Recovering hydrogen from waste incinerator ash as an energy source

March 29th, 2013 by Lund University

Every year, millions of tons of environmentally harmful ash from waste incinerators is produced worldwide.

The bottom ash is dumped in landfills or in some countries it is used as construction material.

Bottom ash from La Collette incinerator in St Helier, Jersey (click image to expand - ©RLLord)

Bottom ash from La Collette incinerator in St Helier, Jersey (click image to expand – ©RLLord)

Bottom ash is left in the open air to age and make it safer because newly produced bottom ash is not chemically inert.

Aluminium in the bottom ash will react with calcium hydroxide and water to form Aluminium hydroxide and hydrogen gas.

Injecting carbon dioxide through the bottom ash can accelerate this process to make the bottom ash safer.

The hydrogen gas produced by bottom ash has been known to react explosively if used inappropriately in construction.

Dr Aamir Ilyas, in the department of Water Resources Engineering at Lund University in Sweden, has developed a technique to safely capture the hydrogen gas produced by the bottom ash.

Hydrogen gas is viewed by many as an increasingly important energy source.  It is used in fuel cells to produce electricity to power building infrastructure and vehicles.

Dr Aamir Ilyas, said “the ash can be used as a resource through the recovery of hydrogen gas instead of being allowed to be released into the air as it is at present.”

 Dr Aamir Ilyas Water Resources Engineering at Lund University SGB v em.jpg

Dr Aamir Ilyas, Water Resources Engineer at Lund University (click image to expand – image courtesy of Lund University)

Refuse incineration is a widespread practice in Europe.

At present, the bottom ash from incineration remains in quarantine, in the open air, at a 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 an explosion.

Dr Aamir Ilyas’s technique involves placing the heavy, grit-like bottom ash in an oxygen-free environment.

The ash is dampened with water to produce the hydrogen gas. The gas is sucked up through pipes and stored in tanks.

“This method removes the risk of hydrogen gas. It also reduces the strain on our landfill sites,” Aamir Ilyas said.

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 contains hazardous substances that do not meet the Swedish Environmental Protection Agency’s strict requirements.

Usually it is used as top cover at landfills.

Today, hydrogen gas is mainly produced from natural gas. However, biogas, oil and coal can also be used as the raw material.

Hydrogen gas is an important raw material in industry and is used in refineries and to manufacture ammonia.

Hydrogen gas is not expensive, but because there is a lack of infrastructure for the production of the gas, the production and handling costs are high.

These costs would decrease in the future once a production system is established.

Kenneth M. Persson, Professor of Water Resources Engineering, and one of Aamir Ilyas’s supervisors, said “there will not be one universal solution that will be used to generate energy.”

“We need to find a number of solutions,” he said.


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