The exhaust-gas temperature leaving a continuously operating furnace is 260°C, and a proposal is being considered to install a heat exchanger in the exhaust-gas stream to generate low-pressure steam at 105°C. the question to be investigate is whether it is economical to install such a heat exchanger, and if so, to find its optimum size. The following data apply:
Table
year factor year factor year factor
1)--0 (8)--3.008(15)--5.275
2)--0.476(9)--3.376(16)--5.552
3---0.937(10)--3.730(17)--5.801
4--1.379(11)--4.060(18)--6.058
5--1.810(12)--4.384(19)--6.295
6--2.224(13)--4.696(20)--6.5
7--2.622(14)--5.002(21)--6.703
Flow of exhaust gas-----7.5kg/s
Specific heat of exhaust gas---1.05kJ/(kg*k)
Value of the heat in the form of steam---$1.5 per gigajoule
U value of heat exchanger based on gas-side area---23W/(m^2*K)
Cost of the heat exchanger including installation based on gas-side area----$90 per square meter
Interest rate----8%
Life of installation----5years
Saturated liquid water enters heat exchanger at 105°C and leaves as saturated vapor
1) Develop the equation for the saving as a function of the area, expressed as a uniform annual amount.
2 answers