Analysis of Compensatory Capacity of Circulating Water Pumps

A power plant has two 125MW turbo-generators, all of which are super high-pressure intermediate reheat double-cylinder double-row steam condensing steam generators produced by Shanghai Turbine Works. Two units were put into production in October 1988 and September 1989 respectively. In the original design, the basic load of the unit was considered. Therefore, 4 units of the single-stage low-speed centrifugal pumps of the single-stage single-suction type produced by the Changsha Water Pump Plant were used. The parallel operation mode was adopted to pass through the I and n mother pipes to the two machines. Water supply to meet the needs of load, temperature and switching, thus ensuring the safe and reliable operation of the unit. However, with the development of the power situation, electricity has entered the market. The two 125MW steam turbine units of the plant have been changed from the original with the peak load to the peak load operation, and frequent peak load adjustment, not only to reduce the load operation, and sometimes even stop one Taiwan unit operation. In this way, the original design of 4 Yuanjiang 48I-28IA circulating water pumps could not meet the needs of the current situation and they need to be transformed.

1 Introduction of circulating water pump The 4 circulating pumps installed in the 3 pump house of the plant are source-grade single-suction single-suction, low-speed high-speed pumps produced by the Changsha Pump Plant and specifically designed to meet the water supply requirements of the 2 125MW steam turbines of the plant. need. Its design parameters are as follows: water volume 10860~16000T/H, lift 0.15~0.25MPa, speed 375r/min, shaft power 684kW. Its imported configuration has type ZH-3000, water volume is 5.5m3/h, height is 17600mm A rotary screen; outlet and recoil sewage single sewage tank, through-flow ratio of 1:3.04 oil-driven secondary rotating filter matching. The pump is equipped with a motor YL1000-16/1730 motor produced by the Shanghai Electric Power Plant with a power of 1000kW, class B insulation, a voltage of 6kV, and a current of 132A. The cooling method is air-cooled. When the two machines are fully loaded, three pumps can be used to meet the water requirements and one pump is used. The condenser used in this machine is a N7100-H double process reciprocal surface condenser produced by the Shanghai Power Plant Auxiliary Plant. The cycle multiplying rate is 50~55 in winter, 65~75 in summer, and the cooling water temperature is 20 Zhang ~ 33 feet, water pressure is 0.15MPa. The pump is characterized by a vertical layout that is easy to use with the motor arrangement, small footprint, compact structure; suck the population down, easy to arrange the suction pipe; by the coupling On one side, a single-row radial ball bearing is installed. On the side of the packing seal, a double-row radial spherical roller bearing is installed. The weight and axial thrust of the rotor are borne by the thrust bearing on the motor. The pump is not provided with a thrust bearing. Due to the large size and single suction of the impeller, it does not affect the amount of water. A top-line linear hub cap is installed under the impeller; it is a high specific speed pump to meet the pressure and water demand of the condenser and other heat exchangers.

2 reasons for the transformation of the plant circulating pump in the actual operation, the long-term lack of water delivery situation. In summer, due to the high temperature in the area, the river water temperature can reach up to 34.5 feet, and the duration is long (with 2 to 3 months); the water level in the dry season is low, the water volume is reduced and the time is longer (about 3 months ). In this way, the vacuum is low for about half a year. At the same time, in summer, due to the high temperature of the river and the small amount of circulating water, the vacuum of the condenser is low, the oil temperature of the oil cooler is high, and the air temperature of the generator and exciter is high, which poses a threat to the safe operation of the power plant. In recent years, the entire power grid has entered the simulation market and the plant has been frequently peaked. Therefore, in order to ensure the vacuum of the condenser during single-unit and dual-machine operation, it is necessary to adopt the operation mode of two pumps, two pumps or two pumps. The power consumption and power consumption of the circulating water pump are increased, and the economical operation of the unit is reduced. At the same time, equipment losses are accelerated, the number of backup circulating pumps is reduced, and the safety of the unit operation is reduced.

From the standpoint of the actual operation of a single pump in the plant, the temperature rise of the cooling water in the summer is about 13C. From this, it can be estimated that the recycle ratio of the condenser under this kind of heat exchange is about 42, which is far from the design. Claim. Therefore, in the current vacuum tightness, cooling water quality and condenser plugging conditions, to ensure that the vacuum is stable at a high value while reducing the plant electricity rate, it is necessary to increase the capacity of the circulating pump.

3 Circulation pump reform measures In view of the current situation, the plant contacted the China Institute of Water Resources and Hydropower Research Institute of Hydraulic and Electromechanical and decided to increase the capacity of the 9-cycle water pump directly connected to the n-tube. The key to the transformation lies in: while ensuring that the new pump has a similar steep drop performance curve and the same specific speed ns as the original pump, the flow rate can be further increased by 20003000m3/h on the basis of the original flow, reducing power consumption and improving the operation of the pump. effectiveness. Under the guidance of this idea, the plant decided to adopt the LY-24 high-tech developed by the Institute of Hydraulic and Electromechanical Research, replacing the original impeller and modifying the population seal ring between the impeller and the lower pump cover and the shaft seal of the upper pump cover. The size of the seal ring, the pump housing, accessories, and the motor all remain the same.

In addition to the need to ensure the manufacture and installation of the circulating water pump, the key to the operation is whether or not to obtain the flow and head that meet the design requirements, whether it will cause the motor over-current, the coil temperature to exceed the maximum allowable value, and whether it can improve. Operational safety and stability. In the manufacturing process, for the high specific speed centrifugal pump due to the increase of the cross-section of the flow, in the same flow section, due to the large difference in the rotation radius, the difference in the circumferential speed is large and the twisted blade must be used. The blade, hub and blade are used. The side cover plates are separately manufactured, and then the combined welding process is performed according to the principle of symmetry to ensure that the smoothness, dimensional deviation and machining accuracy of the overflow surface meet the requirements; at the same time, the installation of the new impeller is also the same as the technical requirements of the original pump.

Through this transformation, the inlet diameter of the impeller is increased from 925mm to 950mm; the outlet diameter is increased from 242mm to 269mm; the impeller outer diameter is increased from 1200mm to 1220mm; the impeller height is increased from 600mm to 620mm. The remaining dimensions are also correspondingly The change to adapt to the original water pump housing the same, to ensure that the size meets the requirements, so as to meet the performance and specific speed requirements under the premise of capacity expansion.

4 Comparison of the performance before and after the transformation. Before and after the technical transformation, the 9 pumps were tested on the spot by the same method used in the provincial pilot test. The specific conditions are shown in Table 1: Table 1 9 Performance of the circulating pump before and after the conversion Water column motor power N / kW efficiency /% transformation after the curve comparison (see): In the normal working water pressure range of 1520 meters water column, the same head, the transformation of the amount of recycled water increased 23763492m3 / h. As the head falls, the leakage flow in the pump decreases; the flow rate decreases, the flow resistance decreases, and the amount of water increases accordingly. In other words, the higher the degree of cleanliness of the entire series of pipelines, the lower the hydraulic pressure at work, and the greater the increase in flow compared to the original pumps, thus ensuring the cooling water volume of the condensers and other heat exchangers in the engine room, ensuring that the single pump in the summer normal operation. From the actual operation conditions during the summer and the 11th machine overhaul of the plant, the 9-cycle water pump can normally and stably ensure the operation of the single pump and the two pumps, which proves that the 9-cycle pump reformation is successful.

Look at the head situation (see): From the curve comparison before and after the transformation can be drawn, in the same flow (that is, to ensure that the heat exchanger has the same amount of cooling water) in the case of a flow value of 13788m3 / h, the water pressure from the original The 15m water column was raised by 7.8m water column. This ensures the positive pressure of the condenser and the generator air cooler and improves the safety of operation; reduces the investment time of the booster pump, thereby saving plant power; and increasing the population water pressure and the outlet water pressure of the industrial pump. The amount of water, improving the cooling water flow rate and heat transfer coefficient of each heat exchanger, flushing away accumulated impurities, ensuring the heat transfer effect, and the safe operation of the unit's various systems are all favorable.

According to the curve in the curve, the flow rate after the transformation of the pump is more than 85% and the flow range is 9900~15336m3/h (that is, AQ is 5436m3/h), and the head range is 19.7~27.75 meters water column (that is, AH is 8.05 meters water column); Look at the efficiency curve of the original pump when it was shipped: more than 85% of the flow range is m32~15264m3/h (that is, AQ is 4132m3/h), and the head range is 15~25.75 meters water column (that is, AH is 10.75 meters water column); It can be seen that the high efficiency zone of the new pump is larger than that of the original pump, and the efficiency is higher than the original pump within the normal working range (ie, the head is within 20 m water column). The actual operation test shows that during normal operation, the efficiency of the pump after retrofitting is increased from 81.76% to 90.51%. In addition, as the water pressure decreases, the efficiency increase value increases, which indicates that the new pump must be operated in an efficient area, and the water pressure must be ensured. Must be within a certain range.

This is because within this range, the friction loss of the cover plate, the leakage loss of the population seal ring, and the impact loss of the impeller due to the flow rate change are all small.

Within the normal working range of the new pump, that is, when the water pressure is between 17.1 and 25 meters water column, the flow rate is 15282~11484m3/h, the shaft power is 872~912kW, and the maximum power is 912kW; the original pump is in the same water In the pressure range, the flow rate is 12042~8748m3/h, the shaft power is 660~684kW, and the maximum power is 684kW. After transformation, the shaft power is obviously increased by 208~228kW. The main reason is that the water volume increases greatly.

Look at the actual value of the indicator table: Under the same conditions, the new pump's water pressure and water volume are significantly higher than the original pump, and the shaft power increase at this time is 136.96~161.64kW, which is smaller than the curve value, which indicates the original pump. The power loss is much higher than the designed power loss. After the new pump is reformed, the operating efficiency is improved and the power loss is reduced.

The curve shape and specific rotation speed can be used to measure the performance curve before and after the 9-cycle water pump rebuilding: the new pump increases the water volume by 2052m3/h when the head is increased from 15m water column to 20m water column; the original pump water volume The change amount is 936m3/h. This shows that the new pump's performance curve is smoother than the original pump, and the change in flow caused by head change is higher than that of the original pump.

Look at the specific speed, although there are no parameters under the design conditions, but through the measured index table can be drawn, the new pump head increase is less than the flow rate of increase, that is, the specific speed of the new pump than the original pump has improved.

Since the size of the population seal ring was modified during this transformation, the leakage of the packing seal was greatly reduced, which was proved in the actual operation of the 9-pump retrofit. It can be seen that modifying the size of the seal ring can reduce the leakage of water in the shaft seal and improve the operating efficiency of the water pump. 5 Use after Modification 5.1 Performance Changes The previous performance comparison has demonstrated that the shape and specific speed of the performance curve have changed after the 9 pump was modified. In response to this situation, in order to ensure the safety of operations, in addition to strengthening the monitoring of the 9 pump, the water level difference of the primary filter, and the water quality of the river, and cleaning the primary and secondary filters, the plant also changed the secondary filter. type. Because the original oil moving secondary rotating filter is not only easy to damage the gears driven by gears, electromagnetic valve faults and water loss when draining large defects, more importantly, there is a dead corner of the sewage, the continuous accumulation of debris on the Internet, causing circulating water pump pressure Increased. Therefore, in September of that year, the plant replaced the secondary filter of the 9-pump into the secondary filter of the EPF type backflushing and electric drive of the double-drain. The actual operation of the inspection, the kind of filter in addition to saving water, not easy to malfunction, the key is the operation of water resistance is small, strong sewage discharge capacity, no pollution dead corner.

This is very useful for adapting the capacity increase of the 9-cycle pump and ensuring that the 9-cycle pump is always working in an efficient, high-volume area.

In addition, because the condenser is the largest user of circulating water pumps, and its tube plates and copper pipes are prone to blockage, operators are required to strengthen the monitoring of the condenser water pressure, water temperature, temperature rise of cooling water, and terminal differential. Properly adjust the water outlet door and perform half-time cleaning.

9 After the capacity increase of the circulating water pump was modified, the flow rate of the inlet water increased due to the increase of the water volume, and the pressure difference before and after the primary filter increased. On the one hand, the operating personnel must strengthen the inspection of the primary strainer; on the other hand, the The situation should also be appropriately modified, such as installing a floating trash rack before the filter to ensure the stability of the operation. 5.2 Parallel Operation Since the 9-cycle water pump is connected to the I, n parent pipes in parallel with the 7, 8, and 10 circulating pumps, the performance curve of the 9-pump is not the same as that of other pumps, so there will be some influence. However, since neither type of curve has an unstable hump shape, and the required lift of the piping system is not allowed to be greater than the maximum lift of the original pump in operation, it does not have much influence on other pumps. In actual operation, through comparison, it was found that the currents of the other pumps before and after the conversion and the outlet pressure did not change much and the operation was stable.

5.3 Motor Coil Temperature After the 9-pump capacity-enhanced retrofit, the current of the motor increases with the increase of flow rate and lift, which is 10-15A higher than that before the transformation. According to the formula of the coil power consumption, the increase of the current is the increase of heat generation. One of the important factors is that in the actual operation, the coil temperature of the 9-pump is also 10 to 12 feet higher. The 9-pump-matching motor adopts class B insulation. By looking up the relevant data, it can be seen that the maximum allowable temperature of the motor with Class B insulation is 130 ft. At the same time, the key to lowering the coil temperature lies in the heat dissipation of the coil: It was found that due to the high lubricating oil level of the guide bush on the motor and the oil spillage from the lower guide bush, the oil level is high. In the normal operation, it is splashed on the coil under the centrifugal force of the shaft; in addition, a large amount of coils are generated during long-term operation. Accumulation of dust is the cause of heat dissipation in the coil. Therefore, at the beginning of August 2000, the coils were cleaned with carbon tetrachloride, and the results obtained were very significant. During the whole summer of that year, when the temperature was 36 feet, the maximum coil temperature was about 95 feet, which was the same as other pumps. This shows that after the 9-pump is increased in capacity, it can still ensure that the motor temperature is within the normal range. This is for circulating water pumps. Safe operation is also very important.

Table 29 Lifting pump motor coil before and after cleaning Table Comparison Pump time Coil temperature Pump operation mode Before cleaning 9 Pump 9 Parallel operation After cleaning 9 Pump 5 Parallel operation 6 Economic performance after retrofit 9 Economic efficiency after retrofitting of pump The technical and economical comparison of the coal consumption reduced by the vacuum increase and the coal consumption corresponding to the increased power consumption of the 9 pump.

Through comparison and statistics of the unit vacuum before and after the capacity expansion of the 9-cycle pump, the vacuum of the condenser has been increased by an average of 1.2 kPa or more under the condition that the unit load is the same. At the same time, through observation during normal operation, it can be seen that after other pumps have switched 9 pumps, the influent pressure has increased to 0.01 to 0.011 MPa, and the vacuum has increased about 1.2 kPa. According to the impact of the economic indicators of the unit on coal consumption ( Each increase in vacuum pressure can save 2.8g/kW coal consumption, h) can be drawn, increase the vacuum of 1.2kPa can reduce the coal consumption 3.36g/kW.h. Calculated with 9 pump annual operation time of 6000 hours, then increase the vacuum due to 1.2 each year The standard coal consumption saved by kPa is 2,018 tons, which is calculated according to the standard coal price of 327.10 yuan per ton, which can save 690,800 yuan.

Due to the increased output of the 9-pump after capacity expansion, the single pump can ensure the stability of the stand-alone operation. It can be calculated according to the original 90-day operation of the two pumps, saving 0.8x30x24x3x1000 = 1728000kWh, and selling electricity by 0.15w/kWh. Yuan calculations, each year h, equivalent to RMB yuan, the economic benefit generated by the transformation of 9 pumps is 60.0088+25.92-8.9=76.95 million yuan.

9 Since the pump has been increased in capacity, the flow rate and lift have been significantly increased, the performance of the pump has been stable, and the value of application has been promoted. The improvement of the economic benefits of each pump is even more attractive.

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