How to Keep Good Circulating Cooling Water of a Water-Cooled Air Compressor

Figure 1: A water-cooled air compressor system.

In response to the requirements of energy conservation and environmental protection, more companies choose to use water-cooled air compressors. The heat generated by the compression of the air compressor is exchanged by the cooler, and the water takes the heat away. The heat will increase the temperature of the circulating cooling water for people's production and daily use to achieve the effect of energy saving and emission reduction.

Thanks to the feature of saving energy, most companies use water-cooled air compressors. Compared with air-cooled ones, water-cooled air compressors will greatly reduce electricity consumption to save a lot in power distribution and power supply for users. And in summer, the failure rate of the air compressor unit could be reduced a lot.

In summer, due to bad circulating cooling water, there are many accidents that cause the main engine of the air compressor unit to shut down. If the temperature of water from the inlet exceeds 35°C, the temperature of the main engine of the air compressor unit will reach 120°C, leading to alarm and stop. It will trigger the high temperature alarm and stop the compressor. So ensuring good circulating cooling water is very important to the water-cooled air compressor unit. This article will briefly introduce the maintenance methods of the water-cooled compressor giving the principle.

Water-Cooled Compressor Working Principle

The main components of a water-cooled compressor include the drive motor, the main engine, the oil and gas separator, the oil filter, the minimum pressure valve, the intake load relief valve, the safety valve, the water-cooled cooler, the oil cooler, etc. The air-cooled compressor and water-cooled compressor defers in the water cooler and oil cooler. Fig. 2 is the flow chart of the water-cooled system.

The basic requirements of most equipment manufacturers for the circulating cooling water of the compressed air unit is to keep clean and no impurities. Besides, the pressure is higher than 0.2MPa, and the temperature difference between inlet and drainage is about 10°C, and the water should be softened.

As for circulating cooling water, it should not corrode cooling equipment and pipeline, and to avoid scales on the surface of the cooler. In addition, the mechanical impurities and organic matters in the water must be restricted to prevent the unit from high temperature malfunction causing system explosion.

Figure 2: The flow chart of a water-cooled system.

Therefore, to ensure the safe operation of the unit, improve the working efficiency of the unit and reduce energy consumption, here are the specifications for the suspended solids, pH value, temporary hardness of water, organics, oil contents and the temperature of water from inlet and outlet in the circulating cooling water:

Non-acidic water with a pH between 6.5 and 9;
Suspended matter content is generally not more than 25mg/L;
Organics are generally not more than 25mg/L;
The carbonate hardness of water is generally not greater than 10mgN/L;
Oil content is generally not more than 5mg/L;
The water temperature of the unit is generally not more than 30°C, and the short-term water temperature in hot areas is not more than 35°C.

Installation Requirements

The circulating cooling water pipeline system must be firstly installed with shockproof soft joints, the thermometer, the pressure gauge, the drainage valve, the cut-off valve, the water filter, the check valve, the target flow controller, etc., and then connected to the inlet and outlet pipes of the cooling tower. Refer to the pipe connection of figure 3.

Figure 3: A cooling tower.

The water supply pipeline should be as short as possible, whose specifications should be according to the effective head of the pump, pipeline flow and velocity, instead of the joint specifications. The cooler head is equipped with drainage and exhaust joints, sealed with screw plugs, which are replaced with (1/4 NPT discharge and 1/2 NPT drain) quick opening valves.

The nozzle of the cooler can follow the installation requirements of different manufacturers. Note the following during installation:

To confirm the correct installation position of inlet and outlet valves.

The temperature and flow measurement device of the circulating cooling water should be complied with the overall arrangement of equipment in the air compressor station room.

Maintenance Methods

Before checking the starting cabinet, you must shut it down and disconnect it to all power switches. The inspectors must own electrician operation certificates issued by the local authorities. Check the surface of the cabinet’s contactor for wear and dents. You should not polish silver-plated contacts.

The newly installed or replaced power connector may become loose after one month of use. You can disconnect it and fasten the connector again. Check it once a year and clean the dust inside the starting control cabinet regularly.

You should check the heat exchanger of the cooler every year. The cleaning cycle can be determined by the scaling and water quality in the tube. The cleaning methods can be divided into manual and chemical cleaning.

Because of the thread inside the heat exchange pipe of the cooler, you must use a special rotary-type heat exchanger cleaning system for manual cleaning. To avoid scratching the heat exchanger of the cooler, you should not use wire brushes.

Check whether the temperature sensor is corroded and scaling. If corroded, the sensor must be replaced; if scaling is formed, chemical cleaning is needed. The chemical cleaning method of the heat exchanger of the cooler is identical with that of the circulating cooling water of the central air conditioner.

By adding the chemical descaling agent to the circulating cooling water to strip the scale of the inner surface of the heat exchanger of the cooler, and add the corrosion inhibitor to prevent the original heat exchanger from damaging after the scale is stripped. If you adopt the chemical cleaning method, the copper pipe of the heat exchanger will leak after being cleaned, which will cause the entire heat exchanger to fail. As a result, you must replace a new cooler.

Figure 4: A type of descaling agent.

Matters Needing Attention for a Shutdown

After the air compressor unit is stopped, the main power switch should be cut off in the distribution cabinet.

If the air compressor unit is in a state of long-term shutdown, you should discharge all the water inside the circulating cooling water system to prevent corrosion and freezing of the heat exchanger pipeline in winter.

When the unit is shut down for a long time, the overall maintenance should be completed. During the shutdown, the air compressor unit should be completely covered to reduce ashes. And only designated persons can operate on the compressor. Each valve in the circulating cooling water system should not be opened or closed without permission.

Conclusion

In short, for a water-cooled air compressor unit, if the open circulating cooling tower is adopted, a circulating cooling water system is necessary to ensure its normal operation. Generally when the air compressor station building is constructed, the design institute will conduct professional calculation and configuration of the specifications and parameters of the circulating water pump, the circulating water pipe diameter and the cooling tower tonnage according to the requirements of the water quantity and water pressure for the air compression cycle provided by the owner, which will be constructed together with the construction of the air compressor station in the early stage.

As for different air compressor units, the inlet and outlet pipe diameter and water consumption parameters are provided, which can be carried out with the whole circulating cooling water system in the air compressor station.

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