Classification and Composition of Oil Depot Loading Systems
I. Classification of Loading Systems
(I) Classification by Loading Medium
1) Refined Oil Loading Systems: For light petroleum products such as gasoline, diesel, kerosene, and aviation kerosene; these are the primary loading systems at oil depots. They are categorized into road loading (tank trucks), rail loading (rail tank cars), and waterway loading (oil tankers).
2) Liquefied Hydrocarbon Loading Systems: For LPG, liquid ammonia, liquid ethylene, etc.; these require sealed loading under cryogenic or pressurized conditions.
3) Heavy Oil Loading Systems (Crude Oil & Fuel Oil): For residues and heavy fuel oils; these require supporting facilities for heat tracing, thermal insulation, and pipeline purging.
(II) Classification by Loading Method
1) Top Loading: A loading arm extends through the hatch at the top of the tank truck to fill the tank. This method involves lower investment costs and is commonly found in older depots; gasoline loading requires a supporting vapor recovery system.
2) Bottom Loading [Mainstream Modern Method]: Sealed loading via quick-connect couplings at the bottom of the tank truck. It offers high safety, low vapor emissions, and the capability for simultaneous multi-compartment loading. Gasoline loading requires a supporting vapor recovery system; this method is widely adopted at road-based refined oil depots.
(III) Classification by motive power
1) Pump-based dispensing system: Centrifugal pumps or submersible pumps provide the delivery pressure; adopted by the vast majority of oil storage stations.
2) Gravity-fed dispensing system: Relies on the liquid level difference between the storage tank and the loading point for gravity flow; mostly used for high-elevation depots in mountainous areas; flow rate is limited.
(IV) Classification by automation level
1) Manual dispensing system: Manual valve operation and manual metering; found in older, small-scale stations.
2) Semi-automatic dispensing system: Preset loading volume via a quantitative controller; valve closes automatically when the target volume is reached.
3) Fully automatic intelligent dispensing system: Features integrated functions such as smart card/license plate recognition, automatic volume control, interlocking safety protection, remote monitoring, data uploading, and access control/security.
(V) Classification by transport mode Road dispensing systems,
rail dispensing systems, and marine/terminal dispensing systems.
II. Complete composition of a dispensing system (General overview; example: road-based bottom-loading skid for refined oil)
Overall components: Process storage and transport equipment, metering and control unit, safety protection unit, vapor recovery system, automation and information system, and utility support systems.
1.Process transfer equipment
1)Dispensing pumps: Submersible pumps (tank farm) or centrifugal pumps (pump house) to provide motive power.
2)Loading arms: Bottom-loading sealed arms or top-loading arms; equipped with quick-connect couplings, seals, and emergency release devices (breakaway valves).
3)Piping and valves: Process pipelines, manual ball valves, pneumatic shut-off valves, control valves, and three-way valves. 4) Filters: Basket-type or bag-type filters to protect flow meters and prevent equipment jamming caused by impurities.
2. Metering and quantitative control unit (Core component)
1) Flow meters: Positive displacement meters (Roots/lobe type, oval gear type) or mass flow meters; mass flow meters are preferred for custody transfer.
2) Quantitative controller / Batch controller: Sets total loading volume, issues start/stop signals, and triggers automatic valve closure upon reaching the target volume.
3) Thermometers and pressure transmitters: Provide temperature and pressure compensation to convert to standard volume and ensure metering accuracy.
4) Sampler: Online oil sampling device for laboratory analysis.
3. Safety Interlock Protection Unit (Critical for Explosion-Proofing)
1) Emergency breakaway valve: Automatically cuts off flow and prevents leakage if the vehicle drives away unexpectedly.
2) Anti-static grounding controller: Grounding clamp; interlock prevents pump startup if grounding is poor.
3) Overfill protection: Overfill probe; emergency valve closure and pump shutdown upon detection of high liquid levels.
4) Explosion-proof solenoid valves & pneumatic emergency shut-off valves: Rapid fuel line cutoff during emergencies.
5) Combustible gas detector: Detects fuel vapor leaks; triggers alarms and automatic shutdown if levels exceed limits.
6) Lightning and static protection facilities: Bonding jumpers, grounding grids, lightning arresters.
7) Fire safety equipment: Fire extinguishers, fire blankets, and foam fire-suppression lines (for large-scale depots) in the loading area.
4. Vapor Recovery System (Mandatory for Gasoline)
Closed-loop collection of gasoline vapors generated during loading: Piping: Vapor return header. Processing unit: Adsorption, absorption, or condensation-type vapor recovery units; returns vapors to storage tanks.
5. Automation & Information Systems
1) PLC control cabinets, explosion-proof control stations.
2) "One-Card" fuel dispensing management system: IC cards, license plate recognition, driver self-service loading.
3) Host computer monitoring system: Remote monitoring of loading flow and pressure; record keeping.
4) Data management: Loading records, reports, traceability; integration with ERP/safety supervision platforms.
5) Video surveillance and access control systems.
6. Auxiliary Utilities
1) Instrument air system: Supplies pneumatic power (dry, purified compressed air) to pneumatic valves.
2) Drainage/Sewage system: Oil collection trenches, oil-water separators, and waste oil recovery lines in the loading area.
3) Power supply system: Explosion-proof power distribution, UPS backup power.
4) Line clearing system: Compressed air or nitrogen purging (for heavy oils, liquefied hydrocarbons).
III. Supplementary: Top-loading vs. Key Differences in Bottom-Loading Systems
1) Top-loading: Uses top-mounted loading arms with open tank hatches, resulting in high vapor emissions; vapor recovery connections are located at the hatch; typically involves single-compartment loading.
2) Bottom-loading: Uses sealed bottom connections; allows simultaneous loading of multiple compartments with sealed vapor return; offers superior safety and environmental protection; the preferred method for new national refined oil depots.
IV. Brief Overview of Differences Between Rail and Waterway Loading
1) Rail loading: Uses loading gantries, high-flow loading arms, and parallel loading bays; includes supporting infrastructure such as rail gantries, overfill protection, and track grounding systems.
2) Terminal/Wharf loading: Uses loading/unloading arms (large-diameter marine arms), ship-to-shore connections, emergency release systems, large-scale vapor recovery units, and containment bunds for spill collection.
V. Brief Overview of Tank Truck Loading Process
1) The tank truck parks at the gantry loading bay; connections are made for the bottom-loading quick-connect coupling and vapor recovery coupling; the grounding clamp and overfill probe are attached.
2) The driver/operator enters the loading volume into the explosion-proof batch controller (often via a self-service smart card system); the system performs a self-check (verifying proper grounding and the absence of overfill or combustible gas alarms).
3)The loading pump starts; the product flows through a filter, air eliminator, flow meter, and electro-hydraulic valve, entering the tank truck via the sealed loading arm.
4) The flow meter tracks the accumulated volume in real-time; upon reaching the set volume, the electro-hydraulic valve performs a staged closure (throttling down before fully shutting off) to prevent water hammer.
5) Gasoline vapors displaced during loading are routed back to a vapor recovery unit for processing, while condensed liquids are recovered into storage tanks.
6) In abnormal conditions (vehicle drive-away, spill, grounding disconnection, or overpressure): the emergency breakaway valve automatically disconnects, and the system interlock shuts the electro-hydraulic valve and stops the pump.
