Pulp and paper industry solutions to environmental pollution (2)

After years of research in our country, the major problems of non-contaminated pulp bleaching technology have been basically solved. The key to the present is to develop a bleaching system that maintains continuous production. Until now, we have successfully developed more than half of stand-alone machines. The non-polluting bleaching technology and equipment developed by our country and adapted to the characteristics of the domestic paper industry can be applied to production soon.
Effluent generated by chlorine bleach bleached pulp can be combined into the black liquor extraction section of the alkali recovery system, into the alkali recovery system, or incorporated into the general wastewater treatment of the subsequent stage.
(2) The use of CIO2 as a bleaching agent in the low-chlorine bleaching technology has been a common practice in foreign countries in the 1980s: In North America, most pulp mills have used CIO2 as a bleaching agent to bleach pulp; in European countries, some manufacturers Chlorine-free bleaching is advocated, but it also gradually transitions to chlorine-free bleaching, but many pulp mills still use CLO2 as a bleaching agent. Several pulp mills in China use CIO2 bleach, but unfortunately some plants are currently in poor condition.
After bleaching pulp with CIO2, the bleaching wastewater not only reduces AOX (adsorbable organic halides) and extremely toxic substances, but also reduces the resin barrier, but the pulp strength is basically not. change. Practice has proved that the higher the replacement rate of CI2, the smaller the amount of wastewater, AOX, and toxic substances. When the complete replacement of CI2 is reached, the bleaching wastewater has reached the current national minimum emission standards.
Therefore, using CIO2 as a bleaching agent to bleach pulp is also one of the effective measures to reduce the pollution of bleaching wastewater. However, the implementation of the low-chlorine bleaching technology has the problem of large construction investment. First, the CIO2 generator is expensive; second, it is the bleaching system and The subsequent washing equipment has a high material requirement and is generally made of titanium steel. The above two issues also affect the promotion of low chlorine bleaching technology in China's pulp and paper industry.
3. Develop other (no less) contaminated pulping technologies to open up new avenues for eliminating paper industry pollution (1) The development of mechanical pulping uses mechanical methods instead of chemically pulping fiber raw materials to obtain pulp, which has low production costs With high yields (about 90%-98%), no or less chemicals are used, and the environmental pollution is far less than chemical pulping. However, in the previously developed ground wood pulp (MP), due to short fibers, most of the lignin and non-cellulose components were not removed, and the paper was susceptible to yellowing and becoming brittle and could not be stored for a long time, thereby being limited.
In the late 1970s, the international papermaking industry began to develop the preheated wood chips milled wood pulp (TMP), and China began to develop in the era. TMP technology is to increase the temperature of the raw material before entering the mill (preheat 115-135 0C), so that the fiber can be easily separated, which not only reduces the power consumption, but also improves the quality of the pulp. Since the 1990s, chemical thermomechanical pulp (CTMP) has emerged. On the basis of TMP, about 5% of the chemicals used in chemical pulping chemicals are added. This can achieve the advantages of TMP, namely high yield and less pollution. , And to make pulp has the advantages of chemical pulp, that is, lignin content is small, the fiber is long and soft. Several major newsprint mills in China have carried out CTMP projects in recent years, but equipment mainly depends on the introduction.
In the research of CTMP, we have carried out arduous research work, mainly on the basis of foreign CTMP technology combined with China's development and promotion of fast-growing wood and non-wood CTMP technology and devices, and has made progress.
(2) Development of waste paper pulping In order to reduce pulping pollution, it is also an effective method to expand papermaking raw material resources and recycle waste paper pulp. In the world, the amount of waste paper used in papermaking is increasing. For example, the waste paper recycling rate in the United States is above 30%, Japan is 43%, and the United Kingdom is 45%. The United States expressly stipulates that the amount of raw materials put into paper mills must contain more than 25% of waste paper. In recent years, the utilization rate of waste paper in China has also been increasing, and the waste paper recycling rate in Guangdong Province has now reached more than 30%.
The main problem of waste paper pulping technology is deinking technology, which uses the deinking agent (NaOH, Na2CO3, H2O2, etc.) and dispersant Na2SiO3, etc. to destroy the adhesion of carbon ink and pigment particles on the fiber. The deinking pulping method includes four steps, namely, waste paper diffusion and fiber dissociation ink and fiber separation to remove carbon ink particles and ink screening and purification to make unbleached pulp. At present, de-inking is performed by flotation method, and the pulper, flotation tank, multi-disc machine, disperser, and screen pulper are mainly used in the process.
(3) The graduated pulping method of biochemical pulping has high yield, low energy consumption, and little pollution. In recent years, it has been included in the scope of cutting-edge research in biology, and research has been accelerated at home and abroad.
The use of biotechnologies in pulp and papermaking is the selection of strains that can efficiently and specifically disperse fibers from a wide range of microorganisms, and can be adapted to industrial mass production levels through various biotechnology processes. Among them are retting and enygmatic pulping. Impregnation is the direct inoculation of bacteria in the fiber material, the bacteria grow and reproduce at the same time secrete a large number of enzymes, the enzyme's catalytic fiber dispersion. This method is simple but requires large fermentation equipment. Enzymatic method is to cultivate a certain kind of bacteria under certain equipment conditions to produce a large amount of enzymes. After certain biotechnology treatment, the enzyme is concentrated and added to the fiber raw materials, and the fibers are dispersed through enzymolysis. Both methods are used. Foreign scientific research results can be slurried in 4-5 days, and domestic scientific research results are pulped in about 10 days. Biochemical pulping still has a certain distance from modern production, and it also has the disadvantage of large area.