Much improved power plant combustion efficiency, increased from an average of about 34% for existing plants to more than 50% for the combustion of solid fuels (coal, lignite, biomass or petroleum coke) and also natural gas, is now possible with greatly reduced emissions to the atmosphere when 10% to 40% moisture fuels are dried to less than 3% moisture. The new method requires sufficient scale and timely application of low-cost off-peak electric resistance heating to be most economical.
The drying of more than 1,000 tons per day of high moisture fuel per drying unit is likely the minimum scale for economical operation. Electric power availability of 10 to 50 megawatts (MW) per hour of operation may be required. Portable drying units may be located adjacent to air-fired pulverized coal boilers.
Oxygen-fired rotary kiln combustors, combined with condensing boilers, are being developed to operate without coal pulverizers, electrostatic precipitators or smoke stacks. There should be no boiler emissions into the atmosphere when optimized. CO2 is recovered from fuel combustion and recycled to grow biomass as in U.S. Patent # 8,673,615. The biomass growth byproduct is oxygen and is available to further reduce fuel combustion costs.
The new rotary kiln oxygen-fired combustors with condensing boilers should operate at a much higher fuel efficiency with relatively lower capital and operating costs than air-fired Rankine cycle pulverized coal boilers, 50 to 300 MW, on about two acres of space.
April 9th, 2015