Page 224 - Boiler plant and distribution system optimization manual

Boiler Plant Calculations 209

Figure 11-5

7. If a boiler is operating at a pressure of 100 Calculate the percentage of flash steam
psig and the total heat in the steam is 1190 formed at 5 psig when dropping pressure
Btu/lb, what percentage of the total heat in from 300 psig. Use values from 8 and 9 above.
the steam is being lost because of the cold
condensate in the example above? 398.7 – 195.5
—————— = 21%
(Ans.: 81.25 Btu/lb 11190 Btu/lb = 6.8%)
960.5
8. How much heat is in boiler water at:
(Ans.) 11. What is the temperature of steam at different
a. 300 psig (398.7 Btu/lb) pressures? See Table 11-19.
b. 5 psig (195.5 Btu/lb)
Pressure
9. What is the latent heat of 5 psig steam? ____ (PSIG) Temperature (Ans.)
(Ans. 960.5 Btu/lb) —————————————————————————
15 ________ 249.8 F [121C]
10. In a steam system, all the steam should con-
dense back into water and must go through 75 ________ 320.1 F [160C]
a steam trap which lowers the pressure from 100 ________ 337.9 F [170C]
system pressure to a lower pressure. Blow-
down water from the boiler also undergoes 150 ________ 369.9F [187C]
this same pressure reduction. As can be seen 200 ________ 387.8 F [197C]
from the above data, the water at the lower
pressure contains less heat. This heat differ- 600 ________ 488.8 F [253C]
ence is given off as flash steam. —————————————————————————