Abstract
The impact of natural CO2 emissions in the development of geothermal areas is presently gaining more attention than ever before. In Italian geothermal fields, a reduction in the natural CO2 emissions has been observed. This paper reviews and provides an analysis of the historical production data of boric acid from 1818 to 1867 used to calculate the natural emissions of CO2 associated with boric acid production that pre-dates the use of geothermal resources for power production, which started in 1913. Boric acid was already being extracted from the natural geothermal fluids in geysers and natural ponds emitting steam and gases. After 1827 the ‘lagone coperto’ (covered lake) equipment optimized production, and the drilling of shallow wells (20–30 m) starting in 1836, which further increased the quantity of its extraction. The first geothermal reservoir was developed at the turn of the century and the Larderello geothermal field began to grow. The use of deep wells, keeping pace with the power production, led to the gradual disappearance of the natural ponds and the ‘lagoni’ (lakes) in the historical area, so the residual natural emission of CO2 is presently restricted to diffuse soil emission. Comparisons of the ancient CO2 emissions with those of the Geothermal Power Plant (GPP) in the Larderello area show that both amounts are in the same order of magnitude, suggesting a balance between the depletion of natural emissions and geothermal activity.
Highlights
The question about CO2 emissions from geothermal power plants has become increasingly important as discussions on climate change have become more common
The rate of natural emission can be altered by fluid extraction in the wells used for power production and district heating or, as has occurred in the past in the Larderello area, for boric acid production
In the Larderello area, natural emission from steam and gas vents progressively disappeared while the steam collection by wells grew, suggesting that the rate of natural soil emission depends on the interplay between the natural mechanism of gas emission from the soil and the utilization and extraction of steam in the geothermal field
Summary
The question about CO2 emissions from geothermal power plants has become increasingly important as discussions on climate change have become more common. The emissions from geothermal energy utilization have been considered non-anthropogenic because they are natural source fluxes released into the atmosphere by natural surface venting. Carbon dioxide is released to the atmosphere naturally from geothermal fields through: soil flux, steam vents, fractures, steam heated mud-pools, and thermal springs. The rate of natural emission can be altered by fluid extraction in the wells used for power production and district heating or, as has occurred in the past in the Larderello area, for boric acid production. In the Larderello area, natural emission from steam and gas vents progressively disappeared while the steam collection by wells grew, suggesting that the rate of natural soil emission depends on the interplay between the natural mechanism of gas emission from the soil and the utilization and extraction of steam in the geothermal field
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