che_july-2024 - 30

Engineering Practice
How to Conduct a Thermal
Audit of an Industrial Facility
The efficiency of steam-generating and distribution systems can be improved
incrementally, but more substantial gains can be found using pinch analysis for better
heat recovery
Patricia Provot
Armstrong International
W
hen it comes to improving
the energy efficiency
of a thermal system,
most industrial organizations
focus on making incremental
improvements to their utilities.
Typically, these incremental improvements
will provide up to 5-10% in
energy savings and CO2 emission
reductions, with payback times
that are under three years. Chemical
process industries (CPI) facilities,
however, are increasingly looking at
completely decarbonizing their facilities,
and therefore, are looking
beyond the traditional ways of utilizing
thermal energy and increasingly
pursuing an approach that
aligns with principles of the circular
economy. By applying circular principles
to industrial thermal systems,
plant managers can recover massive
amounts of energy that have traditionally
escaped the facility as waste
heat. When this waste heat is put
back into the process, it can result in
up to 30-50% reductions in energy
use and CO2 emissions. This article
describes how to conduct a thermal
audit at a CPI site to explore areas
ripe for energy savings.
Incremental improvements
Within most industrial facilities,
steam is used as the medium to provide
heating for process or building
applications (Figure 1). These steam
systems, however, are often very old
and are likely to have been reconfigured
multiple times as the facilities or
processes change, resulting in the
loss of efficiency over time. This is
a drain on a company's bottom line,
but it also negatively affects an organization's
ability to continue operating,
as regulatory bodies have been
tightening their emission standards in
recent years.
The stakes are high, so it is vital to
understand a system's energy consumption,
in addition to its level of
CO2 emissions, safety and reliability.
All of these can be evaluated via a
thermal audit.
Auditing steam generation
It is possible for typical steam systems
to operate at up to 80% efficiency,
but very often, they operate
at only 60% efficiency due to a number
of factors that can be mitigated
after a thermal audit.
A thermal audit begins with measuring
the efficiency of a plant's
steam-generating equipment - determining
how much energy is consumed
(using fuel meters) in the
boilers and how much energy is produced
(using steam flowmeters).
In the boiler house, the first place to
look is boiler stack temperatures and
determine whether more energy can
be recovered through the installation
of an economizer, a condensing economizer,
or by improving the existing
economizers (Figure 2). Next, measure
the percentage of condensate
that is returned to the boiler. Ideally, all
steam not directly used in the process
should be returned as condensate.
Failing to reclaim and reuse condensate
contributes to energy losses.
The
quality
of
make-up
water
FIGURE 1. The diagragm shows a typical steam system, includign steam generation, steam distribution,
steam use and condensate return systems
30
added to the boiler should also be
examined, because higher water
quality leads to lower boiler blowdown
losses. Next, identify the resulting
boiler blowdown requirement
and confirm whether a boiler blowdown
heat-recovery system has
been installed.
Finally, measure the quality of the
combustion to identify whether the
system is maintaining the correct
level of excess oxygen for the fuel
used, and if the air flowing into the
boiler could be pre-heated. Typically,
plants will have some of these
improvements implemented, but
rarely all. Each of these improveCHEMICAL
ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2024

http://WWW.CHEMENGONLINE.COM

che_july-2024

Table of Contents for the Digital Edition of che_july-2024