The slurry circulating pump is one of the most important equipment in the flue gas desulfurization system of thermal power plant. Its main function is to continuously circulate the slurry in the absorption tower, continuously transport the lime slurry to the top of the absorption tower and spray it downward. It is in reverse convection contact with the SO2 (sulfur dioxide), nitrogen oxide, carbon monoxide and other gases in the tower, so that a large number of corrosive gases in the flue gas are absorbed To protect the anticorrosive materials inside the absorption tower from being damaged by high temperature flue gas. More than half of the electric energy consumed by the FGD device is used to drive the absorption tower circulating pump, so there are high requirements for the reliability and service life of the slurry circulating pump, which should have high efficiency. The hydraulic design, structural design and material selection of flow passage components of desulfurization slurry circulating pump are directly related to the efficiency and reliability of pump operation.
Power plant flue gas removal sulfur slurry circulating pump selection factors:
The lime slurry pumped by slurry circulating pump contains a large number of fine solid particles with high hardness, the liquid is slightly acidic pH = 4 ~ 6, the temperature is 45 ℃ ~ 60 ℃, and contains a large number of chloride ion Cl -, sulfate ion, etc. Therefore, anti-corrosion and anti-wear materials must be used to effectively solve the problem of friction and corrosion.
During the continuous operation of slurry circulating pump for a long time, the impeller surface is subjected to the impact wear, corrosion, cavitation and other damage effects of lime slurry, the blades are gradually worn thin, forming cavitation pits, even defects, notches and cracks, which will accumulate into structural damage, leading to impeller scrapping, and seriously reducing the working efficiency and power consumption of the pump. Therefore, there is an urgent need for a reliable repair method of pump components to reduce the purchase cost, reduce spare parts inventory, ensure that the service time of components is not less than that of new components, further extend the service life of impeller, and reduce the labor intensity caused by frequent disassembly and assembly of workers.
According to the material classification, there are three kinds of FGD slurry circulating pumps: metal pump, cast iron rubber lined pump and ceramic pump. At present, the metal pump is used in most power plants in China, mostly made of duplex stainless steel or high chromium cast iron. The FGD slurry circulating pump made of this kind of material has better wear resistance and corrosion resistance.
Power plant flue gas removal sulfur slurry circulating pump model:
The stainless steel desulfurization slurry circulating pump is a horizontal, single suction, multistage and segmented corrosion-resistant chemical pump, which supplies and transports – 20 ℃ ~ 105 ℃ liquid without solid particles, and the allowable inlet pressure of the pump is 0.6MPa. The flow passage parts of the strong corrosion-resistant pump are made of stainless steel, and the shaft is made of stainless steel. Seal part: it is divided into packing seal and mechanical seal. Packing seal is mainly used in the occasions where the leakage requirements are not strict on site or the media contains solid particles. Mechanical seal is suitable for the occasions where the leakage requirements are strict under the conditions of high temperature, high pressure and corrosiveness. Both seals play the role of sealing both ends of the pump to prevent the internal and external media of the pump Flow is also the guarantee of pump body sealing.
Precision casting is used for all flow passage parts of desulfurization slurry circulating pump to ensure the size and smoothness of flow passage, which is more than 2% higher than the measured efficiency of ordinary multistage pump on the market, and has good energy saving effect. Install O-ring on the matching surface of balance ring and pump to prevent high-pressure water from entering the balance chamber and affecting the balance effect of balance plate, reduce the wear of balance plate and extend the service life of products. According to the needs of different users, the balance plate and balance ring can be made of hardfacing hard alloy, alloy steel or qt60omn2 alloy nodular cast iron, with high surface hardness, good wear resistance and long service life.
The main design features of the pump are as follows:
1. Advanced modular design, a large number of local components that have been tested in long-term operation are used, and parts have high interchangeability.
2. High strength, high-quality materials and a variety of selection of inlet and outlet flange and connecting pipe design improve the allowable connecting pipe load of the pump. The material structure of the high-strength and high-quality pump shell is close, and the service life can reach 5 times of that of the ordinary casting. The impeller and guide vane at the flow passage part are made of precision casting, and the efficiency of the smooth and flat casting is more than 2% higher than that of the ordinary casting. It can meet the specific requirements of the system under special circumstances.
3. Fast assembly and disassembly design allows the pump to replace the sealing and bearing parts without disassembling the pump body and the inlet and outlet pipelines, ensuring the inspection and maintenance time.
4. Combination of high efficiency, high reliability and low cost. Through the best matching of impeller and guide vane, reasonable matching clearance and wider axial throttling design, the pump can still maintain its high stability and high operating efficiency after long-term operation.
5. Good cavitation performance, using excellent impeller hydraulic model or special double suction impeller structure, users do not need to configure additional booster pump or improve the height of water inlet tank.
6. The pump is arranged symmetrically, which can basically eliminate the axial force. The residual axial force is borne by a pair of back-to-back angular contact ball bearings. The rotor components of the impeller are arranged symmetrically. The impeller on the rotor components is divided into two ends of the high and low pressure areas. The axial forces are mutually offset and balanced. The instantaneous axial forces of the pump under variable operating conditions and the residual axial forces due to processing errors and screw seals are borne by the thrust bearing mechanism of the bearing components. This kind of pump cancels the axial force balance mechanism such as balance plate or balance drum, completely avoiding the occurrence of rotor locking, parts damage, shaft breaking and even motor burning accident caused by the instantaneous change of pump working condition and the failure of balance plate or balance drum. Greatly extend the service life of the pump.
7. Safe pump body seal design. According to different pressure and structure, the pump body adopts metal face metal hard seal or O-ring seal.
8. According to the user’s requirements, the middle tap and the minimum flow system can be added.
9. The unique structural strength design allows the single-stage lift of the pump to be up to 15mA (150m), the outlet pressure to be up to 15MPa (total lift 1500m), and the core package components composed of the bearing and rotor are not affected by the temperature change, with excellent thermal shock resistance.
10. There is no axial movement when using mechanical seal, which completely overcomes the problem that the friction surface of moving and stationary rings of mechanical seal fails due to poor contact when the old multi-stage pump axial movement is used. In the actual operation, it has been water tight.