Hi Thomas >Hey, just a thought, but since it appears that the most readily >produceable biofuel is methane from digesters, maybe this bears more >discussion.
You won't say that when your digester leaks some air and explodes, and the, um, feedstock hits the fan! I'm not so sure it's the most readily produceable biofuel, I think it's quite troublesome. IMHO both biodiesel and ethanol would be simpler, if it came to a choice and all things were equal (which they seldom are). A good combination might be to use biogas for energy in producing biodiesel or ethanol for fuel. Biogas as mobile fuel has its problems. See the excerpt below from Peter-John Meynell's book "Methane - Planning a Digestor". I'm right with you that biogas needs more discussion on the list, there's been very little, and it certainly qualifies. Stephen Lakios knows a lot about biogas, what do you think Stephen? Anyone else? We don't talk much about woodgas either (producer gas). Nor about using straight vegetable oil as diesel fuel. >Exactly how difficult/expensive is it to compress methane >to the point where it could be used with standard propane fuel systems? >Isn't propane/butane a mixture of biogasses? I don't know, but it seems >that even if a compression system was relatively expensive, the >potential foruse of waste materials for feedstock may make it >worthwhile, and avoid the "there's not enough food for people, how can >we use it for fuel?" argument, which is the one I hear most frequently >talking to people about biofuels. I think many or most of us are using wastes - WVO for biodiesel or any number of wastes for ethanol. If we didn't use them they'd either foul up the landfills and/or the water systems, or just go to waste (eg windfall fruit in a pigless orchard). Optimising waste-use could produce immense amounts of energy with zero loss to anyone and great gain to everyone in environmental improvements, apart from more diversified energy supply and lower fossil-fuel use. Anyway, it's nonsense that there's not enough food for everyone, there's more than enough. The extract from Food First's The Myth of Scarcity below should help you counter that argument. >(I think it's mostly >politics/profiteering myself, but hey...) Right. > Anyway, happy holidays to everyone on the list and good luck with >your endeavors this year. Who knows, maybe this will be our >millenium:-) I think it had better be, if there's going to be one! Happy holiday to you too. Best wishes Keith Addison Journey to Forever Handmade Projects Tokyo http://journeytoforever.org/ >Sincerely, >Thomas Jumper From The Myth of Scarcity http://www.foodfirst.org/pubs/backgrdrs/1998/w98v5n1.html The world today produces enough grain alone to provide every human being on the planet with 3,500 calories a day. That's enough to make most people fat! And this estimate does not even count many other commonly eaten foods - vegetables, beans, nuts, root crops, fruits, grass-fed meats, and fish. In fact, if all foods are considered together, enough is available to provide at least 4.3 pounds of food per person a day. That includes two and half pounds of grain, beans and nuts, about a pound of fruits and vegetables, and nearly another pound of meat, milk and eggs. Abundance, not scarcity, best describes the supply of food in the world today. Increases in food production during the past 35 years have outstripped the world's unprecedented population growth by about 16 percent. Indeed, mountains of unsold grain on world markets have pushed prices strongly downward over the past three and a half decades. Grain prices rose briefly during the early 1990s, as bad weather coincided with policies geared toward reducing overproduction, but still remained well below the highs observed in the early sixties and mid-seventies. All well and good for the global picture, you might be thinking, but doesn't such a broad stroke tell us little? Aren't most of the world's hungry living in countries with food shortages - countries in Latin America, in Asia, and especially in Africa? Hunger in the face of ample food is all the more shocking in the Third World. According to the Food and Agriculture Organization (FAO) of the United Nations, gains in food production since 1950 have kept ahead of population growth in every region except Africa. The American Association for the Advancement of Science (AAAS) found in a 1997 study that 78% of all malnourished children under five in the developing world live in countries with food surpluses. Thus, even most "hungry countries" have enough food for all their people right now. This finding turns out to be true using official statistics even though experts warn us that newly modernizing societies invariably underestimate farm production - just as a century ago at least a third of the U.S. wheat crop went uncounted. Moreover, many nations can't realize their full food production potential because of the gross inefficiencies caused by inequitable ownership of resources. Finally, many of the countries in which hunger is rampant export much more in agricultural goods than they import. Northern countries are the main food importers, their purchases representing 71.2 percent of the total value of food items imported in the world in 1992. Imports by the 30 lowest-income countries, on the other hand, accounted for only 5.2 percent of all international commerce in food and farm commodities. From "Methane - Planning a Digestor", Peter-John Meynell, 2nd edition, 1982, Prism Press, Dorchester, UK, ISBN 0 907061 15 X Where electricity is the required form of energy (and this is becoming increasingly common) the cost of methane generated electricity compares favourably with the mains supply. Such a situation is only practicable when enough gas is produced to warrant semi-continuous operation of the generator. For generators and stationary engines biogas does not need to be compressed, since the gas can be piped direct to the engine. Normal gas consumption is about 16 cubic feet (450 litres) per horse power per hour. However, for automobiles and mobile engines the gas is normally bottled so as to minimise storage space, although Imhoff gives examples of cars and tractors carrying large collapsible bags on the roof. Methane or biogas does not liquefy very easily (its critical temperature and pressure being -82.5 deg C (-116.5 deg F) and 45.8 atmospheres), so that it is not so simple to compress and bottle as some of the other gases, such as propane or butane. In large installations the gas can be compressed to about 350 atmospheres (5000 psi) and stored in special containers. From here it would be transferred to the smaller pressure vessels carried by cars or tractors at about 200 atmospheres (2800 psi). For smaller installations direct filling of the pressure vessels between 2000-3000 psi will be adequate. A typical container size would be about 5 foot long by 9 inches diameter (1.6 m x 0.27m in diameter), capacity 1.9 cubic feet (54 litres) and weigh about 140 lb (63 Kg). This would hold the equivalent of 420 cubic feet of uncompressed methane, which is comparable to about 3-1/2 gallons of petrol (15.9 litres). Coulthard in Australia uses two 280 lb (127 Kg) gas bottles, with gas at 2000 psi; his car has a range of 100 miles (160 Km). However, not only does the storage of the gas occupy three to four times the space that petrol does, but also the weight of the cylinders considerably adds to the overall payload of the vehicle. Coulthard has to have a spring fitted under the rear end of the car to compensate for the extra weight of the gas containers. Obviously if you decide to convert your car to run on biogas, the amount of compression and weight of the cylinders will reflect on the alterations to the car and the average length of journey in between filling up. Running a car on biogas becomes a little more worthwhile for short, local trips, when you can fill up with gas frequently (at least daily). Unless the situation changes, your digester will be your only 'filling station' for miles. There are also inefficiencies in the compression of the gas: it will use up energy (at about 25% efficiency), and as a fuel for the engine the compressed gas will again burn at about 25% efficiency. The actual useful work when gas provides the power for mobile engines must be lower than any other use. Nevertheless, it has been done successfully on a number of occasions - probably the most ingenious and large-scale. operations of this sort were the powering of fleets of sewage-works vehicles during the war. The advantage such fleets have over casual users of sludge gas is that the vehicles are confined to one location and pass the fuel store often enough to fill up whenever necessary. Agricultural tractors confined to a farm would be in a similar situation. Yet besides the inefficiencies in this use of the gas, there could be problems arising from its compression, since it involves extra handling and further possible risks of explosion. A Home Office licence has to be obtained in order to store methane in the liquid state (but it is very rarely necessary to compress it that far). The use chosen for the gas will depend upon the needs of each situation. The domestic uses are obvious and can be applied directly. In the case of autonomous houses biogas represents a supplementary fuel. It is obvious that the wastes from a small number of people, without any livestock, can not produce enough gas to perform any of the principal tasks outlined above - the waste from ten people might produce enough methane to keep a gas ring alight for one hour a day. In a rural or semi-rural situation the position is different, for not only can the waste from the humans be used (with only a small flush of water to prevent over-dilution), but animal and vegetable wastes could provide the main bulk of organic matter for digestion, so that cooking or water heating can be carried out on a reasonable scale. Some designs which incorporate the digester within the house itself are potentially dangerous and invite the half-serious question of what happens when a lighted match is dropped down the lavatory? In all cases the digester and gas holder should be situated apart from other buildings. Refs L.J. Fry, Methane digesters for fuel, gas and fertilisers. (1973) Karl Imhoff, Muller and Thistlethwaite, Disposal of sewage and other waterborne wastes, Butterworths. (1966) J. Coulthard, Sanamatic Tanks, Australia -------------------------- eGroups Sponsor -------------------------~-~> eLerts It's Easy. It's Fun. Best of All, it's Free! http://click.egroups.com/1/9699/0/_/837408/_/977723313/ ---------------------------------------------------------------------_-> Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html To unsubscribe, send an email to: [EMAIL PROTECTED]
