Page 175 - CW E-Magazine (7-11-2023)

Special Report

Heat exchanger fouling – detection, prevention &

removal

INTRODUCTION exchangers, water treatment such as Dr. S.K. ChaKravorty
otential damage toward equip- purification, addition of chemicals, cata- Consultant (Plant Engineering)
ment caused by formation and lytic approach, etc., are used to mini- Email: chakravorty4410@gmail.com
Pdeposition of scale (fouling) mize fouling of the heat exchanging
can be very costly if processed water equipment. Other water treatment pro- detail, from detection to prevention and
is not treated correctly. Chemicals are cesses are also used in steam systems in removal.
commonly used to treat water in the in- power plants to minimize fouling and
dustry. A total of $7.3-bn worth chemi- corrosion of the heat exchanger and Fouling mechanism
cals is released into the air, dumped in other equipment. Most of the chemical Fouling is defined as the formation
streams and buried in landfills every and additives used for fouling and cor- and accumulation of unwanted material
year in the US. 40% of these chemicals rosion mitigation are hazardous to the deposits on heat exchanger surfaces.
are purchased by industry for control environment. So, the days have come These deposits normally have very low
of scale in heat exchangers, cooling to apply chemical approaches benign to thermal conductivity and form insula-
towers, boilers and other heat transfer the environment(5, 6). tion on the heat exchanger surfaces. It
equipment. This percentage also repre- can greatly deteriorate the performance
sents more than $2-bn of toxic waste, One of the critical criteria of heat of the surfaces to transfer heat under the
which contribute to trillions of gallons exchanger design is that the exchanger temperature difference for which the
of contaminated water disposed annu- must be designed for ease of mainte- heat exchanger is designed. On top of
ally into the earth(1). nance, which usually means cleaning this, fouling increases the resistance to
or replacement of parts, tubing, fittings, fluid flow, resulting in higher pressure
Heat exchangers are designed to etc., damaged by fouling and corrosion drop across the heat exchanger.
optimise the surface area of the wall throughout the service period. Mini-
between two fluids to maximize the mizing temperature, in conjunction Many types of fouling can occur on
efficiency, while minimizing resistance with the choice of fluid velocity and heat transfer surfaces: crystallization
to fluid flow through the exchangers reducing the concentration of foulant fouling, particulate fouling, corrosion
within the constraints of material costs. precursors, will reduce the incidence fouling, chemical reaction fouling, bio-
The performance of heat exchanging of potential fouling. Moreover, high- logical fouling, and solidification foul-
surfaces could be enhanced by the est flowing velocity should be allowed ing.
addition of corrugations or fins in heat under the constraints of pressure drop
exchangers, which increases the sur- and erosion from the flow. In addition, Fouling of heat exchangers can
face area and may channel fluid flow or material selection within constraints of have a very costly effect in the process
induced turbulence. Efficiency of heat costs retards the build up of deposits industries as it eventually increases
exchangers can be monitored on-line and allows shorter residence time. fuel consumption, interrupts plant ope-
by tracking the overall heat transfer ration, causes production loss, and
coefficient based on its temperatures, Understanding the causes and types enhances maintenance cost.
which tends to decline over time due of fouling in heat exchangers is key for
to fouling. Due to global energy crisis, selecting the appropriate preventive, Fouling on a heat exchanger is
efficient heat recovery or dissipation of control and cleaning strategies. Over formed in five stages which can be
heat has become a vital challenge for time, the build-up of unwanted materi- summarized as:
scientists and engineers(2, 3, and 4). als on heat exchanger surfaces can lead Initiation of fouling;

to decreased heat transfer efficiency, Transport to the surfaces;

Maintenance of fouled heat ex- increased energy consumption, increased Attachment to the surfaces;

changers can be performed by several pressure drop, equipment failure and Removal from the surfaces; and

methods such as acid cleaning, sand reduced production capacity. Ageing at the surfaces.
blasting, high pressure water jet, bul-
let cleaning, or drill rods. In large This article explores the pheno- There are a few parameters that in-
scale cooling water systems for heat menon of heat exchanger fouling in fluence fouling: pH, velocity, bulk tem-

Chemical Weekly November 7, 2023 175

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