2 replies to this topic

[chemengr84]

Respected ALL,

 

I have the following query which requires your experience based advice. 

 

We purchased a centrifugal pump few years back for transferring atmospheric residue to vacuum column via fired heater. At that time normal flow was ~14-15 m³/hr and MCSF at given impeller size was 9.3 m³/hr. Due to changes in crude mix the residue decreased to 9.5-10.5 m³/hr resulting in unstable operation of pump (being close to MCSF requirement) therefore standby steam driven PD pump is being operated. In order to have a stable pump operation the option of smaller impeller size as well as motor with low rpm were explored however they aren't helpful because of very minute reduction in MCSF and inability to meet head requirements respectively. 

 

Normally spill back/ re-circulation line is installed for pump protection coupled with any of the RO, Control Valve, Globe Valve or ARC to full fill the MCSF but in that case the flow decrease is dictated by the downstream process requirement / turn down operation etc.

 

Please advise if spill back will be helpful in case low flow is available at pump suction and we can not  reduce the downstream flow requirement. Your comments and recommendation of case specific literature is appreciated.

 

Thanks

[Technical Bard]

Yes, a spillback is the best way to deal with this.  I wouldn't use an ARC valve in this service though.  A flowmeter and control valve in the spillback line are the best option.

[thorium90]

Would variable speed drive be a possibility?