WC130 MayJune2023 - Magazine - Page 16
SPONSORED CONTENT
H2OPINION
Choosing the Right Heat Exchanger for
WASTEWATER APPLICATIONS
H
eat exchangers often play an
important role in wastewater
treatment systems but, given the
nature of wastewater streams and
the processes involved, including
evaporation and anaerobic digestion, it is
important that the right technologies are
selected to maximise process and energy
efficiency.
Plate heat exchangers (PHEs) are one of
the most common types of heat exchanger
and they have a compact design with good
thermal efficiency. However, they are highly
prone to fouling and are often only suitable for
relatively clean, non-viscous materials.
Tubular heat exchangers, also known
as shell and tube, comprise a tube or tubes
within another tube or vessel. Because of the
various designs and geometries available, they
are better able to cope with more viscous
materials and suspended solids. Depending
on their design, they can require more space
and can be susceptible to fouling. These issues
are greatly reduced by using corrugated tube
designs, and HRS produces a range of efficient
and cost-effective corrugated tube heat
exchangers for wastewater and environmental
use, depending on the viscosity and physical
characteristics of the product. These include
the DTI and DTR Series of Double Tube
designs for more viscous products, and the
C & K Series of Multitube designs for lower
viscosity fluids which may contain small
particles.
Around 30 million Canadians
are connected to a municipal
wastewater system.
Around 30 million Canadians (~86% of the
population) are connected to a municipal
wastewater system, and between them they
generate some 5,900 million cu. m. of sewage
(equivalent to the volume of water which
flows over Niagara Falls every day). Legislation
such as the federal government’s Wastewater
Systems Effluent Regulations (WSER), means
that the public now expects greater levels
of treatment before wastewater streams are
discharged into the environment.
The considerations for choosing a heat
exchanger for wastewater treatment are
the same as any other application. Including
the physical space available, the available
temperature of the product and process
materials and the required temperatures
after processing, acceptable pressure drop,
and the service materials being employed.
There are also other considerations which
are particularly relevant to wastewater and
sludges. These include the physical nature of
the material and the potential for fouling in
the heat exchanger, ease of maintenance and
the ability to operate reliably for long periods
of time. Finally general considerations include
energy efficiency, capital and operating costs
are also crucial to the final choice of heat
exchanger. The total cost of ownership should
be considered, as units that are cheap to
purchase often have higher running costs or
lower operational efficiencies.
Several types of exchanger are utilised in
wastewater treatment with differing levels
of success. In essence the four types of
heat exchanger encountered in wastewater
treatment are: spiral heat exchangers; plate
heat exchangers; tubular heat exchangers; and
scraped surface heat exchangers.
The HRS DTI Series of
heat exchangers is ideal
for heating sludge, for
example in anaerobic
digestion situations
Spiral heat exchangers (SHEs), sometimes
known as shell and coil heat exchangers, are
almost uniquely used in wastewater and sludge
applications. They consist of a single channel
formed into a spiral or coil, creating a compact
design. However, they require regular cleaning
(which is both time consuming and costly) and
are often unsuitable for sludge-to-sludge heat
transfer.
Scraped surface heat exchangers
(SSHEs) are used where materials are very
viscous or have a high fouling potential, so they
are particularly suited for treating thick sludges
and for use in evaporation systems. The use
of a scraper keeps the tube surface clean and
maintains high thermal efficiency, while the
individual design may provide other benefits,
such as controlling product viscosity during
processing. HRS offer two different types of
scraped surface heat exchanger, but the most
suitable for wastewater applications is the
patented Unicus Series uses a reciprocating
action with a choice of scraper geometries,
making it ideal for applications such as effluent
evaporation, where fouling or low heat
transfer is a problem.
The patented HRS Unicus
scraped surface heat
exchanger is designed
to prevent fouling during
evaporation.
HRS HEAT EXCHANGERS
INFO@US.HRS-HE.COM
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