Pulping operations

By-Products. There are three stages within the pulping operation at which wood-derived chemicals can be recovered as by-products. Turpentine is obtained from the reHef of gases after an initial steaming of chips in the digester. Better yields of turpentine are obtained from batch digesters than from continuous systems. Pines and firs give the best yields. Turpentine is composed principally of unsaturated bicycHc hydrocarbons, of which ca 90% are a- and P-pinenes and 5—12% other terpenes. 

Sallack (1955) was the first to publish a study of dissolver-tank explosions. He was motivated by incidents which occurred in a soda pulp operation with a dissolver tank 4.3 m in diameter and 3.7 m tall. Molten smelt entered the tank at the top and was to be broken up with a jet of recirculating green liquor. Agitation of the bulk liquid was also accomplished by air jets. Operation was normally smooth, but if a boiler upset led to a sharp increase in smelt flow, then the smelt-green liquor breakup operation was inefficient and unbroken slugs of smelt could enter the bulk green liquor in the tank. Explosions could then occur. 

Folke, J. Environmental aspects of bagasse and cereal straw for bleached pulp and paper. Conference on Environmental Aspects of Pulping Operations and Their Wastewater Implications, Edmonton, Canada, 27-28 July 1989. 

Statement 6. Satisfactory separation of oil from sand by the hot water process is impossible unless the natural packing of the bituminous sand is completely broken down in the pulping operation and unless the pulp is subsequently dispersed in excess water. The mineral particles and oil flecks must be free to move independently of each other under the influence of the small forces upon which the process depends. 

EZ. Purification of Guncotton A. Poaching. Preliminary boiling of etude NC reduces its acidity while the pulping operation mechanically breaks. down the fibers into very small fragments. However, these operations do not remove the acidity entirely and it is necessary to subject the pulped NC to additional boiling in water. This operation is similar to that described under "Sour Boil except that it is conducted in an aik medium(See also Ref II). 

The condition of the cellulose fiber in a pulping operation is often followed by measuring the viscosity—degree of polymerization (DP) of the cellulose. In the present work, an increase in brittleness of the paper is the property of interest, and this will be followed by the change in folding endurance. Oxidation of the cellulose will show up by the increase in the carboxyl group. This will be estimated by the pH and titration values of the slurried fiber. 

The possibility of ordering in native celluloses used in papermaking, and the significance of such ordering to the paper properties were explored in an experiment designed to simulate the physical environment during a typical commercial pulping operation (3). 

Generally, the recycle is similar to mechanical pulping operations but product can be higher quality. De-inking and adhesive ( stickies ) removal are peculiar to recycled pulp. 

The resin beads used in most columnar operations range in size from 0.3 to 0.9 mm in diameter, which is a compromise based on the effect of ion-exchange rates, capacities, and hydraulic characteristics. The especially made resins used in resin-in-pulp operations range in size from 0.8 to 1.6 mm in diameter. The apparent density of a resin is defined as that weight of backwashed and settled wet resin per cubic foot, which for resins used in the uranium industry is about 38-45 Ib/ft . In column operations, the attrition losses due to swelling and contraction of resin, abrasion of resin-resin surfaces, and abrasion of resin-equipment surfaces are negligible. In resin-in-pulp operations, an appreciable amount of attrition loss is encountered. 

Eight of the Bahco scrubbers are located on oil-fired boilers in pulp mills. The boilers range in size from 50,000 to 375,000 Ibs/hr of steam and produce 10,000-145,000 ACFM of oflF-gas at about 340°-360°F. Each of these units operates with caustic soda as the scrubbing reagent. The units operate at a controlled pH of 6.5 which maximizes the production of sodium bisulfite and limits unwanted sulfate oxidation. The soluble bisulfite product is utilized in the pulping operation. Particulate and mist concentrations are held to about 0.02 grain/SCFW and SO levels are reduced by 97-99% from about 1500 to about 30 ppm. These units have operated continuously without any operational upsets. 

A problem with NSSC pulping is the difficulty of either recycle or disposal of the waste (spent) pulping liquor. It can be concentrated and burned but this produces sodium sulfate, not sulfite suitable for reuse. If there is a kraft pulping operation near the semichemical pulping operation, the sodium sulfate may provide both sodium ion and sulfate make-up chemical for the kraft... 

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