che_july-2024 - 32

cilities use steam at higher pressures
and temperatures because it is an
easy medium to produce and distribute
(steam requires 100 to 1,000
times less space than water and
requires smaller-diameter piping to
distribute). But very often, the process
does not require these higher
temperatures.
In the quest for net-zero emissions,
the question becomes " why
should we use a steam system that
is 60-80% efficient
in
processes
FIGURE 4. The photo depicts a valve that was
damaged by waterhammer
changer is lower than the condensate
return pressure and the condensate
cannot be returned by gravitational
means. Very often, these applications
will end up draining condensate
locally through a bypass valve.
In order to return that condensate, a
pumping system will be necessary.
When steam is used at higher pressure,
it is smart to check whether it is
feasible to use flash steam (condensate
re-vaporization once it reaches
lower pressures) in a nearby application,
which can help reduce steam
use and consequent energy.
Each of
the
following
improvements
can help reduce the energy
bill and consequent CO2 emissions:
* Condensate return - up to 3%
energy reduction
* Flash steam recovery - up to 1%
energy reduction
Typically, when performing a full
audit of a plant, 5-10% energy reduction
will be found through projects
with a 1-3 year payback. These
projects are often referred to as quick
wins (Figure 6).
A circular approach to energy
Applying a circular methodology (or
" approach " ) to thermal energy can
help reduce up to 30-50% of energy
consumption in CPI plants. However,
it requires a change in perspective,
moving away from following the thermal
system and incrementally improving
it, to understanding the process
and its needs. What does the
process really require?
Do you need steam? A lot of fa32
where
temperatures below 248°F
are needed? " At those temperatures,
hot water can be used in systems
that are >90% efficient.
Where is the energy going? In a
CPI facility, most of the energy used
ends up being lost into the atmosphere.
Simply stated, the first law
of thermodynamics tells us that energy
cannot be destroyed or created
- its quantity within a system
remains stable. When energy is put
to work, sometimes by converting it
from one form to another, it is degraded
to a lower quality of energy.
So, if energy in an industrial plant is
degraded but not destroyed, how
does it leave the plant?
Currently, primary energy is brought
into a plant in the form of electricity
and fossil fuels. In a typical factory,
less than 20% of incoming energy is
used for moving things (motors converting
electricity into mechanical energy)
or lighting the facilities. Due to
energy efficiency, part of this energy
eventually ends up as waste heat
that increases the building's interior
air temperature. Does that mean that
the remaining 80% of the primary
energy used for thermal is going into
the products being manufactured?
Not exactly. In most industries, only
a small portion of the primary energy
is converted into chemical energy
contained in the final product. Furthermore,
the input materials used
in manufacturing are usually at the
same (often ambient) temperature
as output products when leaving the
plant. In fact, the majority of primary
energy ends up as waste heat that is
frequently lost through stacks, cooling
towers and sewage.
The circular approach aims to maximize
heat recovery in a plant to drastically
reduce the energy needed to
operate it and maintain its processes.
When applying this, the following
methodology of pinch is used.
Pinch analysis
Pinch analysis is a methodology for
minimizing energy consumption of
chemical processes by calculating
thermodynamically feasible energy
targets
(or minimum energy consumption)
and achieving them by
optimizing heat-recovery systems,
energy supply methods and process
operating conditions. It is also known
as process integration, heat integration,
energy integration or pinch
technology.
The pinch methodology involves
mapping all heat sources (processes
that are cooled down and where energy
is removed) and heat sinks in
the facility (processes that require
heat and where energy is added).
For each of these heat sinks and
heat sources, we identify the temperatures
available, the kilowatts
needed to be added or removed,
and seasonality (is there a different
load in summer versus winter, and
is the load stable throughout the day
and night?).
Thermal mapping can be time consuming
if the plant lacks meters to
track the processes. In those cases,
temporary ultrasonic strap-on flowmeters
can be used to estimate the
heat sinks and heat sources. Once
the mapping is finalized, pinch methodology
can be used to identify the
heat recovery potential and consequently
the minimum amount of energy
needed for the plant if all waste
heat is recovered.
An engineer can then review the
model to define what is practically recoverable.
Some of the specifics to
be considered include the following:
* Heat sources and heat sinks that
are far apart within the plant might
FIGURE 5. Testing steam traps with a handheld
automated device can yield valuable information
about the steam system
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2024
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