Pulp and paper operations present multiple challenges for air pollution control. Steam boilers produce fly ash, process equipment creates salt cake accumulation, and in-plant processes create various kinds of dust and fumes. AAF applies the appropriate core technologies, with customised installations for the specific industry needs, to meet and exceed goals for reduced emissions and material recovery.
The primary source for gaseous contamination in pulp and paper mills is the pulping process. In the Kraft pulping process, highly malodorous emissions of reduced sulphur compounds are produced. These compounds are measured as total reduced sulphur (TRS) and include hydrogen sulphide, methyl mercaptan, dimethyl sulphide, and dimethyl disulphide. These sulphur compounds are often described as smelling like rotten cabbage.
In the sulphite pulping process, sulphur oxides are also emitted in fairly significant concentrations.
Other pulping processes, such as the mechanical and thermomechanical methods, generate significantly lower quantities of air emissions.
In addition, steam and electricity-generating units using coal or fuel oil emit fly ash, sulphur oxides and nitrogen oxides. A secondary source of corrosive gases in the pulping process is during the bleaching step. These bleaching chemicals, which often include lime, are caustic and cause corrosion to occur.
For particulate filtration, several stages of HVAC-type air filtration products are employed to help keep the wood fibre and associated dust to a minimum. Ensuring that this dust is removed is extremely important to both the paper quality and the maintenance of the pulping equipment and paper production machines.
SAAF Chemical Media provides high efficiency filtration for effective removal of corrosive gases. Media is available as SAAF Custom Blends and SAAF Gas Specific solutions and is designed to safely deliver superior gas removal effectiveness on a variety of target gases.
At a minimum, protection of the control room includes pressurisation with purified air. This prevents corrosive gases from infiltrating the control room and causing corrosion problems. Additionally, recirculation air may require cleaning, if the room is a high traffic area or there are other internal sources of contaminants.
Supplemental real-time monitoring, such as AAF’s SAAFShield® Technology, is recommended for ensuring a quick reaction to outdoor events that may introduce corrosive gases into control rooms, and to monitor odours.