Improved bed material for CFBs increases efficiency

21 October 2015

Researchers at Chalmers University of Technology in Sweden have discovered that a newly developed bed material improves the combustion efficiency of waste and biomass in circulating fluidised bed combustion while reducing operating and maintenance costs significantly. In collaboration with the energy company E.ON, researchers have now proved the concept in commercial boilers.
The findings make combined heat and power technology more interesting from both a profit and a climate perspective, and open the way for 'smarter' next generation designs.
The discovery of how metal oxides' oxygen-carrying properties can be used in CFB boilers has, says Chalmers, been verified and scaled up from the lab to commercial reality within record time.
During last winter, from November 2014 to May 2015, Chalmers researchers and E.ON personnel have conducted long-term testing with the new bed material in a state-of-the-art combined heat and power plant, Händelöverket in Norrköping.
In one of the plant's five boilers a 75 MW CFB boiler, the silica sand normally used to even out heat fluctuations and make the combustion of the fuel more efficient was replaced with an ilmenite-based bed material.
The iron-titanium mineral ilmenite and other metal oxides were found to have a clear advantage compared to regular sand - they can transport oxygen inside the combustion chamber from oxygen-rich volumes to oxygen depleted volumes. When oxygen-carrying bed material is circulated inside the chamber, mixing with the fuel, the oxygen is distributed evenly in time and space.
"This brings forth an array of positive effects, which testing completed in Norrköping confirms. The combustion becomes more uniform and efficient. The boiler's total efficiency increases. The emission of carbon monoxide is lowered radically, as are problem related to ash fouling," says Fredrik Lind of the Department of Energy and Environment and project co-ordinator at Chalmers University.
"We are now sure that we are able to significantly lower the operational and maintenance costs in most of the thousands of fluidised bed combustor plants that are currently in use internationally," he said.
It is too early to speculate on the exact financial and environmental gains but it is clear, says Chalmers, that the profit margin of each CHP boiler will improve significantly.
E.ON is hoping to start using the new ilmenite-based bed material in two boilers in Norrköping this year, and has several other plants in line. E.ON will also use its gathered experience to start offering a service concept that enables a transition to the new bed material.

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