Blending

Most biodiesel users purchase finished B20 or lower blends from their petroleum distributors or biodiesel marketers. In this case, the distributor is responsible for ensuring that the biodiesel has been properly blended and that the cold flow properties of the finished blend will provide satisfactory performance for the area and time of year. You may also want to specify in your purchase contract or agreement that the fuel meet certain low-temperature operability requirements.

Biodiesel blending procedures depend on a variety of factors, including the volume of B100 required to make the blend, the finished blend level, the volume of blended products being sold, tank and space availability, equipment and operational costs, and customer requirements for blends, both now and in the future. Biodiesel is a fuel for diesel applications only and is not to be blended with gasoline.

Generally, biodiesel is blended into diesel fuel via several methods:

• B100 may be splash blended with diesel fuel by the end user in a storage tank or transport truck.
• B100 is blended at a petroleum terminal or rack by a pipeline or terminal operator (usually through injection blending) and offered as a finished blend. This product is sold directly to customers or to a petroleum jobber or distribution company for further sale to customers. This is the preferred method because it ensures complete blending.

The chemical nature of biodiesel allows it to be blended with any kind of distillate or diesel fuel. This includes light distillate fuels such as jet fuel, kerosene, No.1 diesel, and military fuels (JP8, JP5), as well as diesel fuel such as No. 2 diesel for diesel engines and gas turbines and heating oil for boilers and home heating. Once biodiesel is blended thoroughly with diesel fuel, they stay blended together and do not separate over time, if the blend is maintained at temperatures above its cloud point.

B100 should be blended with diesel fuel as soon as reasonable after purchasing, regardless of the time of year. B100 is less oxidatively stable than petroleum diesel and biodiesel blends. Cloud point considerations are less of a concern for biodiesel blends than for B100 during cold weather. If you have only a few B100 customers, you might consider holding a tote of B100 indoors or storing some underground or in heated tanks, depending on your climate, and blending the rest as soon as possible.

Always retain one-quart samples of the diesel and B100 before blending. If any problems arise, these samples may help you determine whether they were caused by the fuel or by something else. Once the customers have run through the current batch of blended fuel with no problems, you can mix the retained samples into the new batch of blended fuel.

Petroleum terminals and pipeline racks responded to increasing demand by installing biodiesel blending capability so jobbers and distributors can receive a biodiesel blend directly at the rack and store and distribute only the blended biodiesel. This finished blend can then be sold to fleet or other applications that have some type of onsite storage. An increasing number of public pumps and key card pumps carry biodiesel blends for individual users or fleets that do not have their own onsite storage capability.

Many blending options are available, depending on your area. As the market continues to mature and volumes increase, the point of blending will likely occur farther and farther upstream in the distribution system where it is most efficient and economical. This is especially true with lower blends of biodiesel such as B2 and B5. Most users find blending their own fuel to be time consuming and costly, so they increasingly request that their petroleum supplier make finished blends available.

The blending process is usually done by splash blending or in-line blending.

• Splash Blending. Splash blending is appropriate for locations where the biodiesel and diesel fuel are loaded separately, or, in some cases, at the same time through different incoming sources, but at a high enough fill rate that the fuels are sufficiently mixed (several hundred gallons per minute for the diesel fuel). In some cases, the tank may need to be recirculated or further mixed to thoroughly blend the two fuels. If mixing is not complete, the slightly denser biodiesel will settle to the bottom. If the entire load is then pumped in to a customer tank,this action will usually be enough to cause complete mixing. But for loads split between customers, the load must be well mixed at the time of blending.
  This pumping is generally enough mixing for biodiesel blends, except in cold weather where the ambient temperature is significantly below the B100 cloud point. Putting B100 into a cold, empty tank truck can cause the fuel to gel, resulting in the two fuels mixing poorly or not at all. In cold weather, it is better to load half the diesel, then the biodiesel,followed by the rest of the diesel fuel.
• In-Line Blending. In-line blending occurs when the biodiesel is added to a stream of diesel fuel a sit travels through a pipe or hose in such a way that the biodiesel and diesel fuel become thoroughly mixed by the turbulent movement through the pipe.The biodiesel is added slowly and continuously into the moving stream of diesel fuel via a smaller line inserted in a larger pipe, or it can be added in small slug or pulsed quantities spread evenly throughout the time the petroleum diesel is being loaded. This is similar to the way most additives are blended into diesel fuel today and is most commonly used at pipeline terminals and racks. In some cases, distributors who carry B100 and petroleum diesel in separate compartments and blend the two as they are loading into a customer’s tank also use this method.
  In-line blending uses two metered pumps and a dual-fuel injection system, so requires an investment in equipment. This approach is the most accurate and reliable for guaranteeing a specific fuel blend. A variety of equipment is available for in-line blending. Systems have to be sized for a specific blend level (B2, B20) and generally cannot handle both types of blends.

In general, blending biodiesel is not difficult if you remember that biodiesel is slightly heavier and more viscous than diesel fuel and the more it is mixed, the better.

Biodiesel has a specific gravity of 0.88 compared to No. 2 diesel at 0.85 and No. 1 diesel at 0.80. If you put the biodiesel into an empty tank and then pour diesel fuel slowly on top, the fuels may not blend properly. If you fill the tank with diesel and then slowly add biodiesel, the biodiesel may go directly to the bottom of the tank. Biodiesel is heavier, so it may stay unmixed at the bottom of the tank. Most pumps draw from the bottom of a fuel tank; if not properly mixed, this bottom layer can contain higher concentrations of biodiesel than the intended blend level. The problems generally manifest themselves in cold months as the high-concentration biodiesel has a much higher cloud point than the well-blended fuel, leading to filter plugging and forming a gel layer at the bottoms of aboveground tanks. Because the low-temperature operability problems may not manifest themselves in the summer and any adverse effects on hoses and gaskets associated with higher blends may take some time to develop, users may go for many months without a problem. Another issue is that a concentrated layer of biodiesel could also start to dissolve tank sediments, which can cause filter clogging in warm months.

Two simple tests can be performed to determine if a tank has been thoroughly mixed:

• Top, middle, and bottom samples of the tank can be taken (see ASTM D4057 or D4177 for the proper way to take a representative sample of a tank) and analyzed for the percent biodiesel or by measuring the specific gravity or density. This can be done with any available means of measuring density or specific gravity (digital density meter, hydrometer). If the values vary by no more than 0.003 specific gravity units from top to bottom, the mix is probably adequate.22 The test procedure for determining the percent biodiesel by infrared spectroscopy is ASTM D7371-14. Several instrument companies currently offer relatively inexpensive equipment to measure the percent biodiesel in the field, similar to equipment used for ethanol in gasoline.
• Put the samples from the three layers in a freezer with a thermometer and check every five minutes until the fuel in one sample begins to crystallize. Record that temperature. Then, continue to check every few minutes until all three samples show crystallization. Compare the crystallization temperatures on all three samples; they should be within 3°C (6°F) of each other. Otherwise, the fuel will require agitation to mix thoroughly. Alternatively, the cloud point of the three samples could be measured, and values should be within 3°C (6°F) of each other. See sidebar at right for an example.

Cold weather blending is a concern in situations where the diesel fuel temperature falls below the cloud point of the B100 you are blending. If the diesel fuel temperature is above the cloud point of the final blend, any crystals that form during blending should go back into solution. This process can be assisted by blending equipment that agitates the two fuels during blending. That agitation helps disperse the fuels and crystals more uniformly and can provide some energy to help the crystals dissolve.

Blends should be stored in tanks that can ensure the fuel temperature will remain above the cloud point of the blend. Blended fuels can be stored below ground in most climates. B20 may be stored in above ground tanks, depending on the cloud and pour points of the blended fuel, the heating capacities for the fuel, and the local ambient weather conditions.