Heavy Oil Truck Loading Systems

When loading heavy oil into trucks, fluidity is preserved by never letting the product, anywhere between the heated tank and the truck compartment, rise above the viscosity the pump, meter and loading arm were designed for. The trouble rarely starts during loading. It starts in the idle time between loads, when the arm, swivel joints, hoses, valve bodies, the meter and any dead legs cool down and make the next load slow or impossible.

The general loading chain of pump, meter, control valve and arm is described on the truck loading systems page. This page covers how that chain is kept hot and drainable on heated heavy oil.

Drawing from a heated tank

Residual fuel oils usually need preheating for handling and atomization, and at heavy oil sites the product is typically kept heated in the storage tank. What matters to the loading line is not the tank's average temperature but the temperature around the outlet nozzle. If the tank heater is far from the draw-off point, or the tank has stood for a long time, the first product reaching the pump may be colder and more viscous than expected. A local suction heater at the outlet and a temperature measurement at the pump suction can be treated as a loading permissive.

Keeping the line hot between loads

Two common methods keep the line hot between loads, and they are often combined:

·         Standby circulation: When no truck is loading, product returns to the tank from a point as close to the arm as practical. Hot oil keeps moving up to the meter and control valve, and the volume that can cool shrinks to the short run between the return point and the arm tip.

·         Heat tracing and insulation: Arms, valves and instrument connections beyond the circulation loop are protected by electrical tracing or steam or thermal oil jackets. Tracing is designed to maintain a hot line, not to melt out a line that has already set.

With standby circulation, decide early whether the returning oil passes through the meter. If the meter sits inside the loop, quantities counted during circulation must not end up in a load record; valve positions and batch controller logic keep the two modes apart. This is a heavy oil practice: for products with limited thermal stability, such as pyrolysis oil, returning heated product to the tank is advised against.

The loading arm: where cold spots concentrate

With its swivel joints and moving structure, the arm is the hardest part to heat. Heat continuity across swivels, insulation that survives movement, and whether product remains in the arm when parked are the key design questions. Jacketed arm and swivel details are covered on the jacketed piping and loading arm page for bitumen; the same principles apply to heavy oil, usually at lower temperatures.

In top loading, a fill pipe reaching close to the tank bottom keeps the outlet below the liquid surface for most of the load, which significantly reduces turbulence and vapor generation. Heavy oil has low volatility, but splash filling a hot product still creates vapor and hot splash hazards. Whether to load from the top or the bottom depends on the truck fleet and terminal layout.

Loading profile and pressure drop

With viscous product, pressure drop through the arm, hoses and valves is far higher than with light products and changes with temperature. Pump and line should therefore reach the target flow even at the cold end of the operating range. Slow start, main flow and slow finish stages still apply, and adjustable opening and closing speeds on the control valve help limit surge at the end of the line. Cut-off at the target quantity is more repeatable when product temperature stays steady throughout the load.

Recording quantity on hot product

The volume of heated heavy oil changes noticeably with temperature, so temperature measurement at the meter is an integral part of the loading system. General volume correction algorithms cover crude oils, refined products and lubricating oils; which table applies is set by product and contract. Recording mass with a Coriolis meter avoids this conversion. Putting the loading temperature on the delivery note also helps the receiver plan heating before discharge.

The truck side: heating coils, insulation and a dry compartment

·         Heating coils and insulation: Some heavy oil trucks have coils to reheat the product before discharge. Whether the terminal connects steam or thermal oil to them, the connection type and the responsibility split should be settled at project start.

·         Dry, clean compartment: Water in a compartment filled with hot viscous product is a serious foaming and overflow hazard; published bitumen loading guidance says loading must not start unless the vehicle is water-free. If heavy oil loading temperatures approach the boiling point of water, a similar check belongs in the loading permissives.

·         Previous load compatibility: A different product left in the truck can put the heavy oil off specification, and a low flash point residue raises the vapor hazard.

Clearing the line after loading

Product left in the arm and in the line between control valve and arm tip can cool and plug before the next load. Draining the arm toward the truck, pushing it out with pressurized gas, or tying the line into the circulation loop are common methods. The method chosen also affects the load record: define whether product downstream of the meter goes to the truck or to a slop tank, and how that is reflected in the loaded quantity. A general comparison of line-clearing methods is on the viscous product transfer page.

Design criteria

How TLY Enerji contributes

Depending on project scope, TLY Enerji contributes engineering for selecting and supplying the meter, control valve, pump and temperature measurement for a heavy oil loading line, configuring batch control, circulation and loading permissives in the PLC, site installation, testing and commissioning, and maintenance support. The scope of heating infrastructure and loading rack construction is defined separately for each project.

What to send us for a loading line review

·         Viscosity data at several temperatures, pour point and flash point

·         Storage tank heating arrangement and outlet nozzle location

·         Loads per day and typical idle time between loads

·         Truck types, compartments, heating coils and top or bottom loading preference

·         Quantity unit and the information required on the delivery note

·         Available steam, thermal oil or electrical infrastructure

Related pages

·         Heated metering skids for heavy oil and fuel oil: Heating the meter and filter on the loading line.

·         Heat tracing systems: Maintaining temperature on arms, valves and lines.

·         Viscous product transfer systems: Pump sizing and line-clearing methods.

·         Fuel oil truck loading systems: Loading several fuel oil grades from one installation.

·         Truck loading systems: General components of the loading chain.

Heavy oil loading FAQ

Why is flow low on the first load of the morning?

With no flow overnight, the arm, valves and any line section outside the circulation loop cool down, and if the tank outlet is far from the heater, the product reaching the pump is more viscous than expected. Standby circulation, tracing on the arm and valves, and temperature control at the outlet let the first load start as fast as the others.

Does standby circulation affect the load record?

It can if it is not set up correctly. If the meter is inside the circulation loop, product passing during circulation must not be added to a load. Valve positions and the batch controller should separate circulation from loading, and loading should start only after the correct line-up is confirmed.

What happens to product left in the arm?

If it is not cleared, it can cool and plug the arm before the next load. The arm can be drained toward the truck, pushed out with gas or tied into the circulation loop. Whatever the method, define in advance where product downstream of the meter goes and how it is reflected in the loaded quantity.

Why does water in the truck matter?

When viscous product is loaded near or above the boiling point of water, water can flash to steam and cause foaming and overflow. Published bitumen guidance says loading must not start unless the vehicle is water-free. If heavy oil loading temperatures approach that range, a similar check should be added to the loading permissives.

Can a diesel loading arm be converted for heavy oil?

Sometimes, but swivel heating, insulation, the temperature rating of seals and pressure drop with viscous product all have to be checked. In many cases the pump, meter and line-clearing arrangement also need to change along with the arm.