Sawsan311
Chemical
- Jun 21, 2019
- 303
Dear All,
Operating pumps in parallel is a process necessity, selection between variable and fixed speed pump depends on the process rangeability (turndown) as well as energy lifecycle analysis. However, in some revamp situations for increasing capacity, fixed speed may be connected in parallel with multiple VSD pumps instead of a VSD pump specially when there is a limitation in accommodating the foot print of VSD auxiliaries such as chiller unit,
From process control perspectives, the control of the VSD can be under downstream backpressure absorbing the variation in the downstream network, fixed speed on the other hand is controlled via a discharge FCV maintaining the pump close to its best efficiency point.
My question is, do you foresee any impracticality of operating fixed speed pumps with VSD pumps in parallel under common suction and discharge. In my opinion, a proper start-up philosophy is required to ensure a smooth transition between the starting of the VSD and fixed speed pump. In most common cases, starting the VSD pump followed by fixed speed pump would contribute in minimizing the load on the motor starting current of the fixed speed pump and initially establishing the pressure in the network prior to starting the fixed speed pump.
Appreciate your views on the subject, some people express concern of operating fixed and VSD pump together stating that VSD pump would have to obey the conditions dictated by fixed speed pump and hence deviating from the objective of VSD control. In my opinion, as long as fixed speed pump is equipped with a discharge control mechanism via throttling at BEP, there should be no concern in operating a VSD pump with it.
Regards,
Operating pumps in parallel is a process necessity, selection between variable and fixed speed pump depends on the process rangeability (turndown) as well as energy lifecycle analysis. However, in some revamp situations for increasing capacity, fixed speed may be connected in parallel with multiple VSD pumps instead of a VSD pump specially when there is a limitation in accommodating the foot print of VSD auxiliaries such as chiller unit,
From process control perspectives, the control of the VSD can be under downstream backpressure absorbing the variation in the downstream network, fixed speed on the other hand is controlled via a discharge FCV maintaining the pump close to its best efficiency point.
My question is, do you foresee any impracticality of operating fixed speed pumps with VSD pumps in parallel under common suction and discharge. In my opinion, a proper start-up philosophy is required to ensure a smooth transition between the starting of the VSD and fixed speed pump. In most common cases, starting the VSD pump followed by fixed speed pump would contribute in minimizing the load on the motor starting current of the fixed speed pump and initially establishing the pressure in the network prior to starting the fixed speed pump.
Appreciate your views on the subject, some people express concern of operating fixed and VSD pump together stating that VSD pump would have to obey the conditions dictated by fixed speed pump and hence deviating from the objective of VSD control. In my opinion, as long as fixed speed pump is equipped with a discharge control mechanism via throttling at BEP, there should be no concern in operating a VSD pump with it.
Regards,