冷却水中铜缓蚀剂的在线监测

AN-PAN-1045

2021-02

铜因其热传导特性而被广泛应用于工业冷却水系统中，但它很容易受到腐蚀。腐蚀会导致效率下降，终导致设备故障，从而造成昂贵的维护、更换和停机时间。可以在水化学中添加缓蚀剂（三唑类），在金属表面形成稀释可溶的保护层。必须保持三唑的浓度以保护铜，这就需要定期测定冷却水中的浓度。带有紫外/可见检测功能的 2060在线离子色谱仪非常适合这种应用，它能够同时精确、可靠地测量冷却水中的多种离子和紫外活性化合物。

In industrial cooling water systems, copper and its alloys are widely used because of their superior heat transfer properties. These materials are susceptible to corrosion, which causes two basic problems. The first and most obvious is the failure of equipment with the resultant cost of replacement and plant downtime. The second is decreased plant efficiency due to loss of heat transfer—the result of heat exchanger fouling caused by the accumulation of corrosion products. Regardless of the type of corrosion, power plants must ensure that it occurs as little as possible. On the other hand, they can monitor substances and parameters that indicate corrosion, such as conductivity, pH value, or the presence of corroding anions and cations. On the other hand, power plants can make sure that added corrosion inhibitors are present in sufficient amounts to prevent equipment failures.

There are two primary concerns about corroded copper from the heat exchanger. First, from an environmental standpoint, soluble copper is toxic and needs to be properly controlled in any discharge stream. Second, soluble copper will plate out on mild steel surfaces and form galvanic corrosion sites that result in severe localized corrosion (also known as pitting) and premature failure of steel heat exchangers. Every cooling water system should include a method of monitoring corrosion inhibitors in the system.

Triazoles (e.g., tolyltriazole, benzotriazole, and 2-mercaptobenzothiazole) are commonly added in the mg/L range to protect copper and its alloys from corrosion by forming sparingly soluble layers on the surface of the metal. After triazole adsorption, copper-azole complexes are believed to precipitate at the liquid-solid interface, thus protecting the metal substrate from further dissolution. These complexes are prone to oxidation and also react with added microbiocides. As a result, the triazoles have to be replenished, which necessitates regular concentration determinations.

Figure 1 Corrosion inhibitors used in the cooling water at a power plant.

Corrosion chemistry monitoring helps to minimize loss of efficiency and protect the components coming in contact with steam and water against damage. Timely and effective monitoring of power plant water chemistry is critical for maintaining efficiency and safety. By using online analyzers, operators gain the information they need to accurately identify trends and address operational issues before costly problems arise.

Figure 2 Chromatogram of a spiked cooling water sample containing 1 mg/L benzotriazole, tolyltriazole, and 2-mercaptobenzothiazole; sample volume: 20 μL; wavelength: 214 nm

Figure 3. The 2060 IC Process Analyzer is available with either one or two measurement channels, along with integrated liquid handling modules and several automated sample preparation options.

These copper corrosion inhibitors are quantified by ion chromatography with direct UV/VIS detection. However, precise, reliable trace analysis requires the method to be automated as much as possible. Inconsistent measurements and slower offline analyses result in fluctuating triazole concentrations in the cooling water. Constant online measurement of the cooling water additives can result in additional cost savings by optimizing parameters and using less chemicals. Metrohm Process Analytics offers a complete solution for this task: the 2060 Ion Chromatograph (IC) Process Analyzer. In a single analysis, the 2060 IC is able to measure numerous ionic and UV-active compounds in aqueous media from ng/L to % concentrations. The analysis system is fed directly and continuously with samples via a bypass in the process. Automated calibration guarantees excellent detection limits, a high reproducibility, and excellent recovery rates.

analytical channels, it is possible to monitor other corrosion indicators as well via conductivity detection, giving a comprehensive overview of the water circuit chemistry. The analyzer can run for extended periods in less-frequented areas as there is adequate space for reagents, ultrapure water and/or prepared eluent, and level sensors to ensure that you are always informed about your chemical consumption. With a built-in eluent module and optional PURELAB® flex 5/6 from ELGA® for continuous pressureless ultrapure water supply, the 2060 IC Process Analyzer can be configured to run even trace analyses autonomously. The possibility to connect one analyzer to up to 20 sample streams means multiple areas within a plant can be monitored by a single instrument.

The analysis is carried out fully automatically. Analyte measurement is performed with direct UV/VIS detection at 214 nm.

Inline eluent preparation ensures consistently stable baselines
Protect valuable company assets (e.g. pipes, PWR, and turbines, which are prone to corrosion)
Safe working environment and automated sampling
High precision analyses for a wide spectrum of analytes with multiple types of detectors