MIL-HDBK-1003/7

b) Net Plant Heat Rate. This heat rate is determined by dividing the

total fuel energy (Btu/hour) added to the boiler by the difference between power

(kilowatts/hour) generated and plant auxiliary electrical power consumed.

Cycle Performance. Both turbine and plant heat rates, as above, are usually

5.1.7.4

based on calculations of cycle performance at specified steady state loads and well

defined, optimum operating conditions. Such heat rates are seldom achieved in practice

except under controlled or test conditions.

Long Term Averages. Plant operating heat rates are actual long term average

5.1.7.5

heat rates and include other such losses and energy uses as non-cycle auxiliaries, plant

lighting, air conditioning and heating, general water supply, startup and shutdown

losses, fuel deterioration losses, and related items. The gradual and inevitable

deterioration of equipment, and failure to operate at optimum conditions, are reflected

in plant operating heat rate data.

Plant Economy Calculations. Calculations, estimates, and predictions of steam

5.1.7.6

plant performance shall allow for all normal and expected losses and loads and should,

therefore, reflect predictions of monthly or annual net operating heat rates and costs.

Electric and district heating distribution losses are not usually charged to the power

plant but should be recognized and allowed for in capacity and cost analyses. The

designer is required to develop and optimize a cycle heat balance during the conceptual

or preliminary design phase of the project. The heat balance depicts, on a simplified

flow diagram of the cycle, all significant fluid mass flow rates, fluid pressures and

temperatures, fluid enthalpies, electric power output, and calculated cycle heat rates

based on these factors. A heat balance is usually developed for various increments of

plant load such as 25, 50, 75, 100 percent and VWO (valves, wide open). Computer

programs have been developed which can quickly optimize a particular cycle heat rate

using iterative heat balance calculations. Use of such a program should be considered.

5.1.8

Steam Rates

Theoretical Steam Rate. When the turbine throttle pressure and temperature

5.1.8.1

and the turbine exhaust pressure (or condensing pressure) are known, the theoretical

steam rate can be calculated based on a constant entropy expansion or can be determined

from published tables. See Theoretical Steam Rate Tables, The American Society of

Mechanical Engineers, 1969. See Table 8 for typical theoretical steam rates.

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