Steam Wetness Measurement Using ECT and Liquid Film Probes
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Solution Overview
Problem
Existing methods for measuring steam wetness in power plants lack accuracy and continuity, especially at low wetness concentrations, with tracer injection providing only intermittent measurements and Electrical Capacitance Tomography and sound-based systems showing limited accuracy.
Innovation Solution
A wetness measurement system combining a liquid film measurement device and Electrical Capacitance Tomography with a plurality of electrodes, where the flowrate of the liquid film is calculated using cross-correlation between probes, and capacitance measurements are used to determine gas phase wetness, improving accuracy and enabling continuous measurement at low wetness concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If Electrical Capacitance Tomography is used for continuous measurement, then measurement continuity is improved, but measurement precision deteriorates at low wetness concentrations
Solution Approach 1:
The patent combines Electrical Capacitance Tomography (ECT) with a liquid film measurement device that uses capacitance probes to measure liquid film thickness and flow rate. By merging these two measurement systems, the patent achieves both continuous measurement capability and high precision at low wetness concentrations (0.1wt%). The liquid film measurement device provides continuous data while the combined system maintains accuracy through complementary measurement approaches.
Solution Approach 2:
The patent employs a composite measurement approach that integrates multiple measurement techniques (ECT and liquid film capacitance measurement) into a unified system. This composite measurement system leverages the strengths of each individual technique while compensating for their weaknesses, enabling continuous high-precision measurement of low wetness concentrations that neither method could achieve alone.
2Measurement precision
If tracer injection is used for accurate measurement below 1wt%, then measurement precision is improved, but measurement continuity deteriorates
Solution Approach 1:
The patent merges tracer injection measurement capability with continuous ECT and liquid film measurement systems. The tracer injection provides reference accurate measurements for calibration, while the continuous ECT and liquid film devices provide ongoing measurement capability. This combination achieves both high precision at low concentrations and measurement continuity.
Solution Approach 2:
The system uses tracer injection measurements as a preliminary action for calibration and validation of the continuous measurement system. By establishing accurate reference points through tracer injection, the system prepares the measurement apparatus to maintain high precision during continuous operation without requiring ongoing tracer injection.
3Device complexity
If the number of electrodes is reduced to simplify installation, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent changes the critical parameter from the number of electrodes to the surface area of each electrode. By increasing the surface area of individual electrodes, the system maintains measurement precision with fewer electrodes. This parameter change simplifies installation while preserving measurement accuracy through optimized electrode geometry rather than quantity.
Solution Approach 2:
The patent applies local quality by concentrating measurement capability in each electrode through increased surface area. Rather than distributing measurement function across many small electrodes, each electrode is designed with sufficient surface area to contribute effectively to the overall measurement, maintaining precision with reduced electrode count.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate continuous wetness measurements down to 0.1wt% with an accuracy of 0.5wt% at 70 bar, enhancing process efficiency and reducing component erosion by reliably estimating wetness in steam flows.
Implementation Method 1
an electrical capacitance tomography device having a plurality of electrodes that are located in the container and have a measurement surface
Implementation Method 2
calculating wetness of the capacitance measurements based on measurement of the Electrical Capacitance Tomography device
Implementation Method 3
calculating a flowrate of a liquid film by cross correlation based on the distance between the first probe and the second probe and the calculated void fraction of the first probe and the second probe
Data Source
Figure 1~2
AI summary
Provided is a measurement system for measuring wetness of the gas phase of a two phase flowing fluid. The measurement system comprises a container (10) for containing the fluid flow having an inner surface (12) with an average cross sectional area (14), a liquid film measurement device (17) adapted to measure a flowrate of a liquid film of the two phase fluid through the container (10), an Electrical Capacitance Tomography device (20) that has a plurality of electrodes (22) located in the container, and a computer (11) adapted to calculate the flowrate of the liquid film in the container (10). The measurement system calculates wetness of the gas phase based on a measurement of the Electrical Capacitance Tomography device (20) and the calculated liquid film flowrate.