Viscosity and temperature effects in biodiesel and HVO metering are managed in three ways: choosing a meter technology that is either insensitive to viscosity changes or proved across them, keeping product temperature on the skid stable and safely above the cloud point, and configuring a separate meter factor and a suitable volume correction method for each product in the flow computer. These requirements are most pronounced with neat biodiesel (B100); hydrotreated vegetable oil (HVO) behaves much like fossil diesel at the meter.
The general components of a metering skid are described on the fuel metering skids page, and cold-weather protection of loading equipment on the biofuel truck loading page. This page looks at FAME and HVO from the meter's point of view.
What biodiesel does to a meter
The US B100 specification allows kinematic viscosity up to 6.0 mm²/s at 40 °C, while the US No. 2 diesel specification caps it at 4.1 mm²/s, and the source guide notes that this higher limit should be considered when blending. B100 running through a skid can therefore be more viscous than fossil diesel on the same skid, and the gap widens as temperature drops. Near the cloud point, crystals form, and once gelling starts, viscosity rises quickly. For the meter, both the viscosity level and its variability at the measurement point become design inputs.
Three other product properties affect the skid. Gums and sediment from oxidized biodiesel can build up in strainers and on meter internals. B100's solvent action can carry loosened deposits from lines that previously handled diesel into the meter. And alloys such as copper, brass and bronze can accelerate biodiesel degradation, which restricts material choices for meters and auxiliary parts.
Choosing meter technology along the viscosity axis
Meter type | Assessment for FAME and HVO | Design considerations |
Turbine meter | Common on clean, low-viscosity products; the meter factor can be affected by viscosity changes | Meter factor shift between B100 and fossil diesel and with temperature; proving by product and temperature band |
Positive displacement meter | Measures volume directly; internal slippage generally decreases as viscosity increases | Higher pressure drop with cold product; strainer protection against sediment and gel |
Coriolis mass flow meter | Measures mass and density directly; density helps track blend ratio and product changes | Pressure drop at higher viscosity; tube material compatibility; conditions for using density in commercial calculations |
No single technology suits every biofuel application. If B100, several blend levels and fossil diesel share one skid, the full viscosity range drives meter selection and proving is planned to cover it. Where only HVO or low blends are metered, the approach used for diesel is usually sufficient.
Managing temperature: heating and insulating the skid
The source guide recommends keeping B100 at least 2.5–5 °C above its cloud point. On a metering skid this serves two purposes: preventing crystals from collecting in strainers and meters, and keeping viscosity within a narrow band during measurement. On outdoor skids, strainer bodies, meters, proving connections and short dead legs are protected with heat tracing and insulation, including transmitter connections and sample lines.
The heating design aims for uniform temperature around the meter; local hot spots can accelerate oxidation and make the temperature reading less representative. The temperature transmitter is placed close to the meter at a point that reflects product temperature. In hazardous areas, electric heat tracing is selected according to the area classification and the applicable trace heater standards. The general engineering of heated metering skids is covered in detail on the heavy oil page.
Volume correction for FAME and HVO
Where product is invoiced by volume, metered volume is corrected to a reference temperature. How the generalized refined product correction used for fossil diesel applies to FAME, HVO and their blends is decided by contract, national regulation and product standards, and should be settled at the start of the project. Metering mass with a Coriolis meter removes the need for temperature correction of mass, but if sales are in volume, density and a correction method are still needed to convert to volume. Which quantity forms the basis of invoicing is covered on the custody transfer page.
Switching between fossil and bio products
Where several products share one metering line, the meter factor, correction method and density input must change with the product, and the batch controller or flow computer applies these parameters automatically based on product selection. The interface volume left in the line after a changeover influences the choice between dedicated and shared lines, and B100 left in a cold line also carries a gelling risk. The density signal from a Coriolis meter is a useful indicator of whether a changeover is complete.
Metering for blend ratio verification
With ratio blending at the terminal, the bio component and the fossil component are usually metered separately and the ratio is calculated from the two measurements. Ratio accuracy then depends on both meters and on correcting each stream to reference temperature with the method appropriate to its own product. The bio-component meter often runs at lower flow with a more viscous product, so it is selected and proved for those conditions. Blend control engineering is covered on the blending systems page, and component-based reporting on the custody transfer page.
TLY Enerji's role
Depending on project scope, TLY Enerji provides engineering support in selecting meter technology for a biofuel measurement point, supplying Coriolis and other flow meters with temperature, pressure and density instruments, configuring product-specific parameters in the flow computer, integrating with PLC or SCADA systems, and carrying out site installation and commissioning. The supply boundary for heat tracing and insulation is agreed based on project data.
Data to prepare for a biofuel metering skid
· Products and blend levels to be metered; fossil products sharing the line
· Viscosity and density data for each product and the supplier's cloud point range
· Installation location: indoors or outdoors, minimum ambient temperature
· Flow range; for blending, bio-component and main stream flows separately
· Invoicing basis: mass, volume at line conditions or volume at reference temperature
· Proving method and which products will be used for proving
· Available heating utilities and hazardous area classification
Related pages
· Biofuel blending systems: Two-meter ratio control and the blending point.
· Biofuel and ethanol custody transfer metering: Sales quantities and component-based reporting.
· Biofuel truck loading systems: Cold flow, oxidation and material precautions at the loading bay.
· Heated metering skids: General engineering approach to heated metering skids.
Biofuel metering skid FAQ
Can B100 and fossil diesel share the same meter factor?
It is generally not recommended. B100 can be more viscous than fossil diesel, and the meter factor, especially on turbine meters, can shift with viscosity. Proving each product separately and letting the flow computer apply the right factor based on product selection is the more reliable approach. How large the difference is depends on meter type, temperature and product, and is established through proving.
Why is a biodiesel metering skid heated?
There are two reasons: to stop crystals that form below the cloud point from collecting in strainers and meters, and to keep viscosity within a narrow range during measurement. The source guide recommends holding B100 at least 2.5–5 °C above its cloud point. Uniform heating matters too, because local hot spots can accelerate oxidation and distort the temperature reading.
Does HVO metering need different precautions from biodiesel?
HVO is produced by hydroprocessing, which yields compounds identical to some in fossil diesel, and its cloud point can be tailored, so at the meter it mostly behaves like diesel. The heating and material precautions needed for B100 are therefore usually more limited with HVO. The decision should still reflect the product specification, any FAME content and the site climate.
How is a blend ratio verified by metering?
In ratio blending, the bio and fossil components are metered separately and the ratio is calculated from the two values. Its reliability depends on the accuracy of both meters and on correcting each stream to reference temperature with its own method. Coriolis density provides an additional check on blend consistency, while definitive product quality confirmation comes from laboratory analysis.