$9-6.$ A steam generation system at a biomass$-$

fueled power plant uses an electrostatic precipitator

$($ESP$)$ to clean its gaseous effluents. The power plant has

consistently made use of the same type of ESP over the

past several years. The installed cost of a new ESP has

been relatively constant at $$80,000.$ Records of operation

and maintenance expenses indicate the following average

expenses per year as a function of the age of the ESP.

The MVs of the ESP are also reasonably well known as

a function of age.

Determine the best time to replace the ESP if the MARR

is $15\%$ per year. $(9\mathrm{.}5)$