Particulate . What is it?
Particulate matter emissions consist of small sized air-borne particles. These solid particles are released from a variety of industries, including pulp and paper mills. They are often a result of incomplete combustion in power and recovery boilers and lime kilns.
Why does it matter?
There are no known health effects associated with particulate matter emissions from pulp and paper mills. However, high levels of particulate matter in the air can result in damage or soiling of various surfaces such as buildings, trees, and motor vehicles.
How is it measured?
Regulatory agencies in Canada and the United States have a standard test that is used to determine the particulate concentration in the air. It consists of passing air through a dry glass fibre filter, allowing for the collection of the small particles. After a set period of time the dirty filter is dried and weighed. The weight of the small particles trapped in the filter is used to calculate the particulate matter concentration in the air, usually expressed in parts per million (ppm).
How do we control it?
The amount of particulate matter generated from a pulp and paper operation can be reduced by improving the burning efficiency of the boilers. Wet scrubbers, electrostatic precipitators and multicyclones can be used to further reduce particulate emissions.
In a wet scrubber, water is sprayed into the exhaust gas stream containing the particulate matter. The water droplets capture small dirt particles decreasing the number emitted to the atmosphere. The water discharge is then processed in the wastewater treatment system.
An electrostatic precipitator collects the particulate matter by introducing an electrical charge on the dirt particles, causing the particles to be attracted to a metal plate where they are collected and disposed of.
Multicyclones remove particles by spinning the gases. A centrifugal force is created which pushes the solid particles to the outside of the multicyclone where they are removed. A multicyclone operates in a manner similar to the removal of rinse water in the spin cycle of a washing machine.
The Thunder Bay mill has a comprehensive Air Improvement Program that has identified a number of projects to reduce particulate emissions from the facility.