Batch Blending is the method of blending fuels where the pre-calculated amounts of each component are batched into a mixing vessel sequentially and then mixed prior to supply. The amounts are calculated typically based on the Wright equations for fuel blend viscosity as used in the ASTM D341 standard. Many of the other properties are found from simple additive calculations.

Batch bending  is, perhaps, one of the earliest and simplest methods but also often the most suspect. In some regions it is not allowed, but INtegrity can help resolve the objections by ensuring accurate quality determination and helps with some quantity problems.

INtegrity CMV not only helps solve the problems, it restores confidence in this method.

Effective and accurate Batch Blending requires:

1. Knowing the properties of the components to be blended together.
2. Determining the volume or mass ratio of the components using a fuel blend calculation.
3. To calculate the mass or volume of each component required to produce a batch of the required total amount.
4. To accurately batch these amounts sequentially into the mixing tank (or barge tanks if blended on the barge).
5. To thoroughly mix together
6. To sample, test and adjust as necessary.

In principal,  this approach is as capable of producing as good a blend as any other method; in practice, pretty much everything that can be wrong often is. INtegrity identifies these problems and allows them to be solved. It is a valuable tool for suppliers and vessels.

The problems with Batch Blending:

Ratio Errors:

Ratio errors result from:

• a ratio calculation based on fuel properties which are in error, and results in incorrect volumes being determined for each component;
• ratio errors result from the incorrect batches of components being added (measurement errors).

Fuel Property Errors:

Assumptions made about fuel quality often prove invalid, especially if the components are not properly managed in storage (see Fuel Transfer) and this leads to serious errors in the blend ratio calculation.

It is essential to homogenise and analyse the components prior to blending.

Measurement errors:

The volume / mass measurements made represent a significant source of error. Flow meters are not always used, Tank level measurements are commonly used and are sometimes inappropriate for the task.

Inadequate mixing:

For any mixing system there is a minimum finite time required for satisfactory mixing. This time can be used as a measure of the mixing efficiency, and often the simplicity of the equipment means that this time can vary from very long to infinite.

Problems occur when the time available is insufficient e.g. Voyage time between terminal and vessel.

Sample, analyse and adjust:

In refinery and some terminal operations this may happen but all too often this sample and adjust step is omitted altogether, especially in blend-on-demand bunkering where the fuel is delivered before the sample results could be obtained.

In some cases the resultant blend isn’t a bad blend, it is just that the various measurement errors mean that the actual quality of the resultant blend is not known.

INtegrity:

The diagram illustrates a batch mixing system where tank eductors have been used to provide enhanced mixing in the tank but the principal addition is of the viscometer (7).

It determines if:

• The fuel (or component) is free of entrained air
• The fuel  (or component) is homogenous
• The fuel is well mixed
• The fuel  (or component) is a consolidation of different batches (commingled but not mixed and re-analysed)
• The density value used in the delivery note, both for MARPOL and for calculating the amount delivered, is correct
• The fuel is ISO 8217 Compliant.

There is no original fuel analysis against which to compare the fuel fingerprint; just a fuel blend calculation. If the component analyses are correct (validated as the components are batched) and it is a two component system, then Integrity CMV has a facility called Blend Ratio Error Recovery which will determine the final fuel properties.

For more information on this facility, contact Razaghi Meyer International.

This diagram illustrates how a single viscometer can be used, with an appropriate pipe work layout, to monitor the component qualities as they are batched into the tank (or compartment on a barge), as it is re-circulated during mixing and as it is bunkered/.

Fuel barges where batch blending is performed usually have re-circulation pumps to mix the blend. Where insufficient time is available using simple re-circulation to mix the fuels, tank eductors are an effective way to speed up and improve the mixing process.

Tank eductors are commonly used aboard offshore support vessels to keep driling muds from separating out.

Fuel Blend calculators rely on a set of equations to calculate the individual properties of a blend from the properties in the component fuels and the ratio in which the components are blended.

Most usually it is the viscosity which is the target parameter. The viscosity of the blend is calculated using the Wright Equation. Most of the other properties are additive.

To assist suppliers blending fuels to the clients specification or to a fuel grade specification, many of the Oil Majors make available free fuel blend calculators as do some others including some test agencies.

Shell Marine Fuels, Exxon Mobil Marine Fuels and DNV PS all supply free calculators.

Integrity uses fuel blend calculations during blending to test if errors between the measured density and viscosity and the calculated viscosity are due to inaccuracies in the component specifications or due to ratio errors.