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(A) pulp and paper process

Pulp and paper according to the process is mainly divided into two processes: pulp and paper, pulp is the process of making pulp from plant fiber raw materials or recycled waste paper, paper is the process of using the appropriate technology to copy pulp into a variety of different properties of paper or cardboard.

Pulp and paper process is complex, different raw materials, different pulping methods to form the pulp characteristics are different, the resulting paper products are also different.

According to the different pulping methods, the most important pulping methods are sulfate pulping, chemical mechanical pulping and waste paper pulping.

Among them, sulfate pulping is currently the most important pulping method, chemical mechanical pulping and waste paper pulping are pulp making methods with good development prospects.

Pulping methods are distinguished by raw materials, mainly wood, non-wood and waste paper pulping.

1. Wood pulping process

According to the different pulping methods, wood pulping is usually divided into chemical pulping and chemical mechanical pulping, where chemical pulping is mainly sulfate pulping and chemical mechanical pulping mainly includes bleached chemical thermal mill mechanical pulping (BCTMP), alkaline peroxide pulping (APMP) and disk mill chemical pretreatment alkaline peroxide pulping (P-RC APMP).

(1) Sulfate method pulping

A pulping method that treats wood chips with sodium hydroxide and sodium sulfide as cooking chemicals.

Depending on the degree of bleaching, sulfate pulp is divided into unbleached pulp, semi-bleached pulp and bleached pulp.

(2) Chemical-mechanical pulping method

The lignin and hemicellulose content of this pulp is higher than that of chemical pulp, and the pulp yield can reach 80% to 90%, while the yield of sulfate chemical pulp does not exceed 50%.

Chemical-mechanical pulping is a process that uses chemical action to pretreat wood chips and then uses mechanical action to separate wood fibers into fiber bundles, individual fibers, and fiber fragments.

2. Non-wood pulping process

Non-wood pulping process using wheat grass, reed, bagasse and other non-wood as the main raw material mainly adopts chemical method, the process mainly includes caustic soda pulping, sulfate pulping and sulfite pulping.

Non-wood chemical pulping process is basically the same, usually: non-wood raw materials after preparation, into the cooking equipment for cooking, non-wood raw materials in the role of high-temperature cooking liquid separation of lignin dissolved, the resulting pulp through the washing and screening section after purification, to obtain a better quality of this color pulp, if you need to get a higher whiteness of the pulp, but also need to bleach treatment.

3. Waste Paper Pulping Process

Waste paper pulping refers to the production process of pulp made from waste paper as raw material, which is processed through pulping and, if necessary, deinking and bleaching.

Waste paper pulp production is mainly composed of four parts: pulping, screening and purification, washing and concentration, and bleaching.

Depending on the raw material, production process and product characteristics, the waste paper pulp production process is mainly divided into non-deinked waste paper pulp and deinked waste paper pulp.

Typical deinking pulping uses a process of mechanical and chemical unit treatment to remove the ink from the fiber. The production process includes dissociation of the waste paper, screening and purification of the waste pulp, deinking, concentration and storage of the pulp, and thermal dispersion.

Deinked pulp can be used for products including newsprint, thin cotton, printing and copy paper, magazine paper (supercalendered / lightly coated paper), certain grades of cardboard boxes, etc.

The process for non-deink pulping is much simpler than deinked pulp, with a mechanically clean process and fewer processes such as deinking and bleaching.

Non-deinked pulp is mainly used to produce products such as boxboard, corrugated paper, and lower grades of cardboard. Most waste paper pulping lines are integrated with paper making.

4. Paper Making Process

Paper making is the process of making various paper products from pulp. Paper companies vary in their paper products and process layouts, which usually include basic units such as pulp preparation, stocking systems, paper machines and paperboard machines.

Both paper and paperboard are produced using common technologies, but due to the different physical and chemical properties of the fiber and non-fiber raw materials and the variability in the manufacturing process, there is a wide range of variability in the performance and quality of the products.

Pulp or pulp board from the pulp shop, need to go through a series of processing procedures such as pulping, adding filler, sizing, color mixing, purification, screening, etc., and then in the paper machine or paperboard machine through sheet forming, dehydration, pressing, drying, calendering and rolling, copying into paper rolls, paper rolls through the slitting, cut into certain specifications of flat paper; or through rewinding, rolled into certain specifications of the roll paper, and finally be packaged.

In certain cases, before slitting or rewinding, super calendering treatment is also required.

Forming of the paper sheet in modern paper manufacturing processes is done on a paper machine. Paper machines are usually classified by the form of their web sections, which can generally be divided into long-web, round-web and sandwich-web paper machines.

The web section of a long-web paper machine consists of a long web case with a horizontal or nearly horizontal web surface for dewatering the paper stock, underneath which are assembled various dewatering elements adapted to different requirements.

Long-web paper machine is a widely used type of paper machine, the general speed in the range of 600 to 800m / min, can be copied most of the paper varieties.

The disadvantage of the long-web machine is that the web is dewatered downward on one side, which inevitably produces paper with variability on both sides, thus affecting many characteristics of the paper, such as curl, smoothness of the paper surface, and printing performance.

The screen section of a circular screen machine consists of a circular screen cage where the paper suspension is filtered and shaped into a wet paper web by the difference in water level between the inside and outside of the screen cage.

Round screen paper machine is a traditional machine, adaptable to a wide range of products from thin paper to cardboard, and has a simple structure, small footprint, low power consumption and low investment costs.

However, due to the limitations of its structure, there are problems such as low speed, small production scale and limited product quality, and is generally used only for low speed and small production volume production copying.

The net section of the paper machine is made up of two forming nets. The paper suspension is injected between the two net clamping areas through the flow box, forcing dewatering on both sides and quickly forming the wet paper web, which has the advantages of high operating efficiency, good forming quality, compact structure and small footprint, etc., and is widely used in the modern paper industry.

(B) pulp and paper industry energy consumption characteristics

Modern pulp and paper production has achieved mechanical automation, equipment operation and system control requires the use of electricity.

Electricity drives the operation of pumps, fans, belt or spiral conveyors, vacuum pumps and compressors, but also drive the mechanical pulp grinding, processing of waste paper fiber hydraulic pulper, pulping, electrostatic precipitator, infrared drying, etc.. Pulp cooking, black liquor concentration, paper drying, chemical additives preparation requires heat energy, heat energy is mainly steam, gas as a supplement.

Many paper-making enterprises carry out cogeneration through their own power plants and use heat to set electricity, converting raw coal and biomass fuel into steam and electricity for use.

Therefore, the energy efficiency of the pulp and paper production process depends on many factors such as the structure of energy varieties, raw material structure, enterprise scale, technology and equipment, and self-produced energy and waste energy utilization.

Each enterprise's energy supply method varies greatly, and there are three main types.

(1) both electric energy and heat energy are purchased.

(2) Electric energy is purchased and heat energy is self-produced.

(3) With self-provided thermal power station, part of the electricity is purchased and the thermal energy is produced by itself.

Due to the different ways of using energy, the comprehensive energy consumption of each enterprise is not comparable. In order to make the energy consumption per unit of product comparable, the Energy Consumption Limit per Unit of Pulp and Paper (GB 31825) calculates the energy consumption per unit of product by counting the energy consumption of the main production system, excluding the energy consumption of auxiliary production systems and subsidiary production systems, and converting both electricity and heat into standard coal according to their equivalent values.

Pulp and paper enterprises have two types of major equipment and facilities.

One category is the process function type (special equipment), such as chipper, cooking pot, even steamer, grinder, alkali recovery system, pulper, paper machine, coating machine, super calender, rewinder and slitter, etc. The energy consumption of these equipment and facilities is not only related to the performance and management level of the professional equipment itself, but also related to the operation of the corresponding process operation and supporting general equipment.

Due to the highly diverse pulp and paper products, even the same product application process may also vary greatly, so many factors must be taken into account production technology.

Another category for the transport function type (general equipment), such as a variety of pulp pumps, pumps, belt conveyors, screw conveyors, fans, etc.. In addition, there are a small number of auxiliary types of equipment, such as mixing, metering equipment.

The main energy-consuming processes in the pulp production process are cooking and black liquor evaporation, and the main energy-consuming processes in the paper production process are sheet drying.

1. Pulping process energy consumption characteristics

Fiber dissociation on the chemical pulping process is the cooking process, on the mechanical pulping process is the coarse grinding process, on the chemical machine method, semi-chemical pulping process is the chemical pretreatment process and grinding process. The cooking process requires a lot of heat, and the coarse grinding process consumes a lot of electricity.

The manufacturing of bleached sulfate pulp consumes about 10-14GJ/Adt of thermal energy, including the drying of pulp, and the electrical energy consumption is 600-800kWh/Adt.

The energy consumption of pulp drying occupies about 25% of the thermal energy and 15% to 20% of the electrical energy. More than 50% of the electrical energy consumption is used for pulping.

The energy consumption depends on the process configuration, process equipment and process control efficiency.

Chemical pulping can be divided into continuous cooking and intermittent cooking according to whether production is continuous or not; according to the equipment used, it can be divided into steam ball (intermittent cooking), vertical pot (intermittent cooking), and