138 posts
TimePosted 14/06/2012 06:54:40
lalbatros says

re WHR Boiler Efficiency calculation

Let's assume this flue gas composition in %vol:

{O2 = 5.17%, N2 = 64.18%, CO2 = 28.75%, H2O = 1.85%, SO2 = 0.05%}

For this composition, I get the average specific heat between 240°C and 400°C:

Cp(400°C,240°C) = 0.265 kJ/kg/°C

Compared to your assumption that Cp=0.24, this is a factor  0.265/0.24 = 110%  higher.

Similarly, I don't understand what you mean by "flows are correct".
If these are measurements, there must be uncertainty, it can easily be 5%.
If these are not measurement, then how are they calculated, is this based on a model, is this model assuling Cp=0.24, ...  ?

The errors you mention are not surprisingly high.
Your excel file contains 15 efficiency calculations.
I don't know their exact meaning and if their can be all treated in the same way.
Nevertheless, the average of these efficiencies is 99.3% .
Their standard deviation is 14.1% .
There is obviously a random source of error, while the efficiency is quite close to 100% in the average. The most likely source of error is the mass flow measurement. Performing more precise calculations for specific hat and density, taking gas composition into account, can only help.



Know the answer to this question? Join the community and register for a free guest account to post a reply.