Poultry litter is used as a biomass fuel for a number of power stations for electricity production and it can also be used on a smaller scale for heat or combined heat and power (CHP).
Using wet residues; Many agricultural residues have a high water content. Although these can be dried out and used as a combustion fuel, in general the energy and cost required is not justified. Most coffee factories in Kenya can adopt this method for production of biogas and electricity.
The diagram below illustrates an Agricultural Waste Bio-digester which Express Drainage Solutions Kenya Ltd can design, supply and install;
For many of these materials bio-digestion at or close to the point of production (to minimize transport) is a much more suitable technology. It produces bio-gas, a mixture of gases, principally methane (CH4) and carbon dioxide (CO2), and the methane can be burned as a fuel for heat or, if on a sufficient scale, for electricity production.
What is a bio-gas digester and how does it work?
- Agricultural residue bio-gas digesters collect waste in an underground tank. Microorganisms break down the waste within the tank by digestion, which releases a mix of gases, mostly methane. The gas rises and collects in a domed ceiling where it builds pressure. A valve and a hose is attached to the top of the tank, allowing it to be piped directly into the house where it is connected to a gas-burning stove or to other utilities. The gas does not smell (like many might suspect) and does not make smoke.
- When the tank reaches capacity, excess effluent that has already undergone digestion (“slurry”) is pushed out of the tank by natural pressure, through an overflow pipe and into a holding bin (displacement tank), where organic waste like leaves, grass or rice husks can be added to create high-quality fertilizer and mulch.
The benefits of Agricultural residues bio-gas production are;
- Reduced smoke inside kitchen and enhanced health by improving sanitation, hygiene, living condition
- Mitigating climate change
- Increased yield by using bio-fertilizer
- Improved soil quality by using bio-slurry
- Reduced pressure on forests
- Reduced work load for women and children – enhance education opportunities and cultural knowledge
- Provision of skill enhancement and employment for rural areas