A sudden increase in cation conductivity levels meant a US power plant could have faced an unplanned shutdown. However, by detecting ppb-level chloride and sulfate ions accurately, the METTLER TOLEDO 3000CS analyzer helped identify the cause of the upset, and energy production was not affected.
This power plant is a major electricity and natural gas provider in the US Midwest. It provides energy services to 2.4 million electric and 900,000 natural gas customers in the states of Illinois and Missouri. The Sioux Energy Center is part of company’s fleet of power plants, and provides electricity to the city of St Louis and its surrounding areas. It is a 1,100 MW coal-fired plant, with two power generation units that have been in operation since 1967.
Precise control of water-steam cycle chemistry
Cycle chemistry in the power plant is monitored and controlled very precisely to ensure there is minimal damage to expensive plant assets from corrosion or deposition. Any disturbance in the chemistry can result in increased levels of contaminants, so it is critical to pinpoint any contamination source quickly to avoid extended exposure to turbines, etc.
The traditional method of monitoring contaminant levels in the water-steam cycle is cation conductivity, and power plants follow guidelines of EPRI, VGB, IAPWS, and other industry organizations to set a maximum acceptable limit for cation conductivity in their cycle. However, cation conductivity is a cumulative indicator of numerous water contaminants, and does not provide details of levels of key corrosive contaminants such as chloride and sulfate. This can cause confusion as to the correct course of action when cation conductivity measurements are above acceptable limits, leading to loss of valuable time in trying to identify and fix the root cause of any contamination event.
Excursion could lead to plant shutdown
During routine operation of the Sioux Energy Center, the plant’s chemists detected an excursion in their cycle chemistry. Cation conductivity measurements for their main steam samples increased rapidly and were beyond acceptable limits. This was followed by high cation conductivity in the hotwell, indicating contamination throughout the water-steam cycle. Such an event could occur due to a number of reasons, and the source contaminant(s) can be several: from less corrosive like carbon dioxide, to very corrosive such as chloride and sulfate. An extended period of high cation conductivity measurements may lead to drastic measures such as plant shutdown, as defined by standard operating procedure and guidelines of the plant. This is a safe and appropriate approach when the source of the high conductivity is not clear, and time is required to find the root cause through off-line water sample tests.
On-line analyzer helps identify root cause
Fortunately, the Sioux Energy Center had installed a METTLER TOLEDO Thornton 3000CS on-line chloride / sulfate analyzer. The 3000CS continuously monitors the water-steam cycle, and as it was reporting levels of < 1 ppb for both chloride and sulfate, the plant chemists were able to immediately rule out those contaminants. This helped the plant chemists to quickly narrow down the cause of the contamination to organics. With this information, the source of the problem – polisher resin leakage into the feedwater cycle – was rapidly identified and corrective action was taken.
Continuous measurements for ongoing monitoring
Pleased that the 3000CS analyzer had helped them resolve this excursion promptly, the power plant has set up the analyzer to monitor various measurement points on both of their generation units. This allows the chemists to detect and react to any excursion going forward, with accurate and reliable information from the analyzer helping guide their course of action.
3000CS Chloride & Sulfate Analyzer
On-line Measurement of Corrosive Ions
The 3000CS is a reliable, on-line analyzer for direct measurement of chloride and sulfate in pure water and power plant cycle chemistry. This instrument detects these highly corrosive ions to prevent damage to critical power plant components.
Direct Detection of Chloride & Sulfate
The 3000CS provides a method for direct, on-line detection of corrosive ions without measurement interference from other ions or common additives.
Fast Monitoring to Prevent Corrosion
Measurement cycles every 45 minutes ensure you can quickly react to chloride and sulfate excursions to prevent corrosive conditions from occurring.
Reduced Monitoring Effort and Costs
Typical chloride and sulfate monitoring requires expensive resources and lab work. The 3000CS eliminates the need for these costly off-line tests.
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