optimization and demand management systems limit peak loads, reduce
consumption, correct power factors, and pay back in six months
Energy prices have risen to new heights, and supply interruptions are an
issue in many areas of the U.S. Efficient use of energy and active
management of energy demand are more important than ever. Electric and
gas utilities are under constant pressure to reduce peak demands, and
this affects their large industrial customers. Many large customers now
have alternate sources of energy to choose from, and this further
complicates the energy use equation.
software vendors are responding to these challenges by offering products
that help end users manage and control energy use. These products fall
into two main categories: process optimization solutions that reduce
energy consumption, and demand management solutions that optimize energy
costs and increase reliability. Demand management systems are especially
effective when a plant's utility supplier offers special rates for load
curtailment and peak shaving. Energy savings through process
optimization works well to reduce energy use around the clock.
This article shows
how process control plants are using these solutions to reduce energy
consumption and lower the price of purchased energy. Examples are given
that demonstrate payback periods from three to six months. If energy
prices continue to climb, these pay back periods will become even
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management (also called tie-line optimization) is a process that allows
users to balance utility energy supplies with internal energy demands
and with internal sources of energy. The first variable of this
balancing equation is the utility energy supply, and this parameter is
Utilities are using
variable pricing to force large industrial users to manage their energy
demand (see sidebar, "Electric Utilities Strive for Efficiency"). This
is not a new trend, but rather an intensification of an existing trend.
"Our power company, Alliant Energy, can enact scheduled service
curtailments at any time with no more than four hours notice," says Gary
Lane, electrical plant engineer, PMX Industries, Cedar Rapids, Iowa. "We
are required to reduce our load from the average 25 MW required to run
our processes at full speed to just 6 MW."
high-quality nonferrous metal products such as copper, brass, nickel,
bronze, and alloys. Its manufacturing processes are energy-intensive,
and the high rate of energy use made acceptance of load curtailment in
exchange for lower rates an attractive option.
The company needed a
demand management system that would help it accomplish this goal. "We
wanted to be able to track monthly power usage, customize our load
reduction strategies, and schedule processes and equipment idle time
around peak electrical usage-without requiring an operator to walk from
substation to substation with a clipboard reading meters," continues
Lane. "Specifically, our goals were load management, cost allocation,
and assistance in diagnosing and troubleshooting minor problems."
PMX selected a
system from Siemens (http://www.siemens.com)
and its local distributor, Hupp Electric Motors in Cedar Rapids. "We
decided to install Siemens' Access power monitoring system with WinPM
software," says Lane. "We originally had one screen, now we have 10
screens that measure and display real-time data including amps,
kilowatts, KVA, power factor, kilowatts per hour, and power factor for
each of our 10 processes along with total plant kilowatt demand.
Historical trending lets us determine how much power a process has used
in a given time period."
The plant has 10 MW
of on-site generation, and the power monitoring system allows the
company to balance electricity usage with utility supply and internal
generation. "Our production group meets daily to negotiate among
departments and to schedule processes around power availability," Lane
says. "We use load profiles to analyze and schedule energy-intensive
processes for off-peak hours. We save as much as $80,000 per month in
energy costs--that's nearly $1 million per year--a number that quickly
justifies the investment in the Access power monitoring solution."
company coping with utility demands for load management is Republic
Technologies Intl., Canton, Ohio, a producer of high-quality engineered
steel bars primarily used in automotive, off-road construction
equipment, and aerospace applications. Republic installed a Rockwell
system to monitor and control power use and to save a significant
portion of the $2 million per month spent on electric power.
The local utility,
American Electric Power (AEP) imposes demand charges if power use
exceeds certain limits. AEP also has the option to curtail the supply of
power to a base level at any time. The solution provided by Rockwell
Automation inhibits or sheds electric furnace loads to control power
demand. The system totalizes electric meter pulses and projects demand
within the 30-minute fixed demand interval. Furnace operators select
priorities to determine the system's actions based on the demand
The system regulates
plant energy consumption to preset limits by calculating energy
projections every five seconds at the plant mains and at each of the
three furnaces. The algorithm permits the system to delay shedding
furnaces as long as possible and also predicts when the next furnace
will be shed.
The system also
handles curtailment dictated by the utility, and includes features that
allow it to dynamically respond to real-time spot power purchases.
Operator screens are designed to assist operators in managing purchases
of power at spot-market prices on an hour-by-hour basis. The demand
management system has been designed with hooks for direct future
interface with the utility.
The company is
looking forward to adding further enhancements. "We would like to
develop an automatic transformer load tap changer control for adding and
deleting capacitance to our system," says Gerry Bruno, Republic project
engineer. "We would also like to develop an online real-time power
purchasing system with AEP that would automatically buy power up to a
certain point, then add the power purchased to our demand limit,"
explains Bruno. The existing system saves more than $70,000 in power per
month, resulting in a pay back period of less than six months.
require real-time optimization of plant processes to control energy use.
Utica Corp. owns and operates a forging plant in Utica, N.Y., that makes
jet and stationary engine turbine blades. The various manufacturing
processes use a great deal of energy to heat treat and forge metal into
the correct forms. The furnaces and presses must be controlled and
scheduled very precisely to meet the quality requirements of the product
system ran each of the 13 electric furnaces independent of total power
demand. "Each furnace was programmed separately, and this approach often
resulted in the inopportune peaking of power usage. This peaking premium
was applied to the power costs at other times of the day," according to
Mark Sherwin, president of system integrator MAS Associates (http://www.masassoc.com).
a system to coordinate furnace operations with production needs and
utility tariffs. "We installed a control system consisting of
Lookout HMI/SCADA software communicating to a
controller at each furnace," explains Sherwin.
rate data is combined with the manufacturing execution system's
production schedule to create a complex optimization algorithm. This
algorithm minimizes electricity use at peak rates while maintaining
furnace operation as required to meet production needs.
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plant engineers and operators cannot optimize energy use without
real-time information. Barrick Goldstrike Mining, Elko, Nev., recently
installed a SCADA system to collect power data and manage energy use.
The plant expects the system to help it meet anticipated demands by its
electric utility for load management.
system consists of a host computer communicating to the field devices
via an Ethernet-to-RS-485 gateway. Field devices are various Multilin (http://www.geindustrial.com)
power relays and power quality meters. Host computer software includes
Wonderware InTouch (http://www.wonderware.com),
GE Power Monitoring and Control System (PMCS) software (http://www.geindustrial.com),
and Symantec pcAnywhere software (http://www.symantec.com),
all running under Windows NT. The SCADA system was designed by
Electrical Systems Consultants, a system integrator in Fort Collins,
Colo., specializing in power and control systems.
tremendous amounts of power in its gold processing operations. "The
roaster facility is a 12,000 ton-per-day crushing, dry grinding, and
roasting gold plant," says Jim Sedey, senior electrical engineer with
Barrick. "The peak load for the facility is approximately 43 MW. Our
largest loads include an 18,500 hp main air compressor for the Air
Products oxygen plant and two 10,000 hp ABB gearless mill drives."
The company hopes to
use the SCADA system to increase efficiency and reduce power use. "We
have been impacted by the rising cost of power in the western U.S.,"
Sedey says. "We feel that there are many opportunities within the plant
to improve energy efficiency by either changing the way we operate the
plant or making modifications to equipment to allow us to reduce energy
usage. This will allow us to lower our overall production costs."
specialized data analysis for monitoring and control of power systems.
"We plan to use the PMCS system to track power usage by plant area and
also to monitor the power usage on some of our larger equipment," Sedey
adds. "We will use the power data and production data to determine areas
where opportunities for energy efficiency improvement exist. We already
use system trending, waveform capture, and event logger tools to help us
troubleshoot power system disturbances and also 5 KV motor problems."
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impose various charges on users to give them incentive not only to
smooth demand, but also to regulate power quality. Many industrial
plants have very poor power factors, and this can have a negative effect
on utility power systems. Inductive loads such as motors reduce power
factors and must be offset by capacitor banks.
It is much more
efficient for users to install these capacitors instead of the utility.
"Power factor correction at lower levels provides an increase in
electrical system capacity. This is because the reactive power to offset
poor power factors no longer needs to be supplied upstream from a large
capacitor bank at the utility interface, so less current flows thorough
the load center unit transformers," explains Archie Proctor, principal
power engineer (retired) for Houston-based Air Products.
installed a SCADA system for its power consisting of 65 Square D CM
circuit monitors (http://www.schneiderautomation.com),
and Square D's SMS-3000 software running on a dedicated NT server. The
server is connected to the plant LAN, and client software is installed
on NT workstations at the utility operator, the power engineer's desk,
and in the accounting office.
The SCADA system
allows Air Products not only to improve power factor but also to comply
with complex utility demands for regulation of power use. "We use
real-time data from the power monitoring system to track instant and
predicted demand for each billing interval. A real-time display in the
utility control room shows the current peak demand and the predicted
peak for the next interval, and compares these quantities to the current
peak target," says Proctor.
The system is
synchronized to the utility billing meter interval, and all kWh and
kVarh pulses from the utility are recorded and totalled. In addition,
demand interval peaks from each operating area are recorded, permitting
allocation not only by kWh, but also by demand. Each operating area is
required to contact the utility operator before starting any motor 300
hp or larger. The system displays a running calculation of how much
additional load can be added and still maintain the interval demand
The plant also has
an on-site cogeneration unit. "We use real-time data from the power
monitoring system to dispatch the cogen unit to limit both kWh and kVarh
at the utility interface to predetermined targets. These efforts
improved the plant load factor from a low of 57% to an average of 88%.
With the use of the real and reactive power from the cogenerator, energy
and demand costs were reduced by 30-50%," concludes Proctor.
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not only want users to manage demand, they also often require users to
cope with supply interruptions or blackouts. Blackouts are expected to
become more prevalent as spare capacity in the electrical supply system
is reduced. On-site generation coupled with an automated power
management control system is becoming a requirement for many users.
often have critical processes that cannot be interrupted. Data storage
must also be secure through any power interruptions. "It is critical
that we have power at all times because of ongoing experiments and data
collection at our facilities. Sample storage spaces along with
manufacturing and computer systems must also be kept online," says Don
Stuck, manager of facilities and scientific instrumentation at the
Collegeville, Pa., campus of GlaxoSmithKline. "If this facility were to
experience electrical problems or power disruptions, it would put us at
considerable risk of losing years of scientific data and research."
To protect the
company's investment, GlaxoSmithKline teamed with Rockwell Automation's
Power & Energy Management Solution group to implement an advanced power
management system. An emergency load-shedding program is used in
conjunction with on-site diesel power generators. In the event of an
unexpected power loss, the system activates on-site diesel generators to
maintain continuous power to critical processes such as refrigeration,
heating, and air conditioning.
During three years
of operation, frequent utility power interruptions have been handled
with minimal disruption. "There hasn't been a time when a control system
didn't get the generator online and loaded within three minutes,"
comments Stuck. "With the previous system, the length of the blackout
depended on when it happened. If it was during the day, we would only be
down five to 10 minutes because personnel were on site. But if it
happened at 2 a.m., it would be upwards of half an hour or more without
electricity. The new system drastically reduces the costly effects of
During peak utility
demands in the summer months, GlaxoSmithKline can run the on-site
generators to support campus electrical needs and sell back excess power
to the local utility. Additionally, GlaxoSmithKline plans to expand the
system to accommodate peak-shaving generators, to add a dual utility
tie, and to add power quality monitoring.
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braking of high-inertia loads such as fans, winders, and rollers is not
a new concept. It has been used for years with DC drives and DC motors.
A more refined version of regenerative braking is now being applied to
AC systems in various process plant applications. This type of system is
experiencing renewed interest in light of higher energy costs and
increased variations in power quality.
One example is
in operation at American Synthetic Fibers (ASF), Pendergrass, Ga., a
producer of fiber extrusions and non-woven fabrics. "A 460 VAC power
source feeds a rectifier with capacitors to produce 700 VDC," says
Martin Wall, director of R&D and special projects for Electric Systems,
a system integrator specializing in power systems. "The 700 VDC power
bus provides power to 43 ABB [www.abb.com] AC drives ranging in size
from three to 200 horsepower. Each AC drive feeds 460 VAC power to an AC
The system combines
the advantages of AC motors, AC drives, and regenerative braking. "A
regenerative control unit connected to the 700 VDC bus regulates bus
voltage," Wall continues. "When one of the motors is generating power,
this power is automatically fed back to the bus via the AC drive. Other
motors can use this power, or excess power can be fed back to the grid."
Another advantage of
the system is improved system stability. "Regenerated power and power
stored in the rectifier's capacitor banks allows the system to ride
through voltage dips," Wall says. "System harmonics from each
drive/motor tend to cancel out and the overall negative effects on the
plant power system are reduced."
Pacific worked with Intec Solutions (http://www.intecsolutions.com),
a local system integrator, to design and install a similar system at its
gypsum paper mill in San Leandro, Calif. The new system consists of
seven ABB AC motor drives ranging from 40-125 hp, all connected to a
common 700 VDC bus supply. "This configuration made sense, because the
high-inertia dryers close to the calendar stack often generate, not
motor," says Chris Hall, president of Intec. "Inherent to a true common
DC bus multi-drive system is the ability for all drives to share energy.
Regenerated energy from the end dryers being pulled by the calendar
stack can be used by those near the presses."
processes within paper mills also allow a manufacturer to stay online
through utility power dips. The 700 VDC common bus is the power supply
to each drive and eliminates the three-phase supply used for each drive
in a shared-bus configuration. Input power semiconductors, pre-charge
hardware, and reactors are eliminated from all drives, reducing hardware
count and increasing reliability.
Elimination of so
much hardware also means less engineering. "A common DC bus system is
cost-effective and attractive to paper producers," says Hall.
"Installation costs are on par with the equipment costs of standalone
drives, each of which needs its own power feed. Plus you get energy
savings inherent to regenerative systems."
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Improvements Reduce Energy Use
cost-effective way to deal with high energy prices is to reduce energy
use. This is often a byproduct of process optimization, but it can also
be the main goal of control system upgrades and refinements. Dixie
ColorWorks, Calhoun, Ga., is the fifth largest carpet manufacturer in
the U.S. Its gas carpet dryers were consuming excess energy before the
process controls were upgraded.
Operators often set
the drying temperature too high to accommodate poor temperature control.
"If damp carpet exits a dryer it has to be reprocessed," explains
Francisco Campa, head process development engineer at Dixie. "This
situation created fear among the dryer operators and would cause them to
always keep temperature settings high to make sure the carpet was dry."
Drying nylon carpet
to moisture levels less than 4% is pure energy waste because the
equilibrium natural fiber moisture content for the carpet is 4.5%. "We
upgraded our dryer controls to Fisher-Rosemount's [www.emersonprocess.com]
DeltaV system and Foundation fieldbus," adds Campa. "The operator
interface is DeltaV Operate running on a Dell PC under Windows NT.
Control strategies are a combination of PID and fuzzy logic."
The upgraded control
platform allows tight temperature settings and prevents temperature
overshoot. "The new control system allows us to target the fiber's
optimum moisture level across the width of the carpet. This is achieved
by accessing recipes with gas burner temperature control adjustments and
stored settings," says Campa. "Fuzzy logic is able to rapidly adjust to
new setpoints with no overshoot even when setpoint changes are large and
control plant that saves energy through process optimization is Alabama
River Cos., Perdue Hill, Ala. Kraft market pulp is the main product
produced at its pulp and paper mill, and its processes consume large
amounts of steam-heated water.
temperature control loops has resulted in significant energy savings.
"We use Expertune's [www.expertune.com] loop tuning software interfaced
to a Foxboro I/A [www.foxboro.com] system for loop tuning and control.
The Expertune software has yielded better loop parameters and allowed us
to save steam by reducing hot water temperature setpoints without
exceeding process limits," says Tom Lemieux, a process systems
specialist with Alabama River.
Thermal Economy of
Memphis, Tenn., is a system integrator that specializes in power,
cogeneration, and energy-related applications. The company recently
worked with a customer to install a Moore Products [www.siemens.com]
control system on two rotary gas-fired kilns used to dry and calcine
earthen clay. The control system monitors various operations and relates
natural gas consumption to production and other parameters such as
material feedrates, product discharge temperatures, burner firing rates,
stack temperatures and pressures, control damper positions, and plant
temperature. Production operators have optimized plant operations to
minimize fuel consumption and improve product quality, says Bruce
Darling, Thermal Economy vice president. "The control system, coupled
with a new burner, provides our customer with improved savings in energy
and operating costs."
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