1.  Green Technology – 10EG603 6 th Sem. 2013 Dr. Rajalakshmi Mudbidre Department of Chemical Engineering RV College of Engineering Bangalore, Karnataka, India

2.  Green Technology – 10EG603 6 th Sem. 2012 CLASS 9- GEOTHERMAL

3. Geysers http://en.wikipedia.org/wiki/Geyser Clepsydra Geyser in Yellowstone

4. Hot Springs Hot springs in Steamboat Springs area. http://www.eia.doe.gov/cneaf/solar.renewables/page/geothermal/geothermal.html

5. Fumaroles Clay Diablo Fumarole (CA) White Island Fumarole New Zealand http://volcano.und.edu/vwdocs/volc_images/img_white_island_fumerole.html http://lvo.wr.usgs.gov/cdf_main.htm

6. Geothermal Energy - Introduction  Energy present as heat (i.e, thermal energy) in the earth’s crust  The more readily accessible heat in the upper most(10 km) or so, of the crust constitutes a potentially useful and almost inexhaustible source of energy  Apparent from the increase in temperature of the earth with increasing depth below the surface  On an average, temperature at a depth of 10 km is about 200 0 C

7. Geothermal Energy - Introduction  US Geological survey define geothermal source as  “ all of the heat stored in the earth’s crust above 15 0 C to a depth of 10 km”

8. A typical geothermal field

9.  The hot magma(molten mass) near the surface solidifies into igneous rock  The heat of magma conducted upward to this igneous rock  Ground water that finds its way down to this rock through fissures in it, will be heated by the heat of the rock or by mixing with hot gases and steam emanating from the magma  Heated water will then rise convectively upward and into a porous and permeable reservoir above the igneous rock

10. A typical geothermal field  The reservoir is capped by a layer of impermeable solid rock that traps the hot water in the reservoir  the solid rock, has fissures that act as vents of the giant underground boiler  The vents show up at the surface as geysers, fumarols or hot spring  A well taps steam from the fissures for use in a geothermal power plant

11. Kinds of Geothermal sources  Four basic kinds  i) Hydrothermal convective systems  ii) Geopressure resources  iii) Petro-thermal or Hot dry rocks  iv) Magma resources

12. Hydrothermal convective systems  Those in which water is heated by contact with the hot-rock Two kinds Vapor-dominated systems Liquid-dominated systems

13. Hydrothermal convective systems  Vapor-dominated systems  Water is vaporized into steam that reaches the surface in a relatively dry condition at about 200 0 C and rarely above 7kg/cm 3 (8 bar)  Most suitable for use in turbo electric power plants, with the least cost  Problems: presence of corrosive gases and erosive material  Less in number : five known sites in the world  Geysers plant in the US, largest in the world today  & Larderello in Italy

14. Hydrothermal convective systems  Liquid-dominated systems  Hot water circulating and trapped underground is at a temperature range of 175 to 315 0 C  When tapped by wells drilled in the right places and to the right depths, the water flows naturally to the surface or is pumped up to it  Contains relatively large concentration (3000 to 25,000 ppm) of dissolved solids  Power production is adversely affected by these solids- precipitate and cause scaling in pipes and heat exchanger surfaces, thus reducing flow and heat transfer  Much more plentiful than the previous one

15. Geopressured systems  Occur in large, deep sedimentary basins  Reservoirs contain moderately high temperature water(or brine) under very high pressure  They are of special interest because substantial amounts of methane(natural gas) are dissolved in the pressurized water and are released when the pressure is reduced  Geopressured water is tapped in much deeper underground acquifers at depths between about 2400 to 9000m

16. Geopressured systems  This water is thought to be at the relatively low temperature of about 160 0 C and is under very high pressure of about 1050 kg/cm 2 (>1000 bar)  It has a relatively high salinity of 4 to 10 percent and is often referred to as brine  Geopressured systems are quite large: they could be used for the generation of electric power and the recovery of natural gas if suitable technology could be developed

17. Hot dry rocks or Petrothermal  These are very hot solid rocks occurring at moderate depths but to which water does not have access  Either because of the absence of ground water or the low permeability of the rock or both  Break-up impermeable rock at depth, introduce cold water, and recover the resulting hot water( or steam) for use at the surface  The known temperature of HDR vary between 150 to 290 0 C  Accounts for large percent of the geothermal resouce

18. Hot dry rocks  A way be found to render the impermeable rock into a permeable structure with a large heat-transfer surface  A large surface is necessary-low thermal conductivity of the rock  Rendering the rock permeable is to be done by fracturing it  Fracturing methods involve drilling wells into the rock and then fracturing it by  i) high pressure water or  ii) Nuclear explosives

19. Magma resources  Consist of partially or completely molten rock, with temperatures in excess of 650 0 C, which may be encountered at moderate depths, especially in recently active volcanic regions  Have a large geothermal energy content but restricted to a relatively few locations  The high temperatures will make extraction of the energy a difficult technological problem

20. Advantages of Geothermal energy over other energy forms  Versatile in its use  Cheaper, compared to energies obtained from other sources  Delivers greater amount of net energy from its system  Least polluting compared to some of the other conventional energy sources  Amenability for multiple used from a single source  Renewable resource that has practically no intermittency, has the highest density

21. Disadvantages of Geothermal energy over other energy forms  Overall efficiency for power production is low, about 15 %, compared to 35-40% for fossil fuel plants  Withdrawal of large amount of steam or water from the hydrothermal reservoir may result in surface subsidence  Steam and hot water gushing out of the earth may contain H 2 S, CO 2, NH 3 and radon gas etc – air pollution  Drilling operation is noisy  Large areas needed for exploitation

22. Resource identification and development  Development begins with exploration – to locate and confirm the existence of a reservoir with economically exploitable temperature, volume and accessibility  Most known reservoirs discovered from surface manifestations such as hot springs  But inadequate- provide meagre or misleading information as to reservoir capacity  Drilling- expensive; something prior to this to forecast geothermal reservoir performance

23. Resource identification and development  The procedure under study include i) rate of upward heat flow in the ground ii) Chemical composition of surface and ground water iii) Electrical resistivity of the ground at varying depths iv) Seismic measurements

24. Resource identification and development  Exploratory drilling and production testing is then used to establish reservoir properties  Deep drilled survey wells commonly reach depths of 6 km, and the technology is available to drill to 15 km  Drilling technology derived from –petroleum industry  Geothermal drilling- challenging and expensive  Temperatures of upto 350 0 C encountered and higher than those in oil well drilling  hard volcanic rock needs to be penetrated – wear of drill bit  Drilling mud used to lubricate and cool the drill bit deteriorates rapidly at temperature above 175 0 C

25. Resource identification and development  Staged development  Modestly sized plant can be installed at an early stage of field assessment  Operation of this plant would provide more information about the reservoir, which can lead to the installation of future stages

26. Resource identification and development  Recovery  Geothermal energy- not as renewable as solar and wind energy  Tapping into the local sources of the earth’s heat results in temporary decrease in the local amount of the heat available  Recovery period of geothermal resource depends on how it is used  Recent survey indicates a recovery period of 100- 200 years

27. Geothermal power generation systems  Two types  Dry Steam Power plants  Wet steam Power plants  Four types  i) Single flash steam system  ii) Double flash steam system  iii) Binary-cycle system  iv) Combined flow system

28. Dry steam power plant  “Dry” steam extracted from natural reservoir  180-225 ºC ( 356-437 ºF)  4-8 MPa (580-1160 psi)  200+ km/hr (100+ mph)  Steam is used to drive a turbo-generator  Steam is condensed and pumped back into the ground  Can achieve 1 kWh per 6.5 kg of steam  A 55 MW plant requires 100 kg/s of steam

29. Dry steam schematic

30. Single flash steam system  Steam with water extracted from ground  Pressure of mixture drops at surface and more water “flashes” to steam  Steam separated from water  Steam drives a turbine  Turbine drives an electric generator  Generate between 5 and 100 MW  Use 6 to 9 tonnes of steam per hour

31. Single Flash Steam Schematic Boyle, Renewable Energy, 2 nd edition, 2004

32. Double flash steam system  Similar to single flash operation  Unflashed liquid flows to low-pressure tank – flashes to steam  Steam drives a second-stage turbine  Also uses exhaust from first turbine  Increases output 20-25% for 5% increase in plant costs

33. Double Flash Steam Schematic

34. Binary-cycle system  Low temps – 100 o and 150 o C  Use heat to vaporize organic liquid  E.g., iso-butane, iso-pentane  Use vapor to drive turbine  Causes vapor to condense  Recycle continuously  Typically 7 to 12 % efficient  0.1 – 40 MW units common

35. Binary Cycle system Schematic Boyle, Renewable Energy, 2 nd edition, 2004

36. Combined flow system  Combination of conventional steam turbine technology and binary cycle technology  Steam drives primary turbine  Remaining heat used to create organic vapor  Organic vapor drives a second turbine  Plant sizes ranging between 10 to 100+ MW  Significantly greater efficiencies  Higher overall utilization  Extract more power (heat) from geothermal resource

37. Geothermal Energy Plant Geothermal energy plant in Iceland http://www.wateryear2003.org/en/

38. Geothermal Well Testing http://www.geothermex.com/es_resen.html Geothermal well testing, Zunil, Guatemala

39. Heber Geothermal Power Station http://www.ece.umr.edu/links/power/geotherm1.htm 52kW electrical generating capacity

40. Geysers Geothermal Plant The Geysers is the largest producer of geothermal power in the world. http://www.ece.umr.edu/links/power/geotherm1.htm