Clean cut

Siemens has developed a scrubbing process that could cut emissions from a coal-fired plant. Siobhan Wagner reports

A coal-fired power plant near Hanau, Germany will use new CO2 scrubbing technology to reduce its impact on the environment.

Siemens is building a pilot facility that promises to trap 90 per cent of the carbon dioxide in the exhaust gas emitted from the E.ON plant. It is claimed that Siemens’ CO2 scrubbing process, based on an amino acid salt solution, will sequester greenhouse gases with less energy than other carbon-capturing techniques.

The Siemens research team has been developing and testing the technology in labs for several years, and now will put it under real operating conditions at the E.ON plant’s Unit 5. The pilot plant will begin operation in the summer of 2009 and will run until the end of 2010.

Siemens’ CO2 scrubbing process is a form of post-combustion capture. With this process, the gas resulting from combustion is mixed in the flue with special cleaning agents. These agents absorb the CO2 contained in the gas so what is emitted into the atmosphere is less polluting.

Afterwards, the cleaning agent is heated to remove the CO2. The solution is then reintroduced to the system so the process starts over again from the beginning.

According to Gerda Gottschick, spokeswoman for Siemens Energy Sector, heating and reintroducing the cleaning agent solution is the most energy- consuming part of this process.

CO2 scrubbing technologies developed so far, she said, can reduce the efficiency of a power plant by 10.4 per cent. The Siemens technology, she added, would be less of an energy drain and only reduce the efficiency of a plant by 9.2 per cent.

Gottschick said the Siemens technology uses an amino acid salt solution. Many other technologies are based on an organic chemical compound known as monoethanolamine (MEA).

‘The amino acid salts exhibit low thermal sensitivity,’ she added. ‘The thermal stability of the solvent provides increased flexibility with the process design, meaning the absorption and desorption process can be performed under a wide range of temperatures and pressures.’

Gottschick said that tests have shown that the heat requirement for solvent regeneration is considerably lower for amino acid salts compared to MEA. This allowed the Siemens team to design an improved flow scheme and structure for their carbon-capture plant.

‘With the reduction of the heat requirement in the regeneration step, we were able to reduce the size of the equipment, piping and overall plant arrangement,’ she added.

In addition to its thermal stability, the amino acid salt solution has almost no vapour pressure. So the solvent is less likely to escape with the emitted gas and almost all of it will be fully retained in the cycle, unlike many other solvents.

Gottschick said all the current data on Siemens CO2scrubbing technology is based on laboratory tests, and the pilot facility at the E.ON plant will help them better understand the solution’s long chemical stability and the effectiveness of the process. In addition, the researchers will aim to further reduce energy consumption.

She added that the test results from Hanau will be the basis for a future demonstration plant.

‘In 2010 we will begin to operate another pilot plant with a different type of fuel such as natural gas or other coal characteristics, and we will be ready for basic engineering in 2010 to get the first demo plant in operation by 2013,’ said Gottschick.

This project is sponsored by the German Federal Ministry of Economics under the COORETEC Initiative.

It is part of the federal government’s fifth Energy Research Programme ‘Innovation and New Energy Technologies’ and promotes research and development in the field of low-CO2 power plant technologies.