Case studies
- Introduction
- Case studies from the United States Motor Challenge Program
- Case studies from the international CADDET database
- Australian case studies developed for Motor Solutions Online
International case studies from the CADDET database
The following short case studies are from the Centre for the Analysis and Dissemination of Demonstrated Energy Technologies (CADDET) database, which features more than 1 600 projects that incorporate world ranking energy efficiency and renewable energy technologies. These case studies focus on improvements made to motor driven systems throughout the 1990s which resulted in ongoing financial gains to business.
Adjustable speed drives controls motor speed of blenders
The Phil Orth Company in the United States wanted better control of the motor speed of its blenders to improve the quality of its bakery mixes, add new products, and reduce its electricity bill. When blending its 900 to 2 725 kilogram bakery mixes, the speed of the company's ribbon blenders has to be slowed to accommodate the varying rate of the bagging lines and to prevent over-mixing.
The company outfitted its ribbon blenders with adjustable speed drives that allowed the speed of the blenders to be controlled. Using adjustable speed drives reduced excess heat in the motors and in the product, met the need for high starting torque at low speeds, provided high production speeds, and resulted in more efficient operation.
Benefits of the new drives include improved product quality, decreased maintenance costs, and an improved ability to make more difficult products. The company has expanded its production from 15 to 18 per cent a year without a corresponding increase in its electricity bill. In addition, the company realised a 33 per cent reduction in the manpower needed to clear product from the blenders. Total annual savings of US$60 000 were achieved.
High efficiency motors on fans and pumps
Delta Extrusion in the United Kingdom replaced five motors with high efficiency motors. Three motors ran continuously and the remaining two ran on a five-day, three-shift operational pattern. Comparison of the performance of the new high efficiency motors with equivalent standard motors showed that efficiency was improved and running costs significantly reduced.
Deltra Extrusion achieved annual energy savings of 14 400 kWh. The greatest savings were yielded by motors running continuously at high loads for long periods. Total energy savings amounted to £408 per year (1992), giving a payback period for the combined project of 1.64 years.
Improving the performance of a waste-to-energy facility
A recycling and solid waste-to-energy plant in the City of Long Beach, California, installed variable frequency drives (VFDs) on the induced draft fans of three boiler systems. The VFDs were designed to operate with the original 500 hp induction motors.
This modification enabled plant operators to continuously modulate induced draft fan speed to maintain the boiler draft set point and allowed fan inlet dampers to be opened to 100 per cent, eliminating pressure drop caused by throttling.
As a result of the retrofit, facility energy consumption was reduced by more than 34 per cent (3 661 200 kWh) and the plant saved more than US$329 500 annually. The decrease in power consumption enables the plant to sell more electricity.
Improving dust collection systems at an aluminium plant
As part of the United States' Motor Challenge program, a team including Alumax staff, third-party engineers, and US Department of Energy staff examined the dust collection system at Alumax's Mount Holly plant to identify ways to reduce energy consumption and increase the efficiency of the system.
The original dust collection system was designed to handle larger volumes of air than necessary for ordinary plant operations. Following Motor Challenge recommendations, one of the fans in each four-fan unit in the dust collection system was taken off-line. The dust collection system then operated with less input power, a motor and drive efficiency of 92 per cent, and a 'wire-to-air' efficiency of 84 per cent.
Benefits realised from this zero-capital-cost project were immediate and significant and included annual energy savings of more than US$103 000. Other benefits included reduced electricity demand (by 382 kW), reduced annual emissions, reduced maintenance requirements, reduced noise, and increased fan control accuracy. By changing the way the system operates, Alumax avoided spending US$850 000 for variable speed drives to improve efficiency. Switching off one fan in each four-fan system provided savings of US$15 000 more than would have been saved with variable-speed drives.
Variable speed drives on a flour mill extract fan
A number of variable speed drives (VSDs) had previously been installed by Rank Hovis Ltd at their Trafford Mill in the United Kingdom for the primary purpose of controlling production output and quality. These installations proved extremely reliable and so another VSD was installed on a dust extractor fan motor. This replaced mechanical dampers, positioned in the duct, which worked against motors running continuously at full speed. The VSD controlled airflow by varying motor speed and hence reduced energy consumption.
Under automatic control measurements showed energy savings of 20 per cent or 114.7 kWh per year. Lower savings were achieved during the monitoring period, investigation showed that automatic motor control had been overridden by operating staff. Future awareness discussions on plant operation will include information on energy efficiency opportunities.
Energy savings were worth £4 900 per year (1992) when motors operated automatically, at an average of 93 per cent of full speed. This gave a payback period of 2.6 years on an investment of £12 900.
Cement plant grinding mill and air compressor upgrades
Holnam Corporation's cement plant in Seattle, United States, produces Portland cement products using a wet slurry process. A first project involved installing sectionalised grinding chambers in the raw mill and finish mill #1 to increase product-throughput speed and energy efficiency and installing a variable speed drive (VSD) on the raw mill's 125 hp cement slurry discharge pump. The second project, at Holnam, involved replacing two 200 hp rotary-vane compressors with two high-efficiency 150 hp rotary-screw air compressors.
Total annual energy savings were 4 700 MWh per year over an estimated 15-year measure life. Total installation cost for all measures was US$843 000, of which US$627 000 was paid by the Bonneville Power Administration and the remaining US$216 000 was paid by Holnam. Annual electricity savings were US$152 000 per year.
In addition, Holnam was saving US$49 000 each year in lower operations and maintenance costs and reduced fines for exceeding air emissions standards. Customer payback for all measures combined, including energy and non-energy savings, was 1.1 years. In addition, the new air compressors at Holnam reduced lubrication oil consumption through a more effective recovery and recycling system.
Adjustable speed drives improve production and reduce energy costs
At James River Paper Company in the United States, the No. 2 paper machine used a 933 kW (1 250 hp) synchronous motor and eddy current clutch, located between the motor and pump, to control pump speed and fluid flow. The production rate of the paper machine was limited because of the power limit of the fan pump. Energy efficiency of the eddy current clutch was low, maintenance costs were high, and reliability was poor.
By controlling motor speed, the speed of a pump can be controlled to match process requirements. This method maximises efficiency and reduces the energy requirements of the process. The James River No. 2 paper machine fan pump was a perfect candidate for replacing the 933 kW (1 250 hp) synchronous motor and eddy current clutch with a 1 120 kW (1 500 hp) motor and adjustable speed drive. The power increase permitted a production increase of eight per cent and an energy reduction of 35 per cent of motor current for the fan pump due to improved efficiency. The retrofit reduced motor starting duty, improved system reliability, reduced maintenance cost, and reduced cooling water usage.
Tests indicated an energy savings of 3 200 MWh, equating to cost savings of about US$95 000 per year. Production increases of eight per cent resulted in increased revenue of US$115 000 per year. Reduced maintenance costs and water savings resulted in a cost savings of approximately US$13 100 per year. The total project cost was US$385 000. This includes equipment cost, installation costs and engineering costs. The simple payback period for this project is 1.7 year.
Energy efficiency in gold mining
At the Barrick Goldstrike Mine in Elko Nevada, United States, several projects were designed and implemented to improve the site's energy efficiency. Goldstrike also improved its gold recovery rate from 75 to 90 per cent. In 1991, the mine produced 546 000 ounces of gold.
The improvements included replacing all 250-horsepower and smaller motors with high-efficiency motors, installing 60 adjustable-speed drives on variable-load motors, demand-side management efforts, installing high-efficiency transformers and accurately sizing distribution lines, implementing a computerised truck dispatch system, and derating the revolutions per minute of ore trucks. Goldstrike also improved its power factor, which is a measurement of how far electrical current lags behind voltage.
The total cost of the project was US$750 million, including expansion of the mine site and improving existing facilities. The money was raised through company stock sales and private financing. In total, the project has saved more than US$1.5 million in energy costs each year since implementation. This equates to a simple payback period of 7.5 years.
Improving ventilation system energy efficiency in a textile plant
The textile facility, located in Fresno, California, United States (owned by Nissinhbo California Inc.), produces approximately 55 000 meters of fabric from the 20 400 kg of raw cotton it processes daily. Improving the efficiency of fans was the object of a US Department of Energy Motor Showcase demonstration. The efficiency project, implemented under the Pacific Gas & Electric Power Saving Program, retrofitted 15 of the ventilation system's fans with Variable Frequency Drives (VFDs). This retrofit allowed the fan control dampers to be locked in a fully open position, which increased the system's air flow control and improved energy efficiency.
Installing the VFDs reduced the ventilation system's total electricity demand from approximately 322 kW to 133 kW. The total annual energy consumption for the fans fell 59 per cent, from
2 700 00 kWh to 1 100 00 kWh. The project cost US$130 000, but annual energy savings were nearly US$101 000. The simple payback for the project was about 1.3 years.
Savings on ventilation at a municipal swimming pool
The municipal swimming pool in Frederikshavn, Denmark, had for some years been one of the town's largest public consumers of electricity resulting in unnecessarily large electricity bills. An analyses revealed that the pool's ten-year old ventilation system did not work optimally, resulting in thousands of DKK being wasted on heat and electricity annually. It was decided to invest in six new low energy ventilator motors and to introduce electronic moisture control in the pool and shower and locker areas.
This resulted in annual electricity savings of 225 000 kWh, which is equivalent to a 65 per cent reduction in electricity consumption. In addition, savings have been achieved through a reduced amount of energy - amounting to 250 000 kWh annually for heating ventilation air. The climate in the swimming, shower and locker area improved significantly after the project. In addition, the swimming pool has experienced the highest number of visitors in its history. The swimming pool will save around DKK324 000 on electricity and heat. The project cost around DKK300 000 giving a pay back period of a little less than one year.
Saving energy at a sewage lift station
The Welches Point sewage lift station, in the United States, handles approximately 750 million gallons of raw sewage each year. The old system used three identical 56 kW pumps, vertically mounted 40 feet above ground level.
Each pump is equipped with a 35-foot floating line shaft that pumps raw sewage to a common header which gradually steps up to ground level. Only one pump would operate under normal circumstances. An additional pump would operate when the sewage level reaches a set high-water level and, during times of exceptionally heavy flow rates, the third pump would operate. Each pump rarely operated for more than 15 minutes at a time. Analysis indicated that the first pump, which operates under normal conditions, could be replaced with a smaller pump driven by a 26 kW motor. This pump operates for longer periods (one to two hours on average), but at a lower outflow rate, reducing friction in the pumping system and lowering energy consumption.
This project has reduced annual energy consumption at the sewage lift station from about 212 MWh to about 176 MWh, for savings of about 36 MWh or 15 to16 per cent. The total project cost US$16 000 and saves about US$2 960 annually, for a payback of 5.4 years.
Variable frequency drives at steel mill
Bethlehem Steel Corporation (BSC), the second largest producer of steel in the United States, had to reduce its energy costs to remain competitive. BSC identified one of the basic oxygen furnaces (BOFs) at its Burns Habor Facility as a prime candidate for energy conservation measures. By installing a variable frequency drive (VFD) and making equipment modifications to the induced draft fans that remove gases from this BOF, BSC could better match the fan's speeds to the BOF's varying requirements, saving energy, reducing operation costs, and decreasing system maintenance expenses.
The energy use of the BOF was cut about 50 per cent, to 15 500 MWh annually, and total annual operating savings were more than US$620 100. With a total capital cost of US$1 225 000, the project's payback was just under two years.
Speed-controlled blower in a sewage sludge processing plant
Midden-Betuwse Slibverwerking BV in the Netherlands collects and processes sludge from several sewage treatment plants. Prior to being dried, the sludge is mixed with woodchips and compost. The mixture is stacked in a three-metre high mound covering a set of aeration tubes, which suck air through the mound. The sludge is digested aerobically. During the digestion process, the temperature in the mound rises to 60°C adjusted by controlling the air flow. In the old situation, the air flow was controlled with a throttle valve on the delivery side of the blower, which resulted in considerable losses of electric energy. It was decided, therefore, to replace the throttle control with a speed control on the motor, which drives the blower.
The control unit consists of a frequency regulator connected to the motor. This regulator allows the rotational frequency of the motor to be varied between 660 and 1 440 rpm. During the first year of operation, the average power demand was some 30 kW less than in the old situation, resulting in an annual saving of 262 300 kWh. Total project costs were NLG 42 800 with savings of around NLG 26 000 per year, making payback in 20 months.
Teamwork and innovative methods save energy
One of the United States' largest cement plants assembled a committee of management, supervisory, and hourly personnel to discuss possible energy-saving methods and projects. One measure recommended by the committee was installing a variable speed fan motor which saved annual energy use. Other changes include optimising the efficiency of the cement-milling process, shutting off electric motors when they are not needed, reducing the use of compressed air, and dewatering a quarry with gravity, rather than electric pumps. Future projects being studied include installing high-efficiency motors, improving fuel efficiency in the cement kiln, improving pneumatic cement transport, incorporating a waste heat recovery systems into the cement kiln, and recycling industrial water.
Installing the 930 kW adjustable frequency drive alone has reduced annual energy use by more than 2 840 MWh. Future plans include installing another such drive on a 1 100 kW fan motor for additional savings of 3 340 MWh. The total energy savings for all the innovative measures taken so far is approximately US$1.4 million. The investment costs are $US3.8 million making payback in less than around 2.7 years.
Speed-controlled centrifugal pump in a whey factory
Borculo Whey products, of the Netherlands, processes whey into several raw materials for the pharmaceutical and food industries. One of these materials is lactose, the production of which involves a refining process, in which 'wet' lactose (nine per cent pure) is dissolved in hot water in a circular process. Wet lactose is transported through a shaking tray to a mixing vessel, where it is mixed with hot water. The mixture is pumped into a buffer vessel, where it is stirred, and from which it is returned to the mixing vessel. Thus, the lactose content of the mixture gradually increases. After approximately one hour, the mixture is discharged from the mixing unit for further processing.
The liquid level in the mixing vessel used to be controlled by regulating the water/lactose flow from the buffer tanks. This was achieved by a choke valve on the delivery side of the centrifugal pump used for the transport. This choke system had several disadvantages: it was inefficient and caused unnecessary wear of the pump. It was decided to replace the flow regulation system with a speed control system on the motor driving the pump.
This has resulted in energy savings amounting to 12 600 kWh per year, with a value of NLG 1 638, and a reduction in maintenance costs of NLG 10 257 per year, making payback in four months.