Turbine Heat Rate Calculator
How to Calculate Turbine Heat Rate
Turbine Heat Rate is a critical performance metric in the power generation industry. It represents the thermal efficiency of a power plant by quantifying the amount of heat energy required to generate one kilowatt-hour (kWh) of electricity. Unlike other efficiency metrics where a higher number is better, a lower heat rate indicates a more efficient turbine.
The Heat Rate Formula
To calculate the heat rate, you need to determine the total energy input provided by the fuel and divide it by the electrical energy output. The standard formula used in the United States (Imperial units) is:
Heat Rate (Btu/kWh) = Total Heat Input (Btu/hr) / Power Output (kW)
Where:
- Total Heat Input: Calculated by multiplying the Fuel Mass Flow Rate (lb/hr) by the Fuel Heating Value (Btu/lb).
- Power Output: Usually measured in Megawatts (MW) and must be converted to Kilowatts (kW) for the formula (1 MW = 1,000 kW).
Step-by-Step Calculation Example
Let's calculate the heat rate for a typical gas turbine with the following operational data:
| Parameter | Value |
|---|---|
| Gross Power Output | 100 MW |
| Fuel Flow Rate | 45,000 lb/hr |
| Fuel Heating Value (HHV) | 21,000 Btu/lb |
Step 1: Calculate Total Heat Input
45,000 lb/hr × 21,000 Btu/lb = 945,000,000 Btu/hr
Step 2: Convert Power to kW
100 MW × 1,000 = 100,000 kW
Step 3: Calculate Heat Rate
945,000,000 Btu/hr / 100,000 kW = 9,450 Btu/kWh
Converting Heat Rate to Thermal Efficiency
Engineers often convert Heat Rate into a percentage representing Thermal Efficiency. Since 1 kWh of electricity is thermally equivalent to 3,412.14 Btu, the efficiency can be calculated as:
Thermal Efficiency (%) = 3,412 / Heat Rate × 100
Using our example above:
Efficiency = 3,412 / 9,450 × 100 = 36.1%
Key Factors Affecting Heat Rate
Several variables can impact the heat rate of a turbine:
- Load Factor: Turbines generally operate most efficiently (lowest heat rate) at full load. Partial loads usually degrade efficiency.
- Ambient Temperature: For gas turbines, higher ambient air temperatures reduce air density, thereby reducing mass flow and increasing heat rate (lowering efficiency).
- Fuel Quality: Variations in the heating value of the fuel (natural gas, diesel, coal) directly alter the heat input calculation.
- Component Degradation: Compressor fouling or blade erosion over time will increase the heat rate.