The process – so far tested only at a laboratory scale, uses chilled ammonia to absorb gas for collection. It was developed by Alston, a major manufacturer of generating equipment, and aims to reduce the energy required to capture carbon dioxide.

It is estimated nearly a third of a power plant’s energy output might be needed to pull carbon dioxide from the waste stream. Alstom hopes to hold it to 15 percent. Researchers at the Massachusetts Institute of Technology yesterday called for prompt work on demonstrating sequestration technologies.

Costs must be kept as low as possible if the technology is to be used on a wide scale. Congress is seen as unlikely to impose enormously expensive restraints on emissions. And under proposals to cap emissions nationally and let companies trade credits for extra reductions, only the cheapest methods of reducing greenhouse gases would thrive in the marketplace.