Producer gas in power generation
Practical Action
Fuel consumption
Figures quoted by different sources vary considerably due to variations in fuel, in gas and in
operating conditions. Good quality producer gas may have a calorific value (CV) of about
4,200 kJ/m3 at normal temperature and pressure (NTP). The problem is that while a high
contact temperature is required in the fire zone of the gas generator for efficient gasification;
a low air-gas temperature is required for efficient engine operation (volumetric efficiency).
Calculated on a cold gas basis at NTP, producer gas has an efficiency of about 72%.
Efficiency = potential heat in gas/total heat in fuel
However, this may be reduced in practice by the incorrect proportion of air admitted, and by
temperatures which in practice will be higher than 'normal' (NTP), hence the importance of
temperature control in gas units.
1 kg air-dry wood (15 -20% mc) produces approximately 2.3m3 gas
1 litre petrol = approximately 2.5 to 3 kg wood
1 litre diesel = approximately 3 to 3.5 kg wood
1 kWh requires approximately 1.0 to 1.3 kg charcoal, 2 to 4 kg wood chip (depending on
moisture content), or 2.4 to 3.2 kg rice husk
Project implementation
While the gasification of biomass materials is technically practicable other criteria will also
have to be considered when deciding to implement a gasification project. This included
gasifier application (i.e. small-scale off-grid electricity production, large scale centralised
generation etc), the availability of appropriate equipment, availability of a suitable and
reliable fuel source, regulations (local and national), operator availability and cost and
financing.
Determining the economic feasibility of a gasifier project requires realistic site-specific
estimates of capital, feedstock, labour and maintenance costs as well as the value of the
electricity and heat produced.
The following factor should be considered:
• the cost of the fuel
• the cost of the gasifier and ancillary equipment
• the cost of money at prevailing interest rates
• the cost of operating labour
• maintenance and replacement costs
• design life of the equipment
• value of the power produced
• value of the heat produced
• cost of disposal of the residual materials (ash, tar etc)
• retail cost of electricity and heat
• benefits of using renewable energy (i.e. using locally available fuels, reduced reliance
on imported fossil fuels, local ownership and control of the technology etc).
Any manufacturing programme would need to consider patent rights, the risk of litigation,
manufacturing rights, and the need for a national programme as part of a total energy policy,
backed by media propaganda and any necessary alteration in legislation to legalise modified
vehicles that might otherwise become illegal or penalised.
Other possible side effects of an introduction of a new fuel system might include reduction of
pollution, a cut in government revenue from liquid fuel tax, the diversion of low value
biomass material to an alternative new and possibly lucrative market, resulting in the possible
impoverishment of soil, crop failure and increased poverty amongst the low income sector of
5