agorwadia
Industrial
- Aug 21, 2024
- 1
Hello,
We have recently re-built our old heat treatment furnace (neutral salt type). It has a steel crucible and LPG is used to provide necessary heat to the pot.
Design:
The design for such small crucible type furnaces are quite simple in general - round refractory construction of the furnace using 70% high alumina refractory. The crucible is placed at the center of the furnace. These typically fuel fired furnaces so a flame is tangentially fired and the flames exit into a pre-heating chamber and then goes into the flue thus recuperating some of the exhaust heat from the primary furnace.
The issue I have is furnace over-pressure. Usually with such small gas fired furnaces the burner is placed using a mounting flange and its quite air-tight so that excess air does not leak into the combustion chamber. Firing rate in our older furnace was around 7-7.5kg of LPG per hour.
The burner blast tube is 4" and the exit port is 4" x 3" (this port goes into the pre-heating chamber before going into the chimney). But with crucible tightly placed the flame back fires from the burner tile. But by lifting the crucible ever so slightly to allow a small crack of about 1/4" on one of its sides the blow-back goes away and the roar of the furnace is as expected. This experiment was done with pre-heating chamber open to ensure there isn't a blockage of draft there.
It seems that the sizing of exit port of 4" x 3" is not sufficient to ensure sufficient draft and such as combustion chamber is being pressurized. In small industries it is quite common for oil/diesel furnaces to have their crucible to be placed with a small gap to ensure sufficient draft but its not ideal in our case as exit-gases/flames can cause small but continuous damages to furnace metal body at the place its being released.
To me if it seems like making the exit port bigger would be the answer. I was wondering if there is any reference books for such calculations or it this would be purely based on trial-error bases.
Thanks.
AG
We have recently re-built our old heat treatment furnace (neutral salt type). It has a steel crucible and LPG is used to provide necessary heat to the pot.
Design:
The design for such small crucible type furnaces are quite simple in general - round refractory construction of the furnace using 70% high alumina refractory. The crucible is placed at the center of the furnace. These typically fuel fired furnaces so a flame is tangentially fired and the flames exit into a pre-heating chamber and then goes into the flue thus recuperating some of the exhaust heat from the primary furnace.
The issue I have is furnace over-pressure. Usually with such small gas fired furnaces the burner is placed using a mounting flange and its quite air-tight so that excess air does not leak into the combustion chamber. Firing rate in our older furnace was around 7-7.5kg of LPG per hour.
The burner blast tube is 4" and the exit port is 4" x 3" (this port goes into the pre-heating chamber before going into the chimney). But with crucible tightly placed the flame back fires from the burner tile. But by lifting the crucible ever so slightly to allow a small crack of about 1/4" on one of its sides the blow-back goes away and the roar of the furnace is as expected. This experiment was done with pre-heating chamber open to ensure there isn't a blockage of draft there.
It seems that the sizing of exit port of 4" x 3" is not sufficient to ensure sufficient draft and such as combustion chamber is being pressurized. In small industries it is quite common for oil/diesel furnaces to have their crucible to be placed with a small gap to ensure sufficient draft but its not ideal in our case as exit-gases/flames can cause small but continuous damages to furnace metal body at the place its being released.
To me if it seems like making the exit port bigger would be the answer. I was wondering if there is any reference books for such calculations or it this would be purely based on trial-error bases.
Thanks.
AG
