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Drive application and analysis in the paper industry
Publish:China EM Technology Limited  Time:2016-02-25

                                                                          Drive application and analysis in the paper industry

Abstract: The paper industry is one of the basic industries, the number of domestic pulp and paper enterprises, wide distribution, plays an important role in the national economy. The main application is Paper frequency division multiple motor drive and fan and pump loads. This paper analyzes the paper industry applications and frequency transformation vision.
Keywords: Inverter Paper Application

1. First, the application background of paper industry
The paper industry is one of the basic industries, the large number of domestic pulp and paper companies, widely distributed, plays an important role in the national economy.
The main application is Paper frequency division multi-motor drives. Because a lot of the old machine using a single DC motor drive, and be allocated by a mechanical speed governor manner, often in the production process due to mechanical wear, belt slippage caused by factors such as speed matching disorders, breaks easily formed, thickness disparities , and because of the high temperature and humid leaving the field to increase motor maintenance. In order to optimize product quality, improve labor productivity, the scene has changed it a lot more motor branch transmission, mechanical transmission part is canceled and DC power, install AC motor drive in each division and configure the appropriate drive, while AC multi-point transmission mode, combined with the speed control, drives configured in different ways tension control, load control. For the production process of the sheet characteristic changing needs of the branch transmission in addition to the paper machine to ensure the synchronization control precision, but also must be able to adjust the speed within a certain range, and speed of each segment can be adjusted individually.
At the same time, the paper industry is also a big fan and pump load, and run-time class load is continuous, all manufacturers are based on the actual working conditions, the need for fans, pumps load for different degrees of adjustment, which makes the inverter in paper industry applications for enterprises to bring great economic benefits.

2. Second, the application analyzes the paper industry drive
    1, paper production capacity
    Chinese paper industry effective production capacity since 1990, in particular, has continued to grow since 1995. According to the China Paper Association survey comprehensive information, in 2004 the national paper and paperboard production enterprises around 3500, the national paper and paperboard production of 49.5 million tons, 43 million tons over the previous year growth of 15.1%. Consumption of 54.39 million tons, 48.06 million tons last year compared with 13.2 percent growth in annual per capita consumption of 42 kg, 5 kg over the previous year. From 2004 to production and consumption situation analysis, annual production and consumption showed a rising trend, and maintained a high growth rate. In particular, the production of paper and paperboard incremental 6.5 million tons, reaching a record high. Production of a large increase in the main varieties of newsprint, lightweight coated paper, coated paper, coated paperboard, cardboard, corrugated paper and so on. A large increase in the consumption of the main varieties are: newsprint, lightweight coated paper, copperplate paper, writing paper, cardboard, coated paperboard, corrugated paper and so on.
    Suppose our country in the next period of time the total GDP at an annual rate of 7% increase, at the same time, taking the past 12 years the average annual population growth rate of 0.91% as a future net annual population growth rate, by 2010, China‘s per capita GDP reached 13,890 yuan, per capita paper consumption will be increased to 60 kg. We can guess that by 2010, the total consumption will reach 69 million tons. In the coming years, there will be nearly 10 million tons of new production capacity. By then, the total production capacity of China‘s paper industry will reach nearly 55 million tons. According to statistics, since 2000, global production of large-scale paper machine 1/2 installed in China. Currently, high-end machine in the domestic market share of 33%, and essentially international giants such as paper machine VOITH, METSO, ANDRITZ based.

    2, paper capacity of the inverter
    Due to the current new machine transmission equipment has more than 80% of the AC drive inverter, so the new annual production in the next 3-4 million per year paper machine drive capacity will be considerable.
    Our factory capacity to introduce VOITH production of 175,000 tons / year of paperboard machine for example, the paper is double-coated white paper, the width of 4.2 meters, including four wire section, four press 10 groups dryer, 1 cold cylinder group size press, two-roll calender 3, 4 air knife coating, a roll portion, a total of 72 drives, design weight 120-500, speed of 600 m / min, the machine branch transmission (refers to the 72 paper machine drive) inverter capacity totaled 5490KW. It can be calculated by a common drive tons of paper capacity is calculated as 31W, then we can next year to estimate the frequency of the installed capacity is about 90,000 KW. In the paper machine system design calculations 1KW / 2000RMB, for a total of about 180 million paper machine main drive market. Of course there is, drive brand consisting essentially of major foreign manufacturers ABB, SIEMENS, AB, YASKAWA, Mitsubishi dominant.
    From the current situation, all of our pulp and paper making machinery production capacity in about 35 to 45 million tons / year in 2004, the pulp and paper equipment manufacturing industry output value of 56.9 billion yuan, the domestic market share of less than about 1 / 4, all the rest will be overseas paper machinery suppliers in the country.
    We also note that increasing the amount of high-grade paper machine will reach historical peak, and rapid advances in increasing the width of the vehicle are prompted new machine installed in the extensive use of the latest high-end vector control inverter type or DTC , while the corresponding mature domestic inverter little, so most imported brands owned by domestic brands share of less than 5%. Of course, we also noted that, since China is becoming the world‘s factory, the drive will be made in China has been gradually localized international institutions machine machinery manufacturers (such as Metso Paper, VOITH Paper) of high-grade paper machine.
Currently on a paper machine drive branch transmission used must meet the following characteristics: (1) wide speed range, in the entire speed range, efficiency must be above 90%; (2) power factor greater than 0.9 or more; (3) input current total harmonic distortion is less than 3%; (4) high reliability, proven technology standard devices IGBT; (5) to reduce the output harmonic components and reduce dv / dt noise and torque ripple effect; (6) the use of communications functions to achieve high-speed serial data transmission.

3. Third, the paper industry‘s development trend variable frequency drive configuration
    Paper production is a continuous process, so continuous and orderly control has become a constraint finished paper quality and yield of the production line bottlenecks. As the inverter is the most powerful way to enter the control originally belonged to DC converter (for medium and large machine) and slip motor (for small and medium machine) papermaking art world, and nearly made good effect on the market.
    At present, the international advanced paper machines in the high efficiency, low consumption direction, which is the market competition. At present, there are a lot of running paper machine is at a disadvantage in this regard, it is necessary to upgrade the technological transformation; and for paper machinery manufacturers must be met head-on, the performance upgrade from the source design.
    Transmission as a core part of the paper machine, its development requires speed and degree of automation is progress. Now run some machine-made paper, the fastest and only 500-600 m / min, and foreign paper machine running speed has reached 1600-1800 m / min, some even over 2000 m / min, the gap is very big. The faster the speed, the higher the efficiency. While current domestic paper machine mostly manual control, even the latest domestic paper machine, which automatically controlled machine, which is not high degree of automation, and foreign large-scale paper machine, its high degree of automation, with high-speed machine and large, rely on manual control is a very difficult thing.

    Here, we will focuses on the digital network, controlled tension and torque, direct drive system to illustrate three different aspects of the development trend of paper machine drive configuration.
    1, the digital network paper machine drive control system
    Currently on a paper machine, basically for the transmission of control in two ways: (1) analog control; (2) digital control.
    Transmission control system analog control structure is simple, easy to manipulate as for less demanding users of technology, speed accuracy to meet the needs of users, and reliable, and has the speed transfer system, fine-tuning the production process to meet the requirements and can load changes in the structure, a flexible change control, it also has a good display screen, the operator can exercise control equipment operating conditions. But it is only applicable low-speed machine, and difficult to achieve integrated management and control.
    Transmission control system digitally controlled, can be widely used in the line is longer, the number of divisions in the transmission of more large-scale high-speed machine. It uses the means of communication to achieve full digital control system, anti-interference ability, poor signal attenuation, high resolution, high-precision control can be achieved, while the process according to the machine requirements and load control more flexible.
    Whether it is two or three control systems control systems, the use of digital technology not only greatly advances the machine speed, and reduce labor intensity and reduce maintenance time. Make substantial progress in yield and economic benefit. All-digital transmission technology division is analog control techniques and total transmission shaft can not be compared.
    In the current digital transmission network, PROFIBUS is always the most popular. PROFIBUS-DP field bus is especially suitable for the need to respond quickly and not the amount of on-site data exchange, is an open field bus systems, and standardization. PROFIBUS-DP field bus has the following characteristics: After a twisted pair or fiber optic cable for data transmission, can be flexible and modular design automation systems, save wiring costs, up to 125 nodes, up to 12Mbit / s, response time is short transmission interval of up 23.8Km, through a variety of application specific integrated circuit (ASIC) and interface templates to simplify the connected devices, PROFIBUS-DP is "Totally integrated" of the system bus, the famous programmable controller sales world Suppliers generally familiar with the advantages of a field level standard interface for PROFIBUS-DP. For the above reasons the location of the machine also uses a lot of electrical control PROFIBUS-DP fieldbus.
 At present, digital transmission network mainly in Xi‘an Pao automated WB-PDD-A system, Hangzhou, Zhang HZ-AC3000 electrical system, electronically controlled by the Shanghai paper machine SIED secondary or tertiary electrical control systems.
    WB-PDD-A paper machine control system for 2640/320 LWC paper machine design and development, electrical transmission system uses the International Standard Industrial Fieldbus PROFIBUS, to the communication speed 1.5MH Siemens latest S7-400PLC, 6RA24 digital DC drives, OP37 smartphone operating unit and the like to achieve the LAN scene set and control the tension of the paper system, speed, load distribution, and other parameters, can paper one line in any gear start, stop, crawling, jogging, relaxation and tension control. System environment for Chinese WIN95 interface, application software with Siemens WINCC configuration software. The system can process parameters, fault status of each drive control point for real-time display, monitoring, storage and printing, and provides historical trends and the completion of the process parameters line changes and save.
    HZ-AC3000 papermaking system uses a microprocessor speed loop, torque and tension ring tricyclic ring automatic adjustment control theory, program settings can be freely adjusted acceleration and deceleration time and maximum / small values ​​based on speed. Closed loop speed control, load distribution control, torque / tension control and relaxation constitute an open tree-speed chain, which is the core of the drive control system, a variety of control methods in harmony here has been the same. For wet portion transmission control, in order to ensure the paper composite effect, we decided to drive roll wire section with velocity loop control; the transmission medium between the same point, using the load distribution between the press roll in contact with each other. For cadres transmission control. Since the paper has established a cadre of tension, so that cadres to control tension of the goal. Regional points of tension drive easily changed within a torque / tension control, and to drive the point area of ​​tension is not easily changed within the speed closed-loop control is used. HZ-3000 also provides a network control system interlock (safety chain, technology chain, chain start and stop the chain, the chain breaks, the fault chain, etc.) and system protection (monitoring phase sequence, phase monitoring, voltage monitoring, overvoltage monitoring instantaneous overcurrent protection, long-time overcurrent protection, the encoder signal loss alarm and protection, overclocking, speed alarm and protection, ground fault alarm, communication fault alarm). Since the paper machine drive control system used in the communication network, data transmission and systems for each machine segment chain information through the network directly to the information communication network layer, namely Ethernet. The Ethernet communication protocol uses openly (EtherNetIP), therefore, data can be transferred to other systems (such as MCS, DCS and QCS systems).
    SIED papermaking system includes three parts: (1) the PC industry and advanced industrial control software pre-installed on a machine, visualization manipulation process, production processes, machinery and equipment used. By MPI (Multi-Point Interface) to communicate with the master station PLC. (2) PLC master the use of advanced high-performance PLC system configuration and provides standard tools for hardware and software configuration, parameter settings, programming, operation, diagnostics. Connected via PROFIBUS-DP interface to the field level PROFIBUS-DP network to 12Mbit / s communication speed to the next level with HMI or transmission control device communication. (3) HMI HMI or transmission control device is connected to the interface via PROFIBUS-DP PROFIBUS-DP network on site. HMI human-machine interface or transmission control device to complete the field data collection, and field level via PROFIBUS - DP data exchange and acceptance of PLC to PLC network master command sent by the master data.

      2, controlled tension and torque
      In the paper and board industry production, generally we need to be tension and take-up control in order to meet the requirements of the production of paper material, such as a super calender, rewinder, machine coater, Cutter. At present, the vector converter for torque and tension control can already basically meet the requirements of the paper production process, which uses two main ways: open-loop and closed-loop tension control tension control.
    Loop tension, the tension detection means by the feedback signal and the setpoint tension tension constituting PID closed loop, then adjust the inverter output frequency command (speed mode) or the output torque command (torque mode). This scenario can be applied to high-precision tension control applications, such as tension control winder.
But the requirements are not demanding, but also requires a high cost of winding, it can be used more practical limit torque vector frequency method, you can save to a tension sensor, PID controller, but only need a simple inverter plus PLC control can be. In this control mode, the actual tension or need to know, which is nothing more than drive through internal testing and calculations to obtain, thus freeing tension detecting means to reduce the cost and difficulty of the system.
    Vector control inverter by the motor flux current and torque current decoupling control to achieve rapid response and accurate torque control, high control precision wide range of speed operation.
    Current technology, has the drive winding and unwinding control many devices already in the machine drive has been widely used, and profile configuration and flexible application access to users.

       3, the direct drive system
       ABB supplied in paper machine drive system has more than 100 years of history. Early is the use of the long axis of the drive, it began to be replaced by a DC branch transmission in the 1960‘s. In 1983, the Division of ABB‘s first drive concept will be applied to the exchange of machine industry. It now appears that all of the new machines and the transformation of most of the paper machine will use the exchange branch transmission.
    In order to improve reliability and reduce operating costs to a greater extent cycle, ABB in the mid-1990s began the development of a new paper machine drive system. The goal is a high-torque direct drive coupled to the end of the paper machine, which can save in most cases to the mechanical part of the drive motor and machine coupling part (such as gear boxes, etc.).
    The first example is a new generation of paper machine drive in mid-1999 of a paper machine in Finland, it has already been up to now. The transmission power is at 234 rev / time-sharing output 90KW. ABB is really a "virtual digital gear-box" to replace the real mechanical gearbox.
    In the direct drive system, the motor through a conventional low-speed connector is coupled directly to the machine parts. The motor is a synchronous permanent magnet motor. ABB can offer this machine is designed for supporting a series of electrical products. Transmission is usually by the cabinet of ABB ACS600 / 800 converter component. On the drive hardware is consistent with the traditional AC induction drive, you can use air and water. The software design is dedicated permanent magnet motor drive software. He promised to use synchronous motors without encoder mode of operation on the paper machine. Part of the transmission control system, control applications and human-machine interface, these are now part of ABB solution on the paper machine consensus. Thus, the direct drive with other programs at the same time ABB drives operate in parallel, and ACS600 / 800 without replacement can be upgraded to the new direct drive system.
    With the development of direct drive technology, a simpler drive system now seems to have the machine can appear in people‘s eyes.
    In a typical paper machine drive, the speed gear motors are usually at 1500 rpm / min to 1800 rev / min. Then you can obtain a suitable machine speed by selecting an appropriate gear ratio. In the direct drive, the motor rated speed is usually at 300 rpm / min to 600 rev / min. Using a conventional induction motor running at this speed, the size of the motor will now be at least 2 times. Obviously it is neither practical nor effective, so this is the reason we want to develop a new motor. In the new permanent magnet motor, replacing the squirrel cage induction motor with permanent magnets conductor.
    In the new rotor design, it has been noticed sufficiently reduced torque resonance smooth torque characteristics to meet the machine needs to run. Since the rotor is virtually non-dissipative, the motor can be designed to a higher power section, the stator and allow higher energy loss. Since the rotor is a permanent magnet, the stator current is no longer required is used as part of the excitation of the rotor, it is possible to produce a more effective torque. Almost loss generated by the stator such as water-cooled but also to achieve higher load stability.

 Users benefit from the direct drive, direct drive benefits are:
(1) As a result of fewer mechanical transmission components can save the plant construction cost and installation costs;
(2) direct synchronous motor, torque ripple is reduced, to better ensure the operational reliability of the machine;
(3) less mechanical transmission components and the province to the encoder makes the machine more reliable;
(4) As a result of fewer parts makes the system more simple, maintenance costs are also greatly reduced;
(5) lower energy consumption.

             A few years ago ABB company had called RSO consulting company in cooperation with a post-traditional direct drive gear replacement energy research, here to talk about the main part of the time of this study. Research of this issue is for a modern, high-capacity machine. Running cost savings are from the user‘s point of view to consider. Running cost savings included in the gearbox, couplings, accessories and spare parts and accessory system gear. Investment, construction work related to the building structure, also need to be counted. Owner‘s expense can be divided into running costs, maintenance costs and other costs arising. Direct transmission to the province gearbox, reduce the size of the base portion can also save floor space and drive. Influence of machine parts also part of the province to the capital plan. After the transformation of the gearbox can free up more space to place the new equipment. Factors affecting the machine, including ground equipment placement, configuration, electrical room and other electrical equipment, but also includes maintenance staff daily inspection channel, exhaust ventilation and other machines. Indirect benefit further comprising providing a larger workspace. Results of the study showed that the total expense savings is about the same size of a paper machine, 20% savings from the acquired 80% of the user‘s capital.

4、Fourth, the paper industry frequency transformation vision
    We are concerned about the new paper machine production capacity at the same time, we must also note that the transformation of an existing machine. Accounting for official statistics, China has more than 3780 tons production capacity, stand-alone production capacity of 100,000 tons production capacity of less than 50,000 tons, and more than one-third of the board machine, there are more than two-thirds of production capacity needs dropped heavily in the transformation, in which at least one third of the machine needs to replace some or all of the original transmission parts (including mechanical gearbox and motor drive), in order to improve speed or reduce energy consumption. Facts have proved papermaking enterprises is high energy consumption enterprises, according to the years of statistics, per ton of paper that can be in more than 500 degrees, power consumption is very serious power.
    During the next five years from about 40 to 600,000 KW pulp and paper equipment installed power needs dropped transformation. According to transform computing system 1KW / 1500RMB, it will have nearly 900 million about 6 to drive the market, because the country had involves the localization of the project, there will be a significant number of employed domestic inverter, so it will be made inverter can competing world market has great potential, which should attract enough attention.

        1, the drive frequency transformation machine section
         Paper production is a continuous process, so continuous and orderly control has become a constraint finished paper quality and yield of the production line bottlenecks. DC speed control system in the history of the paper machine plays an important role, but because of the existence of DC motor maintenance difficulties, poor resistance to environmental capacity, mainly as follows: 1. The commutator wear serious, burned commutator failure, causing long downtime; 2. DC motor repair more difficult, demanding, repair costs are high; 3 tachogenerator easy to wear, resulting in low transmission accuracy; 4. DC speed control system complex, difficult to debug, hard to tune out the general good mechanic machine.
    At present China‘s paper mill branch transmission equipment, previously used SCR DC speed mode, because of slip rings and carbon brushes cause reliability and accuracy is not high, resulting in a mechanical machine backward, the maximum speed is only 200m / min or so, it is difficult compared with overseas 1000m / min high-speed machine.
    Frequency transformation of paper machine drive has very good results, such as improved paper products, increase production capacity from the process, reduce energy consumption and extend the shutdown inspection cycle. For the production process characteristics of the sheet changing needs of variable frequency drive machine can be adjusted within a certain range to ensure the speed, and the speed of each segment can be adjusted individually.

          2, the frequency transformation papermaking ancillary equipment
          Paper machine auxiliary facilities include the following systems: systems for pulp, white water systems, vacuum systems, compressed air systems, chemicals preparation and delivery systems, water systems, steam systems. To make the paper can be continuously balanced operation of its ancillary facilities capacity should generally be more than 15% -30% of the largest paper machine production capacity.
    Where the application has not yet attracted enough attention, which is the most effective means and methods of progressive drive share.

             A, for the slurry system frequency applications
    Slurry supply system following several conditions must be met: (1) the slurry fed to the paper machine should be stable, the error should not exceed ± 5%; (2) the ratio of the concentration of the slurry to stabilize and uniform; (3) reserve certain the amount of the slurry so that the slurry supply capacity can be adjusted to accommodate changes in paper machine speed and variety; (4) the slurry purifying selection; (5) treatment of paper making machine each part broke.
    Under normal circumstances, the system for pulp slurry supply pipeline pump, fan pump and pressure screens purification facilities, Cleaner composition, to achieve the purpose of the above five points, the most important is to rush to pump and from pump It can run at full speed into a speed adjustment frequency operation, to meet the ultimate automation for pulp.

             Frequency application B, the compressed air system
    Compressed air is commonly used in pneumatic paper machine press section of a portion of the pressurized lifting devices, network blanket correction device, air cushion headbox, threading equipment, air knife coating, and various pneumatic and adjustment means, etc..
    Compressed air systems, major equipment air compressors, cylinders, valves, air filters, steam separator and safety valve, the pressure on the paper machine typically needs to be about 5-6BAR. In most of the mills, through two or more compressors in parallel, and then to keep the pressure constant by the gas tank.
    Since the compressor power and greater control pressure is generally adjusted by loading or unloading, the motor is always running at full speed. Practice shows that the control huge energy consumption, serious waste. So now it has been produced using a frequency tends to the frequency of multiple ways to control compressor, pressure and composition of the closed-loop.

             Frequency Applications C, chemical preparation and delivery system
    Because in deinking, pulp, coating, sizing and other parts to use a lot of chemicals, and the amount of paper machine using multiple drives proportional to the speed, so the chemical delivery system (pump) must be used AC stepless speed control system, which is the preferred drive. Mainly based on the chemical pump less power, generally in between 0.4KW-5.5KW, and this segment of the power inverter has been part of the best price-performance, electromagnetic governor many years ago is still widely used and variable speed gear pump have been phased out. According to the latest market statistics, the lowest power inverter moderate brand has fallen to a thousand dollars less.
    In the preparation of chemicals to use a lot of grinding equipment, such as a ball mill, a colloid mill, sand mill, high shear dispersion mixer or the like, their biggest feature is the high power, high energy consumption, harsh environments. There are already manufacturers in the grinding apparatus uses the frequency and achieved good results.
    In a sand mill, for example, its working principle is to be ground by the coating after the feed pump input barrel, rotating at high speed dispersion disk drive, the impact was strong grinding media, grinding and mixing is dispersed into a solvent prepare qualified paint, then by the top sieve outflow. The main motor of the device is 200KW, before the inverter is not used, usually in the early start, jog mode using multiple (three or more) to repeat the coating and grinding media mix; for different paint, sometimes different process speed, but in fact the only full-speed operation; can not grasp the feed rate to ensure that the main motor is not overloaded; energy consumption is very serious. 200KW inverter using a good solution to the above problem, you can easily set Jog speed and slow run time, make sure the paint is mixed with the media to achieve the most uniform; online stepless different species use different polishing rate ; as long as the feed rate from the actual operation of the motor current can be controlled since the feed rate, and there is an overload pre-warning function and avoid tripping function; energy-saving rate, generally up to 20%; reducing gearbox losses, avoid work start frequency impact on the gearbox; due to start, current gentle, to avoid the impact on the grid, improve the safe operation of the grid. Currently in Shandong, Heilongjiang, Hainan, and other paper companies have low-volume applications.

             Frequency applications D, ventilation systems
    Evaporated in the dryer section, the paper sheet after all the water vapor is absorbed by the air must be constantly removed from the machine room by forced ventilation. Dryer section ventilation is good or not, directly affect the economy of the sheet in the evaporation rate of water and the entire drying process;-ventilated, can reduce the saturation vapor in the air, thereby reducing the consumption of the dryer steam, bake progress dry speed.
    Exclude the amount of air drying the evaporation of water necessary, and discharged into the intake air temperature and humidity, but also with the use of the ventilation system, weather conditions and seasons. Typically, in a modern paper machine using forced air circulation in order to effectively use the intake air blower heated to about 80 degrees lower drying air into the dryer section, so that the hot gas is formed between the adsorption dryer upward air flow, and then out to the outside through an exhaust hood exhaust fan will bring together in the hot and humid air (final waste heat recovery). In the high-speed machine, due to an increase in the number of cylinders, they are usually divided into paragraphs and exhaust blower unit. After using the drive, according to the amount of air ventilation experts formula, always adjust the amount of intake air (blower speed) and displacement (exhaust fan speed), without using the traditional throttle control to further reduce energy consumption, reduce fan noise, mechanical life progress.

             Frequency Applications E, water system
    PM is a large water consumption, including white water systems, sewage systems, water sealing systems, sprinkler systems, water purification systems, etc., usually require the use of a constant-pressure water supply pipe network, but the traditional control pressure through bypass and a control valve to carry out, rarely used inverter. However, due to a general lack of water resources in China, and the application of the drive will be able to water by 10% and 30% energy saving, will inevitably reduce the mill‘s daily running costs.
    Inverter used on water systems typically have two modes: the fixed frequency mode, frequency cyclic manner.
    Frequency fixation: fixed frequency output of the inverter to control a pump while the remaining pumps are powered directly by the grid frequency, they start and stop signal from the PLC logic control.
    Frequency loop mode: Drive in a certain order in turn drive the pumps running. Drive according to the requirements of the pressure closed-loop control automatically determines the operation of the pump station number (within a set range), the same time there is only one pump is driven by a variable frequency drive. When the inverter driven pump operation to set the upper limit and the need to increase the frequency of the pump, the pump is switched to the inverter frequency operation, while driving another pump frequency operation.

        3, frequency transformation of the paper industry facilities
        Here it must be also mentioned in the paper industry and paper matching the frequency transformation as part of power plant and sewage treatment section.
        The amount of steam required to change according to the workshop, the amount of time the wind changes, and air volume control are implemented by adjusting the damper so that the air volume control mode not only reduces the efficiency of the fan, but also a lot of power consumption in the baffle, a great pity . And boiler control room is generally away from the drum, induced draft fan, control is very convenient, it is difficult to adjust properly. If the inverter is used for closed-loop variable speed, and can automatically adjust the amount of steam drum workshop according to a desired change, induced draft fan air flow, so that the boiler combustion in the best condition, the coal or oil consumption is reduced to a minimum, to achieve the desired energy saving effect.
    Electrical Equipment Sewage Treatment generally includes the following aspects: (1) biological treatment Series: microporous aeration system; (2) sludge treatment series: dosing system, thickener, belt filter press concentrated one machine, board frame filter press, horizontal spiral centrifuge, etc; (3) disinfection series: chlorination, ultraviolet water processor, ultraviolet disinfection bent like; (4) sludge equipment series: scraper, suction sand machines. From a practical point of view, basically each treatment will need to use the drive after application frequency or a significant improvement.

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