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ME 312

Project #1 System Analysis and Optimization

February 25, 2005

Due: March 15, 2005, at the 11:59 am, Dr. Krauses office in box.

Report in Memo Format

A coal-fired, steam power plant operates on an ideal reheat-regenerative Rankine Cycle

with one reheater and two feed-water heaters, one open and one closed. The system isshown in Figure 1. Steam, at 40 kg/second, enters the high-pressure turbine at 15 MPa

and 620 deg. C and the low-pressure turbine at 1 MPa and 600 deg. C. The condenser

pressure is 5 kPa. Steam is extracted from the turbine at 0.6 MPa for the closedfeedwater heater and at 0.2 MPa for the open feedwater heater. In the closed feedwater

heater, the feedwater is heated to the condensation temperature of the extracted steam.

The extracted steam leaves the closed feedwater heater as a saturated liquid, which issubsequently throttled to the open feedwater heater.

The coal has a heating value (energy released when the fuel is burned) of 27,500 kJ/kg.We can assume that 80% of this energy is transferred to the steam in the boiler.

Determine the following:

a. A T-s diagram for this cycle showing the saturation linesb. The fraction of steam extracted from the turbine for the open feedwater

heater

c. The fraction of steam extracted from the turbine for the closed feedwaterheater

d. The total heat rate input for the cycle, kWatts

e. The pump input power required, kWattsf. The net power output of this cycle, kWatts

g. The cycle thermal efficiency, %.

h. The amount of coal needed, tons/hour.

i. Complete a selection of better extraction pressures, for FWH, by using themethod noted on the next page. Has the cycle thermal efficiency

improved?

Figure 1: Schematic of the System (see page 558, Figure P9-86, in your Textbook)

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Improving Cycle Efficiency by Selection of Extraction Pressures for Feedwater

Heaters

The extraction pressures for multiple feedwater heaters are chosen to maximize the cycle

efficiency. As a rule of thumb, the extraction pressures for the feedwater heaters are

chosen such that the saturation temperature difference between each component is about

the same.

T T etccond to FWH boiler to FWH

= , .

Example:

An ideal regenerative steam power cycle operates so that steam enters the turbine at 3MPa, 500oC and exhausts at 10kPa. Two closed feedwater heaters are to be used. Select

starting values for the feedwater heater extraction pressures.

0 2 4 6 8 10 1212

0

100

200

300

400

s [kJ/kg-K]

T[C]

3000 kPa815 kPa

136.2 kPa

10 kPa

Steam

C

C

C

233.9 C

45.85 C