Quality trim in-line blending is an increasingly popular solution for bunker applications, because it overcomes the blend quality problems caused by blend recipe errors or the effect of ‘different quality layers' in the heavy residual fuel being blended. Quality trim in-line blenders use on-line analysers to continuously adjust the blend ratio to ensure that the blended product meets a specification at all times during the blend. Unlike ratio-control blending a quality trim blender responds to changes in feedstock quality caused by layering in tanks or by errors in blend recipes. This ensures that a blend can be optimised for quality and cost at all times. A quality trim blender can deliver savings of $3 - $10 tonne . Quality trim blenders can be configured to optimise for measured parameters such as viscosity (@50C), density (@15C), sulphur, RVP as well as a number of calculated variables based on feedstock BDN such as TAN. Quality trim in-line blenders have all of the capabilities of ratio control
blenders but with the following additional enhancements:-
Blend for ‘quality' – Blends automatically produced to accuracies of +/-1% for viscosity, 0.2kg/m3 for density and ppm for sulphur ensure high blend quality and cost optimisation at all times.
High accuracy blend at reference conditions – Blends are optimised for quality parameters at reference conditions. (50C for viscosity, 15C for density etc).
Failsafe analyser system– Built-in configurable failsafe in the event of analyser failure to protect for blend errors.
Calculated quality parameters – JISKOOT™ in-line blenders incorporate the capability to ‘limit blends' to calculated parameters. This, for example, enables a blend to be limited to a sulphur content which is dynamically calculated during blending, without the need for expensive sulphur analysers.
Integrated samplers – JISKOOT™ blenders all have the options of an integrated automatic MARPOL compliant sampler.
Mixing and analyser system – JISKOOT™ high performance mixing and analyser systems guarantee the homogeneity of the blended product at all flow rates and accuracy of the on-line analysers.
The principle operation of a JISKOOT™ quality trim in-line blender is that the flow of each component (e.g. Heavy Fuel Oil and cutter) is measured by a flow meter and controlled using a control valve or positive displacement pump. Analysers (one or more) are used to measure the quality of the blended product in-real-time. In operation the JISKOOT™ blender control system generates a demand flow rate (called a set-point) for each component, which is compared to the measured flow and one, or more, quality ‘trim' set-points (i.e. viscosity, density, sulphur) which are compared to the overall measured blend quality. A trim set point, such as viscosity, is a part of the blend recipe, and is used to dynamically trim the volumetric ratios as the blend is in progress. This gives increased accuracy to the overall blended product plus a flow-weighted average of batch quality. During blending any deviation between the flow or quality set points and the measured flow or quality are stored in the blender controller memory and appropriate adjustments automatically made to increase or decrease the respective component flow to achieve the required blend quality. JISKOOT™ blending control can include multiple trim controls that allow different analysers such as viscosity and density to be installed on the same blender. The blending control system has a hierarchy of control that eliminates the obvious problems of the analysers fighting each other. This is particularly useful for suppliers who tightly control more than one parameter such as sulphur content and enables in-line blenders to have multiple streams, rather than the traditional two.