Pulp mills sulfite pulping

Sulfite pulps have properties that are desirable for tissues and top quaHty, fine papers. Because sulfite pulping is not as versatile as kraft pulping, various options have been developed, and the choice of a specific process is dependent on individual mill situations. The unbleached pulp has high (60+) brightness compared to kraft pulp and is easily bleached. However, it is limited to select wood species. The heartwood of pine, Douglas fir, and cedars are not easily pulped. Additionally, pulps produced from hardwood have limited economic value because of low strength. 

NSSC Pulping. The characteristics of semichemical pulps are especially suited to the production of cormgated medium, which is the raw material for the fluted center ply of cormgated boxes. Neutral sulfite semichemical pulping was developed specifically as a semichemical process for cormgation medium and lends itself to small mills having minimal capital investment. For many years, this was the only semichemical pulping process. 

Paper Products. Paper (qv) products account for about 2% of sulfur demand. The largest single segment of demand is in the manufacture of wood pulp by the sulfite process (see Pulp). In this process, the main sulfur intermediate is sulfur dioxide, which is generally produced at the plant site by burning elemental sulfur. Some sulfur dioxide, however, is produced as a by-product at smelter operations, purified andUquefied, and shipped to the pulp mills. The sulfur dioxide is converted to sulfurous acid, and the salt of this acid is a principal component of the cooking Hquor for the sulfite process. 

Uses. The dominant use of sulfur dioxide is as a captive intermediate for production of sulfuric acid. There is also substantial captive production in the pulp and paper industry for sulfite pulping, and it is used as an intermediate for on-site production of bleaches, eg, chlorine dioxide or sodium hydrosulfite (see Bleaching agents). There is a substantial merchant market for sulfur dioxide in the paper and pulp industry. Sulfur dioxide is used for the production of chlorine dioxide at the paper (qv) mill site by reduction of sodium chlorate in sulfuric acid solution and also for production of sodium dithionite by the reaction of sodium borohydride with sulfur dioxide (315). This last appHcation was growing rapidly in North America as of the late 1990s. 

Pulp Manufacture. Sodium sulfite is utilized in neutral semichemical pulping, acid sulfite pulping, high yield sulfite cooling, and some kraft pulping processes (339). Many pulp mills prepare their own sulfite and recycle as much as possible, but use of merchant sodium sulfite by pulp mills is substantial. Much of the by-product sodium sulfite from resorcinol manufacture goes into pulp appHcations as well as a substantial fraction of the lower assay manufactured sodium sulfite. 

The BAT for sulfite pulp mills, also according to the EC, are considered to be the following38 ... 

In addition to process-integrated measures, primary and biological treatment are considered BAT for sulfite pulp mills... 

U.S. EPA, Pulp, Paper and Paperboard Industry—Background Information for Proposed Air Emission Standards Manufacturing Processes at Kraft, Sulfite, Soda, and SemiChemical Mills (NESHAP), U.S. EPA, Washington, 1993. 

NONBIOLOGICAL MATERIALS Kraft and sulfite mills United States 1988 104 mills Pulps ... 

Kallqvist T, Carlberg GE, Kringstad A. 1989. Ecotoxicological characterization of industrial wastewater -sulfite pulp mill with bleaching. Ecotoxicol Environ Safety 18 321-336. 

Hewitt, L.M. Pryce, A.C. Parrott, J.L. Marlatt, V. Wood, C. Oakes, K. Van der Kraak, G.J. 2003, Accumulation of ligands for aryl hydrocarbon and sex steroid receptors in fish exposed to treated effluent from a bleached sulfite/groundwood pulp and paper mill. Environ. Toxicol. Chem. 22 2890-2897. 

There are a number of full-scale activated sludge plants that are in operation in countries such as the United States, Canada, and Finland, which treat effluents from Kraft, sulfite, TMP, CTMP, and newsprint mills [22]. SchneU et al. [70] reported the effectiveness of a conventional activated sludge process operating at an alkaline-peroxide mechanical pulping (APMP) plant at Malette Quebec, Canada. The full-scale plant achieved 74% reduction in filterable COD and nearly complete elimination of BOD5, resin acids, and fatty acids in the whole mill effluent. The treated effluent tested nontoxic as measured by a Microtox assay. Saunamaki [71] reported... 

Kantardjieff, A. Jones, J.P. Practical experiences with aerobic biofilters in TMP (thermomechanical pulping) sulfite and fine paper mills in Canada. Water Set Technol. 1997, 35 (2-3), 227-234. 

The EPA passed its "Cluster Rule that requires kraft and soda pulp mills to utilize elemental chlorine-free (ECF) bleaching and all sulfite mills to use ECF or totally chlorine-free (TCF) bleaching. 

Semi chemical pulps are usually prepared by the neutral sulfite semichemical (NSSC) process, although modifications of the full chemical processes can be used. Active pulping chemicals are (in the sodium-base NSSC process) sodium sulfite buffered with sodium bicarbonate (pH 7,0-9.0) and (in the ammonium-base NSSC process) ammonium sulfite with ammonium hydroxide used as a buffer. Defiberization is usually accomplished by attrition mills of the disk type. 

Another important event could have been chosen on which to base a centennial—the invention of the sulfite pulping process by the Tilghman brothers in Philadelphia. Although dated as 1866 when a British patent for the process was issued, successful laboratory experiments had been made in 1865. In their attempts to adapt the new method to commercial scale, the Tilghmans tried to develop a continuous process but unfortunately could not solve the technical problems involved. A few years later, at the beginning of the 1870 s, experiments on sulfite pulping were taken up in several places in Europe, and in 1874 the first sulfite pulp was produced commercially by C. D. Ekman in a Swedish mill. 

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