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In the construction of electric power engineering, the water supply system has high investment, large engineering quantity and complex construction, which has great influence on the construction cost and investment payback period of electric power engineering. In the scheme design of power plant water supply system, great attention is paid to the selection of natural ventilation cooling tower and circulating water pump, as well as the optimal arrangement of circulating water pump room and circulating water pipeline system, because they directly affect the safe operation of steam turbines and the full-load power generation of generators, and directly affect the economy of power plants. In order to reduce the annual operating cost of water supply system and save the project cost, it is necessary to popularize the application of energy-saving equipment and optimize the system configuration.
The cooling water quantity of steam turbine-generator condenser in thermal power plant changes with seasons, with large cooling water quantity in summer and small cooling water quantity in winter. With the change of steam extraction rate of steam turbine, the cooling flow rate is small when the steam extraction rate is large, and it is large when the steam extraction rate is small. The water supply system adopts a unit with two pumps of the same model in parallel, and distributes the circulating cooling water to two circulating pumps equally. This configuration is in line with the Technical Specification for Hydraulic Engineering in Thermal Power Plants, and has been widely used in the design of water supply system in power plants. However, when a unit is equipped with two pumps of the same model, problems often occur. In order to fundamentally solve the contradiction between the low efficiency of water pump and the unsynchronized change of system flow, it is imperative to develop a new type of efficient and energy-saving water pump.
Application of high-efficiency and energy-saving circulating water pump in water supply system
In recent years, a large number of 135MW thermal power plants have been built all over the country. 18 135MW domestic superhigh pressure and intermediate reheat units were designed in Liyan Power Plant in Shandong, Chacheng Power Plant in Xuzhou, Jinchuan Power Plant in Gansu and Wei Qiao Thermal Power Plant in Shandong. These power plants are located in North China, Northeast China and Northwest China, and also have the characteristics of spontaneous self-use, stable power demand and large fluctuation of heating load, with small heat load in summer, large heat load in winter and long heating period throughout the year.
Taking 135MW heating unit as an example, the condensing capacity of steam turbine condenser under the maximum continuous output of steam turbine is 324t/h, and the demand for circulating cooling water is19640m3/h; /h； The condensing capacity of the steam turbine condenser is 223t/h under the rated extraction condition of the steam turbine, and the required circulating cooling water quantity is12274m3/h; Under the maximum extraction condition, the condensing capacity of the steam turbine condenser is 143t/h, and the circulating cooling water quantity is 4700m3/h. With the change of the operation condition of the random group, the cooling water required by the circulating water system fluctuates greatly from 4700m3/h to19000m3/h..
The water supply system adopts conventional water pump arrangement. In order to meet the requirements of steam turbine operation in summer, the water pump flow is 9800- 1 1700m3/h, and the lift is18.0-21.5m. According to the parallel operation of two pumps in summer, the cooling water required by the circulating water system is19000m3/. In other seasons, running a pump can meet the cooling water demand of circulating water. The flow range of the pump is 9800- 1 1700 m3/h, and when the system runs beyond this flow range, the operation of the pump is uneconomical.
It is not difficult to find that the water demand of the circulating cooling system is 12274t/h under the rated extraction condition of the steam turbine, and the water resistance of the system is slightly lower than that under the pure condensation condition of the steam turbine, by 2.0-3.0 m, the pump head is reduced to 15.0- 16.5 m, and the flow rate of a single pump is increased to/kloc-0. The circulating cooling water volume is only 4700t/h, and the water resistance of the system is greatly reduced compared with that under the pure condensation condition of the steam turbine, which leads to the increase of pump head and low operation efficiency, which leads to the water spraying device of the cooling tower to spray water, increase the flow rate of the water distribution tank and reduce the heat exchange time of the water flow. Because the working efficiency of the water pump is extremely low, the reactive power of the motor increases, which wastes electric energy in vain.
If a new type of high-efficiency and energy-saving water pump is used in the circulating water system of 135MW domestic ultra-high pressure intermediate reheat unit, the contradiction between low pump operation efficiency and unsynchronized system flow change will be fundamentally solved.
Taking G48Sh water pump as an example, when the rotating speed n=485r/min, the pump flow is 17500m3/h, the head is 18m, the pump efficiency is 88%, and the shaft power is 947kw. When the rotating speed n=420r/min, the pump flow is 13200m3/h, the head is 14.5m, the pump efficiency is 87%, and the shaft power is 587kw. The design parameters of the pump are basically consistent with the circulating water system of 135MW unit, and the operation efficiency is high. More than 0/00 G48Sh pumps in/KLOC were sampled and tested, and the actual operating efficiency was 84-88%. The operating efficiency of conventional 48Sh-22 water pump is only 60%.
The water pump adopts the core technology of bipolar two-speed motor, which increases the flexibility of operation and adjustment of circulating water system. According to the change of condenser cooling water volume with seasons and the change of steam extraction volume, the pole number and speed of the motor are automatically adjusted, and the output power and water supply of the water pump are changed at the same time. One high-speed G48Sh pump supplies 3000 tons more water per hour than two 48Sh-22 parallel pumps. The output power of low-speed G48Sh pump can be adjusted from 947KW to 587KW, and the motor power can be reduced by 37%, with obvious energy-saving effect. Because the circulating water system can basically run at a low speed in other seasons except for the high-speed operation of pumps in summer, each pump can save 2.3 million kWh of electricity every year based on the annual operation time of 7200 hours. According to the auxiliary electricity price of the power plant, 0.2 yuan/kWh, the annual power saving of a single circulating pump is about 400,000 yuan, and according to the payback period 10- 15, the annual power saving of a single circulating pump is as high as 4-6 million yuan. For power plants with multiple energy-saving circulating pumps, its economic benefits are very considerable, which is also a development direction of energy-saving technological transformation in many power plants. The conventional water pump with motor is fixed and cannot be adjusted, and the output power corresponding to a certain speed is constant. The price of a single high-efficiency and energy-saving circulating pump is 1.5-0.2 million yuan higher than that of a conventional SH series centrifugal pump with the same capacity, and this part of the investment cost can be fully recovered by running the motor at a low speed for a short time.
The introduction of high-efficiency and energy-saving circulating pump can optimize the hydraulic conditions of the system, broaden the application range of the high-efficiency section of the pump and effectively improve the working efficiency of the pump; The traditional design concept of steam turbine using two pumps with equal capacity is changed, and a new pump configuration is put forward to meet the off-design operation requirements of steam turbine. The main structure adopts horizontal pump shell design, which is very convenient for factory operation and maintenance.
The circulating water system of shiliquan power plant (2× 125MW) was originally equipped with four 48SH-22 pumps of the same model, but there are some problems such as insufficient water supply, low efficiency and poor economy. 1June, 1998, No.4 water pump was replaced by G48SH water pump. After putting into production, the power plant commissioned the electric power laboratory to test the performance of the water pump. The operating efficiency is as high as 87.78% at high speed and 86. 1 1% at low speed, which is 28.26% and 26.5% higher than other unmodified pumps.
Guangdong Yunfu Power Plant (2× 125MW) is also equipped with four 48SH-22 circulating pumps of the same model. Three pumps run in summer and two in other seasons. Due to insufficient circulating water flow and low efficiency, it was changed to G48SH pump, and was commissioned by Guangdong Electric Power Experimental Research Institute for efficiency test. The actual flow of the new pump at high speed is 16537t/h, the operating efficiency is 87.78%, and the motor power is1002 kw. . The actual flow of the new pump at low speed is 13080t/h, the operating efficiency is 86. 12%, and the motor power is 646KW. The operating conditions of the water pump and the unit are consistent. The actual flow of raw water pump is 14400t/h, the efficiency is 59.62%, and the motor power is1089 kw; ; When the maximum efficiency is 70%, the flow rate is 1 1540t/h, and the pump does not match the operating conditions of the unit. At high speed, the water supply of the new pump is 2 137 t/h, the power is 87.7KW lower than that of the old pump, and the efficiency is 28. 16% higher than that of the old pump. At low speed, under the same water supply, the new pump can save 443KW per hour, and the energy saving effect is remarkable.
conclusion
The popularization of any new technology needs a process of understanding. The biggest feature of high-efficiency energy-saving circulating pump is energy saving and high working efficiency, which is worth popularizing in the whole country. However, whether it is suitable for all regions and all 135MW units needs more practical applications and needs to be selected according to local conditions.
The promotion of high-efficiency and energy-saving circulating pump involves not only the configuration of circulating pump in power plant, the standby of pump and the operating cost of pump, but also the interlocking and control of pump and steam turbine operation. Especially in the construction of water intake pump house along the Yangtze River, the geometric size of high-efficiency and energy-saving circulating pump must be carefully selected. For the water intake pump house along the river, the equipment and equipment operation cost are not as high as the structural cost and construction cost of the water intake pump house, especially when the low water level of the water source is quite different from the highest water level, any change in the geometric size of the water intake pump house will affect the project cost.