Processing Furnace Gas Controls
Had a thought and I figured I'd go ahead and toss it out here.
What we have is a gas fired processing furnace with a couple of big tubes blowing flames into an insulated box to heat the ends of tube prior to forging. (That's the simplified version of it and gas control design isn't my thing.) There's a big blower that supplies those tubes or burner nozzles with the appropriate amount of air for the correct mix or ratio of air to gas. We can regulate that air to fuel ratio via a by-pass valve.
We have utilized this burner arrangement for about forty-some years now and it works well enough I suppose.
Problem I'm seeing is this. The blower runs constantly and that in itself isn't an issue at all... but the thing is blowing into the box we're trying to heat... always... the entire time. When the thermostat setting has been met the fuel shuts off but the blower keeps blowing cold air into the box. :surprise2:
This never really dawned on me until just the other day. I mean when you stand near it it's hot like it supposed to be right? When I was peeking into the box to check out the condition of the insulation is when it occurred to me that there was still air blowing out the nozzles after the burn.
This box has a long thin opening in it about 8" high and it runs most of the length of the box. The burner nozzles poke into the box through a small opening at one end of the box. There's a hood above the big long opening and we built a sort of heat exchanger thing above it to utilize some of the scrap heat in another part of the building in the winter. Back to the opening... That long opening is our access to introduce our parts to the heat. When the operator pulls a part out of the one end of that opening to forge it, he sticks a cold stick in the other end. Idea is that as the parts slowly make their way to the operator through this box they get hot and are at correct forging temperature by the time they reach him. Works well....
What I want to do is divert the air that blows in the box when there isn't flame. Seems to me we're blowing the hot out of the box when there isn't flame. This is an insulated box... not refractory cement or brick, so the burner cycles very often depending on set temperature. I expect we could cut our gas consumption maybe as much as in half if we could divert that air when the signal to cut gas comes in?
So my understanding is the gas valve gets a signal from the igniter thermocouple saying that the pilot is lit and O.K.'s the opening of the big burner valve when the box thermocouple asks for more heat. I think the spring in the gas valve needs to see pressure to open... and needs to see pilot signal... and needs process thermocouple call for heat to open. Maybe some other gadgets inline with that also? Doesn't need to see airflow does it? Like a household furnace has to be evacuated and see a light draw before they'll light?
I'm envisioning using the signal from the box thermocouple that says "your set temp has been met" to switch a butterfly valve to divert the burner air. And when the box thermocouple says heat it up... it flips it back to blow into the box for flame air. I seem to recall there being some designed delay on one of the gas control gadgets. (Again... this isn't my arena.) When the furnace cycles you hear a big click from a solenoid somewhere and then in about two or three seconds the burners light.
Guess my question is ... Does this sound do-able? Anybody on here know a lot about this stuff? Figured I'd explore this some before I call in an expert. I like to have an idea of what needs to happen and get an idea of cost before wasting time and especially money!! Also anyone know of a Y or T valve arrangement out there that'd hold up? Think the blower exit is about 3"...
Any input appreciated...
Bob
