Font Size: a A A

Stdies On Displacement Cooking And Bleaching Of Straw

Posted on:2001-07-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q J WenFull Text:PDF
GTID:1101360002950337Subject:Pulp and paper engineering
Abstract/Summary:PDF Full Text Request
Wheat straw, rice straw and reed are important raw materials for the pulp and paper industry in China. According to the mechanism of delignification of alkali cooking of wheat straw, based on the principle of RDH and the experiences of low temperature fast cooking, two-stage cooking, large liquor ratio cooking on straw or reed, the displacement cooking and improved displacement cooking of straw or(and) reed were studied in this paper. The properties of black liquors, the bleachablities of improved displacement cooking pulps were also studied. In addition, the dissolving rules of lignin and carbohydrate components in the improved displacement cooking process, the results of mill-scale experiments on displacement cooking of wheat straw were also researched. The result shown that: Displacement cooking process can be used to produce straw pulp with lower permanganate number, higher strength, higher brightness. Under the conditions of lower cooking temperature and relatively large liquor ratio, the selectivity, of delignification and the cooking uniformity are improved, pulp yield can be reached to 50%-60%. Pulp strength can be reached to 5000-7000m(breaking length). The brightness of crude pulp can be reached to about 40%. The permanganate number can be reduced to less than 10. The black liquors which be used circularly in displacement cooking about 20 times have the features of higher residual alkaline, lower viscosity and lower ratio of organic-to-inorganic substance. The improved displacement cooking fits to the current conditions of Chinese pulp factories. The liquor ratio is relatively large in the first stage, so the cooking liquor is well distributed and penetration is improved. The cooking uniformity is improved. The liquor ratio in the second stage is reduced. Under the condition of same alkali charge, the alkali concentration is increased, the rate of removal of lignin gets faster. The dissolving rule of lignin in the improved displacement cooking is similar to conventional cooking. Before lOO0C,about 60% delignification is attained. But the dissolving rule of carbohydrate components in the improved displacement cooking is not similar to conventional cooking. The quantity of dissolved carbohydrate components in the first cooking stage is less than conventional cooking. The brightness of displacement cooking crude pulp is higher than conventional cooking crude pulp about l0%SBD. Added different kinds of pretreatment to the H202 single bleaching stage, H202 bleaching efficiency could be improved, and the bleached pulp brightness of displacement cooking pulp can be reached be more than 70%SBD.Whith the less chlorine or TCF bleaching sequences of HAP HQP. QOpP A OP0 The bleached pulp brightness can be reached to more than 80%SBD. The mill-scale experiments on displacement cooking of wheat straw showed that the pulp have, the features of higher yield, lower permanganate number, higher strength. Being used circularly, the black liquor have the features of higher concentration of chemical. more residual alkali., higher COD contents lower viscosity and lower silica content. The alkaline recovery system can be used for treatment of the spent liquor.
Keywords/Search Tags:Wheat straw, straw, Reed, Displacement cooking.Improved displacement cooking, H2O2 bleaching, Black liquor, Lesschlorine bleaching, TCF bleaching.
PDF Full Text Request
Related items