The "automatic back flushing method" significantly enhances the gas production rate of biogas digesters. This technique involves replacing the original "three-way" system with a new "four-way" configuration for the digester's feeding mechanism. A pipeline is added from the "stone" (a reference to the dung pit) to the feed inlet of the biogas digester, directing material upward so that the liquid in the water pressure zone automatically returns to the feed port, effectively cleaning the biogas tank.
Depending on the terrain and materials, some "drum pits" are constructed within the "water pressure zone," while others are built outside it. There are two types of back flushing pipeline systems designed for different installation scenarios.
To install this system, a four-way fitting of the same diameter as the original digester lifter is placed in the position where the three-way was previously installed. A four-pass PVC pipe is then laid from the digester’s feed inlet, ensuring the intake is slightly elevated. At the end of the feeder, a check valve is added to prevent material from flowing back into the bucket when feeding.
A threaded connector is also installed on the four-way leading to the drum pit, allowing it to be sealed quickly during back flushing. This ensures that the water pressure liquid doesn’t flow back from the drum pit. At the feed port, the back flush inlet should be aligned parallel to the feed port to avoid blockages during regular feeding.
When installing the back flushing components, all joints such as the four-way and elbow fittings should be sealed with adhesive and buried below ground level to maintain a clean and safe environment around the biogas tank.
This automatic back flushing method offers several advantages. It solves the long-standing issue of washing and agitating the digester from the feed inlet, especially when the biogas tank is located underground in pigsties. With just a simple actuation of the feeder, the digester can be cleaned and refilled automatically, boosting biogas output consistently.
Farmers no longer need to manually carry waste or other fermentation materials to perform cleaning tasks. The back flushing device allows the fermented slurry between the water pressure zone to naturally flow back into the digester through the feed port, reducing labor intensity.
Additionally, the constant movement of the liquid level prevents the formation of crusts on the surface of the fermented material. Even if crusting occurs, it will break down naturally due to the continuous liquid circulation.
By repeatedly drawing up material from the bottom, the system promotes the movement of solid matter and rejuvenates the microbial culture at the base, increasing the gas production rate by approximately one-third.
Each back flushing device costs only 26 yuan and can generate an additional 100 cubic meters of biogas annually. At a rate of 1 yuan per cubic meter of methane, this translates to an extra 100 yuan of income per biogas digester each year. This makes the system both cost-effective and highly beneficial for small-scale farmers.
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