Dissolved Oxygen Detection Equipment for Boiler Feed Water: Ensuring Safety and Efficiency

Introduction

Boiler systems, whether used in industrial processes or power generation, rely heavily on the quality of their feed water to maintain efficiency, safety, and longevity. Among the critical parameters to monitor, dissolved oxygen (DO) stands out due to its potential to cause severe corrosion in boiler components. Even trace amounts of oxygen in feed water can lead to pitting corrosion, which creates small, localized holes in metal surfaces, weakening boiler tubes and other components. This corrosion can result in leaks, reduced heat transfer efficiency, and, in severe cases, catastrophic failures. For power plant boilers, operating at high pressures and temperatures, the risks are even more pronounced, making precise DO monitoring essential.

In China, national standards such as GB/T 1576-2018 for industrial boilers and GB/T 12145-2016 for power plant boilers set stringent limits for DO to prevent these issues. Regular monitoring with advanced equipment ensures compliance with these standards, protects equipment, and optimizes operational efficiency. This article explores the importance of DO monitoring, relevant standards, detection methods, and the role of advanced equipment like the ERUN-SP3-A5 Portable Dissolved Oxygen Analyzer.

Importance of Dissolved Oxygen Monitoring

Dissolved oxygen refers to oxygen gas dissolved in water, which, while essential for aquatic life, is a major concern in boiler systems. When oxygen interacts with metal surfaces, especially under the high temperatures and pressures found in boilers, it triggers oxidation, leading to corrosion. This is particularly damaging in the form of pitting, where corrosion concentrates in small areas, creating deep pits that can penetrate metal surfaces. Over time, these pits can form tubercles or scabs, exacerbating damage and potentially leading to equipment failure.

For industrial boilers, typically operating at pressures below 3.8 MPa, corrosion can reduce efficiency by forming insulating deposits on heat transfer surfaces, increasing fuel consumption. In power plant boilers, which operate at higher pressures (above 3.8 MPa), the stakes are even higher, as corrosion can compromise steam purity, affecting turbines and downstream equipment. Regular DO monitoring allows operators to detect and control oxygen levels, preventing these costly and dangerous outcomes.

National Standards for Boiler Water Quality

China has established clear guidelines for boiler water quality to ensure safe and efficient operation. The key standards are:

• GB/T 1576-2018 - Water Quality for Industrial Boilers: This standard applies to fixed steam boilers, multifunctional boilers, and hot water boilers with rated outlet steam pressure less than 3.8 MPa. It specifies that DO in feed water should generally be kept below 0.05 mg/L (50 ppb) to minimize corrosion risks. For boilers with higher evaporation rates (≥10 t/h), deaeration is mandatory to achieve these low levels.

• GB/T 12145-2016 - Quality Criterion of Water and Steam for Power Plant and Steam-Generating Equipment: This standard governs power plant boilers with main steam pressure of 3.8 MPa or higher. It requires DO levels to be extremely low, typically below 0.01 mg/L (10 ppb), to protect high-pressure systems from corrosion and ensure steam purity for turbine operation.

These standards emphasize the need for precise DO measurement, as even small deviations can lead to significant damage over time. Operators must use equipment capable of detecting trace DO levels to comply with these requirements.

Methods for Measuring Dissolved Oxygen

Several methods are available for measuring DO in boiler feed water, each suited to specific applications:

1. Electrochemical Sensors: These sensors, including galvanic and polarographic types, measure the current generated by oxygen reduction at a cathode. They are highly sensitive, capable of detecting DO levels as low as 1 ppb, making them ideal for boiler applications. However, they require regular calibration and maintenance to ensure accuracy.

2. Optical Sensors: These use fluorescence quenching, where oxygen interacts with a luminescent dye, altering its fluorescence. Optical sensors are low-maintenance and less prone to interference but may be less common in industrial settings due to higher costs.

3. Chemical Methods (Iodometric Method): This involves chemical reactions to quantify DO, suitable for laboratory settings but less practical for real-time monitoring due to its complexity and time requirements.

For boiler feed water, electrochemical sensors are preferred due to their precision and ability to measure low DO concentrations, aligning with the requirements of GB/T 1576-2018 and GB/T 12145-2016.

ERUN-SP3-A5 Portable Dissolved Oxygen Analyzer

The ERUN-SP3-A5 Portable Dissolved Oxygen Analyzer is a cutting-edge tool designed for precise DO measurement in boiler feed water and steam condensate. Its features make it an excellent choice for both industrial and power plant applications:

• Measurement Range: 0-100 μg/L (0-0.1 mg/L) and 0-20 mg/L, covering both trace and higher DO levels.

• Accuracy: ±1.5% full scale, ensuring reliable measurements even at low concentrations.

• Response Time: T90 < 60 seconds, allowing rapid detection of changes in DO levels.

• Temperature Compensation: Automatically adjusts for temperatures between 5-50°C, ensuring accuracy across varying conditions.

• Portability: Compact (180x80x50mm) with a built-in lithium battery, ideal for field and laboratory use.

• User Interface: Features a color touch screen with dual display modes and real-time data curves for easy operation.

The ERUN-SP3-A5 complies with GB/T 1576-2018 and GB/T 12145-1999, making it suitable for monitoring DO in both industrial boilers and high-pressure power plant systems. Its high sensitivity and fast response time enable operators to maintain water quality within the stringent limits required, preventing corrosion and ensuring compliance.

Benefits of Advanced DO Detection

Using advanced DO detection equipment like the ERUN-SP3-A5 offers multiple benefits:

• Corrosion Prevention: By maintaining DO below the specified limits, operators can prevent pitting and extend the lifespan of boiler components, reducing maintenance costs.

• Regulatory Compliance: Accurate monitoring ensures adherence to national standards, avoiding penalties and ensuring safe operation.

• Operational Efficiency: Optimal water chemistry improves heat transfer, reduces fuel consumption, and minimizes downtime due to corrosion-related issues.

• Safety: Preventing corrosion reduces the risk of boiler failures, enhancing safety for personnel and facilities.

• Cost Savings: While advanced equipment requires an initial investment, the long-term savings from reduced repairs and improved efficiency are significant.

Case Study

In a power plant operating at 2800 psi, maintaining DO below 10 ppb is critical. Using the ERUN-SP3-A5, operators conducted daily measurements of feed water and condensate. When DO levels exceeded the limit, they adjusted deaeration processes and oxygen scavenger dosages, preventing corrosion and maintaining compliance with GB/T 12145-2016. Similarly, in an industrial boiler facility, regular monitoring ensured DO remained below 50 ppb, reducing maintenance costs and improving efficiency.

Conclusion

Monitoring dissolved oxygen in boiler feed water is a critical task for ensuring the safety, efficiency, and longevity of boiler systems. Chinese national standards, such as GB/T 1576-2018 and GB/T 12145-2016, set strict DO limits to prevent corrosion and maintain operational integrity. Advanced equipment like the ERUN-SP3-A5 Portable Dissolved Oxygen Analyzer provides the precision and reliability needed to meet these standards, offering benefits in corrosion prevention, compliance, and efficiency. By investing in such technology, boiler operators can protect their systems, reduce costs, and ensure safe and efficient operation.

Table 1: Typical Dissolved Oxygen Limits for Boiler Feed Water

Note: Limits may vary based on specific boiler design and operating conditions. Always consult the relevant standards for precise requirements.

Table 2: Comparison of Dissolved Oxygen Detection Methods