Automatic control scheme for multiple adsorption dryers and air compressors


   With the development of modern industry and the improvement of automation level, various industries have higher and higher requirements for air supply, purification level, automatic control, and continuous and reliable air supply of air compressor stations. For example, the development and change of the air compressor room of a power plant is typical, and at the same time, it needs to meet the traditional requirements in terms of reliability, that is, one standby machine for maintenance and standby at any time. How to use the cross-linked control of multiple units to minimize the number of standby machines and the number of automatic valves in the pipeline system, reduce control costs and complexity, improve the automation of the air compressor station, and improve the working conditions of workers are many investors, Topics of concern to managers and professional technicians. The air compressor model discussed in this article is a medium-sized (10~40m3/min) oil-injected screw compressor with a wide range of areas, which also has reference value for other models.

   1. The working characteristics and structural characteristics of the adsorption dryer:

   At present, there are mainly two types of medium-sized adsorption dryers that are widely used in China, namely, non-heat regeneration and micro-heat regeneration. According to the original state of the inlet valve of the adsorption tower, it can be divided into normally closed type and normally open type (including shuttle valve structure). The intake and exhaust valves (adsorption intake valve and regeneration exhaust valve) that control the alternate switching of the drying tower are all pneumatic (pneumatic actuators, pneumatic membrane valves, pneumatic pilot solenoid valves, etc.). The basic condition for the dryer to enter the working state is "gas and electricity", and the standby state and the overhaul state are respectively "gas without electricity" and "gas without electricity". The gas extraction point of the control gas source (pneumatic valve gas source) is mostly set on the outlet side of the dryer (because the inlet side may contain oil and water), the gas source pressure is generally set at 0.2~0.6Mpa (set by the built-in regulating valve) .

2. Commonly used compressed air system and configuration:

2.1 Double mother pipe compressed air system:

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The system can realize the function of cross automatic start and stop of the dryer, and there is no need to set any automatic valve on the pipeline. Manual valves 3 and 12 are normally open and are closed manually during maintenance. After the maintenance is completed, turn on the standby again. At this time, the compressed air returns from the main pipe and pressurizes the drying tower through the regeneration pipeline to form a standby state of "gas without electricity". Since the control air source pressure point is set on the outlet side of the dryer, it is necessary to set a manual valve 15 as a bypass to establish the system pressure (that is, air) for the first startup. Otherwise, the pneumatic valves of the dryer cannot enter the operating state due to "no air". It must be noted that normally open valves (including shuttle valves) cannot be used for valve 9 in the double bus system, otherwise the standby dryer will become a smooth container.

2.2 Front single header compressed air system:

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The system also has a cross automatic start and stop function, but the exhaust side pipeline valve of the dryer cannot be normally opened in the standby state to prevent moisture from entering the tower, so the valve should be changed to a normally closed automatic valve, and the dryer should be energized Turn on after normal operation. As in Figure 1, the valve 9 must also be a normally closed type, and each time the dryer is turned on, the bypass valve is opened to build pressure for the device. In addition, it should be noted that the front mother pipe in Figure 1 and Figure 2 should not be placed low (such as a trench), otherwise it will become a water collection container.

2.3 Rear-mounted single main pipe compressed air system:

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In this system, the dryer is connected in series with a single air compressor, and the exhaust gas is supplied in parallel through the post-main pipe. This configuration does not have the cross automatic control start-stop function, but it can realize the stand-by of the single-unit series unit and other units. The stop valves 4 and 13 at both ends of the pipeline are manual, and can be assembled together with the bypass valve 15 in the dryer pipe system. The adsorption inlet valve 10 may be a normally open type (including shuttle valve). The above structure is the company's standard product, which has the characteristics of simple structure, unobstructed equipment pipeline, and convenient operation and maintenance.

2.4 Single unit series compressed air system:

This system generally does not require the joint control of the dryer and the air compressor. The dryer also mostly uses our company's standard product, that is, "air intake normally open, with bypass". If a single-unit joint control function is required, pipeline valves 4 and 13 need to be configured as automatic normally closed valves. Among them, the valve 4 is linked with the air compressor, and then the dryer and the valve 13 are started in sequence.

3. Conclusion:

The design of multi-unit air compressor station needs to take into account the technological advancement and economic applicability, and learn more about the structure and characteristics of the selected air compressor and post-processing equipment. Make use of the original equipment's own conditions and functions as much as possible to simplify the system, reduce costs, make the station room configuration reasonable, easy to operate, control linkage, and reduce standby.