Which structural type of melt urea pump performs well?
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I work at a fertilizer factory; the pump used for transporting molten urea is a centrifugal pump with a packing seal. However, the packing often leaks, which results in excessive COD levels in the discharged liquid, requiring frequent repairs； We want to upgrade to a new molten urea pump in order to address the issues of short service life of the packing and frequent leaks. Currently, some manufacturers use mechanical seals for their melt urea pumps, such as those produced by High Quality Pumps in the United States; others employ centrifugal pumps with auxiliary impellers and packing seals. Some experts suggest using magnetic drive pumps (no domestic companies are known to use them yet). Which type of pump is suitable for the current needs of urea production?
What is the approximate temperature of the molten urea being transported? What is the crystallization temperature? Pumps with double-end mechanical seals should work, but appropriate cooling schemes for the pump body and the mechanical seal must be adopted based on the temperature, pressure, and corrosivity of the medium.
We use a secondary impeller along with a packing seal, and it works pretty well. Of course, if high sealing requirements are needed, then a mechanical seal is definitely the better choice. As for whether to use a single seal or a double seal, as well as which type of flushing system to employ, it’s best to let the supplier come up with a proposal. :Lol, using a magnetic pump must be too expensive; there’s no need for that.
For urea melting pumps, a dynamic seal is the most suitable sealing method, which involves a secondary impeller along with packing. During operation, leakage is sealed by the auxiliary impeller; when the machine is shut down, the packing serves as a seal (the packing can also be replaced with a sealing plate). Currently, the manufacturers that produce high-quality pumps of this type are: Xi’an Pump Valve, Jiangsu Feixiang, and Dalian Sulzer. Our factory has Xi’an Pump Valve and Jiangsu Feixiang products, and both work quite well.
The temperature for transporting molten urea is 138–142°C, while the crystallization temperature is around 132°C. Our factory has two evaporation systems; the centrifugal pumps used for transporting molten urea in the newly installed evaporation system are produced by Xi’an Pump and Valve Factory and feature auxiliary impellers along with packing seals. These pumps are difficult to maintain. Additionally, due to their structure, the pump body must be moved every time maintenance is carried out, which makes it tricky to align the pump body properly； Secondly, the instruction manual states that after the pump starts running, the packing gland bolts should be loosened and the packing seal water should be turned off; we did not do this. If the gland nuts are slightly loosened, they will fall off automatically due to the vibration of the pump body, and the result is not satisfactory. Is this the same way in which your melt urea pumps (with auxiliary impellers and packing seals) are operated?
Suggestion 1: For the packing of melt urea pumps, imported Gore packing can be used; it seems that Shenyang Sihuan Packing Factory has now produced a domestic version of this packing, and it can last for a year with each replacement. 2: The melt urea pumps manufactured by Dalian Shenlan use mechanical seals, which deliver excellent performance.