Application of Frequency Conversion Technology in Vacuum Constant Pressure Unit
1Problem raised in the pharmaceutical drying process, in the normal pressure state, when the temperature reaches 100.C, the moisture in the drug can generate vaporization, and often at such a high temperature, many drugs also have a chemical reaction. It is the most evasive thing for pharmaceutical companies. Therefore, in the pharmaceutical industry, the higher the vacuum and the lower the vaporization temperature of the water, the vacuum pump sucks the gas in the drying system to control the system in a constant vacuum range, so that the moisture content in the dried medicine is lower than Vaporization at reaction temperature. However, due to the drying process of pharmaceuticals, the flow rate of the gas generated by the pharmaceutical system is very unstable, and it is sometimes not even gas. If the system generates gas! When vacuum pumping volume is exhausted, the system cannot be pumped to the set vacuum level. Therefore, under the set temperature, the moisture in the medicine is not sufficiently vaporized to reach the drying effect of the medicine, which will affect the quality of the medicine; for example, the amount of gas generated by the system. "With vacuum pumping, the vacuum pump vacuums the system up. When the vacuum is too high, the vacuum pump will generate cavitation, which may even cause serious damage. At the same time, it also causes a lot of energy waste. Therefore, design a constant pressure for the user. A stable and energy-saving vacuum operation scheme is very important.
First of all, let us first understand the characteristics of the work of the water ring vacuum pump and the characteristics of the inverter. 1) The water ring vacuum pump is a volumetric pump. When the type of the water ring vacuum pump is determined, its volume is determined. For the water ring vacuum pump, the relationship between the rotation speed, the pumping amount, and the working point axis power is as follows: n, the first point of the water ring vacuum pump, and the second point of the rotation speed/pm) n2 The first and second points of the water ring vacuum pump The speed formulas 1) and 2) indicate that the pumping volume of the water ring vacuum pump is proportional to the rotation speed, and the power of the working point shaft is proportional to the 1.7 power of the rotation speed. In other words, when the water ring vacuum pump is selected, the amount of air extraction can be adjusted by adjusting the rotation speed.
2) Frequency control of motor: When the frequency f is continuously adjustable, the motor speed can also be continuously adjusted. At present, the inverter frequency adjustment accuracy is high, and the minimum output frequency change amount can reach 0.01HZ. The calculation relationship between output frequency and rotation speed is as follows: Induction motor can be continuously adjusted within double frequency 0.5~100Hz, such as 4-pole motor. The speed range is 14.4~2880. Therefore, combining the characteristics of the water ring vacuum pump and the motor's variable frequency speed control, the motor of the water ring vacuum pump will be controlled by the inverter. If the motor frequency is changed, the air volume can be adjusted, and the inverter accuracy is high. Adjustment can achieve fine-tuning effect.
2 Example analysis The following uses the Xinjiang Pharmaceutical Factory as an example to analyze the feasibility of the variable frequency constant pressure unit: (1) The working characteristics of the system: The vacuum system is a central vacuum system and controls multiple nodes, because the operating points are not opened and stopped. , And it is intermittent, it is possible that only a very small number of operating points are operating, and it is possible that most points are in operation. This is also a feature of vacuum concentration in the field of Chinese medicine.
(2) The customer's request: The vacuum pump is placed in the clean area on the first floor of the pharmaceutical production line. In the explosion-proof zone, the operator of the workshop is all in the clean area on the second floor) and the pharmaceuticals are processed on the second floor. Between the first floor and the second floor, a clean room is needed to change clothes and clean the X. The operator is not convenient to go back and forth between the first and second floors. Therefore, it is required that the vacuum equipment on the first floor can be automatically started and stopped, and the amount of exhausted air be automatically adjusted.
The first solution, although it can adjust the gas volume, its gas volume is a kind of jump-type change. There are only six gas volume combinations that cannot meet the complex changes of the system. For example, when the system generates a gas volume of 16m3/min, the vacuum system cannot reach the dynamics. balance.
Scheme two, according to the characteristics of the water ring vacuum pump and the frequency conversion unit, the minimum gas volume variation of the frequency conversion unit is 0.13, which is almost infinitely variable. The frequency converter will automatically adjust the frequency according to the actual working conditions so that the system can achieve dynamic balance. Table 1 Scheme Selection of Pump Condition Table According to the actual situation of Xinjiang Pharmaceutical Factory, we have made two schemes G scheme one: large and small vacuum pump combination, 2 Set 2BW5 153 units and 2 sets of 2BW5102 units, adjust the amount of pumping by changing the combination, as shown in the following table 1: Scheme 2: Frequency control, 3 sets of 2BW5153 unit vacuum pressure measurement point at 100mbar This range can be in the system Free adjustment when debugging). At the beginning, when the absolute pressure of the buffer tank gas is >280 mbar(a), the first pump is started at the critical speed, until it is in the public frequency state, and the delay time can be adjusted by 3 minutes); the inverter steering control number 2, etc. Until all three vacuum pumps are put into operation.
In (a), the frequency conversion control cabinet reduces the rotational speed of the first pump and reduces the pumping volume until the rotational speed of the pump is low to the critical rotational speed. At this time, if the absolute pressure in the buffer tank is still (2) the energy consumption is compared: If the system gas volume is 16m3/min, the first option is to use 2 2BW5102 + 1 2BW5153+ bypass pipes to supplement the gas to meet the requirements, and the energy consumption is 29kW. In Option 2, 1 set of 2BW5 153 frequency operation + 1 set When the 2BW5153 is operating at 30 870 rpm, the energy consumption is: performance curve, 1450 revolutions at the frequency, shaft power is 10kW, and the shaft power per hour is less g29-24=5kW. The annual workday of the pharmaceutical company is 330 days, one day. After 24 hours of calculation, the annual industrial power consumption is 0.8 yuan/degree. One year later, the second scheme is better than the program. The end of the third quarter is analyzed by examples. It can be seen that the use of variable frequency speed control is sensitive to changes in the amount of gas and can be automatically and intelligently processed in time. Adjust and save energy. It is especially suitable for industries where the system gas volume changes greatly and the work point requirements are strict, such as pharmaceuticals and electronics. The system is stable and the economic benefits are very significant. It is highly praised by users. Therefore, the frequency conversion technology is very worthy of application and promotion in the vacuum constant pressure unit.
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