Let’s talk chlorine. Obviously, balancing chlorine in water treatment is a critical issue, so having a friendly relationship with your chlorine analyzers is important. Customers ask us a number of basic questions about chlorine and its analysis. Here are a few of these questions with the essential answers from our Rosemount Analytical experts.
Q. How do you measure chlorine in aqueous solutions?
A. Reagent-less chlorine measurement requires an amperometric sensor and an analyzer to convert the current signal to a ppm reading. Unless the pH never changes more than 0.2 pH units, a separate pH sensor is strongly recommended when performing chlorine measurement. The preferred installation is in a bypass line with the sensors installed in a low flow cell. Other alternatives are installation in a 1-1/2 inch tee or submersed in a tank.
Q. How do chlorine sensors work?
A. Amperometric sensors use electric currents or changes in electric current to detect ions in a solution. The amperometric sensor tip consists of a membrane stretched over a noble metal cathode. The chlorine in solution diffuses through the membrane to the surface of the cathode. A voltage applied to the cathode reduces the chlorine to chloride. This process consumes electrons, which come from a second electrode (the anode) inside the sensor. To measure the amount of chlorine in the solution, the analyzer measures the number of electrons consumed at the cathode (the current) which is directly proportional to the concentration of chlorine in the sample. Since the sensor is constantly consuming chlorine from the process, it is necessary to have a continuous flow in front of the sensor, or else all the chlorine in front of the cathode will be destroyed, and the sensor will read zero chlorine in the sample.
Q. What types of chlorine sensors are available for real-time measurement and process control?
A. Monochloramine, free chlorine, and total chlorine sensors and systems are available for process control. It’s important to match the application and kind of chlorine to the measurement system.
Q. How do I calibrate a chlorine sensor?
A. Because stable, diluted chlorine and monochloramine standards are generally not available, the sensor must be calibrated against the results of a laboratory test run on a grab sample of the process liquid. (Learn how to zero the Free Chlorine Measuring System with a Rosemount Analytical 499ACL sensor here.)
Q. What affects the accuracy of chlorine measurements?
A. Chlorine measurement accuracy can be affected by fluctuations in temperature as it changes membrane permeability rate, electrolyte conductivity, and the sample pH levels. The need for additional sensors is reduced with the automatic temperature compensation and low sample conductivity requirement on the Rosemount 499ACL (Option -01) free chlorine sensors. Click HERE to learn more about the Rosemount Analytical 499ACL Chlorine Sensor.
There are many more basic questions on chlorine measurement that can be critical to successful water treatment. If you have pressing questions, please comment below.
We’ll address some more chlorine questions in the future.
Hi. I’m Marc Mason, business development manager, and I’m happy to be your analytic expert today. You know the old saying, “You have to spend money to make money”? Well, in the water industry we’re finding that many water plants have to spend money to save money. Recently, Tom Johnson, water industry business development manager at Emerson, wrote an article for Water & Wastes Digest that talks about advanced technologies like radar leveling, reagent-free liquid analysis, ultrasonic control, wireless measurement devices, advanced predictive diagnostics, and SCADA control systems, and how case histories are showing the cost savings that water treatment plants can garner from investing in emerging advanced analytical, diagnostics and measurement technologies, as well as the control systems that manage those technologies. The case history described in the article demonstrates this premise pretty clearly –
Taylorsville-Bennion Improvement District serves 70,000 people in approximately 14 square miles in the center of the Salt Lake Valley, Utah. The district has approximately 16,700 connections and 229 miles of water lines. For many years, it tried to keep its old chlorine and fluoride sensors and analyzers running by constantly rebuilding, recalibrating and replacing parts. While this seemed like the cost-effective thing to do, it was proving too much for the district’s small staff – a situation familiar to many managers. The units were laborious to rebuild and required replacement of two to three probes per year; plus, they used expensive membranes that were difficult to replace and often broke during installation. The district estimates that the cost to operate the old sensors and analyzers was approximately $9,000 per year at its three locations. The units required daily attention and annual rebuilds, adding labor costs to the equation.
When the district decided to replace the old sensors and analyzers with the latest technology, its situation changed drastically. The new systems were built to last three years, versus one year, and were known to be effective as long as 15 years. The new technologies were reagent-free, reducing costs and maintenance, and needed far less frequent calibration. Bottom line: the district now replaces the membranes and electrolyte of the chlorine systems for $150 per year, compared to more than $6,000 in maintenance costs for the old systems. While the new equipment was costlier to purchase, the dramatically lower cost of ownership is rapidly offsetting that differential – a situation that can apply to many technologies.
There are many other examples of cost savings quoted in the article. Click HERE to read it.
How about you? Have you invested in what seemed a costly technology, only to discover it saved money? We’d love to hear your story.
By Rob Clemons, Sales Manager, PCE Pacific, Inc.
Hi. I’m Rob Clemons, Sales Manager for the Instrument and Automation Division of PCE Pacific, Inc. I’ve got a great customer story to share with you. Chances are, most of you don’t own cruise lines, but as you can imagine, cruise lines have very stringent water quality rules – both for potable water and for water used in recreational facilities like hot tubs. The Center for Disease Control (CDC) places strict regulations requiring the continuous measurement of both halogens, such as chlorine, and pH. So we’re very honored to have been selected by the unique cruise line, Un-Cruise Adventures, as their water quality measurement company. This selection might have implications for your application as well.
The analyzer that proved to be ideal for the Un-Cruise Adventures application is the 56 Advanced Dual Input Analyzer configured for FCL (free chlorine) measurement. The 56 is a benchmark in ease of use and met the stringent requirements of the CDC.
The CDC regulations regarding measurement of halogens states:
A HALOGEN analyzer-chart recorder must be installed at a distant point in the POTABLE WATER distribution system where a significant water flow exists and represents the entire distribution system. In cases where multiple distribution loops exist and no pipes connect the loops, there must be an analyzer and chart recorder for each loop. Potable Water; 48 184.108.40.206.2 Data Logger Electronic data loggers with certified data security features may be used in lieu of chart recorders.
Needless to say, the choice of an electronic data logger is far superior in terms of precision, ease-of-use, and reduction in maintenance time. The CDC specifications go on to say:
220.127.116.11 Operation 18.104.22.168.1 Maintenance. A manual comparison test must be conducted daily to verify calibration. Calibration must be made whenever the manual test value is > 0.2 ppm higher or lower than the analyzer reading. 22.214.171.124.2 Calibration (06) The daily manual comparison test or calibration must be recorded either on the recorder chart or in a log. 126.96.36.199.3 Accuracy (05) The free residual HALOGEN measured by the HALOGEN analyzer must be ± 0.2 MG/L (ppm) of the free residual HALOGEN measured by the manual test.
The built-in data logger of the 56 again saves time, and enhances accuracy.
Un-Cruise Adventures is using the 56 equipment to provide CDC-mandated chlorine and pH control of three public hot tubs as well as for ensuring CDC compliance with onboard potable water systems on two passenger vessels. Since pH measurement is part of the free chlorine measurement on the 56, the system saved both time and money. To accommodate Un-Cruise Adventure’s space requirement, the back-panel of the assembly was trimmed down on one side and the 56 analyzer re-installed in order to fit inside a weather-proof enclosure they supplied. Our team is available to customize a system for you. Are there any water quality monitoring issues you have?
Dan Emigh, Port Engineer of Un-Cruise Adventures, stated, “I chose to use the Rosemount analytical equipment from Emerson for this important function based on my past experiences when installing this panel on our first vessel back in 2000. I had fantastic support from the rep and the equipment worked precisely as expected. When it became necessary to add the same type of equipment to the second vessel in 2014 I started by contacting Emerson and again received immediate and full support from the technical staff. As a direct result of the fantastic customer and technical service I have always received from everyone, I have no reason to consider anyone else for our water treatment needs. One phone call to Emerson and questions are answered, issues are resolved, and parts are on their way to our distant ships. Thanks for all the past and present support.”
And we didn’t even have to twist Dan’s arm to say that. Remember, the next time you’re sailing with Un-Cruise Adventures, the quality of the onboard water is in good hands.