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CITY OF SOUTH BEND <br />REPORT ON GAS MIXING & HEATING <br />EQUIPMENT FOR TWO (2) DIGESTER <br />Analysis of Bids <br />Low Bid based on Alternate "A" as <br />submitted by E. R. Knapp & Co.,. -_$ <br />Rochester, Indiana-------------------------------- <br />Low Bid based on Alternate "B" as <br />submitted by C & C Construction 'Co. , - -$ 3 °, <br />Fort Wa ne,. Indiana---------- -- --- --- ----'-- - -' - -- <br />Difference between lowest bids based <br />on low for Alternate "A" and low for 7 Z 6 <br />Alternate " B,'---------------------- ---- -------- - -= - -$ <br />Description & Comparison of Two Systems: <br />Alternate "A" Under Alternate . "A ",.the gas mixing equip- <br />ment is as manufactured by Ralph B. Carter Company and is the patented <br />full bore expendable piston type bubble, introducing a minimum amount <br />of gas into the mass of sludge in order to produce a maximum turnover, <br />pumpage. Approximately 7.5 c.f.m. divided by 0.54 (Volume of piston <br />bubble) = 14 pulsations per minute in a 12" tube pumping approximately <br />1400 g.p.m.:with a tube velocity of 4 feet per second. <br />Six 12" diameter tubes each equipped with expendable piston <br />bubble type guns will be installed in each roof. For mixing without <br />heating one compressor is used which operates two guns (Pumping rate+ <br />2800 g.p.m.), then two more guns in sequence and finally the other two <br />guns until all six guns have been operated in sequences, completely <br />around the digester. The normal horsepower requirement for gas mixing <br />being two .(2) horsepower. For heating all six guns are operated si- <br />multaneously with a total requirement of 5.,horsepower per digester. <br />The bubble producer is like a cone fulcrum set into inverted <br />cylinder. The size of opening for discharge of bubble being approxi- <br />mately 2- 1/2 ".. Plugging or malfunction is extremely unlikely. <br />Alternate "B" - Alternate "B" the gas mixing equipment is as <br />manufactured by P.F.T. as is described as the "Pearth" system. Under <br />this system,.approximately 300 c.f.m. is injected into a vertical 1 -1/2" <br />diameter pipe (called a lance). On the sidewalls and near the lower <br />end a number of small holes are drilled to let the compressed gas <br />release.carrying upward with it a flow.- This system is an unrefined <br />air lift of tthe an inefficient type,but should provide a pumpage rate' <br />as high or higher than the Carter aero -gun. <br />