Optical Fiber Sensing Cable for Media Level Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for measuring liquid levels and interfaces in vessels, such as those in the petroleum and petrochemical industry, face challenges like harsh environments, sensor fouling, and limited penetration depth, leading to inaccurate readings and operational disruptions, especially with challenging crudes forming stable emulsions.
Innovation Solution
A sensing cable with an optical fiber sensor array aligned with a heating element is used to propagate heat pulses and measure temperature profiles, allowing for the identification of media levels and interfaces by determining properties based on thermal energy exchange, which is independent of electrical conductivity and temperature-dependent properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional level measurement methods (float-type, capacitance, wave reflectance) are used, then level detection can be achieved, but measurement reliability deteriorates in harsh environments with high temperature, high pressure, and corrosive conditions
Solution Approach 1:
The patent replaces mechanical float-type level measurement systems with an optical fiber sensing system. The optical fiber sensor array detects level and interface positions through optical properties rather than mechanical displacement, eliminating mechanical wear and fouling issues in harsh environments. The system uses optical time-domain reflectometry (OTDR) to detect changes in optical properties at different depths, providing reliable measurement without moving mechanical parts.
Solution Approach 2:
The patent changes the measurement parameter from mechanical position or electrical capacitance to optical properties (light scattering, absorption, or reflection characteristics). By monitoring changes in optical parameters along the fiber length, the system can detect level and interface positions while being immune to electromagnetic interference and chemical corrosion, thus maintaining reliability in harsh conditions.
2Measurement precision
If float-type level measurement is used, then level detection is possible, but the ability to monitor multiple levels/interfaces deteriorates due to liquid density difference requirements
Solution Approach 1:
The patent divides the sensing system into multiple discrete optical fiber sensor locations along the depth of the vessel. Each sensor location can independently detect optical property changes, enabling simultaneous monitoring of multiple levels and interfaces. This segmented approach allows detection of various liquid-liquid or liquid-gas interfaces without requiring density differences between adjacent layers, as each sensor measures local optical properties independently.
3Measurement precision
If moving displacers are used for level measurement, then level detection works, but sensor failure increases due to coating by liquid
Solution Approach 1:
The patent replaces mechanical displacers with stationary optical fiber sensors. The optical fiber remains fixed in position and detects level changes through optical property variations in the surrounding medium rather than physical displacement. This eliminates the problem of liquid coating on moving parts, as the optical fiber is stationary and can be protected by protective coatings or housing while maintaining sensing capability.
4Measurement precision
If capacitance probes are used, then electrical property measurement is achieved, but false readings occur due to fouling or waxing on the probe
Solution Approach 1:
The patent replaces electrical capacitance probes with optical fiber sensors. Instead of measuring electrical properties that are affected by surface fouling, the system measures optical properties (light scattering, absorption, reflection) that can detect liquid presence and interface positions without being affected by probe surface contamination. The optical measurement principle is insensitive to fouling on the sensor surface.
5Measurement precision
If wave reflectance approaches are used, then level detection is possible, but penetration depth is limited due to material absorption
Solution Approach 1:
The patent introduces an optical fiber as an intermediary sensing element that extends deep into the vessel. Rather than using external wave reflectance methods with limited penetration, the optical fiber is positioned within the vessel to directly sample optical properties at various depths. This allows measurement of multiple levels and interfaces throughout the entire depth of the vessel without being limited by external wave absorption.
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
This method provides accurate and reliable level and interface detection across various media in harsh environments, enabling improved control and partial automation of desalter operations and subsea separation processes, independent of electrical conductivity and temperature variations.
Implementation Method 1
propagating at least one heat pulse through the heating element along at least a portion of the sensing cable to affect an exchange of thermal energy between the heating element and the one or more media exposed to the sensing cable
Implementation Method 2
measuring, over time, a temperature profile of the sensing cable corresponding to the heat pulse at each of a plurality of sensor locations on the optical fiber sensor array
Data Source
AI summary
Systems and methods for identifying the level of media in a vessel with a sensing cable including an optical fiber sensor array aligned with a heating element disposed in the vessel. An excitation source is configured to propagate at least one heat pulse through the heating element along at least a portion of the sensing cable to affect an exchange of thermal energy between the heating element and the one or more media exposed to the sensing cable. An optical signal interrogator is adapted to receive a signal from each of a plurality of sensor locations and measure a temperature profile corresponding to the heat pulse at the sensor locations. A control unit is configured to identify a level of each of media by determining properties of the media exposed to the sensing cable at each of the sensor locations based on the temperature profile corresponding thereto.