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Fossil-Fueled Cogeneration

Combined heat and power (CHP) is sometimes fueled by biomass, like black liquor and hog fuel in pulp-and-paper plants or sawdust and scraps in furniture factories, but it’s primarily fossil-fueled. So why would RMI, whose focus is to speed the U.S. transition away from fossil fuels to efficiency and renewables, be excited about the market adoption of smaller fossil-fuel-fired generators? The answer is cogeneration’s radical efficiency. Traditional power plants convert one-third of their fuel into electricity and two-thirds into waste heat. Cogeneration uses both. Often industrial heat made to run a manufacturing process can also make electricity, even from leftover high-temperature heat that is being expensively disposed of, but without using any more fossil fuel. Or small generators in buildings can heat or cool them with heat left over from making electricity.

Such methods typically save at least half—often two-thirds or more—of the fuel, emissions, and cost of making electricity and heat separately, Moreover, most cogeneration is gas-fueled; gas is often more efficiently burnable than coal and emits only half of coal’s carbon per unit of contained energy. Thus the International Energy Agency reckons that accelerating CHP could save 10 percent of global CO2 by 2030. The most efficient CHP systems can exceed 90 percent efficiency from fuel to useful work. Replacing, say, America’s 920 oldest coal plants with modern combined-cycle gas plants, then using most of the other 40 percent for district heating, would cut their CO2 emissions by more than three-fourths, save money, and help nearby city-dwellers’ pollution-assaulted lungs. The gas-fired cogen system would still be fossil-fueled, but a great improvement, surpassed only by—and competing with—superinsulated, superefficient buildings and renewable electricity.

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