Pulp and Paper
The forest industry is important to the Canadian economy. It contributes up to 3% of the gross domestic product (GDP), and over $34 billion in exports from Canada. Canada is the world's largest exporter of market pulp and newsprint and as a result, over 57,500 direct jobs (excluding wood products) and 250,000 indirect jobs have been created.
The wood fibre sources for pulp and paper mills are sawmill residue (55%), logs and chips (21%) and recycled paper (24%). There are two main pulping processes: mechanical and chemical. In the mechanical process, wood is pulped using the mechanical energy to press the fibres between narrow-gap plates (refiner mechanical pulping - RMP). This process may vary by adding steam (to warm the chips), pressure (thermomechanical pulping - TMP) and sometimes chemicals, or both (chemi-thermomechanical pulping - CTMP).
In the chemical process, wood chips and sawdust are cooked by using an aqueous solution of chemical. This process results in the separation of cellulose fibre from the wood by dissolving the lignin that binds the fibres together. The remaining solution (chemical and lignin) is then recycled to recuperate the chemicals. This is achieved by burning the chemical and lignin mixture (black liquor) to produce energy (recovery boiler) with the remaining residue treated in a caustic plant.
In both processes, the pulp could be washed or bleached depending on its final use. In most mills, the gas produced by the chemical process and washing are collected and burned. The power and recovery boilers generate the steam to meet all the requirements of the mill. The age, technology and emission controls of the boiler will determine the amount of air emissions generated by the mill.
The emissions from the pulp mill vary depending on the process (mechanical or chemical) and as mentioned above, will be determined by the age and technology used. Commonly, these emissions are VOC's, PM10 and PM2.5, SOx, NOx, H2S, Cl2, ClO2, methanol, acrolein, acetaldehyde or formaldehyde.
