Most existing systems rely on complex plumbing to divert the steam used to drive the turbines that generate power in these plants. Such systems are not practical as retrofits to existing plants, MIT says. By contrast, the MIT system requires no steam connection and can operate at lower temperatures than other scrubbing technology.
The new electrochemical CO2 scrubber system is described in a paper published online in the journal Energy and Environmental Science, written by doctoral student Michael Stern, chemical engineering professor T. Alan Hatton and two others.
The system is a variation on a well-studied technology that uses chemical compounds called amines, which bind with CO2 in the plant’s emission stream and then release the gas when heated in a separate chamber. But the conventional process requires that almost half of the power plant’s low-pressure steam be diverted to provide the heat needed to force the amines to release the gas. That massive diversion would require such extensive changes to existing power plants that it is not considered economically feasible as a retrofit.
In the new system, an electrochemical process replaces the steam-based separation of amines and CO2. This system only requires electricity, so it can easily be added to an existing plant, researchers say.
The system uses a solution of amines, injected at the top of an absorption column in which the effluent gases are rising from below. The amines bind with CO2 in the emissions stream and are collected in liquid form at the bottom of the column. Then, they are processed electrochemically, using a metal electrode to force the release of the CO2; the original amine molecules are then regenerated and reused.
As with the conventional thermal-amine scrubber systems, this technology should be capable of removing 90 percent of CO2 from a plant’s emissions, the researchers say. But while the conventional CO2 capture process uses about 40 percent of a plant’s power output, the new system would consume only about 25 percent of the power.
President Barack Obama’s climate plan, announced yesterday, will restrict CO2 emissions from existing coal-fired power plant. Reuters reports the EPA will issue proposed carbon emissions limits for existing powers plants by June 2014 and finalize the regulations a year later.