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LECTURE 21 Geothermal Energy

LECTURE 21 Geothermal Energy. Dr. Rostamkolai. ECE 371 Sustainable Energy Systems. INTRODUCTION. Geothermal energy is the energy captured from the heat of the earth For a long time this has been observed as Volcanoes Geysers Hot Springs. INTRODUCTION.

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LECTURE 21 Geothermal Energy

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  1. LECTURE 21Geothermal Energy Dr. Rostamkolai ECE 371 Sustainable Energy Systems

  2. INTRODUCTION • Geothermal energy is the energy captured from the heat of the earth • For a long time this has been observed as • Volcanoes • Geysers • Hot Springs

  3. INTRODUCTION 10% of this thermal energy is remnant heat from about 4.5 billion years ago, when earth was formed 90% of this thermal energy is from radioactive decay of elements such as uranium, thorium, and potassium Center core of earth is solid and its temperature is greater than 5000oC

  4. INTRODUCTION Surrounding this core is a liquid iron with a temperature of about 4000oC About 99% of the mass of earth has a temperature greater that 200oC At a depth of about 10 km below the surface, temperatures are as high as 300oC

  5. INTRODUCTION A review of geothermal sources noted that thermal energy is available in the upper 10 km of the earth’s crust with a mean temperature gradient of 20-30oC/km However, the thermal concentration of the rock (kJ/m2) is too diffuse to be an exploitable resource on the worldwide basis

  6. INTRODUCTION • Geothermal resources are localized geologic deposits of heat at attainable depths, confined volumes, and sufficient temperatures • 180oC – good for electricity production • 100oC - for thermal energy utilization

  7. INTRODUCTION • There are 4 types of thermal deposits • Hydrothermal – trapped steam or hot water • Vapor-dominated – dry steam [ very rare, temp. > 175oC] • Liquid-dominated – hot water [ 150-315oC] • Geopressurized – sedimentary formations that contain hot water and natural gas (methane) [150-180oC, 9000 psi] • Magma – lava that has risen to reachable depths (less than 20 km) [above 650oC] • Enhanced Geothermal Systems (EGS) – high temperature dry rock formation [above 200oC]

  8. INTRODUCTION

  9. INTRODUCTION

  10. INTRODUCTION • The conversion of geothermal fluids into electric energy is similar to conventional power plants • Geothermal steam contains impurities • Solid particulates • Hydrogen sulfide • Radon • Gases are not permitted to be released to the atmosphere

  11. INTRODUCTION • Problems caused and remedies are • Solid particulates eat through metals • They are removed by centrifugal separators at the well head • Non-condensable gases form acids under wet conditions • Stainless steel and other expensive material are used to reduce corrosion

  12. INTRODUCTION • Additionally, the steam temperature is much lower than the steam in the boiler • Efficiency of conversion to electricity is lower • 12 to 15 % instead of 35 to 40% for conventional power plants • Also, about three times the steam fluid flow is required for higher efficiencies

  13. INTRODUCTION The following table shows the geothermal generation and capacity as a percentage of the total renewables in the U.S.

  14. INTRODUCTION In 2002, the 13.36 GWh of geothermal energy can supply about 0.4% of the 3391 GWh of electricity generation in the U.S.

  15. GEOTHERMAL ENERGY Geothermal energy is not renewable in a real sense However, it is an inexhaustible source of energy It can be tapped from the underground water reservoirs, if Qremoved = Qreplenished

  16. GEOTHERMAL ENERGY Geothermal resource can be used directly or transformed into electricity Fig 8.1

  17. GEOTHERMAL ENERGY However, the final yields, in terms of energy, are different Fig 8.2

  18. GEOTHERMAL ENERGY Annual direct-use energy from geothermal sources for different regions of the world is shown below Figure 8.4

  19. GEOTHERMAL ENERGY Annual electric energy producedfrom geothermal sources for different regions of the world is shown below Fig 8.3

  20. GEOTHERMAL ENERGY

  21. GEOTHERMAL ENERGY Geothermal energy sources at temperatures greater than 150oC are available at depths ranging from 1500 m to 3000 m (good for electricity production) At smaller depths of below 1000 m the temperature is between 90oC and 150oC (good for thermal utilization)

  22. GEOTHERMAL ENERGY • Geothermal sources can be classified as • High temperature – Electricity prod. & direct heating • Greater than 160oC • Medium temperature – Electricity prod. & direct heating • 90 – 160oC • Low temperature – Heat pump for heating & AC • 30 – 90oC • Very low temperature – Heat pump for heating & AC • Less than 30oC

  23. DIRECT USE • It is possible to exploit this energy to produce water at high temperatures (η = 50 - 70 %) • Cold water is injected into a well 5000 m deep • Injected water causes hot rocks to crack and release heat • Heated water diffuses and recovered in other wells • Hot water is pumped through a heat exchanger to heat air or liquid that is circulated to heat a building

  24. GEOTHERMAL ENERGY

  25. ELECTRICITY PRODUCTION Dry-Steam: Steam extracted and cleaned before entering the turbine (15 – 120 MW) Fig 8.6

  26. ELECTRICITY PRODUCTION Flash-Steam: Liquids extracted at high temp. & converted into steam (10 - 55 MW) Fig 8.7

  27. ELECTRICITY PRODUCTION Binary-Cycle: Water or steam from reservoir never comes in contact with turbine (1 MW) Figure 8.8

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