Kraft pulp mill malodorous gases – handling, destruction and safety

Abstract

Growing awareness of environmental issues related to increasing pulp production has spurred research aimed at finding eco-friendly, economical and safe practices. These practices have reduced the impact of unpleasant odors on the environment and made the reuse of malodorous compounds within the chemical circuit of pulp mills possible. Selfsufficiency of chemicals is enhanced when sulphuric acid and sodium bisulphite are selfproduced. Future modern pulp mills could be facilities that are completely odorless, fossil fuel-free, and operate with closed chemical circuits, producing renewable biobased byproducts.

This dissertation investigates technologies in modern pulp mills that maintain the benefits of odor-free processes while enhancing chemical circulation within the mill. It describes and discusses both past and current systems for collecting and handling non-condensable gases (NCGs). The mills studied in this thesis have designed and implemented their NCG systems within the past ten to fifteen years. New innovations have emerged, offering promising methods to further reduce occasional sulphurous odor emissions from the kraft process. These methods explore pretreatment and sulphuric gas stream reuse options in process units where these gases are generated, or during the transportation of these side streams to their final destruction site.

Using modern practices, malodorous gases can be collected to the extent that a kraft pulp mill is essentially odor-free, pending operator errors or major equipment malfunctions. One of the difficult aspects is that NCG systems in kraft mills are often designed case by case, as well as by various equipment vendors and with varying numbers of destruction sites. The actual detail design depends on the chosen layout, with the process configuration depending on individual equipment purchased and even on the design practices by individual suppliers.