Part 2 - Air Stripper System · PDF fileStandard 4&6 Tray Custom 7 Tray Standard Series...

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

• 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

Site Data

Often the highest historical analytical result for each parameter is used for design modeling

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)

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

Model Contaminants

Model Report

One or two parameters will drive the design – a combination of H, concentration and target removal levels. Flow sometimes determines stripper size.

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

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.)

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

• 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

• 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

Example Skid Systems

• 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

System Configuration

• 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

• 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.)

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.

Standard 4&6 Tray Custom 7 Tray Standard Series

Series – same air(like an 8 Tray) Parallel – different flow rates

Blended discharge

Special Situations

• 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

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

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

• 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

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

Survey + Questions?

David FischerQED Environmental Systems, Inc.

Tel: 800-624-2026E-mails: dfischer@qedenv.com

WEB:www.qedenv.com