Temporary Backup Pump for Cooldown System
Temporary Backup Pump for Cooldown System
(OP)
I have been asked to design a temporary pumping system as a backup to a cooldown system. The proposed temporary system would connect two (2) diesel-driven pumps to a discharge header. The normal system header pumps deliver 5,000 GPM at 95 PSI. The proposed backup system would run 24/7 for 1 - 3 weeks.
The operating pressure on the backup pumps need to be below normal system head pressure. When the normal system header pressure falls below 80 PSI, the proposed pumps need to provide a minimum of 4,000 GPM at 80 PSI (static lift is 30' and total discharge pipe run is less than 50').
The system header pressure and flow can not drop below 4,000 GPM or 80 PSI for more than 3 seconds.
Any suggestions would be greatly appreciated. Thank You.
The operating pressure on the backup pumps need to be below normal system head pressure. When the normal system header pressure falls below 80 PSI, the proposed pumps need to provide a minimum of 4,000 GPM at 80 PSI (static lift is 30' and total discharge pipe run is less than 50').
The system header pressure and flow can not drop below 4,000 GPM or 80 PSI for more than 3 seconds.
Any suggestions would be greatly appreciated. Thank You.





RE: Temporary Backup Pump for Cooldown System
Regards checman
RE: Temporary Backup Pump for Cooldown System
Thanks.
RE: Temporary Backup Pump for Cooldown System
Static Discharge Lift?
This implies you're discharging below atmospheric pressure. Is this your discription of a pump's characteristic or someone else's?
RE: Temporary Backup Pump for Cooldown System
Regards
checman
RE: Temporary Backup Pump for Cooldown System
While the elevated tank is out of service (estimated at 1 - 3 weeks), the diesel pumps are required to be running 24/7 but not overcoming the normal header pressure. Should the power fail and the normal header pressure drops, the diesel pumps become the primary cooling pumps and are required to provide a minimum of 4000 GPM at 80 PSI. The flow and pressure can not drop below these values for more than 3 seconds.
The pumps we are looking at have a minimum flow of 2000 GPM. We realize that starting the pumps and getting up to full speed within 3 seconds is not an option. We have considered using a PID loop control with a pump discharge pressure setpoint of 85 PSI. With normal header pressure of 95 PSI the diesel pumps would recirculate back into the suction pit through an electric-actuated valve fitted with a fail to close option (I have been told this is available). If the power fails the recirculation valve begins to close and the pump would speed up to keep the 85 PSI setpoint. The cycle time on a 4" valve is 20 seconds and the velocity through a 4" valve at 2000 GPM is 51 ft/s. We are concerned about the 3 second time constraint as well as the velocity through the valve.
We are still trying to come up with a viable solution. Any thoughts or guidance would be greatly appreciated. Thank You.
RE: Temporary Backup Pump for Cooldown System
On the 51 feet per second you will need ear plugs. What is the choke flow for that valve? I would not count on that valve.
Regards
checman
RE: Temporary Backup Pump for Cooldown System
I don't know the numbers or details but here is ours as I recall.
We have a similar situation as yours where a water tower backs up a process cooling, quench and fire water system. We have both diesel and steam turbine pumps as backup to the system. If the water tower is to be taken out of service some of the primary pumps are taken offline and the standby pumps are brought online to replace the lost capacity of the primaries. The suction of the standby pumps are normally online with the primaries but in case of a fire they can draw on two 1 million gallon potable water storage tanks or in a real crisis they switch to river water. Our electric supply normally has 3 discrete sources and at times 4, but the system has been used 3 times in tthe 50 year history of the plant.
RE: Temporary Backup Pump for Cooldown System