(I) analysis of exhaust temperature plateau factors

The working principle of the two-stage screw air compressor is composed of inlet filter system, compressor and motor assembly, pressure lubrication system with cooler, separation system, air volume regulation system, electrical control system, instrument system, safety protection system, aftercooler, water separator and discharge device. In a two-stage screw compressor, compressed air is meshed through two sets of helical rotors (Yin and Yang rotors). The axes of the first and second rotors are parallel to each other, forming a staged series mode, which is installed in the cylinder body of high strength cast iron. The two end faces of the cylinder block are provided with intake and exhaust orifice in a diagonal position. The tooth groove of the Yin rotor meshes with the Yang rotor and is driven by the Yang rotor. The exhaust end of the rotor is provided with a thrust roller bearing to prevent axial movement of the rotor. After the air lubricant mixture is discharged from the compressor, it enters the separation system, which is located in the oil separator. After the gas mixture flows through the separation system, almost all the oil is removed from the exhaust air, which contains only a few parts per million of oil. The separated oil returns to the lubrication system while the compressed air flows into the aftercooler. The rear cooler system consists of a heat exchanger, a condensate separator and an automatic condensate discharge device (the latter two constitute a water separator). With the cooling effect of compressed air, most of the water vapor contained in the air is condensed out, and then enters the post-processing unit to each gas point. The lubricating oil system consists of oil separator, oil cooler, temperature control valve and oil filter. The separated lubricating oil enters the oil cooler through the temperature-controlled valve for cooling, filters through the oil filter and returns to the compression chamber to complete a cycle.

In addition to the heating temperature rising due to the poor running condition of the running parts, the most important factors affecting the exhaust temperature are the suction temperature, the quality of the lubricating oil, the oil return volume and the oil return temperature.

1. Influence of suction temperature

The suction temperature is mainly affected by the ambient temperature. If the ambient temperature is higher, the suction air temperature is higher, which inevitably leads to the rise of the compression temperature and the subsequent rise of the exhaust temperature. If you want to lower the suction temperature, you need to change the suction orifice to the room, which is not available for improvement.

2. Lubricating oil quality

The main effect of lubricating oil quality is that if the lubricating oil emulsification or oil quantity is too small, the cooling effect of lubricating oil is not enough and the exhaust temperature rises. Check the quantity of lubricating oil and find that the quantity of lubricating oil conforms to the standard. The quality analysis of lubricating oil is also qualified, and the influence of lubricating oil quality can be excluded.

3. Lubricating oil return amount

The oil return amount is mainly related to the oil filter element. The oil filter element of the screw air compressor has a relatively high precision, usually less than 20 m. When the oil filter element is used for too long and easy to be blocked, the oil return is not smooth and the oil return amount is reduced, resulting in the exhaust temperature rising due to insufficient oil supply to the main engine.

4. Influence of return oil temperature

The return oil is mainly cooled by the oil cooler, which is a fixed copper tube heat exchanger, with the shell medium as lubricating oil and the pipe medium as circulating water. Under the condition that the cooling area of the oil cooler is fixed, the circulating water in the pipe is an important factor affecting the return oil temperature. In the oil cooler shell inlet, there is also a temperature control valve, the main role of the temperature control valve is to control the minimum oil injection temperature of the compressor, because the lower oil injection temperature will make the compressor exhaust temperature is low, and the condensate in the oil separator, deterioration of the quality of lubricating oil, shorten its service life. When the injection temperature is higher than a certain temperature, the mixture of air and oil will always be higher than the dew point temperature. The temperature control valve controls the flux of the oil to keep the injection temperature in a suitable range. At the beginning of the compressor, the machine is cold, part of the lubricating oil does not go through the cooler. When the temperature rises and exceeds the set value of the temperature control valve, the lubricating oil will all flow through the cooler. During periods of high ambient operating temperatures, all lubricants will pass through the cooler, so the operating status of the temperature control valve will also affect the return oil temperature.

5. Problems existing in circulating cooling water of oil cooler

Air compressor station circulating water at the end of the circulating water pipe network, adjacent there was hot water circulating water heat exchanger, air pressure machine interstage cooler water consumption, the pressure of 0.3 MPa, and the air compressor station circulating water head of nominal diameter as the DN100, access to the oil cooler pipe nominal diameter as the DN32, the length is about 1.5 meters, with precision pressure gauge pressure at the scene of the oil cooler cooling water inlet measured about 0.2 MPa. This indicates that the circulating water main from the air pressure station passes through the circulating water branch pipe of the oil cooler, and the pressure drop in the pipeline of the oil cooler is too large, resulting in too small pressure difference at the inlet and outlet of the oil cooler, and a serious shortage of circulating water. It can also be seen from table 2 that the temperature difference of circulating water in the oil cooler 2# machine is up to 30℃ and the drainage temperature is 60℃, which makes it necessary to change the drainage to straight drainage in high temperature period to ensure the operation of the air compressor, wasting a lot of water resources.

(ii) short life analysis of oil and gas separation core

After mechanical (primary) separation of the oil and gas mixture in the separator, fine separation is carried out through the oil and gas separation filter. After the main separation of the 0.05% (500 PPM) mixture of oil and gas, the diameter of the oil particle is about 0.01m. When small oil droplets pass through micron-sized glass fiber filter material layer, they aggregate into large oil droplets through inertial collision, direct interception diffusion mechanism and condensation. Under the action of airflow and gravity, oil droplets gather at the bottom of the filter core and return to the nose through the tubing from the core.

1. Lubricating oil quality of air compressor

The choice of lubricating oil is closely related to the service life of oil and gas separation core. The oil filling screw air compressor USES synthetic oil, semi-synthetic oil, mineral oil and so on. Due to the different properties of various oils, the test shows that the high quality oil and gas separation core has different working life under different lubrication conditions.

The selected lubricating oil should be anti-aging, water resistance, high temperature resistance, not easy to volatile. Oil with poor oxidation resistance will form thick sediments after oxidation at high temperature, which are easy to adhere to the surface of the oil and gas separation core and block the micropores of filter material. Oil ages easily at high temperature. When changing the oil, try to change all the used oil to avoid new oil contamination.

2. Oil and gas separator

Liquid liquid droplet size of liquid oil the mixture of oil and gas compresses the nose very widely. Most of the oil droplets are usually 1 thousandth of a meter in diameter and 50 thousandths of a meter in diameter. A small number of droplets can be as small as the same order of magnitude of gaseous molecules, only 0.01 nm. When the oil and gas mixture enters the separator and the collision of mechanical separation (centrifugation, diffusion, gravity) passes through a well-designed baffle,99.7% of the oil mixture should separate the oil content mixture into the oil and gas separation filter element is 0.05%. (500 PPM). Some air compressor manufacturers due to irrational oil and gas separation tank structure design, scale is too small, and the height between the gas and liquid phase is too small, etc., leading to the separation effect of the main (mechanical) oil and gas separator, even after the use of imported filter element started. It is also the key factor to determine the working life of oil and gas separation core.

3. Replace the air filter and oil filter

The core can separate not only the oil but also the solid impurities in the mixture. These solid particles are intercepted by the filter element and deposited on the filter material, increasing the pressure difference (resistance) of the filter element. If the elements in the air filter cannot effectively filter out the dust in the atmosphere, the solid particles in the lubricating oil enter the lubricating oil system, and when the lubricating oil filter element fails to filter out properly, it can cause the addition to the oil and gas separation core filter layer. The service life of oil and gas separation core is related to the pollution degree of lubricating oil. To reduce oil pollution, air filters and lubricating oil filters should be replaced regularly, and their filtration accuracy is required.