Cascades Uses Chlorine Dioxide for Chemical Oxidation of TRS in NCG
As a result of the triai at Cascades’ Fjordcell mill in Jonquière, Que., no organochlorides or other objectionable compounds were measured at significant levels
The total reduced sulfides (TRS) present in non-condensable gases (NCG) are partly responsible for the characteristic odor of kraft pulp mills. These odors originate mostly from the vents associated with pulp production equipment such as digesters, blow tanks and washers, or from black liquor recovery equipment. Since the early 1990s, the Canadian provinces1 and the U.S.2 have implemented regulations that force kraft pulp producers to collect and treat major vents containing TRS.
The traditional approach for treating these gases is incineration, either in a lime kiln, in the plant boilers, or in a dedicated incinerator. However, thermal incineration of NCG has several drawbacks, such as the risk of toxic gas inhalation (leakage points on existing boilers due to age), explosion risks, reluctance of the operating personnel, complexity of the security devices necessary to ensure safe injection of those gases into kilns or process boilers, high operating costs and high boiler modification costs.
Due to the costs involved with NCG incineration, alternate methods were developed in the beginning of the seventies by some mills3, some equipment manufacturers4.6′7 specializing in industrial emission treatment, and by research centres such as PAPRICAN5. Such methods chemically oxidize the contaminants present in the NCG using powerful oxidizers, such as sodium hypochlorite or chlorine dioxide, used to bleach the pulp. These oxidizers are therefore available to bleaching plants on site.
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