Compressor is a kind of industrial production of general-purpose machinery and equipment, widely used in petroleum, chemical, electric power metallurgy, mining, construction, light industry, pharmaceutical, civil and national defense departments, in the national economy occupies an important position. Therefore, the reasonable choice of suitable process production configuration needs of the model is essential to vigorously reduce the purchase cost of the compressor, to save energy, improve production, reduce the burden on the enterprise, increase the revenue of the enterprise giant very great significance.
First, the introduction of Air Compressor
air compressor is the environmental air as raw material, the prime mover (usually motor) mechanical energy is converted to gas pressure energy machine to meet the pressure required by the production process. There are many classifications of compressor, according to the working principle can be divided into volumetric compressor and speed type compressor. Speed type mainly centrifugal and axial flow two basic types. The working principle of speed type compressor is to increase the speed of gas molecules, so that the gas molecules have the kinetic energy into the gas pressure energy, so as to improve the pressure of compressed air.
Second, the principle of air compressor selection
The so-called rational selection of compressors, that is, to consider the compressor unit and compressor station investment and operating costs and other comprehensive technical and economic indicators, so that it is in line with the principle of economy, safety and applicability. Specifically, the following aspects:
1, must meet the production process required by the flow and pressure requirements, that is, the compressor operating conditions require the point (device characteristics curve and the intersection of the performance curve of the compressor) is often maintained in the high-efficiency zone operation, so that both the power and not easy to save power damage to the machine parts.
2, the selected compressor should be small, light weight, inexpensive, but also to have good characteristics and high efficiency.
3, with good anti-surge performance, smooth operation, long life.
4, simple structure, easy to operate, easy to purchase accessories.
5, the choice of compressor station, engineering investment, low operating costs.
The selection of air compressor is mainly based on the working pressure and flow rate of the start-up system. The working pressure of the air source should be about 20% higher than the highest working pressure in the pneumatic system, because we have to consider the loss along the air supply pipeline and local losses. If the working pressure requirement is lower in some parts of the system, a pressure reducing valve can be used to supply air. The rated exhaust pressure of air compressor is categorized into low pressure (0.7~1.0Mpa), medium pressure (1.0~10MPa), high pressure (10~100Mpa) and ultra-high pressure (more than 100Mpa), which can be selected according to the actual demand. Commonly used pressure is generally 0.7~1.25Mpa.
Third, the air compressor selection steps
Compressor performance characteristics:
① air characteristics: local atmospheric pressure, local air relative humidity, etc..
② solid dust particles contained in the air diameter, content.
③ Air temperature: (℃)
④ Required flow rate (Nm³/min or Nm³/h)
a. Flow rate, often called exhaust volume by domestic users. Flow refers to the required exhaust pressure, the compressor unit time excluded from the gas statistics, converted to the amount of intake state.
b, flow rate unit is: m ³ / min (cubic meters / min) or L / min (liters / min), 1m ³ (cubic meters) = 1000L (liters).
c, general, commonly used units of flow are: m³/min (cubic meters per minute);
d, Flow rate is also known as exhaust volume or nameplate flow rate.
6, pressure: design pressure, maximum working pressure, working pressure.
Pressure unit is expressed in many forms, here mainly introduces the Centrifugal Air Compressor commonly used pressure unit; ① working pressure, the domestic users often use the pressure unit; ① working pressure, the domestic users often use the pressure unit.
① working pressure, domestic users often called exhaust pressure. Working pressure refers to the maximum pressure of the air compressor discharge gas; ① working pressure, domestic users often referred to as exhaust pressure.
② common working pressure unit: bar or MPa, 1bar = 0.1MPa; ③ general, users usually put the pressure of the air compressor.
③ General, the user usually refers to the pressure unit: kg / ㎡, 1bar = 1kg / ㎡.
7, piping system data (pipe diameter, length, type and number of piping accessories, etc.).
When designing and arranging piping, the following matters should be noted:
① Reasonable selection of pipe diameter. Pipeline diameter, in the same flow rate, air velocity is small, resistance loss is small, but the price is high; pipeline diameter is small, it will lead to a sharp increase in resistance loss, so that the selected compressor power increases, the cost and operating costs have increased. Therefore, it should be considered from a technical and economic point of view.
② gas pipeline and its pipeline joints should be considered to withstand the maximum pressure.
③ pipeline arrangement should be arranged as straight as possible, minimize the pipeline accessories and minimize the length of the pipeline, must be turned when the bend radius of the elbow should be 3 ~ 5 times the diameter of the pipe, the angle as large as possible more than 90 ° C. ④ compressor shrugged pipe, the compressor's power increases the cost and operating costs.
④ The compressor must be equipped with a gas supply valve and a check valve at the shrugged piping. Valve is used to control the compressor operating point, the backstop valve in the air pressure after a sudden sharp increase in pipeline pressure higher than the compressor outlet, to prevent the compressor reversal, to prevent damage to the impeller and motor reversal.
Fourth, the working pressure (exhaust pressure) selection
When the user is ready to buy a compressor, the first choice to determine the working pressure needed to use the gas end, plus 1 ~ 2bar margin, and then select the pressure of the compressor, (the margin is considered from the compressor installation site to the actual gas end of the pipeline distance pressure loss, according to the length of the distance between the 1 ~ 2bar appropriate consideration of the pressure margin).
Of course, when the size of the pipeline diameter and the number of turning points is also a factor affecting the pressure loss, the larger the pipeline diameter and the fewer turning points, the smaller the pressure loss; conversely, the greater the pressure loss.
Therefore, when the distance between the compressor and the air end of the pipeline is too far, the main pipeline diameter should be enlarged appropriately. If the environmental conditions meet the installation requirements of the air compressor and working conditions allow, can be installed near the end of the gas.
Fifth. Selection of flow rate
① In the selection of air compressor flow, you should first understand the flow of all air-using equipment, the total flow multiplied by 1.2 (i.e., enlarge the 20% margin); A. If the production process has been in the production process, you should know the flow of all air-using equipment.
A. If the production process has given the minimum, normal and maximum flow rate, the maximum flow rate should be considered.
B, if the production process is only given in the normal flow, should be considered to leave a certain margin.
C, the flow rate unit should be unified, currently used in China's flow rate unit: Nm ³ / min or Nm ³ / h. In general, industrial compressors in the process can be ignored in the pipeline system leakage, but must be considered when the process changes on the flow rate.
②Learn the flow parameters of the gas equipment from the gas equipment supplier for selection; ④ The renovation of the air compressor station can refer to the flow value provided by the design institute.
③air compressor station renovation can refer to the original parameter values combined with the actual use of gas for selection; ④ air compressor station renovation can refer to the original parameter values combined with the actual use of gas for selection.
In recent years, the compressor industry has designed and developed many energy efficient products, but at present, in various fields of the national economy, due to irrational selection, many of the compressor is in an irrational operating conditions, low operating efficiency, a large amount of energy is wasted. There are also compressors due to unreasonable selection, can not be used at all, or the use of maintenance costs increase, low economic efficiency. Therefore, the appropriate selection, can protect the unit, extend the unit life, reduce the number of maintenance, reduce operating costs, energy saving, to avoid the number of unplanned stops.