Objective
To generate electricity using high temperature geothermal brines produced by Cesano 7 and Cesano 8 wells (supported by EEC contract GE/00003/79), together with Cesano 5 reinjection well.
First tests to be performed with a 1 MWe turbine, the ultimate objective is a double flash power plant with a rated energy output of 8 MWe.
The innovative aspects of the project are given mainly by the high salinity of the geothermal brine, with the related problems of scalling and in fluid transportation and separation.
The separation plant set up at Cesano 7 well as the first flash stage did not show any type of working problem during the short period of use.
The cause which determined the interruption of the experimentation was the high, and unexpected, H2S content in the geothermal brine produced. The analyses carried out during the short tests showed an H2S content in the noncondensable gas over 8% by volume, i.e. 6.5% by weight, compared with typical figures of other geothermal fluids variable from 0.5 to 1% by weight (and even less in well Cesano 1).
The noncondensable gas content in the brine was about 7% by weight, so that 5 g of H2S per kg of geothermal fluid produced were discharged into the atmosphere. As the well produced 235 t/h of brine, the emission rate of H2S was more than 1000 kg/h, comparable with the H2S discharged from 20 geothermoelectric units of 20 MW each.
The emission of these high quantities of H2S was clearly unsustainable from the environmental standpoint and therefore determined the end of the experimentation.
H2S abatement, though technically possible, was not considered economically feasible with the currently marketed technologies.
The project foresaw the utilization of 500 t/h of geothermal brine. Fluid characteristics rather different between existing wells obliged the use of Cesano 7 for production (flow rate: 170 t/h, enthalpy: 230 kcal/kg, CO2 content: 5%, TDS: 80 g/l), the abandonment of Cesano 8 and reinjection in Cesano 5. The first stage entailed assembling a separator as the high pressure single flash unit at well Cesano 7, designed for a flow rate of 500 t/h, along with simulation tests of the discharging to the atmosphere turbine (nominal output: 1 MWe) and reinjection tests on Cesano 5 well, connected through Cesano 1 well basin, some 11 km away.
The second stage included the installation of a 1 MW generator at well Cesano 7 in order to finalise arrangements for full-scale operation before fitting the second flash (low pressure) unit. The testing of Cesano 7 well had to provide more information on the geothermal reservoir, corrosion, scalling and other data needed for the design of the power plant, while the simulation tests should have given all the data needed for the optimisation of the plant. The addition of the second separation stage would have then allowed the production of second flash steam almost free of gas, to be utilized by a low-pressure condensation turbine, having performed in the previous one the elimination of the incondensable gases.
The drilling of more wells (programmed in the area by ENEL) was necessary to reach the design flow rate of geothermal brine.
Only the construction of the first flash stage needed to feed a 1 MWe turbogenerator unit with the fluid delivered from Cesano 7 (approximately 170 t/h) well was carried out, together with short tests on Cesano 7 well.
Further drilling in the area yielded negative results.
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
00198 ROMA
Italy