Liq. Sulfur Transfer Pumps in parallel operation

[nirlt]

I would like to know following for Liq. Sulfur Transfer Pumps in parallel operation:

1. If three pumps in liquid sulfur service with PT of 130 Deg.C and Sp. Gr. @ PT as 1.5 gm/cc, are working in 2W+1S configuration taking suction from a common header (not sump) from an atmospheric pressure tank, and delivering to a common header having a PCV. Do you feel pump(s) can really get into a operating situation of End Of Curve(EOC) Flow for prolonged time and not for just few seconds during start up ?

If response is 'Yes', what are those situations may be ?

2. In above mentioned configuration of pumps how critical it would be to ensure a positive margin of say 1 meter of liq. sulfur column between NPSHA and NPSHR throughout operating range of Min. Cont. Flow (MCF) to EOC Flow ?

3. In the process of ensuring a min. margin of 1 mlc of liq. sulfur should we compare NPSHR values at different operating points like MCF, rated Point & EOC with NPSHA at rated Points or we should compare NPSHA value at MCF, Rated Point and EOC respectively ? What is industry practice on this aspect ?

 

[BigInch]

The valve will experience a flow change with a change in pressure differential across it. If the pump's discharge pressure - valve's differential pressure at the set point is sufficient to drive EOC flow rate through your piping system, you can reach the EOC flowrate.

You do not have to have NPSHA>NPSHR at flowrates outside your normal operating range, as long as you do not stay at those flowrates for a time long enough for cavitation to cause damage.

It is not common to have NPSH problems at minimum flowrates. If you do, your system has other problems that must be corrected before considering operating at higher flowrates.

Presumedly you only need to ensure that you have NPSHA > NPSHR at your maximum continuous flowrate, which is doubtful that it will be your EOC flow, but refer to paragraph 2 again now.

To ensure that you have enough NPSH margin, you should talk in percentages of excess NPSHA over NPSHR, not meters of head over NPSHR. I'm not sure what it should be for sulfur, but something like 10% to 15% would probably not be considered as an unreasonably safe margin.

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