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The analysis and technology improvement of the centrifugal air compressor and the improvement of the energy center Peng Guoxiong investigate the cause of the surge by the principle of surge generation, explain the hazard and judgment method of surge, and analyze the main factors of surge. The process, equipment and technical requirements of the air compressor station and the pressure air user are started. The process improvement and measures at the production site, the production wind law and the production mode are controlled, and the effective control of the centrifugal air compressor surge is realized. Good results provide an example to solve the problem of abnormal vibration of centrifugal air compressors.
1 Introduction Centrifugal air compressors are key equipment in the metallurgical industry. They have the advantages of high flow, high power, simple and durable construction, high degree of automation, etc., and are widely used due to their easy control and maintenance characteristics.
However, centrifugal compressors also have some drawbacks, such as stable working area and prone to surge. Surge is a unique phenomenon of centrifugal compressors. Surge control is not the main process during process control and operation. However, anti-surge is very important from the measures to protect the compressor; due to the user's production rhythm and use The change of the situation has caused frequent changes in the load of the air compressor, which causes the air compressor unit to frequently surge. In severe cases, the unit is shut down, affecting the user's use of compressed air. In abnormal operation, it should be controlled and reduced as much as possible. A surge occurred in the press.
There are three air compressor stations in Handan New District, three TM1500 centrifugal air compressors manufactured by South Korea's Samsung Group, six TRX160 centrifugal air compressors manufactured by Japan IHI, and ZH10000 centrifugal air compressors manufactured by Atlascopco. The stations are all three-stage compression, two-stage cooling compressors. Under normal operating conditions, the compressor unit continues to provide 0.7 MPa of compressed air to users such as converter steel mills, hot-rolled sheet mills, cold-rolled sheet mills, iron-making blast furnaces and sintering machines.
2 Current situation a. Due to the lack of timely feedback and mastery of production information and production organization mode in production and use, the air compressor station has multiple machines, high pressure and low load surge operation.
b. The technical requirements of the user's wind use are uneven, and the special requirements are too high, resulting in high outlet pressure of the air compressor unit, and surge and venting.
c. The air pressure pipe network is independent and not connected, and the pressure complementary, air volume buffering and mutual transmission cannot be realized, and the air compressor unit has more surge times.
3 Principle and analysis of surge generation 3.1 Principle of surge generation When the centrifugal air compressor speed is set and the flow rate is reduced to a fixed value, severe rotation and detachment occur, and the airflow condition will be greatly deteriorated. At this time, although the impeller is still rotating, it works on the gas, but it does not increase the pressure of the gas, so the compressor outlet pressure drops significantly. Since the compressor always works in conjunction with the pipe network system, the pressure ratio of the pipe network is not immediately reduced. It may happen that the pressure in the pipe network is greater than the pressure at the compressor outlet, and the gas in the pipe network will flow back to the compressor. Until the pressure in the pipe network drops below the compressor outlet pressure, the backflow stops. At this time, the airflow flows forward under the action of the blades, and the compressor starts to supply air to the pipe network. The flow through the compressor increases and the compression The machine resumes normal operation. However, when the pressure in the pipe network keeps rising and returns to the original level, the normal exhaust gas of the compressor is blocked, the flow rate drops, and the gas in the system will reverse. So, the periodic axial low frequency occurs in the whole system. A large phenomenon of airflow oscillation, which is called "surge" of the compressor.
The consequences of surge are severe, the airflow pulsates, and generates strong noise, which causes the compressor rotor and stator to undergo alternating stress and break; causing the interstage pressure to be abnormal and causing strong vibration, resulting in damage to the sealant thrust bearing; The moving element and the stationary element are collided, causing a serious accident.
The occurrence of surge is firstly due to the uncoordinated aerodynamic parameters and geometric parameters in the compressor cascade during variable operating conditions, resulting in rotational detachment, resulting in severe stall. But not the rotational stall will necessarily lead to the occurrence of surge, and the surge is also related to the pipe network system. The occurrence of surge phenomenon involves two factors: internally, it depends on the compressor under certain conditions, the flow is greatly deteriorated, and the sudden change occurs; from the outside, it is related to the capacity and characteristic curve of the pipe network. The greater the density of exhaust pressure and gas, the more severe the surge occurs, and the steel technology and management are heavy. The former is an internal cause, and the latter is an external condition. The internal cause only causes the occurrence of surge when the external conditions are available. Therefore, anti-surge is an important part of the control of the centrifugal compressor.
Surge limit to the compressor, can be approximated by the actual measurement method at different speeds, see the points A, B, C, D. By connecting these surge points, you get a surge line, to the right of the line is the normal working area, and to the left of the line is the surge zone. The surge limit line can be approximated as a parabola through the far point.
The centrifugal compressor and the pipe network form a system of energy supply and use. When the compressor works in conjunction with the pipe network, only when the flow through the compressor is equal to the flow through the pipe network, and the energy head generated by the compressor Equal to the resistance of the pipe network, that is, when the supply of energy is equal to the use, the energy system can maintain the balance of working conditions. The performance curves of compressors and pipe networks are generally expressed in terms of energy heads or pressure versus flow curves. The intersection of these curves determines the operating conditions of the compressor and network system, called the operating point or operating point. When the pipe network characteristics change, the operating point changes accordingly. See changing the pipe network performance curve to change the performance curve of the compressor.
3.2 Joint operation of compressor and pipe network When two compressors with different performances are connected in parallel, the discharge pressure = pc, the displacement Qn = Qi + Q * in the middle, the i and n lines respectively represent i, n compressors respectively The performance curve of the operation, the m line represents the performance curve after the parallel connection, and the discharge pressure pc and EI intersect at point A, which is the operating point after the parallel connection. The OA pipe network is respectively connected to the ai and a2 points on the I and n lines, and these two points are the operating points after the parallel connection between the I and n centrifugal compressors. At this time, pal and pfl2 are less than the analysis, elimination and test verification of the influencing factors of Py parallel operating condition point a. The air compressor has the effect of impeller wear or too much adhesion, and the impeller wears a lot or adheres more. As a result, the air compressor generates a surge fault. As for the sampling inspection of the three air compressor stations, there is no problem that the air compressor impeller wears or has too much adhesion.
b. The air compressor has the influence of heavy corrosion and wear of the diffuser. When the high-speed air flows through the diffuser, it forms a vortex. The air intake of the unit is reduced, the air pressure is not increased, and the output pressure of the air compressor is lowered. Therefore, it is easy to form surge, and after synchronous detection, there is no similar phenomenon in the three air compressor stations.
c. There is a change in the gap between the impeller and the diffuser.
The gap between the impeller and the diffuser is too large, and the air leakage is easy to occur, and the air flow is reduced; the clearance is too small, the air flow is reduced, and in the case where the rear thrust bearing is worn, the impeller and the diffuser are easily collided. . Therefore, if the gap between the impeller and the diffuser is too large and too small, the air flow will be reduced, so that the air compressor can not increase the output pressure, thereby forming a surge fault; for the steel rolling air compressor station with more surge times The 2 and 5 units were sampled, and the gap between the test data and the inspection standard was considered to be within the standard range.
d. Whether the air cooler and the water vapor separator have the effect of the technology and management of the dirty steel. The gas-water separator requires extremely small impurities passing through the cooler. If the fine dust in the air or the wear of the unit itself is easily adhered to the cooler and the water vapor separator, the cooler and the water vapor separator are partially blocked. When the air flow is reduced, the output pressure of the unit is insufficient, and the surge phenomenon is formed. When the water quality of the cooling water becomes worse or becomes dirty, it is easy to cause cooling water blockage in the cooler, affecting the flow of the cooling water, reducing the cooling effect of the compressed gas, and affecting the air pressure. The air volume ratio of the machine and the output pressure of the air compressor are insufficient to form a surge phenomenon. According to this method, the cooling pools of the three air compressor stations are cleaned in time, the cooler is cleaned, and the steel rolling station is inspected. Similar problems exist in the 4 and 3 units of the cold-rolled air compressor station. After the filter element is replaced and repaired, the number of surges of the air compressor unit is small but still exists.
e. The influence of the air temperature change of the air inlet of the air compressor. Under the condition of constant pressure, when the temperature rises, the air density decreases, and the compressed air flow of the unit decreases, resulting in insufficient output pressure of the air compressor and a surge phenomenon. In actual operation, although the number of surges is high when the temperature is high, the surge phenomenon still exists when the temperature is low.
f. Influence of export flow and outlet pressure: As the user's gas consumption changes frequently and the concentration is minimized, the outlet pressure of the air compressor rises and gradually increases. When the air compressor reaches the maximum outlet pressure, the unit begins to enter the surge zone, and then surge occurs; the user volume of the pressure air changes frequently, and the pressure of the exhaust manifold rises, causing the number and frequency of surge of the air compressor unit to increase synchronously. serious. In order to eliminate the simultaneous surge problem of the three air compressor stations, technical research and technology from the pressure wind and the user's internal requirements are carried out to carry out technical research.
(a) Perform targeted technical modifications to the local area to reduce the pressure on the network.
At the end of April, the gas booster pump was installed on the inspection and testing system and the hot-rolling cross-cutting system with very low dosage and high pressure requirements. The gas booster pump group was boosted and supplied in a small range, and the pump pressure was set to 0.6. ~0.8MPa, which guarantees the wind requirement of 0.6MPa for the milling machine and the baler; three used 50m3 refined gas storage tanks are used for cleaning, and then used as a pressure buffer tank to be put into the blast furnace dust removal system, stable The environmental protection equipment in the area is safely operated; the pressure regulating tanks are used in the cold rolling mill, 1, 2 reel, galvanizing line, acid rolling line, etc.; the sintering flue gas desulfurization system uses a small air compressor to supply air separately. The small user is prevented from causing the pressure of the entire compressed air system to rise for a long time and the surge of the air compressor unit.
Through the manual control of the blast furnace slag treatment system, the wind control is automatically controlled, and some points are changed from the pressure air purging belt to the waste water cleaning; the sintering machine gas stripping batching process is changed to the limestone powder batching process, and the pipeline transformation and related Valves are strictly controlled. And the pressure of the safety valve is reset at the level of *48, and the pressure of the pressure at the place is reduced from the original 0.6 MPa to (b) the technical parameters of the key wind equipment of each main unit are adjusted to reduce the technical requirements for the pressure.
Through the operation and technical parameters of the hot rolling mill baler, the original 0.6MPa is reduced to 0.5MPa, and the billet purging time on the mill is controlled; in the converter steelmaking plant, the continuous casting aerosol is used to cool the wind. Optimize, stop using 12~16 nozzles, reduce the number of nozzles used; adjust the pressure of the continuous casting aerosol cooling air pressure end point, adjust the control pressure from the original <0.6MPa automatic alarm and interlock shutdown value, adjust and modify to < 0. Continuous cutting equipment is added to the cooling air duct to increase the shut-off valve, and the automatic control mode is designed. After the tail blank exits the roller for 50 minutes, the continuous cooling equipment is automatically closed. When the continuous casting is started, the equipment cooling air is automatically opened (with Aerosol cooling pressure synchronization); pulse interval of the dust removal system, extended by 23s on the original basis and then pulse; cold rolling mill galvanizing and acid rolling line automatic welding machine and looper motor control pressure (c) according to the user Production organization mode and actual demand, optimize the operation mode of air compressor and pipe network joint, realize air volume mutual transmission, pressure buffer, and effectively control the surge of air compressor unit.
In the rhythm of steelmaking production, the number of units for continuous casting units and air compressor units is determined strictly according to the output of the blast furnace. When the single continuous casting machine of the converter steelmaking plant is produced, only three units are opened, and when the two machines are produced, four units are opened. Operation mode; the cold rolling mill flattening unit performs a fixed-scale purging according to the width of the plate surface, reducing the number and frequency of air compressors, and reducing the total pipe pressure.
Through the operation of the air compressor and the air pressure process pipe network, starting from the use and technical requirements of the user's key equipment, the process and technical requirements of the production site are improved and tackled, and the production wind law and production organization mode are controlled in time. Through the optimization of the technical level of each user, the cold rolling pressure station, the blast furnace pressure station and the steelmaking pressure station can realize the large-scale operation of the pipe network, and the cross-change and buffer of the user usage can achieve the reduction of ''shaving peaks and valleys' The number of surges of the centrifugal air compressor unit. The total pressure of the three air compressor stations in the new area is reduced from 0.65 to 0.7 MPa to 0.52 to 0.57 MPa, and the operation mode of the air compressor is better optimized; The operating parameters are stable at 0.52MPa loading and 0.57MPa unloading, effectively controlling the wind power consumption, pressure wind consumption and total pipe pressure throughout the operation process, and achieving strict control of centrifugal air compressor surge.
Through theoretical analysis and technical test verification of various factors, the results prove that the root cause of the unit surge is that the air compressor outlet pressure is too high, starting from the scientific and reasonable control of the pressure demand, to achieve the optimization of supply and demand balance, to achieve the system The economical and anti-surge vibration pressure station internal unit loading and unloading parameters are reasonably adjusted, and the pressure air mains are pressure-protected for safety purposes.
The dynamic adjustment of the force and the lean management of the economic operation entered the 5 benefit evaluation hand, and the technical effects of the anti-surge of the centrifugal air compressor were as follows.
Through the above user usage and pressure level from the periphery, the air a. The comparison between the number of surges and the vibration value of the air compressor is shown in Table 1. Table 1 Comparison of the operating parameters of the air compressor before and after the adjustment of the air compressor Air compressor station, steel air compressor station cold rolling air compressor station blast furnace air pressure station steelmaking air compressor station main pipe pressure control MPa starter number surge monthly average number of low load when the displacement /% outlet air pressure / MPa production Air pressure difference / MPa vibration / m secondary vibration / pm three vibration / pm table 2 technical indicators unit monthly plan January February March April May June July August September October November November ton steel Compressed wind power consumption kWh / t steel tons of steel consumption pressure air volume m3 / t steel pressure wind power consumption kWh / million m3 b. Comparison of economic and technical indicators of the pressure system see Table 2. The amount of compressed air per ton of steel is reduced from the annual plan of 150m3 / t steel The average value of May-November is 132.92 claws and 3 eight steel. The cost reduction of tons of steel is reduced. The cost of 10,000 tons of compressors is efficient, economical and reliable. It must be started from the pressure system unit to the user's wind facilities and process improvement. Corresponding control measures to further tap internal potential and optimize the system through technical improvements
Tons of steel wind power consumption cost savings: 10,000 tx 6 Conclusion By analyzing the principle and influencing factors of centrifugal air compressor surge, strengthen the monitoring of daily operating parameters of the air compressor and linkage adjustment to eliminate air compressor unit asthma The conditions of vibration ensure the safe and stable operation of the air compressor; there are many factors affecting the surge, centrifugal
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