Unique Gas System

Harvey Ramer

Don't know if this type of gas system was ever used in very large commercial heating?

The system I speak of is on a grain bin dryer that I worked on today. For starters, it is a very large burner. It is piped for liquid directly off of the propane tank. Upon arrival at the burner, the line first enters a vaporizer. The vaporizer is basically a pregnant pipe located directly in the flame. Then it goes through the first regulator which I believe drops it to 10 psi. After that it passes through a modulating control valve. The valve has a cap tube running to a sensor bulb in the supply air plenum and regulates the gas flow to maintain a preset temp. Example, as the ambient temp drops, the flame strength increases. Then the gas passes through double solenoid valves and out to the circular burner manifold.

It's a unique setup for sure. Built in 1979.

delta T

Sounds interesting! I have certainly never seen anything like that. What did you have to do to it?

FranklinD

That sounds almost identical to what we have for backup/makeup heat in our shop. The shop is 200'x200' so it's good-sized. It's setup to run propane or NG as we are on some sort of 'peak demand shedding' plan with the local utility. It automatically switched fuels.

I do know, however, that with ours the vaporizer is a separate unit located outside, about the size of a port-a-potty. It's next to the tank...if give you a size if I could, but it's massive. At least 50 feet long and 10 feet high up on concrete pedestals.

The place was built in '76, I believe. And it is primarily heated with NG radiant pipe heaters with big reflectors at the ceiling (way better than that giant fan blowing around all the time).

I'll take a picture tomorrow. It's a beast.

Harvey Ramer

I had to replace the flame sensor. Kind of a bad safety setup. The flame sensor is normally closed, until it heats up it becomes normally open. There is a Time Delay safety relay with manual reset, that is looking for that open circuit on the flame sensor. If the circuit remains closed, meaning no flame, the manual reset button pops out. In this case, the tip had burned off of the flame sensor and the circuit remained open all the time. If, under these conditions there was a failed ignition, it could have filled the entire grain bin with gas and literally turned it into a bomb.

Steamhead

They probably didn't have flame rectification in those days. I can't think of a better place for a current-model flame-safeguard control setup.

ChrisJ

What's a "pregnant pipe" ?

JUGHNE

There usually was an air flow switch; if fan failed then gas valves close. Sometimes an extra pole on the motor contactor for redundancy. But with a flame out with the defective sensor you hope someone smells the propane coming out of the bin.
Some farmers may never have anything looked at unless it doesn't work and they can't get it going themselves.

So is a "pregnant pipe" in the flame just an oversized pipe to get the liquid to vaporize for use?

Harvey Ramer

Steamhead said:

They probably didn't have flame rectification in those days. I can't think of a better place for a current-model flame-safeguard control setup.

It's a very harsh environment though. Would have to be a pretty robust setup.

Harvey Ramer

ChrisJ said:

What's a "pregnant pipe" ?

Well, I don't really know how to put this. The vaporizer is just an enlarged section of the piping, probably 5 times the diameter. It's directly in the flame. Since propane is pressure/temperature sensitive, it converts the liquid to gas vapors, hence the name vaporizer. There is a temperature limit switch on the pipe as it exits the vaporizer. Prevents the gas from getting to hot and burning the oils out.

Harvey Ramer

JUGHNE said:

There usually was an air flow switch; if fan failed then gas valves close. Sometimes an extra pole on the motor contactor for redundancy. But with a flame out with the defective sensor you hope someone smells the propane coming out of the bin.
Some farmers may never have anything looked at unless it doesn't work and they can't get it going themselves.

So is a "pregnant pipe" in the flame just an oversized pipe to get the liquid to vaporize for use?

This setup has no air proving switch. There is a relay to prevent the gas control from operating till the fan is engaged.

JUGHNE

Bad thing is that the blower fan contactor could be engaged but the motor burned up.

The 2 story tall one I worked on used a HW flameguard with a UV peeper. It was a continuous grain feed design that had a pressure switch mounted near the top, if you run out of corn you lost the pressure, flame and blowers off and loud horn sounded.
It was a large, loud and dirty beast. The pilot alone used a 1" pipe size for NG. The 2 blower motors were perhaps 40 HP each. Staged to come on about 2-3 seconds apart to help out the power company......boy I sure don't miss servicing that.

Harvey Ramer

Yah, these burners make boiler burners look piddly.

Tim McElwain

Harvey send me some pictures especially the controls, I think something is missing which needs to be on any open pipe vaporizer.

Harvey Ramer

I'll get some pics Tim. Might be a day or two. What component do you feel may be missing?

Tim McElwain

I would be looking for some kind of flow switch or gas pressure switch that would open and shut off the system if flow or pressure went below its set point.

As someone mentioned this would be great with a flame safeguard system. Better yet put in a regular designed "vaporizer".