Due to its clear, non-staining, non-hazardous, easy-to-transfer fund projects, China Motor System Energy Conservation Project, United Nations Industrial Development Organization / Lawrence Berkeley Country. Under normal working conditions, the hand 68 dynamic control valves (MV1, MV2 and MV3) and the electric control valve are all closed, and the regulating valve (EV) is collected downstream according to the target pressure and pressure flow control system set by the control system. The actual pressure reached, the valve positioner (PO) constantly changes its opening to maintain the output pressure downstream of the pressure flow controller is always stable. The system can also react to the load changes of the system through software processing by monitoring the downstream pressure change rate and the upstream and downstream pressure difference. The system main execution device is as shown.
2 System energy-saving principle The interaction between the air supply side and the gas side of the compressed air system is a dynamic balancing process. The energy-saving principle of the supply and demand balance control system is actually mainly reflected in the following three aspects.
2.1 Reducing Compressed Air Consumption Combustion air consumption by gas side is mainly composed of gas used by pressure-controlled gas equipment (such as CNC machine tools, painting equipment, etc.) and gas without pressure control (such as leakage, open-circuit purging, etc.).
According to the principle of fluid mechanics, the flow of compressed air is proportional to the pressure exerted by the compressed air on the pipeline within a certain supply pressure range. The following is an example of a cylinder that uses compressed air as a driving force in the industry. The principle of reducing the supply pressure of the compressed air supply and demand balance control system and reducing the system air consumption is as follows: the air consumption of the cylinder and the piston diameter U of the cylinder, the piston rod The diameter of the piston stroke L and the number of reciprocating times N per unit time. For a typical single-shot double-acting cylinder, considering the leakage, the amount of compressed air consumed by the piston reciprocating once is converted to air at atmospheric pressure nine (absolute pressure). The volume is visible, and when the pressure of the cylinder intake air drops, the consumption of compressed air also decreases proportionally.
It is based on the experimental data drawn compressed air (fluid gas coefficient is 61) through the flow curve of the gas flow of small diameter holes with different diameters w. It can be seen that as the pressure rises, the compressed air flows through the small holes The flow rate of the system is obviously increased. The system provides a compressed air flow pressure of different diameters under different pressures for every 0.OIMPa, and the flow rate through the small holes to the atmosphere will increase by 1.43%. According to statistics, in the compressed air system, there is no Pressure-controlled gas (including direct use of compressed air, open-circuit purge and leakage, etc.) typically accounts for 30% and 50% of the total system gas used in industrial applications, and sometimes higher. According to this ratio, if the actual supply pressure of the compressed air system is more than a reasonable supply pressure 篼O.OIMPa, the gas-consuming equipment without pressure control will increase by 0.428%0.714. In addition, the air compressor power consumption and The relationship between the exhaust pressure is: for every O.OIMPa increase in exhaust pressure, the air compressor power will increase by about 0.714%. The two are combined and analyzed. For a compressed air system with a supply pressure of about 0.7 MPa, the air supply is provided. The pressure is 0.IMPa, which is the actual pressure of the system. The energy consumption of the air compressor will increase by 11.42% and 14.28%. If the pressure flow control system is installed in the system, the system can accept the minimum supply pressure to the system. Air supply, control system's compressed air consumption, to achieve energy-saving purposes.
2.2 Lifting off system operation reliability The separate gas storage tank also has a certain gas storage buffer function, but its function can be greatly enhanced after installing the balance control system, which not only stabilizes the system supply pressure, but also improves the system reliability. A separate gas storage tank is like a lake, and the installation of a pressure flow control system creates a dam as if it were a lake. When the water level of the lake rises, the water discharge flow is large, and after the dam is built, the water flow can be controlled according to the downstream needs. In most compressed air systems, the compressor discharge pressure is set higher than the target pressure because the tank has a buffer only when the pressure in the tank is higher than the lowest pressure of the actual gas. The role of gas. With the balance control system, the effective gas storage capacity of the gas storage tank can be effectively improved. The volume of the multi-storage gas can be estimated by the following method: the volume of the gas storage tank is the pressure of the gas storage tank (absolute pressure), The outlet pressure (absolute pressure) of the pressure flow boy control system, /> is the atmospheric pressure (absolute pressure), ignoring the temperature change of the compressed air before and after throttling. According to Boyle's law, it is a constant, and the system can be derived. According to the above analysis, the capacity and pressure of the gas storage tank and the pressure difference between the flow control system can be configured to meet the fluctuating gas demand continuously and effectively, and the system reliability can be reduced while reducing the system energy consumption. It is improved in the following aspects: Due to the voltage regulation of the pressure flow controller system, the supply pressure of the system will not fluctuate greatly, and the operation of the gas equipment in the system will be more reliable and stable, which will improve the quality and reduce the product quality. Waste products have considerable benefits, which indirectly reduce the production costs of enterprises.
Due to the increase of the compressed air energy storage system of the system, when an air compressor in the system is shut down due to reasons, the pressure drop of the system is slower than that without the pressure flow control system, and the time for the operator to respond is also extended accordingly. Improve the reliability of the system operation.
2.3 Lifting off the air compressor operating efficiency Because the operating pressure of the compressor's optimal efficiency point is difficult to match the actual demand pressure, if there is no supply and demand balance in the control system, if the compressor moves near the high efficiency point, Then the pressure of the compressed air actually provided may be much higher than the actual pressure required, which will inevitably increase the unnecessary use of the system; and lowering the supply pressure of the system may cause the compressor to be frequently downloaded, resulting in a decrease in compressor operating efficiency. Not only does it cause energy waste in the compressed air system, but it also shortens the service life of the air compressor. After the supply and demand balance control system is installed, the compressor can still operate at the helium efficiency point, and the supply and demand balance control system controls the supply air pressure of the compressed air system, so that the system can produce compressed air consumption under the same production load. The reduction, in turn, reduces the load time of the air compressor, thereby achieving energy saving purposes.
3 Control system application effect In order to verify the actual effect of the balance control system in the optimized operation of the compressed air system, the system supply and demand balance control system was installed in the compressed air system of the pump casting branch and the tobacco factory respectively, and before and after the control system was operated. The energy saving effect is compared with the test test.
3.1 Pump casting branch application test pump casting plant compressed air system consists of a 20m3 / min butterfly rod air compressor and three lOmVmin piston air compressor, compressed air is mainly used for casting grinding, sand transport and other processes, In normal production, a 20mVmin rod air compressor and two lOmVmin piston air compressors are in operation, and the air compressors are in operation at the peak of production. A one-week test of the pressure of the compressed air system, the flow of fluids and the power of the air compressor found that the system had the lowest pressure during production. 42MPa, the most 篼 is 068MPa. It is the pressure curve of the system during the 6h day of the day when the lowest and last enthalpy pressure are applied.
Time t / h field 4 system pressure curve After the installation of the balance control system in the compressed air system, the target pressure is controlled at 45 ± 0IIMPa, the system flow is significantly reduced, the system can still meet the system requirements when stopping a lOmVmin air compressor Through the test, the energy saving rate reached 15.8%. 3.2 Tobacco Factory Application Test The tobacco plant compressed air system consists of three 21.5mVmin oil-free air compressors, and two air compressors operate under normal production conditions. Before the transformation, the system supply pressure fluctuates between 0.680.72 MPa. After careful investigation of the compressed air pressure demand in the production process and the test of system pressure, flow and air compressor power, according to the characteristics of frequent system fluctuations, The supply and demand balance control system is added to the original compressed air system. The target air supply pressure of the system is set to 0.605 ± 0, 01 MPa. Due to the control function of the supply and demand balance control system, the system's air supply side can be based on the actual required pressure of the system. The constant pressure air supply reduces the average air supply pressure of the system, and the artificial false gas ft also decreases, so that the upload rate of the air compressor is significantly reduced when it meets the production requirements of the same working condition. The monitoring data of the air compressor power supply when the compressed air supply and demand balance control system is out of operation and put into operation when the production is stable in the workshop is the system switching time point at 25 minutes. It can be seen from the figure that after the supply and demand balance control system is put into operation, the unloading time and interval of the 2 air compressors are significantly prolonged. The weight of the air compressor after the system is running and stopped is weighted and averaged. When the pressure flow control system is running, the average power of the two air compressors is 176. 30kW. When the pressure flow control system stops running, two air pressures are used. The average power of the machine is 4. In the compressed air system, the supply and demand balance control system is applied. The gas supply pressure of the system is controlled by the gas storage tank with the appropriate capacity, and the pressure control belt of the air compressor is appropriately set according to the characteristics of the system load change. It can improve the operating efficiency of the entire compressed air system while improving the air supply quality of the system, achieving a very good energy saving effect.
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