Temperature extinction

Variations of extinction stretch rate and extinction temperature of methane/air mixtures with equivalence ratio for the five different cases as in Figure 6.3.4. 

Let us reconsider the critical flame temperature criterion for extinction. Williams [25], in a review of flame extinction, reports the theoretical adiabatic flame temperatures for different fuels in counter-flow diffusion flame experiments. These temperatures decreased with the strain rate (ua0/x), and ranged from 1700 to 2300 K. However, experimental measured temperatures in the literature tended to be much lower (e.g. Williams [25] reports 1650 K for methane, 1880 K for iso-octane and 1500 K for methylmethracrylate and heptane). He concludes that 1500 50 K can represent an approximate extinction temperature for many carbon-hydrogen-oxygen fuels burning in oxygen-nitrogen mixtures without chemical inhibitors . 

C) the mass fraction of methanol was set to the desired amount by switching a three-way tap. At the same time, the outlet temperature of the preheater was decreased gradually. At the moment the flame was extinguished, the characteristic temperatures of the last operating point before extinction were recorded. This procedure was repeated once or twice for every fuel mass fraction in order to estimate the accuracy of the results. Different extinction temperatures for one fuel mass fraction were mostly in the range of 10°C. A series of extinction points (WFuei.i ranging from 4% to 25%) resulted in a so-called extinction line. 

The extinction temperatures depend strongly on the fuel quality. Fig. 2 shows that they vary between 550°C (or even higher) related to 4% mass fraction of CH3OH and values equal to or lower than 100°C when 25% methanol was used. The lines for different locations of the temperature measurements intersect. This intersection is due the heat transfer that takes place in the narrow area around the core tube tip. This fact will be examined further. 

Figure 2 Extinction line extinction temperature as a function of fuel mass fraction. Results of experimental work with a reaction vessel and a burner configuration shown in fig. 1...

We have performed similar experiments using other compounds such as chlorobenzene, acetonitrile, and thiophene in simulated VOC streams and see similar high conversions (>99%) and no apparent catalyst deactivation due to Cl, S, or N. The most important variable in these experiments is temperature. High conversions are realized for all cases when the catalyst is ignited, although sufficient fuel must be supplied to the catalyst to maintain the temperature above the extinction temperature. 

To what inlet temperature must the fluid be preheated for the reactor to operate at a high conversion What are the corresponding temperature and conversion of the fluid in the CSTR at this inlet temperature Suppose that the fluid is now heated 5°C above the temperature in pari tc) and then cooled 20 C. where it remains. What will be the conversion What is the inlet extinction temperature for this reaction system (Ans..- Ta = 87 C.)... 

What are the steady-state concentrations and temperatures [One answer T = 628.645 R, C = 0.06843 Ib mol/ft j Which ones are stable What is the extinction temperature ... 

This plot shows the way to find the ignition and extinction temperatures. The ignition temperature is 358 K. The extinction temperature is 208K. 

From this we can see that the extinction temperature is 23ST and the ignition temperature is 562T. Note that these are the same values as above. 

P9-16. The point of this problem is that what we learned in chapter about the different multiple steady states being stable is not necessarily true. One will find in this problem that the extinction temperature is not exceeded, yet we still fall from the upper steady states to the lower steady states. This problem also allows the student to explore the parameter space,... 

Between ignition and extinction, temperature oscillations were observed in the active portion of the catalyst bed. The oscillating patterns were complex and multiform, depending to a large extent on the catalyst composition and reaction conditions. When, starting from the ignited state, external heating was lowered, the amplitude of oscillations increased and the period decreased, until extinction took place. 

AH X k X [F] allows for all heat losses which show a non-linear dependence on the temperature (e.g. radiant heat loss, heat loss due to the combustion products that escaped from the flame zone) and all potential endothermicities introduced to the flame, e.g. via flame retardants. This endothermic term sets the steady temperature of the flame and creates the critical condition for the flame extinction below extinction temperature is the average rate constant of this... 

The theoretical hysteresis curve is shown in Figure 2 for three different inlet CO mole fractions. The correct qualitative trends are exhlbted the hysteresis is wider (greater difference between the ignition and extinction temperatures) for larger concentrations of carbon monoxide. Other calculations (7) indicate the Ingnltlon and extinction temperatures depend on flow rate, too, reflecting the experimental observations the hysteresis is wider for the lower flow rates. 

Obtain the extinction temperature, i.e., the Tui that results in extinction of the reaction. Also calculate the Tin that gives a conversion of 0.5. Expand the Arrhenius exponential around T(Z) to rewrite it as 4 exp(67). 

If a reactor were operating at and we began to cool the entering temperature down from To,, the steady-state reactor temperature L, would eventually be reached, corresponding to an entering temperature Any slight decrease below would drop the steady-state reactor temperature to the lower steady state value Consequently, Tqj is called the extinction temperature. 

---