Basic characterisation of spent liquors, birch and eucalyptus, has been determined by laboratory analyses. The heating value of the liquors as well as the elemental composition confirms prospects for outlining an advanced recovery boiler and a gasification process. The properties of the liquor samples from the new cooking method differ in a favourable way from the properties of the conventional spent kraft pulping liquor. The corrosive properties of the new sulphur free liquor samples have been evaluated with respect to evaporation and boiler plant conditions. The basic properties of the spent liquor properties affecting the dimensioning of the evaporation plant are known. The pilot scale evaporation tests have been made with spent liquor from the pilot cooks successfully. Concept of the evaporation plant for IDE process has been outlined. The design work on the advanced recovery boiler has been done and some interesting solutions have been found. In order to increase the power production efficiency internal circulations were increased. This meant that efficient feed water preheating system was applied compared to modern Kraft recovery boiler systems. This required the final cooling of the flue gas to be carried out with combustion air as it is carried out in power boilers. Basic studies of spent liquor gasification in atmospheric conditions have been done. Relative differences in gas composition with varying conditions are known. Pressurized gasification tests simulating actual process conditions have been performed. The gasification process has been outlined in co-operation between the partners. The process design of the integrated gasification combined cycle process (IGCC) has been defined. The performance was calculated and the resulting power generated for mill size 3000 t pulp/d was determined to be 220MW. Compared to a modern pulp mill configuration with recovery boiler and production of 2000 t pulp/d a surplus power of 75MW can be achieved by an integrated gasification concept. The feasibility of the sulphur-free process has been studied and found attractive. Both the advanced recovery boiler and the gasification process will lead to significant increase in power production.