DESALINATION, TRENDS AND TECHNOLOGIES Phần 8

234 Desalination, Trends and Technologies Nomenclature Capital letters : Cp D La Lo M P Pa Pe Pu R S T TU V Small letters: a c e f h h’ h’’ qc R so s z Greek letters φo α ε εa εc εac λ ρ σ τ ω Indices : a ar Apparent conductance of heat loss (W/m2°C). Day of the month Latitude (degree). Longitude (degree). Number of months Vapour pressure (Pa) Incident power of absorbed radiation (W/m2) Power of heat loss (W/m2) Useful power (W) Radius of the pupil surface (m) Collecting area (m2) Temperature (K) Universal Time (h) Wind speed (m/s) Aperture diameter of the paraboloid (m). The specific heat (J/kg°C). Thickness of the insulation on the back of the absorbers (m). Focal or friction factor. Exchange coefficient (W/m2°C). Internal heat transfer coefficient (W/m2°C). External heat transfer coefficient (W/m2°C). Mass flow of coolant (kg/s). Radius of the absorber or correction of the earth-sun distance (m). Surface receptor (m2). Collecting surface (m2) Altitude (km). Aperture Half angle of the paraboloid (degree). Absorption coefficient of the absorber (%). The angle of a conical light beam (degree). Emissivity of the absorber (%). Emissivity of the cover (%). Apparent emissivity of the system (%). Thermal Conductivity (W/m°C). Reflection coefficient of the paraboloid (%). STEFAN-BOLTZMANN constant. Transmittivity of the cover (%). Hour Angle (degree). Absorber or ambient. Rear wall insulation. Solar Desalination cmoy moy cv r s v 235 Average cover. Average absorber Convection Radiation. Fluid outlet of the concentrator. Steam or vault surrounding. 5. References [1] G.N.Tiwari, H.N.Singh, R.Tripathi (2003) .Present status of solar distillation. Solar Energy, 75, pp. 367-373. [2] L.Zhang, H.Zheng, Y.Wu (2003). Experimental study on a horizontal tube falling film evaporation and closed circulation solar desalination system. Renewable Energy, 28, pp. 1187-1199. [3] R.DESJARDINS (1988). Traitements des eaux. 2ème édition, Editions de l’école polytechnique de Montréal. [4] A.Al-kharabshesh, Y. Goswami (2003). Experimental study of an innovative solar water desalination system utilizing a passive vacuum technique. Solar Energy, 75, pp. 395-401. [5] S.K. Shukla, V.P.S. Sorayan (2005). Thermal modeling of solar stills: an experimental validation, Renewable Energy, 30, pp. 683-699. [6] H.D. Ammari, Y.L. Nimir (2003). Experimental and theoretical evaluation of the performance of a tar solar water heater. Energy Conversion and Management, 44, pp. 3037-3055. [7] S.A. Kalogirou (2004). Solar thermal collectors and applications. Progress in Energy and Combustion Science, 30, pp. 231-295. [8] R.Y. Nuwayhid, F. Mrad, R. Abu-Said (2001). The realization of a simple solar tracking concentrator for university research applications. Renewable Energy, 24, pp. 207-222. [9] H.E.S. Fath(1998). Desalination, 116, 45. [10] E. Delyannis, and V. Belessiotis, Mediterranean. Conference on Renewable Energy Sources for Water Production. European Commission, EURORED Network, CRES, EDS, Santorini, Greece, 1996, pp. 3-l 9. [11] E.E. Delyannis(1987). Desalination, 67, pp. 3. [12] J. GIRI, B. MEUNIER, (1980). Evaluation des énergies renouvelables pour les pays en développement. Volume 2, Commissariat à l’énergie solaire, France, pp. 194, 199-201. [13] J. R. VAILLANT, (1978). Utilisation et promesses de l’énergie solaire. EYROLLES, Paris, pp. 178,183. [14] A. A. M. SAYIGH, (1977). Solar energy engineering. Academic press, New York, pp. 434, 437,449,455,459. [15] F. BEN JEMAA et al, (1998). Desalting in Tunisia : Past experience and future prospects. Desalination 116, pp. 124. [16] F. BEN JEMAA et al, (1998). Potential of renewable energy development for water desalination in Tunisia. Renewable energy, December, pp. 6. [17] I. HOUCINE et al, (1999). Renewable energy sources for water desalting in Tunisia. Desalination, 125, p p. 126. 236 Desalination, Trends and Technologies [18] N. COUFFIN, C. CABASSUD et V. LAHOUSSINE-TURCAUD, (1998). A new process to remove halogenated VOCs for drinking water production: vacuum membrane distillation. Desalination, 117 pp. 233-245 [19] D. WIRTH, (2002). Etude de la distillation pour le dessalement de l’eau de mer, Thèse de Doctorat, Institut National des Sciences Appliquées de Toulouse. [20] D. WIRTH, C. CABASSUD, (2002). Water desalination using membrane distillation: comparison between inside/out and outside/in permeation. Desalination, 147, pp. 139-145. [21] R. BERNARD, G. MENGUY, M. SCHARTZ, (1980). Le rayonnement solaire conversion thermique et applications. 2ème édition, Technique et documentation, Paris, pp. 30,39,149,197. [22] B. BOURGES, L. BERTOLO, (1992). Données climatiques utilisées dans le bâtiment. Technique de l’ingénieur, B 2015, Paris, pp. 22. [23] A. A. SFEIR, G. GUARRACINO, (1981). Ingénierie des systèmes solaires applications à l’habitat. Technique et documentation, Paris, pp. 55. [24] J. GLEN, K. LOVEGROVE, A. LUZZI, (2003). Optical performance of spherical reflecting elements for use with paraboloidal dish concentrators. Solar energy, 74, pp. 133. [25] R. HOUZE, (1989).Les antennes du fil rayonnant à la parabole, Tome 2, EYROLLES, Paris, pp. 150,154. [26] R. PASQUETTI, (1987). Chauffage des fluides par capteurs solaires à concentration. Technique de l’ingénieur, B 2420, Paris, pp. 4-7,13,16. [27] M. HENRY, (1981). Optique géométrique. Technique de l’ingénieur, A 190, Paris, pp. 5. [28] P. GALLET, F. PAPINI, G. PERI, (1980). Physique des convertisseurs héliothermiques. EDISUD, Aix en Provence, pp. 131,135,136,144,145. [29] J. DUFFIC, B. WILLIAM, (1974). Solar energy thermal processes. John Wiley & Sons inc, New York, pp. 191,194,196. [30] J. DESAUTEL, (1979). Les capteurs héliothermiques. EDISUD , Paris, pp.16-19, 80- 83. [31] A. S. KENKARE, J. P. YIAMMOULLOU, (1983). The performance of a concentrating solar collector in UK weather conditions. Solar world congress. 2, Pergamon press,U.K., pp. 1043. [32] R.Y. Nuwayhid, F. Mrad and R. Abu-Said, (2001) .The realization of a simple solar tracking concentrator for university research applications. Renewable Energy, 24, PP. 207–222. [33] V.V. Pasichny and B.A. Uryukov, (2002). Theoretical aspects for optimization of solar radiation concentrators with plane facets. Solar Energy, 73, pp.239. [34] B. Chaouchi, A. Zrelli, S. Gabsi (2007). Desalination of brackish water by means of a parabolic solar concentrator. Desalination 217, pp. 118–126. 11 Reject Brine Management Muftah H. El-Naas United Arab Emirates University UAE 1. Introduction Desalination has been growing rapidly as an industry and as a field of research that combines engineering and science to develop innovative and economical means for water desalting. Many countries in the world, especially in the Middle East, depend heavily on seawater desalination as a major source of drinking water and have invested considerable efforts and financial resources in desalination research and training. Desalination plants have seen considerable expansion during the past decade as the need for potable water increases with population growth. It is estimated that the world production of desalination water exceeds 30 million cubic meters per day and the desalination market worldwide is expected to reach $ 30 billion by 2015. One of the major economical and environmental challenges to the desalination industry, especially in those countries that depend on desalination for potable water, is the handling of reject brine, which is the highly concentrated waste by-product of the desalination process. It is estimated that for every 1 m3 of desalinated water, an equivalent amount is generated as reject brine. The common practice in dealing with these huge amounts of brine is to discharge it back into the sea, where it could result, in the long run, in detrimental effects on the aquatic life as well as the quality of the seawater available for desalination in the area. Although technological advances have resulted in the development of new and highly efficient desalination processes, little improvements have been reported in the management and handling of the major by-product waste of most desalination plants, namely reject brine. The disposal or management of desalination brine (concentrate) represents major environmental challenges to most plants, and it is becoming more costly. In spite of the scale of this economical and environmental problem, the options for brine management for inland plants have been rather limited. These options include: discharge to surface water or wastewater treatment plants; deep well injection; land disposal; evaporation ponds; and mechanical/thermal evaporation. Reject brine contains variable concentrations of different chemicals such as anti-scale additives and inorganic salts that could have negative impacts on soil and groundwater. This chapter highlights the main concerns as well as the environmental and economical challenges associated with the generation of large amounts of reject brine as a by-product of the desalination process. The chapter also outlines and compares the most common options for the treatment or disposal of reject brine. The chapter focuses on a novel approach to the management of reject brine that involves chemical reactions with carbon dioxide in the 238 Desalination, Trends and Technologies presence of ammonia, based on a modified Solvay process. Reject brine is mixed with ammonia and then exposed to carbon dioxide using different contact techniques. The end result is the conversion of NaCl and CO2 into a useful solid product, namely sodium bicarbonate, and the reduction of the salinity of the treated brine, which may then be used for irrigation. Besides brine management, the new approach will reduce the emissions of CO2 as a major contributor to global warming. Carbon dioxide can be used as a pure gas from gas sweetening units or in the form of flue or exhaust gas from chemical or power plants. 2. Current brine disposal options Since desalination processes generate considerable amounts of reject brine, the industry has adopted numerous disposal options that usually depend on the location of the desalination plant and type of process used. These options include: discharge to surface water or wastewater treatment plants; deep well injection; land disposal; evaporation ponds; and mechanical/thermal evaporation. Management of reject brine has recently become an increasingly difficult challenge due to many factors that include: growing number and size of desalination plants which limits disposal options; increased regulations of discharges that make disposal more difficult; increased public concern with environmental issues; increased number of desalination plants in semi-arid regions where conventional disposal options are limited (Mickley, 2006). Cost plays an important role in the selection of a brine disposal method and it is believed to range from 5% to 33% of the total cost of desalination (Ahmed et al, 2001). Mickley et al. (1993) identified the factors that influence the selection of a disposal method. These include the quantity and quality of the brine; composition of the concentrate; physical or geographical location of the discharge point of the concentrate; availability of receiving site, permissibility of the option, public acceptance, capital and operating costs, and ability for the facility to be expanded. The cost of disposal depends on the characteristics of reject brine, the level of treatment before disposal, means of disposal, volume of brine to be disposed of, and the nature of the disposal environment (Ahmed et al, 2001). A detailed review of the different brine disposal methods can be found in a report by Mickley (2001). The following sections will present a brief summary of the main brine disposal options and highlight the main drawbacks of each option. 2.1 Discharge into surface water It has been a common practice for coastal desalination plants to dispose reject brine into the close-by surface water body, namely sea or ocean. For these plants, such disposal operation has always been deemed the most practical and least expensive. Costs for disposal are typically low provided that pipeline conveyance distances are not excessively long and the concentrate is compatible with the environment of the receiving water body. An assessment of salinity or TDS impact as well as those of specific constituents on the receiving stream must always be considered (Mickely et al, 2006). The main factors that determine the costs of reject brine discharge to surface water include: costs to transport the brine from the desalination plant to the surface water discharge outfall; costs for outfall construction and operation; and costs associated with monitoring the environmental effects of the brine discharge on the surface waters (Mickely et al, 2006). The impact of brine disposal operations on coastal and marine environment is still largely unknown, but the high temperature and salinity associated with reject brine may have detrimental effects on marine life. Moreover, the high level of chemicals could reduce the ... - tailieumienphi.vn