As fossil plants look for new methods of minimizing corrosion, on-line analyzers are gaining importance. An analyzer for chloride and sulfate allows rapid response to rising levels of these corrosive ions.

Growing interest in monitoring low-level chloride and sulfate

Awareness of innovative approaches to protect critical fossil plant components from corrosion continues to grow. In respect to chloride and sulfate, cation or degassed cation conductivity can provide indirect measurement, but cannot provide specific, low-level indication to ensure these harmful ions meet the acceptable limits of < 2 ppb.

Use of neutralizing amines, or filming amines that contain neutralizing amines, may result in the formation of acetate and formate. These ions impact cation and degassed cation conductivity, making it more difficult to assess chloride and sulfate levels.

While ion chromatography can accurately measure low-level anion concentrations, the instrument is expensive compared to most on-line cycle chemistry analyzers and requires more experienced chemistry staff, making it impractical for most fossil plants. These factors have resulted in increased interest in on-line monitoring of chloride and sulfate.

The Electric Power Research Institute (EPRI) has driven efforts to bring automated, on-line measurement to fossil plants. This would lead to a number of benefits:

• Monitor plant conditions to protect equipment more effectively, allowing for rapid response to chemistry excursions and reducing maintenance requirements.
• Drive down measurement costs by not requiring trained personnel to collect and measure samples.
• Ensure extended plant asset life, leading to reduced downtime and unplanned or forced maintenance.

Six month test period for on-line analyzer
As part of this initiative, EPRI independently evaluated the METTLER TOLEDO 3000CS Chloride and Sulfate Analyzer at a coal-fired plant in the Central US.

In coordination with EPRI, plant personnel installed the 3000CS Analyzer and connected each of the units to steam and boiler conditioned sample lines. The output of the analyzer was connected to a distributed control system. Chloride and sulfate concentrations were measured on-line for approximately six months. A cation resin column was installed upstream to remove ammonia from the sample water, which at high concentrations could physically interfere with the measurement. A magnetic trap was also installed to remove any magnetite present in the sample. A clean power supply was ensured so large fluctuations in power would not interfere with the measurement.

Analyzer results correlated closely to ion chromatographs

The 3000CS Analyzer performed very well in the EPRI evaluation, with EPRI publishing its findings at its 12th International Conference on Cycle Chemistry in Fossil and Combined Cycle Plants, in Arlington, VA (USA) on June 27, 2018.

During the evaluation of the 3000CS, EPRI also suggested an improvement that has now been implemented in all analyzers. EPRI observed that when either chloride or sulfate measurement went out of range, both values would display out of range even if the other one was within range. METTLER TOLEDO corrected this by changing the composition of the reagents and improving the data processing firmware in the analyzer.

In their presentation, EPRI also compared the results to grab samples measured on benchtop ion chromatographs, and made the following observations about the 3000CS:

• The analyzer correlated closely to grab sample results analyzed in a lab using ion chromatography.
• Operator intervention was roughly the same as other commonly used on-line chemistry analyzers.
• At a one sample per hour frequency, the reagents lasted 78 days. The cartridge had to be replaced after three months, in line with expected life as specified. The change-out required just 30 minutes.
• Calibration using 5 ppb and 25 ppb standards was straightforward and the analyzer returned to service after rinse down without any issues.

On-line analyzer allows rapid response to contamination

EPRI summarizes these results in their evaluation of the 3000CS Analyzer as an opportunity for fossil plants to consider including this technology in their cycle chemistry monitoring program. On-line measurements of steam samples ensure fossil plants achieve the recommended steam purity of < 2 ppb while also allowing them to rapidly respond to any contamination events. The METTLER TOLEDO 3000CS Analyzer is a valuable tool to meet these recommendations and protect plant assets.

Read more in the application note about the increasing need to measure chloride and sulfate.

As shown in the video, METTLER TOLEDO Thorntonʼs 3000CS Analyzer uses sophisticated Microfluidic Capillary Electrophoresis (MCE) technology to provide a convenient, dependable method for trace-level chloride and sulfate monitoring.