Case study 5: Upgrade of an oil refinery’s pumping systems including installation of variable speed drives
Case study summary
At a San Francisco refinery, installing a VSD on a product transfer pump saved €/$ 120 000 per annum and on a primary feed pump saved €/$ 220 000. Vibration was reduced and mechanical seal and bearing failures have been eliminated. There was no investment cost to the refinery but savings were shared with the contractor.
Other potential applications
Any applications where the pump is sized for an intermittent maximum flow rate but runs mostly at a reduced (but variable) rate.
The energy services contractor agreed to install the VSDs and upgrade the equipment at no charge to the refinery, but took a share of the savings. Their total investment was €/$ 1 200 000.
€/$ 340 000 per annum from the VSDs and €/$ 750 000 from the total project.
Overall about 18 months, but this was not applicable to the refinery who gained immediately with their share of the savings.
Installation and operation details
Conversion of the refinery’s vacuum gas oil plant to a diesel hydro treater (DHT), left the pumps grossly oversized. Several pumps were operating frequently at 40% of best efficiency point, resulting in low hydraulic efficiency, excessive vibration and seal or bearing failure about once a year.
The full range of upgrades consisted of:
• Installing VSDs on the 1650 kW (2250 hp) primary feed pump and the 500 kW (700 hp) product transfer pump.
• Replacing the internal elements on the 1650 kW (2250 hp) secondary feed pump and on a 300 kW (400 hp) power recovery Turbine (PRT).
• Changing operating procedures for the main 3700 kW (5000 hp) and 3000 kW (4000 hp) back-up pumps.
The installation of the VSDs on the primary feed pump and product transfer pump gave energy savings by reducing losses through flow control valves.
The energy saving from the use of VSDs was 500 000 kWh per month. The resizing of the PRT and secondary feed pump, along with a more energy efficient operating procedure for the back-up pumps, saved another 500 000 kWh per month. Cost savings shared by the refinery and contractor were €/$ 340 000 per annum from the variable speed pumps and €/$ 750 000 overall.
The demand charge previously levied on the DHT process was eliminated.
Since the upgrades there have been no seal or bearing failures and process control has improved.
It should be noted that a VSD was not considered appropriate for all the oversized pumps. If the duty is not varying then resizing the pump, e.g. new impeller and diffuser element, reduced impeller diameters or even a new pump, will usually give greater life time cost saving and better pay back than a VSD.