biofuels - the series

January, 2005 Page 6Energy Self-Sufficiency Newsletter

Biofuels -- The SeriesThis article is the first installment in an ongoing series that will explore

methane, ethanol, biodiesel and waste vegetable oil (WVO). We’ll start at the begin-ning with each one and continue as we build a base of knowledge on the subject.Each article will be accompanied by photos and/or diagrams, so that you’ll be ablebuild your system to produce biofuel at your place. We begin the series with methane(CH4). Al Rutan is our Contributing Editor on the subject and is regarded as one ofthe masters of the craft. There’s a short bio of Al elsewhere in this issue. It’s goodreading so try not to miss it. ldb

Utilizing Natural Design Parametersfor Methane Digesters

by Al Rutan

The process of anaerobic fermentation is not“fussy.” The reason this can be said is because we knowthat it occurs in lake bottoms and bogs, swamps and land-fills. Obviously, what goes into a landfill is put therewithout any “rhyme or reason.” The biogas formationthat results does so from organic material that was sim-ply dumped and then covered with dirt to exclude air.

However, it takes from 50 to 100 years for a land-fill to be generating a significant amount of biogas. Andthis is accomplished without any stirring or heating. Butif we want the most biogas possible in the shortest lengthof time, we need to heed the parameters for the optimumconditions of the process.

We like to think of ourselves as “engineers.” Thisis not the best mindset to have when working with livingcreatures. Rather, we should better think of ourselvesfirst and foremost as “biologists.” An engineer tends toimpose on living creatures what he thinks they shouldhave. A biologist is more inclined to be sensitive to whata living organism wants and needs.

Over the last century sewage engineers in manyplaces throughout the world have had time and money attheir disposal to study and document anaerobic activityat close range in their labs. We know from this researchthat optimum warmth is a major factor in rapid gas for-mation and that gentle mixing also is important. Both theseactions mimic what happens in the gut of warm-bloodedanimals, including ourselves.

Another feature of the process that isn’t so readilyrecognized is the fact that in the gut of an animal the anusis at the end of a long tube. We call it the intestine. Whilethe stomach of an animal is similar to a “pot” the majorpart of digestion occurs in the intestine and not the stom-ach. The stomach is a preparation place for what occursin the gut. So if we adhere to a “natural pattern,” thedigester is going to be a tube rather than a “bulk con-tainer.” This makes possible the process of digestion atdifferent points along a route. We are simulating whatoccurs in a gut.

A gut excludes air, has a gentle, involuntary mix-ing action we call “peristalsis,” and provides constant,even warmth throughout at just the right temperature in aliving animal. Given these guidelines, we can look atwhat a well-designed biogas system should display. Wewant to accomplish (1) exclusion of air, (2) constant,optimum warmth, and (3) gentle mixing with a minimumof “machinery” and controls.

It is very easy to start designating all kinds of“bells and whistles” to a project. The genius of the bestdesign is to have as little dependence on “machinery”such as pumps and motors with controls as possible.These are the things that shoot up the cost of a system andthe bacteria are not impressed..

Monitoring is important. But there are variouslevels of complexity when it comes to monitoring. Werequire only the simplest instruments possible. A gooddesign is going to use the natural forces of gravity andand thermosiphon whenever possible to reach the neces-sary guidelines. This is what we call common sense.

Continued on Next Page

The big challenge for any project is the mannerin which warmth is supplied to the digester. Because heatrises the only way to move heat downward if the sourceof heat is above the digester is with a circulating pump.If this is the case, the circulating pump must run con-stantly. Any pump running constantly is obviously a hugeenergy drain.

In the best of all worlds, the design that requiresthe least expenditure of energy is going to supply warmthto the entire bottom surface of the digester tank. This isdone not with pipes or lines of any type but with a“warmth chamber” that covers the entire bottom surfaceof the digester.

So the heat source, no matter what it is, must bebelow the bottom surface of the digester, similar to themanner in which the double boiler on a kitchen stoveprovides even warmth to the unit on top.

For moving warmth around, we need to employthe simple physical action of thermosiphon - the circula-tion of warmth either in air or liquid by the displacementof what is cooler by what is warmer. Thus warmth canbe “moved” if we harness a completely natural process.Again this is really cheap. No pump required.

And for moving the methane gas from one placeto another, there is nothing less expensive and more posi-tive in its action than a gasholder that uses the force ofgravity to exert pressure on the gas. A flexible fabric canexert pressure, but not evenly between maximum expan-sion and half-fill. With a flexible fabric for containinggas the pressure is not a constant force. But in a solidvessel with a provision for expansion serving as a gash-older the pressure is constant and consistent because theforce of gravity is evenly applied no matter how full ornear empty the gasholder is. And again, the force of gravityis really cheap.

If gravity is not employed to move the gas, then afuel pump must be. This is another piece of equipmentthat is not necessary in a project of better design.

One last observation about capturing heat frommachinery. A common way of picking up heat from a gen-erator is from the exhaust by means of a heat exchanger.

My criticism of this approach is not that it doesn’twork but that only a fraction of the heat so generated is“captured.” If one puts one’s hand on the exhaust pipeafter the heat exchanger, the pipe is still exceedingly hot.When heat is being dumped it is not being captured.

The Co-Ray-Vac people have demonstrated withtheir product (an infra-red heater) that one has not“squeezed” all the heat from an exhaust pipe until onecan comfortably lay one’s hand on the end of the exhaustpipe. Then we are sure that virtually all the availableheat has been transferred to a heat exchanger. Anythingshort of this means that valuable and expensive heat isbeing lost to the atmosphere. This is sheer waste andpoor design.

What are the best sources of warmth for keepinga digester at optimum warmth? Obviously, one can burnsome of the gas produced once the digester is up andrunning. But this is not the first choice for supplyingwarmth. Most likely we want all the biogas produced tomore directly provide for our needs. Warmth from thesun is the most obvious choice for acquiring digesterwarmth. And we can think of no better source for har-nessing solar warmth than heat tubes. We recommend theequipment available from Back To The Future Solar:

http://www.btfsolar.com

The details for various sized biogas systems canbe found on the Methane Gas website:

http://www.methane-gas.com

Click on the tab that says “How To Order” for the spe-cifics found with the Plans for various sized digester sys-tems.

Contact Al Rutan at:

RUTAN RESEARCHP O Box 50, Liberty Center IA 50145-0050

Phone 612 805 9377Website: http://www.methane-gas.com


Natural Methane Digester Design . . . cont.

Check out the pictures ofAl and some of the gear de-scribed in the article on the next page . . .

http://www.btfsolar.com

http://www.methane-gas.com/

http://www.methane-gas.com/


Pictured here are views of a methane gas digester systemsmall enough to sit on a sturdy table, yet large enough toproduce enough methane gas to fire a Bunsen burner. Thereason this digester has been assembled is to visuallydemonstrate the fact that a digester does not have to belarge or expensive in order to be practical.

A digester does not have to be large in order to workwell. Gas produced from living creatures occurs in allkinds of situations. All warm blooded animals producegas in the gut—some more than others. The thing that isessential to understand when harnessing the process forour own energy needs is that both the chemistry and thebiology requirements of the organisms that work anaero-bically need to be kept in mind. Even a small digestercan demonstrate these parameters.

In the picture we see a tank before it is covered withinsulation. Beneath the tank is a foil lined enclosure thatworks as a warmth chamber, providing even warmth forthe entire tank.

There is a mixing mechanism in the tank which is turnedfrom time to time by the crank handle at one end of thetank. This mixing mechanism is important. The bacteriathat digest the organic material do not have fins as fishdo making it possible to swim after food. With bacteriaeither food must be taken to them or they must be taken tothe food. A gentle mixing action supplies this neededmotion.

This digester is a displacement flow design. The fill pipeis at one end. The exit pipe is at the other. The organicmaterial that does not become burnable gas leaves thedigester via the exit pipe. Gas production is continuous.

Al Rutan with the digester and warmth chamber

Welder Ross Wood holds the mixing mechanism

Ross with the gasholder

July, 2005 Energy Self Sufficiency Newsletter Page 5Energy Self Sufficiency Newsletter

Page 5

AL RUTAN - THE METHANE MANAL RUTAN - THE METHANE MAN

There were just a few of us, collaborating via the Internet in the closing months of 2004, planning for the New Year’s Evedebut of Energy Self Sufficiency Newsletter. Me, Steve Spence, Laren Corie, Maria ‘Mark’ Alovert, Mike Nixon and AlRutan. The Premiere Issue of ESSN “hit the stands” and life was good.

Then, on 9 January 2005, tragedy came to our renewable energy family. Al Rutan passed on. Death is a natural part of the lifecycle and is inevitable. But that in no way lessened our sense of loss as we mourned Al’s passing and the loss of hiscontribution to our movement and to our publication.

For many people, methane production is a very viable component of energy self sufficiency, and Al’s writings were a valuablepart of our message to you, our readers. Al had contributed several articles to Home Power Magazine before his death, andIan Woofenden and the Home Power staff have graciously given us permission to reprint those articles.

We are proud to present, once again, Al Rutan’s words in the pages of Energy Self Sufficiency Newsletter. Special thanks toIan and the group at Home Power Magazine for their generosity.

Al, welcome back to ESSN. Your wisdom and knowledge are an indispensible part of our message.We’ll always remember you. ldb

Continued on next page

mailto:[email protected]

http://www.powerwerx.com/




Page 6

Gas Use

What about flammable gas? Why consider it? For those of uswho spent much of our youth chopping wood to heat andcook at home, the idea of gas is like something from paradise.The idea and the experience of merely turning a valve to haveinstant flame without all the “bitching” and complaining in-volved in “go get that wood!” is amazing.

Almost everyone likes the ambiance around a campfire on anouting with friends. But for the day to day fuel needs, wewish to have it as “automatic” as possible, and for being con-trolled by a thermostat, gas is unsurpassed.

It is clean and uncomplicated. Clean? Yes, clean. There is nosoot that collects in a chimney from the burning of methanegas. Does it need to be vented? It should be, if at all possible.The fumes from any type of combustion should be consideredsuspect.

Potential problems from the burning of methane are minimal.If the combustion is complete, what is produced is carbondioxide and water vapor. Yet we have no practical assurancethat combustion is always as perfect as it could be.An interesting note historically is the fact that the Indian gov-ernment some 40 years ago pushed the development of home-stead production of methane because so many people weregoing blind from the effects of burning cow dung for fuel. Ourearly pioneers had similar experiences from the burning ofbuffalo chips. Burning raw manure should always be consid-ered a “no-no.”

Low-tech methane production information comes from bothIndia and China–two countries with vast populations, hugepollution problems from waste, and an immense need for fuel,which isn’t readily available.

At Home

Our interest stems from the fact that homestead methaneproduction is one more way to unplug from a utility companyand provide access to energy, which substantially contributesto the quality of life.

So, one has to have the heart for it. Unlike electricity, that isfor all practical purposes quite mechanical, gas production

Home Power #26 • December 1991 / January 1992Alternative Fuels

Prologue to Methane GasAl Rutan, the Methane Man

©1991 Al Rutan

means tending to living things, like a flock of chickens, a bandof sheep, or milking goats. For abundant gas production, thereneeds to be a sensitivity to the special needs of the micro-scopic creatures that produce flammable gas as their wasteproduct. This means providing for their basic wants and–don’tlaugh–giving them a measure of love. All living things–plants,animals, and people–require love in order to flourish. This needextends even to living creatures that can’t be seen with thenaked eye.

A person we know who had a methane system one day wentup to his tank and gave it a good hefty kick as an experiment.The gas production stopped immediately, and started slowlyagain only after some time had passed.

Because one must assume responsibility for the care of acolony of living entities, producing gas to burn has anotherdimension some may need to consider before undertaking sucha venture.

The advantages of gas are many-fold. It is so easy to use. Itis so controllable. It is relatively easy to store. It can be usedautomatically. It will even run your vacuum cleaner if you putthe methane gas through a fuel cell which will turn the gasdirectly into electricity. Plus, it is so clean–no soot, no creo-sote, no ash, and no chopping. What more could you ask?

Making and Using Methane Gas

Methane is a natural gas. The reason it’s called “natural” isbecause it occurs in nature everywhere. It can be the gasfound in a swamp or marsh, the gas found in a coal mine, thesmell coming from a septic tank or sewer line, or the gas soldto us by a utility company under the title of “natural gas.” Theproduct is substantially the same, CH4.

We’ve heard that methane is odorless, and it is. Sewer gaswe know is not. So what is the difference? When the processthat produces gas is underway, there are a variety of gasesproduced at the same time. All such gases result from micro-organisms feeding upon organic matter and producing gas asa waste product. Methane, which is odorless, is one of them.







Page 7Continued on next page

All these burnable gases are produced by anaerobic organ-isms feeding upon organic matter. To say they are anaerobicmeans they only live when air is excluded from the space inwhich they are functioning.

They are the same organisms that cause us to have intestinalgas. Each time a warm blooded animal defecates, some ofthe gas producing organisms are contained in the feces. Thisis why it can be said that methane occurs virtually every-where. Wherever air is excluded from the decomposition pro-cess, the production of methane and accompanying gases islikely to occur.

Stories are legion about a bunch of guys with nothing better todo than ignite the intestinal gas of one of their particularly“gassy” buddies, and then being amazed at how flammablethe experiment was.

The micro-organisms that produce flammable gas are tem-perature sensitive. They want body temperature in order tofunction most effectively. In people that is 98.6°F. In a chickenor a pig the body temperature is 103°F. So right around 100°Fis the optimum temperature for the process to work most ef-fectively. The action can occur at lower temperatures. As thetemperature drops so does the rate at which methane gas isproduced.

People will sometimes ask, “Why can’t I use the gas off myseptic tank to burn in a stove?” The typical septic tank swingsthrough such wide temperature fluctuations, the amount ofgas produced is minimal. Each time a toilet is flushed withcold water, the tank goes into “shock.” Each time some warmwash water from a bath or shower flows into the tank, itbecomes more active until the next shot of cold water. Suchtanks are ordinarily in the ground, which stays at a constant50° to 55°F. The ground is a constant heat sink, draining heataway from the tank. About all one gets from a septic tank, byway of gas, is enough to cause an unpleasant odor.BecauseHydrogen sulfide, which is smelly, is another. It ishydrogen sulfide which gives us the characteristic sewer gasor “fart” smell.

When these gases are encapsulated in the ground over a longperiod of time, the smell is purged, leaving an odorless gas.The sewer gas smell can be removed easily from the mixtureby simply bubbling all the gas through calcium carbonate, whichis simple barn lime, and thereby scrubbing it so to speak. Thegas becomes odorless. The gas companies re-introduce anodor to odorless gas before selling it as a safety measure sothat our noses can detect “loose gas” that could be potentiallydangerous.

All these burnable gases are produced by anaerobic organ-isms feeding upon organic matter. To say they are anaerobicmeans they only live when air is excluded from the space inwhich they are functioning.

They are the same organisms that cause us to have intestinalgas. Each time a warm blooded animal defecates, some ofthe gas producing organisms are contained in the feces. Thisis why it can be said that methane occurs virtually every-where. Wherever air is excluded from the decomposition pro-cess, the production of methane and accompanying gases islikely to occur.

Stories are legion about a bunch of guys with nothing better todo than ignite the intestinal gas of one of their particularly“gassy” buddies, and then being amazed at how flammablethe experiment was.

The micro-organisms that produce flammable gas are tem-perature sensitive. They want body temperature in order tofunction most effectively. In people that is 98.6°F. In a chickenor a pig the body temperature is 103°F. So right around 100°Fis the optimum temperature for the process to work most ef-fectively. The action can occur at lower temperatures. As thetemperature drops so does the rate at which methane gas isproduced.

People will sometimes ask, “Why can’t I use the gas off myseptic tank to burn in a stove?” The typical septic tank swingsthrough such wide temperature fluctuations, the amount ofgas produced is minimal. Each time a toilet is flushed withcold water, the tank goes into “shock.” Each time some warmwash water from a bath or shower flows into the tank, itbecomes more active until the next shot of cold water. Suchtanks are ordinarily in the ground, which stays at a constant50° to 55°F. The ground is a constant heat sink, draining heataway from the tank. About all one gets from a septic tank, byway of gas, is enough to cause an unpleasant odor. Becausethe temperature cannot be maintained at the required work-ing level, such tanks have to be pumped from time to time.The solids cannot be efficiently digested and so keep buildingup.






Page 8

It is the concept of a tank which offers us the most practicalapproach to the task of harnessing the production of meth-ane. Liquid within a tank gives us two immensely importantfeatures–transport and the exclusion of air. Both are essentialfor maximum production.

Some methane production occurs in such places as an ordi-nary barnyard manure pile. The center of the pile is withoutair and with the heat generated by the pile some methane gasis bound to be produced. If we want to harness the concept,we will need a great deal of gas. A solid pile to give us whatwe would need would have to be, literally, a small mountain.In a tank, it’s an entirely different matter. It is much easier tohave the tank “just bubbling away” so that the amount of gascollected in a short time can be significant.

Key Questions

How much gas do I need? That will determine how much gasmust be produced. Next is, how much material do I need toproduce this amount of gas? The third question is, how largemust the equipment be to produce and store this amount ofgas?

Gas is thought of in terms of cubic feet. We can all visualize acubic foot–12 inches square in each direction. The amount ofgas within such a space of 12 inches square is determined bythe compression of the gas. Fortunately, when we are work-ing with methane, we are talking about only ounces of pres-sure–just enough pressure to push the gas to the burner,whether it might be a stove, water heater, or refrigerator.

To estimate the amount of gas needed, the average family offour burns somewhere around 200 cubic feet of gas a day.This covers the combined tasks of cooking, heating space andheating water. Obviously, individuals can trim this amount con-siderably by using efficient appliances, such as flow-on-de-mand water heaters, and high-efficiency space heaters.

The best way to get a handle on this information is to look atthe amount of consumption listed on the utility bill of somefamily you know and then observe their lifestyle.

Processes of Gas

We say that the liquid provides transport. That transport istwo-fold. Obviously, we must transport the material to thetank. Equally important, yet not so obvious, is the transport ofthe micro organisms to the material or vice-versa, so that thematerial can be digested by the life forms. Within the diges-tive tract of a warm blooded animal, this action takes place byperistalsis. We imitate this transport by very gently movingthe contents within the tank from time to time.


How Much Gas Does One Need?

For “home-made methane,” our pressure regulator is not anymore complicated than a heavy rock on an inflatable gas hold-ing bag, or the weight of a solid yet expandable gas holderfloating in liquid. It’s not very complicated.

Key Considerations






Page 9

Concerning The Tank

A simple paddle mechanism works the best. Some systemsre-circulate some of the gas to provide movement, but thishas proven to be less than satisfactory. Often inorganic mate-rial is stirred from the bottom of the tank–material such assand and small rocks if they are present–and the living organ-isms are injured in the process. The best method is a slowmixing action with a paddle of some sort. The paddle may beon a horizontal axis or a vertical axis. It merely has to movethe material very gently a few times each day.

The exclusion of air is essential to have the process work.While we know that even water contains some air–otherwisehow could fish breathe–once the activity of gas producingbacteria becomes established, even the air is mostly excluded.

The tank must be closed so that new air is not able to enter.This is done effectively by having both the fill pipe and theexit pipe extend below the water line. So, air exposure to thetank is limited to the surface of the water level in both the filland exit pipes.

In the past much discussion focused on whether the tank shouldbe horizontal or vertical. It is the consensus that when thetank is horizontal rather than vertical, it can work more effec-tively. (Note the illustration on pg. 25.) The reason is that thefill and exit pipes need to be spaced as far apart as possible.Then the material entering the tank has greater exposure tothe activity within the tank before being moved near the exitpipe.

The gentle stirring action needed, of course, mixes up every-thing. Yet if the new material is forced to “migrate” somedistance before reaching the exit pipe, then the micro-organ-isms will have more time to feed upon it before it is replacedby incoming material.

How big should the tank be? This is determined by how muchmaterial is available to the tank on a daily basis, and ultimatelyhow much gas one wants to generate.

Production Mixture

The input for the tank needs to be a mixture of manure andcarbon material. Carbon material is ordinarily understood aswaste vegetation, but it can’t be just anything. It needs to besomething that when soaked in water for a few days becomesvery soft. The bacteria don’t have any teeth. They have to“gum” it.

Hardness can be misleading. A carrot seems hard, but ifsoaked long enough it turns to mush. Grass clippings, on theother hand, contain a quantity of lignin, that cellulose fiber thatmakes wood very “woody.” Anything with a high content oflignin will not work well in a methane tank. Straw for the mostpart is acceptable. Hay is not.

Even such things as ordinary newspaper work well. Althoughnewspaper at one point was wood, the lignin has been brokendown so that when the newspaper is soaked for a day or so, itturns to mush–good stuff for our purposes. The bacteria wanta mixture of 30 parts carbon to 1 part nitrogen. Manure isnitrogen rich–about 15 parts carbon to 1 part nitrogen, somanure needs to be balanced with more straight carbon ma-terial. This ratio isn’t a critical proportion and the process stillfunctions, but 30 to 1 is the ideal.

Potency


The ability of manure to produce gas varies from animal toanimal. Chicken manure can be especially potent. I have ob-served as high a yield as 10 cubic feet of gas from each poundof naturally moist chicken manure which was mixed with somefinely ground spilled feed.

Hog manure usually yields about 4 cubic feet per wet pound.Cow manure usually yields about 1 cubic foot of gas for eachpound of fresh manure. The reason there is such a differenceis that much of the methane potential has already been re-leased when the waste goes through the digestive system of aruminant. There is usually so much of this kind of manure,using it is still worthwhile. Another good feature of the pro-cess is that raw manure is changed into something which isaged and totally acceptable to be placed on growing things.With any quantity of raw, green manure, this is not the case.

Sizing the System

Having established that we need around 200 cubic feet of gasa day, we need to set about designing a system that will pro-vide this. How much is 200 cubic feet? Visualize an inflatablebag that is six feet wide, six feet long and six feet high, andyou’re seeing a space of 200 cubic feet.

If we say that a mixture of manures will give us 4 to 5 cubicfeet of gas per pound of naturally wet manure we are going toneed about 40 to 50 pounds of manure a day. We would






Page 10

need even less manure if we use chicken waste. These fortypounds are going to be mixed with some type of additionalcarbon material, to which water, preferably warm water, willbe added to give us a “slurry.” This will most likely be about15 gallons of bulk. Visualize the content in three five gallonbuckets.

Size of the TankIt is generally a rule of thumb that the size of the tank needs tobe 40 times the size of daily input. This means that when 1/40th of the volume of the tank is introduced at the input endthen 1/40th of the volume will exit the overflow end simply bybeing displaced. Allowing some space at the top of the liquidfor the gas to collect, the tank should be about 50 times thesize of daily input.

Sewage plants that employ the methane process–and manydo–like to have a holding time of 90 days. In other words thepreference is to have the tank 90 times the size of the dailyinput. The purpose of this is to totally destroy any potentialpathogens. That length of time within the tank does exactlythat. Periodic inspections by the various health departmentsaround the country keep a check on such activity and findconsistently that the 90 day holding time accomplishes thisgoal.

Within a 40 day holding period most of the pathogens areeliminated. Because we are not dealing primarily with humanfeces (although this material may be used with animal waste)the longer holding time is not as imperative. Within a 40 daytime span the greatest amount of gas is produced. In a periodlonger than 40 days, the gas production begins to slow downconsiderably.

Tank Choice

A 1,000 gallon discarded milk bulk tank would be ideal. Be-cause bulk tanks already have a system for cooling the tank,this system could be easily adapted for holding the tempera-ture of the tank at 100°F. rather than cooling it. One type hasthe “radiator” already built-in.

The fact that the tank is stainless steel is also an advantagebecause it would extend the life of the tank considerably overordinary sheet metal. The acids within the mixture do not workrapidly on the tank, but they will deteriorate it over an ex-tended period of time.

Originally, I had an ordinary 250 gallon fuel-oil tank that Iused for demonstration purposes. It lasted for several years.It finally rusted through, but considering the fact the metalwas relatively light gauge to begin with, the tank served well.Because oxygen is excluded in the process and the pH mustbe kept at neutral, the deterioration of the tank was not rapid.

Another great feature of a milk bulk tank is the fact it alreadyhas a mixing paddle as part of the tank’s design. All accessports above the water line would have to be sealed air tightfor effective gas production and, more importantly, just com-mon sense safety.

We need a tank that is 50 times the volume of the daily inputof 15 gallons, or a 750 gallon tank. Obviously, a 1,000 gallontank would be ideal to take care of extra demand for produc-tion or additional material input.


41.5 FEET LONG

CUTAWAY SIDE VIEW

VIEW WINDOW 12 BY 15 INCHES8 INCH FILL PIPE

30 INCH SERVICE DOME

GATEVALVE

SOLARHEATER INPUT

SUPPORT PIERS

FLOOR BETWEEN SLURRYAND SOLAR HEATED WATER

GAS LINE

TANK DRAIN

SOLAR HEATER OUTLET

GATEVALVE

4 INCH DRAINWITH 12 INCH DIP

Al Rutan’s Methane Digester Design






Page 11Gas Storage Tank

The Gas HolderRegarding a gas holder, one may use a solid vessel open atthe top filled with liquid into which another solid vessel openat the bottom is placed. The gas pushes the top unit up out ofthe liquid as the gas is produced.

The simplest type of gas holder is an expandable bag. It canbe something like a waterbed mattress upon which a weightis placed to produce enough pressure to send the gas to thepoint where it is used–a burner of some type.

One may use simply a vinyl of some type, but the best type ofmaterial is a nylon fabric that is impregnated with vinyl–notlaminated, but impregnated–which becomes exceedingly du-rable. If this inflatable bag is placed inside a “silo” of sometype, then there is a measure of assurance that the bag is notgoing to be punctured. The people who work with the nylonimpregnated vinyl–one of the trade names is Herculite–seal itby a process of electro-statically welding it. Using an ordi-nary adhesive may not work because methane has a ten-dency to dissolve a number of adhesives

For NowThe process of making methane gas is relatively simple if oneis attuned to the basic needs of the process. They are: theright balance of material, the right temperature, and the ex-clusion of air. Given these three conditions, the methane pro-cess is virtually unavoidable. The trick is to be sensitive to thefine-tuning of each of these requirements.

Al Rutan

More of Al’s articles will be publishedin the next few months. Peace, ldb





August, 2005 Energy Self Sufficiency Newsletter Page 5Energy Self Sufficiency Newsletter

Page 5

In the last issue of ESSN, Al’s first article ‘Prologue toMethane Gas’ praised the ease with which methane isused – merely turning a valve to have instant vaporfuel. It takes so little effort. If gas is so easy, how doesfifty pounds of stuff get pushed around without any ef-fort? Aw...you caught the inconsistency!

That article says that we need about 50 pounds of waste daily, amixture of manure and carbon material to feed the digester that willturn this material into about 200 cubic feet of gas.

The focus of this article is just this problem. As anyone who hasdone any kind of homesteading knows, there is a hard way and aneasy way to do every job. Part of the endearing quality of Americaningenuity is to see how people can approach a task that is down-right tedious, and by some clever manipulation, make it easier.

Easy is Better

This really became a lesson taken to heart while living at Red Lodge,Montana. I was in the middle of a project raising rabbits for market –lots of them, about 200 breeding does producing litters.

Feeding and watering this number was a time-consuming chore. Imade hoppers for the hay and feed pellets early on, but providingabundant water was a drag. I upgraded from water dishes to waterbottles with a valve. This was an improvement in cutting down thelabor. The big jump was to a system of watering valves fed by littleplastic lines from a central tank with a float valve to control both thewater level and pressure on the water lines.

In one situation, the water was put into 200 little water bowls whichwere constantly being spilled or fouled with waste. In the other,water was supplied by a small pipeline with drinking valves in eachcage. The result was the same – water to drink, but the effort neededwas totally different. The two situations accomplished the sameeffect – abundant fresh water.

More On MethaneAl Rutan, the Methane Man

©1992 Al Rutan

First printed inHome Power #27 • February / March 1992 Alternative Fuels

There is another consideration that must be brought to mind at thispoint. In the methane process, we are working with living creatures.Therefore a moral dimension must be considered if we are going toachieve a measure of serenity for ourselves in this whole process.

To have a genuine sense of well-being about the entire operation,the animals and the space for which the person is responsible musthave an ongoing atmosphere of serenity. If this sounds a little bitlike St. Francis of Assisi, well, so be it and no apologies. The pur-pose of life is not merely accomplishment, but accomplishment in acaring and respectful way.

As people, we harness the work of creatures. Some may maintainthis is not right. I don’t agree. I do feel strongly that the animals withwhich we work and upon which we depend do have the right to areasonable quality of life. So at this point we are talking about ani-mal rights. The concept of animal rights means different things todifferent people. To me, it means that an animal has a right to areasonable quality of life. An animal has a quality life when it feelsgood about itself. This is most clearly evidenced by grooming. Ani-mals, if they feel good about themselves, groom themselves andtheir friends.


Al with a small DigesterAl with a small Digester

Consider the Critters

Death for an animal, or a person for that matter, is not the worst thingthat can happen. Quality of life while something is alive, be it plant,animal or person, is of major importance in the scheme of things.One who homesteads can not be mentally well off if such a person isnot sensitive to the quality of life of the living things around thehomestead. Are the animals feeling good, as evidenced by theirgrooming?

Quality of Life

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There are two natural forces that work well for us. One is gravity andthe other is water. In rolling countrysides, barns are commonly builton hillsides. The hayloft is easily accessible by simply driving inrather than having to go through the labor of hoisting every bit ofhay with some kind of sling mechanism. The hay is forked down tothe animals below, using gravity.

The more that gravity can be utilized for tasks the better. The animalwalks around. It can walk up as well as down. If the housing for theanimals can be above the digester, then this saves work.

Water has long been used for transport. Since the development ofthe flush toilet, in the 1850’s in England by Mr. Crapper (nokidding...that really was his name!), we have been using water tomove feces.

Using water has a problem. What I am going to say now is exceed-ingly important. Many an engineer and university professor work-ing with the methane concept cannot seem to grasp a simple fact. Itis the nature of liquid – especially water – to release heat. Whenwater is heated, it will not retain its heat. We say, “It cools down.”

It is the matter of manure itself. How can a person move it with theleast effort possible? Manure delivery systems have been devisedfor various types of critters, except the horse. To my knowledge,there is no device more automatic than a scoop shovel for cleaningout a horse stall.

If one DOES have animals, the feces HAVE to go somewhere. So atthat point it makes a great deal of sense to turn the waste into vaporfuel (methane) and compost.

When the waste comes out of an animal, it is at exactly the righttemperature – body temperature. As it lies on the ground, it coolsoff. This cooling during the cold time of the year is severe. Thesooner the waste is transported from the animal to the tank thebetter. If the waste loses heat, then the heat must be restored tohave the methane digestive process occur in the best manner pos-sible.

This brings us to the biggest challenges in the entire methane pro-cedure. How do we gather the manure to begin with? How do wegather it as soon as possible after it leaves the animal and before itcools down?

Moving the Material While It’s Warm

Gravity Works for Free

Water Must Be Warm

If we are going to use water in the process of transporting manure,and have it work well, we must understand that water cannot beallowed to stand around waiting for the waste. Warm water can andcertainly should be used to wash down a gathering point below aslatted floor. The gathering point had better not be a holding pit inthe ground because the whole thing will cool off to ground tempera-ture. Another consideration is that in a pit the methane activitybegins right away, so animals above a pit are breathing contami-nated air. This is why holding pits MUST have ventilation fans ifthey are under confinement areas.

A Dilemma

Now, why make a point of this if we are talking about methane andmanure? We are faced with a dilemma. On the one hand we want tocollect waste with the least effort possible and do it as automaticallyas possible. On the other hand, we need to have a measure of sensi-tivity to the needs and quality of life for the animals on which wedepend.

If the animal wanders about freely, it will be very difficult to collectits waste. On the other hand, if the animal is tightly caged or tied, itsquality of life is virtually nil. So what’s the answer?

Somewhere there is a middle ground. Chickens, for instance, domost of their pooping while they are perched at night. Milk cowsleave a quantity of used grass in the gutter while being milked orheld in the barn during the night.

Hogs that are totally confined don’t have much of a life. Hogs thatare confined only through the night will leave a good share of theirwaste behind when penned only part of the time.

Chickens do not do well housed on hardware cloth because theirnatural inclination is to peck and scratch. I’ve seen a roost systemwhere the area under the roost was wired with large chicken wiremesh. The chickens could not get to the manure to disturb it after anight of roosting. They were free to roam at will during the daytime.

Slatted floors are useful for both hogs and cattle from the stand-point of cleanliness if the animals are not required to stand on themat all times. In all these design considerations for an enclosed area,the needs of the animal must be considered if we are to have happyanimals.







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So just how practical is the thought of having animals around ahomestead? The trend is increasing for relying less and less onanimal parts for human food. Folks tend to become more and morevegetarian. We still need the family mule to plow the garden, a fewmilk goats for the delicious and healthful treat of fresh goat’s milk, ora few sheep to produce wool for hand spinning and the cottageloom. There is wisdom in involving some kind of animal support inour homesteading.

Farmers who raise nothing but corn are still hooked into the food“grid” when they drive to the store for their butter, milk, and eggs.Our great grandparents would shake their heads!

Al Rutan

Do We Really Need Animals?Think in Terms of Free Energy

How does one have warm water with which to transport? Each loca-tion will have its own plusses and minuses in working out thisdesign problem. A person has to consider all the ways of capturing“free” thermal energy – solar, wind, whatever, and applying it to thesituation at hand.

We’re most likely looking at periodic washing down of a gatheringarea with warm pressurized water. This will both increase the forceof the wash and cut down on the amount of warm water needed. Themore automatic the concept can be and the less labor intensive, themore of a ideal situation a person can enjoy.

Al Rutan – RIPAl Rutan – RIPAl Rutan – RIPAl Rutan – RIPAl Rutan – RIP





September, 2005 Energy Self Sufficiency Newsletter Page 18Energy Self Sufficiency Newsletter

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THE METHANE PROCESSTHE METHANE PROCESSThird in a series by Al Rutan,

the Methane Man© Al Rutan 1992

First published in Home Power #28 • April / May 1992

Mold and mildew have been seen by everyone.Most people have observed the process of rotting. We knowit is common in nature. Methane gas is just as common, butnot as observable. Anyone near a sewer manhole or a plumb-ing vent pipe can get a whiff of the methane process in ac-tion. The reason for saying this is to alleviate the apprehen-sion that the methane process is going to be difficult to har-ness. It’s no more difficult than making a loaf of bread. If theconditions needed are present, the desired result will invari-ably occur.

What we are considering is a biological process in which weuse the waste product of bacteria. We shouldn’t even call thelittle creatures bacteria but more accurately “methogenic mi-cro-organisms.”

Primeval LifeIn the process of evolution, they antedate the formation ofbacteria. They are one of the very earliest forms of life. Whenscientists explore outer space with telescopes that can sepa-rate light spectrums, they look for the presence of methanegas. If the gas is present, there is evidence for the beginningof life. For our purpose, we are going to refer to thesemethogenic micro-organisms simply as “bacteria.” They arecurious little critters. Their waste product burns. Not only doesit burn, it burns very well. Combustion produces only carbondioxide and water vapor. There is no ash, no soot, no tar, nodirt of any kind. It’s a very efficient fuel.

CharacteristicsThis fuel is composed of carbon and hydrogen. Its chemicalformula is CH4 . It has an octane rating of 110 and producesaround 1,000 BTUs (British Thermal Units) of heat per cubicfoot of gas. Because most gas is invisible, it seems mysteri-ous. If we think about our own chemistry for a minute, itwon’t seem so strange. We know that we breathe in oxygen

and exhale carbon dioxide. So we, ourselves, are gas produc-ing organisms.

Gas MakersIf we think about this, then the process of the methane bacte-ria doesn’t seem so strange. The part that is “strange” is thatit burns. If mixed with sufficient amounts of air, it burns veryrapidly... explosion! In nature, some bacteria operate best inthe presence of air because they require oxygen, and somefunction only when air is excluded. The methane bacteria areof this latter type. When exposed to air, they die. Becausethey live and function only when air is not present, they arecalled anaerobic or “without air” bacteria.

Natural Gas and Sewage GasWhat is the difference between natural gas and sewage gas?Virtually none. For all practical purposes the bacteria whichmake the gas are the same. Natural gas sold by the utilities is90%, or better, methane. It has been made in the ground overeons of time and in most instances is almost pure methanebecause the ground has purified or “scrubbed” the gas. Theonly difference between gas produced in the earth and gasmade in. sewage plants is that in the sewage plants the pro-cess is speeded up. In speeding up the action there are sev-eral gases produced, notably, carbon dioxide. In a sewageplant the mixture is about 70% methane and 30% carbon di-oxide, with trace amounts of hydrogen sulfide. The carbondioxide largely dissipates from “natural gas” over time. Thespeeded-up process product, including the carbon dioxide, isreferred to as “biogas.” Actually all natural gas is “biogas”because all of it was produced from something that was atone time living. The only distinction is that so-called “biogas”is produced in a shorter time from things that have been livingrecently. Making methane for ourselves, we hasten the pro-cess.

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How Does it All Happen?There are two types of “without air” or anaerobic bacteriathat work together to make methane. The first type we’ll call“acid forming.” Their function is to feed upon raw organicmaterial. They produce no methane, only carbon dioxide andsome acids and “food” for the second bacteria type, themethogenic micro-organisms. The “food” consists of simplesugars, simple alcohols and peptides. When the methogenicmicro-organisms in turn feed upon this simpler fare they pro-duce methane. Thus when organic material is placed in a con-tainer where air is excluded, both carbon dioxide and meth-ane are produced.

Need for BalanceThe methanogenic micro-organisms need the food providedby the acid-forming bacteria, but they also need a neutral en-vironment. If the right balance between acid and base (alka-line) is not present, the methane micro-organisms are in troubleand no methane is produced. They have to have a pH of 7 to8.5 in order to be normally active.

What Does pH Mean?I think it’s important not to assume that everyone is familiarwith pH. Websters defines pH as “the negative logarithm ofthe effective hydrogen ion concentration... used in expressingboth acidity and alkalinity on a scale of 0 to 14 with 7 repre-senting neutrality. Numbers less than 7 represent increasingacidity and numbers greater than 7 represent increasing alka-linity.” So the term pH means percentage of hydrogen, ormore precisely, proportion of hydrogen in relation to the hy-droxide ion in a given material. It’s the negative logarithm ofthe hydrogen ion concentration, so a pH of 7 means that theconcentration of hydrogen ions is 10 -7 . Aren’t you glad youasked? Anyway, it’s important information for keeping thedigester healthy and happy. The ideal pH for digestion is from7.5 to 8.5.


The pH Scale

Acidic Neutral Alkaline

a healthydigester

How to Get a ReadingHow does one measure pH? This is the easy part. Chemicalsupply houses and even most drug stores sell rolls of paper(called litmus paper) and/or little plastic strips that turn colorwhen dipped in solution to tell you what the pH is. There is aslightly different color for each of the different pH numbers.You tear off a piece of the litmus paper about 1 1/2 inches

long and dip it into a little of the slurry. The paper will start tochange color within seconds. When compared to the colorscale on the container, you can tell right away what the pH ofthe slurry is.

Why the Process May DragGenerally if there’s a problem, it’s that the slurry is too acidic(pH below 7). If there is a lot of new, raw, green materialplaced in the digester, the acid forming bacteria have a fieldday. The methane bacteria are so annoyed by the high acidconcentration, they simply can’t function. When this occurs,it can take a long, long time for the methane process to getunder way naturally. This generally occurs only in the begin-ning with start up or if too much new material is added at anyone time. If a measured amount of new material – no morethan 1/40th of the total liquid volume of the tank – is added,then the new material is dilute enough not to upset the bal-ance. At start up, though, there’s a lack of micro-organisms,and an inclination towards excessive acidity. Understandingthis, we can see why some of the early literature on makingmethane states that the start-up time can be anywhere fromthree weeks to three months. This is assuming that one isbeginning with totally “new” material without the assist ofsome already partially digested slurry. A three month start-upwould discourage almost anyone from attempting to harnessthe process..

Starting UpPartially digested slurry is kind of like sourdough starter. Ithas large populations of the right kind of micro-organisms todigest raw material and make methane. You can start fromscratch, but it’s faster if you can get some activity that’s al-ready established. When I started a small digester in 1976, Iseeded it with some slurry from the St. Cloud, Minnesota,sewage plant. The plant engineer told me at the time that theplant was so overloaded with wastes from a local meat pack-ing house that the digester was just “going through the mo-tions” and really not working properly. I took some of theslurry anyway. What the heck. It was free and I needed some-thing to get the tank producing. After a few days I started toget methane and then I lost it. The tank was still producing alot of gas, but it was carbon dioxide – it didn’t burn. The pigmanure I had begun to feed the digester along with the slurryfrom the St. Cloud plant was just too much raw material forthe process. So there was a lot of carbon dioxide and acid.The acid forming bacteria were having a feast. I mentionedthe problem to friend with whom I was working at the time.He said, “I make a lot of wine at home. Every once in a whileI have the same problem. When I do I add a little baking soda.It straightens out the condition right away. The nice thing is itdoesn’t leave an after taste. In your case that isn’t a prob-lem!”

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The Benefits of Baking SodaSo I tried the baking soda. It worked like a charm. Withinthree days I had methane on the way. At a seminar I waspresenting a few weeks later, I mentioned this to the group.Baking soda was my “discovery” for straightening out the pHin the digester. One of the people at the seminar sent me aclipping from Business Week magazine a couple weeks later.It was dated June 14, 1976. The headline for the article read“Dosing Sewage With Baking Soda.” It went on to say thiswas a whole new idea for treating sewage plants; they usedto use large amounts of ammonia. The article further pro-claimed that soda not only assisted in the more efficient di-gestion of sludge but increased the volume of burnable meth-ane gas. The most surprising statement of all: bicarbonate ofsoda “acts as a sort of vitamin for bacteria.” This is the secretfor keeping your digester sweet and happy. Just add a little ata time until the pH is just right. Keep adding it periodically ifthe pH keeps dropping until the acid forming bacteria are nolonger producing an override of acid. Don’t be fooled if a lotof gas starts coming. The baking soda itself will produce somecarbon dioxide.

The Nature Of HeatHeat is essential for abundant methane production. In warmclimates the process works with little help when the otherconditions needed occur. For many of us who live in a coldclimate, making methane work is a challenge. One needs tokeep in mind that heat stratifies, whether in air or water.Heated fluids are less dense and tend to rise. This naturalthermal stratification in liquid is, of course, the very reasonwhy the thermal syphon principle in water heaters works sowell. It was this very fact which suggested a digester designwith a false floor containing only water. The bottom, the low-est point of the “working” tank, could be heated by athermosyphon action from some heat source such as solar, oreven a little of the gas itself. The heat from the lowest part ofthis “double boiler” type design would rise through the slurryso that the very bottom of the “working” tank could moreeasily be kept at the desired temperature in the entire digest-ing area. Such a tank would most easily be constructed offiberglass. It could be virtually any size. Next time we’ll thinkabout the barriers to the transfer of heat – insulation – a criti-cal key to any successful operation. This brings us to the ques-tion of whether the operation is a net energy producer or anenergy consumer.

Al Rutan

Photo by Al Rutan

Al with the prototype of his Methane Digester

... and the finished Metal Tank Methane Digester on its trailer(See ESSN July 2005 for internal design)

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October, 2005 Energy Self Sufficiency Newsletter Page 18Energy Self Sufficiency Newsletter

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EVEN MORE ON METHANEEVEN MORE ON METHANEFourth in a series by Al Rutan,

the Methane Man© Al Rutan 1992

First published in Home Power #30 • August / September 1992

Temperature is critical to the success of any methane opera-tion if it is to be considered an energy system. If the primaryconcern is waste management and not energy production, thena net energy loss is not a major consideration. If the intent isto produce energy, a net energy gain from the process is ev-erything.

Body HeatMethane activity, in one of its natural situations, is found in thedigestive tract of warm blooded animals, people included. Forpeople, the normal body temperature is 98.6° F. In a chickenor pig it is 103° F. So right at 100° F is the ideal workingtemperature for the methane process. To maintain this tem-perature outside an animal is a problem if the ambient tem-perature is cool or cold.

Sewage Plants Energy ProducersThere were several methane farm operations launched in theupper midwest with much bravado and publicity. All of themare now out of business. On the other hand, sewage plants ofmedium size still commonly use the process to treat toilet wasteand destroy pathogens, but in each instance they consumemuch more energy during the cold part of the year than theyproduce. The toilet water flowing into each sewage plant isordinarily cold. It would be exceedingly difficult for sewageplants to be anything but energy users rather than producersat any time except in the hottest part of the summer.

Universities’ verdicts at the end of the methane studies werealways the same: “It’s possible, but it isn’t practical. It takesmore energy to run the system than the system can provide.”In harnessing methane as an energy system, it is important toconserve heat in the process of producing gas. A few yearsago a new sewage plant was built at St. Cloud, Minnesota tothe tune of 17 million dollars. I asked the engineer, “Did youinsulate the tank?” He said, “Oh yes. The old one used toactually freeze on the north side during the winter.” My nextquestion 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 sewageplant burned $750,000 a year in fuel oil to keep the digester at100° F. It costs big bucks to flush the toilet in St. Cloud.

Capturing WarmthHeat has to be considered as something that is very slippery.Conserving heat requires understanding insulation. We arefortunate that there are many types of insulation availablenow that simply did not exist a few decades back. On theother hand, there’s a general lack of understanding of insulat-ing properties of common building materials such as wood,metal, and concrete. I recommend Movable Insulation, pub-lished by the Rodale Press in 1980.

Anyone familiar with insulation knows that if it gets wet, it isno longer insulation. Some “closed cell” insulating materialssuch as urethane, styrofoam, and polyethylene foam are moreimpervious to moisture than cellulose or fiberglass insulation.Even closed cell materials can break down if moisture underpressure is present.

Styrofoam is used on the outside of the foundations to providea frost barrier for basements. Soil pressure and moisture cancause the styrofoam to be less than “bone dry” and therebylose much of its insulating ability.

Situating the TankMy personal preference is that the methane tank be as effec-tively insulated as possible. Insulation should be below theflow line of the material entering the tank, but should not beburied in the dirt, regardless ofthe insulation. The temperatureof the ground several feet be-low the surface stays quite con-stant at 50° F – 55° F. To themethane tank, the earth is a“heat sink”, a cool mass al-ways ready to absorb its heat.The best way to fight this heatsink is to insulate the tank and build it above the ground. An-other good reason for a free-standing tank is access to thegrit trap at the bottom. A free-standing tank should be cov-ered with six to eight inches of high quality insulation. Variouspeople have asked if a buried tank would work. I can’t saythat it won’t, but I’ve never seen any that work in a coldclimate, and I have seen several that don’t.






















How Much Gas Can I Get?There’s a wide range of mixes of material you feed a meth-ane digester. It’s similar to what happens when we eat. Someof the material enters our system to maintain it and some of itpasses on as waste. When manure is considered, all of it,minus the water, is designated as “total solids”, and the partthat is digestible to the bacteria is labeled “volatile solids”.The numbers of what is and what isn’t available for gas pro-duction have been gathered repeatedly over the years. Eachaccount is quick to qualify any statement by saying that thereis any number of variables when dealing with animals regard-ing what they are eating and how they are housed. One of theclearest reference sources is a newsletter printed in 1973 bythe New Alchemy Institute in California. Their figures corre-spond to what I’ve experienced.

The numbers run like this: a cow drops an average of 52 lbs.of feces a day, of which about 10 pounds are solids, the restbeing water. Of the 10 pounds of solids, 80% or 8 lbs. arevolatile—can be turned into gas. A horse produces an aver-age of 36 pounds of feces a day, of which 5.5 lbs. are volatilesolids. A pig produces 7.5 lbs. per day of which 0.4 poundsare volatile solids. A human produces 0.5 pounds of feces aday of which 0.13 pounds is volatile solid. Chickens produce0.3 pounds a day which 0.06 pounds is a volatile solid.

All of this is good information, but it still doesn’t tell us howmuch gas we can reasonably expect. If you ask an “expert”in the field, you’ll get an answer something like, “It all de-pends...” All manure contains a degree of nitrogen, but be-cause nitrogen exists in so many chemical forms in nature—ammonia (NH3 ), nitrates (NO3 ), proteins, etc.—it’s difficultto test the total amount of nitrogen in a given material.

Why Consider Nitrogen?The process wants one part nitrogen to every 30 parts ofcarbon. Manure is nitrogen rich, averaging about 15 partscarbon for each part nitrogen, so all the studies show that gasproduction is substantially increased by including some car-bon material along with the manure. The nitrogen proportionmay be even higher in animal waste if urine is included withthe feces because urination is the principle way an animal ridsitself of excess nitrogen.

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Restoring WarmthWhen feces leaves the body, the waste is at exactly the righttemperature for working within the methane digester. What-ever heat is lost in the interval between leaving the animal andentering the digester has to be restored. If the heat needed issignificant, there needs to be a heat source available with anabundance of “free” energy, such as solar or wind.

Relation to FermentationThe methane process is a type of fermentation. Most folkshave baked bread or made homebrew beer or wine at onetime or another. For instance, after a yeast dough is kneaded,it is put in a warm place free of draft and allowed to rise. Adraft could produce cooling. The yeast organisms feed uponthe mixture’s sugar. This produces carbon dioxide bubbles,which cause the dough to rise. There is a similar activity withinthe methane tank. The methane organisms feed upon simplesugars, alcohols, and peptides produced by acid forming bac-teria. Methane gas, CH 4 , is the result.

I’ve been asked if the digestion process within the tank doesn’tproduce some heat, such as the heat produced in a compostpile. It probably does. Because the metabolic activity is sodiluted and spread out within the tank, the heat available isminimal in comparison to the target temperature.

Awareness is EssentialYou’ll need to know how hot the tank is, day to day, season toseason. To eliminate the guesswork, install sensors both in-side the tank and outside the tank. Record temperature bothinside and outside the tank over a period of time. Then youwill know how efficiently the tank is retaining heat, at whatrate the temperature drops when no heat is added, and howmuch energy is needed to raise the temperature. If this isdone, then a reliable calculation can be made of how muchgas is needed to maintain working temperature if “free” heatis not available.

Producing methane gas is relatively easy. The conservationof heat more than any other factor determines whether amethane system will “fly” or not. Of all the systems I’ve seenthat failed, the principal reason is improper handling of heat.

Care and Feeding of your Methane DigesterHaving thought about temperature, we can turn our attentionto feedstock. I work with a mixture of manure and vegeta-tion. Sometimes the question is asked: can’t one use just veg-etation to produce methane? It can be done because MotherNature 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, thereis fresh input of the microbiological organisms needed. Continued on next page





















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To illustrate, straight chicken manure will produce only fivecubic feet of gas for each pound of manure, but chicken ma-nure mixed with paper pulp will produce eight cubic feet ofgas for each pound of manure used. My experience was anoutstanding ten cubic feet of gas for each pound of chickenmanure when the manure contained some ground feed thathad been spilled.

Cow manure will produce only 1.5 cubic feet of gas per pound,but cow manure mixed with grass clippings will produce 4.5cubic feet of gas per pound of manure.

The Nature of BiogasAssume that we have a gas producing system and it’s makinggas nicely and filling the gas holder. What do we actuallyhave? It’s important to understand that it isn’t all methane. Aproportion of it is carbon dioxide, produced by the acid form-ing bacteria, which doesn’t burn. This fact isn’t immediatelyevident because if one ignites the end of a hose coming fromthe gas holder, there is a blue flame.

The fact that is important to know is: if we had pure methanewe would have a hotter flame—about 1000 BTU (British Ther-mal Unit) for each cubic foot of gas. With the dilution of car-bon dioxide, we have roughly 600 BTU for each cubic foot ofgas.

The composition of the gas in our gas holder will be:CH4 methane: 54 – 70%CO2 carbon dioxide: 27 – 45%N2 nitrogen: 0.5 – 3%H2 hydrogen: 1 – 10%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 anddump the carbon dioxide. Interestingly enough, Mother Na-ture has made it very easy to do just that because these gasesall have different specific gravity weights.

How to Get Pure MethaneThe specific gravity of methane is about 0.55 in relation to theweight of air, so it rises, as does hydrogen. Carbon dioxide onthe other hand is twice the weight of air. Within a vertical gascontainer, if the gases are allowed to settle, they will naturallyseparate themselves, the flammable gases rise to the top. Thisfact suggests that a good design should have a petcock at thebottom of a vertical gas holder. Use it to bleed off the accu-mulated carbon dioxide. In the right setting, this isn’t environ-mentally harmful, because the trees and growing things aroundthe yard will welcome a fresh sniff of carbon dioxide.

Al Rutan

Elysium



















December, 2005 Energy Self Sufficiency Newsletter Page 7Energy Self Sufficiency Newsletter


One should be at either the right or left side of center and thepipe at the opposite end of the tank should be on the other sideof center. It doesn’t make any difference to which side ofcenter the pipes are placed. But it’s important that the pipesat the ends of the tank not be in line with each other. Such aplacement of the pipes provides another important advantage— the best position for the stirring mechanism. On the plastictank, the stirring mechanism was vertical with a crank at thetop. After a short time, I learned that this was a poor designfor a stirring device. The seal at the top is difficult to keepvapor tight. If the bearings for the stirring mechanism arebelow the water line, then any leakage is no more than a littlemoisture, but not vapor.

When the Tank Gets “Cranky”Also an oversight in the vertical stirring device design was theomission of a bearing point at the bottom end of the shaft. Itwas left to “float”. With the resistance of the material withinthe tank, the pressure on the one bearing at the crank end ofthe shaft tended to distort the cover of the tank as the crankwas turned.

Ideas that Worked — the Heat BathThat’s the bad news. So what’s the good news? The waterbath for providing heat to the tank. I originally thought thatthis would be an effective way to transfer heat from what-ever source to the tank. In actual operation, the conceptworked even better than anticipated.

Heat is supplied from a two foot square hot water box placedbelow the level of the water bath. The placement of the sourceof hot water under the water bath allows the water to circu-late via a thermosiphon: hot water rises in a closed circuit ofwater. The connecting pipes are two inches in diameter —one for supplying warm water and another for the return ofthe cooler water. The pipes from the hot water box connectto an 18 inch deep metal water bath underneath the tank. Thetank is placed on supports six inches above the floor of thiswater bath.

Al RutanRIP

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Last in a series by Al Rutan,the Methane Man

© Al Rutan 1994First published in Home Power #40 • April / May 1994

In previous articles, I discussed a low pressure storage tank,tank insulation, pH balance, animal treatment, and heat reten-tion. I’d like to share some new information I have learnedsince then. Some things worked and other things didn’t, but allfacts whether positive or negative are part of the masteringprocess.

Currently, my methane demonstration is being upgraded. I amdiscarding the plastic tank that served as a digestion vesselfor the last year in favor of a metal tank. Why the change?For several reasons. First, the problems.

Bonding DifficultiesThe primary difficulty is maintaining a vapor tight seal be-tween the fill and overflow pipes and the tank. The plastictank didn’t cost much when new, so it was too tempting topass up. But experience has shown that it was not a goodchoice. The tank material is polyethylene and the pipes arePVC plastic. While it’s possible to weld polyethylene withheat and produce a bond, it isn’t something that an amateurcan do easily. I attempted to produce a vapor tight seal withvarious types of glues and epoxies, which was achieved withsome success.

But the tank was often moved from one location to anotherby the trailer on which it is mounted. The sloshing within thetank caused the pipes to break the bond with the tank.

A second reason for replacing the plastic tank is that it is tooshort; the tank is three feet in diameter and only five feetlong. The best proportion for a tank is three to five times aslong as the diameter. This rule of thumb became obvious whennew material was introduced into the tank at the fill pipe.What exited through the overflow was working nicely, stillbubbling like crazy.

Slurry Still WorkingThe supposed “waste” or “spent” bucket wasn’t spent at all,but continued to be active after it had been forced out of thetank. A short tank is truly an inefficient design. The fill andoverflow pipes are just too close together. Also, the fill andoverflow pipes should not be in line with each other.

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