Paper manufacturing process

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. 

In practical applications, adequate coagulants should be chosen based on the quality of the floated scum (i.e., recovered titanium dioxide and fiber mixture), which is intended to be reused in the paper manufacturing process. The reused titanium dioxide and fibers should not adversely affect the quality of the paper. 

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturing process and contains a spectrum of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosin acids, such as abietic acid. The conventional refining process to recover these fatty acids involves intensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosin acids can be separated using a UOP Sorbex process ( 93—99) (Tables 8 and 9). 

Membranes are used in the pulp and paper industry in a variety of applications in particular for the purification and recovery of water, and for the recovery of raw materials or energy. The pulp and paper manufacturing process requires enormous amount of water to transport the raw materials, to dissolve impurities, to seal various process equipment, to cool and heat, to wash and clean process equipment, and to generate necessary environment for the formation of the hydrogen bonding network between fibers and fillers, which is the basic mechanism of paper formation. Thus, water and its quality are essential issues in the production of pulp and paper. 

In 1993, the U.S. paper industry manufactured about 77.1 million tonnes of paper and paperboard products. The average usable energy yield of black liquor for the industry then corresponds to about 14 GJ/t of paper manufactured (2.6 EJ/[77.1 X 10 tl), or about 2.3 BOE/t. This clearly illustrates the need to recover energy from the black liquor, if only to minimize production costs. Black liquor can almost be considered to be a co-product rather than a waste by-product. If boiler efficiencies were included in this calculation, the need to recover and use the energy in the paper manufacturing process would be even more apparent. However, these figures also suggest that there is consider-... 

Textiles, as a woven cloth or a nonwoven fabric, are probably the most common industrial filter medium, and are made from natural (cotton, silk, wool) and synthetic fibres. Wire cloths and meshes are also widely used in industrial filtrafions, produced by weaving monofilaments of ferrous or non-ferrous metals the simpler plain weave is used for sieving and sizing operations, and the more complex weaves such as Dutch twills are used on pressure and vacuum filters. At the small scale, particularly for laboratory use, filter papers are common, made from fibrous cellulosic materials, glass fibre or synthetic polymers these papers are made using developments from conventional paper manufacturing processes. 

Wet laid media are derived from paper manufacturing processes and are composed of short staple fibres dispersed in water to form a slurry that is fed to a moving wire screen on which it is dewatered. The randomly orientated fibres form a web which is dried by a sequence of heated rollers. An adhesive or binding agent may be dispersed in the original slurry or sprayed onto the web during or after dewatering. 

The paper manufacturing process ends with the paper web being reeled at the reeler at full width. 

Process chemicals are all additives which are used to solve or prevent problems in the paper manufacturing process, to improve its efficiency and/or to provide ecological advantages. For example these additives allow reduction in the consumption of fresh water and energy, the prevention of foam and deposits, the improvement of drainage and/or reduction in fiber losses. Their proportion related to all chemical additives is only 10% (Fig. 3.3). 

Fig. 9.5 Data mining in the paper manufacturing process (source Voith).

Materials that are related through the sulfonate group include the aliphatic paraffin sulfonates produced by the photochemical sulfonation of rehnery hydrocarbons, petroleum sulfonates derived from selected petroleum distillate fractions, olehn sulfonates, A -acyl-A -alkyltaurines, sulfosuccinate esters and related compounds, alkylaryl sulfonates, and ligninsulfonates, which are a byproduct of the paper manufacturing process. While complete coverage of the class would be prohibitive, some of the most important types are described below. 

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