Study On Clean Bleaching Theory And Experimentalize Of Non-wood Fiber

Non-wood pulp was the main paper-making material, wheat straw pulp, reed pulp and bagasse pulp were in non-wood pulp total 80%, most of the non-wood pulp mills in China were use the traditional CEH bleaching sequence, the bleached effluent were very diffcultly disposed. The"Discharge standard of water pollutants for pulp and paper industry"was promulgated and excuted in 2008, the exist non-wood pulp mills and the new non-wood pulp mills must use technological transformation and new technology, otherwise, it will difficult to adapt the new law. So, the pulping and bleaching properties of the wheat straw and bagasse was studied in this paper in order to release the pressure of the fiber shortage, and provide the technical support for the clean, efficient utilization of non-wood fiber resource.The studied on HP short sequence bleaching process of wheat straw pulp was carried out. The results showed that the lower kappa number wheat straw pulp were easy to bleach in HP bleaching sequence, at hypochlorite charge 4%～5% and hydrogen peroxide charge 3%～4% in HP bleaching sequence, they could bleach to 78%ISO brightness, some could bleach to 80%ISO,the physical property of the bleached pulp was well, HP bleaching sequence could be used as the substitute for the conventional CEH process.The study on OQPO bleaching (lab cooking)soda-AQ wheat straw pulp was carried out. The results showed that when the pH value of sulfuric acid and chelation(Q) pretreatment was less than 3.5, A/Q pretreatment efficiently controlled the metal ions distribution and decreased the kappa number, it played an important role in improving the bleaching efficiency of the pulp. The reaction time 40 minutes of the oxygen in the pressured hydrogen peroxide bleaching is enough, the bleaching pulp brightness is 81.59%ISO and the viscosity of the pulp is 653.0mL/g. The study on OQPO bleaching of alkaline wheat straw pulp (company provided) was carried out. The experiment results showed that the optimal NaOH charge and oxygen pressure were 4% and 0.5MPa, respectively; 4% charge of H₂O₂ in hydrogen peroxide stage was enough, the physics capability of the bleached pulp was better, the effluent of bleaching was low pollution , OQPO sequence bleached Soda-AQ wheat straw pulp accorded with the clean product require. D0EpD1 sequence bleaching Soda-AQ wheat straw pulp, the bleached pulp brightness was up to 89.03%ISO only at 4% charge of effective chlorite, and the bleached pulp viscosity was 1006.5mL/g, the viscosity of the bleached pulp only reduced 86.8 mL/g, D0EpD1 sequence did not damage the wheat straw pulp fiber too much.In the process of pressured hydrogen peroxide bleaching bagasse pulp, the bleaching temperature was the first effected factor, and the bleaching time was the second effected factor. Take all factors (bleached pulp brightness, yield and viscosity) into consideration, the conditions of hydrogen peroxide bleaching were as follows: pulp concentration 10%, temperature 90℃, reaction time 80 minutes, the oxygen pressure was 0.6MPa, EDTA0.1%, Na₂SiO₃ 3%, MgSO₄ 0.5%, NaOH 0.4%, H₂O₂ 4%. In this conditions, the bleached bagasse pulp brightness was 83.2%ISO, yield was 93.57%ISO, kappa number was 4.23, and the viscosity was 879.4mL/g.The studied on the pH value, pulp consistency and added EDTA in chelation pretreatment effected on removed metal ions was carried out. The results showed that the pH value in chelation pretreatment had the quantitative relationship with the removed rate of transition metal ions. EDTA was helped to remove transition metal ions in acid condition. The pulp consistency of the chelation stage was effected the pressured hydrogen peroxide bleaching.The studied on OQPO bleached effluent by GC-MS was carried out. The results showed that there are not AOX in the bleached effluent, the most of organic matter in the waste water was the degradation product of the ligin and carbohydrate, and some of the dissolved out organic matter was inborned in the wheat straw process of growth, there are not toxic substance in the OQPO bleached water.The detect of contamination results of the OQPO bleached waste water showed there are more organic matter in the oxygen delignification stage and the pressured hydrogen peroxide stage than the chleation pretreatment stage, and the pollution load is higher. The waste water in the oxygen delignification stage are all back in the akali recovery system, and the waste water in the PO stage are all reused, so only the Q stage waste water are discharge, the Q stage waste water CODCr and BOD5 are 167mg/L and 56mg/L,the effluent is low pollution load and easy to process.The bleaching sequences HP, OHP, D0EpD1(ECF) and the OQPO(TCF), the chemical cost are almost the same, the ECF bleaching and the TCF bleaching integrated cost are not too much difference, and it higher 30 yuan per ton pulp than the CEH bleaching. The clean bleaching technology: low pollution bleaching (HP, OHP), ECF bleaching and TCF bleaching have their own characteristic, HP and OHP bleaching effective reduced the waste water COD, chroma and AOX; ECF bleached pulp has high quality and the waste water is easy to process, but the equipment investment is high and the waste water still contain AOX; OQPO sequence is the best choice for the non-wood pulp bleaching, this sequence is simple and flexible, the bleached pulp is good, equipment investment is less than ECF bleaching, OQPO bleached waste water is easy to process and there is no AOX in the waste water.