Monitoring Dissolved Oxygen in Boiler
Feedwater Prolongs Power Plant Life

For optimum power plant operation, it is necessary to control corrosive elements in the feedwater of steam-generating systems. This aids in protecting system components and minimizing system downtime. 

Dissolved oxygen (D.O.) is the primary corrosive agent of steam-generating systems. It causes localized corrosion and pitting of the metal system components. Over time, it can dissolve the metal, causing an oxygen tubercle or scab to form over the point of original attack. Once the scab forms the corrosion will continue, even if the system is then properly maintained. High temperatures within the steam-generating system accelerate the rate of D.O. corrosion. It is important, therefore, to closely control and monitor D.O. levels within the system, as part of a routine preventive maintenance program.

Two techniques are traditionally employed by plant operators to control D.O. levels in steam-generating systems-de-aeration and chemical treatment of feedwater.De- aeration equipment heats the feedwater and vents the released gases, including oxygen. Oxygen scavenging chemicals, such as N,N-diethylhydroxylamine (DEHA), and hydrazine are added prior to the steam-generating process to remove as much D.O. as possible.

Power plants typically use on-line analyzers and test kits to monitor D.O. levels. On-line analyzers are capable of continuously and accurately monitoring concentrations at very low levels. However, they can be ineffective during and after periods of startup or maintenance.  On-line D.O. analyzers often require several hours to reach the required
state of equilibrium. In addition, some oxygen scavenging chemicals release by- products which cause falsely high on-line results.

CHEMetrics Dissolved Oxygen CHEMets® and ULR CHEMets ampoules have been
relied upon by power plant operators worldwide since 1972. They are useful for confirming on-line results and calibrating on-line analyzers. In some instances, power plant operators use D.O. CHEMets kits as their sole means of measuring D.O. concentrations.

CHEMetrics Dissolved Oxygen ampoules for boiler applications contain a unit dose of the highly sensitive reagent Rhodazine D(TM) sealed under vacuum.  Because sampling is the most critical aspect of D.O. analysis, a samplingtube is included in each test kit to ensure the sample is taken from a flowing sample stream-this prevents contamination from atmospheric oxygen.

To perform a test, the operator snaps off the tip of the ampoule in the sample. The sample is drawn into the ampoule, where it mixes with the reagent to form a pink color-the color intensity is directly proportionalto D.O. concentration in the sample. Results are quantified by visual comparison or with a hand-held instrument. Testing can be performed over multiple ranges, with detection limits as low as 1 part per billion (ppb).

Dissolved Oxygen CHEMets ampoules provide the power plant operator with a rapid, reliable means of determining parts per billion levels of D.O. without the need for additional equipment, maintenance, or calibration. TheCHEMetrics D.O. method is not subject to temperature, salinity, or dissolved gas interferences (please refer to ASTM D5543-94 for specific interferences). Vacuum packaging eliminates the need for measuring and mixing chemicals, reduces exposure to chemicals, eliminates contaminationfrom atmospheric oxygen, and simplifies testing. In addition, test kits
have virtually unlimited shelf-lives. Most importantly, Dissolved Oxygen CHEMets ampoules are the only method approved by the American Society of Testing and Materials (ASTM D 5543-94) for low-level D.O. monitoring.

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Q. How important is sample temperature when monitoring dissolved oxygen levels in boiler water?
A. Cooling the sample according to test kit instructions is of critical importance to  accurate D.O. testing. High sample temperatures may cause test results to be biased high, especially in ppb-range testing applications. For optimal results, sample temperature should be no higher than 10deg. C above ambient temperature. 

CHEMets® ampoules have a high surface area to volume ratio. When sample temperature is too high, the sample cools quickly as it contacts the ampoule's inner surface. This rapid sample cooling causes the small gas bubble in the ampoule to contract, drawing air into the ampoule. The atmospheric oxygen reacts with the oxygen sensitive reagent, causing positive interference. 

Q. How important is the color development time allotment listed in the test procedures?
A. Timing is very important in colorimetric testing. Some reagents continue to develop color after the specified development time. The most accurate test results are obtained when the reading is taken in the prescribed time frame. 

For answers to other frequently asked questions, click on FAQ. 

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CHEMetrics Test Kits:
Not just for water anymore!

CHEMetrics, Inc. has proudly been supplying analytical test kits to the water testing industry for nearly 30 years. However, you may not know that some of the most interesting applications for our kits have nothing at all to do with water. 

Sulfites in Wine
Wine makers commonly add sulfites to wines as antioxidants and antimicrobial agents. Sulfites, however, have been identified as causative agents in certain allergic reactions suffered by asthmatics. Because of this, the Food and Drug Administration and the Bureau of Alcohol, Tobacco, and Firearms mandate that sulfites in food and beverages, at levels of 10 ppm or higher, be identified. CHEMetrics has developed a reliable method for monitoring sulfites in wine. 

CHEMetrics Sulfite in Wine Titrets® Kit uses the wine industry standard "Ripper" method. Results are measured as ppm (mg/L) SO2, and the kit can be used to test both red and white wines. The CHEMetrics technology, however, is much more convenient and efficient than the traditional "Ripper" method.  Reagents are prestandardized and premeasured into calibrated titration 
cells in unit dose format. The cells are then sealed under vacuum, protecting the user from chemicals and virtually eliminating shelf-life problems. 

Total Petroleum Hydrocarbons in Soil
One of the key features of the self-filling ampoule is stability.  CHEMetrics chemists have taken full advantage of that feature in developing the TPH-in-Soil test.  Without the protection from atmospheric moisture which the ampoule provides, the Friedel Crafts reagent could not reamain active for more than a few hours.  Instead, the new, portable test kit is suitable for quantifying hydrocarbon contamination on-site at any location in the world without concern about reagent strength. 

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Testing in cold weather with CHEMetrics Test Kits

Each year as the weather turns colder and the snow starts to fly in the northern latitudes, many express concern about sampling and testing in cold weather. 

Even though CHEMetrics reagents are aqueous, extremely cold temperatures are required to freeze test ampoules. This is due to a phenomenon known as freezing point depression/boiling point elevation. This effect is observed when two or more pure compounds are mixed together, as in a reagent ampoule (deionized water and chemical reagent). If glass test ampoules and comparators do freeze, you can be assured that they will not shatter. All ampoules are manufactured with additional space for the expansion of the frozen contents. Kit performance will not be compromised if the reagent has frozen. Simply bring the kit to or near room temperature before using. In addition, most of our kit chemistries are not highly dependent on temperature, so with most kits it is possible to perform the test in the cold and on a cold sample. Some reactions are, however, slowed by lower temperatures more than others. It is therefore a good rule of thumb to bring the sample and kit to room temperature before testing, or to confirm results obtained in the cold by repeating the test with a warm sample and kit. 

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At first glance, the EPA guidelines for water testing procedures seem to require expensive, sophisticated analytical equipment and highly trained personnel. In many cases, however, quality control benchmarks can be achieved or exceeded using pre-packaged analytical test kits.  Chemical test kits provide a reliable, inexpensive, and time-saving alternative for testing drinking water, wastewater, and a variety of aqueous industrial samples. By using kits with either visual or instrumental readout, chemists and technicians can reduce time and costs involved, while achieving a level of accuracy that is acceptable for a wide range of industrial and environmental applications. In addition, test kits simplify otherwise complex procedures, resulting in high levels of repeatability in testing, and virtual elimination of resampling costs. 

CHEMetrics, Inc., a leading U.S. manufacturer of water testing kits, offers a wide range of analytical procedures in kit format. Laboratory analysis for contaminants such as phosphate, chlorine, ammonia, nitrite and many others may have routine turnaround times of up to two weeks when processed through a commercial environmental lab. The same tests can be completed in minutes, on-site, using the CHEMetrics self-filling ampoule methodology. 

CHEMetrics' easy-to-use instrumental test kits utilize Vacu-vials® glass ampoules which contain pre-mixed liquid reagents sealed under vacuum in unit-dose format. The ampoule's self-filling capability eliminates the need to measure sample or reagent. In two minutes or less, an analysis can be performed by photometric or spectrophotometric methods. Analyte concentration can be obtained directly, or derived from absorbance or percent transmittance.  Additional benefits include reagent stability, efficiency of packaging/shipping and reduced overall cost.  Excellent accuracy is maintained across the board using CHEMetrics methods for over 50 analytes. 

In summary, the CHEMetrics Vacu-vials instrumental readout system offers rapid analysis, convenience, low demand on operator skill, and low overall testing cost. Kit components are disposable, reducing cleanup time. When the cost of analyst time, cleanup time, amortized instrument cost, and overhead are considered, the EPA method is significantly more expensive than the CHEMetrics analytical system. Most importantly, results derived from kit analyses satisfy requirements for routine monitoring of major pollutants. 

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Custom and Private Label Products

If you've ever labored through a lab procedure, longing for a time-saving, self-filling ampoule method, call us!  Our products often originate directly from customers eager for easier, more efficient ways to perform routine determinations.

To be considered for a custom product, the test should be one that you perform frequently, or one that is widely used throughout your industry.

At CHEMetrics we have extensive experience with private-label packaging and service.  We're very flexible in working with each customer's special needs, from printing labels to custom packaging with four-color art.

For more information on custom products and private labeling, call 1-800-356-3072 and ask for Teresa.  I look forward to building a test that works for you.