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Compressing Costs

Cogeneration, lighting, air compression and drying technologies pay off in energy efficiency and savings.

Plant MaintenanceandEngineeringBy Richard G. Mansfield, Technical Editor Compressing Costs Cogeneration, lighting, air compression and drying technologies pay off in energy efficiency and savings. 

The American textile industry has worked hard in recent years to reduce manufacturing costs by updating equipment, increasing productivity and trimming the cost of labor. Energy efficiency is an area where there is still room to save costs and enhance the bottom line.There are no simple solutions to reducing energy use in any type of manufacturing process. The key to reducing energy costs requires a thorough understanding of each manufacturing step and monitoring its energy use. It also is important to keep abreast of new developments in machinery and control and monitoring systems. Energy-saving technology that is in use in other process industries, such as paper and film manufacturing and their converting, also may be applicable to textiles. Lower energy use also provides corollary savings in reduced emissions from fuel consumption. CogenerationCogeneration is a cost-efficient means of generating both electricity and thermal energy from the same fuel source. The cost efficiency comes not only from the generation of electricity, which can be used to reduce the expense of purchased utility power, but also from the fact that the generated steam is used twice. Another attractive feature of cogeneration is that a variety of fuel types may be used, ranging from natural gas to fuels such as wood or agricultural waste categorized under the term biomass.Among the benefits of on-site cogeneration are the following:greater reliability of operations, because the power is produced on-site and there are no transmission and distribution problems; andreduced power outages a typical plant can function for 95 percent of the year, with scheduled outages only for maintenance purposes.The demand is there [for cogeneration], said Suzanne Watson, senior policy analyst in Washington with the Northeast-Midwest Institute. Its a growing market by necessity. The need for more efficient energy from cogeneration has always been there, but utilities were able to deliver relatively low-cost power for many years when fossil fuel costs were relatively low in price and there were less stringent environmental regulations.The Public Utilities Regulatory Policies Act (PURPA) of 1978 and the Energy Policy Act of 1992 each in its own way encouraged development of more cogeneration in this country. PURPA allowed large oil, chemical and paper companies to actually sell electricity back to local utilities. Utilities, however, were not attracted to cogeneration, because they already had transmission and distribution wires in place. Compressed Air And Air CompressorsCompressed air is widely used throughout industry and is often considered the fourth utility. Compressed-air systems account for $1.5 billion per year of U.S. energy costs, according to the Office of Industrial Technology (OITC) Energy Efficiency and Renewable Energy Group of the U.S. Department of Energy (DOE). In many industrial facilities, air compressors use more electricity than any other type of equipment. Energy efficiency improvements in air compression and delivery systems can result in power savings of from 20 percent to 50 percent.Compressed-air systems consist of a supply side, which includes compressors and air treatment, and a demand side, which includes distribution and storage systems and end-use equipment. The compressor is the mechanical device that takes in ambient air and increases its pressure. The prime mover powers the compressor. Controls regulate the amount of compressed air being produced. Treatment equipment removes contaminants from the compressed air and accessories. The compressed-air distribution system is analogous to the wiring system in the plant.Considerations in selecting equipment systems and developing an appropriate energy management program include the following:cost of gas or electricity for operation of the system energy consumption can represent up to 70 percent of the total cost of producing compressed air;cost of lost production when the air compressor system has a failure;capital cost of backup electrical generation for motor-driven units;future cost of peak power;compressor and auxiliary maintenance schedules; andselection and installation of proper control systems.According to Kaeser Compressors, Fredericksburg, Va., in some cases in which there is a continuous demand at full load for the compressed air, a fixed-speed rotary screw compressor may be the best solution.A fixed-speed compressor operating under dual control (stop/start or on-line mode) will use only 25 percent of full load electrical power and offers energy savings. In cases where the base load varies with an additional load, consideration should be given to supporting the base load with fixed-flow compressors and adding a unit with a variable speed drive (VSD) as a trim device to carry the variation in the load. Compressors equipped with VSDs are much better able to match their variable demand requirements, virtually eliminating the need for the compressor motor to rest in the energy-consuming idle mode.The Kaeser Sigma Control (SFC) compressor line incorporates an industrial PC with microprocessor that is designed to optimize energy efficiency while increasing operational reliability. The system can constantly log and process performance data. The unit allows operating changes using the programmed compressor control modes.The OITC group of the DOE has implemented a number of compressed-air system improvement projects with a number of U.S. industries. In 1997, a program was initiated with now-closed Thomaston Mills of Thomaston, Ga. Prior to the project, Thomastons greige mill was served by seven centrifugal compressors. Six of these compressors were 800 to 1,000 horsepower (hp), with one 350-hp compressor as a backup. The mill also had an auxiliary 200-hp rotary screw compressor.Prior to the survey, the mill had planned to buy a 900-hp centrifugal compressor to provide for the addition of 60 new air-jet looms. The survey showed that by making some modifications to the original compressed-air system and purchasing smaller compressors, the compressed-air needs of the mill could be provided without acquiring the 900-hp compressor.As a result of the survey, Thomaston installed the following equipment:two 350-hp rotary screw compressors to replace the aging 200-hp rotary screw compressor;a pressure/flow controller along with 40,000 gallons of storage in three receivers one 30,000-gallon tank and two 5,000-gallon receivers to stabilize the pressure system;a heavy-duty, mist-eliminating filter downstream of the new 350-hp compressors;a cycling refrigerated dryer downstream of the filter;a programmable logic controller system that linked the compressors with the pressure/flow controller;a pilot-operated regulator to replace the manually adjustable valve serving the humidifying nozzles; andpneumatic drains in the compressor room in place of the solenoid-operated condensate drains.  Cogeneration By U.S. Nonwoven And Textile Producers Foss Manufacturing Co., Hampton, N.H., a diversified producer of needlepunched nonwoven fabrics, is a pioneer in the use of cogeneration for its power and heating uses.In the mid-1970s, Foss installed cogeneration equipment in its plant in Haverhill, Mass. This plant has since been moved to Hampton. Foss installed the cogeneration system in this plant primarily to ensure a better and more reliable source of power. Frequent outages and line fluctuations from the local power supply were reducing Foss manufacturing efficiency.When the Foss operations were moved to New Hampshire, a 4.3-megawatt (MW) gas-fueled cogeneration system was installed. Power reliability became an even higher priority when Foss started the production of specialty man-made fibers, which are used internally and also are sold under the FossFibre® label.Malden Mills, Lawrence, Mass., is another textile firm that is using cogeneration to good advantage. Since 1987, prior to a fire at Malden, the company was investigating cogeneration systems to provide electricity, steam and heat.In late 1998, Malden installed two 4.3-MW low-NOx commercial turbines made by Solar Turbines, San Diego. The permit for the facility took six years to obtain because of state environmental regulations. A permit was granted after the DOE reached an informal agreement to design the cogeneration facility as a test site for new technology.Along with other energy-saving techniques, Malden expects to save more than 4 million kilowatts (kW) per year and reduce plant emissions through cogeneration. Mill LightingAccording to the Rocky Mountain Institute, lighting consumes 20 percent of the electricity used in the United States. If space conditioning loads resulting from waste heat generated by lighting are taken into account, lighting represents 21 to 34 percent of electricity consumption. The institute also projects that U.S. industry can cost-effectively save 70 to 90 percent of the energy used in lighting systems without loss of function. Major Types Of LightingStandard incandescent lights (A-type light bulbs) are the cheapest, most common, yet most inefficient lamps in use. Longer-life incandescent bulbs with thicker filaments are a variation, but they are even less energy-efficient.Tungsten halogen lamps provide better efficiency than A-type lamps. They have a gas filling and an inner coating that reflect heat. Together, the filling and coating recycle heat to keep the filament hot with less electricity. The major drawback of these lamps is their higher cost.Reflector lamps (Type R) are designed to reflect light over specific areas. Typical uses are for stage/theater; store use; and floodlighting, spotlighting and downlighting. Parabolic aluminized reflectors (Type PAR) are used for outdoor floodlighting. The ellipsoidal reflector (Type ER) focuses the light beam about 2 inches in front of its enclosure and projects light down from recessed fixtures. Ellipsoidal reflectors are twice as energy-efficient as parabolic reflectors for recessed fixtures. 
 Fluorescent lamps last about 10 times longer than incandescent lamps and are about three to four times more efficient. Greater energy efficiency is obtained when fluorescents are used in applications where they will be on for several hours at a time. The light produced by a fluorescent lamp is produced by conducting an electric current through mercury and inert gases. Energy savings can be obtained with fluorescents by using lower-wattage lamps, replacing ballasts, periodically cleaning lamps and reflectors, and by using more efficient reflectors.High-intensity discharge lamps (HID) provide the highest efficiency and the longest service life of any type lamp. They are frequently used for outdoor lighting and large indoor arenas. HID lamps use an electric arc to produce intense light. Their use of a ballast requires a few seconds to produce light when they are first turned on. HID lamps and fixtures can save 75 to 90 percent of lighting energy when they replace incandescent lamps. The three most common types of HID lamps are mercury vapor, metal halide and high-pressure sodium. Metal halide and/or high-pressure sodium lamps are more energy-efficient than mercury vapor lamps and have better color-rendering properties. Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamps results in higher light output, more lumens per watt and better color rendering than from mercury gas alone.High-pressure sodium lighting is becoming the most common type of outdoor lighting. It provides roughly 90 to 150 lumens per watt second only in efficiency to low-pressure sodium lighting. This type of lamp has good reliability and long service life. Color rendition ranges from poor to fairly good.Low-pressure sodium lamps work somewhat like fluorescent lamps. They are the most efficient artificial lighting and have the longest service life. Color rendition is poor, and typical uses are for highway and security lighting.Mor-Lite lnc., Greenville, S.C., specializes in supplying lighting equipment for textile mills in the United States, Mexico, and Central and South America. The company uses the latest fluorescent technology brighter T8 or T5 lamps, electronic ballasts and specular reflectors. Examples of the results from lighting installations that Mor-Lite has made in textile mills are shown in Table 1.
 Process HeatingProcess heating is vital to nearly all manufacturing processes. In U.S. industry, process heating accounts for more direct energy use than any other processes in manufacturing. Heating processes, not including steam generation, consume about 5.2 quadrillion BTUs (quads), which is nearly 17 percent of all energy used by industry. Heat derived from combustion of fossil fuels accounts for 92 percent of this energy.The major components of process heating systems are as follows:heating devices that generate and supply heat;heat-transfer devices to move heat from the source to the product;heat-containment devices, such as ovens, heaters, furnaces and kilns; andheat-recovery devices and systems.In most manufacturing operations, heat is supplied by one of four heating methods: fuel-fired heating; steam heating; hot oil/air/water heating; and electric heating, including infrared, microwave and radio frequency (RF).Over the last 20 years, U.S. industry has made significant progress in improving process heating efficiency. However, total industrial energy use in process heating will continue to grow as the economy grows. Today, overall thermal efficiency of process equipment varies from 15 percent to 80 percent. This compares to the thermal efficiency of steam generation, which varies from 65 percent to 85 percent. The lower efficiency for process still provides room for further energy-saving efforts. There are opportunities for improving energy efficiency by using a range of process heating systems, including infrared, microwave and RF types. Infrared Heating SystemsWhat is infrared Our eyes are designed to enable us to detect visible light, which is one of the few types of radiation that can penetrate our atmosphere and be detected on the earths surface. We actually see only a small part of the entire range of radiation, which is called the electromagnetic spectrum. The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, and micro- and radio waves.Infrared radiation lies between the visible and microwave portions of the electromagnetic spectrum. Infrared waves have wavelengths longer than visible waves and shorter than microwaves with frequencies lower than visible waves and higher than microwaves. The primary source of infrared radiation is heat or thermal radiation.Traditionally, products have been dried and cured by baking them in an oven. Infrared heating provides an alternative way of drying and curing. Like sunlight, infrared energy creates heat when it hits a surface and travels through air without heating the air. Most infrared heaters use electric coils, or ceramic plates heated by a gas flame. Infrared heating can be 50 percent to 80 percent more efficient than convection heating. 
 Microwave Drying Of TextilesAlthough microwave systems have had worldwide acceptance for food cooking and processing, they have had limited success in industrial applications. The economic barriers to their acceptance have been high capital equipment costs and high maintenance costs. According to Industrial Microwave Systems (IMS), Morrisville, N.C., there have been some technical breakthroughs in microwave drying systems that have reduced equipment costs to one-fourth of what they were in the mid-1980s. Maintenance costs have been reduced tenfold, and energy efficiency has increased by more than 150 percent.lMS has worked on several demonstration projects with industrial firms and government agencies using their patented cylindrical reactor technology to develop equipment for microwave drying of tubular knitted textiles in California and New York. The IMS patented waveguide design compensates for attenuation (energy being absorbed) and uneven microwave heating. The waveguide also eliminates problems with hot spots. Other promising areas for the IMS microwave systems are tufted carpeting, towels, coatings and materials with poor moisture transport.According to IMS, the advantages of microwave drying for textile products are the following:It can be twice as fast as conventional methods.It provides a softer hand.It can dry coatings without skinning.It eliminates scorching.Products dry at temperatures lower than 200°F.It provides precision control and response and requires no pre-heating or cooling. Radio Frequency HeatingMost nonconductors of electricity such as wood, paper, textiles and plastics show electrical losses when placed in a high-voltage, high-frequency electric field. These losses result in heat being developed in the material. Other terms used for this type of heating are dielectric, high-frequency or capacitive heating. Most heating of this type is done at 10 to 100 megahertz (MHz) because the heat develops directly in the material.Thomas W. Jones, president and CEO of Radio Frequency Co. Inc., Millis, Mass., describes the operation principle of RF drying systems as follows: In a radio frequency drying system, the RF generator creates an alternating electric field between the two electrodes where the alternating energy causes polar molecules in the water to continuously re-orient themselves to face opposite poles much like the way magnets move in an alternating field. The friction of this movement causes the water in the material to rapidly heat throughout its entire mass. RF drying systems for textiles have been in use in the textile industry since 1978. Worldwide, there are more than 1000 systems in operation, but only about 6 percent of these are in the United States.North Carolina State University, in conjunction with the Industrial Electrotechnology Laboratory (IEL), Raleigh, N.C., initiated a project in l991 to document the costs of RF dryer operations in plants. From case studies involving 27 trials of RF dryers at 10 different mills in North Carolina, the project documented the average amount of energy consumed in kW per hour per kilogram (kg) of water removed, and per kg of material produced. Comparisons were made with traditional pressure dryers. The highlights of this study included: moisture control within ±5 percent; average useful energy efficiency of 60 percent; reduced drying costs compared to conventional dryers; and improved product quality with lower waste. Isolating CostsA large amount of information and assistance in reducing energy costs is available to textile and related industries from government sources such as the DOE, as well as from agencies within individual states, universities and trade associations such as the Electric Power Research Institute (EPRI) and the American Gas Association, and from utilities and private consulting firms. Utilizing some of this work that already has been done entails a lot of hard work hard work that requires companies to continually study their energy-intensive processes and closely monitor energy usage. Although solar and wind power energy sources are receiving increasing attention, oil, natural gas and coal will still be the major energy sources for most textile companies for the foreseeable future. Using cogeneration and emerging technologies, energy efficiency pays off.  August 2002



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