China should improve the application of waste pulp

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China should improve the application of waste pulp to help the production of corrugated base paper

in recent years, due to the importance of environmental protection, OCC as raw material has become increasingly common. The waste paper consumption of corrugated materials in Western Europe is as high as 75%, and that in Asia accounts for 71%. South Korea and Taiwan Province of China all use waste paper as raw materials to produce cardboard and corrugated base paper. China, which is short of paper-making raw materials, should attach great importance to the technology of importing waste paper, domestic waste paper and wheat straw semi chemical pulp to develop into the main fiber raw materials of corrugated base paper

in recent years, many production lines in China also produce corrugated materials from American waste corrugated boxes (AOCC). Although the raw material cost of waste paper is lower than that of raw fiber, the research results show that the corrugated base paper with NSSC as the raw material has good stiffness, has better running performance when the corrugator corrugates, can still maintain high tensile stiffness and compression strength under high humidity, and the corrugated box manufactured has better stiffness under wet conditions

in addition, the shortage of imported waste paper resources should also be paid enough attention. In recent years, the export of waste paper in Europe has been small, and the export of waste paper in Hong Kong has also shown a downward trend. Table 2 shows the recycling and export of waste corrugated boxes (AOCC) in the United States ⑥. By 2001, only 3.96 million tons of AOCC could be exported. The same article reports how big is the automotive carbon fiber composite market after 110 years? OCC accounted for 39% of the waste paper exported from the United States in 1996. Based on this calculation, the total export volume of waste paper from the United States in 2001 should be about 10.15 million tons. In 1996, the export flow of waste paper from the United States was 20% in South Korea, 12% in China, 12% in Taiwan, China, 15% in Mexico and 18% in Canada

if the waste paper exported to China is still at the level of 12%, the total amount of waste paper that China can import from the United States is about 1.21 million tons. South Korea, Taiwan, China and Mexico are definitely the main competitors to import AOCC. Taiwan, China imports 900000 tons of OCC from outside the island every year. It seems that it should be soberly estimated that the further development of corrugated materials cannot rely too much on AOCC

on the contrary, in 1998, the domestic consumption of corrugated materials was 9.56 million tons, and the recovery rate of corrugated materials in the United States was 68.9%. If our recovery rate could reach 50%, nearly 5million tons of waste corrugated box materials in China could be recovered, which is a very considerable figure. Although the quality of domestic OCC is not as good as AOCC, this part of raw materials should not be ignored anyway. At present, domestic OCC is still dominated by grass fiber. In the past, people were biased against the recycling of grass fiber waste paper. The research results show that the paper quality of this fiber raw material will be improved to a certain extent in the recycling process ⑦. If additives are used appropriately, corrugated base paper with better quality should be produced

China is short of wood resources, so we should pay attention to the production of corrugated base paper with wheat straw semi chemical pulp. The experience of Spanish SAICA paper mill in producing high-strength corrugated base paper with semi chemical wheat straw pulp mixed with a certain proportion of OCC is worth learning from. The reason why the plant uses semi chemical wheat straw pulp is that European OCC is in short supply and that wheat straw raw materials are relatively cheap. The factory uses self-developed continuous steaming equipment and process to produce semi chemical wheat straw pulp with a large liquid ratio under atmospheric pressure, together with 50% - 75% OCC, to produce high-quality and high-strength corrugated base paper

the quality of semi chemical wheat straw pulp is not a problem. The problem is to solve the wastewater treatment. There is no successful experience of semi chemical wheat straw pulp wastewater treatment that can be used for reference. The above SAICA paper factory in Spain started by mixing the waste liquid of 300t straw pulp produced in the daily process with the white water of the paper machine, which is well compatible with human skin, and anaerobic fermentation is carried out in three 15000m3 tanks, and the biogas produced is sent to the boiler for power generation. The wastewater can be discharged after aerobic treatment

in the mid-1980s, the local sewage discharge standard cod100000mg/l, while the COD of the factory's wastewater after treatment was 5700 ~ 7500mg/l, which could meet the discharge standard. At that time, many articles reported it as successful experience of wastewater treatment; By the late 1980s, the emission standard was set at 5000mg/l, and the factory could only reduce the output of straw pulp to meet the standard requirements. However, with the increasingly strict control of local government emission standards, the COD emission was required to be less than 500mg/l by 1998. Although the plant spent $2million on for two years of research, it still failed to find a good way to meet the standard, and finally had to temporarily shut down the semi chemical wheat straw pulp production line

according to the introduction of Mr. Escudero at the TAPPI papermaking technology report meeting of the 99 China International Paper forest exhibition in November 1999, they are carrying out the development of a new process for improving the market cooperation of lignin precipitation and wet oxidation. It is believed that the waste liquid can be discharged up to the standard after lignin precipitation and wet oxidation, and then anaerobic aerobic treatment, By 2003, it is planned to rebuild a semi chemical wheat straw pulp production line with a daily output of 400 ~ 600t (200 ~ 300t/D for each continuous steaming line). At present, the above lignin precipitation and wet oxidation process is under pilot test. In fact, SAICA paper mill has not solved the problem of waste liquid pollution of semi chemical wheat straw pulp so far

in the past, some NSSC plants discharged the pulping waste liquid into the river. Due to the existence of hemicellulose and acetate, the BOD content of the waste liquid was very high, causing serious pollution to the water body; Some plants concentrate the waste liquid and burn it in a fluidized bed to obtain a mixture of sodium carbonate and sodium sulfide, but it cannot be directly used in NSSC pulp plants. Another mature method is cross recovery. When semi chemical pulp and sulfate pulp plant are together, the waste liquid of the former can be sent to the sulfate pulp plant recovery system for recovery

the content of organic matter in the black liquor of semi chemical wheat straw pulp is high, and the calorific value will not be a problem; The problem is the evaporation of semi chemical pulp black liquor. The additional tariff on evaporation is mainly 20% and 25%; (3) Coated paper: tariffs are mainly 5% and 20%; (4) When the box board corrugated paper reaches a higher concentration, the black liquor has great viscosity and thixotropy

in the past, the Papermaking Research Institute of the Ministry of light industry has studied the properties of straw semi chemical pulp black liquor. The results show that the viscosity of straw semi chemical pulp black liquor is much higher than that of chemical pulp black liquor, and the maximum concentration that can be evaporated is much lower. However, it is proposed that increasing the residual alkali of black liquor can solve the difficulty of evaporation

however, there is still a lack of systematic research on the properties of wheat straw semi chemical pulp black liquor, and the chemical recovery of wheat straw semi chemical pulp is even less experienced. Using wheat straw to produce semi chemical pulp is an aspect of making full use of China's fiber resources. Government departments and industry should pay attention to and support the research and development of semi chemical wheat straw pulp waste liquid recovery and treatment technology

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