MODELLING AND DESIGN OF A DRY BLACK LIQUOR GASIFICATION PROCESS

The purpose of this paper is to present modelling and design of a new type of black liquor gasification process with significant benefits compared to existing Tomlinson boilers and wet gasification processes. The organics are gasified by mainly steam reforming, as the temperature is relatively low (below 850 °C) and the water content of the black liquor relatively high (> 20 % water). The gasification can be with or without direct caustization. Sulphates are reduced to first Na2S, and then most of the sulphur is evaporated as H2S (Hydrogen sulphide), after reaction with CO2 + H2O. The hydrogen sulphide is absorbed in a and used for preimpregnation of the wood chips, to give modified cooking with stronger and brighter fibres out from the digester. With TiO2 added, sodium carbonate is converted into Na2O.TiO2, which dissolved in water gives 4 NaOH + Na2O.(TiO2)3. The direct caustization makes the lime kiln unnecessary. The gas may be combusted in a gas turbine /steam turbine cycle, to produce 2-3 times more electricity than conventional recovery boilers, that is an electrical efficiency of 30-35. Copyright © 2006 IFAC