Summer is coming, how to avoid high temperature screw air compressor failure?

Before entering summer, in order to avoid over-temperature shutdown, compressor users will carry out preventive overhaul on the equipment. Conventional treatment methods include changing lubricant, cleaning oil cooler, air cleaner, cooling water line, etc. This can eliminate most potential high temperature hazards of exhaust gas, but sometimes it can not completely eliminate all potential causes of failure. We must pay attention to them.More detailed analysis of how to avoid high temperature screw air compressor failure.

Although current compressor manufacturers have designed high temperature trip protection devices, frequent trip without thoroughly solving the cause of failure will not only cause unnecessary losses to the equipment itself, but also affect the normal production and product quality of the enterprise.

Generally, the occurrence of compressor over-temperature fault is mostly related to the abnormality of lubrication and cooling system, so we first analyze it from the following aspects.

Lubrication system and oil circuit components

Lubricant for injection screw compressor has many functions such as lubrication, cooling, flushing, sealing, vibration reduction, unloading and protection.One of the most important is cooling.Most of the heat generated by the compressed air in the engine head is taken away by the lubricating oil and a little of it is radiated by the conductive radiation.Insufficient lubricant or abnormal operation of oil circuit components will cause oil temperature to rise, which may cause over-temperature fault.

(1) Lube oil overdue deterioration

Lubricants must be replaced on time, if overdue service will result in poor fluidity and reduced heat exchange performance.The heat from the head cannot be completely removed, resulting in high temperatures in the compressor.

(2) The system is short of oil.

Oil level in oil and gas drums can be checked. After pressure relief during shutdown, the oil level should be slightly higher than that of high oil level mark H (or MAX) when the oil is static.During the operation of the equipment, the oil level must not be lower than the low oil level mark L (or MIX).Stop and refuel immediately if insufficient oil is found or the oil level is not observed.

(3) Insufficient oil supply.

First check whether the oil filter and oil separator are blocked.The oil separator is made of multi-layer glass fiber, which filters the oil mist in the compressed air to prevent the loss of lubricant.When the environment is poor and dust is high, the replacement period should be shortened appropriately.Oil filter and oil separator are designed with differential pressure switch, which can automatically determine whether the filter is blocked by detecting the two true differential pressure of the filter. If the filter is blocked, the filter and separator should be replaced in time.Next, check whether the fuel quantity regulator is normal or not, and properly increase the amount of fuel injected if necessary.The amount of fuel injected has been adjusted when the equipment is shipped, and it is generally best not to change it.

(4) Fault of oil shutoff valve.

Oil shutoff valves are usually two-position two-way normally closed solenoid valves, which open when starting and close when stopping, so as to avoid oil in oil and gas barrel continuing to inject into the engine head and eject from the intake port when stopping.If the oil shutoff valve fails, the main engine will heat up quickly due to oil shortage, or even the screw assembly will be burnt out.

_Failure of temperature control valve

The temperature control valve is installed in front of the oil cooler to maintain the exhaust temperature of the engine head above the pressure dew point.Its working principle is that at the beginning of the engine, due to the low oil temperature, the branch of the temperature control valve opens, the main circuit closes and the lubricant is directly injected into the engine head without the cooler.When the temperature rises above 40 C, the temperature control valve closes gradually and oil flows through the cooler and bypass at the same time.When the valve is fully closed when the temperature rises above 80 C, all the lubricating oil enters the engine head through the cooler to cool the lubricating oil to the maximum extent.

If the temperature control valve fails, the lubricant may not enter the engine head directly through the cooler, thus the oil temperature cannot drop, causing overheating.The main reasons for its failure are: first, the elastic coefficient of the two thermal springs on the valve spool, large and small, changes after fatigue and can not act normally with temperature changes;Second, the valve body is worn, the spool is stuck or the action is not in place and can not close normally.It can be repaired or replaced as required.

Cooling system

The cooling system of screw compressor is mainly divided into air cooling and water cooling.

(1) Air cooler type

(1) For air-cooled compressors, it is necessary to check whether the ambient temperature is too high, which will affect the screw compressor in the following two aspects.

A: The higher the temperature, the thinner the air (as if the compressor was inefficient in the plateau area), resulting in a reduction in compressor efficiency, allowing more time for the compressor to be loaded and carrying more loads, resulting in more heat generated by the compressor, which will definitely increase the compressor temperature.

B: When the compressor is designed, there is a design operating environment temperature (30-40 degrees). The highest temperature of the compressor is close to the protection temperature of the compressor (e.g. 100 degrees Celsius) at the designed operating environment temperature. If the compressor ambient temperature is higher than the designed operating environment temperature, the compressor temperature will be increased, which will cause high temperature of the compressor.

(2) Fan failure of air cooler

If the fan does not turn and the fan is in opposite phase, only one of the two fans is turned on and so on.

3. Exhaust duct problems

Generally, there are such situations as too small overwind surface of exhaust duct, too long exhaust duct and too many bends in the middle of exhaust duct.Generally, however, such design deficiencies are rare.

(2) Water cooler type

1. Check whether the oil cooler is working properly.

The temperature difference of the inlet and outlet water pipes can be checked. Normally, the temperature should be 5-8 degrees Celsius. Scaling or blockage may occur below 5 degrees Celsius, which will hinder the heat exchange efficiency of the cooler and cause poor heat dissipation. At this time, the heat exchanger can be removed and cleaned.

Generally, poor cooling water quality and high hardness are important factors for oil cooler malfunction rather than the failure of the equipment itself.Four water-cooled screw compressors of a power company in Henan often trip due to high temperature alarm during operation. It is found that the main reason is that there is a lot of scaling in the cooler, blocking the cooling water pipe, affecting the flow of cooling water, poor heat exchange effect, and even unable to play a cooling role after all blockage, which causes the compressor to trip due to high temperature and can not be put into normal use.The cooling water source of the compressor cooler is industrial water with high PH value and high hardness (about 10 mmol/L). When the heat generated by the operation of the equipment causes the cooling water temperature to exceed 40 ~C (the compressor manufacturer suggests that the outlet temperature of cooling water should be less than 50 ~C), salt precipitation in the cooling water is intensified, causing scaling on the cooler surface.Frequent scaling requires manual scale removal and heavy maintenance.At the same time, due to poor heat exchange effect of scaling, high oil temperature, low viscosity and wear of bearings, potential safety hazards of equipment are caused.

2. Check whether the inlet temperature of cooling water is too high and whether the water pressure and flow rate are normal.

In general, the inlet temperature of cooling water should not exceed 35%, the water pressure should be between 0.15 and 0.3MPa, and the flow rate should not be less than 90% of the specified flow rate.Often companies using water-cooled compressors do not have separate cooling water systems for their compressors, but share the same cooling system with other processes.Excessive links cause great impurities in cooling water, which forms scale on the wall of long cooling water pipes, resulting in smaller passage of water pipes, lower water pressure and insufficient flow rate.If the working environment can not meet the above requirements, it can be solved by installing cooling tower, improving indoor ventilation and enlarging engine room space.

Intake and exhaust system and control line elements

Failure or insensitive action of intake and exhaust system and control piping elements will imbalance compressor operation and cause high temperature of equipment.We can check each of the following steps.

1. Check whether the air filter is blocked

Air filter blockage can be checked or replaced according to alarm signal of differential pressure switch.

(2) If the oil-gas separator is blocked and the compressed air is not expelled smoothly, it will cause high internal pressure and high temperature.Blockage of oil and gas separator is mainly manifested by high internal pressure, so it is necessary to check and replace oil core on time.

(3) Increased internal pressure of oil separator due to failure of minimum pressure valve

The minimum pressure valve is mounted on the flat cover of the oil/gas separator and performs the following functions:

A. Ensure that the pressure required for lubricant circulation is established prior to starting to ensure lubrication of the unit.

B. Opening after the pressure reaches the minimum pressure valve setting reduces the air flow through the filter element of the refined oil-gas separator, ensures the effect of oil-gas separation and prevents the oil-gas separator element from being damaged by excessive pressure difference.

C. It has the function of a check valve to prevent the compressed air in the pipe network from backflowing into the oil-gas separator and compressor host when the unit is unloaded.During unit operation, the fault of minimum pressure valve will cause the internal pressure of oil separator to rise, and the lubricant cycle can not be established preferentially when starting. The effect of oil-gas separation will become worse, which will easily cause the pressure difference of oil-gas separation filter element to be too big and damaged, thus easily causing high exhaust temperature of unit.

(3) Is the system pressure set too high?

The system pressure of the compressor is generally set at the factory. If the user really needs to adjust, the rated pressure calibrated by the equipment nameplate shall prevail.If the system pressure is adjusted too high, the compressor load will increase and a high temperature alarm will be triggered.

epilogue

In addition to the above reasons, there are other reasons for screw compressor over-temperature fault, such as temperature sensor fault, unloading valve malfunction, etc.In order to ensure the long-term smooth operation of screw compressor, we should not only do regular maintenance every day, month and year, but also strengthen the professional and technical learning in the daily operation process to reduce the risk of misoperation and improve the operation efficiency of the equipment.