Heat Rate Formula

The heat rate is the amount of energy required by an electrical generator or a power plant to produce one kilowatt hour (kWh) of electricity.

It is the rate of heat input required to generate unit power. Heat rate can also be defined as the ratio between thermal power inputs to electrical power output. If the heat rate is low, the efficiency is higher. In thermal generating units, the input and output exists normally in same units. In other words, heat range is equal to chemical energy input divided by the electrical energy released.

The heat rate formula is given by,

Rh = Ws × c × ΔT

Where,

Rh is heat rate in btu/hr,

Ws is steam flow in lb/hr,

c = specific heat capacity in btu/lb ∘F,

ΔT is the temperature difference in ∘F.

Question 1: Calculate the heat rate if steam enters a turbine at 400oF at atmospheric pressure. Steam at 500 lb flows through the turbine each hour during normal operation.

Solution:

Given parameters are,

Ws = 500 lbs/hr

c = 0.48

Tin = 400oF

Tout = 200oF

ΔT = 400 – 200

= 200oF

We have the Formula,

Rh = Ws × c ×ΔT

= 500 × 0.48 × 200

Therefore,  Rh = 48000 btu/hr

Example 2

Determine the horsepower output by using the heat rate value in the question 2 above.

Solution:

Horsepower can be calculated by,

HP = heat rate × 0.000393.

= 48000 × 0.000393

Therefore, HP= 18.864

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