The invention relates to improved steam generation in a chemical recovery process in a recovery boiler. The black liquor obtained from a kraft pulping process is subjected to a lignin separation process forming a lignin rich fraction and a lignin lean fraction. The lignin rich fraction is burnt in a parallel furnace having superheaters, while the lignin lean fraction is burnt in the ordinary recovery boiler. The resulting flue gases from the parallel furnace are merged with the flue gases in a later flue gas position in the recovery boiler, reducing the harsh chemical conditions in the recovery boiler. This results in more efficient steam generation and possibilities of generating more high pressure steam for production of electricity.