Previous columns in this series have examined a number of combustion topics, such as stoichiometry, heat balances and thermal efficiency. The Excel workbook that accompanied each column was devoted to that topic, but it used concepts and procedures developed in previous columns. As a result, readers interested in using all of the concepts had to use more than one workbook or had to move calculations from different workbooks to one workbook. This column describes a workbook that does it all – downloadable Excel workbook BurnerCalc.xlsx, which can be found at www.industrialheating.com/burnercalc. It contains all the calculational tools of previous Combustion Concepts workbooks. Although it’s loaded with features, don’t throw out those earlier workbooks! They have important details you’ll need if you want to modify BurnerCalc’s features or add your own.

BurnerCalc Features

BurnerCalc.xlsx calculates a material and heat balance for fuel-gas combustion with excess air. Four worksheets are involved: DataEntry, Calculations, Results and StoredResults. Worksheet DataEntry has 11 cells for entering the fuel-gas composition, temperature and pressure, and 11 more for specifying the oxidant and offgas properties. Figure 1 shows the DataEntry display for the oxidant and offgas. Any change in a blue-shaded cell results in recalculation of all workbook result values.

    The Calculations worksheet has data for making material and heat balances, as obtained from the FREED database.^[1,2] The procedures outlined in earlier workbooks in this series^[3,4] were used for calculating heat-content equations and heats of reaction for each fuel-gas constituent. Two forms of theoretical offgas temperature are calculated: first, the adiabatic flame temperature (AFT); and second, the combustion flame temperature.^[5] Both calculations require the use of the quadratic formula because the heat-content equations have a quadratic term.

    The results are presented as tables organized by stream and property. For example, Fig. 2 displays the heat-balance summary for the combustion of a typical natural gas using 113.4% stoichiometric air, enriched to 24.6% O₂. The offgas composition is presented in volume and mass units, actual and dried.

    In BurnerCalc, some previous workbook functions have become independent, while others have become dependent. For example, the % stoichiometric oxygen is now a dependent variable, while the flow of air and industrial oxygen are independent variables. You can either use Goal Seek or just change the formulae to the earlier format.

Repetitive Calculations

BurnerCalc is restricted to one-off calculations. This makes it difficult to observe the effect of a series of variable changes. Two new Excel add-ins are introduced in the StoredResults worksheet of BurnerCalc.xlsx: Multicalc for forward-based calculations and Multigoal for what-if calculations.^[6] These allow the user to select a range of values for a primary independent variable from worksheet DataEntry and dependent variables from the Calculations or Results worksheet. BurnerCalc repeats the calculations for every primary variable and prepares a table and scatter plot of the results. Excel’s Trendline tool can fit an equation to the results. IH

References

1. Thermart database program FREED, http://www.thermart.net/

2. Arthur Morris, “Calculating the Heat of Combustion of Natural Gas”, Industrial Heating, September, 2012.

3. Arthur Morris, “Making a Material Balance”, Industrial Heating, November 2012.

4. Arthur Morris, “Making a Heat Balance”, Industrial Heating, December, 2012.

5. Arthur Morris, “Adiabatic Flame Temperature”, Industrial Heating, May, 2013.

6. Single and multivariable solving programs--Multicalc and Multigoal, http://www.thermart.net