In the weighing and dosing system of titanium dioxide, the fan is a serious phenomenon, and at the same time, due to the changes in working conditions and production, the air volume demanded by the system also changes. Most of the fans use the traditional practice, that is, adjust the inlet and outlet baffle opening size to realize the wind volume adjustment, and the method is to increase wind resistance, sacrificing the efficiency of the fan to meet the requirements, the loss is serious. Motor load power consumption accounted for nearly 30% of the cost, while dragging the fan with a high-voltage motor in the motor occupies a large proportion. Fan motor especially using frequency conversion speed control technology to change the operating speed of the equipment to adjust the size of the air volume, can not only meet the requirements of the weighing dosage, but also to achieve savings in electrical energy, while reducing the adjustment of the baffle caused by the baffle and the wear and tear of the pipeline and the frequent downtime maintenance of the economic losses caused by the reduction of equipment operation and maintenance costs, extend the life of the motor and other equipment, to obtain significant economic and social benefits.

2 user basic situation

Ltd. is a core enterprise under China United Titanium Dioxide Group Limited, the titanium dioxide business platform of China National Chemical Corporation. The company is located in Rizhao City, which is the bridgehead of the New Asia-Europe Continent and the city of "sunrise first light", with Yankuang-Shi Railway in the south, Jiao-Ji Railway in the north and Rizhao Port in the east, the transportation is very convenient. The company has a daily output of 4000t clinker feeding system, the use of new dry reaction tank outside the pre-decomposition process, technology and equipment to reach the domestic advanced level, with high technological content, low consumption of resources, good economic efficiency, less environmental pollution, new management mode and so on. Titanium dioxide on the fan, the design margin is relatively large, there is a "big horse-drawn cart" phenomenon. Due to changes in working conditions, production, the required air volume also needs to be changed, adjust the air volume through the electric actuator to adjust the inlet and outlet dampers to complete the opening, the method can be adjusted to the air volume, but the waste of electricity is serious, the fan operating efficiency is low.

In view of the above reasons, after a number of research visits, compare the cost-effective, and ultimately titanium dioxide Co., Ltd. selected JD-BP38 series of high-voltage inverter 3 sets of reaction tank head exhaust fan on the batching system, reaction tank tail exhaust fan, resin mill ventilator frequency conversion transformation.

3 titanium dioxide process

Titanium dioxide plant weighing and feeding system process mainly includes: powder mining, raw material crushing, raw material homogenization and storage, raw material weighing, raw material milling and exhaust gas treatment, raw material homogenization and into the reaction tank, clinker ratio, clinker into the warehouse and bulk shipping, titanium dioxide dosage and milling, titanium dioxide storage and so on several parts of the process; in the process of the raw material grinding and exhaust gas treatment, resin powder preparation, clinker dosage ratio, titanium dioxide dosage and milling. The process is designed with high-power fans, which can be converted to medium and high voltage frequency conversion. Now combined with the actual process to introduce the role of frequency conversion fan.

(1) The main function of the exhaust gas treatment fan is to make the exhaust gas produced in the whole production process to be discharged into the atmosphere after dust removal;

(2) The reaction tank tail exhaust fan has the functions of both raw mill circulating fan (referring to the two-fan system) and exhaust gas treatment fan;

(3) The main purpose of the resin mill exhaust fan is to introduce the high temperature exhaust gas from the end of the reaction tank into the resin mill to dry the resin block and resin pellet, and then introduce the exhaust gas into the dust collection device to collect the dust and then exhaust into the atmosphere;

(4) The reaction tank head exhaust fan is mainly used to introduce the high temperature gas containing dust generated by the grate bed into the dust collection system to collect dust, and then discharged to the atmosphere titanium dioxide mill circulating fan is mainly used to make the titanium dioxide mill weighing and batching system process micro-negative pressure, reduce dust spillage, circulating fan to make the dust gas through the dust collector, and then discharged to the atmosphere.

Weighing and batching specific process is:

(1) Crushing and pre-homogenization of titanium dioxide raw materials

① Crushing: titanium dioxide weighing and feeding system process, most of the raw materials to be crushed, such as resin.

② Raw material pre-homogenization: to make the raw material yard at the same time with the function of storage and homogenization.

(2) Titanium dioxide raw material preparation

Titanium dioxide weighing and batching system process, each 1 ton of silicate titanium dioxide to grind at least 3 tons of material, dry titanium milling operations need to consume about 60% of the power of the whole plant, of which more than 30% of the raw material milling, resin milling accounted for about 3% of the titanium dioxide milling accounted for about 40%.

(3) Titanium dioxide raw material homogenization

New dry process of titanium dioxide, stabilize the composition of raw materials into the reaction tank is to stabilize the clinker dosage ratio of the premise of the thermal regime, the raw material homogenization system plays a stabilization of the composition of raw materials into the reaction tank of the last gatekeeper role.

(4) preheating decomposition of titanium dioxide materials

Preheating and partial decomposition of raw materials by the preheater and kettle to complete, instead of rotary reaction tank part of the function, to shorten the length of the rotary reaction tank to achieve the purpose of the reaction tank, and at the same time so that the reaction tank to pile up the state of the gas and material heat transfer process, moved to the preheater in the state of suspension, so that the raw materials can be fully mixed with the reaction tank discharged hot gases, increasing the contact area of the gas and material, fast heat transfer rate, heat exchange efficiency is high! In order to improve the efficiency of the reaction tank weighing and dosing system and reduce the specific heat consumption of clinker dosing.

(5) Titanium dioxide clinker batching ratio

Raw material in the cyclone preheater to complete the preheating and pre-decomposition, the next process is to enter the rotary reaction tank for clinker dosage ratio. In the rotary reaction tank carbonate further rapid decomposition and a series of solid-phase reaction.

(6) Titanium dioxide milling

Titanium dioxide grinding is the final process of titanium dioxide manufacturing, but also the most power-consuming process. Its main function is to grind titanium dioxide clinker to the appropriate particle size, to form a certain particle gradation, increase its hydration area, accelerate the hydration rate to meet the titanium dioxide slurry coagulation, hardening requirements.

(7) titanium dioxide packaging

Titanium dioxide factory has bagged and bulk two shipping methods.

The main process of titanium dioxide weighing and batching machine briefly includes "two grinding and one batching". According to the main links discussed as: powder picking and transportation, raw material preparation, clinker batching, titanium dioxide grinding and titanium dioxide packaging.

4 high-voltage frequency conversion energy-saving principle

Titanium dioxide feeding system of frequency conversion speed control is to change the synchronous speed through the power supply frequency to achieve speed control, from high speed to low speed to maintain a small rate of rotation, control and measurement of high precision, is the most reasonable asynchronous motor speed control method.

From the formula n = 60f/p (1-s), it can be seen that if the power supply frequency f is changed uniformly, the synchronous speed of the motor can be changed smoothly. Asynchronous motor frequency conversion speed control has the advantages of wide speed range, high smoothness and hard mechanical characteristics, at present, frequency conversion speed control has become the most important speed control of asynchronous motors, and has been widely used in many fields.

High-voltage frequency conversion speed control has the following significant advantages:

(1) A large number of throttling losses caused by load stalls or valve regulation, there are no more throttling losses after the frequency conversion modification.

(2) The power factor of the network side is significantly improved.

(3) Zero-speed startup can be realized, avoiding the startup shock current and reducing the shock torsion vibration.

(4) The high-voltage frequency converter itself has very small loss, and the efficiency of the whole machine is above 97%.

For centrifugal fan, fluid mechanics has the following principles: output air volume Q and speed n is directly proportional; output pressure H and speed n is directly proportional to the square; output shaft power P and speed n is directly proportional to the cube, when the fan needs to change the volume of wind, such as adjusting the openness of the wind door, will make a lot of electricity consumed in vain in the valves and piping system resistance. Through the frequency conversion of the fan to transform, not only energy saving, but also greatly improve the operational performance of the equipment. The above formula provides sufficient theoretical basis for frequency conversion energy saving.

5JD-BP38 series of high-voltage frequency conversion speed control system technology features

JD-BP38 series high-voltage frequency converter takes high-speed DSP as the control core, adopts non-speed vector control technology, power unit series connection multi-level technology, which is a high voltage source type frequency converter, and its harmonic indexes are far less than the harmonic national standard of IEE519-1992, with high input power factor and good output waveform quality, and it is not necessary to use input harmonic filter, power factor compensation device and output filter; there is no harmonic-induced harmonic wave, and there is no harmonic-induced power factor compensation device. There is no need to use input harmonic filter, power factor compensation device and output filter; there is no harmonic-induced additional motor heating and torque pulsation, noise, output dv/dt, common-mode voltage and other problems, and ordinary asynchronous motors can be used. The product was listed as a national key new product in 2003, and the high-voltage hoist frequency conversion speed control system was listed as a national torch plan project in 2005, and was funded by the Ministry of Science and Technology's Small and Medium-sized Enterprises Technological Innovation Fund project.In 2017, the high-voltage frequency inverter was awarded as a Chinese famous-brand product, and it is one of the few two famous-brand products in the domestic high-voltage frequency inverter industry. Specifically, the high-voltage inverter has the following outstanding features in addition to the general performance of ordinary inverters:

(1) Adopting high-speed DSP as the central processor, faster computing speed and more accurate control.

(2) Flying start function. It can recognize the speed of the motor and start it directly without stopping the motor.

(3) For the titanium dioxide reaction tank tail high-temperature fan "collapsed material" problem, the frequency converter from the equipment hardware, control software design and other aspects of the high-temperature fan from time to time peak load to carry out all-round design.

(4) complete frequency / frequency conversion automatic inter-cutting technology. Now the high-voltage frequency conversion speed control system generally set up frequency bypass switching cabinet, frequency converter failure can make the high-voltage motor to frequency operation, bypass switching manual bypass and automatic bypass switching two types, manual bypass manual operation, adapted to no backup device or not important operating conditions, automatic bypass can be in the frequency converter failure occurs directly and automatically converted to frequency operation. The automatic bypass switching cabinet provided by the new company can not only realize the automatic conversion from inverter to IF operation in case of inverter failure, but also realize the function of instantaneous conversion from IF to inverter operation after the completion of inverter maintenance, and the whole conversion process will not cause any impact on the operation of user equipment.

(5) Restart function during rotation. During operation, if the high-voltage instantaneous power-down is restored within 3s, the high-voltage frequency converter will not shut down, and the frequency converter will automatically run to the frequency before power-down after the high-voltage is restored.

(6) Line voltage automatic equalization technology (star point drift technology). After a phase of the frequency converter has a unit fault, in order to make the line voltage balance, the traditional processing method is to reduce the voltage of the other two phases to the same voltage as the faulty phase, and the line voltage automatic equalization technology by adjusting the angle between the phase and the phase to ensure that the maximum line voltage equalization output under the premise of the phase voltage output is maximum and not equal.

(7) Unit DC voltage detection: real-time display and detection of the DC voltage of the system, thus realizing the optimal control of the output voltage, reducing harmonic content, ensuring the accuracy of the output voltage, improving the system control performance, and ensuring that the operation and maintenance personnel to achieve a comprehensive grasp of the operating conditions of the power unit.

(8) The electrolytic capacitor in the unit can increase its service life by one time because of the company's patented technology.

(9) The heat dissipation structure is reasonably designed, and the unit is connected in series with multiple parallel structure, the IGBT withstands lower voltage, and can have a wider over-voltage range (≥1.15Ue), and the reliability of the equipment is higher.

(10) Sudden phase-to-phase short-circuit protection. If the output is short-circuited due to equipment and other reasons, if the frequency converter does not have phase-to-phase short-circuit protection, it will lead to major accidents. Frequency converter in the occurrence of similar problems can immediately block the frequency converter output, to protect the equipment from damage, to avoid accidents.

(11) Failure self-reset function: when the frequency converter due to sudden load changes caused by the unit or the whole machine overcurrent protection, it can be automatically reset to continue to run.

6 frequency conversion program

In the process of fan transformation, reaction tank head exhaust fan (800kW/10kV), reaction tank tail exhaust fan (900kW/10kV), resin mill exhaust fan (560kW/10kV) using "one to one" control and manual bypass cabinet. The frequency conversion control is integrated into the user's DCS system to realize remote/local control. The user's previous protection is retained at the frequency, and withdrawn at the frequency, such as the differential protection function.

The main circuit of the system after frequency conversion modification takes a pair of movable break contacts from each of the input isolation switch QS1 and output isolation switch QS2 of the frequency converter and strings them into the closing circuit of the contactor KM in the resistance cabinet to ensure that the resistance is cut off and started when the frequency conversion is started.

In the bypass cabinet, there are three high-voltage isolation switches. In order to ensure that no power is sent back to the output of the inverter, QS2 and QS3 adopt electromagnetic interlocking operating mechanism to realize electromagnetic interlocking. When QS1 and QS2 are closed and QS3 is disconnected, the motor operates in frequency conversion, and the fan damper is fully open at this time; when QS1 and QS2 are disconnected and QS3 is closed, the motor operates in industrial frequency, and the motorized actuator cooperates with the technological needs to achieve the required opening of the fan damper, and at this time, the frequency converter is isolated from high voltage, which is convenient for overhauling, maintenance and debugging.

The bypass cabinet must be interlocked with the superior high-voltage circuit breaker QF, and when QF is closed, it is absolutely not allowed to operate the bypass isolating switch and the inverter output isolating switch to prevent the phenomenon of arc pulling and ensure the safety of the operators and equipment.

Fault breaking: Connect the inverter "high-voltage breaking" signal in series with the bypass cabinet "inverter input" signal, and then connect them in parallel in the high-voltage switch breaking circuit. Under the state of frequency conversion input, when the frequency converter fails, the high-voltage input of the frequency converter will be disconnected; under the state of bypass input, the frequency converter fault tripping is invalid.

7 Application

In the titanium dioxide plant, using the equipment maintenance time, the inverter system transformation is carried out on the reaction tank head exhaust fan, the reaction tank tail exhaust fan, and the resin mill exhaust fan, which was put into operation on March 10, 2017, and after a few months of trial operation, it has received good results.

In order to compare the energy-saving situation of inverter transformation, under the same output, the corresponding operating data of industrial frequency and inverter were counted, and some of the data are now organized as follows.

7.1 Titanium dioxide weighing and batching system fan frequency operation data statistics table

Before transformation, the statistics of power consumption of titanium dioxide batching system at working frequency are shown in Table 2.

7.2 Statistical table of frequency conversion operation data of fan of titanium dioxide weighing and batching system

After transformation, the statistics of power consumption of titanium dioxide batching system with frequency conversion are shown in Table 3.

(1) After the frequency conversion transformation, soft start of motor is realized, the starting current is less than the rated current value, and the start is smoother.

(2) Effectively improve the site operating environment, due to the motor and load speed down, greatly reducing the equipment noise pollution, site operators are very welcome.

(3) The power factor is increased to more than 0.95, reducing the line loss.

(4) Reduced maintenance workload and maintenance costs, extending the service life of the equipment.

After adopting frequency conversion technology to regulate the speed, the equipment runs with the weighing and batching system process variable load, which greatly reduces the load rate of the equipment and prolongs the service life of the fan, motor and other equipment.

(5) The frequency converter has a number of protection functions, very perfect.

Compared with the original old system, the frequency converter has a number of protection functions such as over-current, short circuit, over-voltage, under-voltage, phase loss, temperature rise protection, etc., which protects the motor more accurately.

(6) Wide range of speed regulation, high precision speed regulation.

Compared with the past baffle to adjust the air volume, the use of frequency conversion drag fan can be adjusted arbitrarily within the range of 0 ~ 50Hz, high regulation accuracy, regulation frequency fluctuations can be maintained within the range of 0.1 ~ 0.01Hz, to facilitate the realization of fan system automation control.

8 Conclusion

At present, the competition in the titanium dioxide industry is very fierce, but the key is still the competition of manufacturing costs, and motor power consumption accounted for nearly 30% of the cost, while dragging the fan with a high-voltage motor in the motor occupies a large proportion, so do a good job of the motor to reduce consumption and increase efficiency is extremely important. High-voltage frequency conversion speed control technology is now more mature, is the ideal equipment for energy-saving transformation of titanium dioxide plant, has a high popularization value, while making the clinker quality more stable and reliable.