Hydrogen production by steam-gasification of petroleum coke using concentrated solar power-I. Thermodynamic and kinetic analyses

The steam-gasification of petroleum coke using concentrated solar radiation as the source of high-temperature process heat is proposed as a viable transition path towards solar hydrogen production. The advantages are three-fold: (1) the calorific value of the feedstock is upgraded; (2) the gaseous products are not contaminated by the byproducts of combustion; and (3) the discharge of pollutants to the environment is avoided. The thermodynamics and kinetics of the pertinent reactions are analyzed for two types of petroleum coke: Flexicoke and Petrozuata Delayed coke. The net process is endothermic by about 50% of the feedstock's LHV, and proceeds at above 1300 K to produce, in equilibrium, an equimolar mixture of H2 and CO. A Second-Law analysis on the processing of this syngas to H2 (by water-gas shift followed by H2/CO2 separation) for power generation in a fuel cell indicates the possibility of doubling the specific electrical output and, consequently, halving the specific CO2 emissions, vis-à-vis conventional coke-fired power plants. Kinetic rate laws are formulated based on elementary reaction mechanisms describing reversible adsorption/desorption processes and irreversible surface chemistry. The kinetic parameters and their Arrhenius-type temperature dependence are experimentally determined using a quartz tubular reactor containing a fluidized bed of petroleum coke in steam and directly exposed to concentrated thermal radiation. Syngas containing approximately an equimolar mixture of H2 and CO and with a relative CO2 content of less than 5% was produced at above 1350 and 1550 K for Flexicoke and Petrozuata Delayed coke, respectively.