pH Calculation by Differential Conductivity Measurement in Pure and Ultra-Pure Water
通过差示电导率测量在纯水和超纯水中计算 pH 值

Summary  摘要

In all kinds of water steam cycles, the correct pH measurement in power plants play a key factor in corrosion risk surveillance. A measurement with a glass pH electrode is possible but requires a pH probe designed for low conductivity, high temperatures and pressure. An accurate pH value can also be obtained by measuring the conductivity before and after a strong acid ion exchanger. These measurements are used to calculate the pH. This is a widely accepted methodology, which eliminates the need for high temperature and high pressure pH probes. This type of measurement, which is commonly used for feed water and boiler water, is very popular in Europe. It is also recommended by the VGB organization.
在各种水蒸汽循环中，发电厂中正确的 pH 测量在腐蚀风险监测中起着关键作用。使用玻璃 pH 电极进行测量是可能的，但这需要设计用于低电导率、高温和高压的 pH 探头。通过在强酸离子交换器前后测量电导率，也可以获得准确的 pH 值。这些测量用于计算 pH 值。这是一种广泛接受的方法，无需高温和高压 pH 探头。这种测量方法通常用于给水和锅炉水，在欧洲非常流行。VGB 组织也推荐这种方法。

Power Plant Water Quality Requirements
发电厂水质要求

In power plant processes, the pH of water used is critical. As water with a pH outside the recommended range can cause corrosion of equipment and infrastructure. Unexpected maintenance or downtime due to corrosion can be quite costly for power plant companies. Monitoring pH and conductivity of the water used in a power plant allows the control of these parameters, reducing maintenance requirements.
在发电厂过程中，使用水的 pH 值至关重要。超出推荐范围的水 pH 值会导致设备和基础设施的腐蚀。腐蚀导致的意外维护或停机对发电厂公司来说可能非常昂贵。监测发电厂使用水的 pH 值和电导率可以控制这些参数，从而减少维护需求。

Measurement Challenges  测量挑战

Measuring pH directly with a standard glass pH electrode presents several challenges. The most critical challenge is obtaining an accurate measurement of the pure and ultra-pure water used in power plant operations. Using a standard electrode in pure or ultra-pure conditions may result in unstable and incorrect readings. Additionally, operating conditions within a power plant may create disruptive electrical potentials, which skews the measurements. Ongoing measurements of pH in ultra-pure water also necessitates frequent electrode maintenance. Standard pH electrodes are fragile and require routine recalibration. A more accurate and reliable alternative is the pH calculation using differential conductivity measurements.
使用标准玻璃 pH 电极直接测量 pH 值存在几个挑战。最关键挑战是获得电厂运行中使用的纯水和超纯水的准确测量值。在纯水或超纯条件下使用标准电极可能导致读数不稳定且不准确。此外，电厂内的运行条件可能产生干扰性电势，导致测量结果偏差。超纯水中 pH 值的持续测量还要求频繁进行电极维护。标准 pH 电极易碎，需要定期校准。更准确可靠的替代方法是使用差示电导率测量计算 pH 值。

Dissolved Oxygen Measurement for Corrosion Protection
腐蚀防护用溶解氧测量

Several organizations, including VGB (Germany) and EPRI (USA), recommend an additional corrosion test based on dissolved oxygen concentration. Cleaner water typically has a higher dissolved oxygen content, which leads to better corrosion protection for steel pipes. If high water purity is not attainable, corrosion protection depends more heavily on the pH value. Therefore, a correct measurement of the pH value is extremely important.
一些组织，包括德国的 VGB 和美国的 EPRI，推荐基于溶解氧浓度进行额外的腐蚀试验。清洁的水通常具有较高的溶解氧含量，这有助于提高钢管的腐蚀防护效果。如果无法达到高水纯度，腐蚀防护则更多地依赖于 pH 值。因此，正确测量 pH 值至关重要。

pH Calculation by Differential Conductivity Measurement in Pure and Ultra-Pure Water
纯水和超纯水中通过差分电导率测量 pH 值

Setup for pH Calculation by Differential Electrical Conductivity (EC):
差分电导率（EC）测量 pH 值的设置：

Two EC probes are necessary simultaneous measurement before and after a strong acid cation exchanger. The setup measures two different EC values. The probe before the cation exchanger measures the specific conductivity, while the probe after the cation exchanger measures the cation conductivity.
在进行强酸性阳离子交换器前后的同时测量，需要两个 EC 探头。该设置测量两个不同的 EC 值。阳离子交换器前的探头测量比电导率，而阳离子交换器后的探头测量阳离子电导率。

pH Calculation Equation  pH 计算公式

The VGB Standard VGB-S-006-00-2012-09-EN uses the following equation to calculate the pH of pure/ultrapure water in the range of pH 7.5 to pH 10.5:
VGB 标准 VGB-S-006-00-2012-09-EN 使用以下公式计算 pH 7.5 至 pH 10.5 范围内纯/超纯水的 pH 值：

pH_B = log [Cond_SC – (Cond_CC/ 3)/ C_B] + 11

Where:  其中：

• Cond_SC defines the specific conductivity
  Cond _SC 定义了比电导率
• Cond_CC defines the cation conductivity (or acid conductivity)
  Cond _CC 定义了阳离子电导率（或酸电导率）
• C_B is a factor which depends on the alkalizing reagent
  C _B 是一个取决于碱化试剂的因素

The table below lists C_B values for common alkalizing reagents:
下表列出了常见碱化试剂的 C _B 值：

 

Alternative for Ammonia Reagent Model:
氨试剂模型的替代方法：

Another equation can also be used for the Ammonia reagent model:
氨试剂模型还可以使用另一个方程：

pH = log [Cond_SC – (Cond_CC/3)] + 8.6
pH = log [电导率 _SC – (电导率 _CC /3)] + 8.6

Additional Considerations
额外注意事项

The following specifications must be satisfied to successfully calculate a valid pH value:
要成功计算有效的 pH 值，必须满足以下规范：

• 7.5 < pH < 10.5 (NH3: 7 < pH < 10; NaOH: 7 < pH < 10.7)
• Phosphate concentration below 0.5 mg/L
  磷酸盐浓度低于 0.5 mg/L
• The reagent must be Ammonia or Sodium Hydroxide
  试剂必须是氨或氢氧化钠
• Below a pH value of 8, the contamination of the sample with other agents has to be very low compared to the concentration of the alkaline reagent
  在 pH 值低于 8 时，与其他试剂相比，样品的污染必须非常低

Temperature Compensation  温度补偿

The conductivity reading of the first probe is converted to a 25°C reference temperature based on a user selected conversion model. For example, in a classic all-volatile treatment (AVT), the temperature conversion model for ammonia is set. There are other compensation models available. Typically, the conversion model used is based on the dominant chemical species.
第一个探头的电导率读数根据用户选择的转换模型转换为 25°C 参考温度。例如，在经典全挥发性处理（AVT）中，会设置氨的温度转换模型。还有其他补偿模型可用。通常使用的转换模型基于主要的化学物质。

The exchange resin should exchange positively charged ions for protons. Therefore, the alkalizing reagent is replaced with water, and the neutral salt, sodium chloride (NaCl), is converted to hydrochloric acid (HCl). Due to these reactions, the temperature compensation model for the second conductivity reading needs to be set to a strong acid.
交换树脂应与质子交换阳离子。因此，碱性试剂被水替代，中性盐氯化钠（NaCl）转化为盐酸（HCl）。由于这些反应，第二次电导率读数的温度补偿模型需要设置为强酸。

Cross Check  交叉检查

A cross check with a glass pH electrode would not be suitable under these conditions due to the very low conductivity and associated risk of mismeasurements.
在这些条件下，使用玻璃 pH 电极进行交叉检查不合适，因为电导率非常低，且存在测量误差的风险。

Advantages of Calculated pH Measurements
计算 pH 测量的优点

pH calculation based off differential conductivity measurement is a reliable and low maintenance alternative to the conventional pH measurement with glass electrodes. This technique is possible even in samples containing mixtures of alkaline reagents. Advantages include:
基于微分电导率测量的 pH 计算是一种可靠且维护量低的替代传统玻璃电极 pH 测量的方法。这种技术在含有碱性试剂混合物的样品中也能实现。其优点包括：

• The calculated pH values are more accurate without the typical restrictions of glass pH electrodes in samples with low conductivity
  计算出的 pH 值在低电导率样品中比玻璃 pH 电极更准确，且不受其典型限制
• EC sensors are stable over a long period of time with minimal maintenance compared to glass pH electrodes
  与玻璃 pH 电极相比，EC 传感器在长时间内保持稳定，维护量极小
• The algorithm yields reliable results
  该算法能获得可靠的结果
• Higher sensitivity due to linear relationship between concentration and conductivity (compared to logarithmic relationship between concentration and pH)
  由于浓度与电导率之间存在线性关系（与浓度与 pH 值之间的对数关系相比），因此具有更高的灵敏度

Sensorex Products for Conductivity Monitoring in Ultra-Pure Water
用于超纯水电导率监测的 Sensorex 产品

Conductivity measurements for the differential pH calculation can be collected with stainless steel conductivity sensors with cell constant k=0.1. These sensors operate well in typical power plant monitoring conditions of temperature, pressure, and conductivity.
使用 k=0.1 的单细胞常数不锈钢电导率传感器进行差分 pH 计算的电导率测量。这些传感器在典型的电厂监测条件下的温度、压力和电导率下运行良好。

Use a conductivity transmitter to integrate sensors into an online monitoring system. Input the equation for the calculation into a PLC to use the conductivity sensor measurements to calculate pH.
使用电导率变送器将传感器集成到在线监测系统中。将计算方程输入 PLC，以使用电导率传感器测量值来计算 pH 值。