Use the data in Example Problem 8.1 and consider one of the two pumps driven by a variable-speed electric motor. Calculate the speed at which the VSD pump should be operated to match the pipeline requirements at 4000 gal/min. Assume that the rated speed for the pump at 3560 RPM produces a head of 1500 ft at 4000 gal/min.
Example Problem 8.1
A pump station installation at Corona consists of two pumps configured in series each developing 1500 ft of head at 4000 gal/min. Diesel fuel (Spgr=0.85, and viscosity=5.9 cSt) is pumped from Corona to a delivery terminal at Sunnymead, 75 miles away. The required discharge pressure at Corona based on pipe size, pipe length, liquid properties, elevation profile between Corona and Sunnymead, and the required delivery pressure at Sunnymead has been calculated to be 1050 psi. The pump station suction pressure is maintained at 50 psi to prevent pump cavitation. Assume the combined efficiency of both pumps at Corona at the given flow rate to be 82%.
(a) Analyze the pump station pressures and determine the amount of throttle pressure and HP wasted.
(b) If electrical energy costs 8 cents per kWh, estimate the dollars lost in control valve throttling.
(c) What recommendation can you make to improve pipeline operation?