How to Generate Power from Garbage
(Page 6 of 12)
May/June 1970
By the Mother Earth News editors
Before buying or building forms for a tank, try to locate someone who builds silo foundations and find out if his forms can be adapted to a gas plant. If they can, you will make a considerable saving in time and money.
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Tanks may also be built of stones or bricks, using a good cement mortar for the joints. Masonry walls should be designed to sustain water pressure, and inside surfaces should be lined with a thick coat of rich sand-cement-lime plaster in order to make the tanks water and gas tight.
DIGESTION TANKS
Rectangular tanks are easier to build than circular ones but during operation in cooler climates, they lose more heat because of their greater surface/volume ratio. Circular structures are also more resistant to both inside water pressure and outside earth pressure, if any, and consequently require comparatively thinner walls.
Each tank should be provided with a manhole for loading, unloading and occasional cleaning. Once a tank is ready for operation, the opening should be kept tightly closed to prevent escape of gas. This may be achieved by inserting a rubber gasket, or a rubber caulking compound, between the border of the cover and the tank. A plaster of clay or concrete might also be used in an emergency.
Figures 1 and 2 show an individual circular digester built of masonry and lined with plaster. Field stone, brick or cinder blocks could be used here. In this plant, the gas-holder is a separate unit (see Fig. 8). Several individual digesters may be utilized. The gas from all digesters is fed to the one gas-holder.
Another type of individual digester, which uses a floating cover for gas storage, is shown in Figure 9. The cover is removed for loading. The digester can be circular, square or rectangular-depending on the ease and economy of construction. Circular covers are easier to keep from binding as they raise and lower.
In areas where night-soil is used as fertilizer, it will be found advantageous to combine latrine and digestion tanks in the manner illustrated in Figures 3-7. Figure 3 shows the view of the plant with housing for the latrine. The housing may be of any suitable local materials. The door should be arranged so the latrine cover can be raised easily for adding manure, straw or other wastes to the digestion tank.
It should be noted that these drawings show the Oriental style of opening for the user. This type of opening is far superior to the old-fashioned, midwest and southern out-house seating arrangement. Admittedly, it is not immediately as convenient as that to which most of us are presently accustomed, but from a health standpoint it is far superior to even the finest porcelain arrangement.
Figures 4 and 5 show the plan of the plant and details of its cross-section, respectively. Figures 6 and 7 show the gas-holder and gas-piping details.
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