Pulp mills kraft pulping

Pulp and Paper Mill Waste Streams Five conditions were chosen for the enrichment of the original waste-activated sludge. Three foul condensate effluents from the pulp mill kraft chemical recovery process were selected based on their high COD (1) the combined evaporator condensates (3200 tank foul condensate or FC 3200), (2) blow heat accumulator overflow foul condensate (FC BHAO), and (3) evaporator foul condensate (FC EVAP). The remaining two media used for enrichment consisted of primary clarifier effluent (primary out abbreviated as l°OUT ) supplemented with methanol, and waste-activated sludge supplemented with methanol (WAS-only). 

Modijications to the Recope Cycle. The recovery system is a principal capital cost in a kraft mill. Consequently, any recovery process that is less expensive to build can improve pulping economics. There have been numerous attempts to improve the kraft recovery process. Two examples are the direct alkaline recovery scheme (DARS) and the autocausticizing scheme using sodium borates (37). Both schemes eliminate the lime loop of the conventional kraft mill. As of 1996, neither is commercially used. 

S oda—Anthraquinone. A few mills worldwide use soda pulping of hardwoods. In such cases, the addition of anthraquinone is immediately justifiable in terms of increased yield and upgraded pulp quaHty. The conversion of existing kraft mills is not as simple because AQ contributes no alkalinity to the process as sulfide does, and most kraft causticizing systems would have to be expanded by about 33%. This conversion is probably not justifiable in terms of the yield gain. The greatest benefit from AQ is for new mills in which expenditures for air pollution abatement devices can be reduced. 

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. 

Closed-Mill Concept. The closed-mill concept, or water circuit closure, has been studied by the pulp and paper industry for many years. In some parts of the paper manufacturing process, up to 98% of the water is recycled within the process, eg, the wet end of the paper machine. However, in the pulp mill, especiaUy kraft mills, effluents are produced owing to the need to purge from the system various metals that come in with the wood, as weU as organic by-products from the pulping process, additives, and especially chloride ions that originate in the bleach plant. 

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. 

Fig. 17. Pretreatment of organic wastewater on trickling filters. Industry types for which coordinates have been plotted are 1, kraft pulp and paper 2, mixed iadustry 3, wet com milling 4, dairy 5, tannery 6, meat packiag 7, food 8, pharmaceutical 9, refinery and 10, textile.

When chlorine dioxide is used for pulp bleaching in conjunction with the Kraft (sulfide) process for chemical pulping, by-product sodium sulfate can be used as a source of makeup sulfur and sodium consumed in the chemical cycle. The demand for sodium and sulfur in pulp bleaching is related to the loss of these chemicals through carryover in unbleached pulp. As process improvements have sought to reduce pollution from pulp mills, less sodium sulfate makeup is required. The trends in pulp bleaching to increase substitution of chlorine with chlorine dioxide have caused an oversupply of sodium sulfate, so that this by-product is often regarded as waste (81). 

Steel Plants Electric Arc Furnaces and Argon-Oxygen Decarhurization Vessels Constructed after August 7, 1983 Kraft Pulp Mills Glass Manufacturing Plants Grain Elevators... 

Coal-cleaning plants (with thermal dryers) Kraft-pulp mills Portland-cement plants Primary zinc smelters Iron and steel mill plants Primary aluminum-ore-reduction plants Primary copper smelters ... 

Kraft pulp mills Digesters hatch and continuous Mercaptans, methanol (odors) Condensers and use of lime kiln. 

Chemical-mediated immune suppression has been identified from the experimental study of several wildlife species. Harbour seals fed either chemically contaminated fish from the Wadden Sea or imcontaminated fish were found to have differing immune responses, with the exposed group showing lowered immune response to microbial infections and certain types of cancer. "" Mink fed fish taken from below a discharge point for bleached Kraft pulp mill effluent have also shown impaired immune function, " showing that the non-accnmillative chemicals in this effluent can actively disrupt endocrine associated functions. 

Ferroalloy production facilities Kraft pulp mills"... 

EPA, 1996b. U.S. EPA, Office of Air Quality Planning and Standards, "Chemical Recovery Combustion Sources at Kraft and Soda Pulp Mills," EPA-453/R-96-012, Research Triangle Park, NC, October, 1996. 

Vickers, K. 1993. Detonation Arresters for Kraft Pulp Mills for Use m NCG Collection Systems. Paper presented to various pulp mills. Westech Industrial Limited, Calgary, Alberta, Canada. 

Coullard CM, Nellis P. 1999. Organochlorine contaminants in mummichog (flindulus heteroclitus) living downstream form a bleache-kraft pulp mill in the Miramichi estuary. New Brunswick, Canada. Environ Toxicol Chem 18(ll) 2545-2556. 

First, we discuss the problem statements and key features of the learning architecture that are specific to complex systems. This is followed by a brief presentation of the search procedures that are used to build a final solution. The section ends with a summary of the application of the learning architecture to the analysis of a Kraft pulp mill. 

The overall system that we will analyze comprises the unbleached Kraft pulp line, chemicals and energy recovery zones of a specific paper mill (Melville and Williams, 1977). We will employ a somewhat simplified but still realistic representation of the plant, originally developed in a series of research projects at Purdue University (Adler and Goodson, 1972 Foster et al., 1973 Melville and Williams, 1977). The records of simulated operation data, used to support the application of our learning architecture, were generated by a reimplementation, with only minor changes, of steady-state models (for each individual module and the system as a... 

Jokela JK, M Salkinoja-Salonen (1992) Molecular weight distributions of organic halogens in bleached kraft pulp mill effluents. Environ Sci Technol 26 1190-1197. 

Saski EK, A Vahatalo, K Salonen, MS Salkinoja-Salonen (1996b) Mesocosm simulation on sediment formation indnced by biologically treated bleached kraft pulp mill wastewater in freshwater recipients. In Environmental Fate and Effects of Pulp and Paper Mill Effluents (Eds MR Servos, KR Munlittrick, JH Carey, and GJ van der Kraak), pp. 261-270. St Lucie Press, Delray Beach, FL. 

Park, H "Thermodynamics of Sodium Aluminosilicate Formation in Aqueous Alkaline Solutions Relevant to Closed-Cycle Kraft Pulp Mills", PhD Thesis, Dept, of Chemical and Bio-Resource Engineering, University of British Columbia, Vancouver, BC, Canada, 1999. 

A bleached kraft pulp mill requires 15,140 to 45,420 L (4000 to 12,000 gal) of water and 8.56 to 12.22 million chu (14 to 20 million Btu) of energy per ton of pulp, of which ca. 4.44 to 5.56 million chu (8 to 10 million Btu) are typically derived from biomass-derived fuel from the pulping process itself.4 Across all facilities, the pulp, paper, and allied products industry is the largest consumer of process water and the third largest consumer of energy (after the chemicals and metals industries).5,6 The large amounts of water and energy used, as well as the chemical inputs, lead to a variety of environmental concerns. 

Table 21.3 presents an overview of wood pulping types by the method of fiber separation, resultant fiber quality, and percent of 1998 U.S. pulp production.1112 Many mills perform multiple pulping processes at the same site, most frequently nondeink secondary fiber pulping and paper-grade kraft... 

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