Air compressor
The compressor is a general-purpose mechanical equipment in industrial production, widely used in various sectors such as petroleum, chemical engineering, power metallurgy, mining, construction, light industry, pharmaceuticals, civil and national defense, and holds an important position in the national economy. Therefore, it is of vital importance to rationally select the model that suits the production configuration requirements of the process. This can significantly reduce the purchase cost of compressors and is of great significance for energy conservation, increasing output, reducing the burden on enterprises, and boosting their income.
The so-called reasonable selection of compressors means to comprehensively consider the comprehensive technical and economic indicators such as the investment and operation costs of the compressor unit and the compressor station, so as to conform to the principles of economy, safety and applicability. Specifically, there are the following aspects:
1. It is necessary to meet the flow and pressure requirements of the production process, that is, the operating condition point of the compressor (the intersection point of the device characteristic curve and the performance curve of the compressor) should often remain in the high-efficiency range for operation. This not only saves power but also is less likely to damage the components.
2. The selected compressor should be small in size, light in weight, and low in cost, while also having good performance and high efficiency.
3. It has excellent anti-surge performance, operates smoothly and has a long service life.
4. Simple structure, convenient operation and easy purchase of accessories.
5. The selected compressor station requires less engineering investment and has low operating costs.
The selection of an air compressor is mainly based on the working pressure and flow rate of the starting system. The working pressure of the air source should be approximately 20% higher than the maximum working pressure in the pneumatic system, as the along-way loss and local loss of the air supply pipeline need to be taken into account. If the working pressure requirement in some parts of the system is relatively low, a pressure reducing valve can be used to supply gas. The rated exhaust pressure of air compressors is divided into low pressure (0.7 to 1.0Mpa), medium pressure (1.0 to 10MPa), high pressure (10 to 100 mpa), and ultra-high pressure (above 100 mpa), which can be selected according to actual needs. The common operating pressure is generally 0.7 to 1.25Mpa.
Compressor performance characteristics
① Air characteristics: local atmospheric pressure, local relative humidity of air, etc.
② The diameter and content of solid dust particles contained in the air.
③ Air temperature: (℃
④ The required flow rate (Nm³/min or Nm³/h
A. Flow rate, which domestic users often refer to as displacement. Flow rate refers to the statistics of the gas discharged by the air compressor per unit time under the required exhaust pressure, converted to the intake state.
B. The flow rate unit is: m³/min (cubic meters/minute) or L/min (liters/minute), 1m³ (cubic meters) =1000L (liters).
C. Generally, the commonly used flow unit is: m³/min (cubic meters per minute);
D. Flow rate is also known as displacement or nameplate flow rate.
6. Pressure: Design pressure, maximum working pressure, working pressure.
There are many forms of pressure unit representation. Here, we mainly introduce the commonly used pressure representation units for centrifugal air compressors.
① Working pressure, often referred to as exhaust pressure by domestic users. Working pressure refers to the maximum pressure of the gas discharged by the air compressor.
The commonly used units of working pressure are: bar or MPa, with 1bar equal to 0.1MPa.
③ Generally, users usually refer to the pressure unit as: kg/㎡,1bar=1kg/㎡.
7. Pipeline system data (pipe diameter, length, types and quantities of pipe fittings, etc.).
When designing and laying out pipelines, the following points should be noted:
① Choose the pipe diameter reasonably. The pipe diameter is large. Under the same flow rate, the air velocity is small, the resistance loss is small, but the price is high. A small pipe diameter will lead to a sharp increase in resistance loss, causing the power of the selected compressor to rise, as well as the cost and operating expenses. Therefore, it should be comprehensively considered from both technical and economic perspectives.
② The maximum pressure that the gas supply pipeline and its pipe joints can withstand should be taken into consideration.
③ Pipeline layout should be as straight as possible, minimizing the number of accessories in the pipeline and reducing the pipeline length. When turning is necessary, the bending radius of the elbow should be 3 to 5 times the pipe diameter, and the Angle should be as large as possible than 90 degrees.
④ A supply valve and a check valve must be installed at the riser pipe of the compressor. Valves are used to control the operating point of the compressor. When the air pressure suddenly surges and the pipeline pressure exceeds the compressor outlet, the check valve prevents the compressor from reversing to avoid damaging the impeller and reversing the motor.
When a user is preparing to purchase a compressor, the first step is to determine the working pressure required at the gas consumption end, add a margin of 1 to 2bar, and then select the pressure of the air compressor. (This margin takes into account the pressure loss in the pipeline distance from the installation site of the air compressor to the actual gas consumption end. The pressure margin should be appropriately considered within the range of 1 to 2bar depending on the length of the distance.)
Of course, the size of the pipe diameter and the number of turns are also factors affecting pressure loss. The larger the pipe diameter and the fewer the turns, the smaller the pressure loss. Conversely, the pressure loss will be greater.
Therefore, when the distance between the compressor and the pipelines at each gas-consuming end is too far, the diameter of the main pipeline should be appropriately increased. If the environmental conditions meet the installation requirements of the air compressor and the working conditions permit, it can be installed near the gas consumption end.
When choosing the flow rate of an air compressor, one should first understand the flow rates of all air-consuming equipment and multiply the total flow rate by 1.2 (i.e., increase the margin by 20%).
A. If the minimum, normal and maximum flow rates have been provided in the production process, the maximum flow rate should be considered.
B. If only the normal flow rate is provided in the production process, a certain margin should be considered to be left.
C. The flow units should be unified. Currently, the flow units used in China are: Nm³/min or Nm³/h. Under normal circumstances, the leakage in the pipeline system of industrial compressors can be ignored in the process flow, but the impact of process changes on the flow rate must be taken into account.
② For new projects, the flow rate values provided by the design institute can be used for selection.
③ Consult the gas equipment supplier to understand the flow parameters of the gas equipment for selection.
④ For the renovation of the air compressor station, the selection can be made by referring to the original parameter values in combination with the actual gas consumption situation.
In recent years, the compressor industry has designed and developed many high-efficiency and energy-saving products. However, at present, in various fields of the national economy, due to unreasonable selection, many compressors are operating in an unreasonable state, with low operating efficiency and a large amount of energy wasted. Some compressors, due to unreasonable selection, cannot be used at all, or the cost of use and maintenance increases, resulting in low economic benefits. Therefore, appropriate selection can protect the unit, extend its service life, reduce maintenance frequency, lower operating costs, save energy consumption, and avoid unplanned shutdowns.
