In a traditional batch-blending process, the final product
composition is created by combining different intermediate
products (held in storage tanks) in a blend tank. The objective
is to create final products that meet customer specifications.
However, in many process manufacturing applications, tankless,
inline blending may provide a better solution, particularly in
grassroots process plants or for expansion projects in existing plants.
Inline blending involves continuous mixing of two or more
intermediate products using flowmeters and control valves, to
obtain a final product of strictly defined proportions. In
theory, inline blending could enable process plants to save
money by reducing the blend time, the need for excessive
storage capacities and mix tanks, maintenance manpower and costly
quality giveaway. Although not as well-established as batch
blending, inline blending has also been around for years.
Blending systems. There are two basic types
of inline blending systems: controlled-rate and flow-responsive
systems. In controlled-rate systems, the flowrate is set by a
blend controller and either manually or automatically
controlled. The flowrate of the feed streams is maintained as
the desired ratio of the component in the end product.
Flow-responsive systems utilize the main feed stream as a
constant to which all other intermediate stocks are blended at
the desired ratios.
1. Typical inline blending system.
Source: Jiskoot Quality Systems.
Product and process optimization.
Blending involves numerous issues. What finished products
are presently in demand by the market? What intermediate stocks
and additives are required to make those finished products, and
are they available? And, of course, which product will net the
biggest profit? This represents a challenging optimization
problem; it requires close coordination between marketing and
Inline blending can help simplify this problem to a certain
degree. Rather than holding several intermediate products in
storage tanks where they are blended one at a time in a mixing
tank, analyzed, re-blended (as needed), touched up and
reanalyzed prior to delivery to the customer, inline blending
allows the product to be analyzed continuously as it is being
blended (enabling corrections to be made online as needed) and
loaded directly to a truck, rail or tanker ship for delivery to
To achieve this, an inline blending system is typically
comprised of two or more feed streams, each fitted with a
strainer, flowmeter and control valve. As the feed streams are
combined, the turbulence created is generally not enough to mix
the components properly, often requiring an inline mixer to be
utilized in the process. Once the intermediate products have
been blended, an inline analyzer with a set trim point (such as
density or viscosity) ensures that the final product meets
minimum quality specifications. The analyzer and blend
controller monitor the flow, ratio and trim of each stream
continuously. Some inline blending unit suppliers also provide
sampling features that take samples at set intervals throughout
the blending process.
By reducing the need for mixing tanks, inline final product
blending eliminates a time-consuming step to the process and
can help reduce capital costs for the tanks themselves and
labor costs associated with maintaining the tanks. Inline
blending can also help increase flexibility and enable products
to be blended on demand, rather than being stored onsite in
anticipation of delivery.
Reduced quality giveaway.
In addition to reducing the time of the blend process and
eliminating the need for separate blend tanks, inline blending
also greatly reduces the risk of quality giveaway. As the
intermediate products are combined at predetermined ratios and
flowrates, and continuously analyzed throughout the process,
production of a final product that over-conforms to the
specifications of the desired product is minimized.
Typically, when batch blending, operators are overly
cautious with their blends to ensure that their final product
meets the customers product specifications. This can
result in costly quality giveaway. When performed properly,
inline blending allows the plant to tighten its control on the
blending process and to more closely match the required
To account and compensate for stratification, tank heel or
other process disturbances
that may cause stream starvation, a trim strategy can be
applied to help further ensure the product quality. A trim
strategy throughout the process reduces variance in product
quality, enhances product homogeneity and helps produce
products as close to the desired specifications as possible. A
trim strategy is a crucial aspect of the process, since it can
help eliminate the need for re-blending or touching
up the product after the fact. HP
Crisafulli has over 10 years experience
in software and manufacturing industries. He joined ARC
in 2006 and holds a BS degree in marketing from Nichols