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U.S. Department of Energy Energy Efficiency and Renewable Energy
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Determines the amount of fuel energy required to produce steam with specified properties at a given flow rate using general boiler operational characteristics.


Deaerator Pressure* psig
Combustion Efficiency* %
Blowdown Rate* %

Steam

Pressure* psig
* °C btu/lbm kJ/kg/K
Steam Mass Flow * klb/hr
* Required [reset]
Allowed Range / Limits
Minimum
Maximum
**Example: Super-heated Steam

Examples: Mouse Over
Saturated Steam Super-heated Steam

Calculation Details and Assumptions below

Steam

 Mass Flow88.3 klb/hr
Pressure8.2 psig Sp. Enthalpy1,613.6 btu/lbm
Temperature621.7 °C Sp. Entropy8.943 kJ/kg/K
PhaseGas Energy Flow150,321
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Boiler

Boiler

Blowdown Rate5.0 %
Boiler Energy133,587
Combustion Efficiency70.9 %
Fuel Energy188,416

Blowdown

 Mass Flow4.6 klb/hr
Pressure8.2 psig Sp. Enthalpy203.6 btu/lbm
Temperature112.9 °C Sp. Entropy1.450 kJ/kg/K
Saturated0.00 Energy Flow998

Feedwater

 Mass Flow92.9 klb/hr
Pressure0.2 psig Sp. Enthalpy180.8 btu/lbm
Temperature100.4 °C Sp. Entropy1.311 kJ/kg/K
Saturated0.00 Energy Flow17,732


Calculation Details

Step 1: Determine Properties of Steam Produced

Using the Steam Property Calculator, properties are determined using Steam Pressure and the selected second parameter (Temperature, Specific Enthalpy, Specific Entropy, or Quality). The Specific Enthalpy is then multiplied by the Mass Flow to get the Energy Flow:
  • Steam Energy Flow = Specific Enthalpy * Mass Flow
    [ Steam Energy Flow = 150,321 = 1,613.6 btu/lbm * 88.3 klb/hr ]

Step 2: Determine Feedwater Properties and Mass Flow

The feedwater flow rate can be calculated from steam mass flow and blowdown rate:
  1. Blowdown Mass Flow = Feedwater Mass Flow * Blowdown Rate
  2. Steam Mass Flow = Feedwater Mass Flow - Blowdown Mass Flow
  3. Steam Mass Flow = Feedwater Mass Flow - Feedwater Mass Flow * Blowdown Rate
  4. Feedwater Mass Flow = Steam Mass Flow / [ 1 - Blowdown Rate ]
    [ Feedwater Mass Flow = 92.9 klb/hr = 88.3 klb/hr / ( 1 - 0.05 ) ]
Using the Steam Property Calculator, properties are determined using Deaerator Pressure and Quality = 0 (Saturated Liquid). The Specific Enthalpy is then multiplied by the Mass Flow to get the Energy Flow:
  • Feedwater Energy Flow = Specific Enthalpy * Mass Flow
    [ Feedwater Energy Flow = 17,732 = 180.8 btu/lbm * 92.9 klb/hr ]

Step 3: Determine Blowdown Properties and Mass Flow

Using the calculated feedwater mass flow and blowdown rate:
  • Blowdown Mass Flow = Feedwater Mass Flow * Blowdown Rate
    [ Blowdown Mass Flow = 4.6 klb/hr = 92.9 klb/hr * 0.05 ]
Using the Steam Property Calculator, properties are determined using Steam Pressure and Quality = 0 (Saturated Liquid). The Specific Enthalpy is then multiplied by the Mass Flow to get the Energy Flow:
  • Blowdown Energy Flow = Specific Enthalpy * Mass Flow
    [ Blowdown Energy Flow = 998 = 203.6 btu/lbm * 4.6 klb/hr ]

Step 4: Determine Boiler Energy

  • Boiler Energy = Steam Energy Flow + Blowdown Energy Flow - Feedwater Energy Flow
    [ Boiler Energy (Flow) = 133,587 = 150,321 + 998 - 17,732 ]

Step 5: Determine Fuel Energy

  • Fuel Energy = Boiler Energy / Combustion Efficiency
    [ Fuel Energy = 188,416 = 133,587 / 0.709 ]

Assumptions

  • Deaerator provides feedwater near the boiling temperature for the deaerator's set operating pressure. (Saturated Liquid)
  • Steam, Boiler, and Blowdown Pressure are the same.
  • Combustion Efficiency is the % of fuel energy that is directly added to the feedwater and not otherwise lost or used.
  • Blowdown Rate is the % of incoming feedwater mass flow rate that leaves the boiler as a saturated liquid at boiler pressure.
  • Does not include any evaluation of any complex boiler configurations or fluctuations in operation.
  • Energy from motors (pumps, fans, etc.) are not considered.
  • Boiler and fuel types are not considered.