Stove Pipe Motor

[Wallybear]

I came up with a new idea today while I was thinking about the wasted energy going out the stove pipe and into the wild blue yonder.

So, what if I took a piece of ceramic pipe and installed a 12 v. generator in the pipe in such a way that the hot exhaust from a wood burning stove wood spin fan blades and generate electricity.

You could then install this motor towards the top of the stove pipe to generate electricity. It would just be a matter of installing a short section of pipe and plugging it into the provided battery bank. It could be used to charge the battery bank that is for emergency 12 v. lights or hooks to an inverter and you could run 110v for a limited time. Also used for charging cell phones and laptops in an emergency.

I do not know because, this is all talk right now, but it is possible that it could run a series of 12 v. LED lights for a small cabin.

A system like this would be good in the northern regions where a wood stove is used 5 months of the year or more. You could also mix it with a solar panel too.

These are all just thoughts running through my head, but if it seems like a good idea to others as well I might build a prototype after I heal up from surgery.

So what do you guys think? If a system could retail for under a $1000 and keep a couple of deep cycle marine batteries charged, would that be interesting?

 

[Wallybear]

Another idea to go along with this one.

A cap vent fan hooked to a 12v. generator at the top of a 12" black steel pipe standing 40' in the air. plumbed into the bottom of this pipe is 8- 4" steel pipes buried 5' in the ground and extending out to the outer edges of the property where the pipes come up out of the ground about 18". Each 4" pipe is capped with a rain cap and screened to keep out water and debris, but allow air flow.

The idea would be to draw in and cool down the ambient air as much as possible and then heat that air as it hits the large black pipe which works as a heat chamber. The rising air would push out the top spinning the fan and generating 12v. power. The added benefit to this cap fan would be that if there was any wind, it would also spin the fan to generate electricity. This could be a good system where the weather is warm but maybe there is not enough wind to justify a wind turbine.

 

[SKR8PN]

Not enough flow out of the pipe to turn the generator fan fast enough to generate anything. Think Turbocharger. They require substantial flow to even get started making any pressure, like over 100,000 RPM's. Then you have to worry about the little things such as friction losses in the bearings,heat containment and loss, and back pressure in the stove pipe causing fumes in the structure. etc.....

 

[patandchickens]

I would wonder how fast it'd get gummed up with creosote, both "and then stop working" and also "and someday catch fire".

You could avoid that by having it in a parallel or jacketing pipe I suppose, but then of course you get far less than 100% heat transfer.

The main issue I think would be finding a turbine (or whatever) that works extremely efficiently and on low airflow. The low airflow thing would be CRUCIAL for your second concept in particular. The extreme majority of turbine-style generators do not work well when turning sllloooowwwwlllly but I believe some designs do exist that are at least *somewhat* better-adapted to those conditions, at least in mid-scale outdoor wind turbine designs. So I suppose you could look into it.

I think you are likely to run into the abovementioned physics problems though, so be prepared for frustration.

Another way to strip as some reclaimable energy from flues is to increase their ability to transfer heat to the house, either by snaking them thru more of the house so there is more *length* of indoor flue to transfer heat, or by heat-exchange jacket-or-parallel-pipe type systems. The former is a very old-timey thing to do, the latter I have only read speculative discussion of. Both of them (I think -- certainly the former one) have the disadvantage that the more you cool the gases in the flue, the more creosote you get, and the more cleaning you need to do if you want to not burn down some night.

Pat

 

[k0xxx]

Skr8pn is correct (IMHO). The problems of low flow, back pressure, creosote, etc., would make this not very workable.

A more workable idea, although cost prohibitive, would be to coil tubing around the flue pipe, Then use the heat to vaporize a liquid for running a turbine, then condense it back to liquid and start the process again. I read a bout a similar setup (using alcohol I believe) about thirty years ago that was used in an industrial setting.

Using the flue to heat water, before it goes to your water heater, may be a more feasible idea.

 

[Wallybear]

The air movement is not a problem. There is more than enough to turn a light generator. The creosote on the other hand is an issue. Not so much for the bearings but for collecting on the blades and having to take it down and clean it all the time. This is especially true for people who do not operate their wood stoves right or burn less than optimal wood.

The heat exchanger idea is still viable and seams the better of the two ideas. Motors (generators) can be built to accommodate the input energy. This would be more like a trickle charger than a main generator to keep a battery bank charged for emergencies or for light LED use at night.

 

[k15n1]

If you can add the generator and it doesn't give you draft problems, I would be surprised.

Anyway, if you want to make your stove more efficient, look into the design factors of masonry stoves. It is possible to get over 90% thermal efficiency without much effort. Unless you really need electricity, I'd skip the fan and put a kink in the stove pipe.

http://www.nlc.state.ne.us/epubs/E5700/T011-1982.pdf

http://oktradingco.com/archive/1980-11-01/67550.htm