4.2.1 Fuel consumption
4.2.2 Manpower employed and operating procedure
4.2.4 Environmental impact
The plant was commissioned in 1978 and had operated for 8000 hours up to January 1983.
The total energy production during that time was 160000 kWh.
The average wood consumption of the plant is 4.1 kg/kWh. This is a relatively high figure but it is acceptable indeed desirable - because of the need to keep the sawmill and its surroundings clear of wood waste. Should the need arise, consumption can be reduced by control of the air flow in the gasifier.
The equipment is serviced by one operator on a part-time basis, continuous attention is not needed. In addition, three employees prepare the fuelwood pieces and stoke the gasifier.
The main operations on any one day are as follows:
1. Turning on an impeller fan to start gas production. After some minutes the combustibility of the gas is tested by lighting it with a small flame.
2. Turning on the gas producer engine to supply power to the sawmill.
3. Starting the water pump which supplies the sawmill with the cooling water for the gasifier/generator and the households.
4. General maintenance, including lubrication and charging the compressed air tank in readiness for the next start-up of the engine.
5. Cleaning of the gasifier and preparation of fuel in sizes suitable for the loading chute. Refuelling of the gasifier is done at noon, half an hour before the end of the first period of work, and again in the evening before the end of the shift.
6. During the afternoon, the operators inspect and service the equipment - lubrication, storage batteries, cooling water, ash outlet, filter outlet, gas temperature.
7. The sawmill's work day ends at 18.00 hours but the engine and generator continue to operate until 22.00 hours for the benefit of the small village. Preparations for this have been completed during the day, and the operator makes a visit every hour until he stops the machine at 22.00 hours. The gasifier has a sufficient reserve for an immediate start the next morning.
The installation has the following features which help to minimize the usual hazards of gasifier operation:
1. Excessive internal pressure cannot build-up because the lid of the feeding chute is permanently left half-open. Should it be operated closed, a quick-release mechanism can be used to relieve pressure.
2. The gasifier is housed in an open shed so that concentrations of carbon monoxide cannot develop.
3. Gas is fed to the engine by suction. If leaks develop in the system the gas cannot therefore escape into the air.
4. Ashes and cinders are discharged onto a water bed so there is no risk of fire from these.
5. The gasifier is sited at a sufficient distance from the sawmill to avoid heating the workplace.
A strict analysis of the environmental impact of the gasifier has not been carried out but, as noted above, simple precautions have effectively eliminated the risks of carbon monoxide poisoning and fire. Moisture and smoke are vented through the gasifier chimmey which is sufficiently high not to cause pollution. Waste water and ashes (1000 l and 19 kg a day) are discharged downhill to a remote swamp. Finally, the exhaust gas of the engine appears to be cleaner than that of an engine operated by diesel fuel.