A Change of Tack

My week out in California has got me fired up again on wood gas. Converting the Lister engine to run directly on wood gas and see it perform so well has given me the assurance that wood gas can be made to work for small scale heat and power production.

In the last 5 years I have slowly established an experimental CHP system based on the Lister 6hp diesel engine. Until now, this engine has run on waste vegetable oil, but with WVO getting more difficult to obtain, I realised that a substitute was necessary. The CHP system is located in my garden workshop, known as the "Energy Shed" and the heat and power is brought back to the house via underground pipes and cables.

Following the success in California, it's now my intention to set up a complete wood fired CHP system to heat and power my house. Woodchips are generated as a waste product from tree surgery operations and so there is a glut of this material produced with no real market. Wood chips can be gasified to make a flammable gas to substitute for the WVO fuel for the Lister engine on my generator set. This will produce more than sufficient power to run the house, and the waste heat will be used to provide heat for the house.

A quick calculation suggest that 1 tonne of woodchips will be needed each month of the heating season. This is about 4 cubic metres of chips, which can be stored in a bunker at the front of the house. A converted wheel barrow will be used to transport up to 300 litres at a time, down the side path to a smaller bunker near the workshop holding enough for about 3 days operation. This is defined by the limited access to the rear of the house - everything has to pass through a 3 foot gate and down a narrow path.

A 200 litre drum full of chips will provide sufficient energy to run the Lister engine for about 10 hours. Spare electricity can be stored in the battery bank to run my inverters, or converted to stored heat in night storage heaters. Spare heat will be stored in a 700 litre thermal store, located in the workshop. This will hold about 60kW of heat, which is sufficient to warm the house overnight, and can be topped up from spare heat from the wood-burning stove.

The Lister will be run from about 8am till 6pm, and with adequate silencing and in an acoustic box, should not cause a distraction. It's a Startomatic generator, which can be remotely started. By retaining the diesel injector, it can be started on WVO, switching over to woodgas when the gasifier is fully operational and producing clean gas.

Waste heat from the engine will be used to dry the woodchips, and pre-cook them using a process called torrefication. This pre-chars the chips, driving off water vapour and volatiles, which improves the gasification process. The intention is that the Lister and the gasifier will work in close harmony, where waste heat is exploited in order to maximise the system efficiency.

The 200 litres of chips should produce 25kWh of electricity and 60kWh of hot water. As this household uses about 7.5kWh of electricity per day, the surplus can be used for heating the workroom and workshop.