Papermaking equipment

Paper 1: Equipment Analysis of Paper Industry

With the rapid development of the paper industry and the state's attention to the introduction of technical equipment and investment in technological transformation, the scale, technological progress, product level and manufacturing capacity of equipment enterprises in the paper industry have changed significantly, greatly narrowing the gap with international advanced paper equipment. Some non-wood fiber pulping technologies suitable for China's national conditions have reached the international advanced level, and the market share of domestic medium-sized pulp and paper complete production lines has greatly increased, which initially shows comparative advantages in the competition with international multinational companies.

Advantages of China's paper industry equipment in international competition.

(1) In the paper industry and equipment industry, the structure and mechanism of enterprise economic types have changed obviously during the Tenth Five-Year Plan period. Leading enterprises in the industry have changed from 50% state-owned large and medium-sized enterprises to more than 95% joint-stock enterprises and private joint-stock enterprises, and the proportion of former state-owned enterprises has dropped significantly. The reform of system and mechanism has obviously enhanced the enterprise's vitality and ability to adapt to the market, accelerated the adjustment of enterprise's product structure and the promotion of comprehensive competitiveness, and laid an important foundation for the sustainable development of the equipment industry in the paper industry. ?

(2) During the Tenth Five-Year Plan period, leading enterprises in the industry basically completed technology introduction and technical transformation, forming a relatively complete design and manufacturing capability. Leading enterprises in the industry have improved their equipment level and manufacturing capacity through technical transformation of national debt and self-financing and special machine tools for processing key parts can meet the requirements of high-precision machining.

Pulping equipment enterprises have formed 4-5 enterprises whose mechanical output value can reach more than 654.38+0 billion yuan; Paper-making equipment enterprises have formed 5-6 enterprises whose mechanical output value can reach 200-300 million yuan. ?

(3) Rapid growth of leading products of leading enterprises in the industry In the domestic paper industry equipment market, especially in large-scale pulp and paper equipment, the proportion of domestic equipment replacing imported equipment is gradually expanding. ?

In terms of pulping system equipment, the domestic horizontal tube continuous cooking and alkali recovery equipment in the 65438+ 10,000 t/a chemical pulping or semi-chemical pulping production line of grass raw materials is adopted, and the market share of domestic key equipment such as drum pulper, heat disperser and deinking device in the 400t/a waste paper board pulping production line is over 80%.

In addition, in recent years, in the process of black liquor extraction, screening and purification, white water recovery, pulp concentration and beating, the market share of domestic drum vacuum pulp washer, double-roll pulp squeezer, pressure screen, large double-disc mill and multi-disc filter has also been greatly improved, and it is matched with the pulp and paper production line with an annual output of 200,000 ~ 300,000 t.

Domestic paper machine equipment: newsprint paper machine and cultural paper machine designed and manufactured by Sino-foreign joint venture with paper width of 4.5m, speed of 1.200m/min and annual output of 80,000 ~1.2000 t; The kraft liner paperboard paper machine designed and manufactured by a large enterprise has a paper width of 5.5m, a speed of 600 m/min and an annual output of 200,000 t; With a width of 4.4m, a speed of 500m/min and an annual output of 654.38+10,000 tons, the market share of these domestic paper machines has reached almost 90%, and they have gradually replaced foreign imported equipment. ?

The key equipment such as headbox, soft calendering, shoe press, upper shaper and coating head are provided by foreign professional companies. The domestic coated white paperboard machine with a width of 4.8 ~ 5.65 m, a speed of 600 ~ 900 m/min and an annual output of 300,000 t has also entered the market. In the complete paper machine equipment with a width of 6m and a speed of 1000 ~ 1200m/min, the dryer and guide roller are made in China. Press roller, vacuum roller, frame, etc. We have begun to cooperate with foreign first-class multinational companies, and the equipment manufacturing level and product quality have been recognized by large domestic paper enterprises, which shows that the gap between domestic equipment design and manufacturing level and international advanced level is gradually narrowing. ?

The new equipment, such as headbox, soft calendering, in-machine coating equipment, air cushion drying, controllable middle and high rollers and sizing system, jointly developed by professional design research institutes and enterprises, has been popularized in various small and medium-sized paper machines with output of 50,000 ~10.5 million t/a, and its market share is expanding day by day. It shows the potential of joint product development in Industry-University-Research. ?

(4) Leading enterprises in the industry gradually attach importance to technical exchanges and cooperation with domestic and foreign companies specializing in electric drive, automation, computer control, environmental protection and supporting companies for bearings, motors, lubrication and other products, and also begin to cooperate with domestic enterprises in metallurgy, machinery, chemical industry, electronic instruments, computers and other industries to solve the problem of special processed parts, special raw materials and spare parts that the industry itself lacks. ?

1.2 What are the restrictive factors of equipment development in China paper industry?

Although some fundamental changes have taken place in the equipment of the domestic paper industry during the Tenth Five-Year Plan period, in the next five years, the equipment industry of the paper industry will develop synchronously with the paper industry, and further change to be quality-oriented and benefit-oriented, providing the paper industry with advanced equipment with low input and high output, saving energy and reducing pollution, and participating in the competition in domestic and foreign markets, but it is still restricted by many factors:

(1) Is it difficult to attract a large amount of capital?

The equipment industry of paper industry is a traditional industry, which needs to transform the modern equipment level of the industry. With the macro-adjustment of the national credit policy, the proportion of enterprises accumulating funds by themselves and financing from the society will increase, and the difficulty will increase.

(2) Difficult to obtain high technology?

At present, the absorption and digestion of foreign new technologies by equipment enterprises in the paper industry mainly focus on manufacturing according to drawings and pushing products to the market in kind. After China's entry into WTO, foreign companies have strengthened the protection of intellectual property rights. It is extremely difficult for domestic enterprises to further acquire the pulping and papermaking technology with high quality, high efficiency, energy saving, consumption reduction and pollution reduction. Therefore, domestic enterprises must attach importance to independent development capabilities.

(3) It is difficult to have high-level professional and technical personnel?

The high-tech professional knowledge of pulp and paper machinery covers a wide range, and a lot of knowledge and experience need to keep pace with the times, and a group of senior talents with new knowledge structure and innovative ability are needed, otherwise the real breakthrough of pulp and paper equipment technology cannot be realized. It is difficult for enterprises to have high-level talents who can conquer high-tech in a short time by their own efforts, and they will also face the competition for talents from international multinational companies in China.

(4) It is difficult to create an orderly competitive market environment?

During the Tenth Five-Year Plan period, a number of leading enterprises in pulp and paper equipment industry have been formed. However, the products of most enterprises in the industry are still the same. They are used to acquiring technology through traditional methods and entering the market at an extremely low cost. In the competition, they broke away from the product quality, technical level and excellent service, and lowered the price unprincipled, which led to an abnormal decline in the profits of the entire paper industry equipment industry, seriously damaging the self-development of pulp and paper equipment enterprises and the accumulation of their own funds.

(5) Product competition and talent competition with foreign multinational companies?

According to their globalization strategy, some well-known multinational companies and some professional companies abroad take China paper market with great potential as their target market. They should not only maintain their monopoly position in large-scale, high-speed and automatic pulp and paper production lines, but also give full play to their capital and technological advantages. They have set up joint ventures and technology centers in China, looking for manufacturing partners, taking advantage of domestic talent advantages and cost advantages, adjusting price policies, and competing for the medium-sized enterprise market with a large domestic equipment market share. The key equipment parts that are vacant in the domestic market are sold at high prices, while the key parts and general parts that can be replaced by domestic equipment are sold at close prices. Paper industry equipment enterprises are bound to face challenges in the international environment of domestic market.

2. The gap and development trend between the main equipment of China pulp and paper industry and the international advanced level.

(1) material preparation equipment

Chipping machine and chip screening Due to the diversification of domestic papermaking raw materials, the development of wood chipping machine and chip screening equipment in material preparation equipment is not fast. At present, the diameter of the wood chipper is 3350mm, and the diameter of the bamboo chipper is1670 mm. With the development of forestry-paper integration and APMP and CTMP high-yield pulping technology, the specifications of domestic chipper and chip screen need to be developed to large scale, and the level of automatic control needs to be improved. Drum chipper and disc chipper with high efficiency and grading according to wood chip thickness have been developed abroad, and the cleaner production of material preparation system has been paid attention to.

Domestic straw fiber preparation equipment for wet material preparation is relatively complete, mainly used for continuous cooking, with a capacity of 300m3/h ... At present, the specifications and capacity of wood chip preparation equipment (drum washing) are not very large, and the 2000m3 wood chip warehouses of domestic paper mills are all imported from abroad.

(2) Cooking equipment system

The equipment and automatic control system of 150 t/d horizontal tube continuous cooking system, which is mainly suitable for grass raw materials, have all been localized, and the pulp yield and operation efficiency have reached the international advanced level. At present, 250 ~ 300 t/d cooking equipment is being developed.

Vertical continuous cooking technology suitable for wood fiber is still blank in China. Its key technologies and equipment: heating cooking and automatic control technology, high compression ratio feeder. Domestic paper mills imported 220,000 tons/year equipment system. In addition, RDH energy-saving batch cooking equipment is suitable for wood pulp, bamboo pulp and other raw materials, and the investment is less than that of continuous cooking equipment system, especially suitable for technical transformation of old factories.

Paper 2:

Frequency conversion application of papermaking machinery

New manufacturer

Since 1990, especially since 1995, the effective production capacity of China paper industry has been increasing. By the end of 2002, there were more than 4,000 paper mills in China, of which more than 2,600 were above designated size. The total output reached 37.8 million tons in 2002. In the next l-2 years, there will be nearly100000 tons of new production capacity. At present, more than 80% of the transmission equipment of the newly added paper machine adopts AC drive frequency converter.

At present, the inverter used in the auxiliary drive of paper machine must have the following characteristics at the same time

(1) The speed range is wide, and the efficiency must be above 90% in the full speed range;

(2) the power factor is higher than 0.9;

(3) The total distortion rate of input harmonic current is less than 3%;

(4) adopting standard device IGBT；; High reliability and mature technology;

(5) It can reduce the output harmonic components and effectively reduce dv/dt noise and torque ripple.

(1) Prospect and analysis of frequency conversion transformation of paper machine.

According to statistics, China's production capacity is more than 37.8 million tons, single machine production capacity is more than 50,000 tons, and board machine production capacity is less than one third of 654.38+10,000 tons. More than two-thirds of the production capacity still needs a lot of investment, and at least one-third of paper machines need to partially or completely replace the original transmission parts (including mechanical gearbox and motor drive) to improve speed or reduce energy consumption.

In the past, the transmission equipment of paper machines in China adopted SCR DC speed regulation. Because of the existence of slip rings and carbon brushes, the reliability and accuracy of paper machine are not high, which leads to the backwardness of paper machine machinery, and the highest speed is only about 200m/min, which is difficult to compare with foreign high-speed paper machines 1000m/min. Papermaking is a continuous production process, so the continuous and orderly control of the production line has become a bottleneck restricting the quality and output of finished paper. DC speed control system plays an important role in the history of paper machine development. However, due to the difficult maintenance of DC vehicles, the environmental resistance is poor, mainly as follows:

(1) The commutator is seriously worn, and the failure of burning the commutator leads to long downtime;

(2) The maintenance of 2)DC motor is difficult, demanding and expensive;

(3) The tachogenerator is easy to wear, which leads to low accuracy of the transmission system;

(4) The 4)DC speed control system is complex and difficult to debug, so it is difficult for ordinary technicians to adjust the machine well.

AC variable frequency speed regulation technology is recognized as one of the most promising AC speed regulation methods because of its excellent speed regulation performance, remarkable power saving effect and wide applicability in the national economy. It not only has the excellent speed regulation performance of DC motor, but also has the simplicity and reliability of AC motor, so it is gradually widely used.

The frequency conversion transformation of paper machine drive has a very good effect, which improves paper products, increases production capacity, reduces energy consumption, and prolongs downtime and maintenance cycle.

Take the transformation of a long wire paper machine in a factory as an example. It has two branches: one is the dryer (cadre) and the other is the wire section (wet section). According to the technological requirements, the paper-making speed is 20- 100 m/min, and the paper basis weight is 9-30 g/m2. Generally, the transmission accuracy of paper machine is required to reach 1-3 ‰. Because of the wide range of speed change, the minimum ration is 9g/m2, which requires high transmission accuracy of paper machine. Therefore, the paper machine drive control scheme of closed-loop system is selected.

(2), energy saving benefit analysis

According to the comparison of paper machine energy consumption before and after the transformation of this factory, the following results are obtained:

Power before transformation: 90m rotating speed P90 = 74a×180v+3× 220 =13980w =13.98kw (DC drive).

According to the production of 300 days a year, the power consumption of the whole machine = 300× 24×13.98 =100656 (kwh).

Power after transformation: 90m rotating speed P90 =1.732×16a× 380v =10530w =10.53 (kW) (frequency conversion drive).

Power consumption of the whole machine = 300× 24×10.53 = 75816 (kwh)

Annual electricity saving =100656-75816 = 24840 (kwh)

It can be concluded that the actual energy saving after application of frequency converter is: 25%.

(3), process benefit analysis

① Improvement of paper machine operation rate: more than 27% (from the average monthly output, excluding other factors) can increase the output value;

② Increase production: 1.6%

To sum up, after adopting the frequency converter, the running performance of the paper machine is improved and the economic benefit is further improved.

(4) Application analysis of frequency converter in papermaking auxiliary equipment

The auxiliary facilities of paper machine include the following systems: pulp supply system, white water system, vacuum system, compressed air system, chemical agent and conveying system, water supply system, steam system, etc. In order to make the paper machine run continuously and evenly, the capacity of its auxiliary facilities should generally exceed 15%-30% of the maximum production capacity of the paper machine, which will cause great energy loss.

Frequency conversion application of pulp supply system

The slurry supply system must meet the following conditions:

(1) The pulp delivered to the paper machine should be stable, and the error should not exceed 5%;

(2) The specific gravity and concentration of mud should be stable and uniform;

(3) Reserve a certain amount of pulp, so as to adjust the pulp supply capacity and adapt to the change of paper machine speed and variety;

(4) Purification and selection of slurry.

(5) Deal with the paper loss of each part of the paper machine.

Usually, the slurry supply system consists of slurry supply pump, slurry washing pump, pressure screen of purification facilities and slag remover in the slurry supply pipeline. To achieve the above five objectives, the most important thing is to change the full-speed operation of pulp pump and pulp flushing pump into variable-frequency operation with adjustable speed, and finally meet the automation of pulp supply.

Taking the pulp pump as an example, the speed control flow of frequency converter is explained: the speed control mode of double closed-loop system should be adopted in this frequency conversion control, with the speed closed-loop in the outer ring and the current or torque closed-loop in the inner ring. On the one hand, the set value of the speed of the pulp pump is obtained by the change of the pulp speed and the net speed ratio, on the other hand, it comes from the pressure controller of the headbox. The former is the main tone and the latter is fine-tuning. The ratio of pulp speed to net speed of paper machine is basically unchanged, so once the net speed of paper machine changes, the rotation speed of pulp washing pump also changes; In order to improve the accuracy of the governor and reflect the actual process of the headbox, it is usually necessary to take the 5% change of the output value of the headbox pressure PID control as the additional speed setting value of the pulp flushing pump. The actual value of the speed is taken from the actual speed sampling of the driving motor, which can be obtained by detecting devices such as rotating tachometer motor or photoelectric rotary encoder. The set value of current is taken from the output signal of speed loop, and the actual value of current is taken from the measured value of current transformer at the output end of AC inverter at each transmission point. Therefore, for the variable frequency speed regulation of pulp pump, PID control is needed to achieve the ideal energy-saving effect.

(V) Frequency conversion application of compressed air system

Compressed air is often used in pneumatic pressurization lifting devices in the wire and press sections of paper machines, correcting devices for net blankets, air cushion headboxes, paper guiding equipment, coating air knives, various pneumatic instruments and adjusting devices.

In the compressed air system, the main equipment includes air compressor, gas storage tank, pressure reducing valve, air filter, steam-water separator and safety valve. The pressure on the paper machine usually needs about 5-6 bar. Most paper mills run more than two air compressors in parallel, and then keep the pressure constant through the gas storage tank.

Because the compressor has high power, the control pressure is generally adjusted by loading and unloading, so the motor always runs at full speed. Practice shows that this control method consumes huge energy and wastes seriously. Therefore, at present, there is a trend to control a compressor unit with frequency conversion and multiple power frequencies, and a pressure closed loop is formed.

(6) Frequency conversion application of chemicals and conveying systems

Because a large number of chemicals are used in deinking, pulping, coating and sizing, the dosage is directly proportional to the speed of multi-drive of paper machine, so stepless AC speed regulation system must be adopted in chemical conveying system (such as pump). A large number of grinding equipment are used in the preparation of chemicals, such as ball mill, colloid mill, sand mill and high shear dispersion agitator. Their biggest characteristics are high power, high energy consumption and harsh use environment. At present, many manufacturers have adopted frequency converters in grinding equipment and achieved good results.

Taking the refiner as an example, its working principle is that after the paint to be ground is input into the cylinder by the feed pump, it is strongly impacted by the grinding medium under the drive of the high-speed rotating dispersion disk, and it is ground and dispersed into the solvent to make qualified paint, and then filtered by the top screen. The main motor of the equipment is 1 10KW. Before using the frequency converter, it is usually repeated several times (more than three times) by inching to make the coating and grinding medium mix evenly. For different coatings, sometimes different process speeds are needed, but in fact they can only run at full speed; Unable to grasp the feed speed to ensure that the main motor is not overloaded; Energy consumption is very serious. Using 1 10KW frequency converter can solve the above problems well, and it is convenient to set the inching speed and slow running time to ensure the most uniform mixing of paint and medium. On-line stepless speed regulation, different varieties use different grinding speeds; The feed speed is only controlled by the actual running current of the motor, which has overload warning function and trip-free function; The energy saving rate can generally reach more than 20%; The loss of gearbox is reduced, and the impact of power frequency start on gearbox is avoided; Because the current is gentle when starting, the impact on the power grid is avoided and the safe operation of the power grid is improved. At present, paper enterprises in Shandong, Heilongjiang, Hainan and other places have been applied in batches.

(7) Frequency conversion application of ventilation system for drying cadres.

After all the water vapor evaporated from dry paper is absorbed by the air, it must be continuously discharged from the papermaking workshop through forced ventilation. Whether the drying section is well ventilated directly affects the evaporation rate of water in paper and the economy of the whole drying process; Good ventilation can reduce the steam saturation in the air, thus reducing the steam consumption of the dryer and improving the drying speed.

The amount of air needed to remove evaporated water from the dryer is related to the temperature and humidity of the incoming and outgoing air, as well as the ventilation system, climatic conditions and seasons. Generally, in modern paper machines, forced air circulation is adopted to achieve high efficiency. The dry air heated to about 80 degrees is sent to the lower layer of the dryer by the air inlet fan, so that the hot steam is absorbed between the dryers to form an upward airflow, and then the hot and humid air collected in the fume hood is pumped out by the exhaust fan (finally, the waste heat is recovered). In high-speed paper machines, due to the increase in the number of drying cylinders, they are usually divided into several sections of blowers and exhaust units. After adopting the frequency converter, the intake air volume (blower speed) and exhaust air volume (exhaust fan speed) can be adjusted at any time according to the calculation formula of ventilation air volume, without using the traditional damper control, further reducing energy consumption, reducing blower noise and improving mechanical life.

(VIII) Frequency conversion application of water system

Paper machine is a big user of water, including white water system, sewage system, sealed water system, spray system and clean water system. It is usually necessary to supply water at constant pressure through pipe network, but the traditional pressure control is carried out through bypass and regulating valve, and frequency converter is rarely used. However, due to the general shortage of water resources in China, the application of frequency converter will save water 10% and energy 30%, which will inevitably reduce the daily operation cost of paper mills.

Frequency converters used in water systems usually have two modes: fixed frequency conversion mode and cyclic frequency conversion mode.

Frequency conversion fixed mode: the frequency conversion output of the frequency converter fixedly controls one pump, the other pumps are directly powered by the power frequency grid, and the start and stop signals are logically controlled by PLC;

Frequency conversion cycle mode: the frequency converter drives each pump in turn according to a certain order. The frequency converter can automatically determine the number of running pumps (within the set range) according to the pressure closed-loop control requirements, and only one pump is driven by frequency conversion at the same time. When the pump driven by the frequency converter runs to the set upper limit frequency and it is necessary to increase the pump, the frequency converter switches the pump to power frequency operation and drives another pump to operate in frequency conversion.