Many farmers, not linked to the power grid, use petrol or diesel power generators to supply electricity for home and workshop use.
Many farmers, not linked to the power grid, use petrol or diesel power generators to supply electricity for home and workshop use. However, a gas producer can be utilised as an efficient and reliable alternative source of energy which extends the usable energy of wood. The use of cheaper construction materials for manufacturing a wood-gas generator to supply wood-gas for food cooking purposes is at present being constructed. As the cost of wood-gas power is far cheaper than the cost of liquid fuel, savings in the generation of electricity from wood-gas should be possible.
Wood-gas
Wood-gas is a mixture of flammable gases such as hydrogen (about 22%), carbon monoxide (about 22%), methane (about 4%) and inflammable nitrogen and carbon dioxide. The hydrogen, carbon monoxide, methane and carbon dioxide are combustion products when wood is burnt under conditions of oxygen starvation.
Wood-gas generators
There are three basic types of wood-gas generators:
(a) Cross flow
(b) Down-draught
(c) Up-draught
The down-draught gasifier is the most commonly used generator because tar and volatile products are cracked into gases before leaving the gasifier.
Material
The experimental wood-gas producer is an Imbert type down-draught wood-gas generator constructed from a mild steel 210 litre drum lined with refractory bricks for the hopper. The hearth is made of high temperature refractory casting material enclosed in a mild steel 210 litre drum.
The orifice size of the constricted hearth is 100 mm. Four nozzles, made of 25 mm diameter mild steel tubing are arranged in a ring for the air supply into the hearth. Details of the components of the gasifier are given in Figure 1.
Air supply
An electrically powered fan is used at present to supply air to the hearth zone. Plans are underway to build and modify a Humphrey gas pump, described later, which will use a small percentage of the wood-gas produced as fuel, to drive a turbine which will supply air for the gas producer.
The Humphrey gas pump
The Humphrey gas pump is simple to build and has a robust construction. This pump has no rotating parts, and expansive force of the ignited gas is exerted directly upon the water.
The first experimental four-cycle pump, as designed by Humphrey, is shown in Figure 2. It consists of a combustion chamber, A, fitted with an inlet valve, B, for the intake of the combustible mixture and an exhaust valve, C, for the exhaust of burnt products. Pipe D connects the bottom of the combustion chamber to a low-level tank, E, and to a high-level tank, F, and between this pipe and the former there is a water valve, G.
The Humphrey gas pump is controlled by the oscillating movement of water in a pipe when an alternating force acts upon the water. The mass of water in the higher tank creates an oscillating water mass that swings between the high and low level tanks.
Operation
The oscillating water column draws water into the column:
1. During the gas expansion after ignition
2. The burnt fuel products are exhausted by the back oscillation of the water mass in the pipes
3. A fresh combustible charge is drawn in by the forward oscillation of the water
4. The charge is compressed by a backward oscillation of the water and is again ignited under compression to repeat the cycle
The Humphrey gas pump is thus an internal combustion engine with two valves. A turbine can use the potential energy of water pumped to the higher tank and convert it to mechanical energy that can supply the air flow for the wood-gas generator.
