Power Plant Pumps
According to the function, the power plants use pumps are divided into steam turbine auxiliary pump (boiler feed pump, preset pump and condensate pump) and desulphurization circulating pump (main circulation desulfurization pumps, FGD peripheral pumps, absorption tower systems).
Steam turbine auxiliary pump
The feed water pump is a water supply device that delivers high temperature and high pressure to the boiler. In the auxiliary machine, the feed pump consumes the most power, accounting for 3%~4% of the unit’s output power, and has high technical requirements.
With the development of the unit to large capacity and high parameters, higher and higher requirements are imposed on the structure, performance, operation adjustment mode of the feed pump and its reliability and economy.
- Double-shell cylindrical boiler feed pump
At present, ultra-high pressure boiler feed pumps with an outlet pressure of 20 MPa or more generally adopt a double-shell tubular structure, which is widely used in large-capacity units of more than 300 MW.
- Single-shell multi-stage segment boiler feed pump
Mainly used in medium and high pressure units and ultra high pressure units below 200MW, the outlet pressure is below 20MPa.
Analysis of the above two kinds of boiler feed water pump adopt sealed form
a). The stuffing box is sealed with a packing sleeve and a flange, or shaft-end sealed with mechanical seal, and cooled with filtered water. The water feed pump has a high lift, up to 100 meters (the large feed pump can reach up to km), and the stress of the mechanical seal is very large.
b). Under the high-pressure high-speed water flow, ordinary stainless steel is easily etched, so the mechanical seal should be made of good material with anti-corrosion, anti-scouring and mechanical properties.
c). The friction pair adopts Tc/Tc sectional ppump, which has a simple structure, but the disassembly and assembly is troublesome, the maintenance is time-consuming. In addition, the water flow along the axis is not uniform for the heating around the pump body, and it takes a long time to warm the pump. The mechanical seal used requires a long life and is suitable for the temperature change of the medium.
- Booster pump
The speed of the feed pump is relatively high. In order to solve the cavitation problem, the pre-feed pump is generally used to increase the inlet pressure of the main feed pump. The seal pattern of the pre-feed pump is similar to that of the boiler feed pump, and the influence of cavitation on the mechanical seal must be considered.
- Circulating water pump
Circulating pumps are used to supply cooling water to the condensers, oil coolers of steam turbine and the air coolers of electric generator. The amount of cooling water in power plants is large, but the pressure is generally not high. Therefore, the requirements for circulating water pumps are high flow rate and low lift. The mechanical seals used are often made of fluoroether rubber or silicone rubber.
- Condensate pump
The structure can be divided into horizontal, vertical and vertical bag type multi-stage condensate pumps.
The horizontal condensate pump is suitable for small capacity units. The structure mainly has three types of single-stage, two-stage and induction wheels. The pump has good anti-cavitation performance, compact structure, easy assembly and disassembly, convenient maintenance, and the structure itself can withstand axial force.
Vertical condensate pump. Widely used in 125~300MW units, characterized by small floor space and dry working environment of the motor, but it is difficult to overhaul.
The mechanical seals used in the auxiliary units of the steam turbine unit have several characteristics:
High pressure, high temperature, severe cavitation and serious corrosion.
Commonly used mechanical sealing mechanisms are generally balanced, high-speed pumps are static, basic frame is usually 304, 316 or 316L, friction pair material is TC / TC or SIC / SIC, hard to hard pairing. The mechanical seal spring of the condensate pump and the boiler feed water pump is made of Hastelloy, and the auxiliary seal ring is made of fluoroether rubber or silicone rubber. The cartridge type is easier to install and minimizes artificial installation errors.
Desulfurization circulating pump
The boiler flue gas is pressurized into the absorption tower through the flue, and the limestone slurry (CaCO3 + H2O) in the absorption tower is pumped from the slurry circulation pump to the top of the tower, and is fully convected by the spray atomization device and the SO2 in the flue gas, and the reaction is generated. Ca (HSO3) 2 is then oxidized by oxidizing air to form CaSO4 · 2H2O crystals, commonly known as gypsum. The limestone slurry pump, gypsum slurry discharge pump, gypsum slurry overflow pump, etc. in the system are simply referred to as FGD peripheral pumps. The slurry circulation pump is called a main circulation desulfurization pump.
- FGD main circulation desulfurization pump
The main faults of the desulfurization circulating pump:
1) The pump material can not meet the special requirements of the conveying medium, resulting in the service life of the product parts not meeting the specified requirements. If the content of Cl- in the medium is very high, the pitting of the material is very serious. If the ratio of the material is improper, the life of the part will be shortened or perforated and discarded.
2) The life of the accessory parts is insufficient. The main reason is that the system can not flush the machine seal requirements of the desulfurization pump. If the design of the machine seal structure is unreasonable, the service life of the machine seal will be reduced, affecting the overall operation effect of the pump and the desulfurization index of the power station. The completion.
3) The efficiency index of the product is insufficient. The efficiency of the product of the desulfurization pump is very strict, because the main power consumption of the system is on the running pump of the system, and the long-term operation. If the efficiency index is unqualified, the operating cost of the power station will be caused. As the cost increases, the user’s efficiency requirements for the main circulation pump are all above 85%. Moreover, there is no spare pump, so the service life of the mechanical seal is relatively high.
FGD peripheral pump
The peripheral pump includes a lime slurry pump, a lime slurry circulation pump, a process water pump, a waste water pump, a waste water circulation pump, a gypsum slurry pump, a gypsum slurry discharge pump, an accident slurry pump, and the like.
From the structural type, the characteristics and lifespan of the double-end mechanical seal without internal flushing water, the single-end mechanical seal with pressure-washing water, and the double-end mechanical seal with sealant are analyzed.
Absorption tower system
The absorption tower is mainly based on a stirrer.