Water and Effluent Treatment Magazine
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22 WET NEWS MARCH 2016 The accuracy and immediacy of online water analysis means its use is increasing. But what happens when the performance of continuous water analysers is not at its best? The challenge: Gaining top marks for continuous water measurement INSIGHT WATER TREATMENT Stringent environmental legislation means there is no room for complacency when it comes to ensuring that water quality sampling equipment is properly maintained C ontinuous water analysers are used to measure an extensive range of param- eters from dissolved oxygen in aeration processes through to chlorine and turbidity. Where traditional extractive methods cause delays and uncertainties, continuous water analysers take ongoing readings which are then automatically relayed to a central monitoring system. The data can then be used for both control and reporting purposes. This may seem effective but stringent environmental legisla- tion means there is no room for complacency. As a matter of best practice, it is important to maintain analysers to the high- est possible levels so that in the event of a water quality incident operators can demonstrate their monitoring and measuring equipment is being correctly with features such as automatic calibration and self-cleaning capabilities will see a gradual deterioration in performance over time as continuous exposure to the measured medium takes its toll. There is a tendency for many end users to rely on self-diagnostic features and alarm capabilities to warn them when something is wrong. Although these provide a useful indication of a real or impending problem, it is advisable to have some form of preventive maintenance regime to help stop faults occurring in the first place and extend the life of the instrument. Following the maintenance requirements provided by the manufacturer is an important part of this. Usually these include recommendations to perform checks and replace standard component parts a maintained. As failures can also result in penalties, and with most plants operating under tight budgets, the need to ensure that water quality ana- lysers are in good working order could not be any greater. Wear and tear Any instrument that is constantly exposed to a process is subject to wear and tear. Even continuous water analysers A solution: A maintenance strategy Designing an effective maintenance strategy for continuous water analysers will enhance performance. ABB's Dr Jonathan Farrington offers some top tips. number of times throughout the year. Be aware, however, that these guidelines may not include considering the lifecy- cle of equipment. A failure to consider the lifecycle can mean that a fault occurs where a replacement part is needed, but cannot be provided. If this hap- pens any repairs are delayed or made impossible, causing the instrument to either become unreliable or be taken offline. T here are some top tips for checking analyser perfor- mance that when followed will help you achieve the best levels of performance. Reagents are crucial for pro- ducing the chemical reaction needed for an accurate meas- urement to take place. There- fore, it is important to check reagent consumption regularly to ensure it does not run out. Reagents also have an ideal shelf life. Before exchanging a used reagent with a new one, check the expiry date. Checking reagent levels will also show whether consump- tion is at the expected rate for the application. Under- or over- consumption can indicate a problem in the analyser's fluid handling system, such as a blockage or restriction. Performing regular visual checks is another top tip. Ana- lysers should be checked thor- oughly with steps including: • Checking for leaks around any sample and drain pipework connections • Examining whether the sample flow is passing through the analyser properly • Checking liquid levels in the reagent, calibra- tion and cleaning solution bottles • Inspection of all tubing and liquid handling components for leakage and/or deterioration • Checking for any indi- cations of malfunctions on the analyser display unit. In many cases, erratic readings don't indicate a fault with the transmitter, but rather external factors such as inconsistent chemical dosing or unexpected changes in water quality • Checking the analyser's high and low measured values. Any discrepan- cies in the measured values may be sympto- matic of a number of potential issues includ- ing variations in ambi- ent temperature which could be affecting the sample Checking calibration is also key. Failure to routinely cali- brate can o‰en mean that prob- lems such as blocked tubes and valves, leaking seals or contam- ination of the reference stand- ard can go unnoticed. As the part of an analyser system in direct contact with the process, sensors bear the real brunt of the adverse The important role played by continuous water quality analysers in safeguarding the quality of both potable and treated wastewater makes it critical they are kept in top working order