Natural gas that contains methane, ethane, and propane is to be burned with humid air. The adiabatic flame temperature is to be calculated from specified values of the following quantities:
Without doing any calculations, predict the direction of change (increase, decrease, no change) in the adiabatic flame temperature you would expect for an increase in (i)
- For a basis of 1 g-mole of natural gas, calculate the gram-moles of each molecular species in the feed and product streams, assuming complete combustion and negligible CO formation. The answer should be expressed in terms of the variables given above.
- Given below are expressions for the specific enthalpies of the feed and product components, relative to their elements at 25°C.
Substance (i) | a |
|
|
|
|
(1) CH4 | -75.72 | 3.431 | 2.734 | 0.122 | -2.75 |
(2) C2H6 | -85.95 | 4.937 | 6.96 | -1.939 | 1.82 |
(3) C3Hs | -105.6 | 6.803 | 11.30 | -4.37 | 7.928 |
(4) N2 | -0.7276 | 2.900 | 0.110 | 0.191 | -0.7178 |
(5) O2 | -0.7311 | 2.910 | 0.579 | -0.2025 | 0.3278 |
(6) H2O(v) | -242.7 | 3.346 | 0.344 | 0.2535 | -0.8982 |
(7) CO2 | -394.4 | 3.611 | 2.117 | -0.9623 | 1.866 |
Derive the given expression for the specific enthalpy of methane from the heat capacity data in Table B.2. Then show that A// for the reactor is given by an expression of the form.
where T is the product temperature, and
Write a spreadsheet program to take as input values of
- , and to solve the energy balance equation
Variable | Run 1 | Run 2 | Run 3 | Run 4 | Run 5 | Run 6 |
|
0.75 | 0.86 | 0.75 | 0.75 | 0.75 | 0.75 |
|
0.04 | 0.04 | 0.04 | 0.04 | 0.04 | 0.04 |
|
40 | 40 | 150 | 40 | 40 | 40 |
|
150 | 150 | 150 | 250 | 150 | 150 |
|
25% | 25% | 25% | 25% | 100% | 25% |
|
0.0306 | 0.0306 | 0.0306 | 0.0306 | 0.0306 | 0.10 |
Suggestion: Near the top of the spreadsheet, enter the values of a, b, c, d, and e for each species. Starting several rows below the last of these entries, list in Column A labels for the input variables and all calculated variables (component molar flow rates, specific enthalpies,
Tad = 1743.1°C.)
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