During 2007, my research and efforts focused on making sure that the HG 3a device was CAPABLE of producing the 45,000 Btu/hr that a reasonably well-built, medium-sized house in a cold climate is likely to need for complete heating on the coldest day. That was clearly confirmed and the HG 3a unit was experimentally measured to be able to produce around double that at around 90,000 Btu/hr.
During much of 2008, research and efforts have been more focused on enabling the HG 3a device to produce LESS heat, for the MILDER months. This is technically not necessary, as excess heat could be easily dumped to outdoors! But that would be wasteful of the heat in the materially carried in to the unit, noting that around five to seven tons of material need to be carried and loaded into the unit during a complete winter, and the idea of having to carry MORE than that seems unattractive! Therefore, modes of operation where smaller amounts of heat are CREATED seem very attractive for such mild-weather operation.
It became clear that THICKER pieces of organic materials were desirable during mild weather. Wood chips and tree bark seem useful in very mild weather. Straw, most kinds of cardboard, newspapers, seem suitable for somewhat cooler weather. The very thinnest pieces of material, such as fine lawn grass cuttings and tree leaves, seem better to save until the coldest weather, for greatest heat production and output.
These differences have other effects. When BALES of straw or hay are used, I have generally just separated the bales into 1/3 sections to fit through the feed door of the HG 3a unit. I have discovered that those chunks tend to stay together! This causes far greater difficulty in rotating the unit, as many heavy chunks of those bales tend to stick together, until they eventually tumble across and down! For this, the small motor we used to rotate the unit had problems!
When thick materials such as straw or wood chips are used EXCLUSIVELY, the effect of slowing down heat production is accomplished, for mild weather heating needs. However, the interior of the HG 3a unit seems to tend to then operate at lower temperatures. If ONLY really thick pieces of material are used, such as tree bark and thin branches, it seems to often operate at around 90°F to 100°F temperature. If ONLY wood chips and straw are used, it often seems to operate at around 105°F to 115°F temperature. This seems to then have the additional effect of slowing down the processing due to the fact that ONLY the mesophilic bacteria can then prosper. They tend to process the material fairly slowly and they cannot digest many of the more complex organic molecules. For now, our recommendation is to NOT allow the system to EVER get above about 125°F during mild weather, because the higher temperatures then allow the far more efficient thermophilic bacteria to rapidly multiply and take over. They rather suddenly increase the heat production of the system by a factor of many times! That might be too much heat for mild-temperature needs, and it also will cause the materials to be decomposed far faster.
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It might seem attractive to load in a MIXTURE of different thickness materials. I have found many attractive benefits of doing that, but there is also a complication! When such a mixture is loaded in, the thinnest materials decompose extremely quickly, so even after one day, the fraction of that material is much less! After two to three days, mowed lawn grass is likely to be all gone, so that the REMAINING mixture is then not so much of a mixture at all, being all the thicker, slower decomposing materials.
My solution to this is to TRY to monitor the mixture of materials inside, and to generally be adding moderate amounts of lawn grass regularly, to try to keep the mixture similar to what I had initially put in.
Once the system gets into the thermophilic bacteria mode (over 125°F) those thicker materials seem to also start decomposing much more rapidly, but never remotely as fast as the cut grass disappears.
Feed corn has behaved differently than expected! The SHELLS of the kernels seem to be very durable, keeping the interior of the kernel from being able to start decomposing! This causes the initial heat-up time to be many days. And depending on how much rotation there is with the unit, the decomposing process can either occur as the desired aerobic process (which seems to have no odors associated with it) or it could proceed by an anaerobic decomposition, which is called fermentation. So without sufficient oxygen near each kernel, the process can resemble the early stages of the operation of a still! In both cases, the bacteria can then decompose the resulting broken-down molecules, so the entire final process still can occur.
If the corn is GROUND, which then breaks apart the shells and exposes the inside of the kernels, the decomposition all goes very rapidly, about as we had initially expected. We are not sure it is worth the time, trouble and expense to grind feed corn to use it in this way.
In ongoing experiments, an extremely wide range of organic materials are being added in to the operating devices. There have been some problems caused by this! Some larger pieces of wood, both from scrap lumber and from trees have been tossed in. The large chunks of straw bales that tumble around in the unit have apparently managed to cause a wood splinter to puncture the tarp in the unit, so now it appears to have a slow leak when in certain positions! The solution to this seems to be to make sure to not include pieces of wood which might create sharp splinters, and also to break bales up into smaller pieces so they do not tumble and fall with such force inside the unit.
As to finding such a leak, we currently do not have any good plan, except to wait until after the heating season and examining the interior with a bright light after having emptied the unit, and then using a patch from a waterbed repair kit. As a result of this, we are generally running that unit with somewhat less water inside it, without the five-gallon constant puddle that we think is desirable in the bottom of the chamber. Our initial concept is that by having such a puddle there, then ALL the organic material is able to get soaked for a couple minutes every half hour or so, so the thermophilic bacteria will have their ideal conditions at all times and for all the material inside the chamber, temp above 125°F, immediate access to moisture, and immediate access to oxygen from the air.
We are operating one HG 3a device inside the living space of a house and WITHOUT sending the processed gases outdoors through a vent pipe. Our intention is to see if any smells are ever created, and whether such smells might be used as a clue to turn on the blower to provide more oxygen (under the assumption that such smells would only be formed if some anaerobic decomposition has occurred). In general, it creates a somewhat musty smell that resembles the smell of woodburning but to less extent.
It can be very useful to have a thermometer inside the chamber. If it is being used in a manner where the inside temperature is lower than 125°F, then some processes should NOT be used with it. Specifically, that temperature is not high enough to ensure that all dangerous things are killed, so you cannot assume that food would be cooked hot enough, and you could not sterilize items in it. Those processes can only be safely done when you operate it at over 125°F.
An interesting variation of the much larger HG 2 system has been built and has shown some wonderful advantages. It might be worth considering! Into their chamber of around 16 tons of wood shavings, these people have added hundreds of small ducts where they can inject hot air (of around 140°F), which is produced by a nearby standard furnace. They also installed dozens of pipes which can introduce hot water into the chamber which is also around 140°F. Personally, I like the safety aspects of the fact that the HG devices do not involve any flame or fire, and that the sopping wet contents make sure that no fire could possibly ever happen. But, for a TRAINING PERIOD while the owners were getting to learn how to properly supply the Thermophilic bacteria with the oxygen, the carbon dioxide and the heat they need to thrive, this idea seems brilliant to me! I would think that as the operation was learned, it might be less necessary to be providing this additional heating, as the Thermophilic bacteria can certainly produce amazing amounts of heat on their own!
The main presentation was first placed on the Internet in February 2007. This Suggestions presentation was first placed on the Internet in September 2008.
C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago