232 posts

### WHR Boiler Efficiency calculation

Dear All I am getting eff. more than 100 % ? Why? Pl. correct me
Steam Temp. |
330 | 330 | 330 | 330 |

Steam Pressure | 18 | 18 | 18 | 18 |

Steam Flow | 10.1 | 12.94 | 9.1 | 20.6 |

Feed water Temp. | 160 | 160 | 160 | 160 |

Feed water press. | 25 to 26 kg/cm² | |||

Enthalpy of Steam (kcal/kg) | 741.0191 | 741.0191 | 741.019 | 741.0191 |

Enthalpy of Feed water (kcal/kg) | 161 | 161 | 161 | 161 |

Flue gas flow( M³/hr) | 246520.1 | 330205.1282 | 259407 | 584249.1 |

flue gas density | 0.52 | 0.52 | 0.54 | 0.52 |

Sp. Heat of flue gas | 0.24 | 0.24 | 0.24 | 0.24 |

Flue gas inlet temp. °C | 400 | 385 | 365 | 365 |

Flue gas outlet temp. °C | 240 | 241 | 240 | 240 |

Total heat input in boiler(kcal/hr) | 4922514 | 5934182 | 4202387 | 9114286 |

heat out from boiler | 5858193 | 7505447.154 | 5278174 | 11948393 |

boiler effiency | 119 | 126 | 126 | 131 |

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16 posts

### re WHR Boiler Efficiency calculation

Hello,

I don't know how exactly did you measure flows; because this is the major source of error (you can see flow specifications, on how to measure flow exactly), howver attached file is for assesing energy performance of boiler. (sorry it isn't attaching)

I hope it'll help.

138 posts

### re WHR Boiler Efficiency calculation

xxxx,

You need to comment your calculations in more details.

By just doing this you might well discover by yourself many possible source of errors.

First of all, the units are missing for 9 lines of the table.

Second, your table does not show clearly how you did the calcualtions.

You could explain one column in full detail, this would be easier to check.

(a drawing would be even clearer)

As Ex-FlSmidth-Designer said, the errors on flow evaluation could in itself create big errors.

There are still many other possible source of errors:

- steam flow: what are the units? t/h maybe?

- flue gas flow: is it in actual m³ or in "normal" m³?

- flue gas flow: is it measured at the input or at the output of the boiler?

- flue gas density: is it evaluated at 400°C or at 240°C(inlet or outlet)?

- flue gas density: for a calculation I did, it was higher

- flue gas density: do you take gas composition properly into account?

- flue gas specific heat: units ???

- flue gas specific heat: how did you evaluate it?

- flue gas specific heat: did you take the composition into account?

- flue gas specific heat: is it the average heat value between 400°C and 240°C

or is this the specific heat value at 400°C ?

- flue gas specific heat: why is it exactly the same for the three scenarios?

- flue gas specific heat: for a calculation I did, it was 0.28 kcal/kg/°C

- flue gas specific heat: do you take water vapor into account?

- flue gas specific heat: ...

- heat input: I see how you made the calculation, should be ok

however "heat input" is a bad name,

you might call it "heat exchanged" (flue gas side or steam side)

If you explain your calculations in more detail, there is really a good chance that you find some approximations and some source of errors and that you improve your balance. You could also add an uncertainty for each data and do some error bar calculation!.

Don't hesitate to put all you data and calculations in an excel worksheet and to attach it to your post. If you do so, do not forget to include flue gas composition.

232 posts