Coal fuels 40% of the world's electricity generation capacity, and represents 46% of the growth in new energy production according to the International Energy Agency. Although the current economic softness has slowed the growth of coal, 200 MW/day of new coal-burning power came online from 2010-2014. Trends towards electrification of transportation and other infrastructure to reduce distributed combustion, will continue to drive the demand for centralized power plants.
Currently, the chorus line of the tune to which politicians dance in the wake of Kyoto protocol commitments for reducing greenhouse gases is "carbon capture and storage (CCS)." But there has been little progress on CCS - the economics of collecting large amounts of contaminated air to pull out the CO2 in the face of other confounding contaminants presents a huge challenge.
MIT doctoral student Katherine Ong and Professor Ahmed Ghoniem suggest a smarter way. They have published a paper in the Journal of Power Sources, Modeling of indirect carbon fuel cell systems with steam and dry gasification which shows that a new type of power plant could double the efficiency of power generation from coal.Doubling the efficiency means half the emissions for the same amount of electricity generated. That's all emissions, including the metals, smog, and other contaminants in addition to the greenhouse gases like CO2.
The accompanying illustration demonstrates how more efficient coal use works:
"At the bottom, steam (pink arrows) passes through pulverized coal, releasing gaseous fuel (red arrows) made up of hydrogen and carbon monoxide. This fuel goes into a solid oxide fuel cell (disks near top), where it reacts with oxygen from the air (blue arrows) to produce electricity (loop at right)."
Many coal plants use gasification today, but send the gases to a combustion and steam turbine process for recovery of energy. The MIT proposal would send the gasified fuel to fuel cells -- another well established technology.
Standard coal plants achieve only abut 30% efficiency, rising to 38% in modern fully integrated plants with substantial heat recovery optimization. Simulation models by the MIT team indicate that efficiency of 55 to 60% could be achieved with their power plant.
The technology would cost more up front, but the investment could be recouped in several years with the higher efficiency, making the proposal acceptable under most capital investment strategies.