school energy&environment

Clean energy

Geothermal energy is universally considered a clean energy.  The characteristic that makes this source renewable and preferable to the others is its constant availability. In fact in the case of geothermal energy , electricity is available  24/24h, 365 days a year. In its natural condition, the geothermal fluid is present in the reservoir in the form of steam, as is the case in Italy in Larderello; or in the liquid form as on Mount Amiata.  In both situations, a layer of impermeable rock isolates the geothermal reservoir from the water of the surface aquifers. Steam is generally associated with other  gases, such as H₂S and CO₂ in variable amounts, and it is the percentage of these so-called non-condensable gases associated with the temperature of the fluid that subsequently determines the possibility of reinjecting or not reinjecting all the fluid to recharge the reservoirs  again.
In order to extract this fluid with maximum respect and protection of the surface aquifers, the wells are shaped like upside-down telescopes, to guarantee the absence of geothermal fluid contamination as it moves to the surface. In this course, the fluid changes state and partially transforms into steam. Consequently, a mixture of steam is obtained,  characterized by a high temperature and therefore a high energy content. For fluids of this type, all over the world, a circuit with direct steam admission and evaporative type cooling towers is utilized. The fluid coming from the well is forwarded to the power plant through an integrated fluid transportation network which has been designed and created choosing courses that follow the morphology of the land and vegetation, exploiting the discontinuities for a better insertion.
Furthermore, in the tracts that are more visible, plant screens are created in order to reduce the visual impact of the geothermal fluid  extraction and transportation operations. From the steam pipes, the high-temperature fluid  is forwarded directly to the turbine, and electricity is generated.
The fluid is then channelled to the condenser where the steam returns to the liquid state while the gas is separated and then treated.
The new generation power plants in Italy are provided with the best technologies available in the environmental sector.  The treatment is carried out using  AMIS  technology for the abatement of hydrogen sulphide H2S and mercury emission. The process enables the abatement of a very high percentage of mercury and hydrogen sulphide. The water extracted from the condenser is sent to a wet cooling tower where it cools by  evaporation. The part that evaporates newly in the process is released in the atmosphere while the surplus liquid part is reinjected in the geothermal reservoir.
The new generation cooling towers are designed in avant-garde technology plants, with very high efficiency equipment to eliminate the droplets in the atmosphere, the drift, and with low-noise fans; they are also much smaller than those of the past and are much more compatible with the surrounding landscape.
Energy forever?
The Earth’s energy is apparently inexhaustible, at least when measured relative to human age span. However even the exploitation of geothermal fields must be carried out with a careful control and a sparing management of the resources.
Geothermal fields tend progressively toward a natural decline that can be effectively contrasted with a studied and targeted reinjection process, through a detailed knowledge of the reservoir. An incorrect reinjection could in fact lead to a cooling, that would decrease the productivity and self-regenerating capacity of the reservoir.