Coalpail.com Forum

Hi guys Ive just found this site and have a lot to learn.
I have a fish farm in South Africa and need to heat the water for about 4 months a year.

Im currently using a home made donkey boiler, made out of a locally built rocket boiler. The rocket boiler is basically a 300 litre drum with a small firebox at the bottom and a 160 mm pipe through the center as a chimney.
It was hugely in efficient, all the heat went straight up, fine for heating water for a shower, but not much more.

I've turned the rocket on its side, and turned it into a donkey boiler running on coal nuts as they are cheaper and easier than wood here.
Im getting fires hot enough to bend the 25 x 5mm angle iron I used as a grate, but not a huge amount of heat in the water. I pump about 3000 liters an hour through the system and get a 5 + degree C temp difference

I need to rebuild the boiler, to replace the grate and make it more efficient. Im thinking of copying this firebox / grate design Downdraft Stove Concept

To get more heat into the water Im thinking of adding back and forth loops of 25mm x 4mm seamless pipe between the fire and the boiler drum, the water will go through this first, then into the drum.

Is it worth putting loops of water pipes under the fire grate, up the back wall and up to the top or will this cool the fire box too much?

The system is open ended so if the pump breaks and the water boils it can either flow into the fish farm, or vent through a stand pipe so Im not worried about steam, but am very cautious of it.

I'd really like to make a down draft boiler, but thats going to have to wait for next winter, my ideal would be something that can put out about 100kw worth of heat!

If anyone has links to a good bunch of plans or ideas please let me know.

Horizontal fire tube boiler will provide the most heat exchange surface.
Scotch marine type design.

Had to look that up Franco.....great information available.

Kevin

HI Franco,
A fire tube is what Im building for stage 2, we use them a lot here for tobacco curing etc. Very expensive to buy though and need clean water so Im going to build a heavy duty version so I can go direct instead of using a heat exchanger.
Even getting small blowers like the Daytons arent imported here so it makes the design a touch more tricky!

If you might source heavy steel reinforcing rod used in concrete pours. they can out perform your angle irons..look for number 5 or larger...numbers equal 1/8inch...so a no. 5 = 5/8 in....metric, IDK
Number 8 would not be too large and very heavy duty.

Ok, so winters on the way back down here.
I've had a couple of quotes for a proper fire tube boiler, all over $ 10K which is out of my budget, but hopefully next year when sales pick up.
Steel prices have doubles this year alone, politics.....

I have a couple of sheets of pretty thin steel, 2mm thickness in the shed that Im going to use.
Ive seen a couple of boilers that use water filled baffles (not sure of the correct terminology" so Im going to try and copy one. and make a heater to last for the next few months.
In the pic you can kind of see, the water flows through the grey areas and the hot air / smoke goes over and under the baffles. I'll make a grate and fire box like Berlin made here Coal/Wood Stove Plans

My main question is, is having the air flowing over 4 baffles too much?

The baffles will be 800mm high, about 32 inches. The water channels will be about 1" and the air channel about 2"
the whole box is 20" wide
Then I have a 3 meter long chimney about 200mm in diameter

any thoughts?
thanks

Ryan

With so many reversals draft will be a problem.

Franco thats what worries me, Maybe I should go taller with only the 1st 2 baffles, No3 becomes the back wall?

Taller is good for a stronger draft. Remember also to provide access for cleaning all surfaces.