The recovery boiler at the Irving Pulp and Paper Saint John, NB, mill has been through several major retrofits to increase its original firing capacity of 1100 metric tons/day of black liquor dry solids to the present level of 1680 metric tons/day. Many problems have been encountered over the years, including tube corrosion and cracking, as well as plugging of flue gas passages, but they all have been overcome through operational changes and process optimization. The latest challenge is to increase throughput without experiencing high total reduced sulfur (TRS) levels that would impact the environment and jeopardize compliance. An optimization program has been in place at the mill since December 2008 to further increase boiler production while maintaining environmental performance. The program, which automates liquor addition at full capacity according to targeted stack gas O2 and TRS levels, enables the boiler to operate at lower stack gas O2 targets and to achieve a 2%-3% increase in liquor throughput, while keeping TRS emissions under compliance.
Optimizing operation to increase recovery boiler throughput