Common Problems with Online Water Quality Analyzers. Greg Macy Director AquatiPro LLC

Transcription

1 Common Problems with Online Water Quality Analyzers Greg Macy Director AquatiPro LLC

2 Objectives Diagnosing Colorimetric Analyzers Identifying Common Problems with Sodium Analyzers Troubleshooting ph Analyzers 2

3 Diagnosing Colorimetric Analyzers Principle of Operation Sources of Errors and Interferences 5 of the most common problems seen within the plants Open Troubleshooting Forum 3

4 Principle of Operation: Lamp λ Measuring Cuvette Optical Filter Measuring Photocell Electrical Output 4

5 Light Absorbance versus Concentration Absorbance Beer- Lambert Law Concentration 5

6 Sources of Errors and Interferences Optical and Water Handling Sections 1.Optical Density Increases: a. Coloration in Sample Cells b. Air Bubbles and Contaminates in Sample c. Contaminates in Reagent Air Programming and Electronics 1.Reagent Programming: Blank values and levels. 2.Calibration Set-up 3.Heater Settings 2.Optical Density Decreases a. Interruption of Reagent Delivery b. Contaminated Reagents c. Sample Dilution During Analysis 6

7 5 of the Most Common Problems seen within the AEP Plants Hach 5000 Waltron 9041 ABB 8241 SWAN Copra Leaking Sample during analysis Reagent Injection Clogging of internal tubing Clogging of internal tubing Replacing pinch valve tubing and solenoid valve Routine cleanings, replacing reagent valves, reagent contamination Routine NaOH cleaning of system Routine cleaning and reagent preparation procedures Sample Regulation and Delivery Mark end of measure set up, set up back pressure regulation. Reagent Leaks Cleaning leaks up immediately to minimize damage to components. Reagent Leaks Cleaning leaks up immediately to minimize damage to components. Programming Calibrations and set up. Reagent Pressure Drops Routine tubing replacement, pressure regulators, capillary tubing modules Programming Reagent blank values to be 0.00 Do not perform reagent blank procedures on low level applications Pinch Valve Tubing leaking Monthly change of tubing Reagent filter clogging Changing out yearly Dirty Sample Cell and Interference Filter Routine cleaning cell and optics Pressure and sample leaks Changing sample tubing, 3 way and 2 ways valves. Pump tubing stretching and tearing Routine Changing of tubing Improper blank calibrations Follow guidelines closely on procedures Reagent Contamination Optical System LCD burn out in hot temps Reagent Preparation, shelf life, dry instrument air Routine cleanings in sample cells, and optical alignments Install cooling fans or enclosures to keep a room temperatures. 7

8 Open Troubleshooting Forum This is your chance to share your experience and ask questions concerning your Silica Analyzers. In addition, consider the following questions. 1.What is it about our readings that might make us second guess our analyzer? 2.Which sample point Silica analyzers require the most maintenance? 3.Which sample point Silica analyzers do we trust the least? 4.What components tend to fail the most? 5.Do we utilize the grab sample capabilities of the analyzer and what is our expected detection limits? 8

9 Identifying Common Problems with Sodium Analyzers Principle of Operation Sources of Errors and Interferences 5 of the most common problems seen within the plants Open Troubleshooting Forum 9

10 What to look out for in this measurement: This measurement is somewhat complex and due to the nature of the measurement, there are things that will need to be considered. During this training we will be addressing these points: 1.Sodium Electrodes are responsive to ph swings as well as other Cations. 2.Sodium Electrodes will become de sensitized after extended exposure to lower sodium levels. 3.Sodium Electrodes are susceptible to drift and routine calibrations are necessary. 10

11 Principle of Operation High Impedance voltmeter ISE Electrode Reference Electrode 11

12 Principle of Operation: Silver/Silver Chloride Element Internal filling solution Glass electrode body Sodium responsive glass membrane Ion Exchange Reaction at a Sodium Glass Membrane H + Ag + Sodium-Glass (NAS 11-18) Gelled Surface Na + K + NH + 4 other Cations Selectivity

13 Response of Sodium Electrode to H + Ions Nernst Equation for the Sodium Measuring Chain: EMF=E 0 +R*T/n*F * log[(c Na +100*C H )/C ISO ] EMF [mv] ph ph 9 ph Ciso log Na [ppb] 13

14 Sodium Electrode Detection Limit finding the best ph. EMF [mv] Mol/l Diisopropylamine Eo+236 Eo+177 Eo+118 Eo+59 Sodium electrode response ph interference Diisoprop. interference ph. 14

15 Nernstian Response of Sodium Electrode Simplified Nernst Equation : EMF = E 0 + S * log [C Na ] EMF [mv] mv = Slope log Na [ppb]

16 Response Times of Sodium Selective Glass Electrodes Sodium [ppb] min electrode etching 10 min Minutes 16

17 5 of the Most Common Problems seen within the AEP Plants Orion 1811/2111 Waltron 9030/31 Hach 9245 SWAN AMI/Solo Trouble calibrating the analyzer: Failure to calibrate: Calibration Errors: Offset is high Technique, background sodium, probe response, signal conditioning board Probe Response, pre amp problems, electronic board problems due to age (most are more than 10 years old) High Background sodium in sample water (>10ppb) Normally due to standard preparation/contamination Reagent/Buffer Delivery: In accurate High readings: Plugging/fowling of flow cells Diffusion tubing breaking, leaking, or slow diffusion rate. Drifting due to long intervals between calibrations, backgrounds in standard preparations. Pinching off of reagent feed line due to set up within cabinet Taking apart flow cell and cleanings with pipe cleaners Plugging or flow restriction Routine changing of restriction tubing assembly and filter elements. Erratic readings due to clogged entrainment T s. Normal Maintenance cleanings Set up errors: Initial programming of instrument for calibrations, flow etc. Cracking flow cells. During outages, reagent needs to be removed. Calibration Errors: During calibrations, sample is loss through overflow due to leaking o rings. Kits needed with Routine Service Pressure relief valves sticking open due to iron oxide build up in valve Taking apart the valve/replacing. Valve control and set up of ph dosing. Leaking reference electrolyte out to fast: When seating glass sleeve on reference electrode, it needs to be firmly seated down. Signal Outputs are lost: Boards have gone out on older units and needing replacements. Electronic Calibrations on older units are out : In house or expert tech calibrations with probe simulators. Plugging or fowling of flow cells and probes. Pre Filter out iron oxide 17

18 Open Troubleshooting Forum This is your chance to share your experience and ask questions concerning your Silica Analyzers. In addition, consider the following questions. 1.What is it about our readings that might make us second guess our analyzer? 2.Which sample points do we have more problems with our sample analysis. 3.What components tend to fail the most? 4.Do we utilize the grab sample capabilities of the analyzer and what is our expected detection limits? 18

19 Troubleshooting ph Analyzers Principles of Operation Sources of Errors and Interferences Open Troubleshooting Forum 19

20 Principle of Operation: General Overview ph Analyzers Although ph analyzers seem very simple they are quite complex and most ultra pure applications are problematic. They require constant flow and are very temperature dependent. Accuracies are therefore affected by : Temperature Compensation (Nerst 59mV per ph unit Changes) Solution (Sample Correction Coefficients) Flow Rates Electrode fowling due to Iron Oxide and particulates Installation cable length, impedance issues, charges separations, and ambient temperatures. The differences in the types of probe has to do with the conductivity of the water. Lower conductivity sources (usually less then 5 micro s/cm) requires a ph reference junction with salt bridge. Otherwise a combination solid state bridge can be used. ph analyzers, particularly in pure water applications are suspect to drift and might need a bi-monthly calibration to align the probe. (if require accuracy >.1pH) 20

21 Temperature Compensation 2.00 ph Error From 25 Degrees C Temperature Error in ph units ph Value 21

22 Operating Electronics: Programming Temperature Compensation Keep in mind that every application might require a different method of Temperature Compensation. Based on the solution charts and guidelines set by your chemical vendor or EPRI, this value should be programmed accordingly. 22

23 Diagnostics Ω MΩ kω TC Measuring Electrode Solution Ground Reference Utilizing the Diagnostic Information within ph Transmitters: Usually, most newer electronics will give the user diagnostic information that will give you a good idea on how your electrodes are tracking in ultra pure water. Most of the time you have to either set up programming in the transmitters or use advanced menus to call up this diagnostic information 23

24 Open Troubleshooting Forum This is your chance to share your experience and ask questions concerning your ph Analyzers. In addition, consider the following questions. 1.Are we utilizing the sample correction coefficient programming capabilities? 2.How often are we performing a 2 point buffer calibration? 3.Are we calibrating out flow/junction potentials with process calibrations? 4.Do we track reference impedance values? 5.What do we do with our probes during outages? 24

25 Preventative Maintenance Cycle 25 Summary Measured ph vs. calculated ph Sample Temperature and Filtration Requirements Importance of Shut Down Procedures Sticking to a regular

26 Close Parameters Supported by AquatiPro LLC Questions and Answers Contact information 26

27 Parameters Supported DISSOLVED OXYGEN HYDRAZINE SODIUM ph & ORP CONDUCTIVITY AMMONIA NITRATE TURBIDITY FLUORIDE HYRDO CARBON SILICA PHOSPHATE OXYGEN SCAVENGERS COPPER IRON CHLORINE CHLORIDE ACID/CAUSTIC AquatiPro supports most makes and models. Visit to quickly locate the right part for your analyzer along with a picture to help you identify tricky components. 27

28 Contact AquatiPro LLC AquatiPro is dedicated to providing sales and professional technical field services: new equipment start up, commissioning, calibrations, preventative maintenance, and training sessions for your complete process analyzer needs. AquatiPro LLC th Street SW Loveland, CO (970) Feel free to contact us with any questions that you might have on your analyzers. 28