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Natural gas ribbon burner help


Joman295

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Every question I have ever had about forging on google has brought me here. This is a very knowledgeable group and I'm looking for some help! I built a forge out of an old propane tank, used 2 inches of kaowool, coated it with refractory and it turned out pretty good. I decided to make a blown ribbon burner with natural gas so I wouldn't have to swap tanks all the time. I have a 4 amp 115 volt jump castle blower. Gas is on a needle valve and there is an air mixer just before the gas inlet. I can get it to light with just the gas on but as soon as I turn the air on it blows the flame out. Any help would be great.

 

Thanks !!

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I have a forced air NG forge also, and have run it with a multi-port outlet (but currently don't use one <replaced with a single flame retention nozzle>).  The responses from the other's agree with my experience as well. 

There is a somewhat delicate balance between the air/gas mixture velocity at the exit to your burner and the flame front velocity ("FFV", that burns back in the opposite direction).  The former is influenced by the quantity of air/gas mixture flowing in the burner ports; which is based on the air/gas pressure at the entrance to those ports.  The pressure at the entrance to the ports is determined by the pressure for each material entering the mixing chamber, the configuration of the chamber, and the geometry of the port entry.  Consequently you need to have the capability to vary both the air and gas pressures in a controllable fashion.  There are many ways to achieve this, but I personally prefer a variable pressure regulator for the gas pressure (particularly if you are using residential pressure natural gas) and either a gate valve, butterfly valve, or variable speed blower for the air.

Note that the FFV also changes depending on what fuel gas and oxidizer is used as well as their temperatures, how well they are mixed,  the temperature of the chamber where they are combusting and, to some extent, the amount of radiant energy in that chamber reflected by the chamber walls.  As noted the idea is to balance the FFV and air/gas flow velocity so you have a stable ignition point just at the outlet of the burner ports inside the forge.

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Thank you guys for all the input. 

 

It is a pretty big blower but I picked it up for $20 so it was had to pass up. I 3d printed a nozzle that bolts to the fan and reduces down to slip over the feed pipe to the forge, I built in a slide gate so I could adjust how much air could escape but it might not be enough. I will have to pick up a gate valve so I can try to get the a/f ratio correct. I have also read that people use dimmer switches to slow down the motor. I thought I might give that a try if I can't find a gate valve at lowes. Has anyone run into problems with the low psi on natural gas? 

 

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Yes, low pressure (7-14" WG) residential natural gas certainly presents a challenge for forges.  Honestly I'm the only one I know of first hand that uses it.  You need a much larger than typical forge size gas line.  It all depends on how far from your main house regulator you are running it.  Mine is 1" for the first 30 ft or so, then a 75" length of gas rated underground plastic pipe at 1.5" and a final connection to the mixer orifice of 1".

Dimmer switches will only work on certain specific types of motor without burning them out in a relatively short time.  Steve can give you a better breakdown on which type, but even a actual VARIAC (which works on my blacksmith supply blower slater for my coal forge) does not work on the Dayton 120V motor for my current gas forge blower.  I don't recommend using one unless you get the go ahead from a competent electrician or electrical engineer.

A 2" gate valve will be rather expensive.  The slide gate should work if well constructed (or use it as a dump valve).

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I am 10 feet from the meter running 3/4" line to a 1/4" hose. I tapped a 1/4" quick disconnect as the supply to the forge. I will snap a picture when I get home. I may be having a gas volume issue?

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If you are on residential pressure I expect your pipe/hose is too small.  The final orifice at the connection to the mixing tube may be adequate.  You also have losses for the needle valve, regulator and quick connects (are these gas rated fittings?).  You can usually find the recommended gas line size in the Fuel Gas codebook.  I would figure for a burner in the 140 MBH size, or there about, for a well insulated forge the size pictured.  It should be easy to tell once you have a reliable method of modulating your air supply.  I didn't see a slide gate in the photos.

Also, check the pressure range for your gas regulator.  Remember that residential pressure gas should not be greater than 14" WG (0.5 psi), so a 0-30 psi regulator that is appropriate for bottled propane will not work well at all.  The photo appears to show that the maximum pressure setting is 14 bar (200 psi or 5,626 " WG).  I'm kind of surprised you get any modulation with this regulator at all, as the range is completely inappropriate for residential pressure natural gas.

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The pressure regulator doesn't do much if anything really. It registers slight needle movement when the shut-off valve is on and the needle valve is closed. All the fittings are gas rated, didn't want to blow my garage up haha. I found this gas pipe chart and I may have to find a way to run larger pipe. A friend suggested calling the gas company and asking them to install a larger meter since the line coming out is only 3/4". The slide is a hole in the side of the tube and I can twist the outer band to allow air to escape but even all the way open it was still blowing quite a bit of air through the burner. I redesigned a better version that can block the air entirely and it should be done printing by the time I'm home today.

Screenshot_20210129-073655.jpg

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I'm so jealous.  I guess I should talk to my power company as well.  On the other hand, my forge already gets up to temperature just fine, and if I up the pressure I might run into issues with melting the liner (and/or my stock)...

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11 hours ago, Latticino said:

might run into issues with melting the liner (and/or my stock)...

OH NO!!! You might have to turn it down! Oh the HORROR! :o You'd have my sincerest sympatheticnessetivity were something so terrible to befall you. Just the very thought has me quivering in reaction, heck my belly is shaking like a bowl of jello!

Nat gas is only maybe 100' from the house but if we hook up we'll get hooked into the main in the sub division down the hill and they'd have to run it through their back yard and up the hill through the forest, PLUS we'd have to pay a share of the subdivision's connection to the main. We can buy heating oil and propane for a couple decades for what ng would cost. 

Guess I'll stick with developing a suitable smoke release for T burners. <sigh>

Frosty The Lucky.

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:D   Glad you caught that one...

I don't even turn it up full most of the times even now (at low pressure), but I do have a problem with the pilot light on my natural gas cabinet heater due to insufficient pressure.  However, I love not having to worry about tanks running out or propane delivery.

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Joman295,

you don’t have large enough pipe starting at your meter, I would recommend running 1 1/4 as close to the forge as possible, then connect with as large of fittings as possible , keep everything as close to the forge as possible. You don’t need a regulator between the meter and forge, the needle valve will replace it. Every extra thing you place in the line creates a restriction. Every 90% fitting equals 10ft of pipe on a UP system. You’re only working with 6” water column (1/4lb) at this time, you don’t have pressure so you need volume. If you switch to a pounds regulator at the meter this will still apply for the forge, but you will have to install a 6” WC regulator before the house piping. 

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Joman295,

I forgot to include that I agree with the others that you aren’t getting enough gas to the forge and your not regulating the air properly, my recommendations  to improve the gas supply/performance are based on 37years working in the NG gas industry 

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That's where I am at now, the issue is the pipe coming out of the meter is 3/4" and if I change the piping size after the meter and make it larger, it will decrease the pressure even more. I found a pressure reducer valve 3/4" 2psi down to 7-10 wc. When it gets here the gas company will come out and swap out my regulator for free. If there is an easier way I'm all ears. Thanks for your input. I'm fairly patient so I will take the time to do the right this time haha

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You won’t be decreasing the pressure by increasing the diameter of the pipe, you will be increasing the volume of gas available. The same amount of pressure will be used to fill the larger pipe. Larger volume is able to supply more gas at the same pressure for an appliance needing a large amount of gas. 
if you can get the pounds regulator installed at no cost do it, you will not regret it, but the larger supply line to your forge will help you more than the increased pressure. I do not know what you’re calling a pressure reducing valve, are you talking about a regulator, like the one installed before the meter at your house? If you’re gas company installs the 2# regulator you will have to install a 6”WC regulator between the gas meter and your house. You can branch off before your house regulator to your forge and supply the 2# to your forge without a regulator and use the needle valve to control it at the forge, just install a cut off valve before the needle valve. 

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  • 2 weeks later...

Joman, to your original issue and question, your flame out is occurring because your air volume it too high compared to your gas volume.

Either:
1) decrease air flow by controlling blower speed or
2) increase gas supply via larger volume or higher pressure.

As a reference I use 5 psi via 1/2" pipe for my blown ribbon burner (4.25"x8.25" burner face). If you can't increase NG pressure or volume, or refuse to switch to propane to achieve higher pressures/volumes, then you will have to decrease your blower speed (i.e. air volume), but this will in turn decrease burner performance and you may find it difficult to reach working temperatures.

For brushless motors (ONLY) you can get some level of blower control using a $20 speed controller found on Amazon.

Router Speed Control

 

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