Page 60 - Handbook of Energy Engineering Calculations

capture CO , either before (pre-) or after (post-) combustion. Department of
2
Energy (DOE) studies show that pulverized-coal subcritical pressure steam
boilers consume some 900 gal of water per MWh (gal/MWh) (3407 L/MWh)

for carbon capture. Supercritical pressure boilers consume some 800
gal/MWh (3028 L/MWh) for carbon capture.
New coal-fired power-generating plants will be planned and designed in
engineering design offices for many years to come, all over the world. Why?

Because coal deposits are enormous in many parts of the world. Further,
ignoring its GHG effects, coal is an abundant, low-cost fuel that plant
operators are familiar with and know how to handle. The big unknown for
everyone—from engineering designers to plant owners—is the fiscal impact

of controls required to reduce GHG emissions from coal-fired electric-
generating plants. The regulators could win, and end the century-long
dominance of coal-fired electric-generating plants. Or engineers could
preserve the coal-fired plants’ dominance by finding low-cost ways to reduce

substantially the GHG emitted by such plants. Either way, engineers will
have a prominent role in the outcome.

ENERGY EFFICIENCY AND HEAT RATE OF STEAM

TURBOGENERATOR

2
A 20,000-kW turbogenerator is supplied with steam at 300 lb/in (abs)
(2067.0 kPa) and a temperature of 650°F (343.3°C). The backpressure is 1 in
(2.54 cm) Hg absolute. At best efficiency, the steam rate is 10 lb (25.4 kg)
per kWh. (a) What is the combined thermal efficiency (CTE) of this unit? (b)
What is the combined engine efficiency (CEE)? (c) What is the ideal steam

rate?

Calculation Procedure:

1. Determine the combined thermal efficiency
(a) Combined thermal efficiency, CTE = (3413/w )(l/[h − h ]), where w =
r
1
2
r
combined steam rate, lb/kWh (kg/kWh); h = enthalpy of steam at throttle
1
pressure and temperature, Btu/lb (kJ/kg); h = enthalpy of steam at the
2