Mitsubishi Heavy Industries Ltd (MHI) and Southern Company, a major US power company, will jointly launch a field test in 2011 to recover high-purity carbon dioxide (CO2) from coal-fired flue gas.
The two companies will set up a CO2 recovery demonstration plant, which is designed to be built at a medium-scale thermal power station in Alabama, the US. Based on the results of this demonstration plant, they will aim to commercialize the recovery plant in the future.
The field test will be subsidized by the US government. The demonstration plant will be constructed in Plant Barry, a coal-fired power station owned by Southern's subsidiary Alabama Power. Recovered CO2 will be compressed and stored in an aquifer deep underground.
The demonstration plant is composed of various facilities such as those for pre-processing, CO2 absorption/reclamation (absorption and reclamation towers) and CO2 injection. The plant will recover 500t of CO2 per day (equivalent to that produced when 25,000kW electricity is generated). The recovery rate is 90% or higher. The purity of recovered CO2 is expected to be 99.9%.
The recovery process is as follows. Coal-fired flue gas contains not only CO2 but also 'impurities' such as SOx, NOx, heavy metals and halogen compounds. These impurities are removed as much as possible in the pre-processing facilities, and the flue gas is cooled to near room temperature.
Flue gas with most impurities removed is taken into the absorption tower. Inside the tower, the gas is brought into contact with an absorbing solution so that only CO2 is absorbed into the solution. The solvent, "KS-1," is an amine-based material co-developed by MHI and Kansai Electric Power Co Inc.
Next, the solution containing CO2 is sent to the reclamation tower, where CO2 and the solution are separated from each other by heating. Then, CO2 is recovered, and the solution is recycled.
MHI has already commercialized a system to recover CO2 from natural gas-fired flue gas. But, in order to apply this system to coal-fired flue gas, an additional process is required to remove heavy metals and halogen compounds because the impurities contained in natural gas-fired flue gas are only SOx and NOx.
Electric Power Development Co Ltd is also testing a CO2 recovery plant for coal-fired flue gas at its Matsushima Thermal Power Plant. However, the amount of CO2 recovered at the plant is only 10t per day. Therefore, a field test needs to be carried out using a larger scale plant for commercialization.
In addition to the field test announced this time, MHI is planning to construct a demonstration plant with a recovery capacity of 3,000t per day in the UK and intends to start trial operations in 2015.