Heater replacement, economic

Fehring, T. and Gaggioli, R., "Economics of Feedwater Heater Replacement." Trans. ASME, July 1977, pp.482-488. 

Any number of methods for economic analysis could be employed here, a discounted cash flow analysis is used. Assume that (a) the heater replacement cost is 235,000 (b) the replacement heater will have a 20-year life and an 18,000 salvage value (c) fuel and maintenance savings are escalated at 6% per year (d) after tax cost of capital is 9%. Table III shows the results of the cash flow analysis of the proposed investment in a replacement heater. As is indicated, since the net cumulative discounted cash flow (+ 29,166) is positive, the replacement of the heater is justified. 

Spare parts for common components such as heaters for barrels, transfer lines, and dies, thermocouples, pressure transducers, drive belts, and fuses should be kept in stock. Since the goal is to keep the line operational at all times, keeping these low-cost but necessary components in stock can reduce the amount of downtime due to simple failures. For operations where the resin is abrasive or corrosive, a spare screw should be kept in stock. As the screw wears in the extruder and the performance decreases beyond an economic limit, then the screw should be replaced with the spare screw and the worn screw should be sent to a screw manufacturer for refurbishment. 

Economizer A counter-flow heat exchanger for recovering additional energy from the combustion products increasing the temperature of feedwater heater and minimizing the temperature difference between saturation temperature and feedwater tem]>erature. Feednmter It constitutes the makeup water to replace the water lost by evaporation and the condensate returned. 

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