Hydrocarbon Processing - August 2021 - 68

Heat Transfer
This approach permits the design to account for flowrates,
the sizes of the particles for fouling fluids, and pressure drops.
Spacing studs facilitate turbulent flow in each channel, enabling
a high overall heat transfer coefficient. It is worth mentioning
that the number of studs and their spacing and arrangement are
proprietary designs by SPHE manufacturers.
True countercurrent flow. As shown in FIG. 3, both hot and
cold fluids flow through channels from one end to the other in
opposite directions, contributing to a true countercurrent flow
and resulting in high heat transfer efficiency, as well as a high
overall heat transfer coefficient for SPHEs.
Ease of inspection and maintenance. Due to its compact
size, an SPHE can be easily accessed from both ends for required
inspections and maintenance, including cleaning by hydro-jetting.
Additionally, SPHEs can be chemically cleaned without
removing any internals. This is in stark contrast to shell-andtube
exchangers, which require a cumbersome arrangement of
a tube bundle puller device, crane, support arrangements and
their associated safety risks, and logistics to transport the bundle
to the maintenance shop for refurbishing.
Construction materials. Since the advent of spiral heat exchangers
in the refining, petrochemicals, and oil and gas industries,
manufacturers have been fabricating these heat exchangers
in various metallurgies, such as carbon steels, stainless-steels,
duplex, super-duplex, titanium, nickel alloys, etc., depending
on the process and end-user requirements. Therefore, no limitations
exist in terms of construction materials, which depends
on the process fluid and conditions provided by the end users.
FIG. 2. Spacer studs are welded on channels at specific locations and
heights to form the channel gaps.
FIG. 3. Hot and cold fluids flowing in opposite directions contribute to
a true countercurrent flow and result in high heat transfer efficiency.
(Source: NEXSON).
TABLE 1. A comparison between spiral and shell-and-tube heat exchangers
Spiral
Service
Design
Geometry
* Effective fouling service
* To be explored for non-fouling services
* True countercurrent
* High overall heat transfer coefficient
* Compact equipment
(occupies small footprint)
Turnaround inspection
(Duration)
Unplanned shutdown
Cleaning
* Significantly shorter time
* No internals to be removed
* Cost is minimized
* Very unlikely
* Very easy for both ends
* In-situ hydrojetting or chemical cleaning
68 AUGUST 2021 | HydrocarbonProcessing.com
Shell-and-tube
* Challenging fouling service
* Ideal for non-fouling services
* Varies
* Larger equipment (occupies larger footprint)
* Requires heavy lift
* Requires bundle puller
* Requires additional space
* Requires more time
* Includes bundle removal and hydrotesting of shell and tubes
individually and combined
* Yes, per historical experience
* Challenging
* Tube bundle removed and hydrojetted internally and externally,
followed by shell and channel
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