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