From napkins to fabrication VFT boiler design

[Spanky]

It's totally OK, The information on the last couple pages was helpful to a few of us it seems.

Let me state this now so that you can all descend on me like wolves when I try to change my mind... I've decided to just go ahead right away and run a condensing system, and I'm going to fire oil. I woke up today and decided to condense and fire oil because condensing is more efficient and it sounds like having a hot well and automatic water level control is wonderful to have, and I would like a clean boat and firing coal certainly wouldn't permit that. For my firebox I was thinking a 10" section of the same pipe I used for my boiler with the "fire pipe" (again not sure what this is called, please chime in with the proper terminology whenever I botch something up) going in tangentially like the normal style.

This weekend I'd like to buy my tube sheets, they'll be 3/8" thick just like the shell. What kind of plate should I get?

[mtnman]

What kind of plate should I get?

I think 1/2" is prudent for tube sheets.

[fredrosse]

The fire pot has to be either 1. Water cooled, 2. Refractory Lined, or 3. Stainless Steel. An ordinary steel piece will be destroyed by a heavy fire in short order (I learned this the hard way). On the Margaret S. I used a heavy stainless steel commercial kitchen pot (15 inch diameter), with a stainless steel tangential inlet pipe (4 inch diameter) welded to it for the burner. That worked OK, but the high pressure propane weed burner made too much noise. I am now changing that out, as I am installing low pressure cast iron burners, the silent type from a home heating boiler.

[fredrosse]

The plate for the tubesheet should be one of the following low carbon steels: SA285 Plate, Grade A or B or C, or SA516 Plate Grade 60 or 65 or 70. Other steels are acceptable, but these would be expensive and not required for the temperatures you will encounter. I prefer the 285 plate, but 516 is easier to find these days. I bought plate from "Steel Plate Products" 80 Cromby Rd, Phoenixville PA 19460. Tele 610 935 9550. They have reasonable prices, and will fill (and ship) small orders. I would recommend you insist on domestic produced (USA) plate, I have missed specifying this, and gotten plate made in Russia, it was definately lower quality than I see with domestic plate.

Ordinary structural low carbon steel plate is not permitted according to the ASME Boiler Code.

The 3/8 inch thick plate you are planning is plenty thick enough for your application, as the tubes will act as stays. Remember the full penetration welding from previous posts on this thread.

[artemis]

The fire pot has to be either 1. Water cooled, 2. Refractory Lined, or 3. Stainless Steel. An ordinary steel piece will be destroyed by a heavy fire in short order (I learned this the hard way). On the Margaret S. I used a heavy stainless steel commercial kitchen pot (15 inch diameter), with a stainless steel tangential inlet pipe (4 inch diameter) welded to it for the burner. That worked OK, but the high pressure propane weed burner made too much noise. I am now changing that out, as I am installing low pressure cast iron burners, the silent type from a home heating boiler.

Before spending a lot of time "doing it yourself" I suggest you go to http://www.bayouclassicdepot.com/kab4_banjo_burner.htm. Their burners can put out up to 210,000BTU in a burner ring that is about 10" diameter. Before you order, give them a call -- they'll set you up with everything you need (just the ring, etc.) and also advise you of the correct burner orifice size, depending on the quantity and pressure of the gas you're going to use.

[fredrosse]

I bought the bayouclassic 210,000 BTU unit in a burner ring that is about 10" diameter. There is no way that burner can get up to 210,000 BTU, or even half that amount on Propane. I got all their stuff, but when I tested the burner it would only go up to about 50,000 BTU before blowing off all the flames from the surface of the burner. Empty claims from many vendors are common in this arena.

The maximun heat duty from a low pressure (silent type pre-mix) asperating burner is about 330 BTU per hour per burner surface hole, and the maximum hole size for propane is about 1/8 inch diameter. Larger holes invite "flashback".

The WOK burner I also bought for experimentation (picture attached, with several of the individual burner heads removed), and this burner could be pushed to 200,000 BTU per hour with high pressure gas in the configuration shown. However individual burner jets would not keep and hold their flame above about 1700 BTU per hour each. This burner made too much noise for me, and I'm nearly deaf already.

[RogerV]

Has anyone looked into this type of gas burner: http://aquaticglassel.com/Propane-Burners.html My initial concern is that this type of burner is mostly for "looks." Stainless steel burners also come in "H" and "U" configurations, but again I don't know how many BTU's they put out.

[Lopez Mike]

From my experience with flames in general, I suspect that the more you try to get a lot of heat transfer in a small place, the more turbulence it takes. And turbulence is noisy whether in the mixing stages of a burner or the flame itself. There are some neat tricks that jet engine designers employ such as surrounding the exhaust of an engine with a cone of cool air but for our purposes, I think that it may not be at all easy or even possible to get a quiet and powerful flame in a small place.

My shop heater has a rated input of around 150K and the burner is quiet but the flame area is about two feet on a side! In addition I have to use a two stage regulation scheme to keep the frost under control. My foundry can be forced to a million BTU but the noise alarms the neighbors and terrifies the cat. They have always suspected me of building a jet airplane over here anyway.

Suddenly I'm more content with my simple wood fire and natural draft. An occasional snap and crackle, though I may have to tow a dingy full of wood to travel far! Barbara has forbidden me to attempt a steam powered chain saw for harvesting drift wood. Sigh.

I suspect that Fred's trick of buying a weed burner and aiming it in at a tangent is still the easiest way to make it work. I suppose you could even put two side by side if more heat was needed.

[fredrosse]

I agree with Mike, high heat flux in a small furnace requires turbulence. The domestic burners I am using will put out a little more than 100,000 BTU/hr, in a 14 inch x 14 inch space, and that is about the limit without high turbulence. The weed burner could put out much more heat, but needed high pressure propane, and made plenty of noise.

[artemis]

I bought the bayouclassic 210,000 BTU unit in a burner ring that is about 10" diameter. There is no way that burner can get up to 210,000 BTU, or even half that amount on Propane. I got all their stuff, but when I tested the burner it would only go up to about 50,000 BTU before blowing off all the flames from the surface of the burner. Empty claims from many vendors are common in this arena...

Put one together for a friend (not a steamboater) a couple of years back:
1. Different orifice size (much larger);
2. 3/8" diameter hose (it's normally 1/4");
3. Two stage pressure reducing valve - first is set at max of 20 psi, second is adjustible, pressure gage immediately after adjustible.

If you follow the instruction adjusting the air supply, etc. you should have no problems. Depending on the quantity snd pressure you'll probably need at large tank or it will "ice up".