Detection and Analysis of Energy Consumption of Various Air Compressors

Air compressor, namely air compressor, is the equipment that uses electric energy to do work and compress air to generate high pressure to drive other mechanical devices to run. It is the core component of the air source device. Air compressor according to its working principle can be divided into: volume type, power type. The positive displacement compressor increases the air pressure by relying on the reciprocating movement of the piston in the cylinder to compress the volume of the gas, thereby increasing the molecular density per unit volume. According to the structure and the way the piston moves, it can be divided into: reciprocating and rotary. Power compressors increase the air pressure by rotating the impeller at a high speed to increase the kinetic energy of the gas molecules, and then convert it into the pressure energy of the gas. There are mainly 4 types widely used: centrifugal compressors, axial compressors, and mixed flow Compressor, vortex compressor.

Although the air compressor is used in all walks of life, especially in the industry to occupy an irreplaceable position, its advantages are obvious, but due to the need to consume electricity to do work, its energy consumption has always been a thorny problem. According to research, in the total power generation in the country, the power consumption of air compressors accounts for 9% ~ 10%, and in the total power consumption of enterprises, it is as high as 15% ~ 35%, and the annual power consumption cost is still high in the whole operation cost, reaching 80%. However, such an imminent energy consumption problem, but few enterprises will do qualitative and quantitative energy consumption detection and analysis, so for the current air compressor energy consumption waste phenomenon, this paper will be on the air compressor energy consumption detection and analysis of a detailed discussion.

2. Working principle of air compressor

the air compressor is an energy conversion device. It uses air as the raw material. The principle of changing the density of air molecules through compression makes the compressed air exceed the atmospheric pressure, and converts the mechanical energy of the motor into gas pressure energy.

Working principle of 2.1 single screw air compressor

the working principle of the single-screw air compressor is to rely on two symmetrically configured star wheels to divide the compression space into two, in which the balance force in the two spaces is symmetrical, and the two star wheels rotate interactively to compress the gas in their respective spaces. Generate high-pressure air. Since the star wheel is made of plastic, it will accelerate the rapid wear of the star wheel in the relative movement with the screw at high speed and high temperature, resulting in a rapid decline in the total amount of compressed gas generated, so this problem is one of the problems to be solved urgently in the manufacturing industry.

The working principle of 2.2 piston air compressor

the piston air compressor has a set of devices that change the mode of movement-the crank connecting rod mechanism, which can convert the rotary motion of the motor into the linear reciprocating motion of the piston, in which the intake valve and the exhaust valve are cyclically opened and closed automatically to complete the suction., Compression and exhaust process. It is the earliest way to use air compressor, the technical means is relatively backward, and because the gas and oil is not significantly separated, resulting in a certain amount of oil in the gas, so this kind of air compressor can only be used for precision requirements is not very high industry, but also there are some inevitable shortcomings: the main engine life is short, the noise is big, the gas pulse phenomenon is serious.

The working principle of 2.3 sliding vane air compressor

the main structure of the sliding vane air compressor is the rotor. There are a certain number of cut grooves in its length. The grooves are coated with an oil film. The oil film is embedded with a sliding vane. The sliding vane can slide in the groove under the action of the oil film. Its specific working principle is that the rotor rotates in the stator in the cylinder. Due to the centrifugal force generated by the rotation, the sliding vane is separated from the chute by the centrifugal force to form several closed compression chambers. As it rotates, the volume of the compression chamber gradually decreases., To achieve the purpose of increasing air pressure. The sliding vane compressor is similar to the piston compressor, the application is relatively early, the way is backward, the oil and gas is difficult to separate, the oil and gas separator is required for separation, and the same cannot be applied to the manufacturing industry with high precision requirements.

Principle of 2.4 centrifugal air compressor

the main structure of the centrifugal air compressor is the impeller. The air entering the compressor will rotate rapidly with the impeller, and the gas will be pressed into the diffuser, the impeller will continue to rotate, and the air will be gradually pressurized. This kind of air compressor avoids the disadvantage of difficult separation of oil and gas, realizes oil-free compression, low energy consumption, convenient maintenance and large displacement.

3. Influencing factors of energy consumption of air compressor

for motor-driven air compressor, energy consumption can be considered as power consumption. Power consumption is generally related to two types of conditions: controllable factors and uncontrollable factors. Controllable factors include: intake pressure, isothermal efficiency of air pump, exhaust pressure and exhaust volume; Uncontrollable factors include: ambient temperature, mechanical efficiency of air compressor.

(1) The ambient temperature is reduced to reduce power consumption. Ambient temperature is difficult to control artificially, and is not the main research factor in energy consumption research.

(2) The intake pressure is increased to reduce power consumption. The intake pressure is mainly controlled by natural factors and unnatural factors. The natural factor is the local atmospheric pressure, and the unnatural condition is the resistance of the suction system, which is mainly determined by the resistance of the filter. Therefore, during use, it is necessary to regularly Clean the filter so that the resistance will not be too high and cause unnecessary waste of electric energy.

(3) The isothermal efficiency of the air pump is improved to reduce power consumption. The isothermal efficiency of the air compressor means that in the process of gas compression, the gas is compressed at the same temperature as much as possible, and the isothermal compression is inseparable from the way it is used. Therefore, in the process of use, pay attention to the cooling effect of the gas in the cooler at all levels, improve the isothermal efficiency of the air compressor, save energy and reduce consumption.

(4) The mechanical efficiency of the air compressor is improved to reduce power consumption. Once the air compressor is manufactured and put into production, this factor becomes a factor that cannot be controlled artificially, because it is an inherent attribute of the air compressor and is determined by its manufacturing process.

(5) The exhaust pressure is reduced to reduce power consumption. Based on the air compressor characteristic curve: the exhaust pressure is reduced, the exhaust volume will increase, which can not only reduce the power consumption but also increase the displacement.

(6) The air compressor exhaust volume is reduced to reduce power consumption. When the compressed air pressure is excessive, the gas equipment should reduce the load work, and the air flow can be reduced by adjusting the guide vane components of the air compressor, thereby reducing power consumption.

4. Energy consumption analysis of air compressor

the process of compressed air system is as follows: air compressor & rarr; pipe network & rarr; gas equipment, so the energy consumption analysis is mainly carried out from these three systems.

4.1 air compressor

the air compressor is an energy conversion device that converts electrical energy into air pressure energy. In its continuous working process, the efficiency of the air compressor directly affects the energy conversion rate, that is, the utilization rate of electrical energy.

Taking the screw air compressor as an example, its main structure is the screw rotor. After working for a period of time, the screw rotor is bound to have a certain degree of wear and tear, and the displacement per unit time is reduced. According to this problem, consider replacing a new rotor. After one year of operation, measure the energy consumption and exhaust volume of the air compressor with the replaced rotor. Compared with the energy consumption and exhaust volume of the previous year without replacing the rotor, it can be found that due to the reduction of the efficiency of the air compressor, the difference in annual power consumption cost before and after replacing the rotor is as high as over 100,000 yuan according to the existing electricity price, which is close to the price of a new rotor.

4.2 compressed air pipe network

the compressed high-pressure air needs to be transported to the gas equipment, which requires the use of the pipe network, which has an irreplaceable role in the entire air system, and the pipe network needs to effectively reduce the pressure loss. Under the condition of ensuring that the air pressure of the gas equipment does not change, the smaller the pressure loss of the pipe network, the higher the outlet pressure of the air compressor. Since the energy consumed by the motor is converted into the pressure and flow of compressed air, the smaller the pressure loss of the pipe network, the smaller the energy consumed by the motor under the same flow conditions. Therefore, in the management of the pipe network, it is necessary to find the bottleneck part of the pipe network as much as possible, that is, the thinnest part of the pipe diameter. When the flow rate in this part is large, it will produce a large pressure drop and increase energy consumption. This requires factory managers to solve this pipeline problem so as to save energy and reduce consumption.

4.3 gas equipment

through the understanding of the main gas equipment, the specific requirements for air pressure are clarified. In order to ensure the continuous and safety of the actual production, the air pressure in the pipe network needs to be higher than the actual required pressure, because the gas consumption will continue to change, and the air pressure caused by the change, the gas equipment still needs to maintain its minimum demand. Due to the limitation of the gas pressure, although the lowest pressure of the gas equipment is ensured, the pressure is inevitably excessive, which will inevitably lead to an increase in energy consumption.

5. Energy consumption detection method of air compressor

through the qualitative analysis of energy consumption in the previous section, the energy consumption level can be quantitatively detected by using the index specific power (kW 67 h)/m3, and its calculation formula is [7]: specific power = air compressor output power (kW) /air compressor exhaust volume (m3 h) can be detected by means of flowmeter, and the air compressor efficiency can be calculated by specific power and actual power consumption. The higher the air compressor efficiency, the smaller the energy loss, the more useful work done by electric energy, the better the performance of the air compressor. At the same time, the air compressor can be used, maintained, managed and replaced scientifically through the analysis of the test results.

Summary

under the severe situation that the global energy supply is in short supply, the problem of energy consumption has become a very prominent problem for enterprises. At present, most enterprises have begun to pay attention to this problem and constantly seek the main reasons for energy waste, and strive to reduce energy consumption on the premise of ensuring production. According to research, air compressor power consumption accounted for the proportion of total power consumption: in some industries as high as 70%, and in the industry as a whole, the average power consumption is still not less than 30%. Therefore, for enterprises, air compressor energy consumption detection and analysis is imperative, through detection and analysis, in order to seek energy-saving space.

Note: The article is reproduced in "Mechanical and Electrical Engineering Technology" Volume 47, Issue 10, 2018, by Dong Xuhui. If there is any infringement, please contact and delete it.