Energy saving analysis of air compressor

The air compressor is a kind of equipment that uses a motor to compress the gas in the compression chamber and make the compressed gas have a certain pressure. In various industries, it is responsible for providing air supply for all pneumatic components and various pneumatic valves in the factory. The biggest energy consumption of air compressor is the consumption of electric energy, which accounts for 77% of the total consumption, followed by the maintenance cost, which accounts for 18% of the total consumption, while the equipment investment only accounts for 5% of the total cost. The power consumption of the air compressor is very amazing. An air compressor can be as little as tens of thousands of yuan and as much as millions. However, the purchase cost is only 5%, which shows the huge power consumption. Therefore, only by finding the causes of energy consumption of air compressors and solving them pertinently can the energy efficiency be improved.

Main aspects of energy consumption of air compressor:

1. Control mode: since the air compressor does not rule out the possibility of long-time operation under full load, the motor capacity can only be determined according to the large demand during the selection, resulting in a large surplus of the air compressor system. Traditional air compressors are started by star delta step-down, but the current can still reach 2-3 times of the rated current when starting at power frequency, which has great impact and will affect the stability of the power grid. Moreover, most air compressors operate continuously. Since the motor of the general air compressor can't slow down according to the change of pressure demand, the output power of the motor is matched with the actual pressure demand on the site, resulting in no-load operation when the air consumption is small, resulting in huge waste of electric energy. According to statistics, air compressors account for almost 15% of the power consumption of large industrial equipment (fans, pumps, boilers, etc.). Problems in loading and unloading gas supply control mode; Through the energy consumption analysis, it is known that the pressure of the compressed gas changes back and forth between Pmin and Pmax due to the load control mode. Pmin is the low pressure value, that is, the low pressure that can ensure the normal operation of the user. In general, the relationship between Pmin and Pmax can be expressed by the following formula: Cpmax = (1+ δ） Pmin is a percentage, and its value is approximately between 10% and 25%. If the variable-frequency speed regulation technology is used to continuously adjust the gas supply, the pressure of the pipe network can always be maintained at a level that can meet the gas supply pressure, that is, near Pmin. It can be seen that the energy wasted by the air compressor under the loading and unloading air supply control mode is mainly in two parts: (1) after the pressure of compressed air exceeds Pmin, the original control mode determines that the pressure will continue to rise (until Pmax). This process is also an energy consuming process. (2) In general, when the pressure reaches Pmax, the air compressor depressurizes and unloads through the following methods: close the air inlet valve to make the motor idle, and vent the excess compressed air in the separation tank through the vent valve. This adjustment method will cause a great waste of energy.

2. Gas leakage: only 10% of the electric energy consumed by the air compressor is converted into compressed air, and the remaining 90% is converted into heat energy. It can be seen that compressed air is ten times more expensive than electricity, but we often ignore this point. In most factories, the sound of air leakage can be heard everywhere, but no one cares. This kind of leakage not only increases the noise, but more importantly, it causes energy waste, reduces the air volume and increases the cost. The needle has a big eye, and the wind blows hard. Because of leakage, especially pipeline leakage, if the leakage problem is solved, a lot of energy will be saved.

Through comprehensive analysis of the main energy consumption reasons, the following energy-saving measures can be taken:

1. Change of control mode: according to the operating characteristics of air compressor, Q1 / Q2 = N1 / N2; H1 / H2 =（ n1 / n2）2 ； P1 / P2 =（ n1 / n2）3 ； (where Q - air volume of air compressor supply pipe network; H - pipe network pressure; P - motor consumption power; N - air compressor speed.) It can be seen from the above formula that when the motor speed is reduced to 80% of the rated speed, the air volume of the air compressor supply pipe network is reduced to 80%, the pipe network pressure is reduced to (80%) 2, and the power consumption of the motor is reduced to (80%) 3, i.e. 51.2%. The energy saving efficiency is also close to 40%, which is the principle of speed regulation and energy saving. After the above analysis, the constant pressure gas supply is carried out by applying the variable frequency speed regulation technology. The actual pressure P is collected by the pressure transmitter and sent to the PID Intelligent Governor for comparison with the pressure set value P0. The actual pressure P is calculated according to the established PID control mode according to the difference, and the control signal is generated and sent to VVVF. The working frequency and speed of the motor are controlled by the frequency converter, so that the actual pressure P is always close to the set pressure P0. The system adopts the pressure closed-loop regulation mode. A pressure sensor is installed on the original pressure air tank to convert the pressure signal into a 4-20mA electrical signal and send it to the PID regulator inside the frequency converter. The regulator compares the signal with the pressure setting value and outputs the control signal. The frequency converter changes the speed of the motor according to the output frequency of the signal, adjusts the air supply pressure and keeps the pressure constant, Keep the air compressor in power-saving operation. At the same time, the scheme can increase the power frequency and frequency conversion switching function, and retain the original control and protection system. In addition, after the scheme is adopted, the motor of the air compressor can be started from static to rotating by the frequency converter, realizing soft start and avoiding the starting impact current and mechanical impact on the air compressor.

Frequency conversion energy saving is shown as follows: (1) the frequency converter adjusts the gas flow by adjusting the rotation speed of the motor, so that the output power of the motor is proportional to the flow demand, so as to maintain the high efficiency of the motor, high power factor, low reactive power loss, and obvious power saving effect; (2) Designed according to the strict EMS standard, the high-speed and low-power IGBT and the high-efficiency loss control algorithm are adopted to minimize the harmonic distortion of the V & t converter and the power loss of the motor; (3) Automatic fast sleep makes the no-load time shorter, the motor stops completely, and saves energy to a large extent. No impact start and low-frequency large torque characteristics ensure that the frequency converter can start and stop at any time with load.

2. Prevention and control of gas leakage: what is the utilization rate of compressed air? It is estimated that only 50% of the compressed air can be sent out, while 30% is leakage, 15% is human demand, and the other 5% is operation problem. In the above group of figures, leakage accounts for 30%, which is the part we can try to control. The leakage of the air compressor exists in the whole system, including the main engine, air storage tank, post-treatment, pipeline, user, etc. It is estimated that the monthly leakage loss of a small hole of only 3mm can reach more than 2000 yuan However, in the whole system, there will never be only one such leakage point, but countless undetectable leakage points. And the losses caused by such leakage points are incalculable. Common leakage points mainly include pipes, joints, flanges, hoses, blowdown valves, branch pipes, etc. Large leaks can be detected by sound judgment, but small leaks cannot be detected by ears and eyes. The current leak detection method is mainly electronic ultrasonic leak detection. When ultrasonic leak detection is used, hundreds of leakage points can be found After the leakage point is found, the main way to cure the leakage is to seal, and the leakage can be blocked with gum material. If the leakage of the connecting part is obvious, it should also be reassembled and sealing materials should be added. The leakage control effect is based on the size of the air compressor, which can save hundreds of thousands of yuan or millions of yuan per year. In addition, non-destructive valve devices can be equipped. These accessories are electronically controlled, small in size, high in automation and low in cost. They can effectively drain condensed water, and their own leakage is almost zero. Moreover, there are many specifications and varieties, which can meet the needs of various air compressors.

There are many energy-saving measures for the air compressor. By analyzing the main energy consumption reasons and using PID control technology and leakage prevention methods to realize the purpose of high-efficiency and energy-saving operation, the economic and social benefits of the enterprise can be improved.

The above content is from the compressed air pipe manufacturers!