Geothermal(地热) Energy

　　1 Since heat naturally moves from hotter regionsto cooler ones, the heat from the earth's center flows outwards towards thesurface. In this way. it transfers to the next layer of rock. If thetemperature is high enough, some of this rock melts and forms magma (岩浆). The magma ascends in its turn towards theearth's surface. It often remains wen below the earth s surface, creating vastareas of hot rock. In such regions, there are deep cracks, which allowrainwater to descend underground. Some of the heated rainwater travels back upto the earth's surface where it will appear as a hot spring. However, ifthis ascending hot water reaches a layer of impermeable (不可渗透 的）rock, it remains trapped, forming a geothermal reservoir. If geothermal reservoirs are closeenough to the surface, they can be reached by drilling wells. Hot water andsteam shoot up the wells naturally, and can be used to produce electricity ingeothermal power plants.

　　2 A few geothermal power plants depend ondry-steam reservoirs which produce steam but little or no water. In thesecases, the steam is piped up directly to provide the power to spin a turbinegenerator. The first geothermal power plant, constructed at Lardarello inItaly, was of this type, and is still producing electricity today.

　　3 Most currently operating geothermal powerplants are either "flash" steam plants or binary (双重的) plants. Flash plants produce mainly hotwater ranging in temperature from 300℃ to 700℃ Fahrenheit. This water is passed through one or two separatorswhere released from the pressure of the underground reservoir, itHashes" or boils into steam Again, the force of this steam provides theenergy to spin the turbine and produce electricity. The geothermal water andsteam are then reinjected directly back down into the earth to maintain the volumeand pressure of the reservoir. Gradually they will be reheated and can then beused again.

　　4 A reservoir with temperatures below 300℃ Fahrenheit is not hot enough to flash seam but it can still be used togenerate electricity in a binary fluid. The steam from this(参照图片) isused to power the turbines. As in the flash steam plant, the geothermal water is recycled backinto the reservoir.

　　23.Paragraph 1_____C____

　　24.Paragraph 2____A_____

　　25.Paragraph 3____E_____

　　26.Paragraph 4____B_____

　　A. Dry steam plants

　　B. Binary plants

　　C. Origin of geothermal energy

　　D. Generation of electricity

　　E. Flash steam plants

　　F. Recyclable water and steam

　　27. A geothermal reservoir is formed when hotwater is trapped under__B____.

　　28. A dry-steam reservoir produces steam with___D___.

　　29. Flash plants produce hot water through___C___.

　　30. In a binary plant, the heat of the geothermalwater can be converted into__A____.

　　A. the energy to turn a turbine

　　B. impermeable rock

　　C. one or two separators

　　D. turbine operator

　　E. little or no water

　　F. hot springs