July 15, 2008

New strategies for conquering environmental challenges

Angela Neville, JD

New directions in capturing CO2

“There is a growing consensus that CO₂ from power plant flue gas is a large source of CO₂ emissions that must be reduced to slow and eventually reverse the trend of climate change,” said speaker Harvey Wen, the manager of advanced technologies at Bechtel Power Corp.

According to Wen, in the past, amine-based CO₂ capture plants were built to produce a small quantity of clean CO₂ for industrial uses. A number of optimized processes, based on existing amine technology, are being developed for implementation in large-scale utility applications.

Given the slow commercialization status of various emerging CO₂ capture technologies, it appears that monethanolamine (MEA)-based flue gas scrubbing is the only viable technology at present, Wen said. Steam consumption for the MEA-based plant has been reduced from more than 3 kg of steam per kg of CO₂ capture to less than 1.5 kg of steam per kg of CO₂ capture. This improvement derives primarily from the use of higher concentrations of MEA solvents and the development of more-efficient additives for corrosion and solvent degradation control.

Wen focused on the next improvement areas that will come to light in the search for novel CO₂ capture solvents. Chilled ammonia is one example, and if demonstrated with good economics, it will have broad applications. Other technologies, including oxyfuel combustion and chemical looping combustion (CLC), are still in development. Oxyfuel combustion is in the advanced development stage and, if successfully demonstrated, can be another option for both new plants and retrofit applications. CLC is a new concept to generate CO₂-rich flue gas and does not require the use of an oxygen plant. However, CLC technology cannot be retrofitted. According to Wen, CLC is in the early stages of development and will not be ready for commercial use in the foreseeable future.