Intro: This project began when a similar stove was seen at a wilderness camp here in Zambia. Although much larger than the one detailed here, it had two inherent faults:a) the funnel-shaped chimney was not detachable, so fume condensation ran down onto the boiler and it was impossible to rod out the fire tubes without complete disassembly and
b) there was no tank insulation, so the water cooled rapidly after the fire had gone out.
However the concept of fire tubes within the tank appealed to me, as it meant greater efficiency.In this project, a disused 48kg gas cylinder was used, providing some 100 lt water capacity. It required careful purging of gas residue and thorough cleaning.
The fire tubes (approx 35 mm ID) were welded directly to the cylinder walls but it was thought later that it would be better for collets to be welded into the cylinder first, then tubes inserted, so that it might be possible to replace the tubes at a later date (if necessary). Ensure that the diam “X” across the outsides of the tubes is less than 
the inside diam of the rim – else the tubes will be obstructed by it.The fire box consisted of a steel 16” truck rim. The fire door in the 
truck rim was cut out at an angle (see the “cuts” made on the two views of the rim) so that the door resealed effectively when assembled. Hinges needed to be substantial and offset sufficiently so that the door swung clean out of the way for wood loading. A handle (hook/ring) was added to aid opening the door and an AIR/SPY hole drilled (say 10mm diam) near the door top. The rim sat directly on the ground but it may be better resting on a concrete base
.
Pipe connections were ½” but ¾” might be preferable. The upper connection (on the cylinder side) was water outlet (HOT) and the lower was water inlet (COLD). Steel nipples were welded onto the cylinder and water pipe connected to them using copper fittings. The ¾” BSP threaded boss at the top should be connected to an expansion pipe leading steam/excess pressure away to a safe exit. This should be sufficiently higher than the pressure head of the system.
truck rim was cut out at an angle (see the “cuts” made on the two views of the rim) so that the door resealed effectively when assembled. Hinges needed to be substantial and offset sufficiently so that the door swung clean out of the way for wood loading. A handle (hook/ring) was added to aid opening the door and an AIR/SPY hole drilled (say 10mm diam) near the door top. The rim sat directly on the ground but it may be better resting on a concrete base
.Pipe connections were ½” but ¾” might be preferable. The upper connection (on the cylinder side) was water outlet (HOT) and the lower was water inlet (COLD). Steel nipples were welded onto the cylinder and water pipe connected to them using copper fittings. The ¾” BSP threaded boss at the top should be connected to an expansion pipe leading steam/excess pressure away to a safe exit. This should be sufficiently higher than the pressure head of the system.
The Prototype:
The cylinder (perimeter) was wrapped with bubble-wrap as a crude form of insulation. Gaps between the cylinder and the rim were sealed with anthill clay but it was soon discovered that no smoke leaked out at all. (Though the stud holes did need to be welded closed) No funnel or chimney of any sort was placed on top of the cylinder – yet the fire tubes “drew” so well that it was reckoned that a chimney would be unnecessary, unless the smoke required to be led completely away from the site. (Using a chimney may then cause condensation to form and drip down on the cylinder, possibly spoiling the insulation.)
The prototype was fed with 4 Kg of rubbish (rotten) wood and the door closed after lighting the fire. The air hole limited the air intake (may need to be adjusted), allowing the door to be closed completely. This ensured a slight vacuum inside the fire box ensuring a clean environment around the stove. The 100 lts water was heated from ambient 20o C to 80o C in approx 2 hours (when the fire had died).
Heat retention in the cylinder would depend on the quality of insulation used. I would reckon to spray on an expanding foam to a thickness of 2cm.
In practice, a non-return valve would be needed to prevent feedback of the hot water into the cold feed system, unless this boiler fed into an (elevated) hot storage tank.
Cleaning: Apart from the obvious daily clearing out of ash, it will be necessary to clean out the fire tubes of soot/tar deposits. This chimney-less stove would permit the rodding out of the tubes with a steel bar, scraping deposits into the firebox, without need of disassembling the stove.
It is hoped that this design may produce a cheap product of reasonable longevity, with ease of repair and economical wood consumption.
The prototype was fed with 4 Kg of rubbish (rotten) wood and the door closed after lighting the fire. The air hole limited the air intake (may need to be adjusted), allowing the door to be closed completely. This ensured a slight vacuum inside the fire box ensuring a clean environment around the stove. The 100 lts water was heated from ambient 20o C to 80o C in approx 2 hours (when the fire had died).
Heat retention in the cylinder would depend on the quality of insulation used. I would reckon to spray on an expanding foam to a thickness of 2cm.
In practice, a non-return valve would be needed to prevent feedback of the hot water into the cold feed system, unless this boiler fed into an (elevated) hot storage tank.
Cleaning: Apart from the obvious daily clearing out of ash, it will be necessary to clean out the fire tubes of soot/tar deposits. This chimney-less stove would permit the rodding out of the tubes with a steel bar, scraping deposits into the firebox, without need of disassembling the stove.
It is hoped that this design may produce a cheap product of reasonable longevity, with ease of repair and economical wood consumption.
Yours, Dusty.
The earth is the Lord’s and the fullness thereof; the world and they that dwell therein.
Ps 24:1
*****
Ps 24:1
*****
So... how long has the nightly model been running reliably? The acidity eats at the exhaust, but on the whole the system is, I think, an even greater success than at first was ever suspected...
ReplyDelete