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Heat Rate Formula

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  • Last Updated : 10 Feb, 2022

The total amount of energy required to produce one kilowatt-hour (kWh) of electricity using a power plant (plant heat rate formula) or an electric generator is referred to as heat rate. It is defined as the rate of input required to generate one unit of electricity. The ratio of thermal inputs to electrical output can also be characterized as heat rate; the smaller the heat rate, the higher the efficiency. Both incoming and outgoing energy in a thermal generating system is usually measured in the same unit. The amount of heat produced is always proportional to the chemical energy supplied divided by the electrical energy freed.

What is Heat Rate?

The heat rate is the entire amount of energy required by an electric generator or power plant to create one kilowatt-hour (kWh) of electricity. 

It is the rate of input necessary to generate unit power. The ratio of thermal inputs to electrical output is also known as the heat rate. The better the efficiency, the lower the heat rate. In a thermal generating system, incoming and outgoing energy are usually measured in the same unit. The amount of heat produced is proportional to the chemical energy supplied divided by the electrical energy freed.

Formula for Heat Rate

The formula of Heat Rate is,

Rh = Ws × c × ΔT

where,

  • Rh = The rate of heat in btu/hr,
  • Ws = In lb/hr steam flow,
  • c = btu/lb degree F specific heat capacity
  • ΔT = the difference in degrees Fahrenheit

Sample Questions

Question 1: Calculate the heat rate if steam enters a turbine at 500 degrees F and leaves at 300 degrees F at atmospheric pressure. During typical operation, 600 lb of steam passes through the turbine every hour.

Answer:

Given : Ws = 600 Ib, c = 0.48, Tin = 500oF, Tout = 300oF

Find : Rh

Solution :

ΔT = Tin – Tout

∴ ΔT = 500 – 300

∴ ΔT = 200oF

We have,

Rh = Ws × c × ΔT

∴ Rh = 600 × 0.48 × 200

Rh = 57600 btu/hr

Question 2: Calculate the heat rate if steam enters the turbine at 700°F and exits at 500°F at atmospheric pressure. 350 Ib of steam travels through the turbine every hour in normal operation.

Answer:

Given : Ws = 350 Ib, c = 0.48, Tin = 700oF, Tout = 500oF

Find : Rh

Solution :

ΔT = Tin – Tout

∴ ΔT = 700 – 500

∴ ΔT = 200oF

We have,

Rh = Ws × c × ΔT

∴ Rh = 350 × 0.48 × 200

Rh = 33600 btu/hr

Question 3: What Does the Heat Rate Mean in a Power Plant?

Answer:

In the context of thermal power plants, the term heat rate might be employed. These power plants, as we all know, convert thermal energy held in fuel (such as gas, coal, oil, and so on) into electricity (with the unit – kWh).

The heat rate is the quantity of heat required to produce 1 kWh (also known as Unit) of electricity. Its unit is kCal/kWh (but in certain cases it is kJ/kWh). The heat rates are expressed in British thermal units (Btu) per net kWh generated by the US Energy Information Administration (EIA) (net heat rate formula).

Question 4: Calculate the Heat rate if steam enters at 335 degree F and leaves at 236 degree F at atmospheric pressure. 550 Ib of steam travels through the every hour in normal operation.

Answer:

Given : Ws = 550 Ib, c = 0.48, Tin = 335 degree F, Tout = 236 degree F

Find : Rh

Solution :

ΔT = Tin – Tout

∴ ΔT = 335 – 236

∴ ΔT = 99oF

We have,

Rh = Ws × c × ΔT

∴ Rh = 550 × 0.48 × 99

Rh = 26136 btu/hr

Question 5: How can you tell the difference between the Turbine Heat Rate and the Gross Turbine Heat Rate?

Answer:

Gross Heat Rate is defined as an expression of the total energy produced by the plant per one unit of mass of fuel in the calculation of any power plant’s output. This is before all parasitic loads, such as the effect of calculating Net Heat Rate or the power that really goes out the door per unit of mass of fuel, are factored in.

The gross heat rate takes into account the efficiency losses and power generated during the full power generating cycle, which includes the feed water circulation system, boiler, condensate recovery system, fuel delivery, and water treatment.

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