An Improved Design of Pump in Sulfuric Acid Solution

1 Introduction

Sulfuric acid submerged pump is a single-stage vertical cantilever centrifugal submerged pump. The pump body is submerged in the medium and is suitable for pumping sulfuric acid or slurry in the fertilizer industry. It can also be used for transporting corrosive solid and viscous liquids in other chemical processes with viscosity lower than 300cp. Transport medium pump temperature below 100 ℃.
Recently, Zhongtiaoshan Nonferrous Metals Company used Jiangsu Shuangda Valve Manufacturing Co., Ltd. concentrated sulfuric acid submerged pump model 200FYL-32 (special shaft), the medium density of 1.84 × 103kg / m3, N = 90kW, Q = 360m3 / H, H = 32 m, n = 140 r / min, impeller diameter D = 340 mm. The actual operation of not more than 10 days, the pump appeared broken shaft and impeller wear serious situation. From the point of view of damage, the position of the broken shaft is at the impeller nut, and the wear of the impeller mouth ring is the most serious, which is mainly caused by the imbalance of radial force.

2, the cause of the imbalance in radial force

The radial force is generated because, in a centrifugal pump using a spiral pressure chamber, radial impeller pressure is exerted on the impeller if the pump is left operating at a design condition. This is due to the fact that when the pump is operating in the design condition, the flow velocity of the liquid at the outlet of the impeller is equal to the flow velocity of the liquid in the pressurized chamber, the flow of the liquid into the pressurized chamber does not produce an impact phenomenon, and the pressure of the liquid throughout the pressurized chamber Is the same, so the role of impeller pressure around the same liquid, the impeller will not act on the radial force; if the pump operating conditions for non-design conditions (such as the flow rate less than the design flow), the pressure in the water The fluid velocity in the chamber should also be less than the flow rate at design conditions and the fluid flow rate from the impeller should be greater than the flow rate at design conditions as seen in the outlet velocity triangle. Thus, the liquid flows into the pressure chamber, it will have a collision phenomenon, the kinetic energy of the liquid into pressure energy, the pressure of liquid in the pressure chamber due to continuous impact along the way to improve the pressure, so from the pressure water chamber diaphragm gradually began to pressure gradually Increase, as shown in Figure 1.

(1) If the flow rate of pump operation is greater than that of design condition flow, the opposite is true: the velocity of the fluid flowing out of the impeller is lower than that of the design condition, and the velocity of the liquid in the pressurized chamber is faster than that of the designed condition Large; impeller out of the flow of liquid into the pressure chamber has a small impact, so that the speed increases, the pressure decreases. Thus, starting from the pressure chamber diaphragm, the liquid pressure gradually decreased, as shown in Figure 2.

(2) When the flow rate is less than the design flow, it can be seen from Figure 1 that the direction of the radial force P due to the impact should point to the separation tongue and turn 90 ° in the same direction of the flow in the volute Direction, it is easy to prove. Figure 1 along the circumference of the pressure distribution line ABC is a rise value is proportional to the angle of the spiral. Beginning at 180 ° from the point of separation and making an identical helix A'B ', the pressure across the tongue from 180 ° to 360 ° is split into two sections, exactly the same A'B as AB Section and the A'BCB section. The radial forces caused by the AB portion cancel out exactly the radial forces caused by the A'B 'portion, and the remaining pressures of the A'BCB' are equal in magnitude. Therefore, the direction of the radial force P should be upward, ie in the direction of 90 ° from the separation tongue. Similarly, when the flow rate is greater than the design flow, this part of the radial force P should be directed downward, that is, from the tongue 270 points. This is the main reason for radial forces.
When the pump flow is less than the design flow, if the dynamic reaction force on the circumference is rotated counterclockwise by 90 °, the distribution of the reaction force R is similar to the shape of Figure 2, and the resultant force should be downward. Turn clockwise 90 °, then get the reaction force of the force direction, which is directed to the tongue. So we can see: When the pump flow is greater than the design flow, the reaction force formed by the radial force should point in the opposite direction of the tongue. P and R are drawn in Figure 1 and Figure 2, and find their resultant F, F is the radial force on the impeller. It can be seen that: when the pump flow is less than the design conditions, the radial force points away from the tongue in the direction of less than 90 °; when the pump flow is greater than the design conditions, pointing to the contrary, pointing away from the tongue less than 270 ° direction. The size of the radial force can be A A Stepanov's empirical formula to calculate:

F = 0.172 [1-Q / Qd] 2 HB2D2ρg

Where: Qd for the design flow conditions; B2 is the width of the impeller exit.

3, to solve the unbalanced radial force program

Sulfuric acid submerged pump structure are generally used single-volute pressure chamber structure and structure with a mouth ring impeller, shown in Figure 3.

For the damage, make the following structural improvements:

(1) The double-helical pressure water chamber (the original structure of a single spiral type), shown in Figure 4. The structure of this double helical pressure chamber is mainly to balance the radial force with two volute-symmetrical structures. As can be seen from Figs. 1 and 2, it balances the radial forces generated when working off-center. This approach reduces the hydraulic efficiency for smaller centrifugal pumps; and for larger pumps, experience has shown that double screw pressurized chambers do not degrade the efficiency of the pump. So you can use this method.
(1) The structure of the impeller is adjusted, ie, the impeller is changed to a single end face and the contact area remains unchanged. The original structure and the improved structure are shown in FIG. 5 and FIG. 6.

The improved structure prevents the impeller from wearing after eccentricity due to larger deflection after shaft deformation. The original structure in the larger deflection will be a great impeller wear and tear, making the impeller shaft will be broken; improved conditions to avoid this situation, the safe operation of the impeller is of great benefit.

4 Conclusion

The improved sulfuric acid pump has been running safely for more than six months and is operating in good condition. The improvement of these two kinds of structures provides a good reference for the design of the pump in the future.

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Technical Parameter

Surface Roughness: Ra 12.5	Machining Tolerance:+/-0.01 mm
Certification: ISO 9001:2008	Standard: ASTM. AISI. DIN. BS. JIS. NF
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