Solar industrial process heat The industrial demand f o r steam, hot water, and hot air accounts f o r a substantial fraction of our total energy needs. The part that solar can play in meeting this demand was discussed by researchers and users at a Department of Energy symposium Stephen L. Sargent Barbara H. Glenn David W. Kearney Solar Energy Research Institute Golden, Colo. 80401 The industrial sector is the largest consumer of energy in the United States, using about 40% of the nation’s gross energy demand of 77 quads ( 1 quad = l o i 5 Btu) in 1977. It is estimated that from 50% to 70% of this
demand is for industrial process heat (IPH), the thermal energy used in the preparation and treatment of goods in manufacturing processes. Achieving President Carter’s stated goal of 20% solar by 2000 (this translates into 2.6 quads of energy from solar agriculture and I P H ) requires the establishment of a strong, substantial market for solar systems, and a strong federal program to stimulate and support the private sector in solar technology development
Timely exchange of information is crucial to the success of such a program. The Solar I P H Conference, organized by the Solar Energy Research Institute (SERI) for DOE’S Agricultural and Industrial Systems Branch, provided a forum for interaction between researchers and potential users of solar IPH systems, examined the status of existing IPH projects, and reviewed the technical readiness and expected future development of solar I P H systems and components. The
Line-focusing parabolic trough collector. Under test at Snndia Laboratories, Albuquerque, N.M. 518
Environmental Science & Technology
0013-936X/80/0914-0518$01.00/0 @ 1980 American Chemical Society
Solar IPH field tests conference was held in Oakland, Calif. and drew about 300 people-nearly double the number attending a previous DOE-sponsored conference on the subject. This year’s conference was designed to stimulate communication between researchers and industrialists. Traditional lectures were complemented by a poster session modeled after the visual exhibits familiar to industry trade show attendees. Reflecting the overall objective of the IPH program to demonstrate both technical and economic feasibility of solar IPH systems, about half of the 40 posters focused on economic and applications analyses, while the remainder presented system and performance data from IPH field tests. Field tests to demonstrate the technical feasibility of solar IPH systems a r e a vital part of the DOE program, and one day of the conference was dedicated to presentations on the status of the various projects. The field tests provide a measure of program effectiveness in determining system performance, reliability, maintainability, and economics. Earlier field tests were aimed at demonstrating how the relatively low temperature technology developed for the residential sector could be applied in industry. By the end of 1978, D O E had funded 18 projects providing industrial process hot water, hot air, and steam. The accompanying list indicates the wide variety of industrial processes and geographical locations where solar energy has potential. In 1979, the D O E program emphasized large-scale, cost-shared systems to determine the degree of economies of scale that could be achieved. Presentations at the conference detailed the six large-scale field tests funded during 1979 and outlined the direction that the program would take in 1980. Four studies of industrial applications accomplished entirely with private funds were also presented.
Industrial uses I n theory, solar energy can be supplied in any form required by industry. In practice, the use of solar energy is currently most cost-effective at low or intermediate temperatures (less than 550 OF). At least 27% of IPH needs fall in this temperature range; and if preheating to 550 OF: for higher-temperature requirements is considered. 5 1 % of industry‘s process heat can be supplied with available solar equipment. Despite the sensitivity of solar efficiency to operating temperature, a large share of industrial process heat can be supplied by the sun.
Location
Sacramento, Calif. Harrisburg, Pa. LaFrance, S.C. Fresno, Calif. Canton, Miss. Decatur, Ala. Gilroy, Calif. Fairfax, Ala. Sherman, Tex. Pasadena, Calif. Bradenton, Fla. Mobile, Ala. Dalton, Ga. Newberry Springs, Calif. Hobbs, N. Mex. San Antonio, Tex. Henderson, Nev. Ontario, Ore.
Process
Collectors
Owner
Hot water (140-212 O F ) Can Flat plate Campbell Operational washing & parabolic Soup Co. (April 1978) York Building Operational Concrete Multiple Products (Sept. 1978) block curing reflector Textile Evacuated Reigel Textile Operational dyeing tube Corp. (June 1978) Hot air (140-212 O F ) Fruit Flat plate Lamanuzzi & Operational drying Pantaleo (May 1978) Foods Kiln drying Flat plate LaCour Kiln Operational of lumber Services, Inc. (Nov. 1977) Soybean Flat plate Gold Kist, Inc. Operational drying (May 1978) Onion Evacuated Gilroy Foods, Operational drying tube Inc. (Sspt. 1979) Low-temperature steam (212-350 O F ) Fabric Parabolic WestPoint Operational trough Pepperell (Sept. 1978) drying Parabolic Johnson & Construction Gauze Johnson bleaching trough Parabolic Home Cleaning Construction Laundry trough & Laundry Orange juice Evacuated Tropicana Construction pasteurization tube Products, Inc. Intermediate-temperature steam (350-550 O F ) Oil heating Parabolic Ergon, Inc. Design trough Latex Multiple Dow Chemical Construction production reflector Hectorite Parabolic Nat’l Lead Design processing trough Industries
Parabolic trough Brewery Parabolic trough Chlorine Parabolic manufacturing trough Potato Parabolic processing trough
Oil refinery
Southern Union Co. Lone Star Brewing Co. Stauffer Chemical Co. Ore-Ida Co.
Large-scale steam Parabolic Bates trough Container, Inc. Haverhill, Parabolic Columbia Gas Ohio trough System Corp. Pepeeko, Parabolic Hilo Coast Hawaii trough Processing co. San Leandro, Engine parts Parabolic Caterpillar Calif. washing trough Tractor Co. Bakersfield, Enhanced oil Fixed-mirror Petro Lewis/ Calif. recovery concentrators General Atomic Bakersfield, Enhanced oil Parabolic Exxon Calif. recovery trough Research & Engineering Co.
Fort Worth, Tex .
Status
Corrugated cardboard fabrication Polystyrene production Sugarcane processing
Privately funded IPH applications Youngstown, Aluminum Fixed halfGeneral Ohio anodizing parabolic Extrusions, Inc. Jacksonville, Beer Evacuated AnheuserFla. pasteurization tube Busch, Inc. Mesa, Car wash Parabolic Andy’s Solar Ariz. trough Truck & Car Wash Richmond, Photographic Flat plate EASCO Va. film processing
Construction Design Design Construction
Design Design Design Design Design Design
Operational (Sept. 1977) Operational (Feb. 1978) Operational (Spring 1977) Operational (Fall 1978)
Process heat e:iergy is conventionally supplied from fossil fuels, either directlq or through a heat transfer fluid such as wati:r, air. or saturated low-pressure stea TI. In general, solar cnergq for process heat can be supplied i n the same Liays. Large quantities of heated water a t tcmper;itures between 120 " F a n d 212 O I - arc used in industry for such proccsscs a s cooking. washing. bleaching, ;ind anodizing. Hot water may be supplied bq direclly heating water in ;ibsorber tubes of flat-plate. evacuated tube. or concentrating collectors and piping this \\atel to the process terminals. Alternatively, a separate fluid m a y be piped t h -()ugh the collector ficld and then u.,cd to heat potable \rater v i a a heat exchanger. Large solar ponds ma) alsg be used to provide large amounts of low-temperature hot \\ ;I t e r . Many industrial processes require large quantities of relatively lowp r chs u r c s a t u r a t e 13 steam . Saturated itciirn a t apprc'riimately 100 psi, equivalent to a tcniperature of about 330 O F , can be produced in a solar s!stcm in two u.nj.s: ( I ) Pressurized \\;iter may be circulated in a collector ficld and thcn fla.hed into steam in a lou-pressure chatnber. or (2) a heat transfer fluid capible of higher-tempcrature operation may be circulated i n thc collector field and then fed to a stcani generator, where the fluid serves ;IS ;I heat source 10 produce steam. Because of the higher temperature required, industrial steam applications norm ;I I I y r eq u i r c tracking con cen trating collectcirs. .uch as the parabolic trough. or ccrtLiin '.)pes of nontracking high-pcrformLincc: collectors. such as the evacuated tube. Lou -temperat u rc (less than 3 50 O F) direct heat is used f'or crop drying and
food processing as well as paint drying, curing, and mineral solution dehydration. Air may be heated directly in collector systems designed to handle air as the circulating fluid, or a liquid may be circulated through the collectors and pumped through a heat exchanger to heat ambient air. High-temperature (greater than 550 OF) direct process heat accounts for a large portion of all industrial heat needs. Industries such a s petroleum refining, primary metals. Portland cement, and glass are the major users. It is unlikely that intermediate-temperature collectors (parabolic trough or evacuated tube) can be used in the near future for process heat a t these temperatures. Other collector types, though, such a s central receivers or parabolic dishes, have potential for direct solar heating in selected processes. For example, it may be possible to locate solar-powered synthetic fuel production plants in the Southwest and provide high-temperature process heat to industry via solar-produced fuels. A portion of high-temperature process energy may also be supplied through solar preheating. This function should not be overlooked since it can conserve nonrenewable fossil fuels.
Status of the technology During one session of the conference, technical experts presented their views on the status of solar technologies important to process heat. This session considered both solar collectors to deliver energy over a wide range of process temperatures-solar ponds. line-focus parabolic troughs, parabolic dishes, and heliostat/central receiver systems-and important issues relating to materials, thermal storage, and system design. Solar ponds offer the potential of
FIGURE 1
Operating temperatures of solar IPH technologies Central receiver Point focus (Parabolic dish & fresnel lens)
550"
150"
Line focm (Parabolic trougri & fresnel lens; also, multiple reflector)
Commercial
Evacuated tu be
1
120"
Flat plate 50
100
200
400
600 8001000
Operating temperature ( O F )
520
IEnvironmental Science & Technology
2000 3000
very low cost process heat u p to temperatures approaching 2 12 F , A solar pond is a large area of water. 1-3-ni deep, designed both to collect and to store solar energy. Therrnal loss mechanisms that occur in natural bodies of water a r e greatly reduced in solar ponds either by using a salt gradient to suppress natural convection or by using inexpensive plastic glar.ings. In the U.S., six salt-gradient pond projects and one glazed shalloLv pond application are being usecl by researchers to investigate the problems and develop the concept. The largest of these-a 2000-m2 pond a t Miamisburg, Ohio-provides heat for the city's recreational building and swimming pool. Israel. which is particularly active in this area. has four ponds ranging from 1100 m? to 6300 m 2 in area to provide energy for industrial processes and to produce electricity. Continued development of solar ponds is needed to find better. cheaper, and more reliable methods of maintaining a stable, nonconvecting layer, extracting the heat, and solving the problems associated with material lifetimes of liners and glazings. Energy a t somewhat higher temperatures can be supplied by flat-plate collectors ( u p to 200 OF) or nontracking concentrating collectors (up to 350 OF), such as evacuated tubes and corn pou nd pa ra bo1ic conccn t r;i tors. These collectors were not discussed specifically a t this conference: rather, the emphasis was placed on highertemperature concentrators. The essential features of high-temperature collectors a r e the ability to track the sun on one or two axes and to concentrate the sun's energy man). 1.imes by reflecting incident solar ray:; onto a receiver. The concentration ratio. defined a s the ratio of collector aperture area to receiver area, can varq from about 40 for parabolic troughs to over 2000 for heliostat/central receivers. Achievable working temperature increases with concentration ratio. T h e discussion of line-focus concentrators centered on development efforts of Sandia L.aboratories of Albuquerque to understand and improve the components and subsystems of the parabolic-trough collector. Sandia has worked on tracking and drive mechanisms, reflector and absorber materials, collector structure, receiver design, foundation requirements, and collector-field piping layout. These studies. conducted bq both Sandia and industrial contractors. have led to several conclusions. First. the thermal efficiencies of commercially available collectors are not yet at the goal 0160% to 70% thermal efficiency a t 600 O F ,
although there appears to be a definite and encouraging trend with successive collector generations. Second, the useful lifetime of existing collectors is less than the 10-20 years dictated by economics. Environmental degradation of materials is the principal factor. Third, existing collector technology is not yet adapted to low-cost materials and mass-production processes which will be required to reduce system costs to an attractive level. T h e point-focusing distributed receiver can achieve very high temperatures using a parabolic dish concentrator to track the sun on two axes. A receiver mounted a t the focal point captures the concentrated radiation and converts it to heat in a working fluid such as hot gas or steam. The working fluid transports the energy to a heat exchanger to provide process heat. This technology is less developed than line-focused collectors, though commercial products do exist and can produce thermal energy a t high temperatures (ceramic designs are projected to operate as high as 3000 O F ) . The primary development of this concept is being carried out through the Jet Propulsion Laboratory and focuses on subsystem problems similar to those encountered on line-focus concentrator development. T h e temperature range and configuration are different; but the goals of low cost, high-thermal performance, durability, and reliability are similar. Ongoing efforts are aimed at improving designs and demonstrating that performance goals can be met with potentially low-cost concentrators. High-temperature process heat requirements can also be met by a central receiver, in which a field of individually guided mirrors (heliostats) reflect incoming solar radiation to a single receiver mounted on a tower. The working fluid-air, helium, molten salt, liquid sodium, or water/ steam-circulates through the receiver and transports the collected energy to the process. Work centered a t Sandia Laboratories in Livermore, Calif. is directed toward the development and testing of high-temperature receivers and durable, low-cost heliostats. Design studies are examining the application of this technology to industrial processes such as gypsum board drying, enhanced oil recovery, uranium ore processing, oil distillation, natural gas processing, and methane reforming. Thermal storage systems were also discussed for industrial applications. Some buffer storage is necessary to smooth out short-term solar fluctuations caused by passing clouds, but
FIGURE 2
A typical solar steam system
present storage system economics are such that storage for longer periods (nighttime operation or completely overcast days) is not cost-effective. Most systems operate in a “fuel-saver” mode, providing solar heat when the sun shines and using a conventional auxiliary system, such as a fossil-fueled boiler, for sunless intervals. Storage will become increasingly attractive, however, as costs are reduced. Even without storage, there are many choices a designer must make with regard to system configuration and detailed design. Some general guidelines were proposed at the conference for systems using air, water, and steam. For a given collector type, the thermal efficiency decreases with increasing temperature, and it is therefore advisable to operate the collector at the lowest possible temperature consistent with the application.
The market The market status of solar I P H systems was considered by five working groups and a panel of solar IPH system users. The working groups considered I P H markets, costs and incentives, system configuration and installation problems, hardware and control system needs, and high-temperature solar I P H . The user panel, which included three industry representatives and three system designers, provided an enlightening discussion of the future of solar IPH as seen from the perspective of potential and actual industrial users. The working groups and user panel helped shed some light on why, in a era of escalating fuel prices and uncertain supply, there is not a rush by industry to install solar IPH systems. A number of factors were mentioned, including a generally adequate supply of con-
ventional fuels, the unproven reliability of solar systems, the unfamiliarity of industry with solar systems, and limitations on land or roof space for collector installations. It was also noted that the most favorable solar conditions exist in areas where there is not yet a heavy concentration of industry. Line- and point-focus concentrators for temperatures up to 600 O F require a high fraction of beam or direct radiation, conditions that exist primarily in the southwestern United States. For a given system, the annual collected radiation can vary by a factor of two or more between these sunny areas and regions of high industrial concentration in cloudier climates. But a consensus emerged that economics is by far the greatest obstacle to an early adoption by industry of solar I P H systems. Fossil fuels still enjoy an economic advantage. Some fuels, such as natural gas, are subsidized through regulated prices. A portion of conventional fuel costs can also be deducted as a production expense for tax purposes, and the remainder passed on to the consumer through increased prices. Another difficulty is that solar systems are capital intensive; this works to their disadvantage in a period of high interest rates. I n addition, a full backup system must be maintained to cover long cloudy periods. Finally, solar systems must overcome stiff company requirements for return on investment. Three return-on-investment figures mentioned at the meeting were 25%, 2870, and 40%. Even conservation measures-which compete with solar for plant investment dollars and are generally more cost-effective-have a difficult time meeting these figures. The user panel members provided insights into why their companies deVolume 14, Number 5, May 1980
521
TheMIRAN-101 isc the factory to monitorethyleneoxide or any one of hundreds of infrared absorbing gases. You can use it as a portable instrument for leakchecking and area mapping, or it can be pernianently located for continuous monitoring Why risk over-exposure to ethylene oxide? Get complete facts on the MIRAN-IO1 today Foxboro Analytical, A Division of The Foxboro Company, Wilks Infrared Center, PO Box 449, S. Norwalk, CT 06856, (203) 853-1616
Another dimension in analytical measurement and control
See
u s a t ?hie A l H A C o n f e r e n c e , B O O i h s 441-445.
CIRCLE 9 01.4 IREADER SERVICE C A R D
522
Environrnc?n?alScience 8 Technology
cided to install an IPH system or not. One system designer, working on three different projects, said that two major criteria for participation in DOEfunded demonstration projects were the public relations benefits and the potential threat of fossil-fuel curtailment. Another firm decided not to participate because the return on investment was insufficient and because the company was uneasy about the personnel requirements that might accompany a solar installation. This response was not atypical and should be kept in mind by the designer during preliminary discussions. O n the other hand, the Johnson & Johnson company decided to install a solar system on its gauze manufacturing plant in Texas due to the interest and enthusiasm of the plant engineering team. The plant engineer was adamant that the local plant personnel must be intimately involved with the design, installation, and maintenance of the system. Only in this way can plant management learn about the operation and characteristics of a solar system and take pride in its successful operation. In general, there appeared to be a common perception among the industry representatives that widespread solar use is about 15 years away. The user panel and working groups found that the most likely early solar users will be industries that want to expand existing plants or build new plants, but cannot obtain increased fuel supplies, face environmental constraints due to plant emissions, or are sited away from conventional energy supplies-for example, remote mining operations. Industries accustomed to being energy self-sufficient, by cogeneration for example, and those willing to absorb some solar system expense for public relations benefits may also be early users. The conference participants agreed that further tax incentives, loan programs, or other financial measures are necessary to accelerate industry adoption of solar systems. They also expressed a positive reaction toward the D O E program of system field tests to gather performance data on different systems. However, they felt that a larger number of tests with a broader variety of system types, processes, and geographic locations would be more useful to the program than a few large-scale experiments.
Future conferences If there was a shortcoming of the conference, it was the relatively small attendance by potential industrial users, compared to system suppliers
and direct participants in DOE-funded programs. The two most likely explanations for this are the lack of perception by many industries of solar as a here-and-now energy alternative, and the three-day conference length, M hich is excessive for many businesses. especially small firms. Both problems can be alleviated by taking the solar I P H story to potential users--through present at ions at est a b I i s h ed industry trade shows and by instituting a traveling solar IPH "road shou" to give half-day mini-conferences at industrial plants or in industry-intensive locations. Both possibilities are being examined by DOE and S E R I . The next solar IPH conference is being planned for Houston i n October 1980. Further information can be obtained from the Conferences Group, Solar Energy Research Instiwte. I617 Cole Blvd., Golden, Colo. 80401,
Stephen L. Sargent is a tecshnic,al .specialist in the Departnient of'Etiergj. Siro 0jJic.e at the Solar Energj Research Institiire. He was preciouslj' a solar progriini munager at S E R I and ar DOE t-leadyirarters in Washington, D.C. He is ii hoard twiiiber of the Engineering Dic.ision. It,iericati Section of the International Sollir Energ), Society, arid i s p u t chiiirtmti (I/ the American Socieri* of .Llec~hatii~:.al Engineer 's Solar Enrrgj, Diuisioti
