The #6
Power Boiler is located at the north end of the Kraft Mill. Originally built in 1975, this boiler was designed to burn wood waste and wastewater treatment solids to generate high-pressure steam for electricity generation and pulp and paper manufacture. The fuel, which consists primarily of bark, oversized chips, knots, and wastewater treatment solids, is fed into the boiler on a continuous basis where it is burned. The boiler is lined with tubes filled with water, which when they come into contact with the heat from the burning fuel, generates steam. The steam, which is at a very high pressure (850 psi) goes into the mill’s steam system and is used to generate electricity in one of three turbines or is used in the process.
The heavy
ash (similar to ash from a home woodstove) is removed from the bottom of the boiler by grates and is collected in hoppers prior to being sent to a licensed non-hazardous industrial landfill for disposal.
As a result of new regulatory requirements on this boiler, the existing pollution control equipment was upgraded in 1996. An
electrostatic precipitator was installed, to replace the
cyclones, which reduced particulate emissions from this boiler by over 98%.
An electrostatic precipitator is similar to electronic air filters located in houses and restaurants. The
flue gas passes through a large chamber that contains electrically charged wires and plates. The particulate in the gas is attracted to the plates due to the electrical charge. The clean gas is then discharged to atmosphere. When there is a sufficient buildup on a plate, a large rapper or hammer knocks the plate resulting in the heavy particulate falling to the bottom of the precipitator for collection. A precipitator is considered a dry system (unlike a
wet scrubber) and the resulting flue gas is dry which results in no visible emissions during warm weather. When the weather is cold, a vapour plume will be visible due to the hot air being discharged. The particulate collected from the precipitator is sent to a licensed
landfill for disposal.
In 2006 the boiler's combustion air system and grates were upgraded to improve bark burning efficiency. As a result of this project there has been a significant reduction in the use of fossil fuels at the facility.