Dec 01, 2021 
Data analysis of air compressor energy consumption and heat recovery benefit
1. Compressed air energy consumption and cost analysis
Compressed air is one of the most widely used power sources in the industrial field. Due to its many advantages such as safety, pollution-free, good adjustment performance, and convenient transportation, it is more and more widely used in modern industrial fields. However, it takes a lot of energy to get high-quality compressed air. In most production enterprises, the primary energy consumption of compressed air is very large.
The five-year operating cost of an air compressor system: the initial investment cost and equipment maintenance cost of the system account for 25% of the total cost, while the electrical energy consumption accounts for 75%. Almost all system waste is reflected in the electricity bill .
According to the evaluation of air compression systems in various industries, it can be found that most of the compressed air systems, no matter whether they are new or old, have poor operating efficiency. Compressed air leakage, improper use of man-made air, and improper system control, etc. will all lead to a decrease in system efficiency, which will result in a continuous increase in customer electricity bills and secondary energy waste. A large number of experiments have also proved that the electric energy consumed by the compressor to increase the potential energy of the air only accounts for about 15% of the operating efficiency, and 85% of the electric energy is converted into heat, which is discharged into the atmosphere through the compressor casing and cooler.
1) The heat recovery system of the oil-injected screw air compressor recovers the compression heat in the high-temperature cooling oil of the air compressor under the condition of ensuring the stable operation of the air compressor, and ensures that the temperature of the cooling oil flowing back to the rotor meets the requirements and is stable; Compression heat accounts for more than 60% of the input power of the air compressor.
2) Oil-free screw air compressor heat energy recovery system, raise the air compressor cooling water drainage temperature to 80℃, use the external recovery skid to recover the compression heat, and ensure that the cooling water flows back to the air compressor for intercooling and aftercooling The temperature meets the requirements and is stable; the recovered compression heat accounts for about 70% of the input power of the air compressor.
3) The centrifugal air compressor heat recovery system can recover the compression heat in the final stage exhaust of the centrifugal air compressor under the condition of ensuring the stable operation of the air compressor, and the recovered compression heat accounts for about the input power of the air compressor 18%.
2. Analysis of waste heat of compressed air system
When the compressor is running, it is actually used to increase the electrical energy consumed by the air potential. It accounts for a small part of the total power consumption. Most of the electrical energy is converted into heat, which is discharged into the air through air cooling or water cooling, so that this heat is It is wasted and not used well. In fact, this part of the heat is still very likely to be used. After analyzing the heat generated by the conversion of kinetic energy and thermal energy during the compression process of the air compressor, 100% of the input power; about 2% is radiant heat, about 4% is the heat left in the air compressor, and about 94% of the heat can be recovered Utilized.
Analysis of recoverable heat: 100% power consumption, motor heat dissipation is about 5%, lubricating oil takes about 75% of heat, compressed air takes 10% of heat, other heat loss is 10%, and 85% can be recovered .
3. Heat recovery and energy saving solutions for compressed air systems
The working process of the air compressor: After the air passes through the air intake filter to filter out dust or impurities in the atmosphere, it enters the main compressor through the air intake control valve and mixes with the injected cooling lubricant during the compression process. The mixed gas is discharged from the compressor to the oil and gas separation storage tank, so that the high temperature and high pressure oil and gas must enter their respective coolers. The compressed air is finally sent to the system after being cooled by the cooler. After the high temperature and high pressure lubricating oil is cooled by the cooler, it returns to the oil circuit and enters the next cycle. According to calculations, in the above process, the heat carried by the high-temperature and high-pressure oil and gas is approximately equivalent to 85% of the conversion heat of the power consumption of the air compressor, and the temperature of the waste heat is usually between 80°C and 100°C. If the waste heat generated by the air compressor is not exchanged, it may cause lubrication and coking, decrease in air production, and increase in motor power. In severe cases, the main compressor will lock up and continue to compress the air normally. In order to make full use of the waste heat generated by the air compressor, the waste heat recovery device is used to cool the high temperature and high pressure compressed air generated by the air compressor, which not only improves the gas production efficiency of the air compressor, but also enables the enterprise to obtain good social benefits. The waste heat of compressed air can produce hot water needed for life and improve energy utilization.
Compressed air system heat recovery application range:
The temperature can be used for boiler preheating at 90℃;
The temperature can be used for process water at 70℃;
The temperature can be used for sanitary water at 60℃;
The temperature can be used for building heating at 50℃;
The temperature can be used for RO pure water at 50℃.
Four, energy recovery system is used for sanitation at 60℃ and at 50℃ for building heating for energy recovery system analysis.
4.1 There are 4 existing 160kW air compressors, 4 of which are expected to be fully open, running 24 hours a day, calculated according to the recovery efficiency of 75%, energy saving per hour: 160kW×2.5×100%×75%=300kW.
Now plans to transform the waste heat of the air compressor to heat recovery, and the recovered heat will be used to heat the bathing water of the company's single apartment building, and the remaining heat will be used by industrial air conditioners.
The heat requirements for bathing are as follows.
The heat demand for heating is as follows.
The waste heat generated during the operation of the air compressor can be used to heat water for bathing and air conditioning at the same time. The annual energy consumption is saved as shown in the table below.
4.2 Adopting a direct heating energy recovery system, which runs automatically throughout the day, completely unattended. Each air compressor of the energy recovery system is equipped with one, and it will run automatically after starting up to determine the oil temperature. If it is higher than the set value, it will signal the control cabinet to start the circulating pump. The energy recovery system automatically adjusts the outlet water flow rate according to the outlet water temperature. The outlet water flow rate increases when the temperature is higher than the set value, otherwise the outlet water flow rate decreases.
The control cabinet detects closed circulating water pressure, water temperature and circulating water tank temperature, liquid level, and controls circulating pumps and heating pumps.
The system checks the operation status of the energy recovery system every day: any oil temperature exceeds the set value and the circulating pump starts to work, the system enters the plate heat exchanger to exchange heat, the temperature in the system exceeds the set value, and the system stands by for water supply. The solenoid valve controls the water level of the hot water tank, and the secondary circulation pump pressurizes the hot water after heat exchange to meet the water supply pressure requirements, and the hot water can be used at any time.
Through this bold attempt, we have experienced that the use of air compressor heat recovery devices can optimize the company's domestic hot water, and use the hot water of the air compressor for secondary use to reduce energy waste. It not only saves electricity, water, fuel and other primary energy consumption, but also saves costs for the company's production and life, and also reduces carbon emissions, which has obvious social benefits.
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