Waste recovery and utilization in the kraft recovery process

In combination with a kraft recovery pulp mill having at least one power boiler which produces hot flue gas containing at least one sulfur compound, a waste heat and sulfur recovery apparatus for extracting sulfur and heat from the flue gas produced by the power boiler for use in the pulp mill, comprising:

• a corrosion-resistant condensing heat exchanger connected to the power boiler for receiving at least some of the flue gas from the power boiler, the condensing heat exchanger having surfaces exposed to condensing corrosive gases from the flue gas, an upper inlet and a lower outlet with a drain, a conduit connected between the power boiler and the upper inlet for supplying the flue gas to the condensing heat exchanger, and a recycle loop connected between the drain and the conduit for recirculating condensate and mixing it with the flue gas;
• means for supplying an alkali sodium-based solution selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium sulfite to the condensing heat exchanger for reacting same with the condensate to form a sulfur containing solution;
• and
• supply line means connected between the recycle loop and the pulp mill for supplying the sulfur containing solution to a multiple effect evaporator of the pulp mill so that water in the solution is evaporated during liquor concentration in the pulp mill.