Process 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.

Hardware and 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 shorter.

Go to Top

Utilities Make Demands
Demand 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 changing rapidly.

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."

PMX manufactures 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."

Another 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 Automation (http://www.rockwell.com) 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 forecast.

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.

Certain applications 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 line.

The existing 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).

MAS installed a system to coordinate furnace operations with production needs and utility tariffs. "We installed a control system consisting of National Instruments'  Lookout HMI/SCADA software communicating to a Honeywell temperature controller at each furnace," explains Sherwin.

Real-time electric 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.

Go to Top

Information is King
Process 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.

The SCADA 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.

Barrick consumes 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."

PMCS provides 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."

Go to Top

Factor in Power Factor
Utilities 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.

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 target.

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.

Go to Top

Service Interruptus
Utilities 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.

Pharmaceutical firms 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 power outages."

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.

Go to Top

Regeneration Pays
Regenerative 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 motor."

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."

Georgia 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."

These high-inertia 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."

Go to Top

Process Improvements Reduce Energy Use
The most 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 frequent."

Another process 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.

Optimization of 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."

Go to Top