stupid questions about chimney

[jrgpots]

1. How high above the damper does the chimney need to be if I use power burners.  12 cubic foot downdraft, 9 inch walls  with  the chimney 13.5" away from back kiln wall?

2. how thick should the chimney wall be...4.5" or 9".

[neilestrick]

I usually build the chimney to the top of the arch so it direct the flame into the overhead hood better and doesn't heat up any steel on the back of the kiln. Go 9" below the damper, 4.5" above.

[Sorcery]

Should've called it a sucky question.

Sorce

[jrgpots]

On 8/19/2020 at 8:46 AM, Sorcery said:

Should've called it a sucky question.

Sorce

You are right.  It would have had a better "draw" that way/

 

Jed

[Sorcery]

19 hours ago, jrgpots said:

You are right.  It would have had a better "draw" that way/

 

Je

Some Blue Heron Flue onto some Logs which where really a new Dam Per the beavers need for a new home!

Sorce

[jrgpots]

Here is my new kiln with chimney.  I salvaged the framework from my previous attempt. I'm still working on the gas works and power burners.  But, there has been progress.

[jrgpots]

view from the side.  Still working with the gas line and burners.

Jed

[Bill Kielb]

Interesting - nice, piping / burners seems confusing.

[jrgpots]

7 hours ago, Bill Kielb said:

Interesting - nice, piping / burners seems confusing.

yes. Because the building retrictions, I had to reduce from a 54 x 54 footprint to a 45 x 45. This put my primary burner ports in line with the chimney. So, I had to kick the chimney off the back wall by 13.5" giving me room for the burner inlets.  The result is that the burner heads take two 90 degree turns after the mixing chamber in order to line up with the ports.  If this causes problems, I will have to mount the burners vertically with a single 90 degree turn afer the mixing chamber to enter the kiln.   I still have not mounted my blowers the the back of the burners.  And finally, my baso valves and pressure regulator have not arrived.   This weekend , I will be installing the upper limit/ power loss shut off circuit.  Lots to do.

Jed

[neilestrick]

@jrgpots There is a ton of heat that radiates from the burner ports. It's the hottest part of the kiln. Because they are sandwiched between the kiln and chimney, you're going to build up a lot of heat there. I don't love it. It's going to degrade the pipe very quickly. Is it dangerous? I don't think so? I would remove more bricks from the side of the chimney to give it some breathing room, maybe replace them with some 1" rigid insulating board if you want a better seal than just one row of bricks.  Also see if you could do it with 45 elbows instead of 90s, or have the main 2" burner pipe come from the side , with just one elbow right before the burner tip like in this picture:

 

[Mark C.]

I'm with Neil

how about restacking the chimney to one single layer so the burners have a straight shot coming in to run cooler

No need more the massive footprint at base of stack. My  stack on the 36 cubic car kiln  base is

23x23x23 and the bricks go up about 12 feet and turn to stainless steel stack. The chimney get a bit smaller up past the damper

or come in sideways like Neils drawing. The heat there will be really hot there-thats why its best to give it more space there.

you only need 23 inches at most between ports with single wall hard brick there

if you want some phots I can post them.

[jrgpots]

Thanks guys. I think i can do the burners as in Neil's drawing.  I can also create more breathing room around the port  by reducing the mass of the chimney base.   I'll post my revisions this coming week.    That being said, I'm proud of my arch. 

Jed

[Bill Kielb]

7 hours ago, jrgpots said:

The result is that the burner heads take two 90 degree turns after the mixing chamber in order to line up with the ports.

Not in favor of doing this but if you must. If this is intended to be an Alpine style burner Then I would insert the orifice bar in the straight section, no use having the flame travel around a corner. This port will be relatively cool as secondary air is drawn into the kiln but in reduction, less air will pass through and it will be quite warm. Generally even in reduction with  reduced secondary  airflow brass parts (Pilot orifices etc...) in this area will not melt. The majority of the burner pipe will be cooled by primary and secondary airflow but I have to agree why subject the burner to this much heat? Bending the air around a 90 Degree fitting will add significant head pressure to your blower reducing airflow, so smoothing this out is definitely a good idea with a straight path being best as well.  Your blower needs to be capable of 10:1 air fuel ratio so speed control is helpful here. You already know how man CFH gas by the btu of your orifice so convert to CFM and Find a suitable blower that will handle the headloss.

Flame retention - you may find it necessary to buy and install flame retention tips to keep the flame near the tip. You can buy ready made which are great or in a pinch insert  something in the tip to trap some gas within the tip of the nozzle. Have used spring wire in a pinch or tack welded an interior washer then ground out the inside to maybe a sixteenth of the Inner wall of the burner. Readymades work best for sure.

Kiln looks nice!

[jrgpots]

1 hour ago, Bill Kielb said:

Flame retention - you may find it necessary to buy and install flame retention tips to keep the flame near the tip.....

Kiln looks nice!

1.   Are the flame retention tip male or female?

2.  I have debulked the are in front of the port and I think I will have the mixing chamber come in at a 45 degree angle.  It will just have a single 45 degree bend into the port.  It's better than two 90 degree bends.   

Jed

[Bill Kielb]

22 minutes ago, jrgpots said:

1.   Are the flame retention tip male or female?

Yes! Sorry couldn’t resist. female is  likely most common.

and......... I assume you are making your own orifice bar which can be mounted vertically in the straight pipe downstream of the elbow.

Typical retention tip below, no special brand, just first google that popped up.

 

[jrgpots]

define orifice bar please.   It is the bar which secures the burner or is it the bar which holds the thermocoupler  or pilot burner.   Every specialty has its own nominclature.  I'm still trying to learn all of pottery's terms.

Jed

[Bill Kielb]

20 minutes ago, jrgpots said:

define orifice bar please. 

Just assumed you were doing the home built Alpine style burner where a 1//4” pipe intersects the burner pipe and several holes are drilled into it (one, two, three) to get the required orifice area for a given btu. There are several Common ways to do this with ordinary pipe.

See picture below, this is what I assumed you were planning.

[jrgpots]

This is what I was planning on using.  I have made similar burners for forge.  I just worry about the airflow around the burner tip. 

[Bill Kielb]

2 hours ago, jrgpots said:

I just worry about the airflow around the burner tip

Yes, see this tee style usually with 1/8” pipe to 1/4”, the  1/2” pipe and cap definitely consumes a bunch of room which will decrease your blower performance a bunch.. I’ve done similar -welding a threadalet or simply drill and tap the schedule 40 rather than the tee, insert steel tube with compression fitting for bulkhead. All work fine, just variations on same idea. I guess I would measure this with the blower and see if it decreased the airflow too much. I don’t know what you plan to size these burners at but with kiln back pressure and all the fitting losses you are likely going  to need 20-30 cfm. The blower in the picture puts out 45 cfm free air so straight through with the cross pipe,  back pressure and losses - it probably barely makes 40 cfm In operation.
Cast pipe fittings are just bulky so if this does not perform then you could certainly trim its size a bunch. I still would not place this upstream of the elbow nor too near the flame tip. Although An argument could be made that upstream from the elbow has the possibility of helping mix the fuel air. My argument would be to design with the least amount of stored mixed fuel air with the least amount of back pressure so without blower operation the flame will still go into the kiln propelled by the energy of the gas discharge from the orifice and likely never backup through the blower In a meaningful way even if I lose power.

[Mark C.]

Yes you want to downsize that  pipe inside to a smaller one so more air is getting in

You can use brass pipe insdie for smaller wall size as well.

I'll dig out my old homemade burners and post the specs. They worked for years -they also had flame retention nozzels  on the 1 1/2 pipes that screwed in past the orvice . I made natural draft burners but you could blow air into them  for more power. If I recall I started with a 2 and 1/2 inch  or 3 inch tee.

[neilestrick]

6 hours ago, Bill Kielb said:

Although An argument could be made that upstream from the elbow has the possibility of helping mix the fuel air. My argument would be to design with the least amount of stored mixed fuel air with the least amount of back pressure so without blower operation the flame will still go into the kiln propelled by the energy of the gas discharge from the orifice and likely never backup through the blower In a meaningful way even if I lose power.

If a power burner system is built properly and safely, then there will be a solenoid on the gas line that will cut off the gas should the system ever lose power. IMO, the issue is not the gas backing up to the blower, but rather just the fact that there will be gas pumping out without air period in the event of a blower shutdown. Even if it's coming out the correct end, most likely it will not enter the kiln anyway, but rather roll up the outside of the kiln since these short stack kilns have very little natural draft. I've seen it happen many times.

The original Alpine burners had very short mixing pipes, like 6". Going to 8" or 10" has a dramatic effect on how well the gas and air mix and how smoothly the burners run. Keeping the gas orifice close to the burner (in the tee like in your photo) will help a lot, too. I agree that the orifice system in the photo is bulky, but I don't think it will be a problem since blowers are rarely ever run at full anyway. As long as you have a large enough blower it shouldn't be a problem, and with a kiln as small as yours a large enough blower isn't go to be anything all that big. Alpine used a 75cfm on their mid size kilns, 51cfm on the little 10 cubic foot models, and 148cfm on the 30 cubic foot and up models. I highly recommend that you put a rheostat on it so you can throttle down the blower speed in addition to using the flap on the intake. It will help a lot to have lower velocity air when the gas is down low at the start of the firing.

[Bill Kielb]

39 minutes ago, neilestrick said:

If a power burner system is built properly and safely, then there will be a solenoid on the gas line that will cut off the gas should the system ever lose power. IMO, t

I absolutely agree the normal safeties need to be there, but in design you try to anticipate uncommon failures or in absence of anticipating every possible failure you look at the inherent safety of the discrete components. If the fan quits working because of mechanical failure or slows down excessively or is blocked excessively just because someone forgot to open the primary air - no use encouraging a face full of flame.

If available at design time pick your best safe available options. The preference is to try and make all parts of the system as safe as practical, not just believe that the safeties built in address every possibility. My argument would be injecting the gas upstream of the elbow is a less safe approach, don’t do it.

[neilestrick]

1 hour ago, Bill Kielb said:

I absolutely agree the normal safeties need to be there, but in design you try to anticipate uncommon failures or in absence of anticipating every possible failure you look at the inherent safety of the discrete components. If the fan quits working because of mechanical failure or slows down excessively or is blocked excessively just because someone forgot to open the primary air - no use encouraging a face full of flame.

If available at design time pick your best safe available options. The preference is to try and make all parts of the system as safe as practical, not just believe that the safeties built in address every possibility. My argument would be injecting the gas upstream of the elbow is a less safe approach, don’t do it.

Agreed, if the elbow is further back from the tip. I was picturing the elbow being right at the tip, though- pipe, elbow, close nipple, retention tip. That's how I've always seen it done.

[jrgpots]

2 hours ago, neilestrick said:

Agreed, if the elbow is further back from the tip. I was picturing the elbow being right at the tip, though- pipe, elbow, close nipple, retention tip. That's how I've always seen it done.

1.  The elbow will be at the ens followed by close nipple and retention  tip.

2. I have a honeywell selanoid gas valve at the back of the gas line before the T to each burner.  It is closed when not powered.  It is part of my high limit loop.  If the power goes out, it closes.  It also closes when high temp limit is reached.   The sensor for this loop will be my lower kiln  thermocoupler.  Does that sound reasonable?

3.  I will redesign the gas nipple to give better air flow around it.  When tested the flame was about 18 to 20 inches in length,  but not a lot of blue. So I think I need to inprove air flow.    I have only used propane for my forges and ealier conversion kiln.  Is natural gas a more "lazy"  flame, because my burners did not have the dragon's breath I am used to seeing with propane?

[Bill Kielb]

1 hour ago, jrgpots said:

have only used propane for my forges and ealier conversion kiln.  Is natural gas a more "lazy"  flame, because my burners did not have the dragon's breath I am used to seeing with propane?

Natural gas can be very blue, propane is hard to make blue. Post a picture of the burner flame outside and inside. Curious. And yes that fit up is likely too restrictive