Chemical Engineering April 2023 - 32

TABLE 3. EXAMPLE - REDUCING STEAM DEMAND IN A 12,000-HP
COMPRESSOR
Backpressure steam
turbine
150 psig steam backpressure
318,000
lb/h steam
Condensing steam
turbine
600 psig steam source 600 psig steam source
135,000 lb/h steam
125 million btu/h fired
duty
7,500 gal/min cooling
water
steam levels. If the facility is long on
low-pressure steam, electrification
of a backpressure steam turbine
will reduce production of excess
low-pressure steam. Conversely,
Motor
382 A at 13,800 V
(three-phase)
98% efficiency, power
factor = 1.0
9.1 MW consumed
cesses. In such
cases, an alternate
source of clean
water will need to
be made available
for these users.
Fuel-gas systems
The fuel-gas system
will frequently
be impacted during
electrification
activities. Fuelif
the
facility is short on low-pressure
steam, electrification of a backpressure
steam turbine may not have
much value, since the steam saved
from electrification will just shift to
the high-pressure to low-pressure
steam letdown station to balance
the low-pressure steam demand.
Electrification of a condensing turbine
reduces high-pressure steam
demand, which is usually generated
in steam boilers. For most facilities,
this can be a significant benefit.
Water systems
Reduction in steam demand leads
to a reduction in the boiler-feedwater
demand, including reduction in
treated-water makeup. Water consumption
is often a major expense
for an operating facility, so this reduction
may have a large impact.
The cooling-water system can also
be impacted by an electrification
project. Many large steam turbines
are condensing turbines, which usually
have large cooling-water surface
condensers. Replacing a condensing
steam turbine with an electric
motor can lead to a significant reduction
in cooling-water demand,
which debottlenecks the coolingwater
system, potentially supporting
other projects that would increase
cooling-water demand, and reduces
cooling-water makeup consumption.
In some cases, an entire cooling
tower, or cooling-water pumps,
may be shut down, reducing power
consumption as well.
Electrification of a condensing
steam turbine, however, eliminates
production of vacuum condensate,
which is often used by some pro32
gas
consumption is reduced if fired
heat is directly replaced by electricity.
Likewise, if steam is replaced by
electricity, fuel-gas consumption at
the steam boilers is reduced. This
is beneficial if the fuel-gas system is
supplemented by purchased natural
gas, because electrification will reduce
natural-gas usage, but could
be an issue if the facility is long on
fuel gas.
Many facilities run close to fuel
balance and will be long on fuel gas
with major electrification changes.
If this is an issue, there may be options
for recovering more LPG range
and heavier material from the fuelgas
pool, or potentially modifying
process-unit operations to produce
less fuel gas.
Projects to increase C3+ recovery
in gas plants can have a very
good payout in
selling more LPG
product, in addition to the benefits
of electrification. If this option is pursued,
product storage and transfer
logistics will need to be understood
so all potential project requirements
are addressed.
It may be possible to reduce the
amount of heavy material that ends
up in the fuel-gas system by making
changes in conversion units,
such as hydrocrackers and fluid
catalytic cracking (FCC) units. Catalyst
or operating condition changes
can be considered for production of
less light-end content from cracking,
which ultimately end up in the fuelgas
system.
The potential impact to the fuelgas
heating value should be evaluated
with the reduction of LPG material
in the fuel gas. Replacing LPG
with natural gas high in methane will
lower the fuel-gas heating value, and
there may be heaters that will experience
fuel-gas hydraulic issues with a
lower average heating value.
Flare systems
Another impact to consider is to the
flare system. The flare load may possibly
increase during a local or total
power-failure scenario if a turbinedriven
pump or compressor not
considered to fail previously is replaced
by a motor. Conversely, if a
steam heat exchanger is replaced
by an electric heater, a power failure
would cut the heat source that
could potentially reduce the total relief
load. Total power failure case is
often the controlling scenario for the
design of the flare and relief header
system. Thus, this may be an important
factor to consider in the case
for electrification.
Electrification considerations
So how can an operator determine
what to do?
The first step is to develop an accurate
power, steam and fuel-gas
balance for the facility. Consider
upset and other operating cases,
such as when individual units are
shut down for maintenance.
Operators should also understand
the reliability of the existing systems
and what outages will have a large
impact on operations.
It is also important to evaluate the
planned project portfolio for the facility,
to look for cases where projects
can facilitate, or be improved
by, including electrification as part of
the project. As an example, if there
are steam-boiler replacement or
reliability improvement projects, or
pump or compressor replacement
projects, there may be synergies for
considering electrification as part of
those projects.
Understanding the costs for incremental
power purchase and import
natural gas is helpful. Operators
should become knowledgeable
about the upgrades the existing
systems within the facility will require
with an electrification project - but
they should also be aware of possible
infrastructure impacts to the
" across-the-fence " electrical supplier,
such as the utility company.
Another crucial factor that must be
considered is which current or future
emissions requirements (including
carbon footprint) impact the facility
and would need to be resolved.
These could be regulatory-driven
or internal company requirements.
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