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Content archived on 2022-12-27

MARTA GEOTHERMAL PLANT FOR ELECTRIC ENERGY PRODUCTION

Objective

Utilization of a medium-temperature (180 deg. C) water-dominated geothermal resource, found in Marta geothermal field in Bolsena area near, the lake of the same name in northern Latium, for the production of electric energy (3 MW) by means of binary cycle unit (ORC). The main innovative aspects are : the utilization of a medium-temperature geothermal resource in a water-dominated field; the use of a binary unit (ORC) directly fed by the two-phase fluid delivered by the producing well; the use of air coolers for the binary unit; the continuous use of a carbonate scale inhibitor for the producing well. The electric energy is fed into the Italian distribution grid and replaces production from thermoelectric units. The payback time for the investments results of 8.6 years.

The wells Marta 1 and Marta 4, productive to a depth of approximately 2000 m, were drilled in Marta geothermal field, a reservoir of the water-dominated type, with a temperature of 180-190 deg. C. Considering the limited production capacity of the reservoir (due to its limited volume), the flow rate of fluid that can be extracted to obtain an operating period of at least 10 years was estimated at 200 t/h. The production parameters of well Marta 1 are as follows :
- flow rate 200 t/h
- total dissolved salts 20-40 g/l
- noncondensable gas content in the fluid 2% by weight
- composition of noncondensable gases (% by weight) : CO2 > 99%
H2S 0.5%
others (H2, N2, O2, CH4, He) complement to 100%
- temperature of geothermal fluid at wellhead 174 deg. C
- operating pressure 13 bars
- enthalpy of geothermal fluid 750 kJ/kg
The utilization plant for the geothermal fluid made available by well Marta 1, consists in a loop that envisages reinjection in well Marta 4 (1.8 km away), for the production of electric energy by means of binary cycle unit with organic working fluid. The production of well Marta 1 is started with the air lift method.
The produced fluid is treated, inside the well, with a carbonate scale inhibitor and feeds, two-phase status, the binary unit. The geothermal fluid leaving the binary unit is then sent to the pressure separator in which the aeriform phase is sent to the cooling tower's fan cyclinder to be dispersed into the atmosphere. The separated liquid phase is sent to well Marta 4 means of a reinjection pipeline; the reinjection in Marta 4 occours by gravity.
The plant includes a startup loop, equipped with an atmospheric separator and a spent brine collection basin.
The plant is complete with the necessary cutoff, regulation and control devices, electrical system for connection to the grid and the distribution switchboard, in addition to monitoring equipment and civil works.
The binaryunit, arranged to maximise power output are fed directly by the geothermal fluid from the well.
The binary unit will be air-cooled.
In the conditions foreseen at Marta the binary unit are capable of generating a gross power on the order of 3000 kW.
To feed the auxiliaries of the binary unit and the other components of the separating plant, an overall absorption of about 500 kW can be estimated.
The installation of binary unit at Marta constitutes the first case of electric power production from a medium-temperature (180 deg. C) water-dominated field in the EC.
There are no other known cases in which binary unit are fed with two-phase geothermal fluid. The net electric energy fed into grid is 20,000 MWh/year and replaces production from thermoelectric sources.

Call for proposal

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Coordinator

ENEL SPA (DPTNDT/G)
EU contribution
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Address
VIA ANDREA PISANO 120
56122 Pisa
Italy

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