The Potential For The Exploitation Of Geothermal — страница 3

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the United Kingdom.? Therefore the future for the development of geothermal resources in the UK using heat pumps looks very promising.AquifersDue to the geographical position of the United Kingdom in relation to plate tectonics and the distribution of high heat flows, only sedimentary basin aquifers and Hot Dry Rock Technology (assisted by heat pumps) may be used.? In the mid-1970?s, the Department of Energy in association with the EEC initiated a programme of research aimed principally at assessing the UK?s geothermal resources by the mid-1980?s.? By 1984, new maps of heat flow (Appendix 5a) and of promising geothermal sites (Appendix 5b) had been produced.? Three radio-thermal granite zones stand out with the highest heat flow values, but heat flow anomalies also occur over the

five sedimentary basins identified, partly because these are regions of natural hot water upflow.? Many shallow heat flow boreholes were drilled during this period, together with the four deep exploration well sites of (Appendix 5b) and (Appendix 6) (see Boyle, G10 p386).The Southampton borehole has led to the development of the first geothermal energy and combined heat and power (CHP) district heating and chilling scheme in the UK.Following successful trials, Southampton City Council formed a partnership with Utilicom, a French-owned energy management company to form the Southampton Geothermal Heating Company (see Smith, M4 p1).This partnership exploits the hot brine (76°C) proved in the exploratory well previously drilled by the Department and the EEC at the Western Esplanade

in central Southampton (see Allen, D12 and Downing, R13).A single geothermal well, was drilled in 1981, to a depth of just over 1,800m beneath a City Centre site in Southampton (Appendix 7).? Near the bottom of the hole, 200 million year old Sherwood Sandstone containing water at 70°C was encountered.? This is both porous and permeable allowing it to hold and transmit considerable volumes of water.? The fluid itself contains dissolved salts and, as in most geothermal areas, is more accurately described as brine.? Within the aquifer the brine is pressurised and so it rises unaided to within 100m of the surface.? A turbine pump, located at 650m in the well, brings the hot brine to the surface where its heat energy is exploited.The brine passes through coils in a heat exchanger

where its heat energy is transferred to clean water in a separate district heating circuit.? Heat exchangers operate on a similar principle to many domestic hot water tanks in which a working fluid (also usually water passing through a coil of pipes in the tank) is used to heat water for washing.In this case, the cooled geothermal working fluid (brine) is discharged via drains into the Southampton marine estuary.? The heated ?clean? water is then pumped around a network of underground pipes to provide central heating to radiators, together with hot water services (see Boyle, G10 p354).A scaled-down district-heating network was installed in 1989, and initially served the Civic Centre, Central Baths and several other buildings within a 2km radius.? Today with improved heat

extraction from the geothermal brine, using heat pump technology, the scheme also includes the BBC South headquarters, Novotel and Ibis Hotels, ASDA, Southampton Institute, Royal South Hants Hospital, West Quay Shopping Centre and many other buildings (see Smith, M4 p1-6).The geothermal heat supply, originally 1 mega watt thermal (1MWt), has now been increased to 2MWt using heat pumps, and this is capable of satisfying the base load demand.? However, during periods of higher demand, fossil fuel boilers boost the plant?s heat output to a maximum of 12MWt.? The Southampton Geothermal Heating Company, which now runs the operation, charges the modest sum of about 1 penny per KWh of heat energy consumed, but it must be emphasised that neither the drilling nor the testing costs were

met by the company, and the scheme was partly financed as an EC demonstration project.? Moreover, most similar geothermal district heating schemes require the drilling and operation of a waste brine re-injection well.? Nevertheless, the scheme is seen as environmentally acceptable, and is saving over a million cubic metres of gas (of 1000 tonnes of oil) a year (see Boyle, G10 p355).The Southampton City Geothermal and CHP scheme provides a useful case study within the UK of a small-scale geothermal scheme that actually works.? So why are geothermal aquifers not being exploited much more widely?? The problem is not just one of marginal economics and geological uncertainty, but is to do with the mismatch between resource availability and heat load, itself a function of population