Energy-saving technical reform of compressed air system Wang Weilin\Gu Chuanyi 2, Zhang Xiaoyan1 (1. Zhenjiang Shipyard (Group) Company, Jiangsu Province, Zhenjiang 212005, Jiangsu; 2. Propaganda Department of Jiangsu Provincial Committee of the Communist Party of China, Nanjing 210013, China) Speed ​​technology and intelligent control, implementing end reactive power compensation and optimizing air supply piping, can achieve significant energy saving effects. These energy-saving measures are easy to implement, with quick results, high returns, and reasonable economics, meeting the requirements of green electricity and low-carbon economy.
1 Overview of compressed air system When constructing, expanding or rebuilding a compressed air system, the specification requirements must ensure safe production, protect the environment, save energy, improve working conditions, and achieve advanced technology and economic rationality. According to the demand for flow and pressure of production gas in our factory, the west air compressor station of the plant is located near the gas load center of the west plant area, and the distance from the 35kV substation is about 300m. The total air compressor displacement is 300m3 at the design time. /min, the rated exhaust pressure is 1.0MPa. For stable air pressure, a gas storage tank for buffering and gas storage is disposed at an appropriate position. The volume is 52m3, the design pressure is 1.16MPa, and the working pressure is 1.0MPa. The main compressed air pipes for supplying gas to the west of the plant are separately laid, and the main pipes are equipped with control valves.
There are two kinds of requirements for the gas pressure of production gas in our factory, the species is about 0.60MPa, and the other is about 0.80MPa. In order to improve the power load rate and make full use of the factors such as valley power, the former use gas time is arranged at 8:00~22:00, and the latter gas time is arranged between 22:00~8:00, from the system. To economically reasonable use of gas.
The compressed air system is an important power facility in shipbuilding and production, and it accounts for a large proportion of power consumption. Take our factory as an example, the power consumption of compressed air stations accounts for more than 50% of the total electricity consumption. Reducing the energy consumption and economical and rational use of air in the compressed air system is an important part of reducing costs and increasing efficiency and achieving green electricity consumption. To this end, in addition to strengthening the operation and management of the compressed air system to eliminate waste, using high-efficiency pneumatic tools to improve efficiency, it can also take some energy-saving measures that are easy to implement, quicker, and more profitable.
-), male, engineer, engaged in technical management work; Gu Chuanyi (1956-), male, technician, engaged in mechanical maintenance work; Zhang Xiaoyan (1986 -), female, engineer, engaged in equipment management.
2 Main energy-saving measures 2.1 There are many types of air compressors for air compressor selection. In the selection, the requirements of the application and the gas quality and the flow and pressure requirements of the production process should be considered. Our factory has selected 8 more advanced screw air compressors with a displacement of 38.2m3/min, an exhaust pressure of 1.05MPa, a power supply of 10kV/50Hz/3ph, and a motor rated power of 250kW, of which one is No. 8 The power supply of the air compressor is 0.38kV/50Hz/3ph. Selecting multiple air compressors to run in parallel is mainly to control the start and stop of each air compressor separately, so as to be in accordance with the demand of gas consumption, in No.1~8 The air compressor is reasonably selected for the capacity to be put into operation, creating conditions for intelligent control.
The high pressure motor is used for the No. 1 air compressor to reduce the loss of the power distribution system. Practice has proved that the use of 10kV high-voltage motor reduces the line loss by more than 80% compared with the 0.38kV low-voltage motor, and can also reduce the initial investment cost of the power cable by more than 70%. The rated voltage of the motor of No. 8 air compressor is chosen to be 0.38kV, because it can be used as the main machine after frequency conversion speed control, so as to save the investment cost of the inverter and reduce the volume of the inverter.
2.2 Application of variable frequency speed control technology In the production process, there is a common phenomenon that the gas consumption time is not fixed and the gas load is not balanced. Under this condition, the frequency conversion speed regulation technology is most suitable, and the energy saving effect is most remarkable.
The main body of the screw compressor is a pair of single-stage variable-capacity rotary machines that are compressed by the meshing spiral main and auxiliary rotors, and the main and auxiliary rotors are simultaneously meshed in the cylinder to complete the compression. The main rotor has helical convex teeth; the auxiliary rotor has a spiral groove that meshes with the helical convex teeth on the main rotor. The air intake of the air compressor is located at the top of the compressor cylinder near the drive shaft side, and the exhaust port is located at the opposite side of the cylinder bottom.
Wang Weilin et al.: Energy-saving technical modification of compressed air system When the main and auxiliary rotors are not engaged at the air inlet, the air flows into the cavity of the main rotor convex teeth and the auxiliary rotor groove, and the compression cycle starts. When the rotor is disengaged from the air inlet, the air is enclosed in a cavity formed by the main and auxiliary rotors and moves axially with the meshed rotor. As the engagement continues, more of the main rotor teeth enter the grooves of the secondary rotor, the volume is reduced, and the pressure is increased. The periodic volume change between the main and auxiliary rotor slots causes the air to be transported from the air inlet to the exhaust port along the rotor axis, thereby realizing the whole process of suction, compression and exhaust of the screw air compressor. The gas is boosted and output to a gas storage tank. Although the intake valve has a 0~1% intake volume control function, the intake valve can automatically adjust the opening of the intake valve to change the intake air to control the compressor. The displacement or closing the intake valve makes the compressor unloaded. It can be seen that this type of air compressor itself is already energy-saving. However, regardless of whether the air compressor is in loading or unloading state, it is still operating at the power frequency, the speed is almost unchanged, and the active and reactive fixed losses are unchanged. When the intake valve decreases with the decrease of the gas consumption, the air compressor is in light load operation, or when the air intake valve is completely closed, so that the air compressor is in no-load operation, the motor still consumes a certain amount of power. . The measured data shows that the air compressor consumes about 40% to 70% of the total load, and the reactive power is large, and the power factor is very low. The frequency conversion speed regulation technology can automatically adjust the speed of the air compressor according to the change of the compressed air load, realize the control of the output power of the air compressor, and play the role of power saving and loss reduction.
The specific method is to select one air compressor (No. 8) as the frequency conversion main supply machine. The inverter with PID adjustment function performs soft start and automatically controls its rotation speed. The air compressors No. 1 ~ 7 are all in the hot standby state. The pressure sensor installed on the compressed air manifold feeds the collected pressure signal to the frequency converter through analog/digital conversion, and performs closed loop control compared with the preset pressure parameter. When the sampling pressure reaches the upper limit of the set value, the power frequency of the main feeder is automatically lowered to reduce the speed, and the minimum speed can be reduced to 10 Hz; otherwise, the frequency is automatically increased to increase the speed of the main feeder until the main supply Resume to run at the power frequency. Since the shaft power of the motor is approximately proportional to the cube of the rotational speed, when the amount of compressed air supplied by the air compressor is greater than the system consumption, the air compressor automatically decelerates; when only the main feeder is operated separately, if the main unit is operated alone, When the pressure exceeds the upper limit of the set value of 0.02 MPa and the set delay time elapses, the main machine can automatically stop. Practice has proved that the energy-saving loss reduction effect of the air compressor frequency conversion speed regulation is very significant.
2.3 Intelligent monitoring Because the gas load fluctuation of our plant is large, to realize the economic and reasonable operation of multiple air compressors, it is necessary to adjust the air compressor capacity put into operation according to the actual gas consumption in time to ensure the basic supply pressure. Stable and save power and reduce losses. If man-made instructions or experience are used to determine the number of air compressors that are put into operation, it is difficult to achieve economic and rational operation by manual operation to control the start-up and shutdown.
If only one of the main feeders (No. 8) is subjected to the inverter speed control to change the capacity, the main supply can only be operated in an energy-saving manner. During periods when the amount of gas used is small, even if the main feeder has been operated to the minimum speed, it is possible that the air pressure is still greater than the upper limit of the set value. If there are more than one air compressor in operation at this time, if it is not timely and selectively shut down other units that have been put into operation, it is bound to continue to be in a situation where the supply of compressed air is exceeded, even if the intake valve is completely closed, the compressor still has No-load loss; if the inverter air speed is used for each spare air compressor, the investment cost is large, and it is not necessary from the technical and economic point of view. Therefore, under the condition that there are multiple air compressors available for adjustment, the use of intelligent monitoring devices instead of manual operation is the best choice for rationally controlling the operational capacity of air compressors.
The specific method is to install the microcomputer intelligent control device, and the operating parameters are collected and controlled from the RS485 interface of each air compressor. According to the actual gas load, the microcomputer issues the tolerance and the injection and cutting commands to automatically control the displacement and The number of air compressors that need to be put into operation. The control flow is as follows: First, the soft start frequency conversion host (No. 8 machine) performs full-load operation at the power frequency, and at the same time, the No. 1 machine in the standby unit (setting the No. 1 machine as the power frequency host) is put into operation and supply air. During the set delay time, if the sampling pressure can reach the upper limit of the set value, it is considered to have entered the normal operating state, and the No. 8 machine automatically switches to the variable frequency speed control condition. When both the No. 1 and No. 8 machines are running at the power frequency state, after the set delay time, the sampling pressure is still lower than the lower limit of the set value, the intelligent device automatically starts the No. 2 spare air compressor to be put into operation and supply air; If the set delay time is exceeded and the sampling pressure is still lower than the set value lower limit, the intelligent device automatically starts the No. 3 spare air compressor to be put into operation, and so on, the intelligent device automatically starts each standby air pressure. The machine is put into operation and supplied with gas. Each spare air compressor can be cycled into operation according to the set cycle time. When any one of the air compressors fails to automatically exit the operation, or cannot be put into operation for other reasons, the smart device is based on the air load. The order of demand and setting automatically starts the standby air compressor to be put into operation. Conversely, when the No. 8 machine is running at the lowest speed (10 Hz) and running at a low speed, and the sampling pressure is still at the upper limit of the set value, it is first automatically unloaded by each air compressor (reducing the opening degree of the valve). After sufficient tolerance, when the sampling pressure is still at the upper limit of the set value, the intelligent air conditioner automatically stops the running spare air compressors one by one according to the set delay time. The first operation is first exited until the 1st to 7th machines are all shut down, so that the air compressor capacity put into operation is always in the most reasonable state, effectively reducing the power consumption.
In the normal air supply state, no matter whether there are several air compressors in operation, or whether to increase or reduce the number of air compressors put into operation, the number will be prioritized in the automatic frequency modulation state. When the No. 8 machine cannot be put into operation due to a fault or the like, it is deemed that the No. 8 machine is fully loaded with the Jiangsu ship line and the sampling pressure is still lower than the set value. The intelligent device is no longer delayed, and the standby air compressor is started immediately. .
The setting parameters such as the upper and lower limits of the supply pressure and the delay time at which the pressure reaches the upper and lower limits can be changed and saved in the intelligent device at any time according to the process requirements, and the simulation map and related parameters are displayed on the display screen of the computer. Operating data can be stored, printed and remotely monitored over the network. At the same time, the manual console is installed in the monitoring room, and the emergency control of each air compressor can be carried out; the emergency control right of starting or stopping takes precedence over the automatic control of each air compressor.
2.4 Using the end reactive power compensation technology The power factor of the eight air compressors in operation is greatly affected by the load, especially when the air compressor is in low load and no-load operation, the power factor is very low. In order to improve the power factor, a high-voltage capacitor is used for the 1st to 7th machines for basic reactive power compensation. At the power supply end of each air compressor, one high-voltage reactive power compensation box is connected in parallel. The rated capacity of the capacitor is 150kVAr, and the reactance of the reactor connected in series with the capacitor is 6%. The high-voltage reactive power compensation box does not need to be equipped with a separate switch and controller, and the circuit breaker of the control air compressor is switched at the same time as the motor.
The terminal reactive power compensation circuit diagram is as shown. Medium, M is the motor, FU is the fuse, L is the reactor, TA is the current transformer, QF is the circuit breaker, and C is the capacitor. For the No. 8 machine, 9 sets of “reactive power compensation and harmonic control integrated modules†are adopted, each group has a capacity of 15kVAr. The power factor controller automatically controls the switching of each compensation module according to the actual working conditions, and maintains the power of the No. 8 machine. The factor is above 0.95. The reactive power automatic compensation control circuit is as shown.
Since 8 air compressors have achieved reactive power local balance, the average power factor of the west compressed air station is increased from 0.70 before compensation to more than 0.95, and the starting current of the 1~7 machine is reduced. Reduces system losses and increases switching life.
2.5 Optimization of gas supply pipe network (1) Increase the volume of gas storage tank. The ideal condition for a compressed air system is that the supply pressure just meets the demand for gas and maintains a constant pressure, which is actually difficult to achieve. With the frequency control and intelligent control, the situation has changed. However, to reduce the number of starts/stops of the air compressor No. 1~7, the volume of the gas storage tank must be increased. Generally speaking, the volume of the gas storage tank should not be less than 30% of the total displacement of the air compressor. In areas where the compressed air load fluctuates greatly, the gas storage tank should be installed nearby. After calculation, the total volume of gas storage tanks in our factory has been increased to 110m3, which can significantly reduce the number of starts/stops of air compressors. It not only saves energy, but also maintains grid stability, prolongs air compressor life and reduces consumables costs. good effect.
(2) Reduce pipeline pressure loss. In the compressed air delivery pipeline, the pressure loss is not as obvious as the waste caused by the "run, run, leak" of the gas, and thus is easily overlooked. The measured results show that if the gas pipeline is long, the elbow is large or the pipeline diameter is small, the pressure loss generated by the compressed air during transportation is considerable, and should not be underestimated. Therefore, when designing the pipeline, care should be taken to minimize the length and curvature of the pipeline, appropriately increase the diameter of the pipeline, and properly adjust the position and reduce the number of various joints (valves, elbows, tees, etc.). When conditions permit, it is possible to carry out the annular laying of the gas supply pipe in one gas unit or the parallel connection of the ends of several gas supply pipes, all of which can significantly reduce the pressure loss of the gas pipeline. After calculation, the gas supply pipeline of our factory can be modified by this method, not only can reduce the pipeline pressure loss of the gas load zone by more than 35%, but also improve the stability of the gas supply pressure, so that the efficiency of the pneumatic tool has Increased. The schematic diagram of the parallel supply is shown.
3 Investment and income Compressed air system energy-saving operation, small investment, quick results, and high returns. The main investment and profit of our factory in the technical transformation of compressed air system are as follows: 3.1 Frequency conversion speed regulation configuration 1 frequency converter and auxiliary equipment (down to page 19) Chen Cuixiang, etc.: An important part of the discussion and improvement of marine cable . For more than ten years, we have developed a cable cutting and winding process, working closely with hundreds of shipyards, cutting, marking, sealing and winding cables according to the cable inventory provided by the shipyard, according to the schedule given by the shipyard. Goods, and some shipyards have realized that the cable is out of stock. This practice has been practiced on thousands of newbuildings, and has achieved remarkable results in reducing shipyard costs, improving construction quality, shortening cable laying cycles, and energy efficiency.
3 Conclusions The ship market boom in the past few years has promoted the rapid development of domestic marine cables, but at the same time there have been mixed phenomena and model confusion.
Domestic marine cables must be in line with international standards as soon as possible, increase the development of new products, improve competitiveness, and at the same time facilitate the selection of cables for designers and reduce the cost of shipyard cables.
A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a check valve, as it prevents or "checks" the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems.
Valves have many uses, including controlling water for irrigation, industrial uses for controlling processes, residential uses such as on/off and pressure control to dish and clothes washers and taps in the home. Even aerosols have a tiny valve built in. Valves are also used in the military and transport sectors. In HVAC ductwork and other near-atmospheric air flows, valves are instead called dampers. In compressed air systems, however, valves are used with the most common type being ball valves.
Hydraulic Valve,Hydraulic Control Valve,Hydraulic Solenoid Valve,Pressure Control Valve
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