Rocket Stove Food Dehydrator

Off Topic
#1

We’ve been making and selling a lot of beef jerky lately… And the 9-tray Excalibur is eating up 600W/hr. Plus, it’s not big enough. I need 10 X the size… The commercial units are expensive and are electrical energy hogs.

Going to try to DIY this…

The idea is that a tall chimney produces a strong upward draft due to the stack effect. What if the rocket stove was made with 4" pipe—small by rocket standards—and I rob the heat off the long chimney with another pipe?

Actually, there is another pipe, sort of a pipe, in a pipe, in a pipe… But i am getting ahead of myself.

Aluminum pot scrubbers, between the chimney and middle pipe would help greatly with pulling heat off the rocket chimney via conduction with a highly conductive metal. And the heat off the pot scrubbers would be captured with forced air from a shop vac.

After a few feet of vertical run, the middle pipe makes an abrupt left turn into the top of the food dehydrator. A baffle plate would ensure equal heat and equal air from the top. 48 stainless steel mesh, 3’ x 3’ drying trays later, and another baffle plate at the bottom, would prevent any heat/air “worm holing.”

The cooler, moister air at the bottom takes a right turn out, and becomes the outer pipe, and final chimney. This would be made with cheap ducting. The bottom leg is for condensation drip, but the remaining ambient heat off the middle pipe and the stack effect make sure the heat goes up and away.

I can get all the heat I need from the rocket stove, or TLUD stove, or generator exhaust pipe—choose your waste heat recapture source—and with an 800W shop vac (filtered air) in blower mode, I can feasibly run the dehydrator all day for about the same electrical cost as i am with a 9-tray Excalibur.

If this rising beef jerky demand continues, I’ll need to run it all day.

Also, this is the same general design as the natural draft solar dehydrators—which could still be run on this unit. This concept comes with some added heat (day or night), and some forced air… Fruits and veggies could be done with solar, but meat needs more heat and more air flow.

Here is my initial idea.

rocket-stove dehydrator.jpg1176×1408 174 KB

5 Likes
#2

Nice idea. The only thing I don’t like about it is the screaming shop vac motor all day. Any way a brush-less motor fan will work?

3 Likes
#3

I have been using a PWM on a small vacuum in blower mode for over 2 years (1000 hrs) for my waste oil heated hot tub.
Dialed down to about 1/4 speed it just makes a low buzzing sound.
Still going strong and you can dial it up for use in cleanup mode

2 Likes
#4

Hey troy good to see you back. Any reason why it has to be a rocket? Why not a tlud of some sort? Both burn clean but the larger reservoir on the tlud might make it less labour intensive. I know you’ve moved on from charcoal but at that scale you would have a great use for all that waste heat. Who is buying all the jerky anyways and how did that come about? Sounds like an interesting story.
Best regards, David Baillie

3 Likes
#5

Yeah keep the stack idea but also force air your burn chamber forget the draft. Build it out of as much aluminum as you can to get all the heat you possibly can. Or do like David suggested and build a charcoal or wood gasifier and drive them with forced air. Id go with a wood gasifier without any filtering. Just build a simple wood gasifier even a fema unit, feed it into your stack like you are planning and light it. If you get your air mixture right it will flare like a torch getting your temps up much hotter. Aluminum might not work for the core tube but aluminum will try to shed heat faster than it can absorb it.

2 Likes
#6

Troy,
Temperature control is very important. The Excalibur is the best dehydrator we have used, and the only one in our collection that will do Jerky. The large fan in the Excalibur blows air horizontally over each tray, which is much better than the cheapie round dehydrators that have a fan at the bottom blowing upwards. For a temperature setting of 155 F, the meat being dehydrated might eventually reach the USDA recommended temperature of 160 F. The USDA now recommends cooking or steaming the meat to 160 first, then putting it in the dehydrator. (As the meat dries, it actually is cooler than the air flowing over it.)
So, now that we have determined that a constant temperature is required, what type of stove will provide this controlled even temperature, with or without solar assist? I tend to agree with the choice of the Rocket Stove, although that is going to need constant attention shoving little sticks into the fuel hole, and relieving the constipating ash that quickly accumulates. A TLUD might not be able to be controlled to provide a constant thermal output, and many multiple fuel cannisters would need to be swapped out. Thermal mass might be able to help. I use about a hundred pounds of cast iron in my solar concentrator in an attempt to help even out temperature variations due to passing clouds.
Repeating myself, Temperature control…Temperature control… I’m looking forward to seeing what your solution might be. (Hooking up a half dozen grid-tied solar panels?)

6 Likes
#7

Ray, good points… Because the temperature control is the biggest challenge in this design, I think this concept needs some refactoring. I think i am going to lose the cold air intake valve—because that also affects air flow and velocity, and I’d like to keep that independent of temp control—and instead, introduce a 3-way ball valve on the shop vac.

The idea being that the forced air travels two paths: 1) up through the aluminum scrubber pads, and 2) outside and independent of any heating. So, essentially, the forced air “Y’s off” and converges just before entry into the dehydrator rack system. That way, by adjusting the 3-way ball valve, you are controlling the percentages of air that is being heated, and the percentage that is not…

If you add a PWM, like Micheal is doing, you can also control the air flow as well…

I suspect that—much like a gasifier air/carb mix valve—you will find a position on the handle of the valve that will be the “sweet spot,” and temperatures will remain fairly constant. This is of course if you master the feeding rate of the rocket stove.

The only real control would come with an Arduino and a servo motor on the 3-way valve, just like the air/carb auto-mixers we see in the gasifier community. Input data would come from the incoming air temperature sensor, and would be constantly taking temperature readings, sending that data to the arduino, and adjusting accordingly.

With this modification, the user could control the air flow with a PWM, and the temperature with a manual or automatic valve.

Open to any other ideas that will make this thing better.

1 Like
#8

David, the jerky business came from my wife making a batch and sharing with neighbors. They all said, “you need to sell this!” So we made some more and shared with local store owners down here in Mexico. Many of them wanted to sell it. And so it began…

I’ve been thinking about a TLUD configuration on this thing, and the only configuration that works (in my mind) would be more of like Gary’s “Keystone TLUD,” where the chimney is off the back of the thing… Doable with a tall thin TLUD too, but I don’t have any experience/confidence with that…

My second favorite would be to modify the tail pipe of a generator to run up the middle of that chimney. The generator would be running on charcoal, the generator would be powering the shop vac, and the exhuast pipe would be providing the heat. That seems pretty nifty to me :slight_smile:

2 Likes
#9

Matt, waste heat from a gasifier is an excellent idea too… Same with exhaust pipe or TLUD… Any waste heat candidate makes sense…

The chimney stack is where the heat exchange happens in this design, and also allows for the optional solar collector hook-up, which is attractive to a lot of off-gridders… But yeah, forced air makes it unnecessary.

The rocket stove seemed so simple on this first iteration… twigs, branches, scraps from the wood shop… Appealing to the rocket stove and rocket mass heater folks.

Of course, now I’m thinking about “fire and forget” configurations, where the fuel is gravity fed into the burn chamber. Baby sitting a rocket stove feed tube is not what I had in mind… The smoking community had some neat ideas on a gravity feeder…

2 Likes
#10

I think at this level you could achieve the same results in simplified gasifier where fuel processing would not need to be so labor intensive. But my first idea of a fema would not work, the lid would need to be sealed in order to force air the the system. But the gasifier could still be be very simple in design. Not sure but you probably could get away with a very large restriction allowing it to flow much more freely than our engine grade systems.

Yeah Ive only built the one style rocket stove and constant monitoring was a requirement along with a constant manual feeding into it. I think a simple gasifier with a secondary air after burn built into your stack with the controls you are contemplating would be more reliable and a neat little system.

3 Likes
#11

Troy, I have been thinking about this a little and as noted, temperature control is critical. One option is using passive solar to heat the dehydrator. This will require a fan (could be PV powered) , a vent and a temperature control. When too hot, the control will open the vent, when too cold, well that is a problem with this system,
Another option you are looking at is using biomass combustion for the heat source. First of all the rocket stove will need constant attention. Fun for about a day, Capturing stack heat will work, but like the solar there needs to be some controls to maintain a constant temperature. What about using water as your heat carrier? Use the stove (whatever you want to use to heat it but I like the TLUD idea with charcoal as a by product) Heat say 200 gallons of water to 200F and then use a small circulating pump to push it to a heat exchanger in the dehydrator, Fire up the stove once or twice a day to keep the water hot, and spend the rest of the day rounding up some beef,
Here is a link about the Lakota Sioux entering into the “jerkey” market, Definately one worth looking into,

http://www.resilience.org/stories/2016-08-12/healthy-snack-invented-on-indian-reservation-now-faces-stiff-corporate-competition
Gary in PA

6 Likes
#12

Gary, I think you’re idea of using water (or some liquid like oil) as a thermal mass is dead on…

I need something that will capture and release heat in a slow, stable rate, and then capture the heat off that… This would be a perfect case for the Keystone TLUD. Even though it’s a batch system, the thermal mass (water or oil) won’t change temperature much at all, even if you take your sweet time loading the next bucket.

What a great way to make charcoal! All that woodgas goes toward a practical use. In my case, beef jerky!

I’m re-thinking this whole thing—out of necessity—and will post a new concept drawing soon.

Thanks!

2 Likes
#13

I heat my home with a wood boiler, and with it’s 200 gallons of water at 200 F it will keep heat for a couple days if you are not drawing any. Pretty simple controls keep the house even temp automatically. I’m sure you could use a similar control system for your dryer.
Edit: From stone cold water ( first fire in fall) it takes about 3 hours to get up to temp with a good roaring fire.

3 Likes
#14

Andy
What brand of boiler do you have and are you satisfied with it?
Recommendations?
Thanks

1 Like
#15

Ha Tom, it’s the homemade brand, and yes I’m very happy with it’s performance. especially for the $50 bucks I put into it.

7 Likes
#16

Troy I suppose you could also use sand as a medium sort of like a hahsa heater then metal ducting for exchanging heat. Probably less efficient then a liquid medium and a liquid to air exchanger but a much cheaper build and probably more failure proof.

2 Likes
#17

Nice build Andrew! What length of wood fit in there?

1 Like
#18

D Baily, I hadn’t heard of the hahsa in decades. Are plans for that still available? When I went looking for them a few years back I couldn’t find them.
J O, I can fit sticks almost 4 feet long in there. But I don’t care to manhandle that size. I cut my wood 20 inch range and sometimes put in two stacks.

3 Likes
#19

I have not found any plans if they are out there. What I have heard of is a couple of people who retrofitted their outdoor boilers with sand after the tanks reached end of life.

1 Like
#20

Great post!

My System
I have a Solar Down Draft Dehydrator. I use a pop can wall heater to help solar gain through the summer. The fan is powered by a solar panel. I have multiple fans that help move air through the system. The system works like a charm.

The Challenge!
My challenge is the apple crop! The weather is cooler and the solar dehydrator does not work as well in cool weather. My current goal is to add a wood heat component to the dehydrator.

Air Movement
I like the plan Troy Martz shared. But not the shop vac. I use computer fans which take minimum power and would work just as well off a small battery I could charge with the solar panel.

Heat Sync
Has anyone tried a heat sync with the rocket stove with a dehydator? Most rocket stove plans I have seen have a large mass they heat up. That mass then radiates heat over time. At the moment I am considering adding a 2 foot by 3 foot heat sync base to store the heat. Build a fire in the morning and evening.

Temp Control
I can monitor the temp over time with an Arduino. I already have one that monitors the temp in my pit greenhouse It would not be hard to modify to use with the dehydrator.

1 Like