressure will instead inhibit the acid production process and ultimately affect the methane production.

[0127] 3. Influence of different hydrogen addition times on methane production in anaerobic fermentation

[0128] According to the thermodynamic equation of acid production in anaerobic fermentation (Reference: Guan Zhengjun, Li Wenzhe, Zheng Guoxiang, etc. Two-phase anaerobic fermentation technology for solid-liquid separation liquid of cow dung [J]. Transactions of the Chinese Society of Agricultural Engineering, 2011, 27(07): 300-305), it can be concluded that during the acid production stage, a higher hydrogen partial pressure will inhibit the production of acetic acid, thereby affecting the methane production. Therefore, it is necessary to study the influence of different hydrogen addition times on the cumulative methane production.

[0129] Experiments were carried out by three methods: adding hydrogen at the end of the acid production period (about the 4th day), adding hydrogen at the end of the methane production peak period (about the 18th day), and adding hydrogen throughout the process. The cumulative methane production and methane concentration are as Figure 6 、 7 shown; the addition method is as follows: in step 3) of Example 2, high-purity and high-quality hydrogen from outside is introduced into the main fermentation tank 2 through the first air inlet pipeline 61 via the external hydrogen addition pipe 81. At the same time, the first air inlet pump 62 and the sixth valve 63 are closed. At this time, pure hydrogen is introduced and there is no carbon dioxide. The daily hydrogen intake is 300 mL.

[0130] According to the experimental results, the cumulative methane production when adding hydrogen at the end of the acid production period is slightly higher than that of adding hydrogen throughout the process. When adding hydrogen at the end of the methane production peak period, the methane production is not much different from that of the control group. Therefore, it is optimal to add hydrogen at the end of the acid production, which can avoid the inhibitory effect of high hydrogen partial pressure on acid production on the one hand and reduce the consumption of hydrogen on the other hand.

Claims

1. An external hydrogen-driven anaerobic fermentation methanation device, characterized in that, It includes several acid-producing tanks, a main fermentation tank, a fermentation liquid reflux tank, as well as a water circulation mechanism and a mixed gas circulation mechanism; The main fermentation tank includes a tank body and an upper cover; the tank body of the main fermentation tank is provided with a feed end, an air inlet end, a discharge end and a first sewage discharge end; The feed end of the main fermentation tank is connected with a main feed pipe; the discharge ends of several acid-producing tanks are all connected with the main feed pipe through a first discharge pipe; The discharge end of the main fermentation tank is connected with the feed end of the fermentation liquid reflux tank through a second discharge pipe; The discharge end of the fermentation liquid reflux tank is connected with the main feed pipe through a reflux pipe; The mixed gas circulation mechanism includes a main gas collecting pipe, a solid-liquid impurity separator, a membrane separator, an external hydrogen addition pipe and several first hydrogen collecting pipes; Second exhaust ends are provided at the tops of several acid-producing tanks, and the second exhaust ends of several acid-producing tanks are all connected with the main gas collecting pipe through first hydrogen collecting pipes; The main gas collecting pipe is connected with the input end of the solid-liquid impurity separator. The solid-liquid impurity separator is provided with a gas output end and a solid-liquid separation end. The gas output end of the solid-liquid impurity separator is connected with the input end of the membrane separator through a pipeline; the membrane separator is provided with a hydrogen output end and a CO2 output end; The CO2 output end of the membrane separator is connected with the air inlet end of the main fermentation tank through a first air inlet pipeline; The external hydrogen addition pipe is connected with the first air inlet pipeline; the external hydrogen addition pipe accesses external high-purity and high-quality hydrogen.

2. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that First discharge pumps and first valves are provided on the first discharge pipes; a second valve is provided on the main feed pipe near the main fermentation tank.

3. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that, A stirring paddle is arranged in the main fermentation tank. The shaft end of the stirring paddle extends upward out of the upper cover of the main fermentation tank, and a stirring motor is arranged at the top of the main fermentation tank. The output shaft of the stirring motor is connected with the shaft end of the stirring paddle.

4. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that The upper cover of the main fermentation tank is also provided with a first exhaust end, and the first exhaust end is connected with a methane gas collecting pipe; a inspection end is also provided on the side wall of the main fermentation tank.

5. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that, A third valve and a second discharge pump are provided on the second discharge pipe; a reflux pump and a fourth valve are provided on the reflux pipe; a second sewage discharge end is also provided at the bottom of the fermentation liquid reflux tank; a main gas collecting pipe pump and a fifth valve are provided at the connection of the main gas collecting pipe and the solid-liquid impurity separator.

6. The anaerobic fermentation methanation device driven by exogenous hydrogen according to claim 1, characterized in that, An air distribution pipe is also arranged in the main fermentation tank. The air distribution pipe extends horizontally left and right along the water direction. One end of the air distribution pipe is connected to the air inlet end of the main fermentation tank, and the other end of the air distribution pipe bends upward and is provided with an aerator.

7. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that, A first air inlet pump and a sixth valve are provided on the first air inlet pipeline; a gas flowmeter is also provided on the first air inlet pipeline near the connection with the main fermentation tank.

8. The exogenous hydrogen-driven anaerobic fermentation methanation device according to claim 1, characterized in that, The mixed gas circulation mechanism also includes a hydrogen storage tank; The hydrogen output end of the membrane separator is connected with the hydrogen storage tank through a hydrogen collecting pipe, and the output end of the hydrogen storage tank is also connected with the first air inlet pipeline through a hydrogen reflux pipe. A seventh valve is provided on the hydrogen reflux pipe.

9. The anaerobic fermentation methanation device driven by exogenous hydrogen according to claim 1, characterized in that, The water circulation mechanism includes a heat preservation water tank, a first water outlet pipe, a first water inlet pipe, a second water outlet pipe and a second water inlet pipe; A jacket layer is also arranged outside the main fermentation tank. The bottom end of the jacket layer is provided with a water inlet end, and the top end of the jacket layer is provided with a water outlet end; The bottom of the heat preservation water tank is connected with the water inlet end of the jacket layer through a first water outlet pipe, and the water outlet end of the jacket layer is connected with the bottom of the heat preservation water tank through a first water inlet pipe.

10. The methane production process using the anaerobic fermentation methanation device driven by exogenous hydrogen as described in any one of claims 1-9 includes the following steps: 1) Anaerobic fermentation to produce acid: First, place the fermentation raw materials and the inoculum containing methanogens in the acid production tank. During the acid production process, the methanogens convert the fermentation raw materials into acetic acid, forming a fermentation broth, and at the same time producing part of hydrogen and part of CO2; 2) Collection and purification of the mixed gas: Take part of the hydrogen and part of the CO2 obtained during the acid production process in the acid production tank as the primary mixed gas, and collect it into the main collecting pipe through the first hydrogen collecting pipe; At this time, open the main collecting pipe pump and the fifth valve, and introduce the primary mixed gas in the main collecting pipe into the solid-liquid impurity separator to remove the solid / liquid impurities mixed in the mixed gas for preliminary purification. The preliminarily purified mixed gas enters the membrane separator, where it is separated into hydrogen and CO2. The separated pure hydrogen flows through the hydrogen collecting pipe to the hydrogen storage tank; 3) Anaerobic fermentation to produce methane: Open the valves on the first water outlet pipe and the first water inlet pipe, and introduce the water with a certain temperature in the insulation water tank into the jacket layer and circulate between the jacket layer and the insulation water tank, so as to make the main fermentation tank reach a certain fermentation temperature; Open the first discharge pump, the first valve, and the second valve, and introduce the materials after acid production in the three acid production tanks into the main fermentation tank. Then open the first intake pump and the sixth valve, and under the action of the first intake pump, introduce the carbon dioxide separated by the membrane separator into the main fermentation tank through the first intake pipeline, the aeration pipe, and the aerator. At the same time, open the eighth valve on the exogenous hydrogen addition pipe, and introduce the exogenous hydrogen into the main fermentation tank through the first intake pipeline. The CO2 and the exogenous hydrogen separated in the first intake pipeline form a secondary mixed gas; When the secondary mixed gas in the first intake pipeline enters the main fermentation tank, it first passes through the aeration of the aerator, and then open the stirring motor and carry out methanation fermentation under the condition of the secondary mixed gas.

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