The Potential For The Exploitation Of Geothermal — страница 5

  • Просмотров 333
  • Скачиваний 5
  • Размер файла 24
    Кб

projects, and hence the risk factor that may be inadequately covered by the drilling contingency in the cost breakdown shown in (Appendix 8).? Phase 1 of this project (1977-80) saw the drilling of four 300m deep boreholes to demonstrate that controlled explosions within the boreholes could improve permeability and initiate new fractures which might then be stimulated hydraulically.? This was highly successful and target impedances of 0.1Mpa1-1 were achieved.? (Incidentally, 22°C water from a measurement borehole now supplies a small-scale, commercial horticultural scheme at nearby Penryn ? a second, albeit minor, UK use of geothermal resources) (see Boyle, G10 p388).If and when drilling and hydro-fracturing technology is improved, large areas of the UK are potentially available

for HDR development.? One estimate by the British Geological Survey is that 360 x 1018J could ultimately be available from this source, enough to provide UK electrical energy for 200 years!? However, major technological breakthroughs, coupled to a significant increase in the market price of conventional energy resources, would be needed to make HDR a viable source of power for the UK.? The Renewable Energy Advisory Group concluded in 1992 that, within the UK, market penetration by geothermal aquifer-based energy systems will be difficult and that hot dry rock systems would not be economically viable in the foreseeable future (see Boyle, G10 p391).? However, when I recently asked John Garnish Director General of Research and Development of the European Commission in Brussels about

electricity production from HDR technology in the UK.? He stated that ? the development of Hot Dry Rock continues, on a collaborate European basis, and is looking very promising.? A pilot plant generating a few MW should be built in the next five years.? If that is successful, then it is realistic to foresee this energy source being able to provide 10-15% or more of the UK?s electricity needs.Environmental ImplicationsAlthough there are many advantages to using geothermal energy, there are some environmental issues that need to be considered before the exploitation of geothermal resources can take place.Environmental concerns associated with geothermal energy include as noise pollution during the drilling of wells, and the disposal of drilling fluids, which requires large

sediment-lagoons.? Longer-term effects of geothermal production include ground subsidence, induced seismicity and, most importantly, gaseous pollution. Geothermal ?pollutants? are mainly confined to carbon dioxide, with lesser amounts of hydrogen sulphide, sulphur dioxide, hydrogen, methane and nitrogen.? In the condensed water there is also dissolved silica, heavy metals, sodium and potassium chlorides and sometimes carbonates.? Today these are almost always re-injected which also removes the problem of dealing with waste water (see Boyle G10 p380). Atmospheric emissions are minor compared to fossil fuel plants. It has been estimated that a typical geothermal power plant emits 1% of the sulphur dioxide, <1% of the nitrous oxides and 5% of the carbon dioxide emitted by a

coal-fired plant of equal size (Appendix 9) (see reference14). A geothermal plant requires very little land, taking up just a few acres for plant sizes of 100MW or more.? Geothermal drilling, with no risk of fire, is safer than oil or gas drilling, and although there have been a few steam ?blow out? events, there is far less potential for environmental damage from drilling accidents.? In direct use applications geothermal units are operated in a closed cycle, mainly to minimise corrosion and scaling problems, and there are no emissions.? So while the acidic briny fluids are corrosive to machinery such as pumps and turbines, these represent technological challenges rather than environmental hazards.The ideal geothermal development site is either in a remote location or well

screened like the quarry at Rosemanowes in Cornwall; unfortunately, not all commercially viable sites have this advantage.An HDR plant in Cornwall would produce no ?greenhouse? gas emissions, no acid rain and no long-term wastes (see Batchelor, A5 p47).? However, there will be a significant fresh-water consumption and the generation of micoearthquakes at depths well below those used in the experimental programme.? The mechanism of micro-earthquake generation is understood and the risk of triggering a damaging event is considered to be insignificant (see Engelhard, L6 p47).ConclusionGeothermal energy is not merely a hope for the future.? High temperature geothermal resources are found in many places on the earth and approximately 8,000MW of generating capacity is installed in 20