When power plants begin capturing their carbon emissions to reduce greenhouse gases – and to most in the electric power industry, it’s a question of when, not if – it will be an expensive undertaking.
Current technologies would use about one-third of the energy generated by the plants – what’s called “parasitic energy” – and, as a result, substantially drive up the price of electricity.
But a new computer model developed by University of California, Berkeley, chemists shows that less expensive technologies are on the horizon. They will use new solid materials like zeolites and metal oxide frameworks (MOFs) that more efficiently capture carbon dioxide so that it can be sequestered underground.
There are potentially millions of materials that can capture carbon dioxide, but it’s physically and economically impossible for scientists and engineers to synthesize and test them all, Smit said. Now, a researcher can upload the structure of a proposed material to Smit’s website, and the new computer model will calculate whether it offers improved performance over the energy consumption figures of today’s best technology for removing carbon.
Fossil fuel-burning power plants, in particular coal-burning units, are a major source of the carbon dioxide that is rapidly warming the planet and altering the climate in ways that could impact crops and water supplies, raise sea level and lead to weather extremes. Even with the move toward alternative, sustainable and low-carbon sources of energy, ranging from solar and wind to hydrothermal, coal- and natural gas-burning power plants are being built at an increasing rate around the world. At some point, Smit said, carbon capture will be the only way to reduce carbon emissions sufficiently to stave off the worst consequences of climate change.
Although no commercial power plants currently capture carbon dioxide on a large scale, a few small-scale and pilot plants do, using today’s best technology: funneling emissions through a bath of nitrogen-based amines, which grab carbon dioxide from the flue gases. The amines are then boiled to release the CO2. Additional energy is required to compress the carbon dioxide so that it can be pumped underground.
The energy needed for this process decreases the amount that can go into making electricity. Calculations show that for a coal-fired power plant, that could amount to approximately 30 percent of total energy generated.
Solid materials should be inherently more energy-efficient than amine scrubbing, because the CO2 can be driven off at lower temperatures. But materials differ significantly in how tightly they grab CO2 and how easily they release it. The best process will be a balance between the two, Smit said.
Smit and his UC Berkeley group worked with Bhown and EPRI scientists to establish the best criteria for a good carbon capture material, focusing on the energy costs of capture, release and compression, and then developed a computer model to calculate this energy consumption for any material. Smit then obtained a database of 4 million zeolite structures compiled by Rice University scientists and ran the structures through his model. Zeolites are porous materials made of silicon dioxide, the same composition as quartz.
The team also computed the energy efficiency of 10,000 MOF structures, which are composites of metals like iron with organic compounds that, together, form a porous structure. That structure has been touted as a way to store hydrogen for fuel or to separate gases during petroleum refining.
“The surprise was that we found many materials, some already known but others hypothetical, that could be synthesized” and work more energy efficiently than amines, Smit said. The best materials used 30 percent less energy than the amine process, though future materials may work even better. The computer model will work for structures other than zeolites and MOFs, Smit said.
Bhown said that the theoretically best material will probably have a parasitic energy cost of about 10 percent, so processes that use 20 percent or less are more attractive.
Key to the team’s success was using graphics processing units (GPUs) instead of standard computer central processing units (CPUs), GPUs reduced each structure’s calculation, which involves complex quantum chemistry, from 10 days to 2 seconds.
This story is reprinted from material from UC Berkeley, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.