Classification, Measurement Parameters, and Applications of Sensors Used in Oil Depots and Gas Stations
Based on the processes for storing and transporting refined petroleum products (gasoline, diesel), sensors are categorized into: liquid level, pressure, temperature, gas detection, flow rate, static electricity/grounding, liquid level switches, inclination, combustible liquid leakage, and security-related sensors.
I. Liquid Level Sensors (Core Instruments for Storage Tanks)
1. Radar Level Gauge (Mainstream Technology)
Principle: Non-contact measurement using high-frequency microwaves.
Application: Underground storage tanks in tank farms; vertical oil storage tanks in depots.
Purpose: Continuously measures oil level height and calculates storage volume; links to high/low-level alarms to prevent overfilling or pump-dry conditions; used for inventory metering and gain/loss analysis, facilitating automatic generation of inventory reports.
2. Magnetostrictive Level Gauge
Principle: Magnetic float and waveguide wire.
Purpose: Simultaneously measures liquid level and oil-water interface; distinguishes between oil and accumulated water at the tank bottom; standard equipment for double-walled tanks and unloading sumps at gas stations; accurately monitors water accumulation to prevent water contamination of refined products.
3. Float-Type Level Switch (Discrete/Switching Output: High/Low Level Only)
Categorized into high-level and low-level floats:
1) High-level: Triggers an alarm and cuts off unloading when the safe fill level is reached, preventing overfill accidents;
2) Low-level: Alerts operators of low oil levels to schedule replenishment;
3) Double-walled tank interstitial float: Alarms if oil enters the interstitial space, monitoring for tank leakage.
II. Pressure Sensors
1. Pressure Transmitter (Standard 4–20mA Signal)
1. Tank farm vapor-phase pressure transmitter: Monitors pressure in the tank's vapor space; excessive gasoline vapors can cause overpressure, while low pressure creates a vacuum; prevents tank collapse and breathing valve failure.
2. Pipeline pressure sensor: Monitors pressure in loading arms, oil transfer pipelines, and dispensing lines;
High pressure indicates pipeline blockage or valves not fully open; sudden pressure drops indicate pipeline rupture or leakage. 3. Vacuum Pressure Sensor: Used with vacuum pumps and vapor recovery systems; monitors negative pressure in vapor recovery lines to assess the operational status of the vapor recovery unit.
2. Differential Pressure Transmitter
Used for large storage tanks at oil depots to calculate liquid levels based on differential pressure; also monitors pressure drop across filters-an increase indicates a clogged filter element, signaling the need for replacement.
III. Temperature Sensors (PT100 platinum resistance sensors are most common)
1. In-Tank Temperature Probe: Measures the actual temperature of the fuel; enables volume-temperature compensation in accordance with GB standards. Since gasoline expands at high temperatures, correcting the volume based on actual fuel temperature ensures measurement accuracy; also monitors for abnormal temperature rises within the tank to identify safety hazards.
2. Pipeline Temperature Sensor: Monitors temperatures in fuel transfer lines and vapor recovery lines; assesses the efficiency of condensation-based recovery.
3. Ambient Temperature Sensor: Measures outdoor ambient temperature; provides data to determine operating conditions for vapor recovery equipment.
IV. Gas Sensors (Safety and explosion-proofing are paramount)
1. Catalytic Combustion Combustible Gas Sensor (LEL)
Target gases: Gasoline vapors and diesel fumes; unit: % LEL (Lower Explosive Limit);
Installation locations: Tank farm bunds, unloading areas, beneath fuel dispensers, vapor recovery equipment rooms, and pipe trenches;
Function: Triggers audible and visual alarms and activates exhaust fans when vapor concentrations exceed limits; cuts off power to fuel pumps when concentrations reach critical levels to prevent explosions or fires.
2. VOC PID (Photoionization Detector) Sensor
Specifically detects trace gasoline vapors; monitors for minor leaks in double-walled tank interstitial spaces and pipe trenches; offers higher sensitivity than catalytic combustion sensors, enabling early detection of slight leaks.
3. Oxygen Sensor (O₂)
Used in enclosed pipe trenches, tank chambers, and spaces where tank cleaning operations occur; prohibits personnel entry if oxygen levels are too low; ensures safety during confined space operations. V. Flow Sensors (for metering oil delivery)
1. Positive displacement flow meters (oval gear flow meters): Used for oil depot loading arms; provide precise metering of loaded oil volumes for trade settlement.
2. Coriolis mass flow meters: Used in high-end oil depots; directly measure mass flow rate, unaffected by temperature or pressure; simultaneously measure density to detect potential oil adulteration.
3. Turbine flow meters: Used in refueling lines and internal transfer pipelines; monitor instantaneous pipeline flow; detect theft or pipeline damage based on flow anomalies; specialized pulse turbine meters are used inside fuel dispensers.
VI. Static Electricity and Grounding Monitoring Sensors (essential for explosion protection)
1. Static grounding alarm (grounding resistance sensor)
Monitors grounding resistance between the grounding clamp and the tanker body in real-time during unloading; triggers an alarm if grounding is poor (resistance is too high) to prevent static accumulation that could ignite oil vapors.
VII. Leak Detection Sensors
1. Double-walled tank interstitial leak sensor (liquid-sensing cable)
Sensing cable installed in the interstitial space of double-walled tanks; triggers an alarm immediately upon contact with leaked oil from the inner tank; distinguishes between water and oil leaks.
2. Trench leak detection cable (oil-sensing cable)
Laid along the bottom of pipe trenches; triggers an alarm if refined oil flows onto the trench floor.
VIII. Specialized Sensors for Vapor Recovery Systems
1. Pressure sensor: Monitors negative pressure in the recovery pipeline.
2. Flow sensor: Measures the volume of recovered gas.
3. Temperature sensor: Monitors the temperature of the condensation unit.
4. Carbon canister status sensor: Determines the saturation level of activated carbon and signals when replacement is needed.
IX. Auxiliary Sensors
1. Inclinometer (tilt sensor): Monitors storage tank foundation settlement and tilting; issues warnings if tank tilt exceeds limits.
2. Humidity sensor: Monitors humidity in power distribution rooms and instrument rooms.
3. Flame detectors / UV-IR flame sensors: Used for tank farm security; provide rapid alarms in the event of a fire. Simplified Categorized Summary (Suitable for Report Writing)
1. Liquid Level: Radar level gauges, magnetostrictive level gauges, float switches; Functions: Measurement, overfill protection, oil-water interface monitoring.
2. Pressure: Pressure transmitters, differential pressure transmitters; Monitoring tank gas pressure, pipeline pressure, and filter pressure drop.
3. Temperature: Pt100 platinum resistance sensors; Oil temperature compensation for measurement, equipment temperature control.
4. Gas Detection: Catalytic combustion (LEL) sensors, PID-VOC sensors, oxygen sensors; Monitoring hydrocarbon leaks, explosion safety.
5. Flow: Oval gear flow meters, Coriolis mass flow meters, turbine flow meters; Product dispensing measurement, pipeline flow monitoring.
6. Grounding/Static Electricity Sensors: Unloading grounding resistance monitoring; Eliminating static electricity hazards.
7. Leakage Sensors: Interstitial leak detection cables, trench sensing cables; Early warning for tank oil leaks.
8. Environmental & Security Sensors: Tilt sensors, flame detectors.
