The inorganic chemistry of wood combustion for power production

Equilibrium calculations were performed to determine the inorganic chemistry involved in the combustion of aspen woodchips with a large excess of oxygen at pressures of 1, 4 and 10 atm. At 1 atm, a potassium-sulfate-rich liquid forms at high temperatures (1050°C) and persists to a temperature of between 975 and 1000°C, where it crystallizes to form solid alkali sulfates. At 4 and 10 atm the liquid crystallizes above 1000°C. The formation of sulfate is limited by the low abundance of sulfur, which is greatly depleted at 1000°C. A large fraction of the alkali remains in the vapor as the KOH molecule at this temperature. Both KOH and CaO react with CO2 in the vapor to form the solid carbonates K2Ca2(CO3)3 and CaCO3 below 800° at 1 atm. At 4 atm, a potentially corrosive molten carbonate forms at temperatures in the range of 800–875°C. Below 800°C all the carbonate crystallizes to CaCO3 and K2Ca2(CO3)3. Upon cooling at 10 atm, the liquid forms somewhat above 900°C and crystallizes somewhat above 800°C to form these solid carbonates. These considerations are applied to a gravel-bed combustor/gas turbine system and methods for improving its operation by temperature control and hot gas cleanup are reported. An economic analysis and future prospects in the United States are discussed to provide a context for this work.