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Post combustion carbon capture by, for example, amine absorption, is a technology fit for both power plants and industrial CO2 emissions, including new builds and retrofits. The retrofitting possibility and the technology's ability to capture emissions from industrial sources is quite unique compared to the main alternatives (pre-combustion and oxyfuel). For these reasons, post combustion will probably survive as a major technology, even though it will most likely not end up as the perferred technology for new built power plants.

Extracting CO2 from atmospheric flue gas is relatively energy-intensive. Nebb has developed Cesam, an oxyfuel process that supplies heat and power to a post combustion absorption unit (amine or other technology).

In the amine post combustion process, CO2 is chemically bound to a solvent at relatively low temperatures in an absorber tower and released from the solvent at relatively high temperatures in a stripper tower. Atmospheric CO2 capture requires heat transfer to the solvent and power to drive fans and solvent circulation pumps.

For an atmospheric absorption process it is normal to extract 80-90% of the CO2 in the inlet flue gas stream.

Cesam is an oxyfuel process that supplies heat and power to the absorption process. The process is illustrated below (bottom of page).

The figure below shows a conventional natural gas combined power cycle with an absorption unit and an oxyfuel process that supplies heat to the stripper tower. Cesam may, however, be applied to any post combustion absorption unit.

In the illustration below, a steam turbine is used in the oxyfuel process. This is an existing unit, that can be applied with minor modifications. In the long run, an oxyfuel gas turbine may be used to improve overall process efficiency. A highly efficient oxyfuel gas turbine will take some years to develop. 

Applying Cesam technology to post combustion installation has several advantages:

  1. Steam not available: The process is particularly well suited to situations where cheap steam is not available in sufficiently large amounts, for example, in areas with power shortages, CO2 capture from industrial processes, and retrofit CCS in general.
  2. Retrofit capture completely independent of the existing power plant: An alternative to Cesam is to extract steam from the gas turbine cycle to supply heat to the stripper tower. By extracting steam from the gas cycle, the cycle will no longer operate according to the design specification. When heat is supplied by Cesam the cycle will operate under its design conditions and the power plant is completely independent of the CO2 capture. 
  3. Increased thermal efficiency for retrofit capture: When the power plant is unaffected by the retrofit capture, the plant does not experience any efficiency loss due to off-design operations. 
  4. Increased power output for retrofit capture: If steam is extracted from the Rankine cycle to supply heat to the reboiler, the power output of the steam turbines will decrease. The absorption unit also requires power to drive the circulating fan and solvent pumps. Together this will decrease the total power output. With Cesam the power produced by steam turbines is unaffected and the oxyfuel process will supply power for the circulating fan and solvent pumps. In addition the oxyfuel turbine produces electricity.
  5. Increased CO2 capture ratio or decreased absorber tower height: A Cesam installation is a complete power plant in its own right with approximately 100% CO2 capture. Hence, by applying Cesam technology, the overall CO2 capture ratio will increase together with the total power output of the plant. If the plant is designed for less than the maximum CO2 capture ratio, the potential benefit may be realized through decreasing the height of the absorber tower.

Nebb is currently performing a concept study of a Cesam process solution for a full scale 430 MW combined cycle gas power plant, and a test plant at Technology Centre Mongstad (TCM). Both studies are with public funding from Climit/Gassnova. A fact sheet can be found here, and a news article about the project can be found here.