Hydrogasification of chars under high pressures

Two Turkish lignites are carbonized at 700 °C and 900 °C, and the methane formation rates of these chars and of the char prepared from an activated bituminous coal are investigated at temperatures between 700 °C and 900 °C and at hydrogen pressures of 2.5 MPa, 5 MPa and 7.5 MPa. The dependence of methane formation rate on time during gasification shows that the type of carbon and the prior thermal treatment influence the rate of hydrogenation. It was shown that hydrogasification occurs in two stages. The first stage occurs as the rapid and volatile reactive parts of chars are responsible for the high reactivity. The second stage is a low rate gasification in which hydrogen attacks directly the residual aromatic carbon structure. The effect of carbonization temperature on the first and second gasification periods is investigated. It is shown that the higher is temperature of carbonization, the less reactive is the char. Then, the dependence of the methane formation rate on hydrogen pressure and gasification temperature is examined, and the results are discussed.