More On Methane Al Rutan, the Methane Man c.1992 Al Rutan Temperature is critical factor to the success of any methane energy system. If the primary concern is waste management and not energy production, then a net energy loss is not important. If the intent is to produce energy, the net energy gain from the process is everything. Body Heat Methane activity in one of its natural situations is found in the digestive tract of warm blooded animals, people included. For people, the normal body temperature is 98.6ø F. In a chicken or pig it is 103ø F. So right at 100ø F is the ideal working temperature for the methane process. To maintain this temperature outside an animal is a problem if the ambient temperature is cool or cold. Sewage Plants =/ Energy Producers There were several methane farm operations launched in the upper midwest with much bravado and publicity. All of them are now out of business. On the other hand, sewage plants of medium size still commonly use the process to treat toilet waste and destroy pathogens, but in each instance they consume much more energy during the cold part of the year than they produce. The toilet water flowing into each sewage plant is cold ordinarily. It would be exceedingly difficult for sewage plants to be anything but energy users rather than producers at any time except in the hottest part of the summer. Universities verdicts at the end of the methane studies were always the same: "It's possible, but it isn't practical. It takes more energy to run the system than the system can provide." The obvious in harnessing methane as an energy system is the importance of conserving heat in the process of producing gas. A few years ago a new sewage plant was built at St. Cloud, Minnesota to the tune of 17 million dollars. I asked the engineer, "Did you insulate the tank?" He said, "Oh yes. The old one used to actually freeze on the north side during the winter." My next question was, "Did you run the insulation into the ground?" His reply, "No. The ground never gets cold." My reply was, "That's right, but it never gets warm either." This sewage plant burned $750,000 a year in fuel oil to keep the digester at 100ø F. It costs big bucks to flush the toilet in St. Cloud. Capturing Warmth Heat has to be considered as something that is very slippery. Conserving heat requires understanding insulation. We are fortunate that there are many types of insulation available now that simply did not exist a few decades back. On the other hand, there's a general lack of understanding of insulating properties of common building materials such as wood, metal, concrete, etc. I recommend Movable Insulation, published by the Rodale Press in 1980. Anyone familiar with insulation knows that if it gets wet, it is no longer insulation. Some "closed cell" insulating materials such as urethane, styrofoam, and polyethylene foam are more impervious to moisture than cellulose or fiberglass insulation. Even closed cell materials can break down if moisture under pressure is present. Styrofoam is commonly used on the outside of the foundations to provide a frost barrier for basements. Soil pressure and moisture can cause the styrofoam to be less than "bone dry" and thereby lose much of its insulating ability. Situating the Tank My personal preference is that the methane tank be as effectively insulated as possible. Insulation should be below the flow line of the material entering the tank, but should not be buried in the dirt, regardless of the insulation. The temperature of the ground several feet below the surface stays quite constant at 50ø FÄ55ø F. To the methane tank, the earth is a "heat sink", a cool mass always ready to absorb its heat. The best way to fight this heat sink is to insulate the tank and build it above the ground. Another good reason for a free- standing tank is access to the grit trap at the bottom. A free-standing tank should be covered with six to eight inches of high quality insulation. Various people have asked whether a buried tank couldn't work. I can't say that it won't, but I've never seen any that work in a cold climate, and I have seen several that don't. Restoring Warmth When feces leaves the body, the waste is at exactly the right temperature for working within the methane digester. Whatever heat is lost in an interval between leaving the animal and entering the digester has to be restored. If the heat needed is significant, there needs to be a heat source available with an abundance of "free" energy, such as solar or wind. Relation to Fermentation The methane process is a type of fermentation. Most folks have baked bread or made homebrew beer or wine at one time or another. For instance, after a yeast dough is kneaded, it is put in a warm place free of draft and allowed to rise. A draft could produce cooling. The yeast organisms feed upon the mixture's sugar. This produces carbon dioxide bubbles, which cause the dough to rise. There is a similar activity within the methane tank. The methane organisms feed upon simple sugars, alcohols, and peptides produced by acid forming bacteria. Methane gas, CH4, is the result. I've been asked if the working within the tank doesn't produce some heat, such as the heat produced in a compost pile. It probably does. Because the metabolic activity is so diluted and spread out within the tank, the heat available is minimal in comparison to the target temperature. Awareness is Essential You'll need to know how hot the tank is, day to day, season to season. To eliminate the guesswork, install sensors both inside the tank and outside the tank. Record temperature both inside and outside the tank over a period of time. Then you can know how efficiently the tank is retaining heat, at what rate the temperature drops when no heat is added, and how much energy is needed to raise the temperature. If this is done, then a reliable calculation can be made of how much gas is needed to maintain working temperature if "free" heat is not available. Producing methane gas is relatively easy. The conservation of heat more than any other factor determines whether a methane system will "fly" or not. Of all the systems I've seen that failed, the principal reason is improper handling of heat. Care and Feeding of your Methane Digester Having thought about temperature, we can turn our attention to feedstock. I work with a mixture of manure and vegetation. Sometimes the question is askedÄcan't one use just vegetation to produce methane? It can be done because Mother Nature does. Swamp gas burning over a marsh is just that. Because the methane bacteria are part of the "flora and fauna" of the digestive tract, every time there is a fresh deposit, there is fresh input of the microbiological organisms needed. How Much Gas Can I Get? There's a wide range of mixes of material you feed a methane digester. It's similar to what happens when we eat. Some of the material enters our system to maintain it and some of it passes on as waste. When manure is considered, all of it, minus the water, is designated as "total solids", and the part that is digestible to the bacteria is labeled "volatile solids". The numbers of what is and what isn't available for gas production have been gathered repeatedly over the years. Each account is quick to qualify any statement by saying that there is any number of variables when dealing with animals regarding what they are eating and how they are housed. One of the clearest reference sources is a newsletter printed in the spring of 1973 by the New Alchemy Institute in California. Their figures correspond to what I've experienced. The numbers run like thisÄa cow drops an average of 52 lbs. of feces a day, of which about 10 lbs. are solids, the rest being water. Of the 10 lbs. of solids, 80% or 8 lbs. are volatileÄcan be turned into gas. A horse produces an average of 36 lbs. of feces a day, of which 5.5 lbs. are volatile solids. A pig produces 7.5 lbs. per day of which 0.4 lbs. are volatile solids. A human produces 0.5 lbs. of feces a day of which 0.13 lbs. is volatile solid. Chickens produce 0.3 lbs. a day which 0.06 lbs. is a volatile solid. All of this is good information, but it still doesn't tell us how much gas we can reasonably expect. If you ask an "expert" in the field, you'll get an answer something like, "It all depends...". All manure contains a degree of nitrogen, but because nitrogen exists in so many chemical forms in natureÄammonia (NH3), nitrates (NO3), proteins, etc.Äit's difficult to test the total amount of nitrogen in a given material. Why Consider Nitrogen? The process wants one part nitrogen to every 30 parts of carbon. Manure is nitrogen rich, averaging about 15 parts carbon for each part nitrogen, so all the studies show that gas production is substantially increased by including some carbon material along with the manure. The nitrogen proportion may be even higher in animal waste if urine is included with the feces because urination is the principle way an animal rids itself of excess nitrogen. To illustrate, straight chicken manure will produce only five cubic feet of gas for each pound of manure, but chicken manure mixed with paper pulp will produce eight cubic feet of gas for each pound of manure used. My experience was an outstanding ten cubic feet of gas for each pound of chicken manure when the manure contained some ground feed that had been spilled into the droppings. Cow manure will produce only 1.5 cubic feet of gas per pound, but cow manure mixed with grass clippings will produce 4.5 cubic feet of gas per pound of manure. The Nature of Biogas Assume that we have a gas producing system and it's making gas nicely, filling the gas holder. What do we actually have? It's important to understand that it isn't all methane. A proportion of it is carbon dioxide, produced by the acid forming bacteria, which doesn't burn. This fact isn't immediately evident because if one ignites the end of a hose coming from the gas holder, there is a nice blue flame. The fact that is important to know is: if we had pure methane we would have a hotter flameÄabout 1000 BTU (British Thermal Unit) for each cubic foot of gas. With the dilution of carbon dioxide, we have roughly 600 BTU for each cubic foot of gas. The composition of the gas in our gas holder will be: CH4 methane - 54Ä70% CO2 carbon dioxide - 27Ä45% N2 nitrogen - 0.5Ä3% H2 hydrogen - 1Ä10% CO carbon monoxide - 0.1% O2 oxygen - 0.1% H2S hydrogen sulfide - trace Wouldn't it be nice if we could separate out the methane and dump the carbon dioxide. Interestingly enough, Mother Nature has made it very easy to do just that because these gases all have different specific gravity weights. How to Get Pure Methane The specific gravity of methane is about 0.55 in relation to the weight of air, so it rises, as does hydrogen. Carbon dioxide on the other hand is twice the weight of air. Within a vertical gas container, if the gases are allowed to settle, they will naturally separate themselves with the flammable gases at the top. This fact suggests that a good design feature is to have a petcock at the bottom of a vertical gas holder. Use it to bleed off the accumulated carbon dioxide. In the right setting, this isn't environmentally harmful, because the trees and growing things around the yard will welcome a fresh sniff of carbon dioxide. Next time we'll consider some of the safety aspects needed in working with homemade gas. Access Author: Al Rutan, the Methane Man, POB 289, Delano, MN 55328 ù 612-860-3998