Moisture

           Most growing things have a large percentage of water in their composition. Some time, take a look at the water content data of the vegetables you eat. It is a natural thing for plants to contain water, only now, we must spend extra heat just to get rid of all that water.

           For a given variety of wood, consider the following, for the same wood species:

Dryness          % Moisture     BTU/lb. Net

Oven dried                 0%                  7100

Air dried                      20                   5400

Green                         50                   2900

Wet                            70                   1100

           That makes a pretty good argument for drying out wood. What it really says, for a given wood variety, is that most of the BTU, the heat content of the wood, may be used to drive out the contained water, or, burning wet wood is an exercise in futility if you want heat.

           Referring to Table 1, these percentages amount to gallons of water per cord! And all of this water must be eliminated before the wood can burn.

Wood Pellets

           Contained in a plastic bag, with a moisture content, typically 3 to 5 percent, makes a good argument for this kind of fuel.

Relative Humidity

           From the Wood Handbook, USDA, we get the following data about the effects of natural environment:

           In wood:

           Relative          Equilibrium

           Humidity         Moisture

                                   Content

           95%                25%

           76                   15

           70                   13

           62                   11

           50                    9

           36                    7

           24                    5

           13                    3

           Just by lying around, wood can gain moisture. It must be dried out, for example:

           It takes 1030 BTU to vaporize each pound of moisture content.

           In 100 pounds of wood with an 11% moisture content, there is 11 pounds of water to vaporize.

           11 X 1030, or 11,330 BTU will be required to get rid of the moisture. In wood of 8300 BTU/lb, average, 1.37 pounds of the wood are used up just for this, before we can begin to get any heat for us, more if the combustion efficiency is less than 100%.

Growing Your Own Trees

           There are advertisements about newly developed tree species that grow phenomenally fast. Grow your own wood lot, they say. In a few years you can have a grove of trees ready to harvest for fuel. Isn't that great? Yes, maybe. Here are some questions you need to answer before jumping into this kettle:

++ Moisture content?

++ What will be the girth of these trees in the few years that it takes them to grow so tall?

++ Is their root system deep enough and strong enough for support? Or will the grove topple like dominoes in the first strong wind?

++ What is the heat content of this variety?

           A fast growing tree is probably less dense, contains more moisture, doesn't develop a strong root system in a short time, and has low BTU per pound. Growing fast doesn't provide the time necessary for these qualities to develop.

           If you have trees and want them to grow faster, for whatever reason, put them on a water drip system so that their root ball never fully dries out and they will grow faster than you can imagine! But all of the above comes into play with this technique, also. The way out is to plant both slow and fast growing trees.

Transporting and Storing Wood Fuel

           Wood weighs about 20 to 50 pounds per cubic foot, or about one to two tons per cord. It is dumped first and stacked later. Moisture, insects, and weather deterioration are the principal factors of degrading, and they thrive best in a wood pile. Consider hauling per ton from the source, plus loading and unloading costs.

           Stacked wood takes about 120 cubic feet per cord. Stacked eight feet high, that's 1.5 feet deep and 10 feet long. It should be loosely stacked to allow for air circulation.

           Stacked wood should be on a firm, stable platform. You don't want that much weight tipping over. Wood stacked on the ground picks up moisture, and the ground can't usually stand that kind of loading, so instability is a problem without a strong, stable platform.

           We've learned enough about moisture to know that the wood must be kept dry. Enclosed, if possible, and near enough to the house so that carrying isn't an impossible chore. Not against the house, because all those woodpile insects may find the house a more inviting home.

           From the volume of wood, we have a size requirement. You can estimate the amount of fuel you will need for a burning season, and from that, the size of the wood shed. We recommend that the woodshed store two season's wood. Store next year's wood this year for curing. When you have used this year's wood, stack that side for the following year. That way, your wood will be about as good as it can be for fuel.

Pitch

           Pitch is tree juice. It accounts for about half the heat content in wood. Refined, it becomes turpentine and resin, several chemicals, a disinfectant, and even a wood preservative. It is both a blessing and a curse. Sap is water soluble, pitch is not. Sap from the Sugar Maple, boiled down, makes syrup.

           When pitch is burned as part of the wood, some of it vaporizes and is driven off because of a low boiling point: another good argument for a hot fire. The part that is vaporized becomes a sticky, tarry substance, particularly bad to deal with. Part of the expenditure of heat is used to vaporize and carry it away from the combustion chamber. That's why we have to watch the stack temperature. If the stack cools enough for the pitch to condense, it will collect in the stack lining, restrict draft, which in turn reduces combustion efficiency and that allows more pitch to vaporize and collect in the stack. You will see the pitch condensation and build up every time you clean the stove glass.

           Deposited in the stack, it doesn't store heat well, and it is flammable. If the stack is heated really hot, some time later, the pitch will start to burn. But the heat is not where it can be used. We have a flue fire. That's one of the best reasons for keeping a hot fire, and you need a pyrometer to let you know that it is hot enough, but not too hot. 

           The amount of pitch contained in wood varies; soft woods generally have more pitch.

           Pitch, in raw wood form, can have its only good use as a fire starter. Solid slabs of pitch can be separated from certain woods and handled themselves as a fuel. In concentrated form, this pitch burns very well and hot, burns easily and doesn't go out. It can be used as a kindling with great effect.

           Don't misunderstand this. Pitch can be used as a fuel, but a combustion system must be designed to handle it. A woodstove is not an efficient pitch-burning system. That's why it goes up the stack, unburned, and causes problems.

           A hot fire is the best solution to pitch build-up in the stack. A good practice is to burn hot for at least a half hour every time you light the stove. This cooks the pitch, turning it into the flaky dust, some of which gets expelled.

Wood Fuel Factors

           The key to wood as a fuel is density, or weight per unit volume, minimum pitch, and the ability to dry out easily. Here again, no hard rule applies because all of these factors vary with each wood species. There is one other factor: What is available in your local area? Eucalyptus is a hard, hot burning wood. Too hot: It warps stoves easily. It grows fast and it is tempting, but make another choice.

Other wood fuel forms

           Chipped Wood is smaller than the hogged variety and burns faster. Being finer particles, its fuel density per unit volume is greater. Chipped wood is more likely to be a form that the individual can manufacture at home with woodworking machinery.

           Hogged Wood is wood that has been coarsely ground or chipped. The name comes from the machine that does it. Wood scraps that are otherwise unfit for burning can be hogged or pelletized.

           Pelletized Wood is wood that is first ground and then compressed by machine pressure into little pellets for burning. Saw dust, wood scraps, old pallets, small branches, all may be pelletized.

           Saw Dust and Shavings are milling waste and another fuel form, but sawdust especially requires special equipment for handling. It is also subject to explosion in a confined space by static electricity and lies beyond the realm of the domestic user as a practical fuel, unless it is pelletized.

           What we have done is create wood in finer form so that it may be more effectively mixed with air for combustion. Except where the wood is a waste product, this additional machining adds extra costs to the fuel.

            Pellet stoves have automatic fuel feeding mechanisms and burn what might otherwise be waste material. If the fuel will more readily mix with air, a hotter fire results. These fuel types require forced air supplies in order to have enough air available to burn the concentrated fuel.

Other Options

Methane From Wood Waste

           Orchards, or other wood growth activities, that produce large quantities of wood waste by pruning and otherwise, may process this waste through a biologic system and produce methane gas, which is an acceptable fuel. When mother nature has done it, we call it Natural Gas.

           Wouldn't it be great if logging operations included a methane plant and utilized all that waste? But could we do without slash burning all the logging trash after all these years? The mills could increase their profits using up some more of their waste. It works just as well to rid fields of unwanted straw, too. That's kind of like found money, isn't it?

           Methane Gas can be used to fuel engines, may be burned directly for heating, or it can be processed into liquid, called methyl alcohol or methanol, and used in place of expensive gasoline, and all of this from waste, which someone else might eat, drink, or breathe.

           No, I'm not wandering. I have made methane and captured it for use as a fuel, from waste, here at home. It can be done on a small scale, if you are determined enough to use renewable energy sources to their fullest extent. It's a great way to use up garbage and manure, as well as branches and leaves, too.

Charcoal

           The production of charcoal from wood reduces the volume and weight of the basic wood fuel. Charcoal production is a normal step in the combustion of wood and processing to this stage can be efficiently accomplished independently. The cost of the processing must be included in the fuel cost, but saving storage space and transportation costs may offset this production cost. For handling purposes it is usually compressed into briquets, which also aid in the burning.

           Charcoal production for domestic use is probably limited to backyard barbeques.

           Today’s clean air laws would probably eliminate the old processing ways. A mountain of wood, piled so that it was densely packed, was allowed to burn for days, weeks, or longer. The pile was unpacked and the pieces which had become charcoal were removed. Partially converted pieces were saved for starting the next pile.

           Imagine what a mountainous pile of wood produced as smoke, vapors, and ashes.

Charcoal Burners

           During World War II in Europe, gasoline was not available to the civilian population. There was none allowed to run autos or especially for trucks needed for hauling items non-essential to the war. Busses also needed fuel.

           Wood scraps were converted into charcoal, the methane gases were captured and used to run an internal combustion engine. They ran trucks and cars on this, a waste product.

           The conversion chamber took the form of a vertical tank, around 50 gallon size, with a removable air tight lid. It was situated behind the truck cab or on the back of an automobile. Of course, every now and then, the driver would have to stop, open the lid and recharge the generator with wood. Then he would wait for the gases to build up sufficiently to run the engine. He would have to haul his wood, too.

            A charcoal/methane converter is another way to get heat from wood, perhaps from wood in a form that could not be efficiently burned in a stove.

           As a transportation fuel, it worked, but very little of its rated engine power was available from an engine operated on wood gasses.

Wood Ashes

           The combustion process yields some residue in the form of unburned solids as an ash. Most fuels are rated by the quantity of ashes remaining after burning. Inefficiently burned fuel will produce more ashes, so efficient burning is important here, too. The ashes must be hauled away for proper disposal.

           In times past, ashes were used to make soap. In times present, they are used to replenish the potash and phosphorous removed from the soil by growing plants, hopefully grown as a food source.

Last Thought            

           Gray Birch will burn even if it is soaking wet and green. Poplar will make a smokeless fire. This comes from old woodsman lore. Good information? Who knows? It might be worth while if you were camping out in the woods, with old woodsmen.

End of Excerpt

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