Getting the bio-component ratio right during truck loading depends on metering each stream separately, controlling the ratio from the start of the load to the end, and delivering a homogeneous blend to the compartment. The point where ethanol meets gasoline, or biodiesel (FAME) meets diesel, is where product quality, commercial quantity and regulatory reporting are fixed at once.
This page covers rack-side blending at biofuel terminals: choosing a method, verifying the ratio, and designing for the very different behavior of ethanol and FAME. Sales quantity and additive dosing have their own pages.
Why blend at the rack, at the moment of loading?
Bio-components are usually stored neat in dedicated tanks and combined with the fossil product at the last step. Ethanol is the first reason. It is fully miscible with water, and an ethanol–gasoline blend holds far more dissolved water than plain gasoline; once that tolerance is exceeded, a separate phase drops out that carries ethanol as well as water. The EPA memorandum cited here gives the example of a 10 % ethanol blend staying single-phase up to roughly 0.5 vol % water at 60 °F. Keeping the finished blend out of long-term storage limits that exposure.
The second reason is FAME in cold weather. Neat biodiesel (B100) starts to gel at a higher temperature than diesel, depending on feedstock, so it is commonly kept in heated aboveground tanks. A well-mixed blend does not separate as long as it stays above its cloud point, so rack blending confines heating and insulation to the B100 side. The NREL handling guide calls terminal or rack blending the preferred method because it ensures complete mixing.
Ratio, sequential and splash blending
The general mechanics are explained on the truck loading systems page; here the focus is on bio-components.
· In-line (ratio) blending: Each product line has its own meter and control valve, the streams flow simultaneously into a common header, and the controller trims the ratio throughout the load. The bio-component is added continuously or in pulses to the moving base stream, and turbulence in the line does the mixing. Because the ratio holds at every point of the load, short loads and interrupted loads still carry the intended blend.
· Sequential blending: Products pass one after another through the same meter and valve, with totals set to the target ratio. The hardware is simpler, but mixing depends largely on movement in the compartment, and a load stopped partway can leave the compartment off-ratio.
· Splash blending: Components are delivered separately into the same tank or truck and mix through the incoming flow or recirculation. With no ratio control during delivery, it is mostly seen at small distribution points rather than at commercial terminal racks.
In-line blending equipment is generally sized for a particular blend level, so if one skid must deliver both low and higher biodiesel percentages, check that the bio-component meter and valve stay in range at both ratios.
Ratio control and two-meter verification
In ratio blending the controller compares pulses from the base product meter and the bio-component meter and positions the bio-component valve to hold the setpoint, so blend accuracy depends on both meters together. Design points to watch:
· Bio-component meter rangeability: At low blend ratios the bio-component flow is a small fraction of the base flow, and the meter must still read that flow during the ramp-up and ramp-down phases of each load.
· The volume basis of the ratio: Ethanol and FAME expand with temperature differently from fossil fuels, and ethanol has its own density and volume correction standard. Whether the ratio is defined on observed volume, volume at reference temperature or mass needs to be settled by regulation and contract.
· Deviation alarms and shutdown: An alarm when the ratio leaves its tolerance band, a load stop where required, and an event log entry.
· Batch records: Separate base product and bio-component totals for every load, which feed both quality control and component-based reporting.
Where the blend point should sit
The closer the blend point is to the loading arm, the smaller the carry-over into the next load. On lanes that deliver different ratios or unblended product, the line volume between blend point and truck sets how much product moves on a product change. The injection point must still leave enough length for the mixture to become homogeneous; the need for a static mixer depends on flow regime and line length.
Product-specific measures on ethanol and FAME lines
Topic | Ethanol line | FAME (biodiesel) line |
Main risk | Water ingress and phase separation in the blend | Gelling in cold weather and oxidation in storage |
Storage and piping | Remove tank water bottoms, limit moisture ingress, keep lines dry | Heat and insulate the B100 tank, pump and lines for the local climate |
Materials | Check seal and elastomer compatibility with ethanol against product data | Some hoses, seals and elastomers can degrade with prolonged exposure; copper and brass accelerate oxidation |
After blending | Avoid long storage of the finished blend | The blend stays stable as long as it is kept above its cloud point |
Specification context | Fuel ethanol for blending has its own product specifications | FAME as a diesel blend component is defined by its own specification |
Blend levels follow the fuel specification of the target market. Under US definitions, E10 means 10 % ethanol and 90 % gasoline, and the number after B gives the volume percentage of biodiesel (B20, for instance). The European paraffinic diesel specification, which includes HVO, allows up to 7 % FAME by volume. Ratios per grade and season should be agreed with the operator before design starts.
Design criteria for a blending system
Parameter | Why it matters in design | Effect on selection |
Target blend ratios, now and in future | Defines bio-component flow relative to base flow | Size and rangeability of the bio-component meter and control valve |
Loading rate and ramp profile | The ratio must hold at the start and end of each load | Control algorithm and valve characteristic |
Type of bio-component | Ethanol is water-sensitive; FAME has cold-flow and oxidation issues | Heating, moisture control and material selection |
Basis of the ratio calculation | Temperature correction differs by product | Temperature and, if needed, density measurement; calculation method |
Products sharing the lane | Product changes create a mixed slug | Distance from blend point to loading arm; line volume |
Recording and reporting needs | Component quantities may have to be reported | Controller and terminal automation system interface |
How TLY Enerji supports blending projects
Depending on project scope, TLY Enerji can support meter and control valve selection for each product line, supply of measurement and control equipment, integration of blend control into the PLC and SCADA layer, installation, testing and commissioning. Scope of supply and the interface with the terminal automation system are defined together through the technical specification.
Data to prepare for a blending system review
· Bio-components to be blended (ethanol, FAME, paraffinic component) and target ratios
· Loading flow range and number of loading arms for each product and bio-component
· Bio-component tank locations, temperatures and existing heating infrastructure
· Whether the ratio is defined on volume or mass, and the accepted deviation band
· Other products delivered through the same lane and how often products change
· Existing preset controller or terminal automation system and the required record format
Related pages
· Additive injection systems for biofuel terminals: Dosing cold-flow and oxidation additives alongside the blend.
· Biofuel and ethanol custody transfer metering: Sold quantity of the blend and component-based reporting.
· Biofuel metering skids: Meter selection on FAME and HVO lines under viscosity and temperature effects.
· Fuel truck loading systems: The fossil fuel lane and loading arm that receive the blend.
· Truck loading systems: General principle of ratio and sequential blending at the loading rack.
Biofuel blending FAQ
Should we choose ratio blending or sequential blending?
Ratio blending holds the target ratio throughout the load, so short or interrupted loads still carry the right blend, but each product line needs its own meter and control valve. Sequential blending uses less hardware, yet mixing happens in the compartment and a load stopped partway can end up off-ratio. The choice depends on load count, product variety and the blend quality terms in your contracts.
Why do terminals avoid storing ethanol blends for long periods?
An ethanol–gasoline blend can dissolve more water than plain gasoline, but beyond that limit a separate ethanol-and-water phase settles to the tank bottom. The blend loses ethanol content and an unusable layer forms at the bottom. Storing ethanol separately under dry conditions and blending at the final loading point shortens the time the blend is exposed to water and reduces that risk.
Does the whole biodiesel blending line need heat tracing?
Heating and insulation are usually concentrated on the neat biodiesel (B100) side: the tank, the pump and the line up to the blend point, sized for the local climate and the product's cloud point. Low-percentage blends behave much more like diesel in the cold. How much of the line needs protection is decided from laboratory data on the actual FAME and the site's lowest ambient temperature.
How can we show that the blend ratio was correct?
In ratio systems the base product and bio-component meter totals are recorded separately for each load, and the achieved ratio is calculated from them. Deviation alarms and event logs show whether the ratio held throughout the load, while periodic meter verification and, where needed, sample analysis support the reliability of those records.