This paper introduces a biogas fermentation method which can provide energy for greenhouse and the patented technology of the fermentation system. The fermentation system specifically consists of a biological acidification fertilizer accumulating device, a buffer regulating tank, an efficient biogas generating device, a sewage sedimentation tank, a sewage temporary storage tank and a biogas buffering device which are sequentially connected through pipelines and valves. The specific steps of the fermentation method include the start-up of the bio-acidification fertilizer accumulating device and the bio-acidification storage of raw materials, the start-up of the high-efficiency biogas generating device, biogas production and supply, shutdown and restart, etc. Compared with the traditional biogas technology, this technology has certain advantages. According to the actual production of greenhouse, it can add the organic waste scattered all the year round into the acid-producing and fertilizer-accumulating pool in time, and then produce biogas at any time through the fermentation system according to the energy demand of greenhouse. According to the production needs, the fermentation residue is taken out in batches to be used as organic fertilizer in the greenhouse. This technology can meet the requirements of flexible adjustment of biogas fermentation in greenhouse according to needs.
Keywords: biogas; Greenhouse; Energy supply; controllability
1. Introduction
Greenhouse is an important technical theme in modern agricultural engineering. The development of greenhouse has transformed the traditional open-air agriculture into controllable agriculture under protected conditions. First, soluble organic matter is very easy to react, and the gas production is within the allowable range of reactor load, which is basically determined by the short-term feed rate, that is, more feed produces more gas, less feed produces less gas, and stopping feeding will stop gas production in a short time. 2. Anaerobic microorganisms fermented by biogas in mature reactors have very strong hunger tolerance, which can endure for a long time without feeding for a long time, and can quickly resume normal and efficient gas production after restarting. The above two technical characteristics of efficient biogas fermentation technology of water-soluble organic matter meet the requirements of energy fluctuation in greenhouse. However, if the purpose of greenhouse energy supply is simply to deliberately buy water-soluble organic matter as fermentation raw material to produce biogas, it will not only have a competitive advantage with fossil energy in cost, but also fail to achieve the purpose of on-site utilization of biomass waste resources, circular economy and environmental construction. Therefore, the efficient biogas fermentation technology of water-soluble organic matter is not suitable for the energy supply demand of greenhouse.
3. Technical content
The invention provides a biogas fermentation system and method, which can be used for greenhouse production by adding organic waste of planting scattered all year round into the fermentation system, and then producing biogas through the fermentation system at any time according to the energy supply demand of the greenhouse. Wherein the fermentation system consists of a biological acidification fertilizer accumulating device, a buffer regulating tank, an efficient biogas generating device, a sewage sedimentation tank, a sewage temporary storage tank and a biogas buffering device which are sequentially connected through pipelines and valves. Its structure is shown in figure 1. Wherein, the biological acidification fertilizer accumulating device and the buffer pool are provided with main control valves; A pump is arranged between the buffer pool and the high-efficiency biogas generating device; The high-efficiency biogas generating device and the sewage temporary storage tank of the sewage sedimentation tank are connected by gravity and gravity of water; The effluent temporary storage tank is simultaneously connected with the buffer regulating tank and the biological acidification fertilizer accumulating device; A pump and a water distributor are sequentially arranged in the middle; The efficient biogas generating device is connected with the biogas buffering device.
In order to ensure that biogas fermentation can meet the energy demand of greenhouse, the above fermentation system is managed according to the following steps.
Firstly, start the bio-acidification fertilizer storage device to store raw materials in bio-acidification. The specific method is as follows.
(1) Collect organic wastes planted in greenhouses or other organic wastes planted as starting materials according to the mass equivalent to 2.5-3.5 times of the average daily output of greenhouses, and crush and pretreat the starting materials;
(2) adding N-containing substances into the pretreated raw materials obtained in step (1), mixing, and controlling the carbon-nitrogen ratio of the mixture to be (20:1)-(30:1);
(3) putting the mixture obtained in step (2) into a biological acidification fertilizer accumulating device used for the first time, adding inoculum for inoculation, and mixing to obtain fermentation raw materials, wherein the addition amount of inoculum is 3%-5% of the dry weight of the starting raw materials;
(4) adde water into that biological acidification fertilize accumulating device in step (3) for fermentation, wherein the water addition amount is at least higher than the initial raw material plane 10cm, and the fermentation temperature is control at 20-40 DEG C;
(5) after 4-5 days of fermentation, the pH value of the fermentation liquid drops below 6, that is, the start of the acidification and fertilizer accumulation device is completed;
(6) According to the method of steps (1) ~ (2), collect and treat the organic wastes generated in the greenhouse at any time, put them into the started biological acidification and fertilizer accumulation device in time, and directly add water to10 cm; Higher than the level of uninoculated raw materials;
(7) Repeat step (6) until one biological acidification fertilizer-accumulating device is fully charged, then restart another biological acidification fertilizer-accumulating device, and repeat operation steps (1) ~ (6);
Secondly, start the efficient biogas generating device, and the operation of the control device can meet the coordination of greenhouse energy consumption and biogas production. The specific method is as follows:
(1) Start-up of high-efficiency biogas generator: put the inoculum into the high-efficiency biogas generator, add water or acid mixture extracted from biological acidification and fertilizer accumulation device to the biogas generator, and let it stand for 3-5d, with the inoculum addition amount of 3-10 kg VSS/m3; Pump that organic acid liquid pumped from the biological acidification fertilize accumulating device into a buffer regulating pool, regulate the organic acid liquid with system effluent or external water in the effluent temporary storage pool, and controlling the chemical oxygen consumption (COD) concentration of the organic acid liquid to be 2,000-5,000 mg/L as raw materials for biogas fermentation; Adjust the hydraulic load in stages according to the rate of 0.5 kg cod/(m3 d) ~ 2 kg cod/(m3 d), and continuously feed until the hydraulic load is 5 kg cod/(m3 d) ~10 kg cod/(m3 d), that is, the start-up of the biogas generator is completed, and the whole start-up takes about 50 ~ 80 days. When starting, the temperature is controlled at 25 ~ 35℃. The principle of load adjustment is that after each hydraulic load adjustment is stable, the next stage of load increase will begin; The effluent from the biogas generating device flows into the effluent temporary storage tank after being precipitated by the sedimentation tank, part of which is used as the liquid supplement of the biological acidification and fertilizer accumulation device, and the other part is used to adjust the fermentation materials of the acidic solution in the buffer adjustment tank.
(2) Biogas production and supply: according to the actual estimated biogas demand time and quantity in greenhouse production, the required amount and time of organic acid liquid are converted into 0.4~0.5m3/kg cod biogas output, and the mechanical acid liquid is pumped out from the bio-acidification fertilizer-accumulating device on time and in quantity into the buffer regulating pool, and adjusted into biogas fermentation material according to the method of step (1); According to the flow rate of 5 kg COD/(m3 d) ~ 30 kg COD/(m3 d) hydraulic load, it is intermittently or continuously sent to the started biogas generating device for biogas production, and the generated biogas enters the biogas buffer device for standby; The flow rate control and intermittent or continuous feeding mode depend on the demand of biogas and the volume of biogas buffer device. When the demand for biogas is large and the volume of biogas buffer device is small, large-flow continuous feeding is adopted, otherwise small-flow intermittent feeding is adopted; When the extract in the bio-acidification fertilizer-accumulating device is less than 800 ~ 1000 mg/L, that is, the bio-acidification fertilizer-accumulating device stops producing acid and continues to extract fermentation liquor from the device.
(3) Stop biogas production: when biogas is no longer needed in the greenhouse after startup, or biogas is not used in the greenhouse for a long time at the end of a biogas use cycle, stop feeding the high-efficiency biogas generating device, and the device will enter a stop state. During the dormancy period, the fermentation materials are supplemented every10 ~ 30 days to ensure the nutritional needs of microorganisms in the system. The adjustment method of adding fermented materials is the same as step (1); The amount of supplementary fermentation materials is 1 ~ 3 times the reactor volume, and the supplementary acceleration amount is 2 ~ 5 kg cod/(m3 d).
(4) Restart after stopping gas production: the high-efficiency biogas plant that has been stopped in step (3) must be restarted before entering the new gas circulation; The restart method is to adjust the fermentation materials according to the method described in step (1) 3 ~ 10d before the start of the new gas circulation, and feed the materials to the high-efficiency biogas plant adaptively according to the load of1.8kg cod/(m3 d) ~ 2.2kg cod/(m3 d).