Abstract: The invention relates to a process and apparatus for the production of thermal and electric energy in a pulp mill, in particular a sulfate pulp mill, according to which process and waste liquor of the cellulose pulp cooking liquor is concentrated, and this concentrated liquor is burned in the recovery boiler in the presence of biogenic fuels, in which case the thermal energy is recovered from the flue gases from the combustion, and this thermal energy is, when so desired, converted to electric energy. According to the invention, the biogenic fuel used is wood bark or similar waste wood, which is dried to a moisture content below 30%, whereafter it is gasified to fuel gas, which is fed into the recovery boiler. The process according to the invention makes the acquisition of a separate bark boiler in pulp mills completely unnecessary, which significantly lowers the investment costs. The process simplifies the apparatus, its operation and maintenance, and improves energy efficiency.

Abstract: A method for adjusting the chlorine equilibrium in a sulphate cellulose process, wherein part of the chlorine contained in the cycle is separated and removed. In the method, strong odour gases from the sulphate cellulose process are introduced into a soda recovery boiler for burning so that chlorine contained in the liquor is in the form of hydrogen chloride (HCl) in the upper part of the soda recovery boiler and can subsequently be separated from the flue gases in a flue gas scrubber. The chlorine equilibrium is adjusted by removing part of the chlorine-containing washing solution.

Abstract: A method for burning secondary sludge in a recovery boiler, in which method secondary sludge is mixed with black liquor. According to the method, an alkali is added to the secondary sludge so as to obtain a mixture having a pH of over 7, whereafter the mixture of alkali and secondary sludge is heated to a temperature of over 80.degree. C. and kept at this temperature for over 30 minutes. Thereafter the heat treated mixture of alkali and secondary sludge is supplied to the thick end of a black liquor evaporation plant.

Abstract: A method for adjusting the sulphur/sodium ratio in a soda recovery boiler when strong sulphurous odour gases are burned therein. According to the method, sodium is introduced into the soda recovery boiler in an amount proportional to the amount of sulphur either as sodium hydroxide, sodium carbonate compounds or soap, whereby the sodium and sulphur react, forming sodium sulphate, which can be removed from the flue gases together with fly ash.