Product Blending - In-Line Blending From
In-Line Blending from Tankage - This blending method also requires the use of
both component tankage and product tankage. However, the components are pumped
simultaneously under flow or flow ratio control through a common blending
header. The contents of the product tank are approximately on-specification at any time
during the blending operation provided the flow ratios correctly reflect the
current component tank properties. An in-line
blending system from tankage is shown in the attachment. Each component is
ratioed either to a master component on flow control or to a total blending
rate signal. Analyzers provide both component and product properties input to
an advanced computer blending control system which in turns control the various
component flow rates. The blend quality control application calculates the
component flow ratios (or component flows) required to meet blend header
product quality specifications over the entire blend. Conventional on-line
analyzers, such as octane engines (for RON and MON), RVP and distillation are
suitable for blend quality control. However, more recently, FT-IR analyzers
have been used. From strictly a blending standpoint, a single FT-IR analyzer is
capable of monitoring multiple component streams as well as the finished
product to allow the control system to make on-stream corrections during the
blend operation to reflect minor changes in component qualities.
This type of blending system is frequently used
for gasoline.
The following factors should be kept in mind when
one is considering in-line blending from tankage:
1. Component tankage permits mixing and testing
of components prior to blending. A minimum of two tanks per component is
preferred. One tank is assigned for the blend and the other for production
rundown. The tank assigned for the blend should be well mixed such that the
component quality will not vary over the blend cycle. Provided component
tank(s) are well mixed and isolated from production rundown, component
qualities can be certified by lab analysis and periodic or continuous sampling
is not required during blend operation. If blend component quality varies
during blend operation (i.e. tank not well mixed and/or blend tank is not
segregated from production rundown) on-line monitoring of component quality
should be considered.
2. This type system is very flexible and permits minimizing product quality
giveaway if components of appropriate quality are available.
3. Multiple grades per product and seasonal
blend variations can often be handled sequentially through one blending header,
thereby minimizing blender investment.
4. Tankage requirements to cover working and
turnaround requirements may be split between blendstock
components and finished product tankage. Consistent with the concept of
minimizing total tankage, component storage is preferred to finished storage
since it provides better flexibility to blend multiple finished products.
5. With accurate component flow/ratio control, the blend may be considered
"on-spec”
as soon as all components are mixed in the blending header. Thus, while the blending
is in progress, sampling of this header will permit blend evaluation and fine
point blend corrections to optimize the blend. Furthermore, this technique will
result in multiple sampling and testing leading to reduced standard deviation
for the blend which, in turn, results in much greater test accuracy/reliability
and further blend optimization.