In many cases the length of a mill outage is set by the time needed for recovery boiler cooling, washing, inspections and repairs.
The ways cooling and washing are carried out can be optimized so that the total outage time can be reduced. The reductions in the total outage time can be obtained by:
- removing most of the smelt while the boiler is still firing black liquor and auxiliary fuel(s)
- monitoring the bed cooling so that washing can start immediately after the bed is cooled to 500 °C
- washing the superheaters first or simultaneously with the other parts of the boiler
- washing the floor with clean water sprayed onto the floor, keeping the water in the pool mixed and circulating using mixing devices installed on the floor.
The experience gained so far indicates that when these actions are carefully planned and systematically executed, significant time savings can be achieved. Usually this does not happen overnight, but instead over a period of a couple of years, as the outage practices and procedures are modified step by step to gradually optimize the outcome.
The information above was excerpted from a paper presented by Valmet personnel at the PEERS 2017 conference and is available as a white paper available HERE.