Wood gasifier stoves

[woodrascal]

Is that the only benefit?

[Donkey]

Umm.. Yes.

[woodrascal]

Thanks for the reply Donkey. That's what I was hoping! I'd much rather have a rugged, well designed rocket driving my heating system that I can build and service myself, than some complicated (and very expensive...)gasifier boiler that has a number of electronic parts that often have a tendancy to break down just when the thermometer drops off the scale!

[Donkey]

If you plan to use a hot water boiler type system to heat your home with, you might want to re-think that a little. Much of the complication of a gasifier-boiler is about safety. You can not meter the heat coming from a solid fuel (rocket stove), if temperatures get dangerously high, there's no easy "off switch".
So, I suppose that is another advantage of gasifiers, you are dealing with wood-gas, that can be piped around and burned separate from the pyrolization of the wood itself. Piped around and/or valved off, so now it can be metered like propane.

Sorry, my bad in not realizing the full scope of your question.

[Donkey]

I COMPLETELY agree with the sentiment. I would MUCH rather have a solid system that I know intimately and can fuel and fix myself.
I just gotta warn people about the hot water thing.. It's no joke.

[woodrascal]

Thanks again Donkey. I'm aware of the potential bomb thing. We already run our DHW and partial central heating circuit (all water based) with our woodfired cooker that has a 23,000 BTU boiler built in. It is an open vented system so if any pump/thermostat/valve fails any pressurised or boiling water spills safely into a metallic F & E tank.

My plan for a rocket heater for the water system (at the moment, anyway...!)would involve a bell shaped boiler which would charge a large-ish super insulated thermal store. All domestic hot water would be taken via a coil in the store tank. The thermal store will have multi coil inputs that could in the future use solar, pv powered immersion or other stove heat inputs. One thing I'm still thinking through is the possible problem of 'flash steam' being created from the intense heat of a rocket riser. I'll probably start another thread asking for advice on this particular project.

[Donkey]

Don't wrap the riser.. Wait till just after the barrel, or build a heat transfer bell/chamber.
Riser temps are crazy hot in a tiny space, that intense heat can be spread over a larger area and it's intensity diffused, bells can be tuned to hold a given heat range.

[talltuk]

Wood rascal, my answer to this is going to be to use an old oil boiler heat exchanger as they are usually cast or steel and can take a heck of a lot of thermal shock, have large water jackets plus have large flue ways through the baffles to keep up draught. I am guessing that a standard oil burner puts out similar heat to a rocket at the bottom of the barrel. I am also going to use a thermal store with an overheat pump to dump into a large thermal mass (earth berm) though this could also be done with a pipe stat valve and thermo siphoning I think. I hope to have all my heat transfer running on thermo sypon with pumps for backup

[talltuk]

Donkey, what is your DHW setup like? I have heard you memtion it but haven't seen any details

[woodrascal]

Nov 8, 2013 20:39:11 GMT -8 Donkey said:

Don't wrap the riser.. Wait till just after the barrel, or build a heat transfer bell/chamber.

I was thinking of building a boiler that effectively takes the place of the barrel in a normal RMH - so that wouldn't work?

I've got a friend who does development work for NASA and the MOD who has experience of using a metal (can't remember the name) that can take huge thermal shock and still survive. Originally I was thinking of a stainless steel 'Barrel boiler' but he reckons that stainless doesn't like temps over 1000 degrees C that can occur at the rocket riser outlet.

How would you arrange your suggested heat transfer bell/chamber to get heat into the water?

Thanks again for the comments and any further help.

[Donkey]

Your idea would work VERY well. It will become a potential bomb VERY effectively.

You don't really need an exotic material and I don't really see a problem with the stainless. As long as the jacket is filled with liquid water, it's temperature CAN'T rise above that of the water itself.

There is a system that I've seen that I can now recommend. One that is effective, (relatively) efficient and safe. I have mentioned it on other threads, I'll re-play here 'cause I think it's a real winner and can think of some ways to make it better..

I'll come back in a bit and write it up, for now I got things to do elsewhere.

[woodrascal]

Thanks Donkey - really appreciate your help and advice with this.

Cheers from the wilds of Wales, UK!

[woodrascal]

Nov 9, 2013 16:31:24 GMT -8 talltuk said:

Wood rascal, my answer to this is going to be to use an old oil boiler heat exchanger as they are usually cast or steel and can take a heck of a lot of thermal shock, have large water jackets plus have large flue ways through the baffles to keep up draught. I am guessing that a standard oil burner puts out similar heat to a rocket at the bottom of the barrel. I am also going to use a thermal store with an overheat pump to dump into a large thermal mass (earth berm) though this could also be done with a pipe stat valve and thermo siphoning I think. I hope to have all my heat transfer running on thermo sypon with pumps for backup

I tried a rough mock-up of this type of setup using an old oil boiler a friend was throwing out. In our open garage I made a 'pocket rocket' from cans and placed the oil boiler so the riser exhaust fed via a 45 degree bend into where the burn tube of the original oil boiler was located. I hooked up the boiler cold water feed to a metal bucket and piped the hot outlet from the boiler to an old radiator. Within around 5 minutes from lightup using thin dry kindling the radiator was warm and after 30 minutes or so very hot water was jetting out of the system.

[woodrascal]

This is the sort of thing I have in mind - It's only a rough drawing and not to scale or full of detail. Please bear with me, it's the first time I've ever used sketch up!

Rocket boiler 111113.skb (167.77 KB)
The sliding flue diverter at the top of the boiler is an idea to help the rocket draft better on light up and also allow the heat from the riser to be a bit 'gentler' to the cold water in the boiler for the first few minutes of firing.

[ronyon]

I have been thinking about how I might make a biochar making rocket stove.
I came back to the idea of using a conventional oven. The heat riser would be inside, and it would have ports to allow wood gasses in. The biochar to be would be stacked around the riser, and the oven door would be shut.
The firebox would be under the oven.
A double oven could be used, with the top oven used as a bell. Inside of that one might use a 5 gallon metal bucket as the unpressurized water envelop for a pressurized coil,but both the bell and the envelop/coil seem smallish...