Geological and Thermodynamic Analysis of Low Enthalpy Geothermal Resources to Electricity Generation Using ORC and Kalina Cycle Technology

Article Geological and Thermodynamic Analysis of Low Enthalpy Geothermal Resources to Electricity Generation Using ORC and Kalina Cycle Technology

Michał Kaczmarczyk * , Barbara Tomaszewska and Leszek Paj ˛ak

Department of Fossil Fuels, Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, 30-059 Kraków, Poland; [email protected] (B.T.); [email protected] (L.P.) * Correspondence: [email protected]

Received: 11 February 2020; Accepted: 12 March 2020; Published: 13 March 2020

Abstract: The article presents an assessment of the potential for using low enthalpy geothermal resources for electricity generation on the basis of the Małopolskie Voivodeship (southern Poland). Identification the locations providing the best prospects with the highest efficiency and possible gross power output. Thermodynamic calculations of power plants were based on data from several geothermal wells: the BańskaPGP-1, BańskaIG-1, BańskaPGP-3 and Chochołów PIG-1 which are working wells located in one of the best geothermal reservoirs in Poland. As the temperature of geothermal waters from the wells does not exceed 86 ◦C, considerations include the use of binary technologies—the Organic Rankine Cycle (ORC) and Kalina Cycle. The potential gross capacity calculated for existing geothermal wells will not exceed 900 kW for ORC and 1.6 MW for Kalina Cycle. In the case of gross electricity, the total production will not exceed 3.3 GWh/year using the ORC, and will not exceed 6.3 GWh/year for the Kalina Cycle.

Keywords: geothermal resources; geothermal water; electricity generation; organic rankine cycle; kalina cycle; geological conditions

1. Introduction The development of the energy sector, including electricity generation, increasingly takes into account the use of renewable energy sources (RES). This is particularly evident in the countries of the European Union (EU), which are obliged to reduce emissions of pollutants into the atmosphere, increase energy eﬃciency and increase the share of renewable energy in the structure of total gross energy generation [1]. However, this does not only apply to European Union countries, because it should be noted globally that in 2018 the share of renewable energy sources in total electricity generation was 26%, in heating and cooling it was 10%, while in transport 3.3% [2]. There is a change of direction in the energy market, in which RES plays an increasingly important role. This arises not only from concern for the environment, but is also an attempt to diversify energy sources in developing countries. This is particularly important in the case of electricity generation, since there is an increase in the consumption of electricity. In 2018, 181 GW of renewable energy capacity was installed worldwide for the purposes of electricity generation, and the total installed capacity reached the level of 2378 GW [2]. Analyzing data for individual renewable energy technologies, it should be noted that, by far at the end of 2018, hydropower was characterized by the largest installed capacity in the world—1132 GW. Wind energy with 591 GW came second, followed by 505 GW from photovoltaic, bio-energy with 130 GW, geothermal energy with 13.3 GW, concentrating solar thermal technologies (CSR) with 5.5 GW, and ocean energy with 0.5 GW [2]. Among the available renewable energy technologies, stable and continuous electricity generation can be provided by hydropower, biomass/biogas, and geothermal

Energies 2020, 13, 1335; doi:10.3390/en13061335 www.mdpi.com/journal/energies Energies 2020, 13, 1335 2 of 20 Energies 2019, 13, x FOR PEER REVIEW 2 of 20 geothenergyermal [3]. energy Solar power [3]. Solar (photovoltaics) power (photovoltaics) and wind and energy, wind despite energy, the despite fact that the theyfact that are thethey most are thedynamically most dynamically developing developing technologies technologies [4], are heavily [4], are dependent heavily dependent on atmospheric on atmospheric conditions, conditions, and energy andgeneration energy isgeneration often diffi iscult often to predict.difficult Henceto predict. the need Hence for the RES need development for RES developmen towards moret towards stable moresources. stable In viewsources. of theIn view above, of thethe generationabove, the generation of electricity of usingelectricity geothermal using geothermal energy isof energy particular is of particularimportance. importance. This is undoubtedly This is undoubtedly a source of energya source that of fitsenergy in with that the fits strategy in with of the a low-carbonstrategy of energya low- carbonmix becoming energy themix basisbecoming of a modern the basis economy of a modern [5,6]. economy [5,6]. TThehe temperature andand hydrogeological hydrogeological conditions conditions determine determine the the technology technology of electricity of electricity generation gener- ationusing using geothermal geothermal energy. energy Due to. Due the typeto the of type energy of carrierenergy andcarrier its temperature,and its temperature, several basic several ways basic are wayshighlighted are highlighted for converting for converting the heat energy the heat accumulated energy accumulated in geothermal in vaporgeothermal or waters, vapor as or well waters, as in hot as welldry rocks,as in hot into dry electricity. rocks, into These electricity. are dry steamThese powerare dry plants steam (180–300 power plants◦C), single-flash (180–300 °C or), double-flashsingle-flash orsteam double power-flash plants steam (150–320 power plants◦C), Organic (150–320 Rankine °C ), Organic Cycleand Rankin Kalinae Cycl Cyclee and (90–150 Kalina◦C) Cycle [7]. Most(90–150 of °Cthe) [7 geothermal]. Most of the power geothermal plants in power the world plants use in the energy world accumulated use energy accumulated in wet or less in dry wet geothermal or less dry geothermalfluids [8]. From fluids the [8 point]. From of viewthe point of the of geothermal view of the conditions geothermal in conditions Poland (temperatures in Poland (temperatures up to 100 ◦C), upit is to necessary 100 °C ), it to is consider necessary Organic to consider Rankine Organic Cycle Rankine (ORC) and Cycle Kalina (ORC Cycle) and technologies. Kalina Cycle A technologies. classification Aof classification geothermal resources of geothermal in Poland resources by temperature, in Poland enthalpyby temperature, and exergy enthalpy was presented and exergy by was Barbacki presented(2012) [by9]. Barbacki In both cases, (2012) the [9]. thermodynamic In both cases, the cycle thermodynamic is based on the cycle use is of based an additional on the use working of an addi- fluid ti(Figureonal working1)[ 10]. fluid Geothermal (Figure water1) [10]. is Geothermal extracted by water the production is extracted well, by the which production transfers well, heat which to the transfersevaporator heat with to the a working evaporator fluid with that a has working a significantly fluid that lower has a boiling significantly point temperature.lower boiling Thepoint energy temperature.released byThe the energy evaporator released causes by the the eva workingporator fluidcauses to the evaporate. working Influid the to case evaporate. of ORC In installations, the case of ORCmany installations, types of organic many working types of fluids organic are used working i.e. R600a, fluids R236aare used and i.e. R227ea. R600a, In R236a systems and based R227ea. on theIn systemsKalina Cycle, based an on inorganic the Kalina working Cycle, fluid,an inorganic a mixture working of ammonia fluid, anda mixture water, isof usedammonia [10,11 and]. The water, Kalina is usedCycle [10 uses,11 a]. changeThe Kalina in the Cycle solubility uses a of change ammonia in the in water,solubility which of isammonia related tointhe water, varying which temperature is related toof the the varying ammonia temperature/water mixture. of the Theammonia/water potential energy mixture. accumulated The potential in the energy working accumulated medium vaporin the working(associated medium with the vapor high (associated pressure of with the working the high medium pressure vapor) of the isworking used by medium a turbine vapor) connected is used to theby agenerator. turbine connected The working to the fluid generator. is returned The to working the evaporator fluid is for returned reuse. In to many the evaporator cases, geothermal for reuse. water In manyis injected cases into, geothermal the rock or water used is for injected other purposesinto the rock such or as used heat generation,for other purposes recreation such etc. as heat generation, recreation etc.

Figure 1. SimplifiedSimpliﬁed comparison comparison of of the the Organic Organic Rankine Rankine Cycle Cycle (ORC (ORC)) and and the the Kalina Kalina Cycle Cycle (based (based on [7,12on [7],)12. ]).

For the thermodynamic calculations, it was necessary to recognize recognize thermal and hydrogeological hydrogeological parameters in the research area. Małopolska Małopolska V Voivodshipoivodship located located in in southern southern Poland Poland was was selected, selected, which resulted fromfrom aa veryvery interesting interesting and and diversiﬁed diversified geological geological structure structure of theof the region, region, as wellas well as theas the fact that the first geothermal heating plant in Poland—PEC Geotermia Podhalańska S.A. operates in this area.

Energies 2020, 13, 1335 3 of 20 fact that the first geothermal heating plant in Poland—PEC Geotermia PodhalańskaS.A. operates in this area. No geothermal power plant has been commissioned in Poland. However many studies have been carried out to determine the potential of electricity generation using geothermal energy which has resulted in the “Atlas of the possible use of geothermal waters for combined production of electricity and heat using binary systems in Poland” in 2014 [13]. This study presents the locations of the 10 best prospects for electricity generation. The evaluation was done in a comprehensive manner, taking into consideration the issue of heat generation which is an indispensable process accompanying the operation of the ORC power plant, and taking into account economic and ecological factors. The results obtained, considered in the context of the amount of electricity generated in the ORC system, indicate that the area with the best prospects is the Podhale region in the Małopolska voivodeship. Studies on a laboratory installation, which will allow one to generate electricity using Polish geothermal resources, have been described in Nowak et al. (2010) [14]. This generates electricity using heat from the district heating network. Electricity production by direct geothermal steam utilization is not relevant for Poland because of accessible geothermal conditions [15]. The global experience resulting from the operation of a geothermal power plant based on the ORC and the Kalina Cycle indicates that electricity generation always takes place in combination with heat generation. The exception is one installation in Chena Hot Springs (Alaska), due to the low temperature of the geothermal source (74 ◦C). Taking into account the Polish conditions connected with the use of geothermal energy and high demand for heat, the calculation was made on the assumption that both electricity and heat will be generated. Key parameters influencing electricity generation are geothermal water temperature and flow rate. Rock mass temperature is determined by the density of the Earth’s thermal flux, thermal conductivity and specific heat of the rocks. The performance of potential geothermal exploration depends on many lithostratigraphic factors and rock tectonics, however, it can be estimated on the basis of the drilling data analysis. Based on a literature analysis [10,12,13,15–20] and considering the parameters of geothermal power plants in the world, the minimum water temperature was assumed to be 74 ◦C and the geothermal flow rate to be 100 m3/h. The temperature standard is based on the operating parameters of the ORC plant in Chena Hot Spring (Alaska), the geothermal power plant with the lowest water temperature in the world. However, it should be added that the installation is also characterized by the low condensing temperature [7,19,21]. In the case of a geothermal water flow rate, the assumed value of 100 m3/h is also dictated by the approximate geothermal capacity of Chena Hot Spring in Alaska (115 m3/h) and in Neustadt-Glewe (110 m3/h) in Germany [21–23].

2. Materials and Methods Data for 184 drilling wells located in the study area were used to identify geological and hydrogeological conditions. Due to the aim of this work, the geological information obtained from drilling depths exceeding 2000 m b.g.s. (meters below ground surface) was crucial. In order to assess the variability of rock mass thermal parameters in the Małopolska, borehole data and additional literature were used [24–29] to prepared maps for the distribution of geothermal gradient and temperatures at depths of 0.5, 1000, 2000, 3000, 4000 m b.g.s. Both the geothermal gradient distribution map and depth temperature distribution maps were made used point data in two- and three-dimensional system and their exposure in the assumed coordinate system. This is possible thanks to the use of mathematical formulas and the interpolation and extrapolation of values in an area not covered by data. The method of kriging was used, which is considered to give the best results for isoline maps created by interpolation [30]. A linear variogram model was used, which is the basic interpolation giving the eﬀect of a regular value grid. The interpolation grid geometry parameters were determined automatically, based on the range of input data variability. Energies 2020, 13, 1335 4 of 20

Albers Equal Area cartographic projection based on Krassovsky ellipsoid (1940), at the Central Meridian 190, was used to present the thermal parameter. The methodology was developed at the Department of Fossil Fuels of the AGH University of Science and Technology in Cracow [25]. Geothermal gradient map was prepared on the basis of temperature interpretation in individual holes, based on the formula [26]: Ts Tp G = − 100, (1) T Z × where:

GT—geothermal gradient [◦C/100 m] Ts—temperature at the top geothermal aquifer [◦C] Tp—average annual surface temperature (mainly 0.5 m above sea level) [◦C] Z—the depth of retaining the ceiling of the tested hydro-geothermal level [m b.g.s.]

In order to use formula (1), it was necessary to determine the average temperature at a depth of 0.5 m above sea level For this purpose, data published by Górecki [ed.] (2006) [25], Górecki [ed.] (2011) [28] and Górecki [ed.] (2012) [29] were used. The data obtained as a result of calculations were used to elaborate a geothermal gradient distribution map. The data used to prepare the depth temperature maps were primarily the thermal profiles of the geothermal wells: BańskaPGP-1, BańskaIG-1, Głogoczów IG-1, Potrójna IG-1, Siekierczyna IG-1 and Zawada 8K. Lack of sufficient thermal data in the studied area, especially in its northern and western parts, caused that as supplementary data were used values from the geothermal gradient distribution map and depth distribution maps presented in the works of Górecki [ed.] (2006) [25], Górecki [ed.] (2011) [28] and Górecki [ed.] (2012) [29]. Temperature maps at the designated depths were made based on the results of calculations according to the formula [26]:

Zp Zs Ts = Tp + G − , (2) T × 100 where:

Ts—temperature at the top geothermal aquifer [◦C] Tp—average annual surface temperature (mainly 0.5 m above sea level) [◦C] GT—geothermal gradient of the tested level [◦C/100 m] Zp—ordinate of the land surface [m a.s.l.] Zs—ordinate of the top geothermal aquifer [m a.s.l.]

In the thermodynamic calculations, it was assumed that the temperature of the geothermal water leaving the geothermal power plant would be at least 60 ◦C. The working fluid condensation temperature was adopted as a constant value of 30 ◦C. The amount of gross geothermal electricity produced was calculated from the gross power and working time. It was assumed that the power plant’s working time would be about 4000 h. In the case of Organic Rankine Cycle, for detailed calculations, four dry working fluids were selected: R227ea, R600a, R236fa, R245fa and two wet: R1234yf and R134a. For the calculations, a thermodynamic model was developed with values of temperature, pressure, enthalpy and entropy at specific points determined using NIST REFPROP 9.1. It was assumed that a power plant based on the Organic Rankine Cycle consisted of a turbine, a condenser, a feed pump, a preheater, an evaporator and a superheater (Figure2). The gross power can be described in accordance with the first principle of thermodynamics [10,17,31,32]:

. . . Wgross = Q η = m (h h ) η , (3) d × ORC wf × wf1 − wf4 × ORC where: EnergiesEnergies 20202019,,13 13,, 1335x FOR PEER REVIEW 55 ofof 2020

. ℎ푤푓2−ℎ푤푓3 휂푂푅퐶 = 1 − , (4) Wgrossgross power [W] ℎ푤푓1−ℎ푤푓4 . Qwhere:d—heat ﬂux supplied to the superheater, evaporator and preheater [W]

ηηORCORC——thermalthermal efficiency efficiency [ [-]-] . mhwf1wf,—mass hwf2, hwf3 flow, hwf4 of— thespecific working enthalpy fluid [kg[kJ/kg]/s] h , h —specific enthalpy [kJ/kg] wf1 Thewf4 Organic Rankine Cycle, along with the characteristic points for which the enthalpy value is required, is shown in Figure 2.

FigureFigure 2.2. PressurePressure enthalpy enthalpy diagram diagram with with applied applied specific specific points; points; Explanation Explanation:: 1–2s 1–2s—isentropic—isentropic ex- expansionpansion of ofthe the working working fluid fluid in inthe the turbine turbine;; 2–2s 2–2s—cooling—cooling of the of theworking working fluid fluid in the in thecondenser condenser;; 2s– 2s–3—condensation3—condensation of ofthe the working working fluid fluid in in the the condenser condenser;; 3 3–4s—isentropic–4s—isentropic pumping pumping of the workingworking fluidfluid byby thethe feedfeed pump;pump; 5—heating5—heating ofof thethe workingworking fluidfluid inin thethe preheater;preheater; 5–6—evaporating5–6—evaporating ofof thethe workingworking fluidfluid inin thethe evaporator;evaporator; 6–1—superheating6–1—superheating ofof thethe workingworking mediummedium inin thethe superheater (based(based onon [[1010]).]).

The efficiency of the geothermal power plant was calculated based on the formula: For the calculation model, it was assumed that the Kalina Cycle consisted of a turbine (combined with a generator), a low-temperature recuperator, a condenser, a feed pump, a high-temperature re- hwf2 hwf3 cuperator, an evaporator and a separatorηORC (Figure= 1 3). Calculations− , were made for mixtures in the pro- (4) − hwf1 hwf4 portion of 82% to 92% of ammonia content in relation to− water. Each of the listed components should where:be considered separately when designing the system. The gross power was calculated based on the formula [10,17,31,32]: ηORC—thermal efficiency [-] hwf1, hwf2, hwf3, hwf4—specific푊̇푔푟표푠푠 = enthalpy푄̇푑 × 휂퐾푎푙𝑖푛푎 [kJ/kg]= 푚̇ 푤푓1 × (ℎ푤푓1 − ℎ푤푓8) × 휂퐾푎푙𝑖푛푎, (5) where:The Organic Rankine Cycle, along with the characteristic points for which the enthalpy value is required,Ẇ gross—gross is shown power in Figure[W] 2.

Q̇ d—Forheat the flux calculation supplied model,to the evaporator it was assumed [W] that the Kalina Cycle consisted of a turbine (combined withηKalina a— generator),thermal efficiency a low-temperature [-] recuperator, a condenser, a feed pump, a high-temperature recuperator,ṁ wf1—mass anflow evaporator of the working and a fluid separator [kg/s] (Figure 3). Calculations were made for mixtures in the proportionhwf1, hwf8—specific of 82% enthalpy to 92% of [kJ/kg] ammonia content in relation to water. Each of the listed components should be considered separately when designing the system. The gross power was calculated based The efficiency of the geothermal power plant was calculated based on the formula: on the formula [10,17,31,32]: ℎ − ℎ . . 푤푓4 푤푓5 휂퐾푎푙𝑖푛푎 = 1. − , (6) Wgross = Q η = m ℎ (h− ℎ h ) η , (5) d × Kalina wf1 푤푓× 9 wf1푤푓−8 wf8 × Kalina where:where: η. Kalina—thermal efficiency [-] Whwf4gross, hgrosswf5, hwf8 power, hwf9— [W]specific enthalpy [kJ/kg] . Q —heat ﬂux supplied to the evaporator [W] d The Kalina Cycle with the characteristic points for which the enthalpy value is required is shown η inKalina Figure—thermal 3. eﬃciency [-]

Energies 2020, 13, 1335 6 of 20

. mwf1—mass flow of the working fluid [kg/s] hwf1, hwf8—specific enthalpy [kJ/kg] Energies 2019, 13, x FOR PEER REVIEW 6 of 20

FigureFigure 3. PressurePressure entropy entropy diagram diagram with with applied applied specific speciﬁc points; points; Explanation: Explanation: 1–2—isentropic 1–2—isentropic expan- expansionsion of the ofworking the working fluid in ﬂuid turbine, in turbine, 2–3— 2–3—mixingmixing of ammonia of ammonia vapors vapors with withthe liquid the liquid part of part the of mix- the mixture;ture; 3–4 3–4 and and 6–7 6–7—heat—heat transfer transfer in inlo low-temperaturew-temperature recuperator recuperator;; 4 4–5—condensation–5—condensation of the working mediummedium inin thethe condenser;condenser; 5–6—isentropic5–6—isentropic pumpingpumping of the working medium through the feed pump;pump; 7–87–8 andand 10–11—heat10–11—heat transfertransfer inin thethe high-temperaturehigh-temperature recuperator;recuperator; 8–9—evaporation8–9—evaporation ofof thethe workingworking mediummedium ininthe the evaporator; evaporator 9–1—separation; 9–1—separation of of ammonia ammonia vapors vapors from from the the part part of theof the mixture mixture which which has nothas evaporated;not evaporated 11–12—expansion; 11–12—expansion in the inexpansion the expansion valve valve (based (based on [33 on]). [33]).

TheDuring efficiency thermodynamic of the geothermal model studies, power plantit was was found calculated that for basedthe geothermal on the formula: water temperature range analyzed the optimum percentage of ammonia in the mixture was 85% to 89%. To determine h h this range, a trial and error method of ηthermodynamic= 1 wf4 analysis− wf5 , was carried out using NIST REFPROP (6) Kalina − h h 9.1 for ammonia content in a mixture of 75% to 90%. Thus,wf9 − thewf8 results of the three types of the mixture where:were presented: 85%, 87% and 89% ammonia content. The turbine pressure was selected in the range of 1500–3000 kPa for optimum results. ηKalina—thermal efficiency [-] h3.wf4 Characteristic, hwf5, hwf8, h ofwf9 R—specificesearch A enthalpyrea [kJ/kg] The Kalina Cycle with the characteristic points for which the enthalpy value is required is shown Małopolskie Voivodeship is situated in the southern part of Poland, bordered by the in Figure3. Świętokrzyskie Voivodeship (north), Podkarpackie Voivodeship (east), Silesian Voivodeship (west) During thermodynamic model studies, it was found that for the geothermal water temperature and the southern border with Slovakia (Figure 4). It occupies an area of 15,183 km2, which is 5% of range analyzed the optimum percentage of ammonia in the mixture was 85% to 89%. To determine Poland's territory. This area is inhabited by approximately 3.3 million people and the level of urban- this range, a trial and error method of thermodynamic analysis was carried out using NIST REFPROP ization is about 49.3%. 9.1 for ammonia content in a mixture of 75% to 90%. Thus, the results of the three types of the mixture Geologically, the Małopolskie Voivodeship comprises several structures, including the Upper were presented: 85%, 87% and 89% ammonia content. The turbine pressure was selected in the range Silesian Coal Basin, the Miechów Trough, the Silesian-Kraków Monocline, the Carpathian Foredeep of 1500–3000 kPa for optimum results. and the Western Carpathians (Figure 4). The geological structure of the research area and its geother- 3.mal Characteristic conditions have of Research been well Area-recognized and described in the literature e.g., [25,28–29]. The terrain is high and mountainous. More than 50% of the area is above 500 m. Within the ´ researchMałopolskie area, 6 national Voivodeshipis parks, situated11 landscape in the southernparks, 10 part protected of Poland, landscape bordered areas by the andSwi˛etokrzyskie 84 nature re- Voivodeshipserves have (north),been established. Podkarpackie In terms Voivodeship of hydrology, (east), Silesian the area Voivodeship of the Małopolskie (west) and Voivodeship the southern is 2 borderwithin withthe catchment Slovakia (Figureof two river4). It basins, occupies the an Vistula area of (90% 15,183 of kmthe area), which and is the 5% Danube of Poland’s. territory. This area is inhabited by approximately 3.3 million people and the level of urbanization is about 49.3%.

Energies 2020, 13, 1335 7 of 20 Energies 2019, 13, x FOR PEER REVIEW 7 of 20

FigureFigure 4. 4.Map Map ofof thethe mainmain geologicalgeological unitsunits ofof thethe MałopolskieMałopolskie Voivodeship Voivodeship (based (based on on [ 24[2,4,3434]).]).

Geologically,The Upper Silesian the Małopolskie Coal Basin Voivodeship covers the western comprises part several of the Małopolskie structures, including Voivodeship, the Upper taking Silesiana small Coalpercentage Basin, theof the Miech wholeów voivodeship. Trough, the Silesian-Krak It is characterizedów Monocline, by an average the Carpathian geothermal Foredeep gradient andof 3.15 the Western°C /100 m Carpathians [35], with (Figurehigher 4values). The geologicalof geothermal structure gradient of the and research temperature area and recorded its geothermal in the conditionswestern part have of beenthe basin. well-recognized The occurrence and of described geothermal in the waters literature was identified e.g., [25,28 in,29 Palaeozoic]. and Mes- ozoicThe formations: terrain is Triassic, high and Locally mountainous. Jurassic, Carboniferous More than 50% and of Permian the area [36 is above]. Due 500to the m. shallow Within Mes- the researchozoic deposits area, 6 national and unfavorab parks, 11le landscape reservoir parks, parameters 10 protected of the landscape Palaeozoic, areas geothermal and 84 nature parameters reserves havewithin been the established. Upper Silesian In terms Coal Basin of hydrology, are characterized the area of by the a temperature Małopolskie of Voivodeship 20 to 100 °C is and within a poten- the catchmenttial flow rate of two not riverexceeding basins, 40 the m3 Vistula/h [24]. (90%The deep of the coal area) mines and of the the Danube. Upper Silesian Coal Basin have a certainThe Upper potential, Silesian but Coalthe temperature Basin covers of the geothermal western part waters of the does Małopolskie not exceed Voivodeship, 45 °C [37]. From taking the a smallperspective percentage of electricity of the whole generation, voivodeship. this excludes It is characterized the possibility by anof their average use. geothermal gradient of 3.15 ◦CThe/100 Silesian m [35],– withKraków higher Monocline values of covers geothermal the north gradient-western and part temperature of the Małopolska recorded in Voivodeship. the western partWithin of the it, geothermal basin. The occurrencewaters were of found geothermal in Palaeozoic waters and was Mesozoic identiﬁed formations. in Palaeozoic However, and Mesozoic the pos- formations:sibility of obtaining Triassic, Locallythem is Jurassic,limited primarily Carboniferous by the and poor Permian recognition [36]. Dueof the to geothermal the shallow conditions Mesozoic depositsof the Palaeozoic. and unfavorable In the case reservoir of younger parameters Mesozoic of the layers Palaeozoic, (Triassic geothermal and on a smaller parameters scale Jurassic) within the the Uppertemperature Silesian ofCoal geothermal Basin are waters characterized does not exceed by a temperature 20 °C [24,38 of,39 20]. to 100 ◦C and a potential ﬂow rate notThe exceeding Miechów 40 Trough m3/h [24 is]. one The of deep the coalstructures mines of thethe UpperPolish SilesianLowlands, Coal and Basin is specifically have a certain the potential,south-eastern but the part temperature of the Szczecin of geothermal–Łódzko-Miechów waters does synclinorium. not exceed The 45 ◦ C[average37]. From geothermal the perspective gradient ofvalues electricity in the generation, Miechów thisTrough excludes range the from possibility 1.72 to 2.96 of their °C /100 use. m and the heat flux density is about 50 mW/mThe Silesian–Krak2 [35,40]. Withinów Monocline the Miechów covers Trough, the north-western the occurrence part of ofgeothermal the Małopolska waters Voivodeship. has been ob- Withinserved it,in geothermalPalaeozoic and waters Mesozoic were foundformations. in Palaeozoic The greatest and hydrogeological Mesozoic formations. potential However, in this area the is possibilityrepresented of obtainingby Devonian, them Reich is limited (Upper primarily Triassic), by theDogger poor recognition(Central Jurassic) of the geothermaland Cenoman conditions (Upper ofChalk). the Palaeozoic. The geothermal In the case waters of younger do not Mesozoicexceed 102 layers °C and (Triassic the maximum and on a smallerflow rate scale is Jurassic)20 m3/h [24 the]. temperatureTherefore, from of geothermal the point of waters view of does electricity not exceed generation, 20 ◦C[24 the,38 Miechów,39]. Trough area is excluded from consideration due to the low flow rates of the production wells.

Energies 2020, 13, 1335 8 of 20

The Miechów Trough is one of the structures of the Polish Lowlands, and is specifically the south-eastern part of the Szczecin–Łódzko-Miechów synclinorium. The average geothermal gradient values in the Miechów Trough range from 1.72 to 2.96 ◦C/100 m and the heat flux density is about 50 mW/m2 [35,40]. Within the Miechów Trough, the occurrence of geothermal waters has been observed in Palaeozoic and Mesozoic formations. The greatest hydrogeological potential in this area is represented by Devonian, Reich (Upper Triassic), Dogger (Central Jurassic) and Cenoman (Upper 3 Chalk). The geothermal waters do not exceed 102 ◦C and the maximum flow rate is 20 m /h [24]. Therefore, from the point of view of electricity generation, the Miechów Trough area is excluded from consideration due to the low flow rates of the production wells. The Carpathian Foredeep is about 300 km long and is from a few (in the vicinity of Cracow) to 100 km (in the eastern part) wide, extending between the Carpathians to the south and the highlands of Central Poland to the north and occupying an area of about 20,000 km2 (6.5% of the area of Poland). Geothermal waters occurring in the area of the Carpathian Foredeep are primarily associated with Neogene (Miocene), Mesozoic (Cenoman, Dogger) and locally Palaeozoic (Carboniferous, Devonian) rocks. The thermal flux in the area of the Carpathian Foredeep is in the range of 60–95 mW /m2. The geothermal gradient is characterized by a large variability and ranges from 1.8 to over 4.5 ◦C/100m. The temperatures of geothermal waters are in the range of 20–90 ◦C, and the flow rate of geothermal waters is typically several cubic meters per hour. Water mineralization in the Carpathian Foredeep rises from east to west in the range of 1–150 g/L[24,41–44]. Despite locally relatively high temperatures of geothermal waters reaching up to 90 ◦C, the problem for their use for energy purposes however is the low flow rate not exceeding several cubic meters per hour. The Western Carpathians are pushed north to the Miocene sediments of the Carpathian Foredeep. In Poland, the Western Carpathians represent the scarp of a mountain chain more than 1300 km long, running from Vienna to the Iron Gate on the Danube. The chain is divided into the Inner Carpathians (late Cretaceous folds) and younger Outer Carpathians (Flysch) and at the boundary between them is a band of pale rock. The occurrence of geothermal waters has been reported in the Western Carpathians in Palaeozoic, Mesozoic and Neogene formations. The thermal flux in the Polish part of the Western Carpathians oscillates at the level of 60–95 mW/m2. The geothermal gradient is characterized by a number of variations, ranging from 2 to over 3.6 ◦C/100 m [28]. The temperatures of geothermal waters are in the range of 20–127 ◦C (temperatures above 80 ◦C occur in the area of the Podhale Basin), and the flow rate is from several cubic meters per hour to a maximum of 550 m3/h (Banská PGP-1) [45,46]. The mineralization of geothermal waters in the Polish part of the Western Carpathians ranges from about 0.5 to over 120 g/L, whereas in the best prospect from the point of view of the prevailing geothermal conditions, the area of the Podhale Basin, it is about 3 g/L[45,47,48]. The best prospect from the point of view of electricity generation is the area of the Podhale Basin. This area (a dozen kilometers wide), is a vast asymmetric depression at the foot of the Tatra Mountains, being part of the Central Carpathian Palaeogean Basin. This basin is composed of the Reglowa and Wierchowa nappes and a crystalline massif of the Tatra Mountains with sediment cover [45,49,50]. The aquifers of the Podhale Geothermal System are limestone and Triassic dolomites (with the most abundant geothermal waters in Małopolskie Voivodeship), sandstones and carbonate rocks (Jurassic) and eocene carbonates. The Tatra Mountains have the functions of a supply area and barrier to the south, while an impermeable northern boundary of the basin is the Pieniny Klippen Belt. The insulating cover is the Podhalansian Flysch [24,45]. The thermal flow in the area of the Podhale Geothermal 2 System ranges from 55 to 60 mW/m and the geothermal gradient ranges from 1.9 to 2.3 ◦C/100 m. Geothermal waters at a depth of 2.0–3.2 km are characterized by a temperature of about 80–95 ◦C (geothermal water temperature rises with increasing depth northward from the supply zone, which is the Tatra), with a flow rate of 50–550 m3/h. The reservoir has an artesian character; the maximum static head pressure is up to 29 bar. The mineralization of geothermal waters in the area discussed amounts to approx. 3 g/dm3 [45]. Energies 2020, 13, 1335 9 of 20

4. Results

4.1. Geothermal Conditions in Research Area Based on the results of the analysis, it should be stated that the highest values of the geothermal gradient (Figure5) are found in the Silesian-Krak ów Monocline—3.0 ◦C/100 m—and locally the eastern part of the Western Carpathians—also 3.0 ◦C/100 m. The lowest values of the geothermal gradient are observed in Podhale, around Nowy Targ and Zakopane—2.1 ◦C/100 m. The range of temperatures at depths of 1000 and 2000 m do not show suﬃcient value from the point of view of electricity generation. In the case of a temperature at a depth of 1000 the values do not exceed 40 ◦C and at a depth of 2000 m 70 ◦C. Temperatures at a depth of 3000 m b.g.s. range from 70 to 100 ◦C (Figure6), reaching the highest values in the central part of the Carpathian Foredeep (near Cracow) and in the south-eastern part of the Western Carpathians (east of Nowy S ˛acz).The lowest temperatures above 70 ◦C can be observed in the central part of the Western Carpathians (near Nowy Targ) and in the Miechów Trough (north of Cracow). The most favorable temperature parameters were observed at a depth of 4000 m (Figure7), which results directly from the rise of temperature with depth. The highest temperature values in the Małopolskie Voivodship are characterized by the area of the Upper Silesian Coal Basin and Silesian–Kraków monocline—with temperatures of 130–140 ◦C. High temperatures are also described in the south-eastern part of the Western Carpathians (east of Nowy S ˛acz)—from 120 to 130 ◦C. The lowest temperature values are observed in the eastern part of the Carpathian Foredeep (near Tarnów) and in the central part of the Western Carpathians (around Nowy Targ and Zakopane)—temperatures do not exceed 105 ◦C. Rock mass temperatures exceeding 74 ◦C were observed throughout the Małopolskie Voivodeship at a depth of over 2000 m. The highest temperature can be observed in the Upper Silesian Coal Basin (above 140 ◦C at a depth of 4000 m) and bordering with that basin, in the Carpathian Foredeep (over 130 ◦C at a depth of 4000 m), as well as in the south-western part of the Western Carpathians, 120 ◦C at a depth of 4000 m). The temperatures of the Central Carpathians and the north–eastern part of the Carpathian Foredeep are the least favourable. Despite the most favourable temperature distribution in the Upper Silesian Coal Basin, geothermal waters at temperatures from 20 to 100 ◦C, the ﬂow does not exceed 40 m3/h [36], which from the point of view of the minimum performance criterion of 100 m3/h, eliminates this area from further analysis. However, the area is characterized by high temperatures at a depth of 4000 m, which exceeds 140 ◦C, giving the basin an opportunity to consider using enhanced geothermal system (EGS) technology. In the area of the Upper Silesian Coal Basin, compact crystalline complexes have been found at a depth of over 3000 m, which are mostly Precambrian igneous rocks [51]. In addition, there is the possibility of using prospective sedimentary structures, which in the area of the Upper Silesian Coal Basin are carbonite [52]. Unfortunately, the area within the Małopolskie Voivodeship is poorly surveyed by deep boreholes. In the case of the Silesian–Kraków Monocline, the possibility of exploitation of geothermal waters is limited by poor recognition of the geothermal conditions of the Palaeozoic. Younger Mesozoic layers are characterized by temperatures of geothermal waters not exceeding 20 ◦C[12] and are too low to be considered for the purposes of electricity generation. As in the case of the thermal conditions of the Upper Silesian Coal Basin, the area of the Silesian-Kraków Monocline is characterized by temperature at a depth of 4000 m of 130 ◦C, which allows one to analyze the possibility of using hot dry rock structures for energy purposes. However, no deep drilling (> 3,000 m) has been made in the Małopolskie Voivodeship. In the present state of hydrogeological and thermal knowledge, the prospect of using geothermal energy for energy purposes is solely via heat pumps, which, however, do not allow the generation of electricity. Energies 2019, 13, x FOR PEER REVIEW 9 of 20 Energies 2019, 13, x FOR PEER REVIEW 9 of 20 reaching the highest values in the central part of the Carpathian Foredeep (near Cracow) and in the rsoutheaching-eastern the highest part of values the Western in the centralCarpathians part of (east the ofCarpathian Nowy Sącz). Foredeep The lowest (near temperaturesCracow) and inabove the south70 °C- easterncan be observedpart of the in Western the central Carpathians part of the (east Western of Nowy Car pathiansSącz). The (near lowest Nowy temperatures Targ) and abovein the 70Miechów °C can Troughbe observed (north in of the Cracow). central Thepart mostof the favorable Western temperatureCarpathians parameters (near Nowy were Targ) observed and in theat a Miechówdepth of 4000 Trough m (Figure (north 7),of whichCracow). results The directlymost favorable from the temperature rise of temperature parameters with were depth. observed The highest at a depthtemperature of 4000 values m (Figure in the 7), Małopolskie which results Voivodship directly from are the characteri rise of temperaturezed by the area with of depth. the Upper The highestSilesian temperatureCoal Basin and values Silesian in the–Kraków Małopolskie monocline Voivodship—with are temperatures characterized of by130 the–140 area °C of. High the Upper temperatures Silesian Coalare also Basin described and Silesian in the–Kraków south-eastern monocline part —ofwith the Westerntemperatures Carpathians of 130– 140(east °C of. HighNowy temperatures Sącz)—from are120 also to 130 described °C . The lowestin the southtemperature-eastern values part of are the observed Western in Carpathians the eastern part(east of of the No Carpathianwy Sącz)— fromFore- 120 to 130 °C . The lowest temperature values are observed in the eastern part of the Carpathian Fore- Energiesdeep (near2020, 13Tarnów), 1335 and in the central part of the Western Carpathians (around Nowy Targ and10 ofZa- 20 deepkopane) (near— temperaturesTarnów) and doin thenot central exceed part105 °Cof .the Western Carpathians (around Nowy Targ and Za- kopane)—temperatures do not exceed 105 °C .

Figure 5. Map of geothermal gradient in Małopolskie Voivodeship. FigFigureure 5. 5. MapMap of of geothermal geothermal gradient gradient in in Małopolskie Małopolskie Voivodeship. Voivodeship.

Figure 6. Distribution of temperature at a depth of 3000 m b.g.s. in Małopolskie Voivodeship. Figure 6. Distribution of temperature at a depth of 3000 m b.g.s. in Małopolskie Voivodeship. Within the Miechów Trough, the occurrence of geothermal waters has been observed with 3 temperatures of up to 102 ◦C and a flow rate typically not exceeding 20 m /h [27]. On the other hand, a Miocene reservoir could be interesting—with a maximum temperature at 76 ◦C and a flow rate of several to locally 120 m3/h [24]. The high temperatures of the geothermal waters in the Miechów Trough do not correlate with the flow rates, as is the case of the Słomniki IG-1 (depth of 2332.2 m, drilled in 1961). It is characterized by a potentially high productivity of over 100 m3/h but the geothermal water temperature is 18 ◦C[40]. Temperatures in the area of the Miechów Trough at a depth of 4000 m have a range from 110 ◦C to 120 ◦C, but finding out if this area has potential for using EGS requires additional geological survey, which results directly from the lack of deep drilled boreholes. Energies 2020, 13, 1335 11 of 20 Energies 2019, 13, x FOR PEER REVIEW 10 of 20

Figure 7. Distribution of temperature at the depth of 4000 m b.g.s. in Małopolskie Voivodeship.

InRock spite mass of locallytemperatures relatively exceeding high temperatures 74 °C were observed of geothermal throughout waters the found Małopolskie in the area Voivode- of the Carpathianship at a depth Foredeep, of over up 2000 to 90 m.◦C, The the highest problem temperature of their use can for energybe observed purposes in the is the Upper low flowSilesian rate, Coal not exceedingBasin (above a dozen 140 °C m at3/ ha [depth24]. The of 4000 western m) and part bordering of the Carpathian with that Foredeep, basin, in whichthe Carpathian borders the Foredeep Upper Silesian(over 130 Coal °C at Basin, a depth is characterized of 4000 m), as by well high as temperaturesin the south-western of the order part of of the 130–135 Western◦C atCarpathians, a depth of 4000120 °C m, at which a depth may of be4000 an m). interesting The temperatures prospect in of the the context Central of Carpathians the implementation and the north of EGS–eastern technology. part However,of the Carpathian the prospective Foredeep zone are isthe poorly least surveyedfavourable. by Despite deep boreholes—only the most favourable two boreholes temperature exceeding distri- 3000bution m canin the be Upper identified: Silesian Piotrowice Coal Basin, 1 (3072.7 geothermal m, drilled waters in 1969) at andtemperatures Spytkowice from 200 (3176.3,20 to 100 drilled °C , the in 1968).flow does In the not temperature exceed 40 m zone3/h [36 of], 120 which◦C there from are the also point other of view boreholes: of theWysoka minimum 3 (2755.0 performance m, drilled crite- in 1990)rion of and 100 Głogocz m3/h, eliminatesów IG-1 (3800.0 this area m, drilled from further in 1974). analysis. However, the area is characterized by high Thetemperatures Western Carpathians at a depth of are 4000 the m, most which extensive exceed ofs 140 the °C areas, giving analyzed. the basin The an temperatures opportunity ofto geothermalconsider using waters enhanced are in geothermal the range ofsystem 20–130 (EGS◦C,) buttechnology. temperatures In the abovearea of 80the◦ CUpper occur Silesian only in Coal the areaBasin, of compact the Podhale crystalline Basin. Thiscomplexes is also have the only been area found where at a the depth flow of rate over is 3000 associated m, which with are relatively mostly highPrecambrian temperatures igneous and rocks ranges [51 from]. In addition, tens of cubic there meters, is the possibility to a maximum of using of 550 prospective m3/h [45]. sedimentary Additional attentionstructures, should which be in paid the toarea the of south-western the Upper Siles partian of Coal the WesternBasin are Carpathians carbonite [52 within]. Unfortunately, the Małopolskie the Voivodship,area within the where Małopolskie the temperatures Voivodeship at a depthis poorly of 4000 surveyed m are by about deep 120 boreholes.◦C. One of the deep drilling boreholesIn the is case located of the in Silesian this area—Siekierczyna–Kraków Monocline, IG-1 (4809.9the possibility m). of exploitation of geothermal waters is limited by poor recognition of the geothermal conditions of the Palaeozoic. Younger Mesozoic 4.2.layers Thermodynamic are characteri Calculationszed by temperatures for Selected of Perspective geotherm Wellsal waters not exceeding 20 °C [12] and are too low toAnalysis be considered of thermal for data the presentedpurposes onof electricity the maps of generation. deep temperature As in the distribution case of the allowed thermal the condi- most favorabletions of the thermal Upper conditions Silesian Coal from Basin, the point the area of view of the of electricity Silesian-Kraków generation Monocline to be indicated. is characteri Takingzed into by accounttemperature potential at a depth geothermal of 4000 reservoir m of 130 capacity °C , which data allows in the Małopolskaone to analy area,ze the the possibility following of production using hot wellsdry rock were structures selected forfor furtherenergy analysis:purposes. BańskaPGP-1, However, no deep BańskaIG-1, drilling BańskaPGP-3,(> 3,000 m) has Chochoł been madeów PIG-1.in the InMałopolskie addition, it Voivodeship. was decided toIn analyzethe present the Bukowinastate of hydrogeological PGP-1 borehole, and although thermal its knowledge, parameters the did pro- not meetspect theof using minimum geothermal temperature energy and for performanceenergy purposes criteria. is solely However, via heat the pumps, purpose which, of calculations however, fordo thisnot allow approach, the generation as extremely of electricity. unfavorable, was to show whether the initial assumptions were correct. Within the Miechów Trough, the occurrence of geothermal waters has been observed with temperatures of up to 102 °C and a flow rate typically not exceeding 20 m3/h [27]. On the other hand, a Miocene reservoir could be interesting—with a maximum temperature at 76 °C and a flow rate of several to locally 120 m3/h [24]. The high temperatures of the geothermal waters in the Miechów Trough do not correlate with the flow rates, as is the case of the Słomniki IG-1 (depth of 2332.2 m,

Energies 2020, 13, 1335 12 of 20

The production wells selected for detailed analysis are shown in Table1. However, in future consideration may be given to the estimation of the potential power and energy production for areas where EGS technology can be used.

Table 1. Geothermal wells selected for analysis of electricity generation in Małopolskie Voivodeship.

Ba ńska Ba ńska Chochołów Parameter Unit Ba ńskaPGP-1 IG-1 PGP-3 PIG-1

Geothermal water temperature ◦C 86 82 86 82 Flow rate of geothermal water m3/h 550 120 290 190 Mineralization g/L 3.122 2.693 2.499 1.244 Geothermal water density kg/m3 990.81 970.52 986.25 970.50 Geothermal water speciﬁc heat kJ/kgK 4.183 4.182 4.187 4.190

The analyses and calculations indicate that in the Małopolskie Voivodeship, existing boreholes and a potential geothermal reservoir can be identified, which under favorable conditions might be utilized for electricity generation. Technologies that might be considered in this respect are the Organic Rankine Cycle or the Kalina Cycle. Potential gross geothermal power, calculated for the selected geothermal wells, will not exceed 900 kW for ORC and 1.6 MW for the Kalina Cycle. In the case of gross electricity generation, the amount for ORC technology will not exceed 3.3 GWh, and in the Kalina Cycle will not exceed 6.3 GWh. The results of the analysis presented in Table2 show that, assuming use of the full geothermal flow rate, the highest gross power is obtained with the BańskaPGP-1 and it is 1568 kW (with an efficiency of 7%) in the most advantageous variants—assuming the use of the Kalina Cycle and 87% ammonia in the active mixture. Gross power above 500 kW (824 kW for a flow rate of 290 m3/h) is also available for the BańskaPGP-3. The calculations confirm the key implications for geothermal water generation of two parameters: temperature and flow rate. The BańskaPGP-1 and BańskaPGP-3 are both characterized by the highest geothermal water temperature, in both cases 86 ◦C and a flow rate of 550 m3/h and 290 m3/h, respectively. Among the technologies analyzed and the working factors, the results obtained for the Kalina Cycle with an ammonia/water mixture of 87% ammonia (Figures8–11) are the most advantageous. This applies to all the solutions analyzed. In contrast to the ORC system, the R245f and R134a dry working fluids are the most preferred for the selected organic working fluids. As a major issue when implementing ORC and the Kalina Cycle in the geothermal water temperature range analyzed, the efficiency of the system does not exceed 10% and in most cases, it oscillates at a level of 6–7%. This is the effect of using geothermal waters for electricity generation with a temperature not exceeding 90 ◦C. The performance values for ORC rounded to the second decimal place are 6% for dry working fluids and 8% for wet working fluids. For the Kalina Cycle, the efficiency was calculated to be 6% for a mixture containing 85% ammonia, and 7% for mixtures containing 87% and 89% ammonia. Energies 2020, 13, 1335 13 of 20

Table 2. Summary of thermodynamic calculations.

Geothermal Water Gross Gross Borehole Name Temperature Flow Rate Working Fluid Efficiency Power Electricity Before/After Evaporator 3 – ◦C m /h|kg/s – kW % MWh R227ea 648 6.05 2700 R600a 795 6.17 3180 R236fa 762 6.16 3049 R245fa 817 6.20 3270 Ba ńskaPGP-1 86/60 550|151.37 R1234yf 655 7.86 2622 R134a 823 7.91 3293 Kalina 0.85 1422 6.14 5689 Kalina 0.87 1568 6.96 6273 Kalina 0.89 1451 6.82 5804 R227ea 120 5.84 481 R600a 140 5.94 560 R236fa 134 5.92 538 R245fa 143 5.91 571 Ba ńskaIG-1 82/60 120|32.35 R1234yf 122 7.54 489 R134a 148 7.50 590 Kalina 0.85 241 5.70 962 Kalina 0.87 272 6.61 1090 Kalina 0.89 252 6.49 1010 R227ea 354 6.05 1418 R600a 418 6.17 1670 R236fa 400 6.16 1602 R245fa 429 6.20 1717 Ba ńskaPGP-3 86/60 290|79.45 R1234yf 344 7.86 1377 R134a 432 7.91 1730 Kalina 0.85 747 6.14 2988 Kalina 0.87 824 6.96 3295 Kalina 0.89 762 6.82 3049 R227ea 190 5.79 761 R600a 222 5.94 888 R236fa 213 5.92 853 Energies 2019, 13, x FOR PEER REVIEW R245fa 226 5.91 90613 of 20 Chochołów 82/60 190|51.22 R1234yf 193 7.54 775 PIG-1 Among the technologies analyzed and the workingR134a factors, the 234 results obtained 7.50 for the 936 Kalina Kalina 0.85 382 5.70 1526 Cycle with an ammonia/water mixture of 87% ammoniaKalina 0.87(Figures 8– 43211) are the most 6.61 advantageous. 1728 This applies to all the solutions analyzed. In contrastKalina to the 0.89 ORC system, 400 the R245f 6.49 and R134a 1601 dry working fluids are the most preferred for the selected organic working fluids.

2,000 9 7.86 7.91 1,800 8 6.96 6.82 1,600 7 6.05 6.17 6.16 6.20 6.14 1,400 [%] Efficiency 6 Gross power [kW] powerGross 1,200 5 1,000 4 800 1,568 1,422 1,451 3 600 2 400 795 762 817 823 648 655 200 1 0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working Fluid

FigureFigure 8. 8.Comparison Comparison of of results results for for BańskaPGP-1, Bańska PGP-1, obtained obtained for for power power and and e ffiefficiencyciency depending depending on on the workingthe working fluid. fluid.

350 7.54 7.50 8

6.61 6.49 300 7 5.94 5.92 5.91 5.84 5.70 6 250 [%] Efficiency

Gross power [kW] powerGross 5 200 4 150 272 3 241 252 100 2 140 143 148 120 134 122 50 1

0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working Fluid

Figure 9. Comparison of results for Bańska IG-1, obtained for power and efficiency depending on the working fluid.

Energies 2019, 13, x FOR PEER REVIEW 13 of 20

Among the technologies analyzed and the working factors, the results obtained for the Kalina Cycle with an ammonia/water mixture of 87% ammonia (Figures 8–11) are the most advantageous. This applies to all the solutions analyzed. In contrast to the ORC system, the R245f and R134a dry working fluids are the most preferred for the selected organic working fluids.

Energies 2020Figure, 13 ,8. 1335 Comparison of results for Bańska PGP-1, obtained for power and efficiency depending on 14 of 20 the working fluid.

350 7.54 7.50 8

6.61 6.49 300 7 5.94 5.92 5.91 5.84 5.70 6 250 [%] Efficiency

Gross power [kW] powerGross 5 200 4 150 272 3 241 252 100 2 140 143 148 120 134 122 50 1

0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working Fluid

FigureFigure 9. 9.Comparison Comparison of of results results forfor BańskaIG-1,Bańska IG-1, obtained for for power power and and efficiency efficiency depending depending on onthe the Energiesworkingworking 2019, fluid.13 fluid., x FOR PEER REVIEW 14 of 20

1000 9 7.86 7.91 900 8 6.96 6.82 800 7 6.05 6.17 6.16 6.20 6.14 700 [%] Efficiency 6 Gross power [kW] powerGross 600 5 500 4 400 824 747 762 3 300 200 418 400 429 432 2 354 344 100 1 0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working Fluid

FigureFigure 10. 10.Comparison Comparison of of results results for for BańskaPGP-3,Bańska PGP-3, obtained for for power power and and efficiency efficiency depending depending on on thethe working working fluid. fluid.

It is true, however, that as far as power plants are concerned, and they are possible with both 600 7.54 7.50 8 systems, the power of the Kalina Cycle is significantly higher. In the case of ORC systems, the largest possible gross power of 823 kW (R134a) for the BańskaPGP-1 is 48% lower6.61 than the6.49 maximum7 gross 500 5.94 5.92 5.91 power for the Kalina5.79 Cycle, which is 1568 kW (with a mixture ammonia5.70 content of 87%). This is 6 primarily due to the differential pressure of the working medium on the turbine, indicating the[%] Efficiency need 400 for further[kW] powerGross pressure optimization in the case of the Kalina Cycle, but not in terms of an5 increase in power output but rather in terms of the life of the plant. The calculated results refer to the use of the 300 4 maximum geothermal water flow and represent the total potential for electricity generation. 432 3 200 382 400 2 226 234 100 190 222 213 194 1

0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working fluid

Figure 11. Comparison of results for Chochołów PIG-1, obtained for power and efficiency depending on the working fluid.

As a major issue when implementing ORC and the Kalina Cycle in the geothermal water temperature range analyzed, the efficiency of the system does not exceed 10% and in most cases, it oscillates at a level of 6–7%. This is the effect of using geothermal waters for electricity generation with a temperature not exceeding 90 °C . The performance values for ORC rounded to the second decimal place are 6% for dry working fluids and 8% for wet working fluids. For the Kalina Cycle, the efficiency was calculated to be 6% for a mixture containing 85% ammonia, and 7% for mixtures containing 87% and 89% ammonia. It is true, however, that as far as power plants are concerned, and they are possible with both systems, the power of the Kalina Cycle is significantly higher. In the case of ORC systems, the largest possible gross power of 823 kW (R134a) for the Bańska PGP-1 is 48% lower than the maximum gross

Energies 2019, 13, x FOR PEER REVIEW 14 of 20

Energies 2020Figure, 13 ,10. 1335 Comparison of results for Bańska PGP-3, obtained for power and efficiency depending on 15 of 20 the working fluid.

600 7.54 7.50 8

6.61 6.49 7 500 5.94 5.92 5.91 5.79 5.70

6 Efficiency [%] Efficiency 400 Gross power [kW] powerGross 5

300 4

432 3 200 382 400 2 226 234 100 190 222 213 194 1

0 0 R227ea R600a R236fa R245fa R1234yf R134a Kalina Kalina Kalina 0.85 0.87 0.89 Working fluid

FigureFigure 11. 11.Comparison Comparison of of results results forfor ChochołChochołówów PIG PIG-1,-1, obtained obtained for for power power and and efficiency eﬃciency depending depending onon the the working working ﬂuid. fluid.

5. DiscussionAs a major issue when implementing ORC and the Kalina Cycle in the geothermal water temperature range analyzed, the efficiency of the system does not exceed 10% and in most cases, it oscil- Due to the growing range of the population in the world, and thus the increase in the demand for lates at a level of 6–7%. This is the effect of using geothermal waters for electricity generation with electricity, it is necessary to search for solutions based on renewable energy sources, including low a temperature not exceeding 90 °C . The performance values for ORC rounded to the second decimal enthalpy geothermal energy. In addition, besides renewable energy, an important role in the future place are 6% for dry working fluids and 8% for wet working fluids. For the Kalina Cycle, the efficiency will be the full use of waste heat. Both of the mentioned heat sources can be used to generate electricity was calculated to be 6% for a mixture containing 85% ammonia, and 7% for mixtures containing 87% usingand ORC89% ammonia. or Kalina Cycle technology [53–55]. This is important from an ecological point of view, as well asIt from is true, an economichowever, andthat geopoliticalas far as power one plants (diversification are concerned, of energy and they sources). are possible with both systems,In the casethe power of ORC of technology,the Kalina Cycle it can is be significantly stated that higher. it confirmed In the itscase usefulness of ORC systems, for low-temperature the largest heatpossible sources gross [53]. power This isof due 823 tokW the (R134a) relatively for the simple Bańska system PGP- configuration,1 is 48% lower itsthan reliability the maximum and flexibility. gross Kalina’s Cycle, despite the greater complexity resulting from the use of a heterogeneous mixture as a working fluid, can be characterized by higher power obtained in the case of low enthalpy geothermal sources [56]. This is confirmed by the research results presented in this article. The power obtained for the Kalina Cycle is about 40% higher than for ORC, with a similar level of efficiency. The results present by Yari et al. [57] confirm the possibility of obtaining greater output power from the Kalina Cycle, as well as the tests carried out by Rodriguez et al. [58] obtained a result by 18% higher than ORC. The discrepancy between the results presented in this article and obtained by Rodriguez et al. [58] probably results from the working fluid used (for ORC, it was R-290, and the ratio of ammonia to water was 84%). In addition, they can be determined by the temperature on the heat source side, which is confirmed by the results obtained by Fiaschi et al. [59]. Authors of this publication compared sources with temperatures of 120 ◦C and 212 ◦C, obtaining a result by 25% for the variant with lower temperature in favor of the Kalina Cycle and a result by 4% worse for the variant with 212 ◦C. Therefore, Knapek’s (2007) [60] statement confirms that the Kalina Cycle is about 25% more effective than ORC. This may indicate a growing disproportion in the powers obtained for the decreasing temperature on the heat source side, in this case—geothermal water. One should agree with the statement that in the case of ORC the working fluid used plays a key role in the case of energy conversion efficiency [53]. This is one of the few issues that the system designer influences from the point of view of obtaining optimal thermodynamic conditions [61–63]. Among other aspects, for this reason, the research presented in this article analyzes six different organic working fluids and three ammonia-water mixtures. Energies 2020, 13, 1335 16 of 20

In addition to the results of efficiency, power and energy obtained, it should be noted that the nominal pressure on the turbine in the case of ORC is lower than in the case of the Kalin Cycle. The consequence of this may be a higher level of costs associated with sealing the installation based on the Kalina Cycle [53]. Another issue is the proportion of the ammonia-water mixture. It should be stated that the higher it is, the greater the energy efficiency, which is confirmed by the research carried out in the work. The potential for electricity generation for the analyzed area was determined based on the use of available geothermal water resources. However, it should be mentioned that the globally developing EGS technology, using the heat of hot dry rocks, may in the future be an interesting prospect in places where the occurrence of high temperatures does not correspond to the possibility of obtaining sufficiently high efficiency of geothermal water extraction [51,52,64,65]. It does not change the fact that including the availability of low-temperature geothermal resources and their potential, ORC and the Kalina Cycle are currently the technologies with the largest scope of implementation [66,67]. Poland has a geothermal energy resource which could not only be used in the heating sector (geothermal district heating, heat pumps) but also for electricity generation. However, the development of the geothermal energy sector in Poland is limited by barriers such as: lack of the appropriate legal regulations and financial conditions, long and complicated legal and administrative procedures and low awareness of geothermal energy in society. In addition, it should be noticed the formal issues that not only concern Poland, but the ubiquitous applications using geothermal energy, such as the Geothermal Reporting Code [68,69]. It is also clear that for further successful progress in the use of geothermal energy in Poland it is necessary to reduce investment costs to make geothermal energy more competitive compared to fossil fuels [70–72]. It is extremely important to take into account the fact that electricity, as well as heat generated using geothermal energy, is considered as ecological. It has no impact on the stage of negative emissions resulting from the conventional fuel combustion processes, which contributes to the development especially in the rural region. This is important, deprived of heating and gas network infrastructure, for those communities where the use of geothermal resources may be a solution to limiting the negative impact of fossil fuels on the environment [73]. However, it should be taken into account that geothermal installations can potentially affect the natural environment, among others due to the drilling process—geological hazards, freshwater use, emission into the water, solid waste, land use, noise emission, light emission and impact on biodiversity. As mentioned above, this does not change the fact that geothermal energy is stable and ecological energy sources compared to other energy carriers.

6. Conclusions In the context of the growing demand for electricity in the world, it is necessary to search for • solutions that would allow the use of unused energy resources. Geothermal energy as a stable source, under certain thermal and hydrological conditions, • complement the energy mix in the context of electricity generation. Research presented in this article has shown that the Kalina Cycle allows obtaining greater gross • power than ORC, up to 40%. The efficiency of thermal energy conversion into electricity is similar for the Kalina Cycle and ORC. • The analysis and calculations show that in the area of Małopolskie Voivodeship existing geothermal • wells and reservoirs that demonstrate the potential for electricity generation can be identified. Among the analyzed locations, the most favorable conditions were found in the Podhale geothermal • system (especially the geothermal wells: BańskaPGP-1 and BańskaPGP-3). The potential gross power of a geothermal power plant, calculated for selected geothermal wells • (assuming the use of the full geothermal water flow rate), will not exceed 900 kW for the Organic Rankine Cycle and 1600 kW for the Kalina Cycle. Energies 2020, 13, 1335 17 of 20

Author Contributions: Conceptualization, M.K. and B.T.; Methodology, M.K., B.T. and L.P.; Formal analysis, M.K. and B.T.; Resources, M.K.; Data curation, M.K.; Writing—original draft preparation, M.K.; Writing—review and editing, M.K., B.T. and L.P.; Visualization, M.K.; Supervision, B.T. All authors have read and agreed to the published version of the manuscript. Funding: The research was funded under the AGH-UST statutory research grant No. 16.16.140.315/05. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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