Hydrogen production and CO2 fixation by flue-gas treatment using methane tri-reforming or coke/coal gasification combined with lime carbonation

The production of hydrogen and the fixation of CO₂ can be achieved by treatment of flue gases derived from fossil fuel fired power plants via catalytic methane tri-reforming or by coal gasification in the presence of CaO. A two-step process is designed to be carried out in two reactors: a) a catalytic gasifier or steam-reformer, operating exothermally at 900–1000 K, with inputs of the flue gas, a carbonaceous source, steam and air, as well as CaO from the calciner, and outputs of H₂, and of “spent” CaCO₃ to the calciner; b) a calciner, operating endothermally at 1100–1300 K, with inputs of spent CaCO₃ from the gasifier, make-up fresh CaCO₃, and outputs of CO₂, as well as of CaO, partly recycled to the gasifier and partly processed in a cement plant. Thermochemical equilibrium calculations along with mass/energy balances indicate that for flue-gas treatment by tri-reforming, CO₂ emission avoidance of up to ∼59% and fossil fuel savings of up to ∼75% may be attained when concentrated solar energy is supplied as high-temperature process heat for the calcination step, all relative to conventional H₂ production by coal gasification. If instead fossil fuel would be used to drive the calcination step, the CO₂ emission avoidance and the fuel savings would be only 20% and 67%, respectively. Estimated annual H₂ production from a coal-fired 500 MWe burner by the proposed flue-gas treatment using either CH₄-tri-reforming or coal gasification would amount to 0.7 × 10⁶ or 0.6 × 10⁶ metric tons H₂, respectively. Estimated fossil fuel consumption for H₂ production by tri-reforming or coke gasification would be 149 or 143 GJ fuel/ton H₂.