New type of bed material turbo charges combined heat and power plants

Ilmenite ore (Foto: © Oscar Mattson under Creative Commons Licence)

Gothenburg, Sweden – Researchers at Chalmers University of Technology have discovered that a certain bed material improves the combustion efficiency of waste and biomass while decreasing operating and maintenance costs significantly. In collaboration with the energy supplier E.ON, the researchers have proven the concept in today’s commercial boilers.The findings make combined heat and power (CHP) technology highly interesting both from a profit and a climate perspective, and open up for smarter next generation designs.

The discovery of how metal oxides’ oxygen-carrying properties can be used in circulating fluidised bed (CFB) boilers has been verified and scaled up from the lab to commercial reality within record time. During last winter, from November 2014 to May 2015, researchers at Chalmers University of Technology and E.ON personnel have conducted long-term testing with a new bed material in a state-of-the-art combined heat and power (CHP) plant, Händelöverket in Norrköping.

Replaced with an ilmenite-based bed material

In one of the plant’s five boilers, P14, a 75 MW CFB boiler, the silica sand normally used was replaced with an ilmenite-based bed material. Bed material in the form of sand is used to even out heat fluctuations and make the combustion of the fuel more efficient.The iron-titanium mineral ilmenite and other metal oxides have a clear advantage compared to regular sand: They can transport oxygen inside the combustion chamber from places where there is an abundance of oxygen to places where there is a depletion in oxygen. 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,” explains Fredrik Lind, PhD at the Department of Energy and Environment and project coordinator at Chalmers University of Technology. „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 says.

Quick commercialisation

It is too early to speculate in the exact gains but it is clear 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 have several other plants in line. Eon will also use its gathered experience to start offering a service concept that enables a transition to the new bed material.

“This is the biggest improvement I have experienced. A little like placing a turbo charge to the process,” says Bengt-Åke Andersson, Adjunct Professor in combustion technology and Senior Specialist at E.ON, who has worked with fluidising bed technology for a long time. “One of the advantages is that it enables the burning of difficult fuels like coarse waste. This could become crucial in the future, if we are to meet our climate goals,” Fredrik Lind adds.

The idea, to test metal oxides as bed material, Professor Henrik Thunman got from another project where ilmenite was used as a catalyst to clean gas from tar in the biomass gasifier at Chalmers University of Technology. All of a sudden, he found himself with a solution for a problem that had eluded researchers and boiler producers for a long time: How to avoid unburned fuel in a commercial boiler? The first scientific results were published in June 2013. Since then, the research has sped ahead toward being implemented in a real application.

More than one hundred man years of research

“This shows the importance of having a critical mass of researchers and quickly being able to scale up basic and applied results. The concept is an offshoot from more than one hundred man years of research combined with the experiences we have built up under more than 10 to 15 years within energy technology,” Henrik Thunman states.

Last winter’s full-scale trial is the last in a long run of tests that have taken place over a period of two-three years, first in the Chalmers Power Plant, and from 2014 paralleled in E.ON’s commercial plant. A key success factor is the fact that the Chalmers Power Plant contains the world’s largest research boiler. Another critical factor is this type of industry – academy collaboration, which Chalmers and E.ON have pioneered since 2007. As of today, Chalmers University of Technology collaborates with more than ten other global companies in similar manners.

The results of the full-scale trials will be published scientifically before long.

Source: Chalmers University of Technology