19
Enhance Steam System Efficiency
Enhance Steam System
Efficiency
Steam Systems eHANDBOOK
TABLE OF CONTENTSListen to Your Steam Traps 6
Checking the sounds they make and other tests can help minimize steam loss
Get Less Steamed Up 10
Software programs can make quick work of optimizing steam and power systems
Get All Steamed Up 13
Steam header balances deserve close monitoring for improved energy efficiency
Improve Efficiency with Direct Steam Injection 16
Technology offers notable cost savings for high-pressure applications
Additional Resources 19
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 3
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Steam Systems eHANDBOOK: Enhance Steam System Efficiency 5
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During a recent energy assessment
in Thailand, I had the opportunity
to work with a steam trap expert at
a petrochemical plant. What I saw there and
the methodology and techniques used in
the steam trap audit prompted me to write
this column. I hope you can pick up some
good ideas and best practices and imple-
ment them in your plants.
Different kinds of steam traps exist and
their working principles rely on pure fun-
damentals of physics and thermodynamics.
Knowing the trap type and understanding
how it operates is imperative in testing its
operating performance. The U.S. Depart-
ment of Energy Steam Best Practices
program (http://goo.gl/0fuDHz ) advo-
cates annual testing of all steam traps.
Steam trap manufacturers and service
providers estimate that 10% of steam
traps fail every year. Should we care about
this? Absolutely. Steam trap failures are
classified generally as open and blowing;
partially leaking; failed closed; and cold
and plugged. Significant problems asso-
ciated with these failures include energy
loss, reduced operating capacity of pro-
cess units, water hammer, and system
reliability issues. So, the bottom line is we
can’t afford to have failed steam traps in
our plants!
The three main testing methods for steam
traps include visual, thermography and
ultrasonic. Most times, you will need a
combination of these to confirm steam
trap operation because a single method-
ology may not provide conclusive results.
For instance, visual has limited applicability
Listen to Your Steam TrapsChecking the sounds they make and other tests can help minimize steam loss
By Riyaz Papar, Energy Columnist
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 6
www.ChemicalProcessing.com
because most condensate return sys-
tems are closed systems. (For more on
thermography, see “Gun for Better Trou-
bleshooting,” http://goo.gl/PSM5lO and
“Use Thermal Imagery for Process Prob-
lems,” http://goo.gl/uyF2u7.)
I have used screwdrivers and stethoscopes
to listen to steam traps but that’s really
old school. Nowadays, ultrasonic method-
ology is considered state-of-the-art steam
trap testing and for good reason. With
enhanced technology and sensor advances
in industry, ultrasonic testing of steam
traps has become very cost-effective. On
my energy assessment trip in Thailand,
we used an ultrasonic tester along with a
visual wave editor that not only provided
me the capability to hear what was hap-
pening inside the steam trap but also a
visual temporal signal of that audio file. In
addition, we were able to estimate the flow
through the traps. Doing all this in the field
and going from one trap to another was an
excellent experience for me and well worth
it from a learning perspective as well as
providing value to the energy assessment.
Training is absolutely essential before
undertaking ultrasonic inspection of steam
traps. This is because it’s important to dif-
ferentiate the acoustics from the traps.
Certain traps (thermostatic, float and ther-
mostatic) can have a continuous mode of
operation and you must know how liquid,
vapor and two-phase flow sounds through
the orifice. Other traps (inverted bucket,
thermodynamic or disc) will always have
an on/off operation; so you should be able
to hear the exact transition from on to off.
Steam trap manufacturers and their service
provider partners are a very good resource
for undertaking steam trap audits and
can provide hands-on training and under-
standing of steam trap operations. I highly
recommend you work with your vendor
to implement an ultrasonic-testing-based
inspection methodology for steam traps.
Like everything else around us, steam traps
have become smarter and manufacturers
have incorporated intelligent sensors for
continuous steam-trap monitoring. This
allows plant operators to know immedi-
ately a trap’s operating status. You often
can justify smart steam traps at certain
locations in critical processes. Never
forget that implementation of a steam trap
management program can offer import-
ant benefits beyond energy savings: the
Manufacturers estimate that 10% of steam traps fail every year.
www.ChemicalProcessing.com
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 7
reliability of operations, safety, and avoid-
ing unplanned costly shutdowns. (For
more on steam trap monitoring and oper-
ation, see “Real-time Monitoring Picks Up
Steam,” http://goo.gl/2o2mZy and “Find
the Perfect Steam Trap,” http://goo.gl/
ST9D9l.)
As we work to make our systems efficient,
our steam traps also have evolved. For
instance, I came across one interesting
variation of a steam trap that had heat
recovery built into it. Given the industry
knowledge base and expertise, I am sure
technology will continue to make more
efficient and robust steam traps, and our
testing methodologies will ensure proper
operations for years to come. For now, let’s
just go and listen to them!
RIYAZ PAPAR, PE, CEM, FELLOW ASHRAE, is director,
Global Energy Services for Hudson Technologies Com-
pany, and has written numerous articles for Chemical
Processing. Email him at [email protected]
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Steam Systems eHANDBOOK: Enhance Steam System Efficiency 8
About 40 years ago, an in-house
team of mathematicians and
engineers built an optimization
model for the steam and power system
at one of my company’s sites. It required
manual data entry, took more than an hour
to solve, and was quite revolutionary for
its time. It provided the minimum-cost
operating strategy for the plant in real time
— well, almost real time.
We didn’t talk about “the digital transfor-
mation” back then, but it was happening
before our very eyes. Since then, advances
in computer hardware and software, as well
as the shift of instrumentation and controls
from analog to digital technologies, have
resulted in great leaps in the capabilities of
optimization systems.
Most optimizers today use commercial
software packages. Optimizations that
used to take an hour or more now only
require seconds, or at most a few min-
utes, on laptop computers. Although
many optimizers still use manual data
entry, automated systems that access
live plant data are widely deployed.
However, utility systems are notoriously
lacking in effective metering, and mea-
surement errors are widespread, so data
reconciliation is essential to account
for imbalances and missing data points.
Generally, steam/power optimizers are
advisory, i.e., providing recommendations
for plant operators to consider when
making adjustments; a few optimizers
exist that can directly adjust some con-
trol setpoints.
Get Less Steamed UpSoftware programs can make quick work of optimizing steam and power systems
By Alan Rossiter
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 10
www.ChemicalProcessing.com
Large petrochemical and oil refining facil-
ities typically house extremely complex
steam and power systems. Such systems
comprise boilers, steam headers, letdown
valves, steam consumers, condensate
recovery systems, and deaerators. They
also include power-related equipment,
such as steam and gas turbines, and an
interface with the electric grid. Most opti-
mization packages have mathematical
models of the individual system compo-
nents, supported by rigorous physical
properties data. This enables them to
create an accurate heat and material bal-
ance. Some models, often called “digital
twins,” have dynamic simulation capabil-
ities allowing them to replicate start-up,
shutdown, trips, and other non-steady
state conditions. This makes them useful
for operator training and other applica-
tions, as well as optimization. (For more on
the capabilities of digital twins, read this
March 2021 article, “Deftly Deal with Dark
Data,” http://bit.ly/3lO4fhB)
Because you can run a steam and power
system to satisfy the plant’s heat and
power needs in a variety of different ways,
an optimizer can help determine which
option is “best,” which usually means
“cheapest.” To do this, it needs the flex-
ibilities or “degrees of freedom” in the
system steam flows through letdown
valves and steam turbines; loading of indi-
vidual boilers and gas turbines; and the
quantities used of different fuels (see the
next article on page 13, “Get All Steamed
Up”). In addition, some optimizers can
handle on/off decisions for “optional”
equipment — e.g., choosing whether to
run a steam-turbine-driven pump or a
motor-driven pump when both options
are available. The optimizer also needs
the “constraints” or practical limits on the
plant’s operating envelope, which may
stem from physical restrictions, or safety
and reliability considerations. If a mone-
tary optimization is required, it also needs
price data. The optimizer can then deter-
mine which operating mode provides the
lowest-cost solution. Alternatively, opti-
mization can help minimize emissions or
some other objective.
The savings from operational optimization
of steam/power systems have typically
been reported as around 3% of total site
energy cost. This may not sound like
much; however, the energy bill for a large
An optimizer can help determine which option is “best,” which usuallymeans “cheapest.”
www.ChemicalProcessing.com
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 11
complex may be over $100 million/yr, so
significant dollar savings can result.
You also can identify opportunities for
facility improvements. For example, the
online steam/power system optimizer at
a large petrochemical complex repeat-
edly hit a flow constraint in one particular
steam header. The site installed a short
bypass line to debottleneck the header
and relieve the constraint. This resulted
in hundreds of thousands of dollars in
annual savings from a very modest invest-
ment. Optimizers for existing facilities
can even run offline to evaluate possible
scenarios (e.g., high rate and low rate;
summer and winter); these studies can
also lead to improvements. For similar
reasons, optimizers serve in the design of
new steam/power plants.
Do you have a steam/power system opti-
mizer at your plant? If not, it is worth
considering, especially if your system
includes steam or gas turbines.
For more information, see, Alan Rossiter
and Beth Jones, ‘Energy Management
and Efficiency for the Process Industries,’
AIChE/John Wiley & Sons, Inc., Hoboken,
New Jersey, 2015, Chapter 19.
ALAN ROSSITER is CP’s Energy Columnist. Email him
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Steam Systems eHANDBOOK: Enhance Steam System Efficiency 12
Steam systems provide the core
energy conduit in most process
plants. Many plants closely moni-
tor the operating parameters of individual
equipment items (e.g., stack temperatures
and excess air in boilers); doing so can
have a big impact on operating costs.
However, sites often ignore steam header
balances. This is unfortunate, as steam
balances can have an even larger impact
on overall energy efficiency [1].
Steam systems produce and distribute
heat in the form of steam, and, in many
cases, generate and distribute power.
The combined production of heat and
power is called cogeneration; it’s an
effective way of both increasing over-
all energy efficiency and reducing the
total cost of providing energy for many
process facilities. Typical equipment
includes boilers, steam turbines, pres-
sure reduction (“letdown”) valves, and
deaerators. Some larger systems also
incorporate gas turbines and heat recov-
ery steam generators.
Steam turbines often drive machines (typ-
ically pumps or compressors), in which
case the power requirement of the driven
equipment dictates steam demand. Alter-
natively, steam turbines coupled to electric
generators allow adjusting steam demand
to balance the steam system. This affects
the power output from the generator, so
the amount of electricity imported from the
grid — or in some cases exported to the
grid — also will change.
Get All Steamed UpSteam header balances deserve close monitoring for improved energy efficiency
By Alan Rossiter, Energy Columnist
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 13
www.ChemicalProcessing.com
Many different types of steam turbines
exist (see: “Count On Steam Turbines,”
http://bit.ly/2FCdE7a). However, in this
discussion, we will consider only the sim-
plest: backpressure turbines, where there is
a single steam inlet and a single outlet, and
the steam leaves the turbine above atmo-
spheric pressure.
Three inefficiencies very commonly occur in
steam balances:
• Steam Venting. In many steam systems,
too much steam reaches the lowest pres-
sure header. The excess must be vented,
which wastes both energy and water.
Common causes include:
a. too much flow through backpres-
sure steam turbines or letdown
valves, which creates more low-pres-
sure (LP) steam than the system
can accommodate;
b. excessive amounts of LP steam pro-
duced in waste heat boilers, or by
flashing vapor from condensate collec-
tion tanks;
c. inadequate turndown capability in boil-
ers; and
d. control problems or hydraulic limits.
• Steam Letdowns vs. Steam Turbines.
When steam passes through a turbine, its
pressure falls, and some of its heat con-
tent converts to power. When it passes
through a letdown valve, its pressure
drops, but its heat content (enthalpy)
doesn’t change (this neglects heat losses
from surfaces, and other minor parasitic
losses). In most cases, the incremental
fuel cost to produce electric power in a
steam system is much less than the value
of the electricity it produces, so a finan-
cial incentive exists to maximize steam
turbine use within the steam system, and
minimize the use of letdown valves. How-
ever, in applying this concept, be careful
to respect all equipment constraints (e.g.,
maximum turbine steam flow, maximum
and minimum boiler load, etc.), as well as
overall system constraints. In particular,
if increasing flow through a steam tur-
bine results in a steam vent, this usually
means we no longer are saving money or
energy. In practice, many steam systems
don’t run close to their optimum steam
turbine loading.
• Deaerator Steam. Most steam systems
use thermal deaerators to drive off
oxygen and other dissolved gases from
In practice, many steam systems don’t run close to their optimum steam turbine loading.
www.ChemicalProcessing.com
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 14
boiler feed water. In principle, only a
small amount of steam is needed. How-
ever, as the incoming water often is far
cooler than the saturation temperature
in the deaerator, a substantial amount of
additional steam is used to preheat the
water. It’s not uncommon to consume
10% or even 15% of the total steam from
boilers to preheat water as it enters the
deaerator.
SOLUTIONSTo improve your steam balance, you first
must understand and develop a good steam
balance. This can be a simple spreadsheet
model, but online tools and commercial
modeling systems and optimizers are
available.
Simple operating changes, such as adjust-
ing steam flows through letdown valves or
steam turbine-generator sets, or changing
deaerator pressure can solve some of the
inefficiencies discussed above. However,
it’s often necessary to add equipment (e.g.,
thermocompressors — see, “Consider a Ther-
mocompressor,” http://bit.ly/2JVKNQP) to
achieve significant savings.
ALAN ROSSITER writes CP’s monthly Energy Saver
column. He can be reached at [email protected]
REFERENCE1. Alan Rossiter and Beth Jones, “Energy
Management and Efficiency for the Pro-
cess Industries,” Chapter 18, AIChE/John
Wiley & Sons, Hoboken, N.J. (2015).
chemicalprocessing.com/podcast/process-safety-with-trish-and-traci
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Steam Systems eHANDBOOK: Enhance Steam System Efficiency 15
The most common method of trans-
ferring energy with steam is indirect
heat exchange, which is used in
familiar applications including process, plant
sanitation and reactor vessels. Condensing
the steam releases latent heat, and a mem-
brane, such as a tube or plate, transfers that
heat into a fluid. The process generates a
byproduct condensate that is discharged
through a trap and returned to its source,
typically a boiler, where it continues to pro-
duce steam.
This tried-and-true method, however, has
a drawback. Because of the pressure drop
as the condensate exits the trap, some
portion inevitably is lost to flash evapora-
tion. To keep the system functional, cold
replacement water must be added. As
the condensate is lost, system efficiency
is impacted. The level of impact varies in
accordance with the steam supply’s pres-
sure — the higher the pressure, the less
efficient the system (Figure 1).
Yet an alternative method exists that is
ideal for high-pressure systems: direct
steam injection (DSI). Here, the steam is not
held within a membrane to keep it separate
from the process fluid but rather is blended
directly into it. The need to recover conden-
sate is thereby eliminated, and, instead of
being lost to flashing, it is used fully. As a
result, the system achieves 100% heat trans-
fer efficiency.
DSI’S ADVANTAGESThe DSI approach offers several advan-
tages — chief among them is cost savings.
The boiler used in a DSI system is fed by
Improve Efficiency with Direct Steam InjectionTechnology offers notable cost savings for high-pressure applicationsBy Tony Pallone, Pick Heaters, Inc.
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 16
www.ChemicalProcessing.com
the same cold replacement
water used in indirect heat
exchangers and requires
greater heat input to con-
vert this water to steam.
However, this is more than
offset by reduced steam
demand at the use point,
yielding a net reduction in
fuel consumption and cost
savings for the end user. A
DSI system can save up to
28% of the fuel required for
indirect heat exchangers.
DSI also offers more pre-
cise temperature control
because of its rapid-re-
sponse adaptation to load
changes. Condensate is
not recovered, eliminating
the need for a flash tank or
condensate return system
(Figure 2). Finally, surface
area is not required to
effect heat transfer, making
for a more compact device
that is easier both to house
and to maintain.
INDUSTRIAL APPLICATIONSDSI systems are well-suited
to a variety of industrial
applications that can benefit
from a steady supply of
on-demand, precisely
controlled hot water. One
system option is a constant
flow heater, which serves
the cross-industry trend
of shifting from steam to
hot water for jacketed
CONDENSATE LOSSFigure 1. In indirect heat exchange, a portion of the condensate is lost due to flashing and must be replaced with cold water. Flash losses vary with steam supply pressure. Source: Pick Heaters Inc.
DIRECT STEAM INJECTIONFigure 2. With direct steam injection, steam is completely con-sumed and no condensate is returned. Flash losses are eliminat-ed. Source: Pick Heaters Inc.
www.ChemicalProcessing.com
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 17
heating, eliminating the potential for hot
spots, burn-on and thermal shock. A variable
flow heater allows for frequent start-stop
applications, making it a natural fit for plant
sanitation and clean up.
The food and beverage industry also has
employed DSI systems for in-line product
cooking, clean-in-place (CIP) heating and
nitrogen gas injection. A sanitary jet cooker
can heat, cook or sterilize water and slur-
ry-type food products on a continuous,
straight-through basis. Some models feature
low-velocity mixing and a nonshearing design
to handle small food pieces without damage.
In the chemical processing industry, DSI
supports automated systems with precise
temperature control that ensures optimal
effectiveness of jacketed reactors and elimi-
nates the potential for destruction and waste
of heat-sensitive products. Other applica-
tions include charging reactor vessels, tank
cleaning and CIP and smooth blending of
condensate streams.
Additional industries that have realized
efficiency improvements by deploying DSI
include pulp and paper, energy and power
and pharmaceutical.
THINKING BEYOND THE TRADITIONALThe biggest obstacle to wider DSI deploy-
ment is insufficient understanding of the
technology. Process engineers long have
been focused on strategies to minimize the
condensate lost in indirect heat exchange
systems. DSI removes condensate from
the equation in a way that may seem too
good to be true. To help determine if a DSI
system is right for your application, a DSI
vendor should provide data and case stud-
ies to back up efficiency and cost-savings
claims, and conduct a customized energy
comparison study.
Although DSI is inappropriate for a few
applications — low-pressure systems, for
instance, or systems processing liquids that
must be kept separate from steam — the
technology represents a giant leap forward
for a range of industry needs.
TONY PALLONE is a writer for Pick Heaters, Inc. For
more information visit www.pickheaters.com.
www.ChemicalProcessing.com
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 18
Steam Systems eHANDBOOK: Enhance Steam System Efficiency 19
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