Effect Of Displacement Cooking On The Characteristics Of Wheat Straw Black Liquor

Pollution of straw pulping is usually more serious compared to that of wood pulping, due to the different component of these two fiber materials. As a result, chemical recovery is difficult to be applied as an effective way of pollution control for straw pulping mills. High viscosity of wheat straw soda black liquor is an important aspect of the chemical recovery problem.Reducing the black liquor viscosity is considered as an effective way to solve the pollution problem of non-wood fiber pulping. Some evidences prove that the viscosity of straw soda black liquor will be reduced after it is circulated for several times in soda cooking. Black liquor displacement cooking of wheat straw soda pulping was carried out in this research, based on the purpose of: (1) to understand the main factors which affect the black liquor viscosity and, (2) to understand the changes of black liquor properties. During the displacement cooking, black liquor extracted from 1st stage is sent to chemical recovery, and black liquor from 2nd stage is reclaimed for the 1st stage of next cooking. Detail conditions of first stage are, effective alkali concentration 12 g/L, 18 g/L, 24 g/L with cooking temperature 140?C, and alkali concentration 12 g/L, 18 g/L with cooking temperature 150?C, respectively. The black liquor was circulated for four times, and the changes of physical and chemical properties of black, such as residual effective alkali, solid content, viscosity, and chemical compositions, were analyzed. The main results are listed as follows.1. Pulp with kappa number of 27.2 and 27.8 can be obtained while the cooking temperature of the first stage 140?C, the alkaline concentration process digestion is 18g/L, and the temperature of the first stage digestion is 150?C, the alkaline dosage for the first stage digestion are 12 g/L, under this two condition the average yield of every circular digestion are 48.8% and 48.3% respectively, and the kappa number is lower relative to the other condition. And under the condition of the temperature of the first stage digestion is 140?C, the alkaline dosage is 18 g/L, the beating degree of the wheat straw pulp is lowest, only 15?SR.2. The viscosity of the 1st stage black liquor at first circulation is lower than from cooking by alkaline process, when the temperature of the first stage digestion is 140?C, and in every different alkaline dosage. The viscosity is lowest, and the viscosity has a little increasing with the circular digestion increasing, but the viscosity of every circular digestion are still lower than alkaline digestion, while the alkaline dosage is 18g/L with the first stage digestion temperature is 140?C.3. The research choosed the black liquor that had been digestion via several times circulation in different process, and then test the level of lignin ,silica, and polyose, then analyze the effect of those materials on the viscosity of the black liquor, the result told us that when the viscosity in a low level, the lignin has effect on the viscosity of the black liquor; while the silica has more effect on it ;and the polyose has some influence on it than the other factors, the mainly influence on the viscosity of the black liquor is the hemicellouse.The result of this research provides new idea and method to the reducing viscosity, and also provides new path to the controlling of the pollution of the straw waste liquor.