CH-18-011 -- Comprehensive Analyses of Variable- and Constant-Speed Pumps and Heat Exchanger and Energy Cost Savings Potential in University of Kansas' Power Plant ✓ Most Recent

Minimizing the waste energy of pumping systems is one ofthe primary foci in facility operation. Thus, investigating capitaland energy costs for running such a facility was studied andanalyzed for this paper. Specifically, a comparative study ofusing variable-speed pumps versus constant-speed pumps wasconducted in the steam power plant at the University ofKansas. This study considers the energy costs/savings of thepumps themselves, whose task is to provide water to the openfeedwater heater (deaerator).Because the pumps affect othersystems in the power plant, overall plant costs/savings are alsoconsidered (i.e., life-cycle costs).

At the outset, the variable-speed pump would appear to bethe most economical choice, even with its more complicatedand expensive design. However, in the University of Kansaspower plant, any excess water that is returned to the storagetank passes through a heat exchanger, which is used to reclaimenergy from the deaerator's vented steam and noncondensablegases before they are released to the atmosphere. However, thisis not the case for the variable speed pump when running inlevel control mode. Thus, in addition to considering just thecomparison of the costs/expenses of the two types of pumpsthemselves, it is necessary to consider the costs/expenses fromthe heat exchanger's operation.

Based on a 20-year life-cycle cost analysis, whencompared with the constant speed pump, the variable-speedpump saves approximately $25,000 in electricity. However,when the lost energy from the heat exchanger's reclamation isalso considered, using the constant-speed pump for that same20 years saves approximately $800,000, which would be paidfor the extra fuel required to compensate for not reclaimingenergy. Thus, in this case, use of the constant-speed pumpingsystem, including energy recovery of the deaerator's exhaust,is strongly recommended.

In light of this analysis, to benefit from both the variablespeedpump and the deaerator's energy reclamation system, itis recommended that there be a power plant redesign that takesadvantage of both systems. Details regarding the specifics ofthe redesign are included in this paper./p> See more