Measuring the HEAT...

Iron Smelting Furnace Temperatures
Short Shaft over Slag Pit

October 9, 2011 / DARC Smelt Team, Neil Peterson recording

On our last smelt, we set up to record furnace temperatures over the duration of the experiment.


The furnace was our standard short shaft type, roughly 25 cm interior diameter, 70 cm total height.
Walls were clay and straw cobb, about 10 cm thickness.
Fuel was hardwood charcoal (mainly oak) graded to .5 through 2.5 cm diameters.
Air volume via the tuyere (set at 20 cm above base) was roughly 800 litres per minute.

Holes were drilled through the furnace walls at roughly every 10 cm, starting at 10 cm above the interior base.
Measurements were taken using an industrial quality digital pyrometer (HH12B from Omega equipped with standard bare metal type K thermocouples).
The probes were inserted roughly 5 cm beyond the interior surface of the furnace wall.
Measurements were taken roughly every hour over the course of the smelt event.

Because the probes did not reach into the central core of the furnace, there is every possibility that the central furnace temperatures were even higher than what was recorded.
Our thermocoples failed (melted!) at roughly 1350 C. On several recordings, this temperature was reached.

Image : Neil takes readings, early in the smelt

Time	Elapsed	base	tuyere	plus 10	plus 20	plus 30	plus 40	top
		10 cm	20 cm	30 cm	40 cm	50 cm	60 cm	70 cm
12:06	:06		653	890	749	579	343
13:05	1:05		1042	1335	1300	1145	1002	610
13:50	1:50	328	1051	plus 1350	1195	1189	1014	660
15:12	3:12	995	1226	1268	1293	1128	1011	608
16:32	4:32			1124	1265 *	909	700	719

Note : It has been suggested by some theoretical researchers that temperatures above 1200 C are impossible to achieve inside a charcoal fired furnace...