1 Introduction
The decarburization system in our workshop adopts the hot potash method to remove CO2 from the low volatility gas to provide a qualified hydrogen-nitrogen mixture for ammonia synthesis and at the same time provides CO2 gas with purity greater than 98% for urea production. The solution circulation is mainly provided by a solution pump (decarburization pump). The pump from the seventies imported from Japan, the technical parameters in Table 1.
The pump performance is good, simple operation, stable operation. Especially MVB2830B type supporting motor, stable operation, the use of over 20 years has never been overhauled.
Over the years, due to the low system load, the normal process flow required for less than 200m3 / h, much less than the pump design capacity of 480m3 / h. In order to reduce power consumption, in 92 years its impeller cylindrical cutting, to achieve the use effect. However, since the first phase of fertilizer "8.13" was put into operation in 1999, the required process flow increased to 240 m3 / h. According to the reconstruction group accounting, and the impeller to restore the original large impeller, basically meet the production requirements at the time. In 2001, the second phase of fertilizer "8.13" was put into operation, and the required process flow increased to 280m3 / h. At this time, the problem was prominently exposed, the flow of large pump could no longer be increased, liquid flow phenomenon occurred in atmospheric tower, operation lost elasticity, The load is hard to increase and the production is very unstable. In order to solve this bottleneck restricting the production, the workshop and the maneuver department formed a special staff to tackle the problem.
2, find the problem
According to the original data, the pump design flow of 480m3 / h, far higher than the fertilizer "8.13" required 280m3 / h, why the actual operation can only reach 240m3 / h, the analysis that the following reasons:
(1) after years of use, the inner wall of the pump volute erosion corrosion wear, so that the arc deviated from the original design value, the gap increases, the return fluid through the impeller and pump casing back to the impeller clearance gap, reducing the outlet flow, pump Some useless work.
(2) Due to the low flow rate required for production over the years, maintenance personnel intend to increase the gap between the impeller wear ring and the wear ring of the pump casing when overhauling. On the one hand, it can meet the production requirements and relax the straightness requirements of the shaft. It relaxes the concentricity requirements of the pump shaft and the motor shaft for alignment, facilitates the overhaul and prolongs the service life of the wear ring. However, the amount of back flow is therefore increased, and the required flow rate can not meet the requirement.
(3) In the production of pump inlet temperature is high, the pressure is low, but also cause a low flow rate of a reason. According to the practical experience, the inlet temperature can be increased by 5-10m3 / h every time the inlet temperature is reduced by 1e or the inlet pressure is increased by 0.01MPa.
(4) For the pump flow is low, we think a big reason is: the introduction of the device without impeller, shaft and other parts drawings. Earlier Japanese manufacturers have discontinued. Later use of the impeller is the maintenance unit reference original impeller mapping preparation. Blade profile and the original design error, the smaller section of the blade than the original, together with the rough casting impeller wall, which have reduced the pump delivery capacity.
3, improve measures
(1) In order to reduce the backflow, strictly control the impeller wear ring and pump wear ring gap 0.50 ~ 0.68mm, but at the same time to ensure the rigidity of the shaft, straightness. After consultation with the processing plant, required in strict accordance with the technical conditions. Such as quenching and tempering should be done to the regular manufacturers, and a written report. After each overhaul, should use the dial indicator to find the correct control tolerance is less than 0.05mm, to ensure that the pump shaft concentric with the motor shaft.
(2) Reasonable deployment of system heat balance in production, try to reduce the inlet lye temperature, the maximum shall not exceed 108e.
(3) In view of the structure of impeller, Yangzhou Luen Hing Pump Co., Ltd. entrusts the professionals to recalculate the design without changing the assembly size through two steps. The first step is to improve the blade involute, Change the overall casting type is welded, eliminating the casting of the inner surface of the bumpy defects. The second step in the intensity of the allowable range of accounting, the appropriate reduction of the thickness of the blade and the front and rear cover, increasing the size of the entrance. The size of each site changes in Table 2.
4, transformation effect
After the new impeller put into operation, smooth operation, traffic increased significantly. After the first improvement of the impeller structure, the flow rate increased from 240m3 / h to 270m3 / h, basically meeting the production requirements. After the second improvement, the flow rate increased to 310 m3 / h, which is higher than the 280 m3 / h required to maintain high-load production. In the case of instability in production, easy to adjust the process, increasing operational flexibility. In the production of CO2 absorption capacity has been increased, eliminating the phenomenon of two towers of liquid, eliminating the constraints of the workshop to increase the load of a major bottleneck for the 400 tons of fertilizer Nissan laid the foundation.
Differential Cap, Differential Vent Cap, Differential Part
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