General Trend of Pump process
At present, the general trend of Pump process development can be summed up as follows:
(1) Large capacity and high lift. With the increase of pump capacity, equipment can be reduced, construction cost can be reduced and energy can be saved. It is easy to manage and adopt automation, at the same time, it can improve the technical and economic indicators and operational reliability of the unit.
Domestic 300 MW units are equipped with two boiler feed pumps, each with a driving power of 5500 KW. Overseas 1300MW units only use one feed pump, its driving power is 50000KW; 1800MW units feed pump power is 55000KW; and even there are feed pumps with driving power up to 75000KW. The outlet pressure of the feed pump also develops from 13.7-15.7 MPa and 17.7-20 MPa of supercritical pressure to over 50 MPa of supercritical pressure.
(2) High-speed. In the 1960s, due to cavitation and material problems, the speed of the pump is generally only 3000r/min. In recent years, with the continuous development of science and technology, the speed of the pump is getting higher and higher. For the pump, increasing the speed can improve the single-stage head of the pump. Therefore, when the total head is the same, the number of stages of the pump can be reduced, the length of the pump shaft can be shortened, the volume can be reduced, the weight can be reduced, raw materials and manufacturing costs can be saved. For example, when the speed of the feed pump of 660 MW units in the United States is increased from 3000 r/min to 7500 r/min, the single-stage head can reach 1 143 m, the series can be reduced from 5 to 2, and the weight can be reduced by 3/4. It can be seen that the economic benefits brought by the increase of rotational speed are very significant.
(3) High efficiency. Pump is a general mechanical product, its power consumption is objective. Therefore, improving pump efficiency is of great significance to energy saving. As early as the 1970s, China began to carry out technical transformation and renewal of low efficiency pumps, such as centrifugal pumps and axial flow pumps whose efficiency is less than 60%, so that the efficiency of improved feed pumps can reach about 79%. In the 1980s, China introduced the technologies of KSB, WEIR and SUIZER respectively, and produced the third generation high-pressure boiler feed pump with an efficiency of more than 82%.
It is worth noting that in 1995, the results of the national pump operation survey showed that the actual operation efficiency of centrifugal pumps in China was 10%-30% lower than that in developed countries. Therefore, in addition to improving the efficiency of the pump itself, it also needs to improve the efficiency of its operation in the system.
(4) High reliability. As the pump is developing towards large capacity and high speed, the requirement of reliability is higher and higher. Because only the pursuit of high efficiency and sudden reliability, the energy savings in operation can not offset the economic losses caused by the shutdown of the pump accident. Therefore, while improving efficiency, reliability should be put in the first place.
The reliability of pumps should be guaranteed from design, manufacture to installation and operation.
(5) Low noise. Noise pollution, like air pollution and water pollution, is harmful to people's health.
At present, many countries have done a lot of research on the mechanism of noise control, noise detection technology, and noise limitation standards, and formed a new discipline.
(6) Automation. With the development and application of computer technology and network technology, the DCS (Distributed Control System) of computer network monitoring and control has been realized in all units above 300 MW, namely distributed computer control system or distributed control system for short. Overseas, monitoring and control of electric part of thermal power plant has been evenly integrated into DCS system, so as to realize the monitoring and control and management of computer network system of the whole thermal power plant, and become an automated thermal power plant. In DCS system, the pump is no longer a single machine control, but a network monitoring control. It can realize automatic start and stop of pumps, real-time monitoring, display and control of flow, pressure, temperature and other parameters on-line, as well as on-line fault diagnosis, automatic interlocking and protection.