Working Towards a Safer Recovery Boiler Operation, 2016 Pulping, Engineering, Environmental, Recycling, Sustainability (PEERS) Conference Proceedings

he recovery boiler is an integral part of the pulp mill. It is used for two purposes; to recovery the pulping chemicals from the black liquor and to produce thermal energy in the form of high pressure steam. This steam is used both for process and electrical power production. Chemicals are recovered in the form of smelt from the bottom of the furnace. Smelt is comprised of molten sodium salts, mostly in the form of sodium sulfide (Na2S) and sodium carbonate (Na₂CO₃) with a smaller amount of sodium sulfate (Na2SO4). It is critical in a recovery boiler to prevent contact between water and molten smelt as this can lead to a violent physical reaction better described as an explosion. In addition to the risk of explosion, combustion in the recovery boiler creates very hot gases and highly corrosive molten ash in the lower furnace. The black liquor that fuels the recovery boiler is also hot and highly caustic. Traditionally, operators have performed a number of physical tasks around the recovery boiler that potentially may have them come into contact with smelt, black liquor, hot gases and ash during furnace pressure excursion (positive furnace pressure) and process upsets (smelt rushes, heavy dissolving tank activity). These tasks include rodding and cleaning the smelt spouts and air ports as well as inserting, removing and cleaning liquor guns.  

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