AWWA MTC61228

This paper now examines the costs, capital and operating, of the various competitive energy recovery devices (ERDs), as they would be encountered over a warranty period, assumed here to be 5 years. The Francis turbine has been excluded because of its significantly poorer efficiency relative to the other devices. Also, in the last 3 years, ERD manufacturers have made significant improvements in their units and this paper updates the power consumption of all devices based on information from current international tenders. Basic case study conditions for this paper are 800-psi (55 bar) to 900-psig (62 bar) single stage, operating applied pressure over 5 years at an availability of 95%, 36,000 mg/L feed water concentration and 45% recovery. Case differences include temperature variances from 18° C to 25° C with plant capacities at 2 MGD (7,570 m³/d), 12 MGD (45,420 m³/d and 35 MGD (132,475 m³/d). The ageing factor of the spiral wound cartridges, required to establish the pressure increase with time, is assumed at 7%/yr. For simplicity and symbolism of every device's performance, just one membrane manufacturer's computer projection program is used. The cases considered also have varying power costs of 4¢/kWh, 10¢/kWh and 25¢/kWh. High-pressure and booster pumps and motor types, VFD usage, train sizes, etc. are chosen via "industry standards" to be compatible with the capacities under study. Train sizes of 0.5 MGD (1,893 m³/d) for the low capacity system, 2 MGD (7,570 m³/d) for the middle capacity system and 3.5 MGD (13,248 m³/d) largest system will be used. Membrane projections assume 6 cartridges per pressure vessel and will base pressures, etc., on initial startup and five year projections for simplicity. Includes tables, figures.