Solare termico altre applicazioni. G.V. Fracastoro

Transcription

1 Solare termico altre applicazioni G.V. Fracastoro

2 CSP per produzione elettrica Usati in combinazione con un impianto a ciclo termodinamico (Rankine o Stirling) point concentration systems (parabolic reflectors) Tower Systems Linear parabolic (trough) collectors

3 Principi degli impianti a concentrazione A aperture A ass Vantaggi: Maggiore densità energetica = maggiore temperatura (fino a 600 C), Minore superficie assorbente, minori perdite Svantaggi : Necessità di inseguitori solari Uso della sola radiazione diretta concentrator absorber

4 Parabolic dish system

5 Sistemi a torre The solar power tower (also known as 'Central Tower' power plants or 'Heliostat' power plants) is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). Early designs used these focused rays to heat water, and used the resulting steam to power a turbine. Now liquid sodium in place of water is used; this can be used to store the energy before using it to boil water to drive turbines. In this way power may be generated also when the sun is not shining.

6 Example: the Seville plant Europe's first commercial concentrating PS10 solar power tower is operating near Seville. The 11 MW solar power tower produces electricity with 624 large movable heliostats. Each of the mirrors has a surface measuring 120 m 2 that concentrates the Sun's rays to the top of a 115 meter high tower where a solar receiver and a steam turbine are located. The PS10 solar power tower stores heat in tanks as pressurized steam at 50 bar and 285 C. Storage is for one hour.

7 Parabolic trough systems

8 Archimedes : the Enel-Enea plant at Priolo (Sicily) Combined thermodynamic cycle Molten salts (Na and K nitrates) Peak Power : 23 MW th, 4.7 MW el 72 linear parabolic trough reflectors ( m 2 ) Yearly production: 9.22 GWh Two heat storages (100 MWh) to level the electricity produced high temperature level: 550 C low temperature level: 290 C

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10 Solar cooling systems Absorption systems Adsorption systems Desiccant cooling

11 Thermally driven absorption chiller Figure 9. Scheme of thermally driven absorption chiller.

12 Solar cooling through absorption refrigeration systems Advantages In-phase demand and offer Use of free heat as primary source to produce cold Absorption technology well known and tested Disadvantages Low COP ( ) High cost

13 Typical features Small-average size ( kw) Lithium bromide water (LiBr-H 2 O) systems Heat input Hot water (90-95 C), single effect (COP = 0.75) Steam or superheated water (180 C, COP =1)

14 Solar desalination Multiple effect humidification Reverse osmosis

15 Multiple-Effect-Humidification (MEH) Multiple-Effect-Humidification (MEH) desalination process is based on evaporation of salt water and the subsequent condensation of the generated steam. The produced steam is virtually clear and does not carry any solvents. Following condensation, one can collect clear, salt-free and healthy fresh water. In the process, sea water is heated by the sun via highly corrosion-protected heat exchangers. The heated salty water enters an evaporation chamber produced from corrosion free materials. Here the salty water evaporates from efficient antibacterial surfaces. The produced steam is transported to the condenser in a second step without any additional energy demand. During condensation, the main part of the energy used for evaporation is regained, using materials with extremely low thermal resistance.

16 Multi-effect evaporator A multiple-effect evaporator is an apparatus for efficiently using the heat from steam to evaporate water. In a multiple-effect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last. Because the boiling point of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel (at the highest pressure) requires an external source of heat. Double-effect falling film evaporator. Condensing vapors from flash tank B1 heat evaporator A2. 1=feed, 2=product, 3=steam, 4=vapors

17 Reverse osmosis Reverse osmosis is a filtration process that is often used for water. It works by using pressure to force a solution through a membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration Here, solar energy is collected and converted into electrical or mechanical energy to initiate the process. Sea water is pumped into a tank with an ultrafiltration membrane, which removes viruses and bacteria. This water is fit for cleaning and bathing. Ten percent of that water undergoes nanofiltration and reverse osmosis in the second stage of purification, which removes salts and trace contaminants, producing drinking water. A photovoltaic solar array tracks the sun and powers the pumps needed to process the water.