Biogas Yields
Biogas yield depends on the composition of the substrates utilized in the process. Energy crops typically increase the yield substantially with solid feed systems. Solid feed systems are those where chopped energy crops are continuously fed into the process.
A Complete Waste-to-Energy Solution
A biogas plant consists of the following components:
Slurry and biomass are stored in the liquid manure storage, an area where feeding liquid material and additional biomass quantities are fed into the system. This liquid material is pumped from the liquid storage area into the heated digester which is the main area of any biomass plant. The mix in this digester is always specific to the input materials and must be well mixed and homogenous so that the bacteria and substrates are in close contact. This ensures a high gas yield. Included in a digester’s design is a pressure protection system which adjusts to both over-pressured and under-pressured scenarios as well as a gas holder or foil covering.
When this substrate is digested it is then pumped into a larger storage tank, repository, or lagoon. In this condition, it can be used for fertilizer, bedding, or pelletized for other uses.
A combined heat and power generator (CHP), also known as a cogeneration unit, converts the biogas generated into electricity and heat. Options available from CleanCap includes world-leading high and medium speed gas engines, complete drive systems, distributed energy systems, and fuel injection systems as stand-alone systems or as part of a larger solution.
Power is generated by a CHP unit through combustion which converts the biogas into electricity. This electricity can be used to power facilities, equipment, as a heat source, or as revenue through either private or public power sale.
A flare and scrubber system is utilized throughout the disinfection process to destroy volatile organic compounds (VOCs), odors, and gases.
Environmental Conditions
Environmental conditions greatly affect the digestion of biomass with one of the most important factors being temperature. Temperature influences both the speed and stability of the anaerobic digestion process which in turn affects biogas production. There are two optimum temperature ranges that can be utilized in creation of bacteria to aid the digestion process:
Mesophilic – Between 32 and 45°C
During Mesophilic temperature ranges, methane bacteria experiences optimum growth which is why many biogas development facilities operate within this temperature range. The output is high gas yields and strong process stability.
Thermophilic – Between 50 and 65°C
Thermophilic digestion at 55°C is advantageous in processes that utilize animal by-products or organic waste. With this process a disinfection is required, and thermophilic temperature ranges are considered for the operation of the plant. The disinfection process is simple and requires the mass to be heated for one hour at 70°C. This often results in a higher gas yield, but considerations must be made to assure stability as there is increased sensitivity to disturbances and irregularities during thermophilic digestion.
Waste heat from the co-generation plant is often used to produce the heat necessary to heat the bacteria to the optimal digestion temperature.