Unique Advantages of Tray Strippers for VOC Removal UnderStrippers for VOC Removal Under

Fouling Conditions

Dave FischerDave FischerQED Environmental Systems Inc.Ann Arbor, MI / San Leandro, CA

Copyright © QED Environmental Systems, Inc. 2007, 2008, 2009; all rights reserved.

T i O i

• Description of the Air Stripping process

Topic Overview

Description of the Air Stripping process• Air stripping for fouling conditions• Unique E Z Tray® advantages• Unique E-Z Tray® advantages• E-Z Tray product features/benefits• The QED Air Stripper Modeler• The QED Air Stripper Modeler• Design Principles/Oddities

Pil t T ti• Pilot Testing• Case Studies

Air StrippingA process that removes or “strips” volatile organic compounds from contaminated water by contacting clean air with

t i t d tcontaminated water across a high surface area, causing the volatile compounds to move fromcompounds to move from the water into the air.

Process is governed by H ’ LHenry’s Law.

Driving dissolved volatile organic contaminants fromorganic contaminants from water into air.

Air StrippingCounter-current flow means the cleanest air

t t th l tcontacts the cleanest water. This ensures efficient mass transfer throughout the entire oug ou e e eflow path.

Air Stripping

Air water contact happens in the active tray areas. yHigh air to water surface for transfer is created by the turbulent froth mixture.

Air Stripping

The froth in action.

Tower Stripper

MethodThin film of water flows

hi h fover a high surface area packing

Ad tAdvantages• Lower energy use in the air mover, due to lower overall pressure drop

Disadvantages• Flow turn-down difficult• Difficult to clean• Tall structure

Tower Stripper

If fouling conditions d l th tdevelop, the tower can quickly loose mass transfer area. Small local areas ofSmall local areas of deposition can produce flow short circuiting that furthercircuiting that further limits available contact area.

Sliding Tray Type StripperMethodAir bubbles - froth and turbulent mixing creates mass transfer surface area

Advantages• Easy access• Less prone to fouling• Less prone to fouling• Less intrusive at site• Wide flow turn-down

Disadvantage• Requires larger blower• Requires larger blower

Poll

What methods have you used for dissolved liquid / VOC control?

Types of Fouling

• Iron oxides• Hardness (scale)( )• Suspended solids• Bio solids, slimes,• Oils & Greases• Free phase DNAPLFree phase DNAPL

E-Z Tray® Advantages … Cleaning

E-Z Tray Tower Stacking TrayAir Strippers Air Strippers Air Strippers----------------------------------------------------------------------------------------------------

• Single person cleaning

• Packing access and removal is

• Major disassembly and multi person crew

difficult needed

E-Z Tray® Design

Lightweight, front slide out trays provide easy access. Trays rangeprovide easy access. Trays range from 24-73 lbs and are about 24 inches wide with lengths ranging from 2.4 to 6 feet

Single person maintenance saves on cleaning and labor costs -- made possible by front access serviceability Stripper

Blower

serviceability

Trayy

24-73 lbs = 11-33 kg; 24 inches = 61cm; 2.4-6 feet = 0.7-1.8 m

E-Z Tray® Advantages … Footprint

E-Z Tray Tower Stacking TrayAir Strippers Air Strippers Air Strippers----------------------------------------------------------------------------------------------------• Reduced footprint

for installation and maintenance

• Small footprint but very tall structure often required

• Lots of space needed for disassembly, lifting from all sides, pipe disconnection anddisconnection and tray stage stacking

E-Z Tray® Advantages … Monitoring

E-Z Tray Tower Stacking TrayAir Strippers Air Strippers Air Strippers----------------------------------------------------------------------------------------------------

• Easy process monitoring and inspection, even

• Condition of packing and air flow distribution are very

• Difficult or impossible to observe air and liquid flow distribution

while in operation difficult to observe during operation

E-Z Tray® Advantages … Modeling

E-Z Tray Tower Stacking TrayAir Strippers Air Strippers Air Strippers----------------------------------------------------------------------------------------------------

• Easily modeled online by customer to help process

• More complex design process due to structural aspects,

• Online modeler not offered

evaluation assistance normally required

E-Z Tray® vs. Tower Cost

Capital cost for tray strippers is less than a

$350,000

$400,000

strippers is less than a comparable tower stripper

Hard to strip wastewaters$250,000

$300,000

($

)

Hard to strip wastewaters dramatically increase tower cost if multiple stages are required $150,000

$200,000 Tow er – easyTow er – hardTray – easyTray – hardC

ap

ita

l Co

st

O&M costs for tower cleaning are expected to be much greater for tower

$50,000

$100,000

strippers0 200 400 600 800 1000 1200

$0

Flow (gpm)

Derived from data from the FRTR web site (Federal Remediation Technology Roundtable)

0-1200 gpm = 0-4540lpm

E-Z Tray® Design

One piece shell with single gasketed door cuts down ongasketed door cuts down on possible air leaks

Clear front door gives easy visual check of air stripper performancep

Front access cleaning means piping stays put no need topiping stays put – no need to break connections

Ancillary Equipmenty q p

• Pressure Switch• Skid

• Liquid Flow Meter

• Air Flow Meter

• Blower

• Infeed Pump

• Bag Filters

• Solenoid Valve

• Discharge Pump

• Gravity Drain • Solenoid Valve

• Tank

• Gravity Drain

• Control Panel

• Level Switches

QED Air Strippers (specifications)

A wide range of models tomodels to match liquid flow andand removal needs.

QED Air Strippers

E-Z Tray E-Z Tray E-Z Tray E-Z TrayyModel 6.4

yModel 16.4

yModel 24.4

yModel 96.6

Modeling the ProcessWeb based Modelhttp://www.qedenv.com/modeler

Xin = aqueous concentration entering the air stripperXout = aqueous concentration exiting the air stripperYin = gas concentration entering the air stripperNth = number of theoretical trays in the air stripper The performance modeler is based on the designNth = number of theoretical trays in the air stripperS = stripping factorKh = Henry’s Law constantL = liquid flow rateG = gas flow rate

The performance modeler is based on the designprocedure discussed in -- Kibbey, T. C. G., K. F. Hayes andPennell, K.D., ‘‘Application of Sieve-Tray Air Strippers tothe Treatment of Surfactant-Containing Wastewaters’’,AIChE Journal, Vol. 47, No. 6, June 2001. Also -- Perry, R.H., and D. W. Green, Perry’s Chemical Engineer’s Hand-book, 7th ed., McGraw-Hill, New York 1997.

1 – Pick Contaminants

Henry’s Constant (H)Larger H = more easily stripped (atm/mol frac)Larger H = more easily stripped (atm/mol-frac)

• vinyl chloride - 1245• TCE – 648

• MTBE - 32• acetone - 2 4TCE 648

• benzene - 309acetone - 2.4

2 – Other Information

Process Variables

• Temperatures (air and water)• Altitude (air density)• Flow rates (air and water)• Flow rates (air and water)

- Process impacts- Hydraulic impacts

3 – Pick a Stripper

• First pass – pick the stripper model that matches project flowproject flow

Metric units available onModel SiteModel Site

4 – Contaminant Concentrations

• Concentration in ppb (ug/L) – 1000ppb = 1ppm• Each contaminant behaves independently

5 – Review Model Results

(URL listed to allow easy remodeling)

Successful Process Requirements• Dissolved volatile organics

in a water matrix• No free-phase organics• Clean air (concentration gradient

driven)

Impact of dirty air

driven)• High surface area of contact

between air and water• High air to water ratio• Sufficient contact time• No surfactants or other H lowering

Clean air Contaminated air

• No surfactants or other H lowering factors (dissolved polar organics)

• Stripper is level

Stripper PerformanceStripper Performance

• Air and liquid flow issues• Air and liquid flow issues• Air flow restrictions• Water/air temperatures• Water/air temperatures• Free phase product or other sorptive

compounds that decrease strippingcompounds that decrease stripping• Surfactants or other polar organic chemicals

that can influence Hthat can influence H

Free Phase Product

• Coats walls• Residual source in sump• Residual source in sump• Co-dissolution issues• Interferes with performanceInterferes with performance

Free Phase Organics

Lower removal efficiency

90 00%

100.00%

Water + Hydrocarbon

Co-solubility effects can sequester certain VOCs from

70.00%

80.00%

90.00%

certain VOCs from the stripping process

Coating and free 40.00%

50.00%

60.00%

pilotmodel

(% V

OC

Rem

oval

)

gphase can coat walls and accumulate in the sump as a VOC source 10 00%

20.00%

30.00%

source

20.00% 40.00% 60.00% 80.00% 100.00%0.00%

10.00%

(% Maximum Flow)

Example – site handling tanker ballast water with a combination of free phase hydrocarbons and VOCs dissolved in water

Surfactants / Polar Organics

• Lowers effective H for all t i t

H(atm/mol-frac)

800contaminants• Foam can lead to demister fouling• Foaming 600

800

TCE• Foaming

– Anti-foam additives (stripping effectiveness not recovered)K k t t k i t d i t 400– Knock-out tank prior to demister

200

benzene

polar organic

Example - closed DOD site with low level dissolved TCE. Visual indication of non typical foam in upper stripper trays. Consistent 60-85% reduction in stripping capability vs theoretical 0

00

MTBE

polar organicimpacted TCE

60 85% reduction in stripping capability vs. theoretical performance prediction.

Temperature Effectsp

• Higher water temperature = better strippingHi h i t t ll i t t• Higher air temperature = small impact on water temperature

• Example:Example:

Water Flow 200 gpm

Air Flow 1300 cfm

Water Temp

79.6 FAir Temp

gp

80 F

50 F

Equilibrium

Air Temp

Air Temp

100 F

120 F

80.3 F

80.5 F

PollPoll

What methods have you used to clean ytray air strippers?

Fouling - Preventative Measures• Clean trays

– Backup tray set

g

• Sequestering agents (decrease cleaning frequency)

i i– inorganic polyphosphates

• Bio-foulingOzone etc– Ozone, etc.

• pH adjustment– In/out

P t i id ti• Pre-stripper oxidation and filtration

Bio FoulingBio Fouling

Example – pH adjustment to minimize inorganic tray foulingcaused a bio-component to rapidly develop a protective slime.

Inorganic Stripper ApplicationsInorganic Stripper Applications

Ammonia hard to strip• Ammonia – hard to strip • (H = 0.7-5.5 atm/mol-frac)

• Hydrogen Sulfide – easy to stripHydrogen Sulfide easy to strip • (H = 545 atm/mol-frac)

• Radon removal – extremely easy to strip• (H = 4680 atm/mol-frac)

Ammonia Removal

pH adjusted > 11 prior to air stripperprior to air stripper, then adjusted back to required level

Model assumes the dissolved gasthe dissolved gas NH3

Hydrogen Sulfide Removaly g

pH adjusted < 6 100p jprior to stripping then adjusted back to required level

70

80

90

to required level

Model assumes 30

40

50

60

H2SHS-S2-

%%

Model assumesthe dissolved gas H2S 0

10

20

30

5 6 7 8 9 10 11

pH

Pilot Testing

• Prepackaged, just add electricityjust add electricity

• Rental• Used for scale-upUsed for scale up

design• Allows H correction

from results when NAPLs, surfactants, t k t betc. are known to be

present

Case Study 1

• VOC treatment of tanker ballast waterballast water

• Strippers replaced an aging activated sludge treatment process that was unable to handle changes in flow and concentrationconcentration

• Process string includes free-phase removal and airphase removal and air treatment

• Pilot testing used prior to design

Case Study 2• VOC reduction prior to SBR

treatment of pharmaceutical wastewater

• Stripper air flow rate much lower than flow from SBR

• Allowed smaller CATOX air treatment unitair treatment unit

Before After

Thermal Oxidizer

VOC

Thermal Oxidizer

Less VOCVOC

Treatment Plant Treatment Plant

Case Study 3

• Gasoline spill in high value gresidential area

• Space for process eq ipment limitedequipment limited

• Need for low profile - sound pand appearance

• Strippers housed i t l hi iin metal shipping containers

Case Study 4

• Large industrial Li id I

Air Out

chlorinated cleanup • Strippers one component

in a multi-unit / multi-

Liquid In

phase process string• EZ-Tray design allowed

space saving stripper placement

• Strippers used in series for higher removal Liquid Out

Air In

q

Max. plant flow = 4MGD (3000gpm; 15MLD)

Normal operating range = 1.3-1.7MGD (1000-1400gpm)

Summary

• Air strippers are effective at removing dissolved

y

volatile organic compounds from water • The primary process factor is air to water ratio• The process can be modeled using on-line

computer tools -phttp://www.qedenv.com/modeler

• Air stripping equipment needs to be maintained pp g q pto ensure continued design removals

Questions?David Fischer

QED Environmental Systems IncQED Environmental Systems, Inc.

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

WEB:WEB:www.qedenv.com