Every year, millions of tons of environmentally harmful ash is produced worldwide, and is mostly dumped in landfill sites or, in some countries, used as construction material. The ash is what is left when rubbish has been burnt in thermal power stations. A researcher from Lund University in Sweden has now developed a technique to use the ash to produce hydrogen gas. The method is presented in a new thesis.
The technique has significant potential: 20 billion litres of hydrogen gas a year, or 56 gigawatt-hours (GWh). Calculated as electricity, the energy is the equivalent of the annual needs of around 11 000 detached houses. Hydrogen gas is valuable and is viewed by many as an increasingly important energy source, for example as a vehicle fuel.
"The ash can be used as a resource through recovery of hydrogen gas instead of being allowed to be released into the air as at present. Our ash deposits are like a goldmine", said Aamir Ilyas, Doctor of Water Resources Engineering at Lund University and the developer of the technique.
Refuse incineration is a widespread practice in Europe. The technique involves placing the ash in an oxygen-free environment. The ash is dampened with water, whereupon it forms hydrogen gas. The gas is sucked up through pipes and stored in tanks.
It is the heavy, grit-like bottom ash that is used. In combustion, a lighter fly ash is also formed. The bottom ash remains in quarantine, in the open air, at the site for up to six months to prevent leaching of environmentally harmful metals and the risk of hydrogen gas being formed, since accumulation of hydrogen during indoor storage can result in explosion.
"A bonus is that this method removes the risk of hydrogen gas. It also reduces the strain on our landfill sites."
In some countries, processed bottom ash is sometimes used as a construction material for roads and buildings. This doesn't happen at present in Sweden because the ash conta
|Contact: Dr Aamir Ilyas|