Device and method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane

Abstract

A device and method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane, the method comprising a biological filter startup stage and a biological oxidation of ultra-low concentration coalbed methane stage. In the biological filter startup stage, a bacterial solution made from activated sludge is pumped into the gas phase reaction zone and all porous carriers are immersed, so that the microorganisms adhere to the surface and pores of the carriers. After a period of time, all liquids in the device are drained and recovered, leaving only a layer of liquid film on the surface of the filler. Ultra-low concentration coalbed methane is alternately introduced into the gas phase reaction zone from both ends of the device to provide a carbon source for the aerobic methane oxidizing bacteria in the biofilm on the surface of the filler, enabling them to grow and reproduce rapidly, and this operating mode is maintained until the device is successfully started. In the biological oxidation of ultra-low concentration coalbed methane stage, the circulating bacterial solution used in the startup stage is replaced with a sterile fresh nutrient solution, and the remaining operations are the same. In this stage, the aerobic methane oxidizing bacteria in the biofilm selectively oxidize the methane in the ultra-low concentration coalbed methane into carbon dioxide and water.

Description

Technical Field

[0001] The present invention belongs to the technical field of methane treatment, relates to the biological conversion of coalbed methane, and particularly relates to a device and method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane. Background Art

[0002] Coalbed methane released during mining is one of the main sources of methane emissions. Methane-rich coalbed methane is mainly divided into three types: gas pre-extracted from the coal seam before mining, gas discharged from the working area of ​​the mine, and gas diluted by ventilators during coal mining (mine ventilation). The former has a higher methane content and can be utilized through direct power generation, replacement of natural gas, synthetic fuels, etc., and the relevant technologies are relatively mature. The methane content of the latter two is low and easily fluctuates. They are often enriched and concentrated through deep cooling, membrane, hydrate, adsorption and solvent absorption methods, or burned using thermal oxidation technology to recover waste heat. Enrichment and concentration technology has always had the technical difficulty of separating methane and nitrogen. Thermal storage oxidation technology requires higher temperature conditions, and the use of catalysts also increases the cost burden.

[0003] Microbial methane oxidation is an environmentally friendly treatment method. Methanophiles can oxidize CH4 to CO2 and H2O through a series of enzymatic cascade reactions. Type II methanotrophs are also capable of assimilating CH4 into polyhydroxyalkanoates (POHs). Compared to purification, separation, and oxidative combustion technologies, bioconversion can further reduce economic costs and safety risks. However, due to limitations such as a single inlet flow and the low solubility of methane in water, existing methane biofiltration systems often suffer from slow startup, slow effectiveness, low stability, and uneven microbial distribution. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a device and method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane, so as to remove the unidirectional substrate limitation of the bioreactor, stably maintain the high uniformity of aerobic methane oxidizing bacteria in the device, and ultimately achieve efficient biological oxidation of ultra-low concentration coalbed methane.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane includes a chamber, which is divided into a gas phase reaction zone, a first gas diffusion zone and a second gas diffusion zone. The gas phase reaction zone is filled with a porous carrier with water holding and adsorption capacity, and the gas phase reaction zone is connected to a liquid storage tank; the first gas diffusion zone sends the gas to be treated from a first direction to the gas phase reaction zone at a first time, and the second gas diffusion zone sends the gas to be treated from a second direction to the gas phase reaction zone at a second time; the angle α between the first direction and the second direction has a value range of 90°<α≤180°, the first time and the second time are in an alternating relationship, and nutrient solution is sent to the gas phase reaction zone through the liquid storage tank in the alternating interval.

[0007] In one embodiment, the first gas diffusion zone is separated from the gas phase reaction zone by a first microporous plate, and the second gas diffusion zone is separated from the gas phase reaction zone by a second microporous plate.

[0008] In one embodiment, a gas circuit valve is provided on the transport pipeline of the gas to be treated, the first outlet of the gas circuit valve is connected to the first gas diffusion zone, and a first air humidifier is provided on the connecting pipeline, the second outlet of the gas circuit valve is connected to the second gas diffusion zone, and a second air humidifier is provided on the connecting pipeline.

[0009] In one embodiment, the first gas diffusion region occupies 3-10% of the total volume of the chamber, and the second gas diffusion region occupies 3-10% of the total volume of the chamber.

[0010] In one embodiment, the first direction is vertically upward, ie, an upflow direction, and the second direction is vertically downward, ie, a downflow direction.

[0011] In one embodiment, the gas phase reaction zone has at least two exhaust ports, namely a first exhaust port and a second exhaust port; the first exhaust port is located at the end region of the first direction, and the second exhaust port is located at the end region of the second direction.

[0012] In one embodiment, the filling rate of the porous carrier in the gas-phase reaction zone is not less than 80%.

[0013] The present invention also provides a method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane, which is implemented based on the bidirectional flow biological oxidation of ultra-low concentration coalbed methane device, including a biological filter startup stage and a biological oxidation of ultra-low concentration coalbed methane stage;

[0014] The biofilter startup stage and the biological oxidation ultra-low concentration coalbed methane stage both include:

[0015] Step 1: pumping liquid from a liquid storage tank into a gas phase reaction zone, wherein the porous carrier is continuously immersed in the liquid, and then all the liquid is drained; a layer of liquid film, i.e., a surface biofilm, remains on the surface of the porous carrier;

[0016] Step 2: sending the gas to be treated into the gas phase reaction zone through the first gas diffusion zone to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier for their growth and reproduction;

[0017] Step 3: stop the gas supply, pump the liquid in the liquid storage tank into the gas phase reaction zone again to soak the porous support again, and then drain all the liquid;

[0018] Step 4: sending the gas to be treated into the gas phase reaction zone through the second gas diffusion zone to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier for their growth and reproduction;

[0019] Step 5, stop gas supply and repeat steps 1 to 4;

[0020] During the startup phase of the biofilter, the liquid in the storage tank is a bacterial liquid made from activated sludge. The immersion in steps 1 and 3 allows the microorganisms to enter and remain on the surface and pores of the porous carrier. The termination condition of step 5 is that the methane removal rate of the biofilter reaches more than 80% and the methane content in the exhaust gas varies by less than ±5%.

[0021] In the biological oxidation of ultra-low concentration coalbed methane stage, the liquid in the liquid storage tank is a sterile fresh nutrient solution, and the immersion in steps 1 and 3 enables the biofilm attached to the surface and pores of the porous carrier to obtain nutrient elements from the nutrient solution to maintain biological activity.

[0022] In one embodiment, the volume content of methane in the gas to be treated is less than 30%; the components of the sterile fresh nutrient solution do not contain a carbon source, and the methane in the mixed gas serves as the only carbon source for the microorganisms.

[0023] In one embodiment, the nutrient solution is in an aerobic stirring state in the storage tank.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The biofilm is in an alternating state of immersion and drainage. In the immersion state, the nutrient supply of aerobic methane oxidizing bacteria is fully guaranteed, while in the drainage state, the gas-liquid contact area on the biofilm surface is greatly increased, which can accelerate the methane oxidation rate of aerobic methane oxidizing bacteria.

[0026] 2. The bidirectional air intake mode makes the microbial communities at both ends of the device periodically in a period of abundant carbon source, improving the one-way substrate reduction phenomenon of traditional biological filters and making the distribution of methane oxidizing bacteria in the reactor more uniform.

[0027] 3. The method of the present invention has a simple operation process and can achieve efficient biological removal of low-concentration methane under mild conditions, providing an effective way to mitigate the greenhouse effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of a reactor used in an embodiment of the present invention.

[0029] Figure 2 is the daily change in methane removal rate during the biofilter startup phase.

[0030] Figure 3 is the methane removal efficiency of the biofilter at different empty bed residence times. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0032] like Figure 1 As shown, the present invention is a bidirectional flow biological oxidation device for ultra-low concentration coalbed methane, comprising a chamber divided into three main regions: a gas phase reaction zone 1, a first gas diffusion zone 2, and a second gas diffusion zone 4. The gas phase reaction zone 1 is filled with a porous carrier 14. The porous carrier 14 should have good water-retention and adsorption capabilities, typically such as sponge particles, with a single side dimension of 5-10 mm and a total size of preferably 5 mm x 5 mm x 5 mm. The gas phase reaction zone 1 is connected to a liquid storage tank 7, which is used to deliver a nutrient solution for aerobic methane oxidizing bacteria to the gas phase reaction zone 1.

[0033] The first gas diffusion zone 2 supplies the gas to be processed from a first direction to the gas-phase reaction zone 1, and the second gas diffusion zone 4 supplies the gas to be processed from a second direction to the gas-phase reaction zone 1. The angle α between the first and second directions is within the range of 90° < α ≤ 180°. That is, the first and second gas diffusion zones 2 and 4 supply gas in opposite directions and may have an angle therebetween, and the gas supply times do not overlap. The first time is defined as the time for gas supply through the first gas diffusion zone 2, and the second time is defined as the time for gas supply through the second gas diffusion zone 4. The first and second times are alternating, but they are not closely connected, but rather have an alternating gap. This alternating gap is the time for nutrient solution to be supplied to the gas-phase reaction zone 1 via the liquid storage tank 7.

[0034] According to the above structure, bidirectional air flow allows the microbial communities at both ends of the chamber to alternate between periods of carbon source abundance, ensuring uniform distribution of methane-oxidizing bacteria in the gas-phase reaction zone and avoiding the substrate reduction phenomenon caused by traditional unidirectional air flow. Furthermore, liquid is supplied between the air supply intervals, causing the biofilm to alternate between soaking and draining. The soaking state fully ensures the nutrient supply for aerobic methane-oxidizing bacteria, while the draining state significantly increases the gas-liquid contact area on the biofilm surface, thereby significantly accelerating the methane oxidation rate. For example, the first and second time periods are preferably equal in duration.

[0035] In some embodiments of the present invention, the angle α is preferably equal to 180°, i.e., completely symmetrical reverse air supply. Furthermore, the first direction is set to be vertically upward, i.e., upflow, and the second direction is set to be vertically downward, i.e., downflow.

[0036] At this time, a liquid drain port is provided at the bottom of gas-phase reaction zone 1, above first gas diffusion zone 2. This drain port is connected to liquid storage tank 7 via a drain pipe 16 with a water stop valve 8. A liquid inlet port is provided at the top of gas-phase reaction zone 1, below second gas diffusion zone 4. This inlet port is connected to liquid storage tank 7 via a liquid inlet pipe 17 with a peristaltic pump 6. Thus, by activating peristaltic pump 6, liquid is supplied to gas-phase reaction zone 1, and by opening water stop valve 8, liquid is discharged from gas-phase reaction zone 1.

[0037] In this embodiment, during operation, the gas to be treated flows into the gas-phase reaction zone 1 of the device in both upflow and downflow directions. The porous carrier 14, in a drained state, converts the methane component into carbon dioxide and water. During downtime, no mixed gas flows into the device, and the porous carrier 14 is immersed in a nutrient solution, allowing the biofilm to obtain nutrients and promoting microbial growth and reproduction.

[0038] In some embodiments of the present invention, the first gas diffusion zone 2 is separated from the gas phase reaction zone 1 by a first microporous plate 3 , and the second gas diffusion zone 4 is separated from the gas phase reaction zone 1 by a second microporous plate 5 .

[0039] The function of the first microporous plate 3 and the second microporous plate 5 is to redistribute the gas in the first gas diffusion zone 2 and the second gas diffusion zone 4 and form a uniform micro-airflow, so that the gas can fully contact the aerobic methane oxidizing bacteria biofilm in the gas phase reaction zone 1 to increase the methane oxidation rate.

[0040] In some embodiments of the present invention, a gas valve 9 is installed in the pipeline transporting the gas to be treated. To facilitate experiments, a high-pressure steel cylinder 13 is provided to temporarily store a portion of the gas to be treated. The gas valve 9 is connected to the outlet of the high-pressure steel cylinder 13. To control flow, a mass flow controller 12 is installed at the outlet of the high-pressure steel cylinder 13. The first outlet of the gas valve 9 is connected to the first gas diffusion zone 2, and a first air humidifier 10 is installed in the connecting pipeline. The second outlet of the gas valve 9 is connected to the second gas diffusion zone 4, and a second air humidifier 11 is installed in the connecting pipeline.

[0041] In this embodiment, the first air humidifier 10 and the second air humidifier 11 can humidify the gas to be treated and provide humidity for the biological filter, thereby preventing the porous carrier 14 from drying out and causing the death of microorganisms during the air supply process.

[0042] In some embodiments of the present invention, the first gas diffusion zone 2 occupies 3-10%, and more preferably 5%, of the total volume of the chamber, and the second gas diffusion zone 4 occupies 3-10%, and more preferably 5% of the total volume of the chamber. In other words, the preferred ratio of the gas-phase reaction zone 1 to the total volume of the chamber is 90%. The effective volume of the liquid storage tank 7 is 1.2-2 times the volume of the gas-phase reaction zone 1.

[0043] According to this ratio, the volume of the nutrient solution stored in the liquid storage tank 7 is always larger than the volume of the reactor, ensuring that the nutrient solution can completely immerse the filler in the reactor during the soaking stage.

[0044] In some embodiments of the present invention, the gas phase reaction zone 1 has at least two exhaust ports, namely a first exhaust port 18 and a second exhaust port 19; the first exhaust port 18 is located in the end area of ​​the first direction, and the second exhaust port 19 is located in the end area of ​​the second direction.

[0045] In this embodiment, when air is introduced through the first gas diffusion zone 2, the exhaust gas generated by the device is discharged from the first exhaust port 18 and collected by an air bag. When air is introduced through the second gas diffusion zone 4, the exhaust gas generated by the device is discharged from the second exhaust port 19 and collected by an air bag. Alternatively, the exhaust gas can be discharged into the atmosphere after being decontaminated.

[0046] In some embodiments of the present invention, the filling rate of the porous carrier 14 in the gas phase reaction zone 1 is not less than 80%, that is, 80-100%.

[0047] In some embodiments of the present invention, the reaction temperature in the gas phase reaction zone 1 needs to be kept constant at 25-35° C., and this temperature can be feedback-controlled by the temperature control system 15 outside the chamber and the temperature sensor inside the chamber.

[0048] In some embodiments of the present invention, the gauge pressure in the gas phase reaction zone 1 is 0 bar.

[0049] According to the above-mentioned bidirectional flow biological oxidation device of ultra-low concentration coalbed methane of the present invention, the bidirectional flow biological oxidation method of ultra-low concentration coalbed methane of the present invention is divided into a biological filter startup stage and a biological oxidation stage of ultra-low concentration coalbed methane.

[0050] The biofilter startup phase involves allowing microorganisms in the activated sludge solution to adhere to the surface and pores of the packing, allowing them to adapt to the internal environment of the biofilter. Using methane from the gas to be treated as a single carbon source for these microorganisms, aerobic methane-oxidizing bacteria become the dominant microbial population adhering to the surface and pores of the packing. During this phase, the liquid in the liquid storage tank 7 is the activated sludge solution. The process includes:

[0051] In step 11, the liquid in the liquid storage tank 7 is pumped into the gas-phase reaction zone 1. The liquid level is preferably sufficient to submerge all of the porous carriers 14. The porous carriers 14 are continuously immersed in the liquid, allowing microorganisms to enter and settle on their surfaces and pores. Afterward, all of the liquid is drained. A layer of liquid film, i.e., a surface biofilm, remains on the surface of the porous carriers 14.

[0052] When the drainage pipe 16 and the inlet pipe 17 are provided, the bacterial solution can be pumped in by starting the peristaltic pump 6 and closing the water stop valve 8, the immersion can be maintained by closing the peristaltic pump 6, and the bacterial solution can be discharged by starting the water stop valve 8 and recovered into the liquid storage tank 7. For example, the immersion time is between 30 and 180 minutes.

[0053] In step 12, the gas to be treated is sent into the gas phase reaction zone 1 through the first gas diffusion zone 2 to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier 14 for their growth and reproduction.

[0054] When the gas circuit valve 9, mass flow controller 12, first air humidifier 10 and first microporous plate 3 are set as mentioned above, and the first gas diffusion zone 2 and the second gas diffusion zone 4 are respectively located directly below and directly above the gas phase reaction zone 1, by adjusting the gas circuit valve 9, the mixed gas flows out of the mass flow controller 12 and then passes through the first air humidifier 10 in sequence into the first gas diffusion zone 2, and finally enters the gas phase reaction zone 1 in an upflow manner through the first microporous plate 3.

[0055] In step 13, the gas supply is stopped and the activated sludge-derived bacterial liquid is again pumped into the gas-phase reaction zone 1. The liquid level should ideally submerge all of the porous carriers 14. This allows the porous carriers 14 to be re-soaked, allowing the microorganisms to enter and settle on their surfaces and pores. Afterward, all the liquid is drained. A layer of liquid film, i.e., a surface biofilm, remains on the surface of the porous carriers 14.

[0056] Similar to step 11, when drain line 16 and inlet line 17 are provided, the bacterial solution can be pumped in by activating peristaltic pump 6 and closing water stop valve 8. Soaking can be maintained by closing peristaltic pump 6. The bacterial solution can be discharged by activating water stop valve 8 and recovered in liquid storage tank 7. For example, the soaking time is between 30 and 180 minutes.

[0057] In step 14, the gas to be treated is sent into the gas phase reaction zone 1 through the second gas diffusion zone 4 to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier 14 for their growth and reproduction.

[0058] Similar to step 12, when the gas circuit valve 9, mass flow controller 12, second air humidifier 11 and second microporous plate 5 are set as mentioned above, and the first gas diffusion zone 2 and the second gas diffusion zone 4 are respectively located directly below and directly above the gas phase reaction zone 1, by adjusting the gas circuit valve 9, the mixed gas flows out of the mass flow controller 12 and then passes through the second air humidifier 11 into the second gas diffusion zone 4, and finally enters the gas phase reaction zone 1 in a downflow manner through the second microporous plate 5.

[0059] Step 15: Stop gas supply and repeat steps 11 to 14 until the change in the methane content at the outlet is less than the set value. The device is successfully started and this phase ends. For example, the set value is ±5%.

[0060] The biological oxidation of ultra-low concentration coalbed methane is the formal treatment stage, where aerobic methane-oxidizing bacteria in the biofilm selectively oxidize methane in the ultra-low concentration coalbed methane into carbon dioxide and water. In this stage, the liquid in the liquid storage tank 7 is a sterile fresh nutrient solution. The process of this stage includes:

[0061] In step 21, the liquid in the liquid storage tank 7 is pumped into the gas phase reaction zone 1. The porous carrier 14 is continuously immersed in the liquid so that the biofilm attached to its surface and pores obtains nutrients from the nutrient solution to maintain biological activity, and then all the liquid is discharged.

[0062] Similar to step 11, when the drainage pipe 16 and the inlet pipe 17 are set up, the nutrient solution can be pumped in by starting the peristaltic pump 6 and closing the water stop valve 8, the immersion is maintained by closing the peristaltic pump 6, and the nutrient solution is discharged by starting the water stop valve 8 and recovered into the liquid storage tank 7. For example, the immersion time is between 30 and 180 minutes.

[0063] Step 22, at the first time, the gas to be treated is sent into the gas phase reaction zone 1 through the first gas diffusion zone 2 to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier 14 for their growth and reproduction.

[0064] Similar to step 12, when the gas circuit valve 9, mass flow controller 12, first air humidifier 10 and first microporous plate 3 are set as mentioned above, and the first gas diffusion zone 2 and the second gas diffusion zone 4 are respectively located directly below and directly above the gas phase reaction zone 1, by adjusting the gas circuit valve 9, the mixed gas flows out of the mass flow controller 12 and then passes through the first air humidifier 10 into the first gas diffusion zone 2, and finally enters the gas phase reaction zone 1 in an upflow manner through the first microporous plate 3.

[0065] Step 23, stop the gas supply, pump the liquid in the liquid storage tank 7 into the gas phase reaction zone 1 again, soak the porous carrier 14 again, and allow the biofilm attached to its surface and pores to obtain nutrients from the nutrient solution to maintain biological activity, and then discharge all the liquid.

[0066] Similar to step 11, when the drainage pipe 16 and the inlet pipe 17 are set up, the nutrient solution can be pumped in by starting the peristaltic pump 6 and closing the water stop valve 8, the immersion is maintained by closing the peristaltic pump 6, and the nutrient solution is discharged by starting the water stop valve 8 and recovered into the liquid storage tank 7. For example, the immersion time is between 30 and 180 minutes.

[0067] Step 24, at the second time, the gas to be treated is sent into the gas phase reaction zone 1 through the second gas diffusion zone 4 to provide a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier 14 for their growth and reproduction.

[0068] Similar to step 14, when the gas circuit valve 9, mass flow controller 12, second air humidifier 11 and second microporous plate 5 are set as mentioned above, and the first gas diffusion zone 2 and the second gas diffusion zone 4 are respectively located directly below and directly above the gas phase reaction zone 1, by adjusting the gas circuit valve 9, the mixed gas flows out of the mass flow controller 12 and then passes through the second air humidifier 11 into the second gas diffusion zone 4, and finally enters the gas phase reaction zone 1 in a downflow manner through the second microporous plate 5.

[0069] Step 25, stop the gas supply and repeat steps 21 to 24.

[0070] In the present invention, the dominant bacterial community in the biofilm on the surface and within the pores of the porous carrier 14 is aerobic methane oxidizing bacteria. Throughout the entire process, the nutrient solution in the liquid storage tank 7 is maintained in an aerobic stirring state to improve treatment efficiency. In the present invention, the methane in the gas to be treated serves as the sole carbon source for the microorganisms; that is, the nutrient solution used does not contain a carbon source.

[0071] The methane content of the gas to be treated in the present invention is less than 30% (v / v). For example, when using a high-pressure steel cylinder 13, the gas composition therein is a methane / air mixture with a ratio of 1% (v / v) methane and 99% (v / v) air. In this embodiment, the total volume of the chamber is further selected to be approximately 2.5 L, with the first gas diffusion zone 2 and the second gas diffusion zone 4 each accounting for 5% of the total volume, approximately 0.1 L; the gas phase reaction zone 1 accounts for 90% of the total volume, approximately 2.3 L; the liquid storage tank 7 has a volume of 4 L; the reaction temperature is set to a constant 30°C; during the biofilter startup phase, the MLSS of the bacterial liquid produced from the activated sludge is 4500 mg / L, and the porous carrier filling rate is 100%.

[0072] A 24-hour cycle consisted of a 22-hour high-efficiency biological oxidation phase and a 2-hour wet immersion phase for the biofilm carriers. Both the biofilter startup phase and the actual ultra-low-concentration coalbed methane treatment phase consisted of five steps, totaling 24 hours. These steps included 11 hours each for upflow and downflow air intake, and 1 hour each for the two biofilm carrier immersion phases. Under 30-minute space-time conditions, the biofilter took three days to start up. Following successful startup, the bioreactor remained in the ultra-low-concentration coalbed methane biological oxidation phase.

[0073] The first time and the second time are maintained for 11 hours respectively. The biofilm carrier is immersed in the nutrient solution for 1 hour before changing the air flow direction each time. When the biofilter is formally treating ultra-low concentration coalbed methane, the nutrient solution in the storage tank is updated every 4 days.

[0074] Each liter of nutrient solution is diluted by eight nutrient stock solutions: A (10 mL), B (10 mL), C (10 mL), D (10 mL), E (1 mL), F (1 mL), G (5 mL), and H (10 mL).

[0075] The specific formula is as follows:

[0076]

[0077] The method of the present invention was used to carry out biofiltration experiments on low-content (1% v / v) methane mixed gas in a methane bioconversion system. Figure 2 and Figure 3 The results showed that the bioreactor could be successfully started up in just three days with an empty bed residence time of 30 minutes. When the empty bed residence time was 5 minutes, the system still achieved a methane removal efficiency of 80-85%. The microorganisms in the packing in the upper, middle, and lower parts of the device were evenly distributed, and there was no significant difference in biomass.

[0078] For those skilled in the art, based on the above principles, several changes and improvements can be made to the method of the present invention, and these changes and improvements should also be included in the scope of protection of the present invention.

Claims

1. A device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane, characterized in that: The invention comprises a chamber, wherein the chamber is divided into a gas phase reaction zone (1), a first gas diffusion zone (2) and a second gas diffusion zone (4); the gas phase reaction zone (1) is filled with a porous carrier (14) having water holding and adsorption capabilities, and the gas phase reaction zone (1) is connected to a liquid storage tank (7); the first gas diffusion zone (2) sends the gas to be treated from a first direction to the gas phase reaction zone (1) at a first time, and the second gas diffusion zone (4) sends the gas to be treated from a second direction to the gas phase reaction zone (1) at a second time; the value range of the angle α between the first direction and the second direction is The angle of the first time and the second time are in an alternating relationship, and the nutrient solution is fed into the gas phase reaction zone (1) through the liquid storage tank (7) during the alternating interval; the first gas diffusion zone (2) and the gas phase reaction zone (1) are separated by a first microporous plate (3), and the second gas diffusion zone (4) and the gas phase reaction zone (1) are separated by a second microporous plate (5); the first gas diffusion zone (2) occupies 3 to 10% of the total volume of the chamber, and the second gas diffusion zone (4) occupies 3 to 10% of the total volume of the chamber.

2. The device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 1, characterized in that: An air circuit valve (9) is provided on the transport pipeline of the gas to be treated, a first outlet of the air circuit valve (9) is connected to the first gas diffusion zone (2), and a first air humidifier (10) is provided on the connecting pipeline, and a second outlet of the air circuit valve (9) is connected to the second gas diffusion zone (4), and a second air humidifier (11) is provided on the connecting pipeline.

3. The device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 1, characterized in that: The first direction is vertically upward, that is, an upflow direction, and the second direction is vertically downward, that is, a downflow direction.

4. The device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 1, characterized in that: The gas phase reaction zone (1) has at least two exhaust ports, namely a first exhaust port (18) and a second exhaust port (19); the first exhaust port (18) is located in the end region of the first direction, and the second exhaust port (19) is located in the end region of the second direction.

5. The device for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 1, characterized in that: The filling rate of the porous carrier (14) in the gas phase reaction zone (1) is not less than 80%.

6. A method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane, based on the bidirectional flow biological oxidation of ultra-low concentration coalbed methane device according to any one of claims 1 to 5, characterized in that: It includes the biofilter startup stage and the bio-oxidation stage of ultra-low concentration coalbed methane; The biofilter startup stage and the biological oxidation ultra-low concentration coalbed methane stage both include: Step 1: pumping the liquid in the liquid storage tank (7) into the gas phase reaction zone (1), the porous carrier (14) is continuously immersed in the liquid, and then all the liquid is discharged; a layer of liquid film, i.e., a surface biofilm, remains on the surface of the porous carrier (14); Step 2, sending the gas to be treated into the gas phase reaction zone (1) through the first gas diffusion zone (2), providing a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier (14) to grow and reproduce; Step 3, stop the gas supply, pump the liquid in the liquid storage tank (7) into the gas phase reaction zone (1) again to soak the porous carrier (14) again, and then drain all the liquid; Step 4, sending the gas to be treated into the gas phase reaction zone (1) through the second gas diffusion zone (4), providing a carbon source for the aerobic methane oxidizing bacteria on the surface and in the pores of the porous carrier (14) to grow and reproduce; Step 5: Stop gas supply and repeat steps 1 to 4; During the startup phase of the biofilter, the liquid in the liquid storage tank (7) is a bacterial liquid made from activated sludge, and the soaking in steps 1 and 3 allows the microorganisms to enter and remain on the surface and pores of the porous carrier (14). The termination condition of step 5 is that the methane removal rate of the biofilter reaches more than 80%, and the change in the methane content in the exhaust gas is less than ±5%; In the biological oxidation of ultra-low concentration coalbed methane stage, the liquid in the liquid storage tank (7) is a sterile fresh nutrient solution, and the immersion in steps 1 and 3 enables the biofilm attached to the surface and pores of the porous carrier (14) to obtain nutrient elements from the nutrient solution to maintain biological activity.

7. The method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 6, characterized in that: The volume content of methane in the gas to be treated is less than 30%; the components of the sterile fresh nutrient solution do not contain a carbon source, and the methane in the mixed gas serves as the sole carbon source for the microorganisms; the sterile fresh nutrient solution is prepared by diluting the following nutrient mother solution, and the formula is as follows: 10 mL of 20 g / L CaCl2·2H2O; 10 mL of 100 g / L MgSO4·7H2O; 10 mL of 0.4 g / L Fe-EDTA; 10 mL of nutrient solution D, consisting of 27.2 g / L KH2PO4 and 61 g / L K2HPO4; 1 mL of nutrient solution E, consisting of 0.2 g / L FeSO4·7H2O, 0.01 g / L ZnSO4·7H2O, 0.03 g / L H3BO3, 0.003 g / L MnCl2·4H2O, 0.003 g / L Na2MoO4·2H2O, 0.002 g / L NiCl2·6H2O, and 0.02 g / L CoCl2·6H2O; 1 mL of nutrient solution F, consisting of: 0.005 g / L calcium pantothenate, 0.002 g / L biotin, 0.002 g / L folic acid, 0.01 g / L pyridoxine hydrochloride, 0.005 g / L riboflavin, 0.005 g / L thiamine hydrochloride, 0.0001 g / L cyanocobalamin, 0.005 g / L niacin, 0.005 g / L p-aminobenzoic acid, and 0.005 g / L lipoic acid; 5 mL of 0.5 g / L CuSO4·5H2O; 10mL of NH4Cl with a concentration of 26.75g / L.

8. The method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 6, characterized in that: The nutrient solution is in an aerobic stirring state in the liquid storage tank (7).

9. The method for bidirectional flow biological oxidation of ultra-low concentration coalbed methane according to claim 6, characterized in that: The internal gauge pressure of the biofilter is 0-5 bar.

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