Napier Grass to BIO CNG

The technology is based on the biochemical conversion of organic materials from high molecular weight compounds to low molecular weight compounds.

The first stage of this process is hydrolysis. Hydrolysis produces organic acids and alcohols. Organic compounds + Н2О→ С5Н7NО2+HCO3.Further conversion of obtained dissolved compounds like organic acids and alcohols (С5Н7NО2, HCO3) into gases – СН4, СО2. С5Н7NО2 + HCO3 + Н2О → СН4+СО2+NH4. The biological process of consecutive (phasic) conversion of organic compounds takes place in the anaerobic environment i.e. in the oxygen-free tank (biological reactor).

In the first stage of fermentation, substrate hydrolysis takes place under acidogenic bacteria influence. In the second stage, elementary organic compounds come through hydrolysis oxidation by means of hetero-acidogenic bacteria with the production of acetate, carbon dioxide, and free hydrogen. The other part of the organic compound including the Biogas plant working principle acetate forms C1 compounds (elementary organic acids). Produced substances are the feedstock for methanogenic bacteria of the third type. This stage flows in two processes of A and B type the character which depends on caused by different bacteria type. These two types of bacteria convert the compound obtained during the first and second stages into methane CH4, water H20, and carbon dioxide CO2.

Methanogenic bacteria are more sensitive to the living environment compared to acidogenic bacteria. They require a completely anaerobic environment and a longer reproduction period. The speed and scale of anaerobic fermentation depend on bacteria metabolic activity. That is why the biogas plant chemical process includes the hydrolysis stage, oxidation, and methanation stage. For that kind of substrate, these processes take place in the same reactor

Napier grass is transported to the biogas plant area and discharged into a loader with a moving floor every day. Loaders input substrates to the digester using augers.

Mixing is performed by vertical paddle mixers. In digesters the substrate is brought up to a temperature of 53-55 C by heating elements, allowing the constant temperature to be sustained for the entire digesting period. To prevent a rise in temperature (for example, in summer), the biogas station is equipped with a cooler (dry cooling).

In case of power failure, the station and the cooling system are backed up by a diesel generator. The digester operating regime is thermophilic.

The average time of processing in the digester is 26 days. Worked substrate is supplied with a pump to the separator area where it is separated into solid and liquid bio-fertilizer.

Solid bio-fertilizer is discharged to the separation area and transported for storage; the liquid filtrate is directed to a filtrate tank from where it is pumped to technological needs or to the lagoon. Biogas goes up and transported with pipe to external gasholder.

The gasholder’s weather protective film protects the gasholder from precipitation and damage by foreign objects. The weather protective film is fixed firmly by a special system. To protect the gasholder from overpressure, digesters are equipped with safety valves, which start working at a pressure of 5 mbars and bleeds biogas into the atmosphere. The biogas then goes through a gas pipeline to a biogas cooler area and then to a compressor, where the pressure is raised up to 80-150 mbar to meet engine requirements.

After the compressor, biogas is fed to a biogas upgrading plant where raw biogas treats through the removal of CO2, H2S, siloxanes, and other soluble gases to produce primarily methane gas (~97%) which is clean and dry.

All technological processes are controlled and operated by an automatic system. Biogas plant work is monitored at the central control room monitor. The control room is equipped with a central control unit, which allows the switching of any biogas plant module into automatic or manual mode with local or remote control.