Copper tubes in a vertical fire tube boiler

[froya66]

Hi fellow steamboaters

I am trying to design a VFT boiler for Frøya, maximising the effective heat area within the PED limit product of 200 Bar x l.

With a minimum acceptable distance between the fire tubes of 10 mm, I have so far calculated an effective heat area of approx 0.8 m2 (The SBA VFT 100 has 1.3 m2, but a product number of 400 Bar x l.

The question of combining copper and steel has often been discussed, but despite the fact that someone talks against it, at least some of the SBA designs make use of it.

So far I have not been able to find any reference to relevant material standard for copper tubing in boilers.

Any suggestions?

What would I get if I ordered a boiler with copper tubing by a UK boiler supplier?

Best regards
Jørgen Hansen

[fredrosse]

What pressure are you going to use? Bar Gauge Pressure.

[steamboatjack]

Jorgen,

Have a talk with TRS boilers at www.TRS-welding.co.uk for the spec. I have had boilers with copper tubes in steel tube plates with no problems. You do have to keep the water in good condition, keeping the pH up and the oxygen out but you should do this with any boiler. Plus of course the three rules..... blowdown,blowdown,blowdown.
Also have you considered "Cunifer" (copper,nickel,iron) now used in the Water tube designs of John King.
Regards Jack

[froya66]

Hi Fred and Jack

The pressent boiler has an effective heat area of only 0,3 m2.

When I go puffing it makes steam enough for approx 4,5 knots at approx 7,5 Bar G.

When the pressure rises abowe 8 Bar G I turn of the puffing.

In order to stay below the product number 200 bar x l at the new boiler I have to let the safety valve blow at 9 Bar G.

Hopefully the new boiler can make steam enough without puffing, and in that case I will try to lower the gearing between engine and propeller to decrease the pressure a litle.

I know Terry from Klaus Buldt to whome he made a VFT 101.

Last week I sent Terry a mail asking for the price for a VFT100. As the boat is very small and the space is limited I also asked if he had a design for a smaller boiler (between 0,8 and 1 m2) I got no answer so far.

Best regards
Jørgen

[fredrosse]

Some dimensions for your boiler
Is this in the range you are considering?

9 BARG 130.527 PSIG
22.2 1.0 31.8 Tube OD, Wall, Pitch, mm
304.8 9.5 Shell OD, Wall, mm
438.26 438.26 SHELLSIDE LENGTH, mm
Config A first row of tubes, tube center is alligned with vertical shell centerline
Config B first row of tubes, tube centers straddle vertical shell centerline
55 48 Number of Tubes
169 180 PED: BARg * liters shellside
1.60 1.39 EFFECTIVE TUBE INSIDE SURFACE AREA, M2

[froya66]

Fred

Thank you for your suggestion.

Actually I was considering a wet leg VFT like the SBA designs.

I have calculated for an outer shell OD 324 x 6,3 and a firebox OD 272 x 8. With fire tube OD 20 x 1,5 I can only have 55 tubes due to the small diameter of the lower tube plate.

Shell height 580, firebox height 270, distance from water level to top tube plate 100, grate thickness 20.

This gives 0,78 m2 effective heat surface and PED 195 bar x l at 9 bar G

Your calculation highlight the fact that you can get more tubes into the pressure part of a dry leg VFT.

May be I should reconsider. A dry leg is also much simpler to fabricate.

Best regards
Jørgen

[Gudmund]

Jorgen,

You can see my boiler working in a couple of weeks. It has copper tubes and a wet leg. It is a bit bigger than you will need as it seems to be perfectly matched to my stuart 6A.

Gudmund

[froya66]

Hi Gudmund

Hopefully that is all the wet legs we get in Silkeborg

I have planed to interview you detailed about how the SBA boiler inspection system works, so be prepared!

I would be very happy if you could bring copies of whatever certificate you got, for my information.

Best regards
Jørgen

[VANYA]

Hello Jorgen,

In your boiler design for your steamboat did you build the designed VFT 100 or VFT 101 boiler or a modification of it?

I would be interested to know if this size boiler would run a Stuart # 1 single cylinder engine.

Hayden



Actually I was considering a wet leg VFT like the SBA designs.

I have calculated for an outer shell OD 324 x 6,3 and a firebox OD 272 x 8. With fire tube OD 20 x 1,5 I can only have 55 tubes due to the small diameter of the lower tube plate.

Shell height 580, firebox height 270, distance from water level to top tube plate 100, grate thickness 20.

This gives 0,78 m2 effective heat surface and PED 195 bar x l at 9 bar G