Hydrocarbon Processing - April 2021 - GP-29

PROCESS TROUBLESHOOTING

Mitigate fouling in process
units via advanced analysis
S. WILLIAMS and D. B. ENGEL, Nexo Solutions, The Woodlands, Texas

Fouling, or the undesired accumulation of solid material on a surface, is
an increasingly prevalent and challenging problem in processing plants across
many industries. As plants move to reduce costs, contaminated feedstocks and
ineffective process protection lead to
higher fouling rates and associated problems. The costs associated with fouling
problems have been estimated at more
than $4.37 B/yr in the U.S. alone in 2019.
Filter plugging and reduced lifetime,
reduced heat transfer in heat exchangers, column packing obstruction, and reduced throughput are a few of the harmful effects caused by fouling, in addition
to under deposit corrosion. Plants must
maintain low costs and high throughput
to achieve profitability; therefore, the
need for root-cause analysis and cost-effective fouling solutions is critical. Several
different techniques, including advanced
analytics and expert troubleshooting, can
be utilized to mitigate fouling, depending
on the nature of the situation.
Proactive solutions. The tendency of a
fluid to foul process equipment is related
to many factors. This is generally caused
by suspended solids, dissolved components or separate liquid phases such as
emulsions (and the potential combinations thereof). Predicting fouling tendency based on process conditions and
stream quality alone is often speculative
and inaccurate. A good method for determining fouling tendencies is a validated laboratory simulation of the process
and its conditions.
Hot liquid process simulator. One
of the best laboratory tests used to simulate process conditions to determine
fouling tendencies of a process fluid is
the hot liquid process simulator (HLPS).
The HLPS is a dynamic laboratory bench

apparatus used to simulate fouling in a
scaled-down and accelerated way (FIG. 1).
By using actual process fluids in the test,
the HLPS produces essential information related to process fouling and keeps
plants a step ahead of fouling events. This
article describes how the HLPS was used
to identify the root source of fouling in an
aqueous stream, and enabled the facility
to devise a more informed and effective
mitigation strategy.
The HLPS consists of a reservoir
charged with the sample fluid that is
pumped through a test section. Electrically heated metal elements or rods (FIG. 2)
positioned vertically in the test section
form an annulus through which the fluid
flows, and the temperature of the element
is controlled by a thermocouple located
in the interior. Process conditions are
simulated by adjusting the flowrate of the
fluid and the temperature of the elements
or rods. The temperature can be adjusted
up to 650°C, and the system is typically
pressurized to 600 psi with nitrogen to

FIG. 1. The hot liquid process simulator (HLPS).

prevent vaporization of volatile components in the process fluid.
The HLPS measures the degree of
fouling by differential temperature (∆T)
or differential pressure (∆P), depending on the nature of the process fluid. In
∆T mode, the temperature of the fluid at
the inlet of the annulus is compared with
the outlet temperature. As foulant material deposits on the heated element, heat
transfer from the element to the fluid
deteriorates, and a subsequent decrease
in the outlet temperature is recorded
(FIG. 3). In ∆P mode, the fluid is pumped
through the annulus into a small, 1.7-micron filter. Any foulant material in the
fluid, generated by exposure to the heated element in the annulus, will accumulate in the filter and cause the differential
pressure to increase as a function of time.
Fouling tendency analysis can be used
to predict fouling in many liquid streams,

FIG. 2. Heated metal rods used in HLPS
testing of treated and untreated aqueous
samples. Hydrocarbon deposits and increased
total deposition were observed on rods used
in the testing of non-extracted samples.
Gas Processing & LNG | MARCH/APRIL 2021

Hydrocarbon Processing - April 2021

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