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01, gas volume control and regulation

80% of the total cost of compressed air is reflected in energy consumption, so different types of compressors should choose different control and regulation systems according to different regulation systems。The difference between different compressor types and manufacturers can make a world of difference in performance。The most ideal state is to make the compressor full load and air consumption exactly consistent。

For example, this requirement can be achieved by carefully selecting the gear ratio of the gearbox, which is common in process compressors。Most devices that consume compressed air are self-regulating, meaning that increasing the pressure will increase the flow rate, which is why they form stable systems such as pneumatic conveying, anti-icing and freezing。Under normal circumstances, the flow must be controlled, and the control equipment used is integrated with the compressor. There are two main categories of this type of regulation system:

1.Adjust the gas volume by constantly controlling the speed of the drive motor, or continuously control the valve according to the change of pressure to achieve continuous adjustment of the gas volume。The result is a small pressure change (0.1至0.5bar The size of the change is determined by the amplification function of the adjustment system and its speed。

2.Load and unload regulation is the most common regulation system, and the pressure change between the two is also acceptable。The method of adjustment is: completely cut off the air flow at higher pressure (unloading), and when the pressure is reduced to the lowest value, the flow is restored (loading).。The pressure varies depending on the number of times the load/unload cycle is allowed per unit time, usually the pressure is 0.3 to 1bar Range variation。

02. Basic principle of gas volume regulation

2.1 Adjustment principle of Positive displacement compressor (pressure relief valve)

The basic principle method is: to release the excess pressure into the atmosphere, the simplest design of the pressure relief valve is loaded with a spring, and the spring's jumping force determines the final pressure。The relief valve is usually replaced by a servo valve controlled by a regulator, where the pressure can be easily controlled, and can also act as a relief valve when the compressor is started with pressure, but the relief valve causes a lot of energy consumption, because the compressor must be continuously operated at full back pressure。There is a scheme for small compressors, the valve is fully opened, so that the compressor is unloaded, the compressor works at atmospheric pressure, using this method power consumption is more affordable。

2.2 Bypass regulation

In principle, by-pass regulation and pressure relief valves have the same function, the difference is that the pressure release air is cooled and returned to the compressor air intake, this method is commonly used process compressor, gas should not be directly discharged into the atmosphere, the cost is too expensive。

2.3 Inlet throttling

Inlet throttling is an easy way to reduce flow by creating a low pressure at the inlet and increasing the compression ratio of the compressor for a smaller adjustment range。The spray compressor allows a large compression ratio, which can be reduced to a maximum of 10%, which results in relatively high energy consumption due to the high compression ratio。

2.4 Pressure relief valve with intake throttle

This is the most common adjustment method, you can get the maximum adjustment range (0 to 100%), and low energy consumption, compressor unloading (zero flow) power is only 15 to 20% of the full load。When the intake valve is closed, leave a small hole and open the air to discharge the air from the compressor。The compressor host works in the imported vacuum and low back pressure state, it is important that the pressure release should be fast, and the volume to be released should be small, so as to avoid unnecessary losses when the full load is converted to no load。The system requires a system volume (gas tank), the size of which depends on the required pressure difference between unloading and loading, and the number of cycles allowed per hour。

Less than 5-10kW compressor commonly used on/off method to adjust, when the pressure reaches the upper limit, the motor completely stop;When the pressure falls below the lower limit, the motor restarts。This method requires a large system volume or a large pressure difference between the startup pressure and the shutdown to minimize the load on the motor。In the case of a small number of starts per unit time, this is an effective adjustment method。

2.5 Speed adjustment

The speed of the compressor is controlled by an internal combustion engine, turbine, or frequency-modulated motor to control the flow rate。It is an effective way to maintain a constant outlet pressure。The adjustment range varies according to the type of compressor, but the spray compressor has the largest range。When the load degree is low, the speed regulation and pressure relief are usually combined, with or without the intake throttle。

For compressors powered by a power motor, the speed of the motor can be controlled by an electrical appliance, thus providing an opportunity to control the speed of the motor and keep the compressed air constant within a small range of pressure changes。For example, an ordinary induction motor can achieve this requirement by adjusting the speed with a frequency converter, continuously and accurately measuring the pressure of the system, and then allowing the pressure signal to control the frequency converter of the motor, thereby controlling the speed of the motor, so that the gas volume of the compressor can precisely adapt to the air consumption, and the system can be maintained at ±0.1bar 。

2.6 Variable exhaust port adjustment

The exhaust volume of the screw compressor can be adjusted along the length of the housing, moving the position of the exhaust port towards the intake end。This method requires high power consumption at partial loads and is relatively uncommon。

2.7 Unload the suction valve

Piston compressors can be unloaded by mechanically forcing the suction valve in the open position。As the position of the piston changes, air moves in and out。The result is minimal energy loss, usually less than 10% of the full load shaft power。On dual-acting compressors, it is generally multi-stage unloading, and a cylinder is balanced at one time, so that the gas volume can reach the corresponding supply and demand。A partial unloading method is used on the compressor, which allows the valve to be opened when the piston is in a partial stroke, thus achieving continuous gas volume control。

2.8 Clearance volume

By changing the clearance volume on the piston compressor to reduce the degree of inflation of the cylinder, thereby reducing the gas volume, it can also be changed by means of an externally connected volume。

2.9 Load, unload, and Stop

For compressors with a power greater than 5kW, this is the most common method, with a large adjustment range and low loss, in fact, this is a combination of on/off adjustment and various unloading systems。Positive displacement compressor, the most common regulation principle is "produce air"/" do not produce air "(loading/unloading), when the air is needed, a signal is sent to a solenoid valve, in turn guide the compressor inlet valve to reach the full open position。The intake valve is either fully open (loading) or fully closed (unloading), with no intermediate position。

The traditional control method is to install a pressure switch in the compressed air system, and the switch has two settable values, one is the minimum pressure (loading) and one is the maximum pressure (unloading).。The compressor works within the set value limit, for example, 0.5bar。If the air requirement is small, or not required at all, the compressor runs without load (idling), and the idling period is set by a time relay (for example, 20 minutes).。oversetTime, the compressor stops, and no longer starts, until the pressure drops to the minimum value。This is the traditional reliable, reassuring control method that is now most commonly found in small compressors。

This traditional system is further developed to replace the pressure switch with an analog pressure transmitter with a rapid electronic regulation system。Together with the regulating system, the pressure transmitter can feel the pressure change in the system at any time。The system starts the motor in time and controls the opening and closing of the intake valve。能在±0.2bar Inside, achieve fast and good adjustment。If no air is used, the pressure will remain constant and the compressor will run empty (idling).。The length of the idling cycle can be determined according to the number of starts and stops that the motor can withstand, without overheating, and the economy during operation。The latter is because the system can decide whether to stop or continue idling according to the direction of air consumption。

03、小结

In short, compressed air in different applications, different gas consumption, each air compressor gas mode is different, but according to the size of the user's gas consumption, the compressor unit relies on its own gas control and adjustment mode to achieve uninterrupted and continuous gas supply。Different compressor manufacturers are also using different regulation principles to improve the performance of their own brands of compressors to maximize energy efficiency and meet customer requirements;With high accuracy and small maintenance, it can measure parameters such as pressure and flow rate to meet the application of different occasions。