Výroba papiera

Frequency Conversion System for Packing Papers of Orient Paper, Inc.

I Overall Solution
The system is with the control method of PLC combined with inverters. Each drive point is with buttons for site speed regulation. The block diagram of the system is shown as Figure 6. The inverter is with SLANVERT SB70G series, and PLC is with S7-200 series. The whole system can provide the following functions:

(1) The drive points of each individual shall be able to start and stop separately and shall be adjustable for their speeds;
(2) The complete machine shall be sync speed increasing and decreasing;
(3) Speed regulation of one individual can result in a sync speed regulation at this individual and its subsequent individuals;
(4) The speed shall be automatically recovered as original operating speed after paper tensioning;
(5) The maximum design speed shall be adjustable according to production requirements;
(6) The system shall be with emergency stop function.

Figure 6 System Block Diagram

2.1 Control of Speed Chain
According to the paper machine and production process flow, papers on the paper machine prolong longitudinally at wet end due to traction action; papers continue to prolong longitudinally when the dry end starts; after the water content of papers reduces, such prolonging reduces; and when papers enter paper calendaring and reeling machines, they prolong once again due to traction. Therefore, in the whole production line of the paper machine, the speed of each individual is different so as to keep tension for paper web. Meantime, the speed of each individual of the paper machine shall be adjustable so as to avoid loose of paper web or breaking caused by tensioning, with speed regulating range of each individual: 10-15%.



Figure 7 Calculation and Control of Speed Chain

After transmitting the speed command of drive points to inverters, visit location register to determine the node number of the sub-register. If the node number is not “0”, conduct corresponding processing for this node until the whole chain is processed completely. After that, check the node number of brother registers and process another chain. Thus, it is only required to initialize the location register to form any branch speed chain. As shown in Figure 6, the first individual point of the paper machine is regarded as the main node of the speed chain, namely its speed determines the working speed of the whole paper machine, so regulation of its setting speed is to regulate the speed of the complete paper machine. For example, in PLC, if speed regulation signal is detected, then change speed unit value; the speed at “1” point is just the operating speed setting value of the first inverter, which is sent to the first inverter for execution and to the second for calculation. The speed value of the first individual is multiplied with the ratio of the second individual (b1×a) is the setting value of the second inverter. If the speed of the second individual cannot meet operating requirements, this means the ratio of the second individual is not suitable. You can regulate the ratio of the second individual (b1) to meet required operating requirements. This regulation is equivalent to be with a high-accuracy gear box in PLC so that any stepless speed regulation is available. During normal production, if the ratio is suitable and it is required for paper tensioning or releasing for some reasons, press appropriate buttons of this individual, and then PLC will add one positive or negative offset to appropriate speed chain to realize such paper tensioning or releasing functions. In the figure, the “2” point includes speed values for commands for speed regulating and paper tensioning and releasing etc., which are send to the second inverter for execution and to the next step for calculation at the same time. And so forth, the control system of speed chains is formed.

2.2 Reeling Tension Control
Tension control shall be used for the paper reeling part of the paper machine. If the paper machine has high production requirements for papers, the tension close-loop control can be added in the calendaring part. The tension control is with two methods available for selection: 1) the close-loop control with direct tension detection; 2) the close-loop control with indirect tension calculation and testing. The inverter for tension control shall be with SB70G series.

1. Close-loop Control with Direct Tension Detection
The SB70G module has two levels: one level for universal functional modules such as PID control, multi-step frequency, and automatic energy-saving operation etc.; another level for special functional modules such as location control, textile application, and constant-pressure water supply application etc. The SB70G also has rich programmable modules with complete functions and flexible programming, including: 1 two multi-function comparators that can define faults by themselves; 2 two logical units that can carry out calculations such as “and”, “or”, and “xor”; 3 two timers that can realize various time-delay functions; 4 one counter that can preset values and can save data after power off; 5 four arithmetical units that can add, subtract, multiply, and divide and can calculate absolute values.

Besides, SB70G also has built-in process PID with complete functions, which is essential in close-loop tension control. Details are shown below.

The input and feedback channels of PID have many categories for selection, and the feedback signals also can be set as many types of calculation results that are calculated from analog values. The PID can be preset and has two sets of parameters that can be switched over during operation. Users can freely carry out programming for resources of SB70G, not only able to use its programmable functional modules to coordinate with special functional modules, but also able to use these two types of modules to realize special functions for various industries. The programmable functional modules of the SB70G are like a group of jiasaw puzzles which can form numberless ideal patterns in users’ hand. This makes it be able to provide solutions platform and integration solutions for various industry requirements and thus it is very valuable for reduction of system cost and increasing of system reliability.

The control structure of the system is shown as below: the operating frequency of the master machine (four cylinders or calendaring inverter) is used as the main setting frequency for slave machines (calendaring machine or reeling inverter); the output of tension control PID regulator performs corrections for the main setting frequency so that there is no difference between the feedback tension and setting tension. The output signal from the tension sensor is used as PID feedback, and the PID setting is set as ideal tension value with numbers. The operating signals of the master machine are used as start/stop commands for slave machines.
The system diagram is shown as below:

2. Close-loop Control with Indirect Tension Calculation and Detection
Based on the operating frequency of the master machine (four cylinders or calendaring inverter) which represents the speed of the production line and on the real-time roll diameter of reeling papers, calculate the main setting frequency of corresponding slave machine (reeling machine), which shall be used as feedforward; while, the PID regulator shall be used to control PID tension output of papers; and the setting frequency shall be subject to continuous corrections, and the corrected frequency shall be used as setting frequency of the reeling motor. This compound control method integrating feedforward and feedback has a high control accuracy, and many inverters special for tension control use this method. The SB70G can realize this control through programming by programmable control modules, with convenient use and flexible methods. The control block diagram of the system is shown as below:

Tension Control System of SB70G Paper Reeling Machine

Note: in this diagram, D0 refers to the percentage of initial roll diameter, and the final roll diameter is regarded as 100%.
T0 refers to initial tension value, and the maximum tension of tension sensor is regarded as 100%.
K refers to tension taper parameter and shall be set by users within range of 0-100%.
The analog operating frequency (representing production line speed) of master machine shall be input through AI1.
Lap scoring signal shall be input through “Counter” with photo-electric switch.
The PID feedback value shall be input through AI2 from tension sensor.
The reset signal for roll diameter is added to preset an initial value as count value.
The following will explain this combined method by two parts.

Part I Calculation of setting frequency for reeling machine
Users need know three values: initial roll diameter, final roll diameter, and paper thickness. Based on the three values, calculate the following values required for parameter setting:
1. D0 (percentage of initial roll diameter)=Initial roll diameter/final roll diameter.
2. Setting value of counter =Final roll diameter/(paper thickness×2)
3. Preset value of counter =Initial roll diameter/(paper thickness×2)

Take the following example for explanation:
If the final roll diameter of papers is 1000mm, initial roll diameter of 100mm, and film thickness of 0.05mm, then:
Setting value of counter =1000/(0.05×2)=20000;
Preset value of counter = 100/(0.05×2)=2000.

At this moment, the count value of counter (with setting count value as 100%) is equivalent to an output signal of a roll-diameter sensor, i.e. real-time roll-diameter value D (with final roll diameter as 100%). The power-off memory of the counter realizes the power-off memory function for roll diameter, and its reset realizes the function that the roll diameter is reset to initial roll diameter.
Considering the frequency of master machine as F0, frequency of slave machine as F, and current roll diameter as D (with final roll diameter as 100%), we know:
It is able to calculate that: F=F0×(D0/D);
First, calculate the value of D0/D through arithmetic unit 3; and then calculate the value of F0 (i.e. AI1) through arithmetic unit 2, which is multiplied to the output of arithmetic unit 3 so as to get the value of F. At this moment, the result of arithmetic unit 2 is just the main setting frequency of the reeling machine, so the frequency setting channel for reeling machine is set as the setting of arithmetic unit 2. By this, the setting of main setting frequency of reeling machine is complete.

Part II Setting Calculation of PID
With the method of close-loop tension control, the setting value of PID shall be set as tension value required by users. The result of arithmetic unit 1 is just the real-time tension value required by users, and the setting channel of PID is set as the setting of arithmetic unit 1. By this, the setting of setting channel for PID is complete.

Arriving here, the design of tension control solution is complete. Besides, some external wiring and parameter setting required for control shall be done, including: the in-service signal of master machine is used as start signal of slave machine so that slave machine operates following with master machine; regulate relevant PID parameters based on actual situations to achieve best control effects.

The automatic control of each individual of the paper machine utilizes joint control of PLC and inverters, which is the development trend for design and transformation of paper-making drives. Its practicability, reliability, economy and intelligent can provide a high cost performance for users. After transformation, equipment has a higher automation degree, production process is more reliable and stable, and the energy saving of low-speed operation of inverters can bring significant economic benefits for users.


In control system, the speed sync of each individual is completed by PLC and inverters together. PLC is responsible for each individual and speed chain calculation. The inverters carry out speed instructions from PLC and complete fine speed regulation (including cascade and complete-machine fine speed regulation) by themselves.

The speed chain of inverters is with binary tree data structure to carry out data transmission functions. First, perform mathematical abstract for all drive points to determine a number for each drive point in the speed chain, and the number shall be consistent with the internal address of the inverter. Then, determine the upper and lower as well as left or right numbers for each node point according to the binary tree data structure. That is to say, the location of any drive point in the speed chain shall be decided by three data, and then fill the location in the location register. It is shown as Figure 7.


Application of SB80 SLANVERT Inverter in Drive System for Paper Machine

In this case, the SLANVERT series inverters and Siemens S7-200 PLC are combined to form a set of control system for cultural paper machines. Through communications between PLC and inverters, control such operations as start, stop, speed increasing, speed decreasing, and paper tensioning. The functions such as load distribution and speed chain are achieved automatically by software so as to fully meet requirements of process and electrical control.

1. Requirements of Paper Machine for Electrical Drive Control System
1.1 The structure sketch of the paper machine is shown as Figure 4. It is 1760/250m/min long-mesh multi-cylinder cultural paper machine, producing 40-65g/m2 senior cultural papers, with stable-state accuracy of ≤0.01%.

Figure 4 Structure Sketch

1.2 In order to produce high quality products, the paper machine has the following requirements for the electrical drive system:
(1) The working speed of the paper machine shall have big regulation range of 1:8.
(2) The speed shall have higher stability margin, and the overall speed shall be increased and decreased stably. It is required the accuracy of paper machine at stable speed shall be: ±0.05-0.01%.
(3) The speed difference shall be controllable, and the speed ratio shall be adjustable and stable. The change of speed difference within certain range shall not cause sudden change of paper quality, and the error rate shall be controlled within 0.1%. The speed of each individual of the paper machine shall be adjustable at a range of ±10-15%.
(4) The drive points of all individuals have following functions: slight increasing and decreasing of speed; separate and interlocked action among these individuals; and simultaneous start and stop.
(5) The paper machine has property of constant torque loads, so the inverter with constant-torque control property, high resolution ratio, and good communication capability shall be selected.

2. Composition of Control System
The system principle is shown as Figure 5. For the drive system of this paper machine, the S7-200 small-size PLC is used as the control center of the system; SLANVERT SB80 series inverter is used as drive unit, with resolution ratio of frequency at over 0.01Hz; special frequency-conversion motor serves as execution unit; Omron PLC serves to provide speed feedback signal to let the drive of the paper machine operate in close-loop of the speed, with accuracy at stable speed: up to 0.01%. The PLC, via MODUBUS protocol and RS485 network, together with inverters, achieves the following functions: speed chain function, speed difference control, load distribution function, increasing and decreasing of overall speed and that of all individuals, as well as paper tensioning and releasing functions etc., which ideally satisfy requirements for normal work of the paper machine.

Figure 5 System Principle Diagram

3. Design of Speed Chain and Control of Speed Difference
The speed chain is with binary tree data structure to carry out data transmission functions. First, perform mathematical abstract for locations of all drive points to determine a number for each drive point in the speed chain, and the number shall be consistent with the internal address of the inverter. Then, determine the upper and lower as well as left or right numbers for each node point according to the binary tree data structure. That is to say, the location of any drive point in the speed chain is decided by three data. After filling it in the location register and transmitting the speed of drive points to inverters, visit location register to determine the node number of the sub-register. If the node number is not “0”, conduct corresponding processing for this node until the whole chain is processed completely. After that, check the node number of brother registers and process another chain.

4. Design of Load Distribution
The drive structure of the paper machine has flexibly connected drive points, drying-cylinder part, and pressing part. Between these parts is required not only speed sync, but balance of load rate, or else over-current of one drive point may be caused by overload, and over-voltage of another drive point may be caused by such driving, which will influence normal papermaking, even may tear coarse cotton cloth and damage inverters and machines. Therefore, it is required to automatically control the load distribution among drive points between two drive parts.


RS-485 Based Network Realizes Multi-motor Control for SB61 Inverters by PLC

I General
The multi-motor and multi-individual drive of the paper machine requires stable speed and no breaking of papers, and acceptable pulp consistency, with rated deviation within fluctuating range meeting standards, generally acceptable range of fluctuation: ±1%-±10%. During paper making, paper wed extends longitudinally and contracts transversally as wite section and pressing; and both directions contract as drying. The speed ratio between individuals shall be regulated based on above described change laws during production. However, during production, the stable speed ratio is required, frequent individuals shall track and change their speed automatically along with frequent individuals, and timely correction of deviation shall be done to keep speed ratio change range of no more than ±3%. The paper-making production line with many drive points, on the one hand, has many motors required to be controlled, and on the other hand, is with motors distributed in a far distance. Therefore, the attenuation and transmission of the speed chain in long-distance transmission is easy to be disturbed to reduce reliability and stability of the system and even break down. The RS485 communication control network, consisting of PLC and inverters, has advantages such as long transmission distance of signals, strong capacity of resisting disturbance, and low cost. It is especially fit for multi-motor control system for paper-making production line.

II Composition of Electrical Drive System
SLANVERT SB61G series inverters use speed-sensorless vector control algorithm, with high speed regulating accuracy. But the setting of inverters is with speed-sensor vector control manner, with motor accuracy at stable speed: ≤±0.25%, which absolutely can meet requirements for low-speed paper machine with speed lower than 200m/min. Besides, SB61G series inverters have RS485 serial communication interfaces, which is convenient for networking with PLC. In regard to PLC, the OMRON is selected to be used for compact CQM1H under distributed control. The RS485 interface of SB61G inverters is connected with CQM1-SCB41 serial communication module so as to control inverters via communications with PLC. In order to facilitate operation and monitoring, another interface RS232C is connected with computers (or HMI) through CQM1H-SB41 to prepare process flow chart and establish real-time database, history database, real-time curves, and history curves and others on the MCGS platform. By this, the process flow chart, history data, alarming data, and operating parameters of inverters at each individual part of the paper machine can be visually displayed on computers so as to facilitate monitoring for production process by yield workers. Some modifications for process parameters can be conducted based on site conditions, for example, fine regulation for speeds at each individual part of the paper machine.
The system structure is shown in Figure 3.

Figure 3 System Structure

The speed of the paper machine has reached 180m/min, while the speed under site operating is generally about 200m/min, and the paper web has a wide width, so the accuracy requirement for electrical drive at stable speed is high. Therefore, the E6B2-CWZ3E 600p/r pulse coder is used to form speed measurement feedback. The SB61 has had an interface for three-phase pulse coder, not requiring addition of PG card. Thus it is convenient to form a close-loop feedback with a pulse coder to stabilize the speed of each individual part and to ensure operating accuracy of the paper machine.

III Complete Machine's Speed Chain, Fine Adjustment, and Crawling etc.
The overall speed of the paper machine is set with IPC (Industrial Personal Computer), and the speed for drive point of each individual part is stored in program control of PLC in proportion; there is fine regulation in each individual with adjusting range of ±10% of the max speed; in any case, each individual can carry out separate/interlocked operation to realize separate operating/crawling and start/stop.


Transformation of AC Individual Drive Paper Machine

For a corrugating machine of a company, its AC individual drive has 7 driving points, and the powers of its AC motors are respectively as follows: 18.5kW for three, 22kW for two, 30kW for one and 37kW for one. The original drive of the machine is electromagnetic variable-speed motor, which is easy for electromagnetic speed regulation and has a low price, but it has a low stability and efficiency.

In order to improve performance of the paper machine and for energy saving, a transformation of frequency conversion and speed regulation is carried out for it. Due to the low speed of the paper machine, the SB61G series inverter with open-loop control can meet requirements of production process. The speed chain is with master/slave control mode, namely, the wite section is used as main setting, with subsequent pressing tracking the speed of the main controller, drying tracking the speed of pressing, and reeling tracking the speed of drying. The frequency conversion control system of the paper machine is shown in Figure 1.

Figure 1 Frequency Conversion Control System of Paper Machine

In this case, the output terminals y1 and y2 of inverters output 4-20mA signals, which serve as next-stage speed signal and can be subject to fine regulation by the potentionmeter. Regulation of one stage will change subsequent speed after this stage, so this will not cause change of subsequent speed ratio and new out-sync.

For the inverter, it is not required to add any sync controller at the peripheral of the production of the paper machine. It is easy to realize sync speed regulation, with few faults and convenient use. Transformation of frequency conversion removes electromagnetic speed regulation with low-efficiency and brings significant energy-saving benefits, wining high praises from users.


Transformation of Frequency Conversion and Speed Regulation for Line Shaft Drive Paper Machine

A company produces cultural papers with paper machine of 1760/110/min, line shaft drive, Z2 series DC motor, power of 75kW, and n=750r/min. However, its silicon controlled speed regulating board fails usually and influences normal operation of production, so it is prepared to change DC speed regulation as AC speed regulation to reduce shutdown working hours. At the same time, it is required to raise speed to 150m/min to improve working efficiency.

First, calculate the motor power required for the speed of 150m/min, considering the paper machine is constant torque loading and the motor power increases in proportion to the increasing of the speed, thus:


That is,


Therefore, the 110kW AC motor shall be selected.
Then, calculate the rotating speed of the motor at 150m/min, as follows:


Therefore, the 6-phase AC asynchronous squirrel cage motor with rated rotating speed of 960r/min shall be selected. When the inverter operates at 55Hz, motor rotating speed is 1050r/min, and when the machine speed is 150m/min, the motor rotating speed is 1023r/min. This can meet requirements. However, operating of the inverter at over 50Hz is constant power operation, so the torque has certain reduction. But considering certain margin is provided in design of the paper machine, such reduction of the torque will not influence operation of the paper machine. The weak magnetic point of the inverter also can be adjusted as 60Hz, and thus the inverter has constant torque property in the total range of 0-60Hz, but the low-speed torque reduces slightly.

The SB70G132KW SLANVERT Inverter, together with air switch, quick fuse, and other low voltage devices, shall be installed in a 2200×800×600-sized control cabinet. Beside the paper machine has a remote control box, where there are start/stop buttons, frequency regulating potentionmeter, digital speed display, inverter fault display and so on.

In this case, through frequency conversion transformation, the speed of the 1760/110/min paper machine increases from 110m/min to 150m/min, and its yield increases from 10t/d to 13.5t/d, obtaining obvious economic benefits. This is a typical case that utilizes inverters to improve working efficiency, but the machine has certain limits on increasing of the speed. If the speed is over 150m/min, you can feel the paper machine has some obvious vibration. Therefore, in order to ensure safety of equipment, the upper limit frequency of inverters shall be set as 55Hz, and it shall be limited to regulate the speed to over 150m/min by workers.


Application of SLANVERT Inverter in Paper-making Auxiliaries

In pulp and paper production, the maximum production capacity depends on the capacity of paper-making machines. Auxiliaries (various machines such as pulper, mill, pulp pump, fan etc. and their drive motors) are configured based on situations of the master machine, and certain margin is considered in design process. Therefore, regulation is required for many pulp pumps during actual operation. Throttling is traditional flow regulating manner and has problems of slow response, low-accuracy, and big energy consumption etc. The inverter featuring good regulating performance, good energy-saving effect, and other factors has been applied to flow and speed regulation in pulp and paper making factories.

I Process Flow of Waste Paper Pulping
1. Pulping of Waste Papers
As paper-making industry, waste papers used by pulp manufacturers are sourced from the following three categories: broke paper from paper factories; waste paper before using, such as printing and cutting wastes; and waste paper after using, mainly including those recycled from families and shops. The first two categories are clean and have good quality, but have a small quantity and are costly. The third category is big-quantity and stable source of waste papers, but they contain a large number of impurities, which have to be removed so as not to influence product quality for use.

Pulping is generally classified into two types of low consistency and high consistency. After pulping by low-consistency hydropulper, the pulping task will be further completed by a deflaker. The deflaker is comprised of high-speed rotating disc and fixed disc and it fiberizes the paper pulp depending on high-frequency hydro turbulent flows generated between fluted discs. The high-consistency hydropulper has an auger-bit shaped rotor. During high-consistency pulping, the inter-friction among pulp is intensified so as to shorten pulping time and reduce energy consumption. It is difficult to break up impurities such as plastic pieces and wet strength papers, which can be removed in frequent screening procedures. It is also benefit for deinking and reducing consumption of chemicals.

2. Purification and Screening
Purification and screening are two methods of removing impurities in waste papers and have different impurity-removal principles. The purpose of purification is to remove light-heavy impurities in waste paper pulp after fiberizing, and it separates impurities from pulp because they have different densities. Pulp under a certain pressure enters conical cylinder along tangential direction and generates a centrifugal force by rotating in the cylinder so that materials with big-density are thrown onto the cylinder wall and slide down along the wall to the bottom before discharging. At the axle center of the cylinder, a low pressure area is formed because of the action of centrifugal force. This area is a negative-pressure zone, where materials with low-density ascend along the center and are discharged from the top. Normal equipment for use includes high-consistency cleaner, low-consistency cleaner, and reverse cleaner etc. The high-consistency cleaner is mainly used to purify impurities with high density and big grain size in waste paper pulp, such as metal foreign substances, small stones, paper fasteners etc. with pulp density of about 5%. The low-consistency cleaner is used to remove impurities with high density and small grain size in pulp, such as mud, sand, and coal ash etc. with pulp density of about 0.5%. Reverse cleaner is used to remove impurities with a density lower than fiber, such as plastic piece, wax, and asphalt etc. Its principle is the same as general cleaners but it has a reverse use method because its pulp is discharged from the bottom and impurities discharged form the top. The impurities in pulp which have a density close to fiber can be removed by screening, for which the pressurized screen is a normal device.

3. Deinking
Deinking is for removing printing ink in waste papers. The previously described purification and screening processes cannot complete deinking, which requires special technology. The deinking process is used to remove ink in waste papers and to enhance whiteness of pulp. The modern waste-paper deinking methods include washing method and flotation method. Deinking of waste papers is a combination process of mechanical and chemical actions, and it mainly includes two key procedures.

(1) Separation of Ink from Fiber
Under joint actions of machines and chemicals, waste papers are dispersed as pulp and the ink is separated from fiber at the same time. Normally, deinking is carried out under alkaline conditions, and chemicals to be used include NaOH, Na2SiO3, H2O2, and surface active agent etc. Normally used pulper equipment is high-consistency hydropulper. Compared with low-consistency pulper, it is easy to separate ink from fiber and to disperse ink grains into smaller ones, so it has a shorter pulping time and less energy consumption. Its pulping conditions are as follows: temperature of 55-90℃, pH value of 9-11, pulp consistency of 8-16%, and pulping time of no less than 1h.

(2) Removal of Ink from Pulp
This process is the core part of deinking technology, and its two basic methods are washing method and flotation method. Washing method is the earliest method used in deinking. It uses a large amount of water to wash pulp materials repeatedly to wash away ink in the pulp, and the filtered waste water can be recycled after clarification treatment. Washing method is fit for removing ink grains of smaller than 10Lm, so the surface active agent with disperse action is required to be added during pulping process to remain sufficiently small ink grain size and hydrophily. After through repeated dilution and concentration, the dispersed ink is removed. Flotation method is an emerging deinking method that is developed in current decades. It is to add flotation agent in pulp to generate foam adsorbing ink grains, and the foam emerges from the water before it is removed. Flotation method is fit for the ink with grain size range of 10-100Lm. In order to let ink grains reach this range, the collection agent is used to change ink grains into those with better hydrophobicity. Then, they will be removed from a flotation tank together with foam. The two methods have different principles and advantages. At present, in order to adapt to different types of waste papers, the two methods are usually used in a combined manner, namely the process of first flotation and then washing.

4. Present Pulping Method of Pulp and Paper Industry
Currently, the simplest method used for pulping is as follows: first, add in waste papers and water and pulp them for a specified period, directly add in chemicals such as rosin size and aluminum sulfate into hydropulper to complete sizing process, and then carry out molding and drying. The advantage of this method is low equipment investment, but its disadvantages include: poor adaptability of raw materials, for which only relatively clean and simplex waste papers can be used, such as leftover bits and pieces used to produce corrugated cases, and waste paper edges in printing industry; high energy consumption; strong equipment corrosion because normal sizing processes are carried out under acid conditions.

Conveying of pulp in pipes requires driving of pulp pump, so the fan pump is widely used in high-speed paper machine enclosed pulp supply system. According to speed control principle of paper-making process, a pressure transmitter can be increased to realize the technology of frequency conversion and transformation for PID-controlled fan pulp. The practice has proved, installation of frequency conversion and control system can adapt to different speeds and changes of use amount of different varieties so that the fan pump always operates at high-efficiency state and so the process conditions are greatly stabilized. Replace valves with inverters to regulate pulp flow so as to reduce energy consumption of fan pump and achieve an energy-saving rate of over 30%.

II Application of SLANVERT Inverter in Paper-making Auxiliaries
Paper machines refer to those product papers through wite section, pressing, drying, and reeling for pulp, while the auxiliaries for meeting production conditions of the paper machines, such as vacuum pump, pulper, fiberizer, mixer, and transfer pump, are called paper-making auxiliaries. Their design provides certain margins, so these auxiliaries such as vacuum pump, pulper, fiberizer, and mixer basically have no regulating means during operation, and motors operate at the frequency of 50Hz in any case. In fact, production conditions may have changes sometimes, so, if inverters are utilized to properly regulate the operating frequency of the motors for these auxiliaries such as vacuum pump, pulper, fiberizer, and mixer, certain energy-saving effects can be achieved. The transfer pump has regulating means, but they all belong to throttling regulating such as valves, which make a bigger damping in output pipe network and result in waste of electricity. If the inverter is installed, it can regulate the rotating speed of the transfer pump based on actually required pulp amount and can save a large amount of electricity because the output power of the centrifugal pump is in proportion to the third power of the rotating speed.

There are many auxiliaries at the paper-making production line, which basically all require frequency conversion and speed regulation for energy saving. The practices prove, paper-making auxiliaries after being implemented with frequency conversion and speed regulation bring an average energy-saving of 12% and the economic benefits are obvious. A paper-making factory of Fuyang, Zhejiang, has the following auxiliaries at its production line:


Equipment Name Quantity (set) Power (kW) Inverter Model Remarks
1# Hydropulper 1 220 SB61G220  
1# Fine Screen 1 160 SB61G160  
2#Hydropulper 1 160 SB61G160  
2#Impurities Separator 1 45 SB61G45  
1#Unloading Pump 1 30 SB61P30  
1#Coarse-screen Pulp Feeding Pump 1 55 SB61P55  
1#Coarse-screen Pulp Feeding Pump 1 30 SB61P30  
2#Coarse-screen Pulp Feeding Pump 1 55 SB61P55  
2#Coarse-screen Pulp Feeding Pump 1 30 SB61P30  
Desander Pulp Feeding Pump  1 90 SB61P90  
Mixer 11 18.5 SB61G18.5  
1# Pulp Chest Mixer 1 18.5 SB61G18.5  
Coarse-screen Accepted Pulp Mixer 1 18.5 SB61G18.5  
Sand-reduction Accepted Pulp Pump 1 18.5 SB61P18.5  
3# Fine Screen Pulp Feeding Pump  1 18.5 SB61P18.5  
Desander Pulp Feeding Pump  1 45 SB61P45  
1# Fine Screen 1 30 SB61G30  
Classifier 1 75 SB61G75  
Classifier Pulp Feeding Machine 1 18.5 SB61G18.5  
Double Disc Refiner 1 132 SB61G132  

The SLANVERT Inverter with appropriate power is selected for energy-saving transformation, and by measuring, this can bring an average energy-saving amount by 12.4%, and the rate of return on investment is 1.8 years, achieving good economic benefits.