DIGESTER CONFIGURATION, SIZING, HEATING
S. A. Weeks
HORIZONTAL VS. VERTICAL
uNo clear difference in biogas productionuUnmixed vertical is “vertical plug flow”uMixing does occur naturally within digestersuMixing with pumps, props, or recycled Biogas
consumes considerable energyuDesign may depend on land “footprint”
available
HORIZONTAL VS. VERTICAL (CONT.)
uLoop horizontal to reduce lengthuLooped design has inlet and outlet at same
enduLooped design makes future influent-effluent
heat exchange easieruVertical allows gravity flow of effluent to
storage, and gravity emptying
DIGESTER INTERNAL HEATING SYSTEM
uCrusting may occur on internal pipesuElectrolysis may occur on internal pipesuDigester has to be emptied to fix exposed
internal pipesuNot allowed for Municipal systemsuPipes poured within floor or walls=easy
cleaning, but poor heat transfer
EXTERIOR HEAT EXCHANGERS
uMunicipal systems use spiral heat exchangers---they are expensive
uShell & tube exchangers will plug with large manure solids
uShell & tube exchangers work with separated manure liquids (with back flush system)
uShell & tube with ground manure?
EFFLUENT-INFLUENT HEAT EXCHANGE
uWill yield lots of excess heat from systemuMay be necessary for manure from
uninsulated barns in NortheastuWill tend to plug with large manure solidsuEasy to accomplish with separated liquiduPossible with ground manure?
STEAM HEAT
uDirect injection of steam into manureu Initial, successful test at Foster Brothers
Farmu1,000 Btu available per pound of water
converted to steamu 167 Pounds of manure (one cow) @ 40
degrees to 100 degrees requires 10 pounds of water converted to steam
BIOGAS BOILER ISSUES
uOperate boiler continuously (heat dump)uAdjust gas valve pressure to match Biogas
productionuNozzle openings larger than natural gasuAvoid pilotsuKeep water temperature hot to reduce heat
exchanger build up
DIGESTER CLEANING
uThe “unmentioned” issueuDepends on “grit” in influentuCalcium carbonate (calcite) an issue at NYC
Watershed projectuPeriodic cleaning needs to be scheduled for
warm weatheruConical bottoms greatly assist cleaning