Author Topic: Want to build a gas fired deck oven. Any plans available and suggestions? (Read 13336 times)

Sqid · « **Reply #140 on:** August 29, 2012, 11:34:35 AM »

You're probably right Don, that I had said previously I was using natural gas. I assumed that because this country is so rich in gas deposits that it would be a taken. Alas, again I am mistaken, we are in fact using LPG

I had fired the burner up this afternoon for the photo sesssion but I don't have high pressure at home and the flame was barely visible. That was my first attempt at posting pictures on the internet so feel encouraged to have another go! I shall get some pics tomorrow.

Sqid · « **Reply #141 on:** August 29, 2012, 11:38:19 AM »

Oh and the burner wasn't copied from anything. The place that did it had never used SS before and had never made an H design. Funny thing though, the guy who was actually doing the work was Burmese.

buceriasdon · « **Reply #142 on:** August 29, 2012, 12:46:22 PM »

Richard, I know you will have problems with an even burn from one end to the other with such a long burner. The size of tubing limits the amount of gas that can be pushed along evenly to the end. I assume first off you used a LPG(smaller) orifice not a NG size jet. How much pressure does your LP regulator allow? If you still find poor combustion at the opposite end of the gas inlet, and I think you will, you may have to enlarge the holes slightly in the problem area or add a manifold that supplies gas along it's length. I wanted to wait until you had tested the burner, although looking at the photo left me with doubts. Sorry to be such a wet blanket.

I await further test then with greater pressure.

buceriasdon · « **Reply #143 on:** August 29, 2012, 05:41:28 PM »

Richard, I have to apologize here as I must have missed you saying the H burner was running the length of the oven area. What I had envisioned were several shorter H burners run off a main gas feed line and running perpendicular to the oven. I would have sent up a red flag had I fully understood what you were describing, but I didn't. However the more I study your burner the less confindent I am about it's workability. If anyone wants to jump in and say, Don, you're full it, by all means be my guest. Scott posted a picture of what I thought was being discussed at post No. 79
Don

Chicago Bob · « **Reply #144 on:** August 29, 2012, 06:43:23 PM »

I have heard where another gas inlet was added on to the opposite end when a pipe run was too long for the original single inlet to provide enough umph. Is this what you are referring to Don?

"or add a manifold that supplies gas along it's length."

Sqid · « **Reply #145 on:** August 29, 2012, 10:46:54 PM »

Don - Could you explain what LP and NG stand for?

There doesn't seem to be a problem with the evenness of the flame. Even though it is 3'6" long, the gas is piped directly to the middle of the H and from there goes to the 4 extremities (only a distance of about 2').

Several shorter burners running perpendicular to the gas pipe supply line would heat the deck more evenly. This is the configuration that all the Thai locally made ovens use and the confiiguration that the manufacturer suggested and have experience with. The big difference is that I want to make mine light automatically. Without having a burner running parallel to the face of the oven it becomes complicated to light 4 burners.

I very much like the configuration posted by Scott at reply 79. I prefer the jpg image to the Blogett but availability and ignition pushed me to an H design. It's along the same lines that Marsal explain is superior to there competitors U shaped design.

As it is, I'm not satisfied with the burner now. Still looking out for better. I may well try increasing the number of ports as Scott suggested; which not only will help with reliable ignition but will increase the Btus.

Bob. The idea of two gas inlets is a new one to me and worth thinking about. Thanks.

And Don:

Quote from: buceriasdon on August 29, 2012, 12:46:22 PM

Sorry to be such a wet blanket. I await further test then with greater pressure.

I read this several times and thought no problem with the wet blanket bit but waiting for further failed test with pleasure is a bit sadistic! Eventually I realised I was misreading 'pressure' as 'pleasure'.

.

scott123 · « **Reply #146 on:** August 30, 2012, 12:23:25 AM »

Quote from: Sqid on August 29, 2012, 07:45:14 AM

Hi Scott. How ya doin?

That's a bummer! I thought I was going 'cutting edge' oven design with an aluminium plate. Trying to avoid getting hot spots in the oven.
Steel is cheaper 6mm. About $7 sq ft
Stainless 6mm. About $19 sq ft
Different thicknesses are available.

Is there any major advantage to using SS rather than normal steel and would 1/8" be suitable for both?
Maybe steel, then aluminium, then firebrick hearth?

The burner ports are 8mm apart. If I double the number of holes they will be very close - 3mm. Does that sound about right?

Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit. If you have the pressure, then I'd say drill out more holes.

Heat accelerates oxidation/rusting in steel, so theoretically, very thin steel plate might rust faster in the deflector role you're considering for it. I believe 'aluminized steel' is made to counteract that. This being said, I really don't see 1/8" or thicker steel ever rusting through at these temps. Any good design should give you burner access, so, with that access, you should be able to check deflector wear as well. If you do see any rust, go with ss next time. For now, though, I think you'll be perfectly fine with regular steel.

Chicago Bob · « **Reply #147 on:** August 30, 2012, 12:45:37 AM »

Quote from: scott123 on August 30, 2012, 12:23:25 AM

Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit. If you have the pressure, then I'd say drill out more holes.

More holes is a good thing...they should stager at an advantageous/opposing angle though. Still gonna need fuel coming in at the a$$ end ..too long of a run no matter how much psi you present on the front end..IMHO of course..

Sqid · « **Reply #148 on:** August 30, 2012, 12:48:08 AM »

At optimum gas flow. Flames are about 1"

Sqid · « **Reply #149 on:** August 30, 2012, 12:49:52 AM »

At maximum gas flow. I don't know what pressure I have but I know it's not very high.
You can see that the flame is blowing out in places.

Chicago Bob · « **Reply #150 on:** August 30, 2012, 01:00:20 AM »

That design is choked up....additional gas inlet port recommended....plus, need to open up more flame holes if you ever want to see some btu's...

scott123 · « **Reply #151 on:** August 30, 2012, 01:17:25 AM »

Richard, is this home gas pressure or work gas pressure?

Do you have a reliable gauge for measuring the pressure?

Sqid · « **Reply #152 on:** August 30, 2012, 01:19:03 AM »

Quote from: scott123 on August 30, 2012, 12:23:25 AM

Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit. If you have the pressure, then I'd say drill out more holes.

Heat accelerates oxidation/rusting in steel, so theoretically, very thin steel plate might rust faster in the deflector role you're considering for it. I believe 'aluminized steel' is made to counteract that. This being said, I really don't see 1/8" or thicker steel ever rusting through at these temps. Any good design should give you burner access, so, with that access, you should be able to check deflector wear as well. If you do see any rust, go with ss next time. For now, though, I think you'll be perfectly fine with regular steel.

I don't think I've got enough pressure to double the total aperture of the ports. The gas comes in 25Kg cylinders that they tell me is high pressure. Its a little more than my home gas but not a lot. Maybe I could double the number of holes but make the new one 1mm instead of 2mm?

The reason I liked aluminium was to spread the heat. I know that's what 'deflectors' are for but I want to really spread the heat evenly.

The possibilities for a stone hearth are limited. Fire bricks look like the best option atm. On closer examination of the imported 9"x9" ones available I found out they are 2.5" thick. As there will be about 20 separate bricks for the hearth I want them to be heating up at the same rate (trying to avoid hot spots). Therefore aluminum looked good.

I'm now thinking along the lines of: 3mm steel plate, topped with 6mm aluminum, topped with the fire bricks. Overkill on thermal mass but ........ The other thing I have been thinking is to make the surface of the aluminum act like a stone, i.e. rough it up: and use that as the hearth. Aluminum is not very hard and causes Parkinsons Disease. So maybe steel aluminum steel sandwich and rough the top layer of the steel up. Just thoughts!

Quote from: Chicago Bob on August 30, 2012, 12:45:37 AM

More holes is a good thing...they should stager at an advantageous/opposing angle though. Still gonna need fuel coming in at the a$$ end ..too long of a run no matter how much psi you present on the front end..IMHO of course..

Like the idea of staggering them - make sense.

In you're next post Bob, you saay choked up. The control systems I'm looking at all have a blower to pump air into the burner. Should sort it out. Just don't really like the look of my burner after having seen the weber with millions of holes burning perfectly evenly!!

Sqid · « **Reply #153 on:** August 30, 2012, 01:28:49 AM »

Gas pressure
Home 27lbs/sq in
25Kg cylinder 33 lbs/sq in
Could increase the pressure to about 50 lbs/sq in if I talk to the supplyer and get them to put a different head on the cylinder.

Chicago Bob · « **Reply #154 on:** August 30, 2012, 01:42:57 AM »

pics are already showing pressure flame out...

scott123 · « **Reply #155 on:** August 30, 2012, 02:55:08 AM »

Richard, Marsal seems to possess pretty strong deflection kung fu. The deflectors might be bent in some manner, perhaps to provide rigidity/stability and also better deflection. I have to admit, a flat 3 mm steel plate might not give you that level of even heating.

Steel + firebrick + H shaped burner should go a long way in giving you an evenly heated hearth. According this page

http://www.ehow.com/how_5761350_soften-aluminum-plate.html

Aluminum anneals at 700. For you to reach a hearth of 650, the aluminum closer to the burner will most likely end up in the 800 realm, even if above steel. I would go with 6 mm steel and see where that gets you. The conductivity and thickness should go a long way in evening out the heat.

27 psi is more than enough for a 200K btu banjo burner, but, perhaps the lengths of the runs are impacting the BTUs here. I'm not really sure how they should, though. Regardless, if you can get 50, get 50.

If you do add holes, I would stick to holes of the same size, but I like Don's idea of a greater concentration of holes at the extremities. First see what it will do with 50 psi, though.

lennyk · « **Reply #156 on:** August 30, 2012, 04:39:30 AM »

Can you use an adjustable regulator ?
Here in Trinidad the common regulator is simply a snap on head to the tank and the switch basically presses down the release pin in the tank a fixed distance, however you can get regulators which don't use a switch but a knob which turns and can move the pin further than the switch type regulators.

buceriasdon · « **Reply #157 on:** August 30, 2012, 07:38:27 AM »

Richard, I meant LP for liquid propane,NG for natural gas. You didn't answer my question. Which size jet/orifice did you use, a smaller propane hole size or a larger natural gas orifice size? They are not interchangable. I have more but it seems important parts of posts are not being addressed.
Don

buceriasdon · « **Reply #158 on:** August 30, 2012, 07:45:40 AM »

Bob, Yes that is exactly what I am talking about. A certain diameter tube with a certain about of burner holes will only be capable of carrying a certain amount of gas. Which gives you more volume of water given a certain pressure at the inlet, a water hose that is 1/2" in diameter or 1"? Notice I'm saying volume not pressure.
Don

Quote from: Chicago Bob on August 29, 2012, 06:43:23 PM

I have heard where another gas inlet was added on to the opposite end when a pipe run was too long for the original single inlet to provide enough umph. Is this what you are referring to Don?

"or add a manifold that supplies gas along it's length."

buceriasdon · « **Reply #159 on:** August 30, 2012, 08:10:07 AM »

Scott, Without an increase in tube diameter simply turning up the gas pressure will not result in better more even combustion. You will not get better results on a propane grill by switching to a high pressure regulator, the burner isn't designed for that.
Don