Final Report for FNC13-922
My wife and I operate a three-acre residence adapted to keep our three (sometimes four) horses housed, happy, and healthy. We have also raised several ducks as egg-layers, keep a small garden, and tend a few fruit trees. It is by any definition a “small acreage horse farm.”
Whether it's saving every bent nail, setting aside any potentially useful piece of timber, or fixing that which others have long given up on, I continue to pursue a model of sustainability which prior generations knew well. While often driven by economic factors, such dogged frugality also serves to minimize one's waste-stream and negative ecological impact. We utilize no pesticides and strive to make our home and maintenance practices as energy efficient as possible.
- Create, cure, store, and combust compressed horse manure “bricks.”
- Evaluate combustion in a conventional non-catalytic wood stove.
- Establish markers for labor required, drying times, and best type of mix/mixing method.
- Produce one-cord-equivalent (15-20 MBTU) of combustible matter.
The first and most basic initial step was to confirm what I already knew and had witnessed many times – that horse manure burns. I collected sun-dried dung from our paddock and used it in our woodstove on its own and also added to a wood fire. The latter was much more reliable given that a sufficiently dry dropping was a rare occurrence. Even when much of it was dry, any surface in contact with the ground tended to absorb or retain moisture. This was a phenomenon that would haunt us through the entirety of the project.
Three conjectural methods of processing the manure were proposed, based on our understanding of similar materials, with the aim to increase the volumetric energy density and ease handling and storage. These three processes were compressing the manure, tamping it into forms, and cutting it from existing (aged) manure heaps. Believing that compressing the manure would be the best option this was tried first, but we quickly discovered that it overcomplicated things, making a huge mess and having a very low cyclic rate (3-10 minutes per brick, depending on press).
Because of this, we tried simply forming the loose manure mix (manure, bedding, waste hay/chaff) into forms, and this worked satisfactorily enough that it seemed to be worth investing more energy in. The final option, cutting blocks from a manure pile directly, was done only experimentally on two occasions. It works and is quick and simple but its dry time is so long (often several weeks) as to make it impractical with our climate and available storage.
One innovation proposed by Maribeth was to wrap the blocks in newspaper, and this I employed for the bulk of those produced, by laying the newspaper into the forms, filling with manure mix, tamping and folding the top over the brick. This eased the removal from the form greatly and helped hold the brick together as they often would break up if having too little binder (an excess of bedding material being a common cause) or being insufficiently combined or compressed, as well as making them easy to set alight.
After the first winter this practice was abandoned however after finding that hundreds of newspaper-wrapped bricks are very attractive to mice. Interestingly, they don't seem to bother with the bricks themselves, so this method – like much of the project – has its pros and cons.
During this time a number of bricks were also formed and left to wet to see if they would dessicate in the dry air of nature's freezer, but they did not. This necessarily limits when bricks can be made and dried, giving a distinct disadvantage over wood which can be cut and split as needed. All of the needed or desired manure bricks would need to be dried and laid up ahead of time.
The main issue we encountered was simply the climate here in Wisconsin, which on its own is not conducive to proper drying of the manure (or keeping it dry thereafter). Most of those places in the world which heavily rely on dung as fuel are arid or semi-arid (also a contributing factor to not having sufficient firewood) and so drying is accomplished easily. Many times was a batch of nearly dried blocks ruined by an unexpected rainfall. This recurrent frustration was the reason for building the solar dehydrator, though we also experimented with stacking blocks in our horse trailer (another structure which can get quite warm in the sun!), which kept them out of the rain and speeded drying, but was a hassle to unload whenever we actually needed to use the trailer. It is, however, a good option to explore.
Given the difficulties in drying reliably to the desired <20% moisture content, a solar dehydrator was constructed. Others who have produced compressed manure blocks commercially, such as Eagle Valley Eco Fuel, have dried them using ovens, but this certainly takes away from the low/no-energy input aspect that is so desirable in the product. Turning to the freely available energy of the sun we were already using but intensifying it was immediately beneficial, keeping the bricks out of the weather and reaching temperatures of 120-130 degrees F (40-50 degrees above ambient) but more importantly by virtue of this fact reducing relative humidity within the dehydrator. This stage of the project sadly was completed too late to be of any meaningful impact, but again, seems to be part of the answer. Its only downside is its limited capacity (~30 bricks) and having to load and unload it.
Aside from Maribeth and myself, the only person directly involved was Sterling Morrow, who graciously permitted us to use his six and twenty-two ton presses and make a mess of his shop floor.
Our results were mixed. What began as a promising foray into “free fuel” became a smack on the forehead realization as to why anyplace that has available and affordable wood or coal uses it and not dung to heat and cook. Sometimes the things you already know must be reinforced through experience and this was one of those times. Overall, I have viewed not achieving the majority of set objectives as a bit of a failure, but this is also a part of such experimentation and ultimately is just a step towards future success.
Total number of bricks produced was only ~720, though ~120 of these were scrapped from the above issue(s). The approximately 600 bricks remaining represent a theoretical energy content of 3MBTU, which in itself is only 20% of the proposed minimum goal, and accounting for less than ideal drying and subsequent combustion, these values are optimistic.
Much of what was burned was used in conjunction with wood, and the moisture content contributed to lower combustion temperatures and subsequently higher levels of creosote buildup.
It is doubtful that on its own the latter is a concern, but simply stated, the practical use during our grant period of the manure bricks was supplemental heating and they never rose to where they could match wood for our needs. That is not to say I feel it was of little value, for it does rapidly reduce the amount of manure to be put in a pile or reduce the pile itself. A typical 10 cu/ft. wheelbarrow load is sufficient to create fifty bricks, immediately reducing in volume by approximately 50%, then being burned to produce Nitrogen-rich ash, and preventing runoff.
Just this year Finland-based Fortum Energy Group announced plans to use horse manure for electrical generation in supplementing and replacing fossil fuels, and cite similar figures to my own in the proposal for this project that a typical home can be heated with the energy content produced from three horses and their waste bedding. While these larger scale operations typically burn the waste in a biomass furnace (the chopped or loose material being blown in from a hopper) it indicates the principle of use and reasoning behind doing so is sound. A carbon-neutral fuel, readily available, which through its use reduces the impact of manure runoff into surface and groundwater.
In the future I will construct and utilize a CINVA Ram (http://opensourceecology.org/wiki/Cinva_Ram), and test its use with this material. While the compression methods we tried seemed less than desirable, the CINVA Ram would speed things up considerably. I believe this may be the ultimate solution and will pursue its application in the future.
The single greatest thing I learned from this grant was that while this was something I planned to do for myself regardless, having to do it for others, as it were, added immeasurably to my stress over it! That said, our participation was a valuable incentive to work on it despite the numerous other concerns of life.
My recommendation to others regarding this project is to view this as a supplemental heating method only, at least initially. It is a simple and ancient method which still works today and has benefits despite its drawbacks. Have fun with it. It's a great conversation starter.
The primary means of outreach has been our website, which we are continuing to update and expand. Coinciding with the completion of the project I am also submitting an article to
Backwoodsman Magazine based on what we have tried.
My overall experience with the program is positive. I am pleased that such a program exists and to have been able to be a part of it. My single concern over the course of the program was having our home (as opposed to a business) address/contact information available publicly on the SARE web page, though I suspect this may be unavoidable in the receipt of USDA funds.