The Process of Build a Small Pulp And Paper Mill
Building a small pulp and paper mill requires a comprehensive consideration of all aspects in the design phase. Here mainly includes: the selection and demonstration of construction site, the determination of production process and production plan, pulp balance calculation, heat balance, equipment calculation and selection, key workshop construction, economic cost, the determination of environmental pollution treatment system and so on. Even building a small pulp and paper mill is still a systematic project that needs to be seriously thought. Next, we will introduce you to some knowledge of the construction of small pulp and paper mill simply.
The Selection and Demonstration of Construction Site
Combined with production, mill size and condition and other factors, the construction party can determine the construction site. The construction party must give full consideration to the conditions of resources and the market, transportation, water and electricity to make the mill get close to major resource supply sites and the market as possible as it can.
A small pulp and paper mill needs a lot of raw material and chemical products to maintain normal operation of paper pulping machine. It also needs a lot of water, so it has to be close to the water, which will be very beneficial to the production. Taking into account that the paper is a high energy-consuming project and hydropower is a cheaper energy that can reduce production costs. The location of the paper mill should be convenient for transportation and reduce transportation costs and risks.
The Determination of Production Process and Production Plan
The construction of a small pulp and paper mill requires the determination of production process and production plan. The determination will influence the selection of paper pulping machine.
The preparation of raw material includes dry method, wet method and dry-wet method, which will determine what kind of equipments shall be selected for the screening, dust removal and purification in preparation stage. Equipments in preparation stage include: debarking machine, saw wood machine, chipper, screener, machine and cutting equipment.
What kind of cooking method shall be selected during the cooking stage, alkaline method or acid method? That determines the selection of the cooking equipments. Because there are many methods of chemical pulping, a variety of fiber raw materials and different production scales, the structure and form of chemical pulping equipment can selected in a wide range. In general, according to different operation processes, chemical pulping equipments can be divided into two categories: intermittent type and continuous type.
Main equipments of the intermittent chemical pulping equipments are the steaming ball and digester. The steaming ball and digester belongs to the rotary type, which are popularly used in small and medium pulp and paper mill that adopts alkaline method, sulfate method or neutral salt method of pulping equipments. The digester is a kind of vertical fixed equipment. Due to different corrosive natures, process characteristics, structures, forms and volumes of the digester, Therefore, it is divided into sulfate type and sulfite type. The volume of digester is generally larger, so it is often used for medium and large pulp and paper mills.
In addition to the main equipments, the intermittent chemical pulp equipments still need to be equipped with necessary ancillary equipments, such as circulating pump, liquid circulation heater, waste heat recovery equipment and blow tank.
According to different main cooking equipments, continuous chemical pulping equipments can be divided into tower (or vertical) continuous digester and horizontal tube and inclined tube continuous digester. But tower continuous digester is usually used for large and medium pulp and paper mills, and most widely used worldwide.
The selection of chemical pulping equipments is mainly based on investment, production scale, fiber raw material and others. The volume and number of the digester depends on production scale, type, equipment costs and the overall balance of the entire plant.
In the washing stage, washing machine is black liquor extraction equipment. Due to many types of washing and concentrating equipments, the classification methods are also rich. They can be divided by working principles and characteristics of equipments or different filter pressures generated by the equipments or the different concentrations of equipment outlets and washing principles. Low-concentration washing and concentrating equipments mainly include rotary screen concentrator, drop-type concentrator and mesh concentrator. Medium-concentration washing equipments include vacuum washing thickener, pressure washing thickener, horizontal belt vacuum pulp washing machine. Its inlet pulp concentration is 1%-4% and the outlet pulp concentration is10%-17%. It can be used not only for pulp washing, but also for pulp concentration. High-concentration washing and concentration equipments include spiral type, twin roll type, ring binocular and twin-net squeeze type. Its inlet pulp concentration is 3% and the outlet pulp concentration is 35%. Due to the continuous improvement of the extraction rate of the waste liquid for cooking and the development of technologies, high-concentration bleaching and high-concentration beating and the high-concentration washing and concentration equipments have been rapidly developed in recent years. Displacement washing equipments mainly include atmospheric and pressure replacement washing tower, twin roll, KMW type displacement press washing machine and drum displacement washers and so on. Such equipments are mainly used for the pulp washing role.
During the bleaching stage, the pulp bleaching process can have different sequences of processes and bleaching stages due to different pulping materials, the pulping processes, the bleaching agents used, and the degrees of whiteness required by the pulp. Basically, all kinds of bleaching sections are equipped with washing and concentration equipments, pulp conveying equipments, mixing equipments of pulp and bleaching auxiliary agents, bleaching reaction tower, bleaching agent preparing system and so on. These equipments are relevant to pulp concentrations in the bleaching stage. Bleaching can be carried out at low, medium and high pulp concentrations for a given bleaching section or line. If it is used waste paper pulp, the construction party also needs to buy repulper and waste paper deinking equipment.
Calculations of pulp balance, heat balance, equipments and economic costs are all based on the exact needs of a small paper mill for each production process. The construction party needs to consider the prices of all of machines, for example, paper pulper machine price. The reasonable paper pulper machine price is common aim of any construction party.
The Environmental Pollution Treatment System
With the aggravating of pollution and the improvement of people's environmental awareness, the disputes and conflicts caused by pollution increase year by year are more and more serious. A huge number of waste gas and waste water produced by paper pulping machine is endangering in human health. Therefore, it is necessary to prepare a qualified waste gas and waste water treatment system for papermaking.