MBAA-Rocky Mountain District Technical Summit

25 June 2010Measuring Dissolved Oxygen with Optical Technology

Brian VaillancourtMettler-Toledo Ingold

Bedford MA 2010

2

Agenda

Introduction

Current Technology

Challenges with DO measurements

Oxygen Measurement in Breweries

New Optical Technology

Theory of Operation

Benefits

Summary

3

Introduction

Technology Advancements

4

Current DO Measurement

Dissolved oxygen measurement in Breweries is predominantly amperometric

- Proven technology

- Technology offered by a multiple manufacturers

- Extensive portfolio for a wide application coverage

- Wide temperature range

- CIP & Sterilizable

- Accurate at low oxygen levels

There are challenges with amperometric technology:

- Process conditions can damage the membrane

- Speed of response from saturation values is slow

- Flow dependences

- The high Impedance measurement makes it susceptible to moisture problems

Optical DO measurement offers a solutions for these challenges with amperometric technology

Today

But

5

Why Measure Oxygen – Key to Quality

Requirements to oxygen measurement equipment:- Ability to measure in beer

- Low limit of detection

- Stable measurement signal

- No flow dependence

- Fast response

- Low maintenance

Reduction of oxygen level in beer is directly linked to product quality and shelf life cost savings

Oxygen is considered one of the top beer spoilers

Oxygen in beer reduces the shelf life

The lower the DO when the product is packaged, the longer it will remain “Fresh, Crisp & Clean tasting”

DO in the beer before filling, contributes to nearly 1/3 of the total packaged oxygen “TPO”

Key requirements for successful oxygen control:- Avoid any ingress of oxygen at all process stages

- Increasing demand for lower oxygen value in water and CO2

6

Oxygen Measurements in the Brewery

water preparation mash tun lauter tun wort copper whirlpool

wort cooler

yeast propagationstorage tank fermentation tank

CIP stations

separator

Kieselguhr filter

PVPP filter

water deaeration

filling lines

waste water treatment

bright beer tank

DO

DO

DO

O2

DO DO

DO

DO

DO DO

Fermentation/Storage

Brew house

Filtration/Filling

DO DO

7

Challenges for new Technology

Reliable Measurement

-Robustness-Ease of use

Maintenanceplanning

-Diagnostics

The measurement works

- Accuracy- Reliability

8

Keep your focus

Optical DO systems allow you to concentrate on your process

9 Internal usage only

Every Day Challenges

85%AirIs this value

correct

How long will it be correct?

What happens if the instrument has a

problem?

When do I have to perform recalibration /

maintenance?

Do I have all Information?

Will I be informed about the

status or problems? Is the instrument

o.k.?

10 % Air!

ISM offers a comprehensive approach for reliable measurement andmaintenance planning

5 Internal usage only

Challenges for new Technology

Reliable Measurement

-Robustness-Ease of use

I can planmaintenance

-DLI-ACT

-Diagnostics

The measurement works

- Accuracy

18 Internal usage only

Simplified SOP through Optical DO

1. Detach cap sleeve

2. Detach membrane body

3. Dispose electrolyte

4. Clean or replace membrane body

5. Clean electrode

6. Fill in electrolyte

7. Bubble free installation of membrane body

8. Clean outside

9. Install cap sleeve

10.Polarize sensor (6h)11.Calibration

1. Detach cap sleeve

2. Detach OptoCap

3. Install new OptoCap

4. Install cap sleeve

5. Calibration

Optical sensors offer higher operational availability

Total: more than 6 hours Total: few minutes

Today's standard Optical Systems

9

What is Fluorescence Quenching?

Fluorescence quenching is the basic principle of the optical oxygen measurement

Fluorescence is a phenomenon where a material absorbs light (energy) of a specific wavelength (color) and after a short time emits light with a different wavelength (color)

Fluorescence quenching describes a reduction of the fluorescence intensity and a time shift caused by another substance (quencher, e.g. oxygen).

The quenching depends on the amount of oxygen present in the process solution. The oxygen is quantified by measuring the time shift.

O2

O2

O2

LED

DetectorEmitted fluorescence light

Opto-Layer

Sensor tip

10

Partial Pressure and Dissolved Oxygen

Henry’s Law states “ The partial pressure of a gas in a liquid is

equal to the partial pressure of the gas in the vapor above the

liquid.”

The sensors deliver information which is proportional to the oxygen partial pressure in the liquid. This information is translated by the transmitter into % saturation, mg/l or ppm

Transmitter100%

Partial PressureO2 in Air

Partial PressureO2 in Liquid

Equilibrium

11

PAir =

760 mm Hg

PAir =

1580 mm Hg

System Pressure =

760 mm Hg

System Pressure =

1580 mm Hg

The Dissolved Oxygen concentration in solution changes with change in partial pressure.

The user must compensate for changes in pressure to ensure an accurate measurement

Partial Pressure

12

Tank Pressure

Tank hydrostatic pressure has virtually no influence on DO measurement up to 100 meters depth. (<1.0%)

10M

PAir =

760 mm Hg

PAir =

760 mm Hg

System Pressure =

760 mm Hg

System Pressure =

1580 mm Hg

13

Partial Pressure

Partial Pressure is the pressure that a single gas exerts in a mixture of gases

- Oxygen is 160 mm or 212.2 mBar at saturation

Humid Air displaces the Partial Pressure of Oxygen

- Example At 20oC 0% Humidity the Partial Pressure of Oxygen is 212.2 mbar

23.3 mbar Humidity the Partial Pressure of Oxygen is 207.4 mbar

4.8 mbar or 2.26% Difference between the Partial Pressure of Oxygen in Dry Air vs Humid Air

14

Amperometric Sensor

Teflon

Silicone

S.S. Mesh

ElectrolyteLayer

Teflon

Cross Section of the Electrode Tip

(not to scale)

15

Theory of Operation of Amperometric Sensors

O2 diffuses through the gas- permeable membrane (the higher the partial pressure in the liquid, the more O2 diffuses)

O2 is dissolved in the electrolyte

O2 is reduced at the cathode

The oxidation-reduction reaction generates a current

The current is measured by the transmitter and converted

1

2

3

1

23

18

20

0

0.2

0.4

0.6

0.8

1

0% 20% 40% 60% 80% 100% 120% 140%

Oxygen – Fluorescence Relation

Due to the nonlinearity of the sensor signal, accurate calibration is essential for high accuracy

The decay time and therewith the delay time (phase-shift) of the fluorescence light is directly related to the concentration of oxygen (quencher). But the shape of the function is not linear like amperometric and follows the so call Stern-Volmer equation.

O2 (Air concentration)

De

lay

tim

e

Optical

21

AmperometricOptical

Calculated non linear signal Sensor-specific calibration Calibration necessary because ageing

of the sensor influences the whole

calibration curve Two-point calibration (Air & Zero)

Linearity between nA and Oxygen value Direct information from the raw signal Offset or slope correction possible

because ageing prevailing influences

the slope

0

0.2

0.4

0.6

0.8

1

0% 20% 40% 60% 80% 100% 120% 140%

De

lay

tim

e

O2 (Air concentration)

0

0.2

0.4

0.6

0.8

1

0% 20% 40% 60% 80% 100% 120% 140%

Se

ns

or

Cu

rre

nt

(nA

)

O2 (Air concentration)

Optical vs. Amperometric Technology

22

Technology Polarographic OpticalDetection limit 1-3ppb 1-3ppbAccuracy ± (1ppb +1% of the

reading)± (2ppb +1% of the reading)

Response Time

T98 (Air – N2)

< 90 s < 20 s

Temperature during measurement

-5 to 80°C -5 to 60°C

Pressure during measurement

9 bar 12 bar

Material wetted parts 316L stainless steel

Membrane: Silicone /Teflon

316L stainless steel:

Sensor: Silicone

Optical vs. Amperometric Technology

23

Key Enhancements / Improvements: SOP

1. Detach cap sleeve

2. Detach membrane body

3. Dispose electrolyte

4. Clean or replace membrane body

5. Clean electrode

6. Fill in electrolyte

7. Bubble free installation of membrane body

8. Clean outside

9. Install cap sleeve

10.Polarize sensor (6h)

11.Calibration

1. Detach cap sleeve

2. Detach OptoCap

3. Install new OptoCap

4. Install cap sleeve

5. Calibration

Optical sensors offer higher operational availability and improves handling safety

Total: more than 6 hours Total: few minutes

Today's standard Optical Systems

24

Key Enhancements / Improvements

Time consuming sensor verification is replaced by enhanced self testing of the whole measuring system

Performance Check-Time consuming controlling and

documentation Response time Air and zero current Slope Drift

Automated Self Test-Communication

-Electronic component

-Optical component

-OptoCap quality

Total: about 30 minutes Sensor status directly available without additional testing

Today's standard Optical Systems

25

Sensor Performance: Response Time

Optical

Amperometric

60 Seconds0

5

10

15

20O

2 / p

pb

The response time in liquid phase of the optical is 50% faster than amperometric systems leading to higher efficiency

DeaeratedWater

Beer

26

Sensor Performance: Response Time

Optical

Amperometric

< 1 Minute

O2

/ ppb

The response time after a CIP cycle using non-degassed water is significantly shorter for optical sensors

30 Minutes

400

200

0

50

2000

Water Beer

27

Sensor Performance: During No Flow

Optical

Amperometric

Time / h

0

2

4

6

8

10O

2 / p

pb

The optical sensor shows no significant stop-flow effect leading to reduced alarm frequency

Flow Stop

1 2 3 4 5 6

28

Sensor Performance: During No Flow

Optical Sensor

Flow Stopped

Process conditions that affect the operation of amperometric sensors are not affected with the optical sensor

Optical sensors will show actual DO in process which is difficult to accept

Which results in blaming the instrumentation and not dealing with actual oxygen ingress

29

Sensor Performance: Extensively Tested Multiple optical system manufacturers were tested

Test included amperometric technology

The test period lasted 14 months

30

Sensor Performance: Other Benefits

Not susceptible to Hydraulic Shocks (measurement Stable)

No Damage from Hydraulic Spikes (Press-Vac)

Does not see CO2 bubbles as O2- Only responds to the presents of O2

Process Orientation of sensor is not important- Does not contain an electrolyte

Opto Cap life expectancy is 12+ Months- Easily replaced onsite and recalibrated

Does not require frequent “calibration”, but only “validation” - Verification has been necessary to become comfortable with this

new technology

31

Sensor Performance: Not without issues

Optical spot can not be pulsed during CIP process or at high temperatures- Results in a shift in the calibration values

- Most manufacturers deal with this issue by turning off the LED by a temperature shut-off or remote signal to the transmitter

More frequent pulse rate will deplete (bleach out) the optical spot at a faster rate- The pulse rate can be programmed

Multiple/Frequent (weekly) process calibrations will eventually require a two-point calibration be done- Drift rate is less than 1 ppb per month

32

Summary

Optical oxygen measurement systems

Provide

- Signal stability

- Faster Response time

- Extensively less maintenance then amperometric systems

- Ease of maintenance

- Process improvement

- Improved product quality

33

From Brew House to Filler Lines