HEAT OF THE EARTH.

Press, Volume LXIII, Issue 19156, 12 November 1927, Page 8

HEAT OF THE EARTH.

♦ —- SUGGESTED UTILISATION HIGH TEMPERATURE AREAS. (FROM OUR OWN CORRESPONDENT.) LONDON, September 30. During the Bession of the British As> Bociation at Leeds, Mr J. L. Hodgson, in a paper read before the Section of Engineering on "An Examination oi the Problem of Utilising the Earth's Internal Heat,'' said if there seemed a possibility that we could, at little oi no increase of cost, obtain the heat we required from the hot rocks which were everj'where beneath us, instead of by destroying a highly elaborated chemical substance such as coal, that possibility was worth careful consideration and examination. A simple calculation showed that a cubic mile of hot rock cooled down by lOOOdeg. Fah., would yield as much heat as the burning of 200,000,000 tons of coal, which heat, if used at 20 per cent, efficiency, would maintain 50,000,000 horse-power for one year. An extension, of the calculation showed that the heat stored in the hot rocks of the earth's interior was at least 30,000,000 times the heat available in the world's coal reserve. Only a small section of this heat, available down to a depth of say, 30 miles under the land areas, was, however, likely to be of interest to engineers during the next few centuries. Use of Thermal Springe. In Iceland thermal springs had long been used to- warm the soil, and so assist the growth of vegetables, while the Maoris at Whakarewarewa ÜBed the heat obtained from such springs for washing and cooking. At Larderello, and a£ Big Sulphur Creek, near San Francisco, experiments had been made with bore-holes. At the latter place four bore-holes delivered 137,5001b per square inch. In these cases the hot water or steam was produced by water penetrating porous or fractured surface rocks, which had been raised to a high temperature and absorbed a part of their residual heat. There were many such high temperature areas available around the bases of Vesuvius, Etna, Hecla, and other volcanoes. Though the abstraction of heat from such areas scarcely touched upon the real problem of utilising the earth's internal heat, it had been shown that they yielded very large elements of power. Boring for Heat. Mr Hodgson discussed two types of possible bore-holes. The first he termed i "low temperature" type, which would penetrate only to such depths that suitably cooled workers could' control the machines which did the drilling and sleared away the debris. The second type would penetrate rocks or volcanic pipes which were of such high temperature that it was impossible for the workers to descend into the passages, leat bore-holes of this type would have to be made by means which were controlled at the surface. Calculations showed that bore-holes 10 miles deep and 2ft in diameter, or 30 niles long and 10ft diameter at a depth if 5 miles, should be capable of a coninuous heat yield of 4000 h.p.