Fuel Truck Loading Systems

The core chain of a fuel truck loading system is the same as for any other liquid: pump, strainer and air eliminator, meter, control valve and loading arm, all managed by a preset controller. That general engineering is covered on the truck loading systems page. What sets fuel apart is that one truck often carries several products, gasoline is highly volatile, additives and bio-components are injected at the time of loading, and the low conductivity of some fuels makes static electricity a design topic in its own right. This page looks at how those product-specific requirements shape the loading system.

Multiple products per truck and product segregation

Distribution tank trucks are usually divided into compartments and carry different products on the same trip: gasoline in one, diesel in another, a premium additized grade in a third. The first job of the loading system is to make sure the right product goes into the right compartment. Arms are either dedicated to one product, or a single arm delivers several products in sequence. In the latter case, the volume left in the line and meter at each product change, the loading sequence and a separate meter factor for each product all need to be planned.

In Europe, a dedicated standard defines the digital interface between product recognition devices on the tank vehicle and the loading facility. Where such a system is in place, compartment product data is passed to the preset controller or terminal automation system, and a wrong product selection can be blocked before loading starts. Where it is not, matching of order, arm and compartment relies on procedures and operator confirmation.

Gasoline vapor: what changes at the loading point

As a compartment fills, the vapor and air mixture inside is pushed out. For gasoline, releasing that vapor to atmosphere is prohibited in many regions. EU rules require the displaced vapor to be routed through a vapor-tight connection to a vapor recovery unit at the terminal and require bottom loading at road tanker gantries. US rules require the terminal and truck vapor collection systems to be connected during every load. For the loading system, this means a vapor return connection next to each set of arms, a permissive confirming that it is connected, and attention to back pressure in the vapor line while loading.

Two ideas should be kept apart. Vapor return is the vapor-tight path from the truck to the terminal; vapor recovery is the processing of that vapor in a dedicated unit. A truck loading system normally includes the first, while the recovery unit is a separate terminal-level investment. Diesel and jet fuel are less volatile, but where arms at the same bay also handle gasoline, vapor management still enters the design.

Additive injection and blending at the rack

At fuel terminals, performance and proprietary additives are usually injected into the product stream during loading rather than into the storage tank. The additive injector doses in proportion to the quantity from the main product meter and is controlled by the preset controller. Several finished grades can then be made from one base product, using recipes defined at bay level.

Bio-component blending follows one of two common approaches. In sequential blending, components pass one after another through the same meter and valve. In ratio, or in-line, blending, each component has its own meter and control valve and they combine at the same time in a common header. The choice depends on the ratio accuracy required, whether mixing inside the compartment is sufficient and how much equipment each bay can carry. Receipt, storage and quality of components such as ethanol and biodiesel are covered on the biofuel blending page.

Static electricity, grounding and loading rate

Low-conductivity fuels can build up charge as they pass through piping, filters and meters. The charge collects on the liquid surface in the compartment and can become an ignition source. Fuel loading therefore combines three measures: verifying that the truck is grounded before loading and stopping the load if that connection is lost; starting at a low rate until the arm outlet is submerged; and leaving enough distance or residence volume between charge-generating elements such as filters and the loading point for the charge to relax. Numerical rate limits depend on the product, the pipe size and the standard applied, and are set in the project specification.

Compartment overfill prevention

The overfill sensor in each compartment is tied into the loading permissive chain. EU rules for bottom loading specify two-wire thermistor, two-wire optic or five-wire optic sensors, or an equivalent fail-safe system. Terminals serving mixed fleets may see several sensor types, so the rack monitor must recognize all of them. This layer is separate from overfill protection for storage tanks.

Design criteria

TLY Enerji's role in fuel loading projects

Starting from system design and engineering, TLY Enerji provides supply of flow meters, valves, pumps and instruments, installation, commissioning and maintenance for fuel truck loading facilities. Automation and control of loading operations can be included depending on the project. For items such as the vapor recovery unit, terminal automation software and site infrastructure, the scope of supply is set against the technical specification.

Information needed for a loading system proposal

·         Products and grades to be loaded, including additized product recipes

·         Bio-component blending needs and target ratios

·         Truck types, compartment counts and adapter standard

·         Number of arms per bay and target loading flow rate

·         Applicable vapor return and recovery regulations and existing infrastructure

·         Overfill sensor types and whether a product recognition system is used

·         Whether loading is the point of sale and which proving method applies

·         Existing terminal automation or enterprise resource planning (ERP) interface

Related pages

·         Truck loading systems: The general loading chain from pump to arm and the loading profile.

·         Bottom loading at fuel terminals: Loading integrated with vapor recovery and the adapter interface.

·         Fuel custody transfer metering: How the loaded quantity becomes an invoiced quantity.

·         Fuel terminal automation systems (TAS): Passing orders and recipes down to the preset controller.

·         Multi-bay fuel loading terminals: Planning the product and bay matrix for capacity.

Fuel loading FAQ

Should additives go into the storage tank or be injected during loading?

Both are used. Injection during loading lets a terminal make several additized grades from one base product without extra tanks, and the additive quantity is recorded for every load. Tank additization can be simpler when there are few grades and the recipe rarely changes. The decision rests on the number of grades, available tank capacity and how often recipes change.

Why does loading start at a low flow rate?

Loading at full rate before the arm outlet is below the liquid surface increases splashing, vapor generation and, with low-conductivity products, static charge build-up. The preset controller therefore starts at a low rate, switches to the main rate after a set quantity and slows down again near the end to stop at the target quantity. The switch-over quantities are set according to the project specification.

Can gasoline be loaded without the vapor return hose connected?

Not where vapor collection is mandatory. That is why the vapor return connection is checked as a permissive by the preset controller or rack monitor. Even where no regulation applies, vapor management in gasoline loading should be treated as part of the safety and environmental assessment.

If one arm delivers both gasoline and diesel, how is intermixing limited?

The product sequence, the line volume left at each product change and which compartment that volume goes to are planned together. Line volume is usually kept small, quality-sensitive products are moved to dedicated arms and a separate meter factor is set for each product on multi-product arms. Shared arms for jet fuel are avoided in most projects.