Technical
In the Lethbridge biogas/cogeneration plant the process of biogas production starts with the pick-up and delivery of various organic residues. Trucks will drive over an on-site truck weigh scale and continue into the 2 bay receiving/unloading building where the unloading process takes place behind closed doors. The raw material will be unloaded into either the 2 pre-storage tanks through a manifold (liquids) or into the in-floor hopper of the solid feeding system (solids). A two-stage odour control system is installed to treat the building air before it is released through a stack into the atmosphere.
The anaerobic digestion process takes places in 3 anaerobic digesters which operate under mesophilic conditions at 38 degree C. Digester feeding and digester emptying occurs at a constant rate to ensure a stable mix and suitable filling levels in the digesters. Each digester is equipped with 4 agitators and the biogas extracted from the digesters is stored under a double membrane roof within the digesters. The digesters are equipped with a biological desulphurization system to clean the biogas and remove traces of H2S.
The biogas is conditioned and additionally treated with activated carbon prior to being used in 2*1.425 MW fully containerized GE/ Jenbacher specialized gas engines that are designed for lower methane gas applications. With a very low parasitic load for the biogas plant itself (<10%), the majority of the electricity produced is fed at the 25 kV distribution level into the Alberta power grid. Waste heat is captured from the gas engines water jackets to supply the process with constant heat.
After the anaerobic digestion process the digested material is a valuable organic fertilizer. It is re-loaded within the receiving/ unloading building into the trucks. It is then used for land application purposes from the participating suppliers of livestock manures.
In 2017, Lethbridge Biogas integrated a high temperature, high pressure thermal hydrolysis process into the existing anaerobic digestion plant. The Biorefinex© thermal hydrolysis process operates at a temperature of 180 °C and a pressure of 12 bar to break tissue down to their original small molecular building blocks. This results in a dramatic reduction in viscosity, the destruction of all infectious agents (incl. the prion responsible for BSE/mad cow disease) and the increase of biodegradability. This new and innovative approach allows the safe disposal of animal by-products incl. full carcasses at the Lethbridge Biogas plant without any negative environmental impacts. Standard methods of animal by-product disposal include incineration, burial, rendering, landfill and composting can have negative effects on air, water and soil.