Wood gasification with exhaust gasses.

[spedley]

Hi, this is my first post so sorry for jumping straight in but I was looking for a forum that seemed knowledgeable and active and this is where I ended up!

I'm in the beginnings of planning a wood heater to heat my smallish swimming pool (9000 litre).  I've been looking at a rocket heater and it seems the most appropriate design because of efficiency and ease of construction.
During my analysis I have come to the conclusion that the biggest bottle neck in terms of power output is the rate of fuel consumption.  This is limited by the [usually] cold air drawn past the burning wood and into the system.  I believe this is where much of the efficiency comes from - forcing the wood to smoke and then burning it at high temperature further up the chimney.

My eventual conclusion is that power output can be massively increased if some of the extremely hot - and oxygen free - exhaust gases can be diverted back into the wood chamber causing the wood to rapidly gasify and feed-back into the combustion chimney.  Obviously this would require a separate air intake into the chimney to make it work and to allow the now potentially dangerous wood chamber to be sealed to prevent exhaust gases leaking back through the fuel feed.

It is this point where I am thinking how to add new fuel to the fire that I realise this has probably already been done and I just need the name of it too Google for my answers! :-)

So, can anyone point me in the right direction - what is the name of this type of heater?

[Daryl]

The standard downdraft pulls all of the gases back through the coals, which would alleviate the need for recirculation. There are also gasifiers, including masonry stoves and rockets with two chambers for combustion. I don't think I have seen a stove similar to what you are describing.

By the way, welcome.

A random thought that bounces through my head...I've always wondered about the back wall of the riser. Seems like an awful lot of wasted heat there.

[spedley]

I resolved the issue of adding new fuel to the stove - I don't need to. The stove has a purpose which is to heat 9 tons of water by 20 degrees centigrade. My calculations indicate this should take roughly 20Kg of wood which means I can design it to fit 20Kg+ in the firebox and it should not need refueling!

I've got a plan for my first test. Unfortunately it is a bit of a dodgy diagram but it will remind me of the details when I come to test it. The general outline is it is made of a drum with two internal tubes - one an air intake and the other the combustion chamber/chimney.
To prime it the air intake tube is pushed up allowing air in the bottom of the stove and acts as a conventional rocket stove.
When up to temperature the fuelbox is closed/sealed and the air tube is pulled down which closes the bottom air intake. This also pulls the upper air intake (the top of the tube) down to align near the fuelbox top-holes. My hope is that the increase in pressure from combustions will force some hot air into the fuelbox and gassify the wood forcing it out the bottom air holes and back into the main combustion-chamber/chimney. It should also allow me a bit of control.

Hopefully I can find a parts for a small scale experiment over the weekend.

[mkrepel]

Sorry for the late post, but I couldn't resist.

Did you end up building something? How did it work? If you need 20 KG of wood, maybe you could feed your needs with a batch box rocket. That is a little larger than most of these will hold in one load, but you could load it twice. That should get the required heat where you need it. This would afford you the advantage of not needing to constantly tend the stove and reloading wood for several hours while you deposit the requisite heat. Take a look at the experiments that have been done by Peterberg and others concerning this technology.