A waste by-product of the poultry industry has become an unlikely energy resource, following research by a scientist at the University of Limerick. He has shown that litter cleared from chicken sheds can be burned to deliver useable amounts of heat. "You are effectively reducing the waste by 90 per cent and using that to heat the sheds," says Dr Brian Kelleher of the university's chemical and environmental sciences department.
The research project, which he manages, got under way after the Kantoher Poultry Producers Association approached Dr Martin Leahy of the department. The Environmental Protection Agency also supports the work. The fuel source for this project is not in short supply: 20,000 chickens can produce a tonne of litter a week.
The droppings are a surprisingly good energy source, says Kelleher. "It has half the calorific value of coal. So you would need double the volume, but getting this volume isn't a problem."
The challenge was to find an efficient combustion system that could break down the waste at low cost. "It was decided to look at fluidised-bed combustion," he says, referring to a method used for difficult-to-burn materials. Fluidised-bed technology involves blowing hot air up through sand, which makes solid sand act like a fluid. Propane is used to raise the temperature of the sand to a target ignition temperature of up to 800 degrees. "You heat the sand particles to the required temperature, and you drop material on to these hot particles, and it combusts."
The research group, which includes Dr Martin Leahy, Dr J.J. Leahy and Anne Marie Henihan, used a test rig in Portugal to optimise the technology. The moisture content of the litter has to be below 25 per cent, from a starting point that could be as high as 40 per cent. Several heat-capture options are being assessed. Fluidised-bed technology allows for full fuel combustion, with heat exchangers collecting the heat, or it can be used to gasify the litter, producing a carbon-rich gas that can be used as a fuel.
The object is to produce enough heat to warm the chicken sheds and, perhaps, aid drying of stored litter, to give a continuous supply of fuel. "We are trying to provide a cheap alternative fuel," says Kelleher.
Similar research is under way in the UK, but using a larger, more expensive and complicated "moving grate" technology. The larger litter volumes produced there allow for electricity production rather than localised heating.
Small, low-cost units could be installed adjacent to the chicken sheds and the recovered heat used to provide energy anywhere on the farm, possibly even heating the farmer's home.
This idea is to be tested in the coming weeks. A prototype shed-heating system is going on to the west Limerick farm of Jack O'Connor. Initial chemical analysis shows that the exhaust stream includes carbon dioxide, water vapour and trace amounts of chlorine. The team is tracking down the chlorine source, which could arise in the feed or in cleaning agents. The only other output is 10 per cent by volume of fly ash.