On Demand Blending:
Many fuels are supplied as “on demand” blends: the fuel is blended as and when required and only as much as is required is blended. In some regions these methods are not allowed for HFO (yet are successful with white products such as diesel, aviation fuel and gasoline).
This may be in the terminal when loading fuel barges or on the Jetty loading vessels, or it may be performed on board the barge during bunkering.
This means that the fuel blend properties cannot be supported by an analysis of the final blend but instead, a fuel blend calculation is supplied, which is, or should be, based on the fuel component analyses.
There are two principal methods of inline blending:
In both systems the components are inline blended and the blend ratio is achieved by controlling the flow rate ratio of the components.
Mechanical blenders use linked proportioning valves where as one valve opens the other closes. This action is controlled by balancing the pressure drops in the two flow streams. The balance point is adjusted to produce a blend of the required properties.
The valve position is affected by the pressure drop in each of the two component flow streams; this will vary according to changes in flow rate and/or changes in the fluid viscosity.
Accuracy depends on the efficiency of the mechanism and the original calibration of the valve control.
Meter blenders maintain the flow rate ratio based on the measured flow rates of each of the component streams.
The properties of the final blend depend on the accuracy with which the blend ratio is calculated and maintained and the known properties of the components.
Both inline systems benefit from the use of the INtegrity digital viscometer for viscosity trim control.
Viscosity is not a simple additive property; it is very sensitive to small variations in ratio. Small errors in the blend ratio can result in significant viscosity errors. The immediate advantage to using the digital viscometer is that blend can be very accurately controlled to the target viscosity and hence to the target ratio.
This results in an almost complete elimination of the “give-
(This is illustrated most plainly in charts 2 and 4 on the “Bad Bunkers Illustrated” page.)
Benefits: the INtegrity system determines if:
The simplest implementation of INtegrity with inline blenders is the addition of the INtegrity digital viscometer to monitor the line density, the base density and the base viscosity of the final blend.
This is illustrated in the diagram at right:
Meter 8 is not an actual meter but represents the summated values of the component streams to yield the total amount delivered.
In this system Mass flow rate and total depend on using the density value declared in the fuel component analyses.
A variety of cross checks can identify if there is a mass flow measurement error and if this is due to component quality errors.
As with batch blending, it also uses the Blend Ratio Error Recovery application to validate the blend ratio and or that the fuel component analyses are true.
Component Quality Validation:
In the Batch blending schemes, because each component flows past the digital viscometer in turn, each component analysis can be verified and it can also be established that the component is free of entrained air, is homogenous and is not a consolidation of two or more different batches itself.
This means that component analysis error is not a source of the final blend properties error. All that remains is a simple error in achieving the target ratio which is simply corrected.
Blend ratio Error Recovery
This mechanism, developed by Razaghi Meyer International, which can be used with
Blending one HFO with another (e.g. For sulphur content) reduces the effectiveness of this method.
It is not valid for multi-
Alternative Approaches for Multi-
This is illustrated (below right) as a two component scheme.
Each of the component flow streams has its own digital viscometer.
Thus, for each component, we can verify if:
Density is measured inline and in each flow stream so the determination of the mass flow rates is more precise and more dependable than simply using the base density attributed to the component to calculate the density at the meter temperature.
Because the density and viscosity are measured in each component stream flow meters may be viscosity corrected for improved wide range accuracy and the mass flow rate computed live.
The digital viscometer in the blend header provides the final quality check on the blend and it is used to trim the blend ratio to maintain the target viscosity.
Because the component properties have been validated, various other factors can also be validated and the wealth of process data available to INtegrity means that a variety of different quality checks can be performed both instantaneously and cumulatively to monitor the efficiency and accuracy of various measurements.
INtegrity can be very simple or it can be highly sophisticated.
With fuel costs such a significant issue; with the penalties for off spec fuels so damaging both financially and (with the advent of stricter pollution legislation) because the penalties can involve criminal sentences, suppliers and buyers of fuels are ever more sensitive to the question of fuel quality. This makes multiple viscometers a valuable aid even for two component blends.
INtegrity is a vital tool not just to help achieve those quality targets but also
to demonstrate that quality in a meaningful and documented form, with a variety of
To find out more, contact Razaghi Meyer International.