VAPOUR TURBINE
The present invention relates to a vapour turbine which can be used for obtaining energy from geothemial vapours.
Vapour turbines which operate with geothermal vapours come into contact with aggressive and/or corrosive substances for the components of the turbine itself.
Even small quantities of aggressive substances such as chlorides and sulfides, cause the corrosion of the vapour turbine components, such as rotor blades, stator blades and sealing laminas.
The materials currently used for vapour turbine components are martensitic stainless steels which are strongly subject to con'osion phenomena on the part of aggressive and/or corrosive agents.
The corrosion is particularly high in the transition area between overheated vapour and damp vapour (Dew Point).
In this area, the solid particles contained in the geothermal vapour form large deposits on the surface of the blades.
During the functioning of the turbine, the deposits accelerate the corrosion process due to the increase in localized concentration of corrosive agents such as chlorides and sulfides.
CoiTosion of the turbine components jeopardizes the correct functionality of the turbine itself as well as the preventive maintenance plan programmed for it. In order to reduce maintenance interventions and consequently also substitution of the components themselves, the geothennal vapours containing aggressive substances in a higher quantity than a predetermined percentage, are "washed" with water. This reduces the concentration of aggressive substances present in the geothermal vapours.
A first disadvantage is that the washing operations of geothemial vapours causes an increase in the running and maintenance costs of the plant, also increasing its complexity.
Another disadvantage is that washing the vapour reduces the enthalpy available at the turbine inlet and consequently the useful work of the turbine itself is reduced. An objective of the present invention is to provide a vapour turbine operating with overheated geothemial vapours nomially containing corrosive agents which avoids the washing of said geothemial vapours.
A further objective is to provide a vapour turbine operating with geothemial vapours, nomially containing corrosive agents which has a high conversion efficiency of the energy available at the inlet.
Another objective to provide a vapour turbine operating with geothennal vapours, normally containing corrosive agents, which operates with overheated geothemial vapours and which has a high useful life.
Yet another objective to provide a vapour turbine operating with geothermal vapours, nomially containing conosive agents having reduced maintenance costs. These objectives according to the present invention are achieved by providing a vapour turbine as illustrated in claim 1.
Further characteristics of the invention are indicated in the subsequent claims. The characteristics and advantages of a vapour turbine operating with geothemial vapours will appear more evident from the following illustrative and non-limiting description of the present invention.
According to the present invention, a vapour turbine is provided, operating with geothemial vapours containing aggressive or corrosive agents such as chlorides and/or sulfides in particular.
The vapour turbine comprises a series of stator blades and a series of rotor blades, each stator blade of said series of stator blades comprises a surfacing consisting of a nickel alloy containing a quantity of nickel ranging from 54% to 58% by weight to avoid the washing of said geothemial vapours, at the same time maintaining a high useful life of said series of stator blades and said vapour turbine. It is advantageously possible to convert, by means of said turbine, a greater quantity of energy as the non-washed geothemial vapours have a higher enthalpy with respect to washed geothemial vapours.
Said turbine is ad\ antageously particularly efficient for geothemial vapours containing a quantity of chlorides higher than 2 ppni avoiding the washing thereof. Said nickel alloy is preferably a nickel-chromium-molybdenum alloy. Said nickel alloy preferably comprises a quantity of chromium ranging from 21% to 23% by weight, a quantity of molybdenum ranging from 12% to 14% by weight. Said nickel alloy is preferably a super-alloy of nickel known commercially as HASTELLOY C22.
Said surfacing made of nickel alloy preferably has a thickness ranging from 20 µm to
250 |.mi.
Said turbine preferably also comprises a series of sealing laminas made of said nickel
alloy and in particular made of HASTELLOY C22.
The purpose of this is to avoid the washing of said geothermal vapours, maintaining a high usefiil life of said series of stator blades and said series of sealing laminas of said vapour turbine.
Each rotor blade of said series of rotor blades of said vapour turbine preferably comprises a surfacing made of chromium carbide to avoid the washing of said geothemial vapours, at the same time maintaining a high useful life of each rotor blade and of the
vapour turbine itself.
Said surfacing consisting of chromium carbide preferably has a thickness ranging
from 100 µm to 700 µm.
According to a further aspect of the present invention, the use of a surfacing consisting of a nickel alloy, in particular HASTELLOY C22, for a stator blade of a \ apour turbine operating with geothemial vapours containing corrosive agents, such as chlorides and/or sulfides in particular, is evident to avoid the washing of said geothemial vapours, maintaining a high useful life of said stator blade.
According to another aspect of the present invention, the use of a surfacing consisting of chromium carbide for a rotor blade of a vapour turbine operating with geothemial vapours containing corrosive agents, such as chlorides and/or sulfides in particular, is evident, to avoid the washing of said geothemial vapours, maintaining a high useful life of said rotor blade.
Advantageously a vapour turbine of the present invention is capable of operating with overheated geothemial vapour and is also capable of avoiding washing operations of the geothemial vapour when this contains corrosive substances such as chlorides and/or sulfides in a quantity higher than 2 ppm,.
It can thus be seen that a vapour turbine according to the present invention achieves the objectives specified above.
The vapour turbine of the present invention thus conceived can undergo numerous modifications and variants, all included in the same inventive concept. Furthemore, in practice, their dimensions and components can vary according to technical demands.

CLAIMS
1. A vapour turbine operating with geothermal vapours containing corrosive agents or aggressive substances such as chlorides and/or sulfides in particular, said turbine comprising a series of stator blades and a series of rotor blades, characterized in that each stator blade of the series of stator blades comprises a surfacing consisting of a nickel alloy containing a quantity of nickel ranging from 54%) to 58% by weight, to avoid the washing of the geothermal vapours, at the same time maintaining a high useful life of the series of stator blades and vapour turbine.
2. The turbine according to claim 1, characterized in that said nickel alloy is a nickel-chromium-niolybdenum alloy.
3. The turbine according to claim 1 or 2, characterized in that said nickel alloy comprises a quantity of chromium ranging from 21% to 23% by weight and a quantity of molybdenum ranging from 12% to 14% by weight.
4. The turbine according to any of the claims from 1 to 3, characterized in that
said surfacing consisting of nickel alloy has a thickness ranging from 20 µm to 250
µm.
5. The turbine according to any of the claims from 1 to 4, characterized in that it
comprises a series of sealing laminas made of said nickel alloy to avoid the washing of said geothemial vapours, maintaining a high useful life of said series of sealing laminas and said vapour turbine.
6. The turbine according to any of the claims from 1 to 5, characterized in that each rotor blade of said series of rotor blades comprises a chromium carbide surfacing.
7. The turbine according to claim 6, characterized in that said chromium carbide
surfacing has a thickness ranging from 100 µm to 700 µm.
8. Use of a nickel-chromium-molybdenum alloy surfacing for a stator blade of a vapour turbine operating with geothermal vapours containing corrosive agents, such as chlorides and/'or sulfides in particular, to avoid the washing of said geothermal vapours, maintaining a high useful life of said stator blade.
9. Use of a chromium carbide surfacing for a rotor blade of a vapour turbine operating with geothermal vapours containing corrosive agents, such as chlorides and/or sulfides in particular, to avoid the washing of said geothermal vapours, maintaining a high useful life of said rotor blade.
10. A vapour turbine as previously described and illustrated and for the puiposes specified above.