2 ton/day production scale system
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Input Processing
The Mix Tank is the input point for solid material which is
added to the BioConverters. It consists of a trough-like Tank, a Grinder, a
Pump, and a Heat Exchange.
Effluent is loaded into the Tank by a Transfer Pump and raw
waste material, i.e. food waste, paper waste, and/or green waste is dumped in
at the mouth, where it is drawn through the Grinder with the Pump which
discharges back to the Tank through a Heat Exchange. This action gradually
grinds and heats the material. The resulting slurry is then loaded into the
BioConverter(s). -
BioConversion
The BioConverter is the heart of the BioConversion system. It
provides an environment for the cultivation and maintenance of anaerobic
bacteria, which biologically convert the organic waste added to the system
into the output products of the system. A typical BioConverter consists of a
cylindrical, translucent fiberglass vessel, which contains a heating coil for
the temperature maintenance and sparging tubes for mixing/gas transfer.
Pressure sensors are used to measure liquid level and gas pressure and a RTD
measures the liquid temperature and acts upon the heating coil to maintain the
temperature set point.The following equipment provides support for the BioConverter:
The Transfer Pump provides a means of moving slurry through and around the system. Valves provide for various flow paths for the transferring of liquid. The BioConverter may be operated in series or parallel fashion, in an up-flow mode for low solids or in a down-flow mode for high solids. Effluent can be removed from any vessel and pumped back to the Mix Tank, or over the Screen, or into a Surge Tank to allow maintenance of any Vessel or Tank.
The Gas Blower provides pressure/flow to the Sparging Tubes in each Vessel. A Gas Cooler lowers the temperature of the pressurized gas below 100 F. Valves allow sparging to be accomplished in any or all Vessels simultaneously.
The Air Compressor with Air Dryer provides dry instrument air for the actuation of valves throughout the system. It also provides drying air for the Gas Sample Analyzer.
The Hot Water Pump circulates a heat transfer fluid through the Engine Exhaust Heat Exchange and Engine Jacket Water Heat Exchange where it is heated. The fluid then passes through the Mix Tank Heat Exchange and BioConverter Heating Coils where it is cooled and transfers active heat. It then returns to the Hot Water Pump through the Radiator Fan for final temperature adjustment.
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Gas Processing
The equipment in the gas processing area functions to clean,
measure, separate and store the gas produced by the system. A solid media
hydrogen sulfide scrubber removes hydrogen sulfide from the BioGas. A
Membrane Separation System separates the BioGas into two streams. The reject
stream returns to the BioConverter vessels through the sparging tubes. The
product stream of approximately 99% methane is compressed using two Gas
Compressors and stored in four High Pressure Storage Bottles.
Various instruments comprise the Gas
Measurement System. Two Annubars with Differential Pressure Sensors provide
for gas flow measurement. Respective Sensors correct both for the Temperature
and Pressure. A Gas Analyzer System provides for 0-100% measurement of
Methane, Carbon dioxide, and Hydrogen. And a selectable 0-25,0-10 or 0-1%
measurement of Oxygen is also performed. This information combined with flow
data allows for the calculation of the mass of the BioGas being produced.
System performance is thereby determined.
A Safety Flare provides for the burning of gas or gas components
relieved from the system. Safety relief valves on all vessels connect to a
header leading to the Safety Flare.
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Solids Removal
The Vibrating Screen is the primary device for removing solids
from the system. BioConverter effluent is passed over the screen with the
Effluent Pump. The portion of the effluent which is smaller than the Screen
mesh size, e.g., the liquid containing dissolved solids and bacterial solids,
passes through the Screen and is held in a Surge Tank for further processing
by the Ultrafilter. The coarse, non-converted solids "shake" off the vibrating
screen, fall on to the Dryer Input conveyor and are loaded into the Dryer.
The Filter is the secondary device for removing or classifying
solids from the system. It consists of a Batch Tank, Pump, Filter Module and
Heat Exchange. The screened effluent is added to the Filter Batch Tank. The
Pump circulates this liquid through the Filter Module, Heat Exchange and back
to the Batch Tank. This action separates the effluent into two streams,
Permeate or Filtrate and Retentate or Solids Concentrate. Filtrate is removed
into appropriate containers for use as dilute nutrient fertilizer. What does
not pass the filter (due to its molecular size) is gradually concentrated in
the Batch Tank. This concentrate is a bacterial solids emulsion, a portion of
which is periodically discharged to the Mix Tank to inoculate the input
solids. The remainder is harvested as a soil inoculant, slow release liquid
fertilizer or BioFeed additive.
The
Dryer provides blending and moisture adjustment for the non-converted and
bacterial solids which are removed from the system. It consists of a Blender/
Dryer, Evacuation Blower and Input and Output Conveyors for loading and
unloading the unit. The Input Conveyor loads coarse solids from the Vibrating
Screen. The Evacuation Blower draws hot exhaust gas from the Engine Generator
through the unit. The Heat Exchange providing temperature control for the
bioconversion process has cooled this hot exhaust from 1200 degrees F. down to
400 degrees F. This cooled exhaust pasteurizes and removes moisture from the
solids.
Upon completion of the drying cycle, the resulting Biosoil is
removed from the Dryer by the Output Conveyor which discharges into the
Bagging System Surge Hopper for input to a bulk bag or smaller units.
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Residual Liquid Treatment and Removal
In the course of daily operation a wet Sump
receives washdown water from the waste receiving and liquid handling stations.
The sump is equipped with a Pump, which can transfer this volume to the Mix
Tank or Storage Tanks for admixing to the daily waste received. If sufficient
wastewater is available for that purpose, the Sump Pump charges the BioFilter
with the wastewater volume collected.
The
BioFilter is a small constructed wetland of emergent plants growing in a
cinder /gravel base with an overflow weir at the opposite end leading to a
second Sump/Pump which can transfer the stripped overflow liquid to storage,
to irrigation, or to a membrane-lined pond for storage.
The retention time in the BioFilter will vary with the volume of
cleanup water charged to it. It serves as a useful nutrient removal device of
the soluble solids in the wastewater, capable of stripping in a ten day period
concentrations of COD ten times the concentration of dilute sewage
wastewater.
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Power Generation and Heat Recovery
Electrical energy and heat for operating the system is made
available from a bi-fuel engine generator capable of utilizing the Biogas
produced on a daily basis.
Output Processing
UNISYN of Hawaii
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