The bagasse is a very important raw material for non-wood fiber pulp making. With the characters of rich and concentrated source, convenient treatment, and wide applications, bagasse pulp receives more and more recognition from paper and pulp industry.
As the development of bagasse pulp making, bagasse pulp is applied to various types of papermaking. For meeting the strict requirement of the industry, we should focus on the quality of bagasse pulp. How to promote bagasse pulp quality? As a paper pulper machine manufacturer with rich experience, CNBM will talk about the strategies on the quality promotion of bagasse pulp for reference.
Strengthen the preparation
The material preparation is a vital part of bagasse pulp process. In other word, the preparation directly decides the pulp quality. So it is necessary to pay more attention to preparation.
The first step of preparation is depithing. As we all know, the bagasse usually contains 35%-40% bagasse pith, it is made up of parenchymal cell and epidermal cells, collectively known as parenchyma cell. These parenchyma cells have strong liquid absorption, which will have a bad influence on bagasse pulp production. For example, during the pulp cooking process, the bagasse pith absorbs a large number of alkali residue and result in over-cooking. Not only increase the chemicals consumption but decrease the uniform of coarse pulp and pulp yield. Besides, the higher contains of bagasse pith will lead to the difficulty in filtering water during the pulp washing process. Bagasse pith also leads to high chlorine consumption, low whiteness and easy to be yellow in the bleaching process. So, strength depithing is an important way to improve bagasse pulp quality. There are three methods of bagasse depithing including dry method, wet methodtype and semidry method.
The second step of preparation is sugar elimination. Generally, the fresh bagasse contains 1.5%-2.0% residue sugar, it is used after spontaneous fermentation, which required a three-month stocking. The stoking of bagasse needs good ventilation, otherwise, the heat produced by the fermentation is hard to dissipate, resulting in decomposition of bagasse and seriously affect the quality of bagasse pulp.
The pulp cooking process is another core link. In order to make good pulp and paper, you should cook the bagasse according to the properties of bagasse.
Compare with wood fiber, the bagasse has many differences in chemical composition and fiber construction. The bagasse has a low content of lignin, easy to be removed during pulp cooking. In addition, the construction of bagasse is loose and easy to be penetrated by alkali liquor. The research data show that kraft cooking of bagasse will largely remove lignin at the low-temperature stage when the temperature raises up to 140℃, the total delignification rate reaches 92.1%, at this moment, the bagasse is dispersed into pulp. Thus it can be seen that bagasse has better delignification rate than that of wood. In conclusion, low-temperature and high-speed cooking will be a suitable cooking process.
There are a numbers of organic and inorganic soluble substances in the cooked pulp should be washed out. The pulp with high clarity contains less foam, which is good for next sections.
Bagasse pulp has short fiber and bad drainability, also contains many parenchyma cells, so it is difficult to wash. Based on the properties of bagasse pulp, we should do more work on the washing equipment selection and operation. The vacuum drum washer stands out because of small floor space and low cost. As for the operation, properly add washing temperature, strength filter screen washing and decrease pulp layer thickness to improve the pulp clarity.
The bagasse pulp is easy to be bleached after good depithing, so a lot of pulp mills adopt single stage Chlorate bleaching. However, due to the drastic process, single stage bleaching produces large damage on fiber, and yellow index is high. So, for high-whiteness and high-quality papermaking, the better choice is three stages bleaching. The CEH bleaching is a typical three stages bleaching, it requires higher operation technique. The Chloride section should control the chloride consumption, not only meet the need of chlorinated delignification but also avoid super chlorination. In real pulp production, the chloride consumption relies on watch end color of pulp and measure end chloride.
Speak to the alkali treatment of bagasse pulp, the alkali consumption is about 2.0%-2.5%, the temperature should be controlled at around 60℃, process-time is 1.5h, insufficient alkali is bad for dissolving chlorinated lignin and colored matters.
The key to hypochlorite bleaching is PH value and temperature of bleaching. Avoid bleaching under neutral condition or high temperature. In general, the temperature is controlled at 38-40℃，final PH is controlled at 8-9. How to control the final PH value in the hypochlorite bleaching? The simplest way is potentiometric titration on the inlet of the washer, the light red standard for alkalescence, the colorless standard for neutral or acidity, and must increase buffer base, adjust the alkaline zone of PH value.