Through the electrical control transformation of the vacuum pump system of a paper mill in Hubei, the application of frequency converter speed regulation and energy saving is introduced; through the actual comparison of the operation before and after the transformation, it fully shows that the use of frequency converter to control the vacuum pump has a lot of energy saving space. The process control is more convenient and the economic benefits are significant.
Keywords: vacuum pump, frequency conversion control, energy-saving renovation
In the paper production process, vacuum technology is mainly used for on-line pulp dewatering and white water degassing (for high-speed paper machines); in the wire section and press section, it can remove moisture from paper sheets and blankets; in the paper machine steam and condensed water Vacuum technology is used in the system to maintain the pressure difference of the multi-stage steam ventilation in the dryer section. Therefore, the application of vacuum technology in the paper machine production process is very common.
Energy saving and environmental protection have always been the direction of the country’s advancement. Paper companies are high-energy-consuming companies. The energy consumption of the vacuum system accounts for about 25% of the entire paper machine process, or even higher. At present, most paper manufacturers The vacuum system of the enterprise still uses the adjusting exhaust valve to control the vacuum degree, which increases the power consumption. In addition, the power frequency control current fluctuates greatly, and it lacks protections such as overload, overcurrent, and undervoltage; it seriously affects the service life of the equipment and increases the cost of equipment maintenance. Therefore, the frequency conversion control transformation of the vacuum pump of the paper mill is particularly important.
2. Process requirements
Vacuum pumps are widely used in the paper industry. In the main steps of pulping, preparation, papermaking, and processing in modern papermaking procedures, vacuum systems are used in many processes. The equipment and accessories in the papermaking workshop that rely on vacuum pressure difference for dehydration, drainage, and exhaust (steam) can be classified as the vacuum system of the paper machine. According to the different processes of each process, different vacuum degrees need to be given to meet production requirements. According to customer site surveys and customer needs, the frequency conversion control of on-site vacuum pumps mainly has the following requirements:
1. It can realize free switching between frequency conversion and industrial frequency, and safety interlock;
2. It can switch between local control (local potentiometer) and remote control (DCS4~20mA signal control) of the inverter;
3. The inverter can feed back the running signal to the upper computer DCS system;
4. The inverter provides the analog quantity (4~20mA) corresponding to the load current to the host computer DCS for load judgment;
5. The system provides indications of frequency conversion, industrial frequency and frequency conversion failure;
6. Realize multiple protections of the motor, such as soft-starting and overcurrent, overload, undervoltage, and overvoltage;
7. When the inverter fails, it can automatically switch to industrial frequency operation or start the standby pump to ensure the normal operation of production;
3. System transformation plan and characteristics
There are a total of 8 vacuum pumps with different powers ranging from 132KW to 280KW in the No. 1 workshop of the customer site. The customer originally used soft-starting, and each process link used an exhaust valve to control the vacuum at all levels. The customer first carried out a retrofit test on the No. 8 280KW pump. The system design uses the easy-drive CV3100 series of high-performance general-purpose inverters. The vacuum pump is a constant torque load. Due to the uninterrupted operation of the paper industry equipment, the 315KW inverter is selected.
In order not to waste the customer’s original system, the plan is designed to switch between frequency conversion control and the original soft start control system; the frequency converter realizes the local potentiometer and 4-20mA signal control switching through the DI port; set TA and TC as frequency conversion operation. AO1 corresponds to the frequency conversion current output 4~20mA signal feedback to the host computer DCS, so that DCS can always monitor the operation of the inverter. The control system through frequency conversion has the following characteristics:
1. The power saving benefit is significant, and the power saving rate is as high as 5%-20%;
2. Ramp start function to eliminate the inrush current during traditional start;
3. The vacuum pressure is stable, which effectively improves the quality and quantity of products;
4. Reduce motor heating and wear of moving parts, extend motor service life, and reduce maintenance costs;
5. Automatic conversion of mains and power-saving states, automatic fault alarm, and no influence on normal operation;
After more than a month of on-site testing, the easy drive CV3100 inverter can fully meet the needs of the on-site unit, and the power saving effect is significant. After half a month's actual test with the watt-hour meter, when the inverter runs at 47.5HZ, it can save 260 degrees of electricity per day.
Calculated by working 300 days per year: 260x300=78000KWh can be saved every year. Calculated by 0.6 yuan per kilowatt-hour of electricity, the annual electricity cost can be saved 78000x0.6=4.68 (ten thousand yuan). Based on Hubei Industrial Power 0.93 yuan, the annual electricity cost can be saved 78000x0. 93=7.254 (ten thousand yuan) And the field test is the highest paper product test according to the requirements. If other paper products are produced, the vacuum degree is lower, the frequency of the inverter is adjustable, and the power saving space is huge. On the whole, customers can recover their input costs in less than a year or even half a year.
With the continuous development of the equipment manufacturing industry, industrial equipment will gradually develop in the direction of high precision. The use of variable frequency drives will not only protect the motor, save energy and reduce consumption, but also improve the automation level of the equipment. Eki Electric Co., Ltd. has many years of application experience in the automation industry, and can provide safe and reliable frequency conversion solutions according to customer site requirements and working conditions. CV3100 series high-performance general-purpose inverters are widely used in many application fields such as metallurgy, electric power, chemical industry, municipal administration, and equipment manufacturing industry.
5. On-site photos