Biogas Plant Projects in the Agricultural Sector of Kenya - KUT Umweltschutz Feasibility Studies

The planning and construction agency AKUT Umweltschutz in Berlin has experience with the construction of nearly 150 farm-scale plants and one bigger plant for slaughterhouse-waste in Kenya. It carried out some feasibility and concept studies for specific biogas plant projects in the agricultural sector of Kenya. The concepts and results for three big plants and two smaller ones are as follows:

Biogas Plant Project in North-Western Kenya

• Substrates: leaves from agricultural production, slurry from septic tanks and high contaminated wastewater from cooling and washing processes.
• The input amount is about 126 t/d.
• 6 fully mixed fermenters with 1,800 m³ each.
• 60 % of the gas is going to be used in a CHPS of 520 kWel.
• In-house use of all electricity.
• The rest of the gas will be used to produce superheated steam for drying processes. The slurry is supposed to be used in energy wood plantations.

Biogas Plant Project located at a flower farm north-west of Nairobi

• Substrates are residues from floriculture.
• The input volume is about 49 t/d.
• 3 fully mixed fermenters with 800 m³ each, and one storage tank for digested slurry.
• All the produced Biogas is used to run a CHPS of about 300 kW. The produced electricity is 2.7 Mio kWh per year and cannot all be used in-house.
• Due to the hydroponic growing systems there is no use for organic slurry. Unfortunately flower farms have normally only little need for heat.

Biogas Plant Project ocated at a big agro industrial farm in Nanyuki

• Substrates are residues from vegetable production and canning.
• The daily input is about 58 t.
• 4 fully mixed fermenters with 1,200 m³ volume each and 1 storage tank for the digested slurry.
• All Biogas will be used in a CHPS of 400 kWel. All the electricity can be used in-house.
• Only 20 % of the produced heat can be used for drying purposes and hot water production. The slurry is supposed to be used in the fields as fertilizer

Biogas Plant Project located at a flower farm north-west of Nairobi.

• Substrates are residues from floriculture. The input volume is about 11 t/d#
• 1 fully mixed fermenter with 1,800 m³ volume and 1 storage tank for digested slurry.
• The whole amount of produced Biogas is used to run a CHPS of about 80 kW. The produced electricity is 600,000 kWh per year.
• The slurry cannot be used as fertilizer due to the hydroponic method of growing.
• As only the electric output of the CHPS can be used in-house, the plant cannot run economically.
  

Biogas Plant Project located at an agro industrial complex in Njoro

• Substrates are residues from vegetable processing and canning. The input volume is around 5.4 t/d.
• 1 fully mixed fermenter with 230 m³ and 1 storage tank for the digested slurry.
• The whole amount of produced biogas will be used in a CHPS of 14 kWel.
• All electricity and heat can be used in-house to supply the production areas, for drying purposes and hot water production and will in this case replace firewood.
• The slurry is supposed to be used in the fields as fertilizer.
• Although all produced heat can be consumed in-house, the economic balance is not favourable to the low prices for firewood.

All plants were planned with the aim to use as much locally available technology and expertise for construction as possible. The following origin of the components has been found reasonable:

From Kenya:

• Concrete tanks with and without concrete roof
• Pipes for substrate and gas, Valves
• Electric installation, beams
• From Germany:
• CHPS, Gas storage membrane, Agitators, Feeder,
• Process-control and measure systems,
• Gas over and under pressure security valves

The studies carried out between 2006 and 2009 came to the following general conclusions (Burkard, 2009):

• Substrates from typical agricultural production in Kenya can be used for biogas production.
• However, crucial for economical operation of biogas power plants is the feed-in tariff for electricity that cannot be used in-house. Most of the projects are on hold until there are appropriate feed-in tariffs available for the national grid.
• In case of only in-house use of electricity the feasibility studies are showing that plants can only be operated economically if there is a profitable use for the thermal energy output of the CHPS too. However, in most cases there is not enough thermal energy demand.
• Use of slurry is recommended
• Capacity building for operators should be done
• With support of the GTZ Project PSDA two small biogas power plants were installed (Email from Romas Radtke 3.3.2010):

The original purpose of a plant in Keekonyokie was to deliver electricity for a refrigerating storage house. This storage house was built, the cooling compressor was purchased but the thermal insulation has not been installed yet. In the meantime, the gas generated from slaughterhouse waste is fed into a mini gas grid and provided to 6 restaurants. The designated generator set consists of an adapted diesel engine for dual fuel use and a generator with 20kWel output. Estimated costs are 0.14 EUR / kWh compared to a grid price of 0.16 EUR / kWh.

At the Abdul Sidis farm, vegetable residues are used as feedstock and the (off-grid) electricity generated by a 20 kWel genset is mainly used for a water pump. Estimated costs are again about 0.14 EUR / kWh compared to Diesel generated electricity at a price of 0.36 EUR / kWh. Daily savings are estimated to reach 10 EUR.

Both plants seem to work well in technical terms.