Page 84 - Handbook of Energy Engineering Calculations
P. 84
gives 1443.05 + 327.5 = 1770.55 Btu (1867.9 J) as the heat input per pound
(kg) of steam.
The work done per pound (kg) of steam is: For mercury = (lb Hg/lb steam)
(h − H ) = 11.23(151.1 − 120.7) = 341.4 Btu (360.2 J). For steam = H −
m1
me
c1
H = 1499.2 − 909.1 = 590.1 Btu (622.6 J). Summing, as before, the total
se
work done per pound (kg) of steam = 931.5 Btu (982.7 J).
6. Compute the binary cycle efficiency
The binary cycle efficiency = [work done per pound (kg) of steam]/[heat
input per pound (kg) of steam]. Or binary cycle efficiency = 931.5/1770.55 =
0.526, or 52.6 percent.
7. Calculate the steam cycle efficiency without the mercury topping turbine
The steam cycle efficiency without the mercury topping turbine = [work done
per pound (kg) of steam]/(H − H ) = 590.1/(1499.2 − 69.7) = 0.4128, or
sf
s1
41.3 percent.
Related Calculations. Any binary cycle being considered for an installation
depends on the effects of the difference in thermodynamic properties of the
two pure fluids involved. For example, steam works under relatively high
pressures with an attendant relatively low temperature. Mercury, by
comparison, has the vapor characteristic of operating under low pressures
with attendant high temperature.
In a mercury-vapor binary cycle, the pressures are selected so the mercury
vapor condenses at a temperature higher than that at which steam evaporates.
The processes of mercury vapor condensation and steam evaporation take
place in a common vessel called the condenser-boiler, which is the heart of
the cycle.
In the steam portion of this cycle, condenser water carries away the heat of
steam condensation; in the mercury portion of the cycle it is the steam that
picks up the heat of condensation of the mercury vapor. Hence, there is a
great saving in heat and the economies effected reflect the consequent
improvement in cycle efficiency.
The same furnace serves the mercury boiler and the steam superheater.
Mercury vapor is only condensed, not superheated. And if the condenser-
boiler is physically high enough above the mercury boiler, the head of
