Hydrocarbon Processing - August 2021 - 67

Heat Transfer
A. B. ALHAZEMI and S. B. ALHARBI,
Saudi Aramco, Madrid, Spain
Spiral heat exchanger technology
Heat exchangers are some of the most critical equipment in
the oil and gas industry, as they provide the required temperature
of fluid to sustain the plant's operation.
At the inlet of process plant facilities, accumulation of high
sludge (high fouling) is a perennial issue that leads to inefficient
performance of exchangers: shell-and-tube heat exchangers, to
be precise. This also eventually leads to a drastic reduction in
equipment reliability and an increase in the number of maintenance
intervals, as well as high turnaround duration. Maintenance
costs will be high over time, as additional inspection and
maintenance are required due to the anticipated tube failures.
Even in such fouling environments, shell-and-tube heat exchangers
are widely used due to their well-known designs and
ease of fabrication with low manufacturing cost. Shell-and-tube
heat exchanges always suffer from scaling formation created
by high fouling. This results in frequent shutdowns to perform
proper turnaround inspection and maintenance.
To overcome these issues, the spiral heat exchanger (SPHE) is
a technology best suited for such applications with the potential
for high fouling; an SPHE's self-cleaning design can remove sludge
due to the turbulent flow created during the SPHE's operation.
As mentioned, the SPHE design feature creates a turbulent
flow, preventing scaling within the equipment internal. Compared
to the shell and tube, an SPHE is smaller, saving considerable
space within the plant layout. The mechanical handling
and cleaning of an SPHE is also much easier, as there are no
internals like bundles within shell-and-tube exchangers. An
SPHE consists of a shell and plates (which are welded to the
shell) in a spiral shape that are separated by spacing studs to accommodate
both hot and cold fluids in a countercurrent flow.
This inherent design feature of an SPHE results in a compact
design and enables cleaning of the internals by a hydro-jetting
process and chemical cleaning.
Shell-and-tube heat exchangers often require a capital spare
bundle to avoid long procurement lead times when in need of
bundle replacement. Therefore, stocking spare bundles increases
the CAPEX and requires long-term preservation and storage
within the warehouse.
Based on the design features explained here and a case study,
insight is provided of the advantages of the SPHE in terms of
minimized plant footprint utilization, operation, mechanical
handling, maintainability and ease of inspection.
DESIGN FEATURES
The SPHE's distinct design features overcome historical issues
related to high fouling. The SPHE is internally shaped as
FIG. 1. Flow turbulence created by the curved pathway of the fluid
acting with the spacing studs pushes any deposits as they form.
Source: NEXSON.
Hydrocarbon Processing | AUGUST 2021 67
a spiral-hence the name-that provides a continuous path for
both fluids, with no hard corners or edges. The equipment is
self-cleaning due to the turbulence created by the spacing studs
between the spiral plates. SPHE design features are detailed here.
Compact design. Due to its compact design, the SPHE has
a small footprint compared to shell-and-tube heat exchangers.
The overall space requirements and complexities within the
SPHE unit are greatly reduced. With this compact design and
absence of tubes bundle, a heavy lift crane, tube bundle puller
and extra space are not required during installation, operation
and maintenance activities. Additionally, turnaround inspection
duration and labor requirements are reduced.
Self-cleaning. Flow turbulence created by the curved pathway
of the fluid acting with the spacing studs pushes any deposits
as they form (FIG. 1), facilitating a self-cleaning process within
the SPHE.
High overall heat transfer coefficient. With the spacing
studs and the resultant fluid turbulence created within the spiral
channels, the design provides a higher overall heat transfer coefficient
compared to other heat transfer designs.
Spacing studs. The design and construction of an SPHE are
made up of concentric channels that are separated by spacer
studs. The studs, shown in FIG. 2, are welded on channels at
specific locations and heights to form the channel gaps. The
channel gaps and width are designed to meet requirements and
working conditions unique to the end users. This versality in
design allows the SPHE to be customized easily based on process
conditions provided by the end users.
Hydrocarbon Processing - August 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - August 2021
