Very comprehensive! Several Typical Air Compressor Waste Heat Recovery Forms
Several Typical Air Compressor Waste Heat Recovery Forms
(Abstract) This article introduces waste heat recovery systems of several typical air compressors, such as oil-injected screw oil-free screw air compressors, centrifugal air compressors, etc. The characteristics of the waste heat recovery system are expounded. These rich ways and forms of waste heat recovery of air compressors can be used for reference and adoption by relevant units and engineering technicians to better recover waste heat, reduce energy costs of enterprises, and reduce environmental impact. Thermal pollution achieves the purpose of energy saving and environmental protection.
▌Introduction
When the air compressor is running, it will generate a lot of compression heat, usually this part of the energy is released into the atmosphere through the air-cooled or water-cooled system of the unit. Compressor heat recovery is necessary to continuously reduce air system losses and increase customer productivity.
There are many researches on the energy-saving technology of waste heat recovery, but most of them only focus on the oil circuit transformation of oil-injected screw air compressors. This article introduces the working principles of several typical air compressors and the characteristics of waste heat recovery systems in detail, so as to better understand the ways and forms of waste heat recovery of air compressors, which can better recover waste heat, reduce energy costs of enterprises, and achieve The purpose of energy saving and environmental protection.
Several typical air compressor waste heat recovery forms are introduced respectively:
Analysis of waste heat recovery of oil-injected screw air compressor
① Analysis of working principle of oil-injected screw air compressor
The oil-injected screw air compressor is a type of air compressor with a relatively high market share
The oil in the oil-injected screw air compressor has three functions: cooling-absorbing heat of compression, sealing and lubrication.
Air path: External air enters the machine head through the air filter and is compressed by the screw. The oil-air mixture is discharged from the exhaust port, passes through the pipeline system and the oil-air separation system, and enters the air cooler to reduce the high-temperature compressed air to an acceptable level. .
Oil circuit: The oil-air mixture is discharged from the outlet of the main engine. After the cooling oil is separated from the compressed air in the oil-gas separation cylinder, it enters the oil cooler to take away the heat of the high-temperature oil. The cooled oil is re-sprayed into the main engine through the corresponding oil circuit. Cools, seals and lubricates. so repeatedly.
Principle of waste heat recovery of oil-injected screw air compressor
The high-temperature and high-pressure oil-gas mixture formed by the compression of the compressor head is separated in the oil-gas separator, and the high-temperature oil is introduced into a heat exchanger by modifying the oil outlet pipeline of the oil-gas separator. The amount of oil in the air compressor and bypass pipe is distributed to ensure that the return oil temperature is not lower than the oil return protection temperature of the air compressor. The cold water on the water side of the heat exchanger exchanges heat with the high-temperature oil, and the heated hot water can be used for Domestic hot water, air conditioning heating, boiler water preheating, process hot water, etc.
It can be seen from the above figure that the cold water in the heat preservation water tank directly exchanges heat with the energy recovery device inside the air compressor through the circulating water pump, and then returns to the heat preservation water tank.
This system is characterized by less equipment and high heat exchange efficiency. However, it must be noted that energy recovery devices with better materials need to be selected, and they need to be cleaned regularly, otherwise it is easy to cause blockage due to high temperature scaling or leakage of heat exchange devices to pollute the application end.
The system performs two heat exchanges. The primary side system that exchanges heat with the energy recovery device is a closed system, and the secondary side system can be an open system or a closed system.
The closed system on the primary side uses pure water or distilled water to circulate, which can reduce the damage to the energy recovery device caused by water scaling. In case of damage to the heat exchanger, the heating medium on the application side will not be contaminated.
⑤ Advantages of installing heat energy recovery device on oil-injected screw air compressor
After the oil-injected screw air compressor is installed with a heat recovery device, it will have the following benefits:
(1) Stop the cooling fan of the air compressor itself or reduce the running time of the fan. The heat energy recovery device needs to use a circulating water pump, and the water pump motor consumes a certain amount of electric energy. The self-cooling fan does not work, and the power of this fan is generally 4-6 times greater than that of the circulating water pump. Therefore, once the fan is stopped, it can save energy by 4-6 times compared with the power consumption of the circulating pump. In addition, because the oil temperature can be well controlled, the exhaust fan in the machine room can be turned on less or not at all, which can save energy.
⑵. Convert waste heat into hot water without any additional energy consumption.
⑶, increase the displacement of the air compressor. Since the operating temperature of the air compressor can be effectively controlled within the range of 80°C to 95°C by the recovery device, the concentration of the oil can be kept better, and the exhaust volume of the air compressor will increase by 2%~6 %, which is equivalent to saving energy. This is especially important for air compressors operating in summer, because generally in summer, the ambient temperature is high, and the oil temperature can often rise to about 100°C, the oil becomes thinner, the air tightness becomes worse, and the exhaust volume will decrease. Therefore, the heat recovery device can show its advantages in summer.
Oil-free screw air compressor waste heat recovery
① Analysis of working principle of oil-free screw air compressor
The air compressor saves the most work during isothermal compression, and the consumed electric energy is mainly converted into the compression potential energy of the air, which can be calculated according to formula (1):
Compared with oil-injected air compressors, oil-free screw air compressors have more potential for waste heat recovery.
Due to the lack of cooling effect of oil, the compression process deviates from isothermal compression, and most of the power is converted into compression heat of compressed air, which is also the reason for the high exhaust temperature of oil-free screw air compressor. Recovering this part of heat energy and using it for users’ industrial water, preheaters and bathroom water will greatly reduce the energy consumption of the project, thereby achieving low-carbon and environmental protection.
Fundamental
① Analysis of working principle of centrifugal air compressor
The centrifugal air compressor is driven by the impeller to rotate the gas at high speed, so that the gas generates centrifugal force. Due to the diffusion flow of the gas in the impeller, the flow rate and pressure of the gas after passing through the impeller are increased, and compressed air is continuously produced. The centrifugal air compressor is mainly composed of two parts: the rotor and the stator. The rotor includes an impeller and a shaft. There are blades on the impeller, in addition to the balance disc and part of the shaft seal. The main body of the stator is the casing (cylinder), and the stator is also arranged with a diffuser, a bend, a reflux device, an air inlet pipe, an exhaust pipe, and some shaft seals. The working principle of the centrifugal compressor is that when the impeller rotates at high speed, the gas rotates with it. Under the action of centrifugal force, the gas is thrown into the diffuser behind, and a vacuum zone is formed at the impeller. At this time, the fresh gas outside into the impeller. The impeller rotates continuously, and the gas is continuously sucked in and thrown out, thus maintaining a continuous flow of gas.
Centrifugal air compressors rely on changes in kinetic energy to increase the pressure of gas. When the rotor with blades (that is, the working wheel) rotates, the blades drive the gas to rotate, transfer work to the gas, and make the gas obtain kinetic energy. After entering the stator part, due to the sub-expansion of the stator, the speed energy pressure head is converted into the required pressure, the speed decreases, and the pressure increases. At the same time, it uses the guiding effect of the stator part to enter the next stage of the impeller to continue boosting, and finally discharges from the volute. . For each compressor, in order to achieve the design required pressure, each compressor has a different number of stages and segments, and even consists of several cylinders.
② Centrifugal air compressor waste heat recovery process
Centrifuges generally go through three stages of compression. The first and second stages of compressed air are not suitable for waste heat recovery due to the influence of outlet temperature and pressure. Generally, waste heat recovery is performed on the third stage of compressed air, and an air aftercooler needs to be added, as shown in Figure 8. It shows that when the hot end does not need to use heat, the compressed air is cooled without affecting the operation of the system.
Another waste heat recovery method for water-cooled air compressors
For air compressors such as water-cooled oil-injected screw machines, oil-free screw machines, and centrifuges, in addition to the waste heat recovery of the internal structure modification, it is also possible to directly modify the cooling water pipeline to achieve waste heat without changing the body structure. Recycle.
By installing a secondary pump on the cooling water outlet pipeline of the air compressor, the cooling water is introduced into the main unit of the water source heat pump, and the temperature sensor at the inlet of the main unit evaporator adjusts the electric three-way regulating valve in real time to control the inlet temperature of the evaporator at a certain setting. With a fixed value, hot water at 50~55°C can be produced through the water source heat pump unit.
If there is no demand for high-temperature hot water, a plate heat exchanger can also be connected in series in the circulating cooling water circuit of the air compressor. The high-temperature cooling water exchanges heat with the soft water from the soft water tank, which not only reduces the internal water temperature, but also increases the external water temperature.
The heated water is stored in the hot water storage tank, and then sent to the heating network for use where a low-temperature heat source is needed
