News – What`s happening in energy research

read short description
subscribe News

Prof. Dr. Bernd Epple is head of department for mechanical engineering at the Technische Universität Darmstadt. He conducts research on energy systems and energy technology.
© Christina Geimer, BINE Informationsdienst
Interview with Prof. Dr. Bernd Epple from the TU Darmstadt

Chemical looping is a pre-combustion method for fluidised-bed reactors.
© TU Darmstadt

“CO2 reduction costs ten euros per tonne”

Researchers at the Technische Universität Darmstadt are hoping to discover emission-free ways of burning natural gas or coal. The technology is based on flame-free combustion. Prof. Dr. Bernd Epple, head of the department of energy systems and energy technology at the TU Darmstadt, explains the ECLAIR project. His team in the research partnership is investigating the “Emission Free Chemical Looping Coal Combustion Process”.

BINE Information Service: How does combustion and CO2 separation work in the ECLAIR project?

Epple: “The purer the CO2 exhaust gas flow, the simpler it is to separate the CO2. For this purpose, the combustion must be conducted with pure oxygen.
We oxidise a metal with air at a temperature of 1,000 degrees Celsius. The metal oxide created provides the oxygen for the combustion in a second reactor. There, the fuel is first gasified using steam. The gasification products then react with the metal oxide. In other words, we need no energy-intensive oxygen which has been cryogenically produced.”

What levels of efficiency do you achieve using this method?

Epple: “If we succeed in completely converting CO2 and steam in the fluidised-bed reactor, then we will have no additional loss of efficiency for the CO2 separation.

Until now, however, we still have a certain quantity of CO and hydrocarbon which we need to post-combust. For this post-combustion, we need cryogenically produced oxygen. The amount of oxygen used for post-combustion should be as low as possible. Our goal is to achieve less than one per cent efficiency loss. To this is added the efficiency loss resulting from compression of three per cent. We will therefore then have an efficiency loss of four per cent. That is our aim.”

What discoveries have you made in your tests relating to operation so far?

Epple: “We have conducted tests on a smaller scale with 100 kilowatts and on a 1-megawatt scale. The gasification is working. The oxidation of the metal also worked well. However, to date, the efficiency loss has still been over one per cent. With the ACCLAIM project, we will continue to optimise the process over the coming three years, and will put it to the test in the one megawatt plant.”

How much greater is the cost of the incinerator with two coupled fluidised-bed reactors compared to existing fluidised-bed reactors?

Epple: “Although we need double the area for the reactors, overall, the influence on the size of the power plant is insignificant. The additional costs for the construction are below ten per cent of the total investment costs for a new plant.

The operating costs are very low, since we need no additional oxygen. We work with a natural ore which is cheap to buy and which is constantly present in the circuit of the plant. The CO2 separation costs are around ten euros per tonne.”

This CO2 reduction price is low compared to other methods. Why has there been little interest in the technology so far?

Epple: “The method used is a fluidised-bed method which is not very common. This method can only be retrofitted to existing fluidised-bed plants. There are not many of these. However, it is an interesting option for new plants.”

What in your view is the market potential for fluidised-bed reactors?

Epple: “New fluidised-bed reactors are being built. There is a 500-megawatt plant in Poland. A very large number of plants are being built in Korea. We forecast that a demonstration separation plant will be realised in ten years.”

You are also researching the carbonate looping method alongside chemical looping. What are the advantages and disadvantages of both technologies?

Epple: “Carbonate looping is a post-combustion method. It can be retrofitted, not only to power plants, but also to all types of flue gas emitters, such as a waste incinerator or a Combine-Cycle power plant, for example. The temperature of the exhaust gas flow can be selected as required for this method, since the reaction is exothermic.

With chemical looping, we are hoping to achieve the efficiency advantage mentioned before. If we need no additional oxygen, the method is more energy efficient. To achieve this, we have to design the operation in such a way that no post-combustion is needed.”

What is the CO2 used for after it has been separated using these methods?

Epple: “There are different ways of using CO2: for supporting plant growth, breeding algae, gasifying greenhouses or producing plastics. With Power-to-Gas for example, it is used to generate hydrogen or methane. It has the highest potential for the crude oil industry. CO2 is already used in enhanced oil recovery to increase the extraction of crude oil. These companies pay money for the CO2. With this raw material, the viscosity of the crude oil is improved, making it flow more easily. Additional crude oil can be extracted due to the pressure. The extraction of a crude oil deposit can be increased by between 50 and 70 per cent.
Another possibility is simple storage in hollow spaces or saline aquifers. There are large hollow spaces beneath the North Sea, for example.”



BINE subscription

Subscribe to newsletter


Participants in the EU-project ECLAIR
TU Darmstadt, EST