[Gasification] Steam injected into flame

[Jeff Davis]

On Tuesday 25 July 2006 07:20 pm, andy schofield wrote:
>   Then consider the thermal inertia of a few grams of burning low-btu gas
> at no more than 1200C.

That reminded me of another e-mail, some time ago. I am NOT disagreeing, I 
just find this interesting! I pasted the e-mail below:




*******************************


Dear Oscar and All:

Excellent question and I'm your man. 

It is difficult to measure any true flame temperature.  The density of 
the gas is ~ 1/10,000 of the density of any solid you can put in there, 
so the instrument perturbs the true temperature.  Only calculations or 
spectroscopic (sodium line reversal technique etc.) can come close. 

The North American Combustion Handbook, Vol 1 is an incredible source of 
real information on real flames.  (The author, Richard Reed, is probably 
my nth cousin where 3,n,10).  Dodge is ~ correct that the stoiciometric 
flame temperatures for all air flames are ~ 2000 C, but I think he is 
200 C too high in his 2000-2400.  The handbook lists 2319 Cfor the 
acetylene air flame and that's the highest.  It lists 1735 C for coke 
oen gas, the lowest.  CO is 2100 C and hydrogen is 2045. 

If you put a wire in a 2000C Bunsen flame it may reach 800-1100 C.  The 
wire loses heat by radiation which increases as T^4.  It gains from 
flame convection proportional to flame velocity ^1 power. 

So beware thermocouples in flames as a "measure" of temperature.  It is 
a measure of heat transfer. 

On the other hand, there are "suction" thermocouples (surrounded by 
radiation shields and drawing gas at high velocity over the TC that give 
a much closer estimate.  However, even Pt-PtRh TCs don't go up to the 
required 2000C. 

On the other hand, the calculation of flame temperatures is relatively 
simple if you have the Janaf tables of gas enthalpy. 

None of this applies to oxygen flames which are ~3200C and involve 
calculation of dissociation of the H2, H2O, CO and CO2. 

I hope this makes us all wiser and more careful in our statements about 
"flame temperatures". 

Onward in science...

TOM REED       BEF

Oscar Jimenez wrote:

>Dear All.
>
>I am assessing the possibility of using producer gas in a ceramic plant
>which formerly used electricity as the source of heat energy for
>producing ceramic stuff. 
>One main issue in our analysis is to know the producer gas flame
>temperature for carrying out the same duty as previously, when using
>electricity. 
>I have been looking for this specific information but found nothing.
>Lately I started looking for ways for estimating such temperature. So I
>opened some text books on thermodynamics (Samuel Glasstone '
>Thermodynamics for Chemist' ) and found an equation for estimating gas
>flame temperature. It seemed to me rather complex and lengthy to be
>involved in such a procedure.
>On the other hand (Dodge F. Barret ' Chemical Engineering Thermodynamics
>' ) says: 
>........the theoretical flame temperature for burning gas in air with no
>excess do not vary much with different gases in spite of very great
>differences in heat of combustion.......Most calculated flame
>temperature for complete combustion in air with no excess and no
>preheating of air or gas lie between 2000 and 2400 degree centigrade.
>Now my question is: ...may I take such figures, given by Dodge F. Barret
>in his text book, as a good rule-of-thumb to be used in my ceramic plant
>business...??????? Comments and advice will be highly
>appreciated....!!!!!!!
>
>Thanking all of you in advance.
>
>Kindest regards.
>
>Oscar.

-- 
Jeff Davis
Somewhere 20 miles south of Lake Erie, USA
http://www.velocity.net/~jeff0124