Timing is everything

nicholas bonham-carter

Since I have no experience with forced draft gas burners, I would like someone to tell me what the sequence of events is on a call for heat with a gas burner. Another words, how long will it take burner to start up. Is this seconds of purge,etc, or minutes to be on.

I am thinking of this in connection with a dual boiler setup. The atmospheric burner is virtually instantaneous, and maybe that is why SlantFin chose them for their multi boiler caravan series.

If the system is running on the lead boiler at the end of the day, and the temperature is dropping, and steam pressure falling, will there be a long period of time before the lag boiler comes back on line?

This might be one of the great benefits of a vacuum system where he air only has to be let out once at the end of every warm spell.--NBC

Joe V_2

Forced Draft Burners

rough numbers:

30 second purge, 5 seconds to go back to low fire, 10 seconds stable pilot, 15 seconds stable main flame, then run.

We have a sequencer to control the roll over and keep the boilers warm by firing their burner at low fire if the aquastat cools below 200 degreesF while they are in lag.

  So at rollover time, lag burner comes on and goes through it's purge sequence, lights up, and fires in unison with the lead boiler for about 20 minutes (10 minutes in the summer) then becomes the lead burner as the the other boiler shutsdown.

Maintains a steady pressure without thermal shocking boilers. 

Otherwise, on a cold day (30degrees) we would lose 25+% of our operating pressure while the lag boiler fires up then zooms to high fire until it can produce steam.  Operating this way, it would take about twenty minutes until pressure is returned to normal.

nicholas bonham-carter

Important information

Thanks very much, I will now start to digest it all!--NBC

Joe V_2

you are welcome

our system is for both heating and heat transfer in chemical processes. we run at 90psi and cant afford a big dip in pressure. We keep the boilers hot to minimize the dip in pressure if there was a power blip or flameout.



I am certain, there are less expensive ways to accomplish thie same thing. Tell us more of the system you have in mind. I'm sure others will have more relevent information closer to your application.

nicholas bonham-carter

Firing an old Dunham system

I plan to have two boilers, each sized to 1/2 the maximum load (918 sq ft of EDR) If I stage the lag boiler at 2 ounces, and the lead boiler at 8 ounces, then the system will be running for part of each cycle at 1/2. I the pressure drops enough to fire the lag boiler, then by the time it comes up to pressure, then the pressure may have dropped enough for air to start coming back in. This is a clear situation where the old Dunham vacuum principles will prove their worth, as the air will not come back inside the piping, and then need to be chased away, "like the Raccoon from the garbage can" ( who wrote that gem?--NBC

JStar

Pressure

Calcuate how much pressure you need to get steam to the end of the mains and close the vents. Make that number the cut-in for the lag boiler. You'll always be making at least enough steam to keep the vent closed and the mains hot.