A few representative case studies have been selected for which the available data allow a more detailed analysis. These case studies are the Villafortuna-Trecate and Gaggiano fields in Northern Italy (Middle Triassic petroleum system in the thrust belt in Northern Italy) and the Irminio field (Late Triassic–Early Jurassic petroleum system in the Hyblean foreland domain in Sicily).
4.1. Villafortuna-Trecate
Villafortuna-Trecate is a field located in the Piemonte region, between the municipalities of Trecate, Romentino, and Galliate (
Figure 4). The larger part of the wells is near Galliate and Romentino. A cascade plant system composed of an Organic Rankine Cycle (ORC) power plant, a district heating plant, and an aquaculture plant is proposed. One system will serve the municipality of Galliate and a second one the Romentino. For the municipalities of Galliate and Romentino, there are, respectively, six wells and three wells available. The produced water, after use, will be sent to existing reinjection wells.
From literature data and based on a previous analysis of productive well potential [
14], the single well can produce a flow rate of 100 kg/s of hot water having a wellhead brine temperature of 130 °C.
The geothermal fluid is supplied first to the ORC plant. A thermodynamic analysis of the binary plant, the working fluid selection (isobutane), the sizing of the condenser, and the cooling tower is included. To evaluate the number of supplied consumers, a precautionary consumption per capita of 1400 kWh per year was assumed.
From the preheater of the ORC plant, the geothermal fluid at a temperature of 84 °C is fed to the district heating (DH) plant. Assuming a heating request of 2 kW per person, the number of inhabitants served was evaluated. The geothermal brine exits from the heat exchanger of the DH plant at the temperature of 50 °C, suitable for aquaculture applications.
For the aquaculture plant, the selected species is shrimp, which need a constant water temperature of 35 °C. Indoor ponds constitute the plant. The annual heat requirement supplied by the geothermal energy includes the heat loss from convection, radiation, and evaporation. The evaluation assumes the following mean values for air properties: air temperature of 20 °C, relative humidity of 30%, and saturation pressure of 0.007 bar.
Table 2 and
Table 3 illustrate the basic data of plants and economic pre-feasibility.
The results indicate that the proposed power plants, whose size guarantees a surplus of energy to be sold, can supply the yearly electrical demand of Galliate and Romentino municipalities. The cost of the power plants was obtained considering a mean value of 2000 €/kW. An energy price of 0.06 €/kWh and a working time of 7500 h were used to evaluate the annual revenues. The estimated annual revenues ensure the recovery of the investment in 4.5 years for the power plant of Galliate and in 5 years for the power plant of Romentino.
The DH plants may guarantee the cover of the thermal need of 71% of inhabitants of Galliate and 100% of inhabitants of Romentino. To estimate the DH plant cost, a value of 1800 €/kW was used. Considering 3110 working hours per year and a price of thermal energy equal to 0.075 €/kWh, the investment cost would be recovered in about eight years for both of the municipalities.
For the economic evaluation of the aquaculture plants, two values were used for the installation cost, 155 €/m2 for the plant of Galliate and 163 €/m2 for the plant of Romentino. Considering a price of 7 €/kg for the shrimp and a shrimp production of 4.5 kg/m2, the payback period would be about five years for both of the plants.
4.2. Gaggiano
The oil field of Gaggiano is located in the southwestern portion of the Province of Milan and belongs to Middle Triassic petroleum system in the thrust belt in Northern Italy. The selected wells are located near the municipalities of Tainate and Noviglio (
Figure 5). The production performance, based on the analogy with the Trecate field, is more conservative with a flow rate of 50 m
3/h, and the wellhead temperature of the water is estimated to be 125 °C. Considering the availability of two production wells and one injection well, and the agricultural vocation of the territory, the proposed cascade scheme is composed of a DH plant, a greenhouse, and an aquaculture plant.
From the two wells, it is possible to obtain a thermal power of 6 MW; 2 MW will be used to feed the greenhouses and 4 MW to feed the DH plant. For both of the plants, the outlet temperature of the feeding water is 70 °C; this fluid will be mixed with water at 20 °C to supply the thermal request of an aquaculture system.
Assuming a heating request of 2 kW per person, the plant may guarantee the cover of the thermal need of 40% of inhabitants of Gaggiano. Using the same hypotheses of the Trecate case study for the plant cost, energy price, and the total number of working hours, the recovery time of investment cost is 7.4 years.
For the 6000 m2 of greenhouses in Gaggiano, the total installation cost is 0.33 M€. Considering as reference cultivation tomatoes, the selling price was assumed equal to 1.0 €/kg. The annual revenue of 0.09 M€ guarantees that in 3.67 years, the investment may be recovered.
Using the same evaluation procedure and the same species previously described for Galliate and Romentino aquaculture plant, the Gaggiano aquaculture plant presents a payback time of 5.1 years.
Table 4 illustrates the basic data of plants and economic pre-feasibility.
4.3. Irminio
The Irminio oil field (
Figure 6) is located near the Irminio River between the municipalities of Ragusa and Scicli. The Irminio field belongs to the Late Triassic–Early Jurassic petroleum system in the Hyblean foreland domain in Sicily. There are currently four production wells and an oil centre, where oil is separated from natural gas and water and stored before marketing.
An evaluation of possible use in a greener way of the wells was studied. As a result, the oil company installed a cogeneration unit (CHP) with thermal power of 570 kW and electrical production of 360 kW. The proposed solution was to design a roadmap for the conversion of the plant into a green plant, based on the use of produced heat both from wells and CHPs, to produce biogas and biomass for biodiesel production.
The flow rate produced by wells at a temperature of 40 °C is sent to a heat exchanger to heat the anaerobic digester. To satisfy the thermal power demand of the digester, a part of the produced heat from the CHP is also supplied. The process temperature is around 35 °C, working with mesophilic bacteria. The digester was designed based on the population in Scicli (262,000 people) and assumed to have an organic waste production of 130 kg per capita. The residence time chosen was 30 days for the digester and 60 days for the storage tank to obtain good digestion of the biomass. The daily production is 4038 m3 of biogas. The biogas can feed the CHP unit.
The larger part of the produced hot water from the CHP is used to produce algae. The algae farm is built close to a power plant, the CO2 produced by the power plant could be utilized as a carbon source for algal growth, and the carbon emissions would be reduced by recycling waste CO2 from power plants into clean-burning biodiesel. Practically, all the CO2 produced by the cogenerator will be introduced in the indoor pond to feed the algae. In this way, it is possible to feed 1800 m2 of ponds for algae cultivation.
The biogas power plant (
Table 5) has a total installation cost of 2.05 M€. Considering the price of electricity equal to 0.06 €/kWh, the annual revenue from electricity is 151,200 €. Taking into account that almost 1000 m
3 of biogas per day are consumed to supply the CHP, the remaining 1.1 Mm
3 of biogas can be sold each year, generating an annual income equal to 0.24 M€. The total annual revenue will be around 0.4 M€ and a simple payback period of 5.2 years is obtained.
In Gela, on the refinery site is going to build a plant to distillate algae and produce biodiesel. This opportunity can be assumed to reduce the investment cost to build only the cultivation part to 170 €/m
2. The total installation cost (
Table 6) concerning the 1800 m
2 of indoor ponds is 306,000 €. The annually produced biodiesel is 155,000 L and, considering a price of biodiesel equal to 0.452 €/L, the annual income is 70,000 €. A simple payback period of 4.37 years is found. Of course, the cost for transporting algae must be taken into account for a more detailed analysis.