The QHCZ furnace wall thickness monitoring system has been successfully applied in blast furnace operations, proving to be an effective tool for measuring the thickness of the furnace wall. It offers advantages such as a simple structure, reliable performance, and high measurement accuracy.
1. **Ultrasonic Sensor Design Process**
The ultrasonic sensor was designed based on the characteristics of the blast furnace smelting process, using non-destructive ultrasonic testing to measure the wall thickness. The ultrasonic probe does not directly contact the furnace wall. Instead, a pre-buried one-piece component (measuring rod) is used, which is simultaneously eroded by the furnace wall. Point A is the hot end of the measuring rod inside the furnace, where it meets the high-temperature airflow. Point B is the coupling point between the ultrasonic probe and the measuring rod. As the furnace wall erodes, the measuring rod shortens, and its remaining thickness can be determined by analyzing the reflected echo from the rod.
2. **Rod Material Selection and Experimentation**
In theory, when ultrasonic waves travel along the rod, reflections and transmissions occur at the hot end interface. The reflection coefficient (r) and transmission coefficient (t) depend on the acoustic resistance on both sides of the interface. To meet design requirements, the acoustic resistance at the hot end should be much higher than that of the rod. In laboratory tests, different materials like aluminum, copper, ceramic, and steel rods were tested under simulated conditions. However, aluminum had a low melting point, copper conducted heat too quickly, and ceramic rods were fragile. Steel rods showed significant ultrasonic attenuation, especially above 1000°C, making them unsuitable. After extensive testing, a special iron rod was chosen, which could withstand temperatures up to 1300°C and provided consistent reflected echoes.
3. **Probe Frequency and Measuring Rod Diameter Selection**
In the belly section of the blast furnace, the distance from the hot end of the rod to the outer surface of the furnace skin is typically around 1 meter. To avoid water leaks and potential hazards, the probe must be kept away from the furnace skin, which increases the rod length and weakens the echo. A moderate frequency was selected to ensure good penetration and accuracy. Through experiments with different diameters, a 40 mm diameter rod was found to provide optimal echo strength and ease of installation.
4. **Feasibility Test and Scope of the Measuring Rod**
A feasibility test was conducted at Baotou Steel’s No. 2 Blast Furnace. After several months, the rods were retrieved and found to match the actual wall thickness. However, rods installed in the upper part of the furnace waist showed poor echo signals due to their tapered shape, which affected wave propagation. Based on these findings, it was concluded that the measuring rod should be placed between the upper part of the belly and the lower part of the furnace body, where the material properties allow for better signal reflection.
5. **Enhanced Reflected Wave and Noise Suppression**
Field testing revealed two key issues: noise interference and weak echo signals. To address this, damping materials were added to reduce pulse width and improve resolution. A 15° angle was introduced on the damping block to minimize clutter. Coupling agents were tested, and an adhesive-based coupling method was selected for its stability at high temperatures and resistance to corrosion. The coupling surfaces were precisely machined to enhance wave transmission.
6. **Protection of the Measuring Rod in Production**
To ensure the durability of the system, a spring-loaded protective coupling was added to prevent damage from vibration or impact. The wiring was protected against fire and moisture, and the outer casing was rust-resistant. Data collectors were relocated to a central cabinet for easier access and maintenance, improving reliability and reducing downtime.
7. **Data Processing and Error Compensation**
Temperature gradients in the measuring rod can affect measurement accuracy. Software-based temperature compensation was implemented during data processing. Long-distance signal transmission also caused distortion, so careful calibration and signal source quality control were essential. By recording peak heights at different temperatures and analyzing statistical trends, measurement errors were minimized, keeping the error range within 2–10 mm.
8. **Features and Applications of the Measurement System**
The system uses a distributed network structure with multiple channels, allowing hundreds of detection points. It supports waveform display, erosion cross-sections, vertical profiles, data printing, historical query, real-time data display, and online data upload for expert systems. This comprehensive solution ensures accurate and continuous monitoring of the furnace wall thickness, enhancing operational safety and efficiency.
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