The Navajo Stove: The Rumors are True...

Navajo Beta Stove - Gasket is Added

Here at the Woodstock Soapstone Company, we have been very busy.  For the past 3-4 months, we have been fervently working on a stove designed for use by Navajo American Indians who live on the Navajo Nation Reservation at the “4 Corners”  (where Colorado, Utah, Arizona, and New Mexico meet).  The first beta stoves were shipped by truck transportation to the Navajo Nation earlier this week, and three of our crew are flying out on Sunday to install the stoves, train operators, and learn more about how the stoves will be used.

The Wood/Coal Challenge:
On the Navajo Reservation, the residents burn wood and coal in their stoves – and not just any coal, but sub-bituminous coal.  The coal is mined on the Navajo American Indian Reservation, and is used for the Navajo Generating Station near Page, Arizona, but is also used for residential heating on the reservation to achieve extended burn times at night.  It is a low-density coal with high water content – and a very high-energy content.

The dual fuel design requires two different airflows – one for wood, and one for coal.  Our design turned out to be a small hybrid wood stove for clean wood burning, and a coal draft system powered by under-fire primary air and lots of secondary combustion.  Needless to say, we are really looking forward to beginning the field-testing of our design.  Beta testing will begin next week in Navajo American Indian homes in Arizona and New Mexico.

Doors are painted, handles are added

Race to Zero Emissions:

This project fits perfectly with our mission to design cleaner and cleaner stoves.  We have always focused on wood, but when the EPA asked us if we could try to design a  dual fuel stove specifically to meet the needs of the Navajo American Indians, it fit right in with our interests, so we jumped at the opportunity.  We expect to learn quite a bit in the  next six weeks of beta testing!

Keep your eyes on our blog, we will be posting more after we are "on the ground" in the Southwest.

R2Z Detour: Introducing Our First Test Stove

As we noted in an earlier post, we are taking a slight detour in our Race to Zero.  We are testing older stoves made in the 1970s and 1980s.  Stoves which were made with little technology to reduce emissions or improve efficiency.

Huntsman Stove - Before the Makeover

Our first test stove is a “Huntsman” (made by Atlanta Stove Works, circa 1977) step stove.  It is a welded steel stove, with a huge firebox (well over 5 cubic feet), and cast iron doors with six draft controls.  The bottom is lined with firebrick, and the side walls are also lined up to 9” in height (one layer of firebrick).  As with many steel stoves of this vintage, the stove itself is almost “overbuilt” (1/4” and 5/16” boiler plate), and as long as the firebricks are replaced periodically, it will last for a few more decades.  

Huntsman Stove - After the makeover

Interestingly, even though the Huntsman stove is physically huge, it weighs almost exactly the same as our new Absolute Steel Hybrid - just over 500 pounds.

Our first goal is to establish a careful baseline profile for these older stoves in terms of heat output, emissions, and efficiency at low, medium, and high burn rates.

Next, we want to see if we can design a retrofit catalyst and heat exchanger that will improve the performance metrics (heat output, emissions, and efficiency) enough to make them competitive with some of the stoves in today’s market.

We have wired the Huntsman in our research department so that we can measure surface and gas (O2, CO2, and CO) temperatures  at multiple locations.  The stove is on a scale, which allows us to measure the rate of fuel consumption.  Finally, we can (and will) get particulate catches for most of the baseline runs using Method 5G3 (the same Method the EPA uses).  We will use the Canadian CSA B415 algorithm for calculating efficiency.  We are trying to run parallel to the same methods and standards used by the EPA.

We are using cordwood for our testing because it is readily available, and is much less expensive than the cribs the EPA has used for emissions testing during the last few decades.

We’re doing our best to keep loads representative in terms of species, weight, and moisture content.  One of the nice things about R&D testing is that we can operate with a certain degree of informality that you can’t do with certification testing.  We are just interested in seeing if we can “move the needle” before we pay attention to all of the fine points of test protocol.

We hope to get baseline data on at least three stoves (one small; one medium; and one large), and we hope to develop mathematical models for different aspects of our testing – an example would be the heat transfer achieved by our device.  More on that in the next week or so.

Obviously, there is an opportunity to reduce emissions in old stoves.  We think there are additional opportunities to extract more heat (both by radiation and convection) around the area where our device would be installed.  Without getting too esoteric, we may be able to point the catalyst directly at the surface(s) we want to use as primary radiators.  Finally, the catalyst should introduce a considerable pressure drop into the system.  This resistance may result in increased stack temperatures around our device, a reduction in stack flow, a lowering of the burn rate, and some improvement in efficiency.  Well - we are hoping to get these results!

The questions are: (1) How much of a reduction in emissions?  (2) How much additional heat extraction?  (3) How much of an improvement in efficiency?  (4) At what cost and what degree of difficulty?

We expect to be busy in the lab with this project for 3 to 4 months, at least. We don’t know if we can succeed with this R2Z Detour, but we think it’s worth making a serious effort.

R2Z Detour: Once There was a Thought...

In the beginning, there was a thought, and that thought grew into an idea, which became a project. And that was good.  We here at Woodstock Soapstone are always creating, tinkering and thinking outside the firebox. 

There are a lot of old woodstoves still in service that predate EPA regulations.   These are hefty stoves, made of cast iron or welded from plate steel and lined with firebrick.  Many are well over 30 years old, and might last another 30 years if the firebricks are periodically replaced and appropriate parts and gaskets maintained.  

Warner Stove

In our race to zero emissions, we thought we would take a side trip, a detour if you like, and look at a situation that is painful to us.  How can we get these old pre-EPA-regulation stoves that are still being used, to burn with more heat and lower emissions? These old stoves are not efficient, or clean burning.  

Warner Stove

Other people have (obviously) thought about this problem. In fact, in 2014, the Puget Sound Clean Air Agency had a retrofit design challenge to encourage development of retrofit pollution reduction devices for woodstoves.

Retrofit stove pipe catalysts have been available since the early 80's, but the concept has never been fully developed.  One of the simplest catalytic retrofits is a catalytic damper that pivots in and out of the exhaust stream (below) in an effort to reduce emissions.

Catalytic Retrofit

Similarly, others have tried to extract more heat from the stovepipe by inserting a heat exchanger downstream of the flue collar.  Some heat exchangers merely relied on convection, while others used a fan.   

Heat Exchanger

 We are in the very early stages of developing a retrofit stovepipe device that would increase efficiency and produce a cleaner burn in older wood stoves. We are eager to use today’s technology and improved materials to create a device that both increases heat output and reduces emissions.

We are in the early stages of getting baseline data for how some of these older stoves actually perform.  We have already started to fiddle around in the lab and some of the early signs are encouraging, though there are some difficult hurdles we will have to get over before we can even think about a commercially viable retrofit solution.

Consistent with our other recent projects, our goal will be a device that is simple, effective, and affordable.

We are considering making the data and development of this project publicly accessible.  Many of our customers are engineers, and we can use all of the thoughtful input we can get.   Again, we are very early in the project, but stayed tuned for the next chapter in this newest adventure here at Woodstock Soapstone.