Biogas Plant System - Rottaler Modell

The company BME GmbH in Bavaria led by Walter Danner offers a “High Performance, Temperature Controlled (HPTC)” biogas plant system called “Rottaler Modell”.

According to communications from Walter Danner, at least 3 of these plants have been installed in Eastern Africa, 3 are under construction and 2 in concrete planning:

• In Kenya in Mombasa (2007), Murang’a, Homabay, Bungoma (8/2009)
• Further plants are planned in Dagoretti (KE), in Kigoma, Tanzania, in Zanzibar, Uganda, Ruanda and Madagascar.

Each of these plants is adapted to the individual local situation. Different volumes and capacities are possible.

• The plant has a two-stage digestion system, with separate 1) Hydrolysis and acidification and 2) Methanisation.
• It has a controlled temperature of 37°C with insulation and solar heating system.
• Due to this design even high fibrous material can be digested and a high biogas output per m³ digester volume and day is possible.
• The digester and a separate storage are made from plastic bags of a three layer material.
• Desulphurisation is done exclusively by addition of a little bit of air into the gas storage tank. Due to the steady fermentation temperature and constant gas production and composition this method seems to work very well.

A typical plant has a 25 m³ digester bag, a 20 m³ biogas storage bag and two 4 m³ hydrolysis units, a bio filtering system for filtering the hydrolysis gas generated in the hydrolysis unit, desulphurisation pump and condensation trap.

The company calculates costs for the installation of the plant of about 30,000 EUR. Assuming

• an output of 60m³ biogas daily
• the calorific and financial value of 2 LPG cylinders of 13kg,
• a payback period of 2.5 years is calculated by the company.

The first HPTC plants in Africa apparently used diesel engines substituting up to 80% of the diesel by biogas. In 2009, a small generator set running only on biogas was developed. It was put into operation with a HPTC plant in Bungoma, Kenya in September 2009. The plant uses the slaughterhouse waste as main feedstock.

The 10 kW generator set has been developed from a commercially available petrol generator set used at construction sites in Europe. It consists of a Honda motor and a Chinese generator. This motor was selected as it is free of non-ferrous metal with a copper content (“Buntmetallfrei”) (this material is especially damageable by sulphur compounds). After modification this genset has two fuel inlets. To start the engine a small amount of petrol is used. After about one minute the engine can be run completely on biogas. The modified generator set costs about 1,500 EUR. However it is not sold separately. The BME GmbH only offers the complete system with the HPTC biogas plant and the motor.

The company has good relations with UNIDO, has been present at several UNIDO conferences and constructed several plants in UNIDO projects.

In a slaughterhouse in the Lake Victoria port town Homabay, BME constructed another biogas plant in the context of a UNIDO project in cooperation with the Homabay Municipal Civic Authorities.

According to press releases the plant will utilise waste from the slaughterhouse to generate electricity for lighting and gas for cooking, drying and frying fish. The plant was completed in by the end of 2009, and has the capacity to produce 9 kW of electricity. This is expected to be sufficient to light about 100 houses and provide cooking gas to 50 houses and a community kitchen. In future, arrangements are expected to compress biogas in cylinders for sale (Source: Nairobi - 18/07/2009. http://www.afriquejet.com/news/africa-news/kenya:-unido-to-construct-biogas-plant-in-western-kenya-2009071831935.html).

According to information from BME the plant has not been put into operation by January 2010 as an agreement on the cost and profit sharing has not yet been agreed upon between the involved stakeholders. With such a lack of ownership the future of the plant remains unclear.

BME GmbH emphasises - in accordance with other biogas experts - that a profitable construction and operation of power generating biogas plants is in certain cases possible even without special feed in tariffs. This holds true especially in remote areas where the electricity generation with small diesel generators is extraordinary expensive.

At the moment BME in co-operation with the World Bank is constructing a biogas power plant for fishermen at Kioga Lake in Uganda. Information on the ownership of this plant was not available. The calculated cost for the electricity from the biogas plant is 0.23 US$ / kWh; the price for electricity generation from a diesel generator is about 0.40-0.50 US$ / kWh (Phone communication from Walter Danner 22.2.2010).

In Madagascar, BME is planning a biogas plant for a sisal plantation without any public support. The generated power is expected to substitute the energy consumption of the farm which is currently generated by a diesel generator as well as to provide electricity to neighbouring farms.

However, during discussions with different biogas experts (Franz et.al.) concerns regarding this model were raised:

Apparently it is very difficult to visit any of those plants; a special permission is needed. Hence an independent assessment of the plants is not available.

In any case, these small but sophisticated high temperature plants seem to be far more expensive than the more common ones. If the higher price can be compensated by a higher and more stable production remains to be proven.