1 Today, as the world's energy is getting more and more tense, the issue of energy conservation and energy recovery has been mentioned on the important agenda, and it has received great attention from various experts and product developers. The energy recovery of the compressor is one of the more efficient energy-saving measures.

2 effectiveness of energy recovery

According to the engineering thermodynamics theory, when the gas is in the isothermal compression process, the external work on the gas will be converted into heat. Figure 1 shows the distribution ratio of the energy conversion of the oil-injected screw compressor during operation.

It can be seen that most of the compressed oil and gas mixture is taken away after the power consumed by the compressor is converted into heat during operation. These oil and gas mixtures are separated and carried away by a cooling medium (water or air) in their respective coolers (oil coolers and gas coolers), wasted in vain. In theory, in addition to 2% radiant heat and 4% of the heat carried away by the gas, almost 94% of the heat can be recovered. If the energy recovery rate is 70%, then an oil-injected screw compressor with a power consumption of 250kW can recover 175kW per hour. If it is operated for 8h per day and the electricity cost is 1 yuan/kWh, it can save 1400 yuan per day. Its economic benefits are considerable. The water-cooled and air-cooled energy recovery devices are respectively introduced according to two commonly used heat exchange methods.

3 water-cooled energy recovery device

Water-cooled energy recovery units are typically placed between the compressor and the cooler, and are independent of the way the compressor is cooled, whether water-cooled or air-cooled. It is mainly composed of heat exchangers and thermostatic bypass valves. The recovered water temperature can reach up to 90, which is widely used in places requiring high temperature water or hot water, such as bathroom, canteen, food industry or heating equipment.

The working principle of the water-cooled energy recovery device is described below in terms of its working conditions.

3 1 compressor starting state

When the compressor is started cold, the temperature of the cooling oil is low. At this time, the oil cooler bypass valve and the heat exchanger bypass valve are closed, and the cooling oil directly enters the compressor without passing through the heat exchanger and the cooler.

3 2 heat exchanger working condition

After the compressor runs for a period of time, the temperature begins to rise. When the temperature of the cooling oil rises to the set value of the heat exchanger bypass valve, the valve automatically opens, and the cooling oil enters the heat exchanger to transfer heat to the cooling water, and then Go to the next process. If the temperature of the cooling oil after heat exchange is still lower than the set value of the oil cooler bypass valve, it will enter the compressor cycle without entering the oil cooler to prevent the cooling oil temperature from being too low in the compressor working chamber. Condensed water. If the temperature of the cooling oil after heat exchange is higher than the set value of the thermostat oil cooler bypass valve, it is first cooled into the cooler and then into the compressor cycle.

3 3 Heat exchanger is suspended

When the hot water of the energy recovery device is temporarily not needed to stop the supply, heat exchange does not occur in the heat exchanger, and the cooling oil is still maintained at a high temperature (usually greater than the set value of the oil cooler bypass valve), so the cooling oil After entering the oil cooler through the oil cooler bypass valve, it enters the compressor to ensure the normal operation of the compressor.

4 air-cooled energy recovery device

The air-cooled energy recovery device has a simple structure, is convenient to use, has low cost, and has high energy recovery rate. However, it can only be applied to air-cooled compressors, which has certain limitations. Its heat is mainly used for heating in winter or drying of articles, etc. It has high efficiency in the northern region. For example, with a heating time of 100 days per year, a compressor with a power of 250kW runs 8 hours a day, and can recover 140,000 kW of heat per year. The economic benefit is 140,000 yuan (according to the electricity cost of 1 yuan / kW h1).

Air-Cooled Energy Recovery Device As shown, the compressor is a box-type air-cooled structure. An air inlet window and an air exhaust window are respectively arranged at the top of the box cover, and air passages for cooling air inlet and exhaust are respectively arranged in the inlet and exhaust air windows, wherein the air inlet air passage can be provided according to the environmental facilities of the compressor station room. No, and the exhaust duct is led to where hot air is needed. When the compressor is working, the cooling air enters the compressor unit from the air inlet, and after sufficient heat exchange with the cooler in the unit, the hot air is discharged by the exhaust window and led to the place of use.

5 Conclusion

In summary, the energy recovery of the oil-injected screw compressor has the advantages of simple structure and convenient use, as well as pollution-free, noise-free, high energy recovery rate (more than 70%), and provides effective energy saving for the majority of users. way.

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