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Question 9.6.3: Ignition Temperature and Flammability Limits Propane gas and......

Ignition Temperature and Flammability Limits
Propane gas and air are to be mixed and fed to a combustion reactor. The combustion is to be initiated with a gas torch. Determine the minimum and maximum percentages of propane in the feed to the reactor and the minimum required temperature of the torch flame.

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From Table 9.6-2,

Minimum mole% C_{3}H_{8} for combustion = 2.2%
Maximum mole% C_{3}H_{8} for combustion = 9.5%

The torch flame temperature must be at least as high as the autoignition temperature of a propane–air mixture, which from Table 9.6-2 is  \boxed{493°C } .

TABLE 9.6-2   Flammability Limits, Flash Points, and Autoignition Temperatures for Selected Species. Excerpted from Crowl and Louvar.¹¹
Flammability Limits Temperatures (°C)
Species Lower Upper Flash Point Autoignition
Paraffins
Methane 5.3 15.0 -222.5 632
Ethane 3.0 12.5 -130.0 472
Propane 2.2 9.5 -104.4 493
Butane 1.9 8.5 – 60.0 408
Olefins
Ethylene 3.1 32.0 — 490
Propylene 2.4 10.3 -107.8 458
Aromatics
Benzene 1.4 7.1 -11.1 740
Toluene 1.4 6.7 4.4 810
Alcohols
Methanol 7.3 36.0 12.2 574
Ethanol 4.3 19.0 12.8 5558
Ketones
Acetone 3.0 13.0 -17.8 700
Methyl Ethyl Ketone 1.8 10.0 -4.4 514

¹¹D. A. Crowl and J. F. Louvar, Chemical Process Safety: Fundamentals with Applications, 2nd Edition, Prentice Hall, Upper Saddle River, 2002.

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