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MBAA-Rocky Mountain District Technical Summit 25 June 2010 Measuring Dissolved Oxygen with Optical Technology Brian Vaillancourt Mettler-Toledo Ingold.

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Presentation on theme: "MBAA-Rocky Mountain District Technical Summit 25 June 2010 Measuring Dissolved Oxygen with Optical Technology Brian Vaillancourt Mettler-Toledo Ingold."— Presentation transcript:

1 MBAA-Rocky Mountain District Technical Summit 25 June 2010 Measuring Dissolved Oxygen with Optical Technology Brian Vaillancourt Mettler-Toledo Ingold Bedford MA 2010

2 1 Agenda  Introduction  Current Technology  Challenges with DO measurements  Oxygen Measurement in Breweries  New Optical Technology  Theory of Operation  Benefits  Summary

3 2 Introduction Technology Advancements

4 3 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 4 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 CO 2

6 5 Oxygen Measurements in the Brewery water preparationmash tunlauter tunwort copperwhirlpool wort cooler yeast propagationstorage tankfermentation tank CIP stations separator Kieselguhr filter PVPP filter water deaeration filling lines waste water treatment bright beer tank DO O2O2 Fermentation/Storage Brew house Filtration/Filling DO

7 6 Challenges for new Technology  Reliable Measurement - Robustness - Ease of use  Maintenance planning -Diagnostics  The measurement works - Accuracy - Reliability

8 7 Keep your focus Optical DO systems allow you to concentrate on your process

9 8 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. O2O2 O2O2 O2O2 LED Detector Emitted fluorescence light Opto- Layer Sensor tip

10 9 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 Transmitter 100% Partial Pressure O 2 in Air Partial Pressure O 2 in Liquid Equilibrium

11 10 P Air = 760 mm Hg P Air = 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 11 Tank Pressure  Tank hydrostatic pressure has virtually no influence on DO measurement up to 100 meters depth. (<1.0%) 10M P Air = 760 mm Hg P Air = 760 mm Hg System Pressure = 760 mm Hg System Pressure = 1580 mm Hg

13 12 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 20 o C  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 13 Amperometric Sensor Teflon Silicone S.S. Mesh Electrolyte Layer Teflon Cross Section of the Electrode Tip (not to scale)

15 14 Theory of Operation of Amperometric Sensors O 2 diffuses through the gas- permeable membrane (the higher the partial pressure in the liquid, the more O 2 diffuses) O 2 is dissolved in the electrolyte O 2 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 2 3

16 15 Optical O2 Operation Mode The presence of oxygen “quenches” the fluorescence  smaller light intensity and shorter lifetime Fiber-optic Temperature Sensor Detector Cap-sleeve Metal body Opto-layer with chromophor Glass optical isolation (black silicone) Opto-cap O-Ring Sensor Head Reference LED Media Optical Filter Sensor shaft Excitation LED O2O2 O2O2

17 16 Optical O 2 Phase shift measurement By modulating the excitation, the phase-shift of the modulated fluorescence signal can be measured Amplitude 0.1 μs Reference 360°

18 17

19 18 The oxygen concentration can be calculated from the fluorescence decay time High oxygen concentration low oxygen concentration Time Fluorescence intensity Fluorescence Intensity Decay Slower decay time Faster decay time

20 19 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. O 2 (Air concentration) Delay time Optical

21 20 Amperometric Optical  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 Delay time O 2 (Air concentration) Sensor Current (nA) O 2 (Air concentration) Optical vs. Amperometric Technology

22 21 TechnologyPolarographicOptical Detection limit1-3ppb Accuracy± (1ppb +1% of the reading) ± (2ppb +1% of the reading) Response Time T 98 (Air – N 2 ) < 90 s< 20 s Temperature during measurement -5 to 80°C-5 to 60°C Pressure during measurement 9 bar12 bar Material wetted parts316L stainless steel Membrane: Silicone /Teflon 316L stainless steel: Sensor: Silicone Optical vs. Amperometric Technology

23 22 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 hoursTotal: few minutes Today's standardOptical Systems

24 23 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 standardOptical Systems

25 24 Sensor Performance: Response Time Optical Amperometric 60 Seconds 0 5 10 15 20 O 2 / ppb The response time in liquid phase of the optical is 50% faster than amperometric systems leading to higher efficiency Deaerated Water Beer

26 25 Sensor Performance: Response Time Optical Amperometric < 1 Minute O 2 / 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 WaterBeer

27 26 Sensor Performance: During No Flow Optical Amperometric Time / h 0 2 4 6 8 10 O 2 / ppb The optical sensor shows no significant stop-flow effect leading to reduced alarm frequency Flow Stop 12345 6

28 27 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 28 Sensor Performance: Extensively Tested  Multiple optical system manufacturers were tested  Test included amperometric technology  The test period lasted 14 months

30 29 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 30 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 31 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 32 From Brew House to Filler Lines

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