Retrofit of circulating pump in 300 MW unit of Zhujiang Power Plant

Keywords: Circulation pump; Technical innovation; Increased flow; Turbine

Flow? Retrofit of circulating water pumps for 300 MW generating units in Zhujiang Power Plant

ZAN Yuming

(Shenzhen Kingon (Group) Co., Ltd., Shenzhen, Guangdong 518040, China)

Abstract: In view of the insufficient water supply and blade intensity of the circulating water pumps in Zhujiang Power Plant, the circulation water pumps were retrofitted with the aim of increasing flow and saving energy. How to change the original motor, pump case and pipes, etc , The blade angle was increased by 3 degrees counterclockwise; the blade molding surface was modified suitably; the combined type impeller was changed to monoblock cast impeller, and the manufacturing procedures for the impeller optimized. All these measures enhance the blade intensity and increase the flow of the circulating pumps, thus improving the economic efficiency and the reliability of the plant with significant economic benefit obtained.

Keywords: circulating pump; technical retrofit; flow increasing; steam turbine

Zhujiang Power Plant 4 sets of 300 MW domestic-made imported turbine generator set, equipped with eight 1600HLB-16 vertical mixed flow pump, the original pump design parameters: flow 19 600 m3 / h, lift 16.77 m, speed 370 r / min, pumps Efficiency 87%. Rated motor parameters: Power 1 250 kW, current 158 ​​A, voltage 6 kV, frequency 50 z, speed 370 r / min. As the condenser area of ​​the steam turbine generator used in the Pearl River Power Plant is relatively small compared with that of the same type of domestic unit, the condensing effect is poor, resulting in insufficient vacuum in the unit and affecting output. In addition, the 1600HLB-16 circulating pump impeller used in the power plant is a combined structure with low strength and cracks and ruptures at the root of the blade. The actual output of the pump can not meet the design requirements. These problems seriously affect the safe and economic operation of the unit, and the circulating pump is one of the main consumers of electricity in the power plant, which accounts for about 20% of the electricity consumption of the entire unit. Therefore, the circulating water pump in the Pearl River Power Plant is retrofitted , Can improve exhaust vacuum, operating efficiency and safety and reliability, has a very significant economic value and social benefits.

A circulating pump transformation

As circulating pump volume, weight, price is more expensive, in order to increase the flow and the impeller shell all the transformation, is bound to cause a great waste. And the shell and the impeller all re-design and manufacture, the pump installation size, import and export flange diameter also changed, to bring great inconvenience to the installation. Therefore, the actual transformation, the use of the shell does not move, the motor does not change, only to transform the small change program of the impeller. The specific requirements are as follows: a) When the modified impeller is installed, it is completely interchangeable with the original impeller, and other parts of the pump do not change; b) The modified pump impeller performance parameters must satisfy the original system and the original matching motor unchanged , Pump flow from the original design of 19.6 × 103m3 / h, increased to 21 × 103 ~ 22 × 103m3 / h, to ensure that the motor does not exceed the power; c) the modular structure of the impeller into a whole cast impeller to improve blade strength.

1.1 impeller hydraulic technology transformation

Because the improvement requires that the pump casing not move and only the impeller is modified, the design of the impeller is limited by the geometrical size and hydrodynamic characteristics of the original pump casing. Moreover, the flow rate after the reformation is greatly increased, which inevitably leads to a marked increase in the flow velocity in each overcurrent passage , Hydraulic loss also increases. In this condition, to ensure that the pump efficiency does not decline, you must use advanced design methods, optimize runner passages such as runner, study the relationship between the matching flow components, the minimum hydraulic losses, to obtain the best performance.

In order to enhance the strength of the pump blades, the original impeller pump will be transformed into an integral casting impeller. Combination of experiments and experience to determine the new impeller blade placement angle from the original 0 ° to 3 ° counterclockwise increase. The blade design is based on the similar conversion method. After the initial axial dimensions of the impeller are obtained, the impeller inlet neck diameter and hub diameter are corrected according to the size of the housing and the shaft. Correction to improve the anti-cavitation pump performance, increase the import of flow impeller area. After the correction is reasonable but also for axial fluid cross-sectional area of ​​?? water changes in the inspection and check the flow lines. Find unreasonable phenomenon and then re-amended, and then check until reasonable. Impeller design selection of reliable and efficient hydraulic model, the model performance curve shown in Figure 1, the model conversion formula is:

Where: λ - amplification factor, λ = 4.1;

qV, p - physical pump volume flow, m3 / h;

qV, m - model pump volume flow, m3 / h;

Hp - physical pump head, m;

Hm - model pump head, m;

np-- physical pump speed, 370 r / min;

nm - model pump speed, 1 450 r / min;

ηp - physical pump efficiency,%;

ηm - model pump efficiency,%.

1.2 processing and manufacturing process optimization

As high speed centrifugal pump blades for the twisted leaves, the use of ordinary wood mold casting impeller will have a greater deviation, the impeller over-flow surface is also rough. Therefore, the manufacture of modified pump impeller, the use of non-deformed plastic mold. Blade mold surface using a combination of rigorous inspection model to ensure compliance with design requirements. Molding using advanced combination of new technology mud core, sand sand resin used to improve the accuracy of the casting geometry and relative position accuracy, reduce surface roughness (Ra12.5 ~ 25) and reduce the original imbalance. The stainless steel castings for solution treatment, improve mechanical properties, reduce segregation, improve corrosion resistance. Blades all polishing, roughness Ra3.2 ~ 6.3, improve efficiency. Impeller rigorous static balance, non-destructive testing of leaves.

2 after the test results and analysis

2.1 test results

According to the pump test standards, the circulating pump model was tested. Circulating water supply test using the unit system, adjust the pump outlet valve to adjust the circulating water. A total of 6 different flow conditions were measured. Model pump test data in Table 3, in which the pump head and pump efficiency is calculated as follows:

Where: p1, p2 - pump inlet and outlet pressure, Pa;

ρ - circulating water density, kg / m3;

g - acceleration of gravity, 9.81 m / s2;

v1, v2 - pump inlet and outlet flow rate, m / s;

ΔZ - pump out, inlet pressure gauge elevation difference, m;

Pu - pump effective power, kW;

qV is the pump volume flow, d1, d2 is the diameter of the pump inlet and outlet pressure gauge; Pu = ρgqVH / (3 600 × 1 000), is the pump head; Pa = Pd · ηd Pd for the motor input power, ηd for the motor efficiency.

According to the model conversion formula (1), (2), (3) on the data in Table 3 conversion, get the physical pump data in Table 4. Table 5 is based on the pump design experience, the data in Table 4 were amended to provide the manufacturer to the power plant +3 ° impeller to improve design parameters. Table 6 for the Guangdong Electric Power Research Institute in 2001 to improve the Pearl River Power Plant No. 2 circulating pump test, obtained 1600HLB-16 circulating pump measured data.

2.2 Experimental Analysis

According to the data in Table 1, Table 5 and Table 6, the flow rate, lift and efficiency of No.2 pump after reformation (+ 3 ° impeller) basically meet the design requirements. The pump's high-efficiency operation range is about 21 × 103 ~ 22 × 103 m3 / h, reaching the transformation agreement "pump efficiency of not less than 80%" requirement. In the meantime, the range of high efficiency pump operation is also widened toward the direction of large flow. Under the same head condition, the pump flow rate after the improvement is increased by 2 000-2 500 m3 / h from the original design rated flow rate (19.6 × 103 m3 / h) h, therefore, the improved circulation pump can operate in a long-term high efficiency range. The experimental results show that the efficiency of the circulating pump is 87% lower than that of the original design. The reason is that due to the cutting of the impeller chamber before the transformation, this modification is only to rebuild the impeller, and the impeller chamber has not been modified accordingly. As a result, Extensions in the impeller and impeller room with the outside, greatly increased the impeller chamber volume loss, thereby reducing the pump efficiency. In addition, the inlet diameter of the impeller chamber was originally designed to be 1.13 m, and the velocity of water entering the impeller was 6.65 m / s. When the water column of such a large flow velocity impacted, it was not located at the blade edge in the impeller chamber. The collision water collided with the inlet flow to generate turbulence and vortex , So that the fluid flow at the inlet of the vane deteriorates, resulting in a decrease of hydraulic efficiency of the pump and a decrease of 5% -6% of the overall efficiency of the pump.

After the transformation to ensure that the motor does not exceed the rated current at the same time improve circulation pump flow, and can make circulation pump running in the high-efficiency zone, the winter load rating with three pumps two machines, the summer load rating with four pumps and two machines running. To run 7,000 h per year calculation: to improve the cause of insufficient circulating water, in order to ensure the vacuum, winter four pumps two machines to run, three pumps and two machines improved operation. Four pumps and two machines Three pumps and two machines Each unit consumes more than 600 kWh of electricity per hour, equivalent to 360,000 yuan a year. In addition, an increase of circulating water to improve the condenser vacuum, the same coal consumption, increase unit static output, improve unit economy.

3 Conclusion

Pearl River Power Plant No. 2 circulating pump impeller transformation, the use of the overall cast stainless steel impeller to improve processing technology, optimize the impeller profile line, the angle of the original design angle counterclockwise increase 3 °, to ensure that the motor does not exceed the rated current and improve the circulation pump Flow rate, and the circulation pump running in a high efficiency area. The experiment and actual operation show that the reformation of the No.2 circulating pump impeller is more successful. It not only solves the condition of the condenser vacuum which is caused by the small amount of water in the actual operation cycle, but also improves the energy saving effect obviously to ensure the safe and reliable operation of the impeller. The successful experience of its transformation not only provided the basis for the reform of other circulating pumps in Zhujiang Power Plant, but also provided successful experiences for the similar circulating pump retrofit.

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