1.    Background

This Combustion File (CF) presents tools with which the user may calculate [GLOSS]lower calorific value[/GLOSS]s of solid [GLOSS]fuel[/GLOSS]s. This first version contains two calculation tools through which the user may:

o         Calculate the Lower Calorific Value – LCV – of a solid fuel based on measured data of [GLOSS]Higher calorific value[/GLOSS] based on CF21.

o         Calculate the LCV of a solid fuel based on measured elemental analysis data and moisture content, based on CF225.

The calculation tools may be acquired by the user by downloading an [GLOSS]Excel Workbook[/GLOSS] containing the calculation tools, each embedded in a protected worksheet.

Users of this combustion file should note:

o         This workbook can be downloaded by the reader and saved to a local hard disk.

o         To achieve this click on the “[GLOSS]xls[/GLOSS]” icon on the left hand side of the banner above. The file will be retrieved from the server, and with up-to-date versions of the browser, will appear in a separate window, from which it may be saved to the user’s hard disk.

o         With the exception of the data entry cells for the calculation tools, the data in these worksheets are protected – thus the reader cannot change the worksheet without knowledge of the protection password.

o         However the reader can copy and paste the data into his/her own project workbook as required – at this point the accuracy and integrity of the data becomes the responsibility of the reader.

o         To overview the data available – see text and tables below.

All credits and sources, and where necessary, instructions/advice for data use, are presented in this html file. These are not necessarily reproduced in the Excel Work Sheets.

2.    Calculation of LCV from measured HCV data

This calculation is based on CF21 – What is the relationship between the higher and lower calorific value of a fuel?

The Higher Calorific Value is conveniently measurable. But it includes the latent heat of condensation of the moisture contained in the fuel as fired as well as the that of the water produced for hydrogen contained in the fuel during combustion.

The Lower Calorific Value does not contain these and in most cases represents the reality for available heat for boilers and industrial furnaces.

The relationship between the higher and lower calorific values of a fuel is expressed by:

Q_L = Q_H – 2.454 (W + 9H)            (1)

Where:

• Q_L = Lower Calorific Value (MJ/kg)
• Q_H = Higher Calorific Value (MJ/kg)
• W = wt% moisture in fuel/100
• H = wt% hydrogen in fuel/100

3.    Calculation of LCV from proximate and ultimate analysis data

This calculation is based on CF225 – How do I calculate the Lower Calorific Value of solid fuels?

The calculation is based on an empirical equation, developed by Boie [2]:

QL = 34.8c + 93.9h + 6.3n + 10.5s– 10.8o –2.5w (in MJ / kg fuel)        (2)

where c, h, n, s, o are the mass fractions of carbon, hydrogen, nitrogen, sulphur and oxygen, respectively taken from an [GLOSS]ultimate analysis[/GLOSS] of the fuel, adjusted for the ash (mineral matter) (a) and moisture concentrations (w), as fired.

Note that, inorganic materials such as ash are actually omitted from the equation because they do not significantly produce or consume heat. However the as-fired mass fraction of ash (mineral matter) is required to prepare data for the calculation. Some energy is required to heat these materials from ambient [GLOSS]temperature[/GLOSS] to the operating temperature, but this is considered of minor importance.

For the example [GLOSS]coal[/GLOSS] specified in CF225, the Lower Calorific Value is calculated according to Table 1 below:

Table 1: Example calculation of the Lower Calorific Value of a coal

Acknowledgements

The author would like to acknowledge the original authors of the CF from which the present CF is derived.

Sources

[1] Pratt AD, “Principles of Combustion in the Steam Boiler Furnace”, Babcock & Wilcox Ltd, London, 1965

[2] Schramek, Taschenbuch für Heizung und Klimatechnik, Munich, 1999