I need to build an NG burner for my 14"bore x 20"height furnace to run off residential NG and have some ideas and looking for some feedback. It will host an A60 and melt up to ~50lbs of aluminum. I was thinking I'd target at least 300kbtu and maybe up to 500kbtu if I can get it. I can tap a 2" main that is on a run about 75ft from the primary service regulator with no other appliances accessing the line. I measured between 6" & 7" wc but that's static and don't know if I can count on that....in the summer maybe. I have a 3-stage central vac motor and was considering using it to power an ejector to aspirate the NG, the opposite manner NA propane foundry burners are typically configured as far as fuel and air. The 3-stage blower is driven by a universal motor so I can easily control speed and it can develop a lot of head compared to most blowers. It delivers about 95cfm through a 2" orifice (72 ft/sec velocity) and still 60cfm through a .75" orifice (325 ft/sec) I was going to use the head to drive a high velocity stream of air to power the ejector and introduce the NG in the low pressure region of the ejector hoping to get some boost and hopefully insure introduction of NG always sees sub-atm delivery pressure.....unless the burner becomes blocked....then you have a whole new ball game. Even though the .75 orifice is still about 1/4 sonic flow (which could yield more ejector boost), I picked that diameter because with a little excess air I figured I needed ~60cfm to hit 300kbtu/hr. I also have a second blower that could be incorporated. I also considered a multistage ejector using compressed air to aspirate both NG and combustion Air. What do you think of that scheme? What intervening safety mechanisms should it have? What other configurations would you suggest for safe/simple NG burner in that power range? Best, Kelly
Now you are talking MY LANGUAGE... pssst... Ribbon burners.... My next build will be run by NG. I'll do a video soon of my ribbon burner so you can see what has been working for me on the forge.. Forge, furnace, foundry.. all the same animals according to the youtube "experts"
some base line information. a hair dryer will provide sufficient air for about 175 kbtuh NG. flame spread is about 75 ft /sec. the combustion mixture needs to be slower then that or it will blow out. The flame will form at the point that the velocity drops blow the 75ft/sec. You want the flame to form at about 1/2" from the outlet of the burner tube. If the burner tube is large enough the velocity can drop below the flame spread rate and the flame will back up into the burner, I use baffle plates at the outlet of my larger burners to generate a a velocity point to control were the flame is located in the burner. the baffle plate can also be used if the burner has a bend to close to the oulet. The NG field regulator located at the meter is normally set to deliver 7" WC up to about 600kbtuh on a residential system. lower pressures at the burner is caused by pressure drops through the piping between the meter and the appliance. Most burners are orificed and designed with a secondary regulator set to operate at about 3.5" WC. That said I do not use a downstream regulator but use the full line pressure from the field regulator and adjust fuel flow at the burner. When I am melting engines and cylinder heads my tilting furnace fires at about 240 kbtuh NG and about 2 GPH waste oil, for about a total of 550 to 600kbtuh. I also fire my crucible furnace at about 80 kbtuh for stabilization, drossing and skimming etc before pouring into the ingot molds. My typical melt is between 125 and 200lbs and takes about 1.5 to 2.5 hrs. I'll post some more information including orifice sizing etc. I can also provide break down photos of my burners if you want. NG and low pressure propane burners are very simple to build and operate. Residential NG can go to about 400 kbtuh for the foundry usage and still operate the normal appliances in the house, if you start going over that you may have problems with the other appliances. Art B
I always ball parked about 20scfm of air per 100kbtu/hr figuring 10:1 air fuel ratio, just under 17 scfm for stoichiometric burn but figure 15-20% excess air, thus ~20scfm. Sound about right? Those velocities I was citing were the air velocities in the injector tube. The outer tube where the NG would be introduced and mixed with the air would be 2" and that would drop the velocity below 75 ft/sec. My furnace Tueyer is 2.5" and I'd like the burner tube to be 2" if possible. Still not sure I can envision the baffle plate. I had a patio project that included a big burner in a fire pit and several torches. Also have several heated outbuildings and code required supporting infrastructure to handle all appliances in simultaneous max operation so I had a bigger regulator and meter installed. The utility company installed them for free. -Guess they consider it business development and are happy to sell me gas. That would be great. Thanks Art. Best, Kelly
This kind of Baffle plate??????? This is inside my ribbon burner. My local yeahoos wouldn't dream of giving me a bigger regulator without tons of rigmarole.
Jason's burner has a baffle plate, i use larger holes in mine typically with a large center hole 1/2"to 3/4" and 4 other holes around the outside. that type is used in a 2" burner tube when i need to control the flame point, I'll take some pictures tomorrow of my tilting furnace burners. Art b
Art, I'd like to see whatcha running. I'm sure I took the long way around to get from A to B. Those of us lucky enough to have natural gas close by are fools for not taking advantage of it. It's super cheap in texas and I can ditch the fuel tank setup, barrel of used motor oil and collecting sump Jet-A from my airplane buddies. It's easy to see that even a pissy little 7" wc source would be enough to melt metal. After all, our home heating furnaces do a fine job of heating thousands of square feet. My friend has a 400k btu heater on his pool here. It will take a good sized pool from 50degrees to 95 in about 12hrs. I asked him one day what's it cost to run that thing, his answer was, he didnt want to know. Here's a couple more shots of my ribbon burner. That's a 2"hole and the little ones were 1/4" I think. Mizzou refractory that extends into the forge. The steel never sees the heat. This shot was before kaowool and more mizzou was added. This is just the refractory sticking through from the ribbon burner. You can see here where I hook up the NG... WAAAAYYY before the burner. Small blower goes on that end Works like a beast, cheap as chips.
Even Large boiler burners fire at 3.5" WC the largest boiler I have fired was burning about 20,000,000 the fuel was delivered to the boiler at 5 psi but the burner fuel train had a regulator that brought it down to 3.5" WC the inlet piping was 1.25" pipe at 5 psi but the piping after the regulator was 2.5" Art B
It's interesting to see the various gas burner designs, I expect there's as many burners as there are furnaces. The only one I've seen used for LP gas for a metal melting furnace with blower has been a straight 1/2" copper tube with no restriction entering the tuyere. Forced air probably makes all the difference to the gas mixing and ignition not to mention the rate of fuel burn. To describe it, the right angle steel pipe with copper tube in the first drawing it fitted to the furnace in the second drawing.
Sounds like all I need is regulator (maybe not even that if my supply pressure is stable enough), gas orifice, blower control, and maybe a baffle (I get it now) to tune the position of the flame front. Before I scour eBay, any economical high flowing regulators you can recommend? May not be needed but might provide good stability. Best, Kelly
There's a type of high pressure/high flow gas regulator used a lot for gas fired pottery kilns known as a "Red devil" gas regulator that works well for furnaces. You can buy a large BBQ regulator and open it up to adjust the pressure higher, then you use one of these to go even higher:
Mark, is that propane or natural gas regulator? Looks too small to be NG. I have NG but residential NG is <= 7" water column pressure. Best, Kelly
Apologies for my confusion, it's for bottled gas, commonly know here as LPG or liquid petroleum gas. Town gas with it's in ground plumbing is rare these days outside of capital cities in Australia , almost everything gas is now delivered by truck. That fig.4 furnace was originally run off town gas with a weight sitting on top of a 1950's mercury filled gas regulator diaphragm to increase flow. Three town gas regulators were paralleled up by the gas supplier but apparently there is some law of fluidics that prevents paralleling of gas regulators to increase flow rate. On a slightly related note, my avatar pic is of the local gas works exploding in 1986, there is a complete LPG rail car airborne in that fireball about 300' in the air. I'll bow out of the discussion now
I understand. LP here in the USA = Liquid Propane which of course only refers to its stored state. Is town gas what we refer to as Natural Gas...aka methane? Best, Kelly
Town gas was coal gas, methane, hydrogen and carbon monoxide. I think it's made by injecting steam into a low oxygen coal fire and stored in those massive telescoping gas tanks of 1920's 1930's vintage.
To those that do not know... 7inches water column is about a QUARTER of a single psi. I fart harder than that. That red regulator would be useless for natural gas... Household natural gas has ZERO smell. The gas company adds mercaptan to it to make it stink like rotten eggs. Funny how some people cannot smell it at all.
I wouldn't worry about adding a regulator, the main field regulator at the meter will provide stable enough pressures for a Foundry or forge burner. I use orifice sizing for flow control. the first picture is a 85 to 125 kbtuh burner the washer between the hair dryer and the burner tube is for air control on when running on the lower end of the firing rate. this picture shows the gas inlet piping coming in at an angle, this generates a sufficient enough venturi for fuel mixture etc. this particular burner is attache to the furnace tyer which adds another 2.5" in length between the gas pipe and the furnace, this works ok without a baffle plate. this picture shows the drilled pipe plug put in the inside of a a nipple in the gas piping, I just drill the pipe plug with the size orifice i need for the gas flow i want. All that is needed to convert between NG and Low pressure propane is the correct orifice size.
the next few post will be about my tilting furnace burners. The first pic shows the burners firing on NG The two burners firing in the back are firing at about 80 kbtuh the 3" duel fuel burner in the end is firing at about 135 kbtuh it gets turned down to about 50 k when firing with oil. The second picture is firing the duel fuel burner on waste oil. I do plan on using a 5k ignition burner on the next furnace instead of trying to fire it duel fuel The next furnace will have 2 or possibly 3 waste oil burners and will fire at 500 to 750 kbtuh, the gas or propane will only be used for ignition.
These pictures are about the duel fuel burner. The duel fuel burner is based on a hago/ delvan nozzle. I use a 3/4 gpm nozzle with about 5 psi delivery pressure fr0m the oil tank. As long as the ambient temperature is above freezing i don't use the oil heater, below freezing it is necessary, unless the oil has a lot of tranny fluid in it. when using the oil heater I take the oil temp to about 200F. The oil tank is a 20 gal garage oil drain tank, modified with an oil filter on the fuel outlet line. the air control has 2 regulators the first regulator provides the air for the oil nozzle atomizing air , it also feeds the 2nd regulator that controls the pressure on the oil tank .
This post is about the duel fuel burner. The burner is 3 in diameter with a 2 in air feed from the blower, the vane axiel fan delivering about 1" WC pressure. The end block of the burner is also the manifold for the air, waste oil and natural gas. the natural gas has 2 feed tubes with needle valves for fuel control. At the time I made the burner I was not sure whether I would have NG, so I made it so that it could be used with either propane or NG by readjusting the needle valves. In order to keep the NG flame from burning up inside the burner i placed a baffle plate at the outlet of the burner.
