Biogas Leak Detection Method
1. Slow Gas Production or Leakage from Biogas Digesters
(1) If the biogas digester is filled with water and the water level remains unchanged, but the pressure gauge's water column does not rise, it may indicate a leak. To check for leaks, you can use the flame test method.
The procedure is as follows: Open the gas pipeline valve, fill the pool to the cover plate, expel all air inside the tank, then close the valve. Remove some water from the pool so that the water level drops about 600mm below the cover. After 24 hours, if no changes are observed (such as no drop in water level or leakage from the movable cover), light a candle or oil lamp and place the air pipe nozzle near the flame. Then open the valve. If the flame is drawn into the nozzle, it means the tank is sealed properly. However, if the flame doesn’t react normally, it indicates a leak.
After the digester has been charged for several days (5–10 days in summer, 20 days in winter at temperatures above 10°C), if gas is still not produced, it might be due to a leak. At this point, direct the gas pipe away from the methane tank (at least 10 meters away) and ignite it carefully. Do not light the gas directly at the pipe’s end to avoid backfire. Turn on the valve. If no gas comes out and the flame remains unaffected, it suggests a leak. If gas is released but doesn't burn, vent it several times and try again. If it ignites, it’s normal for the gas to be inconsistent in quantity.
(2) If the pressure gauge shows a very slow rise in the water column, and there is insufficient gas with no fire or heat, you can use positive and negative pressure testing. Record the initial height of the water column, release the gas, turn off the valve, and remove some water from the pool to create more than 100mm of negative pressure. After 24 hours, refill some water into the pool and observe the pressure gauge. If the water column height is the same as before, the tank is not leaking, but gas production is slow. If the column rises higher, it indicates a leak.
(3) If the digester initially produces gas normally but then experiences a sudden drop in output, it could be due to air leakage.
(4) During operation, if the water column moves in the opposite direction of the intake air, indicating negative pressure, it suggests a leak in the digester.
2. Methods for Identifying Leaks in Biogas Digesters
To detect internal leaks, start by inspecting the exterior, then move inward, gradually eliminating possible causes and identifying the exact location of the problem before repairing it.
(1) External Inspection Method: Use a plastic tube with a valve, tie one end securely, submerge it in a basin of water, and blow air into the other end using a pump or your mouth. Observe for any bubbles forming in the tube, valve, or connectors. Where bubbles appear, there is likely a leak. When using biogas, apply soapy water to the pipes, valves, joints, elbows, and connections to check for bubbles. Pay special attention to the joints between the ducts and the tank cover, as well as the movable cover.
(2) Internal Inspection Method: After eliminating external leaks, if the tank is still suspected of leaking, drain the liquid and ensure all gas is removed. Then visually inspect the tank cover, walls, and bottom for cracks, voids, or loose pipes. Tap the tank with your fingers or a stick—if it sounds hollow, it may indicate a damaged sealing layer. Check the joints between the inlet/outlet pipes and the tank wall carefully. Also, look for signs of water seepage on the tank walls. For hard-to-see areas, sprinkle dry cement powder or ash on the surface; wet spots or lines indicate leaks. Once identified, mark the location for repair.
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