Why is a minimum circulation line not provided in some centrifugal pumps? For instance, in our stripper reflux pump it is provided, while in our diesel hydrotreater stripper it is not.
Answers
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10/03/2009
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A:
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keith bowers, B and B Consulting, kebowers47@gmail.com
It is a matter of prudence, risk management, and good practice for the conditions. High horsepower pumps will almost always be provided with minimum flow protection to ensure against overheating and cavitation. If the pump is deadheaded (blocked discharge), all the driver energy is turned to heat and will quickly raise the temperature of the pump fluid and casing to dangerous levels. Mechanical seals will be ruined and loss of containment usually results, leading to a very dangerous vapor cloud with explosion and fire risks.
Pumps handling low boiling point materials like LPGs will often have warmed recirculation loops to provide fresh warm fluid as a flush to the seals to prevent frozen crystal formation on the seal faces, which will cause very rapid wear and leakage. Also, low boiling materials are more easily vaporized under low flow conditions, leading to bubble formation and collapse (cavitation) in the impeller which can severely damage it quickly.
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09/03/2009
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A:
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Samuel Sinanan, IPSL, Samuel.Sinanan@ipsl.co.tt
A minimum circulation line is provided on a pump when it is envisaged that the pump will operating below its minimum limit. Your Stripper Reflux pump may operate at variable flows depending on the heat input into your Stripper Column, whereas the other pump, while having to be turn down at lower throughputs, may still operate above the minimum flow limit.
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