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Dave Fischer
QED Environmental Systems Inc.
Ann Arbor, MI / San Leandro, CA
Copyright © QED Environmental Systems, Inc. 2007-2015; all rights reserved.
Part 2 - Air Stripper System Design
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• Site data used for design
• Modeling the process and stripper sizing
• Blower and water pumps
• Controls and sensors
• System configuration
• Special situations
• Economics and case studies
Topics Overview
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Site Data
Often the highest historical analytical result for each parameter is used for design modeling
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Additional Site Information for Design
• Site history of DNAPL and/or LNAPL
• Parameters that are hard to strip (DRO, etc.)
• Is O&G above detection limit (is O&G MDL low enough)
• Is there air contamination near the blower inlet
• Does stable foam form if target water is shaken in a jar
• Is there an offset between TOC and the sum of the target organics
• Is there a site history of surfactant use
• Are high shear pumps used to capture the water (stable emulsions of NAPL)
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Air Stripping – Technology Overview
Higher Henry’s law constant = more volatile contaminant
Henry’s law constant is temperature dependent (increases with increasing temp).
Increasing air to water ratio (A/W) improves removal efficiency for marginally volatile contaminants.
Some contaminants will not respond to air stripping (1,4 dioxane, methanol, tert-butyl alcohol).
Easiest to strip
Hardest to strip
Dissolved gases (methane, carbon dioxide)
Chlorinated solvents
Light hydrocarbons (BTEX)
Heavy hydrocarbons (DRO, naphthalene)
MTBE
Ammonia
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Model Contaminants
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Model Report
One or two parameters will drive the design – a combination of H, concentration and target removal levels. Flow sometimes determines stripper size.
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Stripper SizingE-Z TrayModel 6.4(65 gpm max)
E-Z TrayModel 16.4(150 gpm max)
E-Z TrayModel 24.4(250 gpm max)
Iterative modeling determines the required E-Z Tray Model
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Process Instrument Diagram (PID)
Used to identify all the elements in the system and delineate the scope of supply.
Often used to detail system interactions with other – overall –system processes and controls (plant SCADA, etc.)
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Ancillary Equipment
• Pressure Switch
• Liquid Flow Meter
• Air Flow Meter
• Bag Filters
• Solenoid Valve
• Tank
• VFD drives
• Sensors and transmitters
• Skid
• Blower
• Infeed Pump
• Discharge Pump
• Gravity Drain
• Control Panel
• Level Switches
• Blower silencer
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• Site elevation, air temperature range
• Off-gas back-pressure (off-gas treatment,
piping, etc.)
• Sound issues
• Inorganic contaminants (corrosion)
• TDH
• VFD rated motors
Blower/Pump Design Considerations
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• VFD motor control (cost savings vs. more
costly panel design)
• Key process parameter air to water ratio (A/W)
• Air flow sensor (pitot vs. mass air flow)
• Integration with other controls (SCADA)
• Remote connection, alarm “dial-out”
• HMI (human machine interface)
• Safety
Controls and Sensors
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Example Skid Systems
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• Piping connections (RH / LH)
• System height
• Front access for tray removal
• Blower inlet (cold climate considerations)
• Junction box vs. local control panel
• Special connections, connection(s) location
System Configuration
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System Configuration
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• Adjustments to unit specifications (higher air flow, slightly
higher water flow, etc.)
• Power considerations
• Operation modes (batch, extended shut-down)
• Environmental
• Strippers with a non-standard number of trays
• Blended flow calculations
• Strippers in series (use effluent from first model run as
influent for second)
Special Situations
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• Contaminants that are not listed in the model contaminant
table
• Calculation of “effective H” from field pilot data
• Results less than 1ppb
• Pilot cases where concentrations are >> 25% water
solubility
Special Situations (cont.)
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How certain field analytical results are modeled
TPH, DRO, GRO, Total-BTEX, TVPH, F1 – F4, C6-C10, etc. All represent groups of organic compounds, with ranges of Henry’s constant (H). A representative compound is used to stand for the group. Typical practice:
• BTEX – modeled as benzene (lowest H out of the BTEX)• TPH – modeled as either benzene (TPH-GRO) or naphthalene
(TPH-DRO)• F1 (C6-C10) – model as GRO = benzene• F2 (C10-C18) – model as DRO = naphthalene• F3 and above (>C16) = difficult to strip
This method carries RISK if the group actually has more lower H components
than that of the representative. Model individual components if you need to meet
specific targets.
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Standard 4&6 Tray Custom 7 Tray Standard Series
Series – same air(like an 8 Tray) Parallel – different flow rates
Blended discharge
Special Situations
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• Sliding Tray Stripper – $0.10-$0.35/Kgal
• Tower Stripper – $0.48/Kgal
• Activated Carbon (GAC) – $0.95-$1.57/Kgal
• Oxidation process – $0.88 – $2.42 /Kgal
Considering 10 year project life & equivalent removal efficiency – equipment
cost, install cost, operating / maintenance cost (energy, GAC replenishment),
and annual flow treated (x / 1000 gallons). Legacy & lifecycle costs are
becoming a major design requirement.
Process Economics for high efficiency VOC removal
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Case Study 1 - Alaska
• VOC treatment of tanker
ballast water
• Strippers replaced an aging
activated sludge treatment
process that was unable to
handle changes in flow and
concentration
• Process string includes free-
phase removal and air
treatment
• Pilot testing used prior to
design
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Case Study 2 – Cedarburg, WI
• Landfill near a 700gpm supply well causing low level vinyl chloride hits
• System modeling based on a long list of possible future contaminants, based on LF monitoring data
• City operates an older tower stripper on another well treating an unrelated TCE issue – in operation 18 years
• Sequestering agent used for tower and E-Z Tray
• E-Z Tray footprint helped to keep project costs low
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• System design starts with a model run or pilot
data
• The PID diagram specifies the overall system
configuration and control details
• System configuration is somewhat flexible
• E-Z Tray systems are very cost efficient for VOC
removal
Summary
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Thursday, April 23, 2015, 1:30 pm EDT
Part 3 – Operating an Air Stripper System
• Operating and monitoring a stripper system
• Maintenance and troubleshooting
• Safety
• E-Z Tray advantages
Join Us for Part 3
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Survey + Questions?
David FischerQED Environmental Systems, Inc.
Tel: 800-624-2026E-mails: [email protected]
WEB:www.qedenv.com