Air compressor anti-surge automatic control

Centrifugal compressors are vane rotary compressors (ie turbine compressors). In the centrifugal compressor, the high-speed rotating impeller exerts a centrifugal force on the gas, and a diffusing action on the gas in the diffusing passage causes the gas pressure to rise. Centrifugal air compressors are widely used in industrial production with high flow, high power and high degree of automation control, but they are prone to "surge" during operation, and surge will have a certain impact on production and equipment. According to the air compressor surge mechanism and the engineering example, the problems in the anti-asthmatic process are analyzed to ensure that the air compressor can be automatically adjusted during the surge condition, that is, the equipment can be automatically adjusted to protect the safety of the equipment.

2 The surge mechanism of the air compressor surge is generally caused by the decrease of the suction flow of the air compressor. The first is the rotation stall of the air compressor blade. When the air compressor is deteriorated due to the blockage of the air flow passage, the air compressor The working state is developed from the rotating stall to the surge. At this time, the exhaust pressure and the outlet volume of the unit are strongly oscillated, and the air compressor current also changes drastically, accompanied by intermittent, very dull airflow noise. ''Asthma'' whistling. Slight surge will not damage the air compressor, but should avoid the air compressor running under surge conditions, because too frequent surge will damage the impeller, more severe asthma The vibration will increase the vibration of the machine, which may cause the tile to burn or even damage the spindle.

Surge is an inherent characteristic of the air compressor caused by the compressibility of the gas, and is also a peculiar phenomenon of the centrifugal air compressor. Therefore, anti-surge becomes an important task of the centrifugal air compressor control system. In the automatic control system, anti-surge is achieved by controlling the air compressor's anti-surge valve and inlet guide vane action.

3The centrifugal air compressor generates the surge process. The air first enters the air compressor through the filter from the air inlet, and then passes through the impeller. The rotation of the blade causes the gas to obtain a certain kinetic energy; then the gas expands along the air compressor flow passage through the gas. In the pressure device, the gas molecular velocity is continuously reduced, and the kinetic energy of the gas is mostly converted into the static energy of the gas, and a small part of the kinetic energy of the gas is converted into heat energy; when the hot high pressure gas passes through the interstage cooler, the gas temperature is lowered. In order to achieve a gas-level compression process, the expected pressure value is reached by stepwise compression. During the operation of the compressor, if the suction quantity is reduced to a certain metallurgical value in Hebei, once the compression ratio decreases, the gas pressure in the output line is higher than the compressor outlet pressure, and the compressed gas is quickly poured into the compressor, waiting for the line pressure. After the drop, the gas flow direction is reversed. At this time, the air intake gas flow rate and the outlet pressure of the air compressor fluctuate greatly at a low frequency, and the surge occurs repeatedly.

4 factors affecting the occurrence of centrifugal air compressor surge (1) flow. As the gas flow rate decreases, the outlet pressure of the air compressor gradually increases. When the maximum outlet pressure at the speed is reached, the unit begins to enter the surge zone, and then surge occurs. It is generally believed that the actual minimum flow during the operation of the centrifugal air compressor should be more than 60% of the design flow.

(2) Inlet temperature. Under constant pressure operating conditions, the higher the gas inlet temperature, the more likely it is to surge. Therefore, centrifugal air compressors are more prone to surge in summer than in winter.

(3) The rotational speed of the impeller. In the case where the amount of air used is constant, the higher the rotational speed, the more likely the surge will occur. In the case where the external pressure is constant, the lower the rotation speed, the more likely the surge occurs.

(4) The difference between the inlet and outlet pressures. In general, the greater the pressure difference between the inlet and the outlet, the more likely the surge will occur. That is to say, the lower the inlet pressure, the more likely the air compressor will surge, and the higher the outlet pressure, the more likely the surge will occur.

5 Anti-surge control process of air compressor The anti-surge control of centrifugal air compressor is to make air pressure when the air compressor is about to surge, by adjusting the inlet flow of the air compressor or adjusting the outlet pressure of the air compressor. The machine's operating point is kept away from the surge zone, allowing the crew to operate under safe conditions. There are two kinds of control of air compressor surge: one is equal flow control, and the other is isobaric control.

(1) Equal flow control. When the flow rate of the centrifugal air compressor is reduced, the outlet pressure of the air compressor is increased, and the operating point of the air compressor system is close to the surge line. In order to prevent the occurrence of surge and maintain the inlet flow rate unchanged, the system opens the air compressor outlet vent valve (anti-surge valve), at which time part of the gas is directly discharged into the atmosphere, so that the system pressure is reduced, and the operating point of the system returns to the safety line. Within.

(2) Isobaric control. Due to airway blockage and the like, the flow rate of the air supply at the outlet of the air compressor is reduced, and the pressure of the outlet gas is increased. When the pressure of the gas outlet rises to near the surge region, the opening degree of the inlet guide vane can be reduced, so that the air compressor can be reduced. The inlet flow rate is reduced and the air compressor outlet pressure will gradually return to the original pressure value. The reduction of the gas flow rate enables isostatic control, which is energy-saving control, does not increase the shaft power of the air compressor, and does not waste more energy. However, in the case that the system is close to the surge line, it is risky to operate according to the control scheme. Because the outlet pressure is increased until the system approaches the surge line, the flow rate is reduced more easily, so the system performance is required. The curve is still some distance from the surge line, and the exit flow is reduced to ensure safety.

6 anti-asthmatic automatic control design 000kW centrifugal air compressor, Taiwan is Demag's VK50-3 type, Taiwan is Cooper's 3MSG16 -15 type, all three-stage compression, respectively, as 15500m3 / h And the air compressor of the 16000m3/h oxygen generator unit is programmed and controlled by Yokogawa CS3000 distributed control system.

The CS3000 distributed control system of the air compressor configures the CS3000 distributed control system configuration of the 500m3 oxygen generator air compressor. The anti-asthmatic line abscissa of the equipment is the intake air flow, and the ordinate is the outlet pressure. For example, the air compressor outlet pressure, inlet flow rate and anti-surge valve control input and output channels, F1 is the measured pressure and flow corresponding to the anti-surge curve, F2 is the critical surge curve pressure and flow correspondence, F3 is the flow display instrument, F4 is the block for participation control, FIC-01 and PIC-03 ​​are the regulators for the inlet flow and outlet pressure, and PF-01 is the high selector for selecting the input signal. It can be seen that within the specified range of pressure and flow, the flow value corresponding to the pressure is used as the given value of the flow regulation, the output of the flow regulator is compared with the output of the pressure regulator, and then the high value signal output is selected. F2 is the block corresponding to the pressure and flow relationship of the critical surge curve. When the cross coordinate of the pressure and flow meets the critical surge line, the full open signal is directly output to the high selector PF-01 in the operation block F4, and the output is output. The valve is fully open. In this design, the anti-asthmatic valve is fully open when it is 100% open, so a high-selector is selected.

The CS3000 distributed control system of the 000m3/h oxygen generator air compressor is configured with the CS3000 distributed control system of the 000m3 oxygen generator air compressor. The anti-surge design of the equipment is more complicated, and the anti-asthmatic line abscissa is the air compressor current. The ordinate is the outlet pressure.

(1) Control of the inlet guide vanes. The output guide number of the inlet guide vane is %% buckle 1001, and the output channel is %Z031112. Its control is completed by PY1001 (air compressor inlet guide vane opening, AS-L automatic low signal selector), PY1001 to 2 input The signal is low-selected, the path is ASH1A (SS-L signal low selector), and the other is IGVMINSH (CALCU general-purpose operation block). The function of ASH1A is to select the low level of the three signals. The first way is PIC1 (air compressor outlet pressure control, PID adjustment block), the second way is HIC1 (guide vane selection remote control, DSET constant setting block), third The road is C1 (air compressor motor current, PID adjustment block). The input signal number of the first signal PIC1 is PT1019, and the input channel is %Z053102. The setting is given by CAL1020C (air compressor outlet pressure setting calculation, CALCU general operation block), and the function of CAL1020C is to send the upper level RAMP1. The output is used as the given signal of PIC1. The upper level of RAMP1 (air compressor set value change speed limit, RAMP ramp block) is CAL1020A (air compressor outlet pressure setting calculation, CALCU general operation block).

Off, internal switch) is the sum of SV of "ON (air compressor outlet pressure increase setting, DSET constant setting block), UPP is *OFF*, CAL1020A output is PSV1020 SV. Second signal HIC1 setting The range is 30%~100%, which can only be given from 30%. The input signal of the third signal C1 is CI1020, and the input channel is % redundancy 034101, which is the motor current signal.

The function. ATMINCTL (air compressor unloading to minimum opening, internal switch) is *ON*, RAMP-IGV (loading and unloading IGV-MIN-RAMP curve, VELLIM change (4) vent valve control method. The vent valve output bit number is %%81002, the output channel is %Z031113. Its control is completed by PY1002 (AS-L automatic low selector), PY1001 performs low selection of two input signals, one is PY1002A (SS-L signal low selector), the other way It is RAMP-BOV (Load Unloading BOV Control RAMP Curve, VELLIM Rate of Change Limit Block).

The function of Hebei Metallurgy PY1002A is to select the low level of the three signals. The first way is PIC2 (air compressor outlet pressure control, PID adjustment block), the second way is HIC2 (anti-surge valve selection remote control, MLD manual operation block) The third way is FIC1 (air compressor motor current, PID adjustment block). The input of the first signal PIC2 is taken from the input signal of the PIC1, ie the air compressor outlet pressure. The setting is given by CAL1020B (CALCU general-purpose operation block). The function of CAL1020B is to give the SV of the previous PSV1020 (air compressor outlet pressure setting, DSET constant setting block) as the given signal of PIC2. The second signal HIC2 is controlled by the upper level HI (CALCU General Purpose Operation Block).

(5) The function of HI. When the MV of V1002 (venting solenoid valve control, SO-1 switch meter) is controlled, the output of HIC2 is valid; when the MV of V1002 is fully open, the output of HIC2 is 0. The input signal of the third signal FIC1 is the motor current. The signal is taken from the same channel as C1. Its set value is given by FY1020 (flow calculation, CALCU general operation block), FY1020 function is to increase the PV value of HC2 * 1.07+20 (this is the equipment given by the equipment manufacturer (on page 82) in energy In the field, he proposed that companies should pay attention to two new demands: the key varieties of advanced ultra-supercritical units with high parameters of 700 degrees Celsius. In order to further improve power generation efficiency, countries are arranging the development of high-parameter units with 700 degrees Celsius ~ 760 degrees Celsius, which can increase 10%~ 20% efficiency, reducing power consumption coal consumption by about 50gKkW*h).

At present, China has started research on such units and plans to open demonstration projects in 2020. The steel required for units above 700 degrees Celsius will be transformed from ferrite and martensite to austenite and heat resistant alloys. Steel pipes, steam turbine components, etc. will have corresponding major changes.

Second, the X100 or X90 ultra-high-strength oil and gas transmission pipelines and supporting drills are made of steel. X100 pipeline steel has higher requirements in terms of plasticity, safety and strength, and cracks occur. The transported high-pressure gas will spread quickly. Therefore, steel companies should make progressive research and development on the hoop stress and fracture toughness of the steel. In the field of transportation, the development of social activities, home transportation tools and modern logistics industry has placed new demands on steel for automotive and rail transportation. Among them, automotive steel will be light weight and safety as the key goal: the development of the third generation of automotive steel. The third-generation automotive steel has increased the strength of the ultra-light steel body while reducing weight, achieving the goal of reducing fuel consumption and improving safety performance. Weng Yuqing proposed that the industry, academia and research alliance should be established to promote the engineering and industrialization of the second and third generation steel. The bainite wheel/rail system adapted to the development of large axle weight, high speed and heavy load will become the demand for steel for new generation rail transit. In the field of marine engineering equipment, Weng Yuqing refers to the function), as a given value of FIC1. This expression is also the correspondence between the outlet pressure and the current in the anti-asthmatic curve.

(6) The function of RAMP-BOV. The BOV-RAMP (manual operation block for unloading BOV control output, MLD-SW with output switch) is rate limited and output to PY1002. In this design, the anti-asthmatic valve opening is 0 when fully open. Therefore, a low signal selector was chosen.

7 Conclusions From the above two examples of design, it can be seen that the automatic anti-surge control should be determined according to the performance of the equipment. By controlling the action of the anti-surge valve and the inlet guide vanes, the unit is guaranteed to work below the surge line to the utmost extent. In addition, the maintenance of the anti-surge control device is important for the anti-surge of the air compressor, such as the improvement of the response sensitivity of the anti-surge control valve, and the stability and reliability of the air compressor flow measurement, and the intelligent anti-surge valve positioner is adopted. The air compressor inlet filter automatic cleaning device and the internal cleaning of the air compressor interstage cooler have a positive effect on preventing the surge of the air compressor.

Out, China does not have mature steel varieties for use in the East China Sea and the South China Sea.

The environment in these areas is prone to severe corrosion of steel, and complex environments such as deep water high pressure, high temperature and low temperature will also lead to difficulties in material and equipment development, and it is urgent to develop new alloy systems. He said that there is a big gap between China's marine engineering steel and advanced foreign countries. Special steels are basically dependent on imports, and existing varieties are no longer able to meet the development needs of the target growth. “The key to common key materials for advanced equipment industry is quality, not variety. For example, there are only four steel mills in China that can produce aerospace bearing steel, but the service life is only 1/4 to 1/5 of foreign countries. It is not necessary to develop high purity. High-quality, high-performance aerospace bearing steel." Weng Yuqing said.

He also proposed that "the bearing design, manufacturing, operation and key systems of bearing steel should be integrated for quality management and control." In addition, the gap between gears and molds can not be ignored. At present, about one-third of China's high-end gears rely on imports. The number of imported high-end molds exceeds the total output of domestic molds. The industrialization and engineering of mold steels are far from reaching international standards. In the future, the demand for high-end gear steels and large-scale precision die steels will continue to grow, and steel companies should pay attention to the development of steel grades such as EMU gearbox molds and ultra-high-speed precision molds. Weng Yuqing appealed: "For these special types of steel products that rely on imports, we hope that steel companies and research institutes will give more attention and research."

(Excerpted from China Metallurgical News, October 26, 2013, first edition)

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