Anaerobic digestion technology, i.e. CSTR, IC, UASB, EGSB, HIRAD , as a major process of environmental engineering and protection, has been widely used in many areas like municipal solid waste (MSW), waste water treatment plant (WWTP), sludge treatment, food waste treatment, and industrial waste water treatment, etc. The anaerobic structure can be realized in many forms like egg-shaped digester, concrete tank, lipp tank, enamel assembling tank, or carbon steel welding tank style.
Biogas, as a by-product from anaerobic digestion, was once neglected and just discharged to air freely, which caused odour problem and potential safety hazard of explosion problem. In recent years, the implementation of environmental protection law has been reinforced than ever. The new idea and policy of "Green, Recycling, Low-carbon" is widely accepted. Biogas, is now recognized and utilized as "Green Energy". It can be simply burned by a flare, or utilized as green fuel of biogas Boiler or CHP cogeneration or injected to gas grid with upgraded CNG gas quality.
A typical case study shows that the electricity generated by biogas covers 100% of the total electricity required by running a complete WWTP (Waste Water Treatment Plant). In this case, Environtec has provided a complete line of biogas treatment products including: Desulfurization, Double Membrane Gas Holder, Filter, Gas Booster, Flare and so on.
A typical anaerobic biogas process is described as follows:
Biological desulfurization is the best practice technology(BMP)in the industry at present, which utilizes the me tabolism of microorganism itself, does not need to consume desulfurizer, has low operating cost and is fully automatic.
Each anaerobic tank can be installed a Gas Dome (MHD) on it for collecting the biogas. The gas dome has the function of inspection window, pressure sensor, liquid level detection, and also overpressure and negative pressure protection.
The biogas first goes through the Gravel Filter to remove solid particles. Meanwhile, a lot of condensate water can be collected and discharged automatically. The pressure loss is normally 1-2mbar.
Biogas then enters the desulfurization system. According to the inlet H2S concentration of raw gas, different processes i.e. Biological Scrubber, Dry Type Desulfurization can be chosen. Biological Scrubber, using microbial metabolic principle without consuming any chemicals, has proven itself with lowest operating cost and Best Practice Technology (BMP).
Biogas then goes to the gas holder for storage with a stable operating pressure. The design of storage time is normally 1-8 hours, and pressure is normally 15-25mbar. Double Membrane Gas Holder (DMG), in comparison with traditional steel tanks, can avoid the steel corrosion problem and the freezing of water sealing problem in winter time. DMG with its unique feathers of outstanding shape and outlook, quick and easy installation, low investment cost, has proven itself the Best Practice Technology (BMP) for biogas storage.
Before it enters the end-user, biogas shall go through Ceramic Fine Filter to reduce small particles i.e. with 3-8um. According to engineering and design requirements, Biogas Booster can be chosen to increase the pressure to i.e. 20-30Kpa. Further more, the Biogas Chiller can be also designed tother with the Biogas Booster to reach the Relative Humidity requirement as from biogas generator, with i.e. RH 60%-80%.
Biogas Flare, as an emergency safety device, is mandatory by regulation in order to burn off excessive biogas. Flare can be interlocked with biogas holder level signal or pipe pressure signal for automatic control. Biogas flare is always designed with concealed (enclosed) flame type, which means no flame is visible from outside.