University of Maribor Faculty of Energy Technology Volume 13 / Issue 2 SEPTEMBER 2020 www.fe.um.si/en/jet.html 2 JET Journal of ENERGY TECHNOLOGY ✓_____ JET 3 VOLUME 13 / Issue 2 Revija Journal of Energy Technology (JET) je indeksirana v bazah INSPEC© in Proquest's Technology Research Database. The Journal of Energy Technology (JET) is indexed and abstracted in database INSPEC© and Pro-quest's Technology Research Database. 4 JET /_____ ra JOURNAL OF ENERGY TECHNOLOGY Ustanovitelj / FOUNDER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Izdajatelj / PUBLISHER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Glavni in odgovorni urednik / EDITOR-IN-CHIEF Jurij AVSEC Souredniki / CO-EDITORS Bruno CVIKL Miralem HADŽISELIMOVIC Gorazd HREN Zdravko PRAUNSEIS Sebastijan SEME Bojan ŠTUMBERGER Janez USENIK Peter VIRTIČ Ivan ŽAGAR Uredniški odbor / EDITORIAL BOARD Dr. Anton BERGANT, Litostroj Power d.d., Slovenia Izr. prof. dr. Marinko BARUKČIČ, Josip Juraj Strossmayer University of Osijek, Croatia Prof. dr. Goga CVETKOVSKI, Ss. Cyril and Methodius University in Skopje, Macedonia Prof. dr. Nenad CVETKOVIČ, University of Nis, Serbia Prof. ddr. Denis DONLAGIČ, University of Maribor, Slovenia Doc. dr. Brigita FERČEC, University of Maribor, Slovenia JET 5 Prof. dr. Željko HEDERIC, Josip Juraj Strossmayer University of Osijek, Croatia Prof. dr. Marko JESENIK, University of Maribor, Slovenia Prof. dr. Ivan Aleksander KODELI, Jožef Stefan Institute, Slovenia Izr. prof. dr. Rebeka KOVAČIČ LUKMAN, University of Maribor, Slovenia Prof. dr. Milan MARČIČ, University of Maribor, Slovenia Prof. dr. Igor MEDVED, Slovak University of Technology in Bratislava, Slovakia Izr. prof. dr. Matej MENCINGER, University of Maribor, Slovenia Prof. dr. Greg NATERER, Memorial University of Newfoundland, Canada Prof. dr. Enrico NOBILE, University of Trieste, Italia Prof. dr. Urška LAVRENČIČ ŠTANGAR, University of Ljubljana, Slovenia Izr. prof. dr. Luka SNOJ, Jožef Stefan Institute, Slovenia Prof. Simon ŠPACAPAN, University of Maribor, Slovenia Prof. dr. Gorazd ŠTUMBERGER, University of Maribor, Slovenia Prof. dr. Anton TRNIK, Constantine the Philosopher University in Nitra, Slovakia Prof. dr. Zdravko VIRAG, University of Zagreb, Croatia Prof. dr. Mykhailo ZAGIRNYAK, Kremenchuk Mykhailo Ostrohradskyi National University, Ukraine Prof. dr. Marija ŽIVIC, University of Slavonski Brod, Croatia 6 JET Tehnični urednik / TECHNICAL EDITOR Sonja Novak Tehnična podpora / TECHNICAL SUPPORT Tamara BREČKO BOGOVČIČ Izhajanje revije / PUBLISHING Revija izhaja štirikrat letno v nakladi 100 izvodov. Članki so dostopni na spletni strani revije -www.fe.um.si/si/jet.html / The journal is published four times a year. Articles are available at the journal's home page - www.fe.um.si/en/jet.html. Cena posameznega izvoda revije (brez DDV) / Price per issue (VAT not included in price): 50,00 EUR Informacije o naročninah / Subscription information: http://www.fe.um.si/en/jet/ subscriptions.html Lektoriranje / LANGUAGE EDITING Terry T. JACKSON Oblikovanje in tisk / DESIGN AND PRINT Fotografika, Boštjan Colarič s.p. Naslovna fotografija / COVER PHOTOGRAPH Jurij AVSEC Oblikovanje znaka revije / JOURNAL AND LOGO DESIGN Andrej PREDIN Ustanovni urednik / FOUNDING EDITOR Andrej PREDIN JET 7 Spoštovani bralci revije Journal of energy technology (JET) V Sloveniji predstavljajo termoenenergetski procesi zelo pomemben delež k pridobivanju toplotne in električne energije, kakor tudi v pogonih avtomobilov, tovornjakov in ladij. Eden pomembnejših termoenergetskih procesov v sodobnih termo in jedrskih elektrarnah je Rankinov proces v vseh njegovih variacijah. Avtor Rankinovega procesa je škotski termodinamik William J.M. Rankine (18201872), ki je ta proces objavil leta 1859. V zadnjem času se kaže v svetu velik napredek v aplikaciji vodikovih tehnologij. Pričakuje se, da bodo cene vodika v prihodnjih letih drastično upadle, kot so pričele padati tudi cene gorivnih celic. Trenutna številka revije JET prikazuje idejo masovnega pridobivanja vodika s pomočjo soproi-zvodnje električne energije, toplotne energije in vodika v Rankinovem procesu. Zaradi ekoloških dejavnikov ter dejstva, da bo klasičnih virov v bližnji prihodnosti zmanjkalo, je velikega pomena izkoriščanje obnovljivih virov energije. V tej številki revije JET je prikazana tudi ideja proizvodnje toplotne energije s pomočjo sonca v sončnih kolektorjih. V ta namen je raziskana analiza življenjskega cikla sončnih kolektorjev. Analiza življenjskega cikla daje zelo natančen vpogled o dejanski uporabnosti in ekološki sprejemljivosti energetskih naprav. Vsem bralcem želim obilo zanimivega branja. Jurij AVSEC odgovorni urednik revije JET 8 JET Dear Readers of the Journal of Energy Technology (JET) In Slovenia, thermal energy processes represent a crucial share in the production of thermal energy, electricity as well as in the power processes of cars, trucks and ships. One of the most important thermal energy processes in modern thermal and nuclear power plants is the Rankine process in all its variations. The process is named after the Scottish thermodynamicist William J.M. Rankine (1820-1872), who published this process in 1859. Recently, the world has shown great progress in the application of hydrogen technologies. Hydrogen prices are expected to fall drastically in the coming years, and fuel cell prices have also started to decline. The present issue of JET magazine discusses the idea of mass production of hydrogen through the regeneration of electricity, heat, and hydrogen in the Rankine process. Due to ecological factors and the fact that conventional resources will run out in the near future, the use of renewable energy sources is of great importance. The current issue presents the idea of producing thermal energy with the help of the sun in solar collectors. To this end, a life cycle analysis of solar collectors is investigated. A life cycle analysis of each energy device on the actual usability and ecological acceptability of energy devices is conducted. I wish all readers plenty of interesting reading Jurij AVSEC Editor-in-chief of JET JET 9 Table of Contents / Kazalo Multi-purpose use and lifecycle analysis of solar panels Večnamenska uporaba in analiza življenjskega cikla solarnega panela Dušan Strušnik, Urška Novosel, Jurij Avsec..................................11 A review of the use of Rankine cycle systems for hydrogen production Pregled sistemov z Rankinovim procesom za proizvodnjo vodika Urška Novosel, Jurij Avsec............................................27 Reversible Pump-Turbines - Study of Pumping Mode Off-Design Conditions Reverzibilne turbine-črpalke - analiza nestacionarnih pojavov v črpalnem režimu obratovanja Uroš Ješe, Aleš Skotak..............................................37 The properties of the material gadolinium and the working agent used in the installation of magnetic refrigeration devices Lastnosti gadolinija, delovnega sredstva, ki ga lahko uporabljamo v magnetnih hladilnih napravah Botoc Dorin, Jurij Avsec, Adrian Plesca, Gabor Georgel, Rusu lonut....................45 Instructions for authors.............................................55 10 JET im Journal of JET v°lume 13 (2020) p.p. 11-26 Issue 2, September 2020 Type of article 1.01 Technology www.fe.um.si/en/jet.html MULTI-PURPOSE USE AND LIFECYCLE ANALYSIS OF SOLAR PANELS VEČNAMENSKA UPORABA IN ANALIZA ŽIVLJENJSKEGA CIKLA SOLARNEGA PANELA Dušan Strušnik1, Urška Novosel2, Jurij AvsecR Keywords: heat pump, life cycle analysis, Rankine cycle, solar panel, thermochemical cycle Abstract The combined use of renewable energy technologies and alternative energy technologies is a promising approach to reduce global warming effects throughout the world. In this paper, the solar panel is used in combination with a heat pump or with biomass sources to obtain heat, electricity, and hydrogen. Based on the Rankine thermodynamic cycle, hydrogen could be obtained from water with electrolysis and the CuCl thermochemical cycle. Furthermore, this study contains a life cycle analysis of solar panels. Povzetek Kombinirana uporaba tehnologij obnovljivih virov energije in tehnologij alternativnih energij je obetaven pristop za zmanjšanje učinkov globalnega segrevanja v svetu. V tem prispevku se sončna plošča uporablja v kombinaciji s toplotno črpalko ali z viri biomase za pridobivanje toplote, električne energije in vodika. Na podlagi Rankinovega termodinamičnega cikla bi lahko s pomočjo CuCl termokemičnim ciklom iz vode pridobivali tudi vodik. Poleg tega študija prikazuje analizo življenjskega cikla solarnega panela. R Corresponding author: Dušan Strušnik, Energetika Ljubljana d.o.o., TE-TOL Unit, Toplarniška 19, 1000 Ljubljana, E-mail address: dusan.strusnik@gmail.com 1 Energetika Ljubljana d.o.o., TE-TOL Unit, Toplarniška 19, SI-1000 Ljubljana, Slovenija 2 University of Maribor, Faculty of Energy Technology, Hočevarjev trg 1, SI-8270 Krško, Slovenia JET 11 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 1 INTRODUCTION The production of electricity and heat from renewable sources is becoming more efficient and economically viable. Given current environmental problems, the utilization of renewable energy sources is becoming desirable. The demand for thermal energy accounts for more than half of the world's total energy needs. Currently, most of that heat is generated from hydrocarbons and their derivatives. Some small amounts are produced through renewable energy sources throughout the world. In the future, it is expected that the production of heat from renewable sources will significantly exceed the current level. For this purpose, all types of renewable energy sources should be taken into account. Particularly interesting is the use of solar energy with solar collectors, which have a yield of over 60%, [1]. Currently, there are several solar thermal generation systems, including plate collectors, vacuum collectors, and hot-air collectors, with which solar and thermal energy can be simultaneously obtained. In the foreground, there are also solar panels, which can be used in different ways: mounted on the roof, to cover the facades of houses, and similar. In this way, they could acquire a good portion of the energy required for home and industrial heating. Fig. 1 shows a wall mounting and a roof mounting of a solar panel with aluminium tubes and rock wool insulation material. Figure 1: a) a wall mounting solar panel and b) a roof mounting solar panel In this case, the solar panel is comprised of aluminium tubes, rock wool insulation material, transparent cover, circulation pump, etc. The panels are usually roof-mounted; however, they can also be mounted on the building walls or on frames on the ground. The insulator located between represents the thermal building envelope and should keep heat losses as low as possible. If the solar panel is mounted in the wall, rock wool represents the thermal building envelope. Due to this sophisticated revision of sandwich panels, the field of application can be extended to office buildings, residential buildings, public buildings (e.g., education, culture, health, etc.). 12 JET Multi-purpose use and lifecycle analysis of solar panels 2 SOLAR PANEL MULTI-PURPOSE USE ANALYSIS 2.1 The solar panel as a hydrogen producer The main idea of the present article is the use of solar energy and biomass (wood chips) to produce cheap hydrogen. We combined two processes for hydrogen production: electrolysis and the thermochemical CuCl cycle. The working Rankine cycle system combined with the CuCl process, [2], and the electrolysis system is presented in Fig. 2 and Fig. 3. Additional energy source System with concentrated v _r solar power ¿¿3, ix 1 — Electric energy — Heat Distric heating Pump Figure 2: Solar panels in combination with Rankine cycle Figure 3: T-s diagram of the Rankine cycle Apart from hydrogen production in the process, we can also use waste heat from the Rankine cycle for district low-temperature heating of buildings and houses. All necessary data to calculate thermodynamic efficiency are presented in Table 1. JET 13 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Table 1: Results of the Rankine system calculation Rankine system and CuCl system State Pressure [bar] Enthalpy [kJ/kg] 1 300 3883.43 2 300 3599.4 3s 0.06 1972.8 3 0.06 2135.46 4 0.06 151.5 5 300 186.765 Parameter Value * 10 MW Ii 0.9 Til 6.831 kg/s S- -13.552 MW »V 403.346 kg/s, AT = 8 K Wi 240.9 kW Vu 0.85 Qald 25.252 MW WL.il 1.94 MW This relatively small cogeneration unit was built for the Posavje region of Slovenia. The idea of the present work is primarily to exploit solar energy for hydrogen production. Large amounts of solar energy are available, especially in the summer, spring, and autumn. To this end, we have used a model of covered solar panels, with which we could obtain approximately 20 °C of temperature increase. Additional heat for the processes is obtained from wood chips. With the help of solar calculation software found on the web page "The European Commission's science and knowledge service", [3], we have calculated the average amount of solar hours. For solar panels integrated into building for Posavje region, we calculated 1060 effective solar hours for solar angle 450 and 716 effective solar hours for solar angle 900. Fig. 4 shows the production of hydrogen per day with the Rankine cycle system, electrolysis and CuCl system. On the basis of thermodynamic calculation, we could determine the amount of hydrogen produced by the CuCl process and by electrolysis per day. As seen in Fig. 4, the total production of hydrogen is 3931.5 kg/day; the ratio between the hydrogen obtained by electrolysis and the CuCl process is more than 5. 14 JET Multi-purpose use and lifecycle analysis of solar panels Figure 4: The amount of produced hydrogen 2.2 The solar panel as a cooling system The use of thermal energy produced by a solar panel for cooling processes is also extremely interesting from a technical point of view. For this purpose, two cooling systems are presented. The first system represents cooling by means of an absorption refrigeration device and solar panels (Fig. 5). The second system represents cooling by means of solar panels, the ORC system and compressor heat pump (Fig. 6). Pump Figure 5: Cooling by means of an absorption cooling device and solar panel JET 15 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Figure 6: Cooling by means of solar panel, ORC system and compressor heat pump 3 LIFE CYCLE ANALYSIS OF SOLAR PANEL Life cycle analysis is a tool for assessing the energy and environmental profile of a product or technology from design to recycling. It provides global guidance and criteria, based on which decisions are made on further product development and which accompany the product or technology throughout the life cycle. Life cycle analysis covers the entire energy and environmental aspect from production, transport, installation, lifetime and decommissioning of a product. It is a methodology that includes four life cycle phases in a comprehensive and transparent way, on the basis of facts and expertise and in conformity with the ISO 14040 standard [4]. These phases are study goal and scope definition, data acquisition, modelling and interpretation of results. As regards new process and product development, the relationship between processes, product characteristics and environmental impacts have to be taken into consideration for each product. The international ISO 14025 standard, [5], was introduced to ensure comparable environmental efficiency among products. The main stages of life cycle analysis are presented in Fig. 7. 16 JET Multi-purpose use and lifecycle analysis of solar panels RESOURCES Figure 7: Main stages of life cycle analysis The life cycle analysis of solar panels comprises several phases, and each phase covers input-output data on materials, energies and environmental impact factors. Other authors developed life cycle analysis in a similar way, [6], [7]. In the solar panel production phase, the life cycle analysis includes extraction, production and transformation of raw materials required for the manufacture of a solar panel first as a semi-finished product, then as a product and finally an end product. The phase of a life cycle analysis involving solar panel production comprises three steps: material production, product manufacturing, packaging, and distribution. The phase of a life cycle analysis involving the solar panel application includes installation, use, and maintenance of a solar panel. The phase of a life cycle analysis involving recycling and waste management includes energy consumption for solar panel recycling and waste management. The environmental factor assessing the environmental burden accompanies all life cycle stages. The life cycle analysis model of a solar panel comprises input-output data and system boundaries. The input data relates to the data on raw materials, energy and hazardous waste used for solar panel manufacture. The output data relates to air emissions, aqueous waste, solid waste, energy, recycled material, and other products. The air emission data includes the data on produced or reduced greenhouse gases of the solar panel life cycle. Aqueous waste affects water management due to its discharge into the environment and the related environmental impacts in the solar panel life cycle. Solid waste is waste generated in the solar panel life cycle without the possibility of recycling. The energy on the output data side constitutes the solar panel energy life cycle and is the ratio between the energy invested, required for the solar panel production, and energy generated by the solar panel in its life cycle. Recycled material is material that can be reprocessed or reused in any other way and has been used in the solar panel life cycle. Other products are undefined products, occurring in the solar panel life cycle. A schematic arrangement of the analysis model of the solar panel life cycle is presented in Fig. 8. JET 17 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 1B (2020) Issue 2 Input Dataset Resource ■ Energy Hazardous Waste ~ Row Materials Exfraction ■ Bauxite ■ Basalt Rock ■ Dolomote Rock ■ Recycled Ahmiinntn AD Factors For Obtaining Row For STAF Pane! Natural Gas ' Transport Water 1 Cryolite Energy ■ Anode Block Manufacture ■ Aluminum AHoy ■ Rockwool ■ Water ■ Transport J STAF Pane! Energy And. Materials Needed ■ Natural gas ■ Energy Use And. Maintenance J STAF pane! technical action ■ Operation ■ Testing of performed factor ■ Spare parts ■ r.fiprnirak ■ Transport ■ Energy and file! ■ Ecology Recycling Management STAF Pane! Decommissioning Equipent And Material ■ Transport ■ Spare Part Demolition Fina! Disposa] Solid State Management Output Dataset fr Emissions To Air „ Water Waste t Solid Waste - Energy Recycling Materials Other Products Figure 8: Schematic arrangement of solar panel life cycle analysis model The quality of a life cycle analysis largely depends on the accuracy and precision of data and databases used. As a result of technological progress and increasingly stringent environmental regulations, the data and databases are constantly subject to changes and updates. The data from various databases differ because they are subject to various regional environmental regulations. The source of primary data in the life cycle analysis of a solar panel was the data provided by the solar panel manufacturer, i.e., Talum, d. d., [8]. As a secondary source of data, ee used the databases created by private or academic database developers: Ecoinvent Database, [9], Eurostat, [10], data from scientific literature, [11], [12], data from technical literature, [13], [14], etc. We split the data used in the life cycle analysis model of a solar panel into the following groups: materials, energy, waste, waste heat and air emissions. 3.1 Materials The materials group contains all materials used in the life cycle analysis model of a solar panel. They were split into two groups, namely aluminium materials for production, installation and packaging of aluminium and materials for production, installation, and packaging of rock wool. 18 JET Multi-purpose use and lifecycle analysis of solar panels Table 2 shows the database of average quantities of materials used for the solar panel manufacture. Table 2: Average quantities of materials for solar panel manufacture Aluminium Rock wool Material kg/panel kg/kg(AL) Material kg/panel kg/kg(Kv) Water 1558.336 193.8 Water - 4.468 Bauxite 39.774 5.100 Bauxite - 0.086 PE-foil 0.183 0.082 PE-foil - 0.009 Alumina 14.786 1.910 Briquettes 12.321 1.097 Anode blocks 3.502 0.450 Basalt rock 5.655 0.504 Coke 2.462 0.316 Portland cement 1.158 0.103 Aluminium 1.362 0.175 Dolomite rock 0.653 0.058 fluoride Tar pitch 0.494 0.063 Phenol 0.236 0.021 Green residue 0.045 0.006 Formaldehyde 0.236 0.021 Carbon residue 0.543 0.07 Impregnation 0.022 0.002 Calcium fluoride 0.008 0.001 Iron oxide 0.287 0.025 Cryolite 0.008 0.001 Acrylic dispersion 0.056 0.005 Calcined soda 0.004 0.0005 Total 6.399 Total - 201.974 Total 2 20.624 Total 1 1621.507 Total 1+2 1642.131 As much as 94.9% of water is consumed for the solar panel production, and such water is to a large extent disposed of into the environment as wastewater. The quantity of water required for alumina production is as high as 90%. On average, 39.77 kg of bauxite or 2.4% of the total material consumption is required for the manufacture of one panel. Total consumption of alumina and briquettes amounts to 1.6% of the overall material consumed for the manufacture of a single solar panel. The total quantity of material consumed is 1642.131 kg/panel. The overall amount of the material used for the production of one kilogram of aluminium is 201.974 kg/kg(AL), whereas the overall amount of the material used for the production of one kilogram of rock wool is 6.399 kg/kg(KV). 3.2 Energy The energy group comprises all energies dealt with in the life cycle analysis model of a solar panel and used in the production or processing stages for the solar panel manufacture. Energy consumed by a solar panel during the one-year or the forty-year operation period and energy generated by the solar panel during the one-year or forty-year operation period is also taken into consideration. In solar panel energy production, the average annual solar radiation for Central Europe [15] is taken into consideration for south-facing orientation and tilt angle of 15°. The energy consumption was split into three groups. We used the consumption of energy per JET 19 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 unit of one kilogram of aluminium for the aluminium production and transport, the energy consumption per unit of one kilogram of rock wool for the production and transport of rock wool and energy consumption per unit of solar panel for the manufacture and transport of solar panels. The one-year and forty-year energy consumption and production for solar panel operation are also included. The database of average energy amounts for the manufacture and operation of solar panels with south orientation and a tilt angle of 15° is shown in Table 3. Table 3: Average energy amounts for the manufacture and operation of solar panels with south orientation and a tilt angle of 15° Production, process, operation kWh/kg(AL) kWh/kg(Kv) kWh/pan Primary aluminium 23.99 - - Secondary aluminium 2.61 - - Briquettes - 0.579 - Rock wool - 1.879 - Ship transport 0.18 - - Rail transport 0.03 - - Other transport 0.01 0.024 - Aluminium panel manufacture - - 208.6408 Rock wool production - - 26.9895 Assembly and packaging - - 1.1772 Recycling - - 1.426 Consumption for one-year operation (1) - - 251.286 Production - one-year operation (2) - - 614.324 Consumption - 40-year operation (3) - - 698.616 Production - 40-year operation (4) - - 24572.96 Net production - one year (2-1) - - 363.038 Net production - 40 years (4-3) - - 23874.34 The amount of energy required for primary aluminium production and transport is 23.99 kWh/kg(AL) on average and 2.61 kWh/kg(AL) on average for secondary aluminium production and transport. The ratio between primary and secondary aluminium in the aluminium panel production is 80% to 20%. Rock wool is made from prefabricated briquettes. The briquette production requires 0.579 kWh/kg(KV) of energy on average, and the rock wool production and transport, however, requires 1.879 kWh/kg(KV) of energy on average. Therefore, the overall energy required for the production and transport of one kilogram of rock wool amounts to 2.388 kWh/kg(KV). We made a comparison between energy flows of average one-year and 40-year solar panel operation at the average annual solar radiation for Central Europe, south-facing orientation and a tilt angle of 15°. We also took into consideration the average consumption of energy for the operation of a circulating pump that sends a fluid to circulate through the solar panel. The average energy consumption for one-year operation, including the average energy consumption for solar panel manufacture and transport, amounts to 251.286 kWh/panel. In one year, a solar 20 JET Multi-purpose use and lifecycle analysis of solar panels panel fa cing south and having a tilt angle of 15°, feroduces 614.3241- kWh/panel on average. Net production in one year is the deference between tlie average annual energu produced and the average energy consgmpWon foo one-year operation, amounting to 363.038 kWh/panel. Furthermore, a similar calculation was made for the 40-year operation. Fig. 9 shows graphical presentations of average energies of the life cycle analysis of a solar panel. Thermal Electrolysis 13,75 SWf/Sg(AL) Alumina Manufacture 7,27 SWf/Sg(AL) Boxite Minin2 0,32 2Wf/Sf(AL) Anode Mia nufrcture 1,21 SWf/Sg(AL) Primary Casting 1,21 SWf/Sg(AL) Transport 0,23 SWf/Sg(AL) | Casting t,9 SWfUSg(AL) i Griding And Preparation 1 0,7 SWf/Sg(AL) | Transport 0,01 SWf/Sg(AL) Energy For Primary A luminum Production Energy For Secondary Aluminum Production Coal 1,514 kWh/kg(RW) Electricity 0, 296 kWÍVkg(RW) Gas 0,045 kWh/kg(RW) Eiesel 0,012 kWh/kg(RW) Transport 0,012 kWh/kg(RW) Electricity 0,452 kWh/kg(RW) Eiesel 0,045 kWh/kg(RW) Transport 0,012 kWh/kg(RW) Enersgyp For Roc kwool Production Production 614 kWh/panel Net Production 363 kWh/panel Operate Consumption 251 kWh/panel One Year Operation Energy Energy For Br iquettes Production Production 24573 kWh/panel Net Production 23874 kWh/panel Operate Consumption 698 kWh/panel 40 Years Operation Energy Figure 9: Graphical presentation of average energies of life cycle analysis of a solar panel JET 21 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Over the one-year period of operation, a solar panel facing south and having at a tilt angle of 15° would produce 2.4 times more energy than the amount required for the manufacture, installation and one-year operation. Over the 40-year period of operation, a solar panel facing south and having a tilt angle of 15° would produce 35 times more thermal energy than the amount required for the manufacture, installation and 40-year operation of a solar panel. 3.3 Air Emissions In the air emissions group, we used all emissions of CO2, the greenhouse gas, covered by the model. The CO2 emissions were split into three groups: emissions in the production and transport of primary raw materials, emissions in the production and transport of rock wool, and emissions in the manufacture and transport of solar panels. The database of average amounts of CO2 for the manufacture and operation of a solar panel facing south and having a tilt angle of 15° is shown in Table 4. Table 4: Average amounts of CO2 for solar panel manufacture and operation Production, process, operation kg(CO2)/kg(AL) kg(CO2)/kg(KV) kg(co2)/panel Primary aluminium 10.471 - - Secondary aluminium 0.8447 - - Briquettes - 0.3734 - Rock wool - 0.6181 - Ship transport 0.0513 - - Rail transport 0.0081 - - Other transport 0.0027 0.007 - Aluminium panel manufacture - - 83.127 Rock wool production - - 10.399 Assembly and packaging - - 0.457 Recycling - - 0.546 CO2 production - one-year operation 1 - - 98.898 CO2 reduction - one-year operation 2 - - 226.865 CO2 production - 40-year operation 3 - - 277.818 CO2 reduction - 40-year operation 4 - - 9074.604 Net reduction of CO2 - one year (2-1) - - 127.97 Net reduction of CO2 - 40 years (4-3) - - 8796.786 The amount of greenhouse gas emissions in the primary aluminium production and transport is 10.471 kg(C02)/kg(AL) on average and 0,8447 kg(C02)/kg(AL) on average in the secondary aluminium production and transport. The ratio between primary and secondary aluminium taken into consideration in the aluminium panel manufacture is 80% to 20%. Rock wool is made of prefabricated briquettes. The amount of greenhouse gas emissions in the briquette production and transport is 0.3734 kg(C02)/kg(KV) on average and 0,6181 kg(C02)/kg(KV) on average in the rock wool production and transport. Therefore, the total amount of greenhouse 22 JET Multi-purpose use and lifecycle analysis of solar panels gas emissions in the production and transport of one kilogram of rock wool is 0.9915 kg(CO2)/kg(KV) on average. Graphical presentation of the average amount of released CO2 of the life cycle analysis of a solar panel is shown in Fig. 10. Thermal Electrolysis 6,89 kg(CO2)/kg(AL) Alumina Manufacture 2,57 kg(CO2)/kg(AL) Anode Manufacture 0,49 kg(CO2)/kg(AL) Boxite Mining 0,08 kh(CO2)/kg(AL) Transport 0,06 kg(CO2)/kg(AL) CO2 Emission For Rimary Aluminum Coal 0,454 kg(CO2)/kg(AL) Electricity 0,115 kg(CO2)/kg(AL) Transport 0,036 kg(CO2)/kg(AL) Gas 0,009 kg(CO2)/kg(AL) Diesel 0,0034 kg(CO2)/kg(AL) | Casting 0,57 kg(CO2)/kg(AL) I Griding And Preparation 1 0,23 kg(CO2)/kg(AL) | Transport 0,0017 kg(CO2)/kg(AL) CO2 Emission For Secondary Aluminum | Electricity 0,176 kg(CO2)/kg(AL) ] Process 0,149 kg(CO2)/kg(AL) ] Transport 0,036 kg(CO2)/kg(AL) | Diesel 0,0122 kg(CO2)/kg(AL) CO2 Emission For Rockwool CO2 Emission For Briquettes Figure 10: Graphical presentation of the average amount of released CO2 of the life cycle analysis of a solar panel 3.4 Carbon Footprint We made a comparison between the carbon footprint of one-year and 40-year operation of a solar panel facing south and having a tilt angle of 15°. All CO2 gas emissions generated in all stages of solar panel manufacture and transport were taken into consideration in the operation, as well as the greenhouse gas emissions generated in the solar panel operation and circulating pump drive. Those greenhouse gas emissions were reduced by the amount of reduced greenhouse gases to obtain the carbon footprint result in the one-year and 40-year period. Reduced greenhouse gases are gases emitted into the air if the energy generated by a solar panel is produced by burning fossil fuels. The carbon footprint of one-year and 40-year operation of a solar panel facing south and having a tilt angle of 15° is shown in Fig. 11. JET 23 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 .100 S 0 O -100 -200 Produced 98,9 CO2 Reduced -226,9 CO2 Net -127,9 CO2 5000 CM O o One Year Footprint -5000 -10000 Produced 227 CO2 Reduced -9074 CO2 - Net -8796 CO2 40 Years Footprint Figure 11: Carbon footprint of one-year and 40-year solar panel operation Over the one-year period of operation of a solar panel facing south and having a tilt angle of 15°, 98.898 kg(co2)/panel of greenhouse gas are emitted into the air and 226.9 kg(C02)/panel of greenhouse gas are reduced. The one-year carbon footprint is negative, since over the one-year period of a solar panel operation, 127,9 kg(C02)/panel less C02 is emitted into the air than if the energy generated by a solar panel in one year is obtained by burning fossil fuels. Over the 40-year period of operation of a solar panel facing south and having a tilt angle of 15°, the amount of C02 emitted into the air is 227.818 kg(C02)/panel and the amount of C02 reduced is 9074.604 kg(C02)/panel. The 40-year carbon footprint is negative also in this case, since over the 40-year period of a solar panel operation, the amount of C02 emitted into the air is by 8796.786 kg(C02)/panel lower than if the energy generated by a solar panel in the period of 40 years is obtained by burning fossil fuels. 0 4 DISCUSSION AND CONCLUSION The positive environmental impact of solar panels is reflected mainly in the green production of thermal energy and in its negative carbon footprint. The green production of thermal energy means that solar panels generate 35 times more thermal energy in their life cycle than the energy needed for raw materials production, manufacture, installation and transport of solar panels. The negative carbon footprint, in contrast, means that solar panels contribute in their life cycle to the C02 air emissions reduction in comparison with the thermal energy generated by solar panels by burning fossil fuels. Another advantage of solar panels is that at the end of their lifetime, the materials used in solar panels may be almost fully recycled and reused. A negative impact on the environment, however, is associated primarily with the production of aluminium used in solar panels. The aluminium production process requires huge amounts of water which, to a large extent, is disposed of as wastewater or red mud in alumina production. Moreover, the aluminium production process requires high consumption of electricity that is still largely generated in Slovenia by burning fossil fuels. The heat that is released in the aluminium production processes is almost entirely discharged into the environment. 0ther heating systems operating in accordance with the solar radiation exploitation principle have characteristics and properties similar to solar panels. Energy payback time ranges from 24 JET Multi-purpose use and lifecycle analysis of solar panels less than a year to three years. Carbon footprints of solar heating systems are negative, which means that they generate far fewer greenhouse gases than by using fossil fuel heating appliances. For example, a photovoltaic panel reduces greenhouse gas emissions, namely by 0.6 kg CO2 for each kWh of energy produced. Furthermore, energy for the manufacture of photovoltaic panels is 30 times lower than the energy generated by a photovoltaic panel in its lifetime. The advantage of solar panels in comparison with other solar panels lies mainly in the fact that the materials used for the manufacture of solar panels can be easily almost fully recycled and reused. References [1] Z. Chen, S. Furbo, B. Perers, J. Fan, E. Andersen: Efficiencies of flat plate solar collectors at different flow rates, Energy Procedia, Vol. 30, p.p. 65 - 72, 2012 [2] J. Avsec, U. Novosel: Application of alternative technologies in combination with nuclear energy, Transactions of FAMENA, ISSN 1333-1124, vol. 40, spec. issue 1, p.p. 23-32, 2016 [3] The European Commission's science and knowledge service, Available: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php (10.07.2020) [4] ISO 14040. Environmental management - Life cycle assessment - Principles and Framework. [5] ISO 14025. 2006. Environmental labels and declarations - Type III environmental declarations - Principles and procedures. [6] I. Millera, E. Gen;era, S. H. Vogelbauma, R. P. Browna, S. Torkamanid, M. F. O'Sullivana: Parametric modeling of life cycle greenhouse gas emissions from photovoltaic power, Applied Energy, Vol. 238, p.p. 760-774, 2019 [7] B. Kim, C. Azzaro-Pantel, M. Pietrzak-David, P. Maussion: Life cycle assessment for a solar energy system based on reuse components for developing countries, Journal of Cleaner Production, Vol. 208, p.p. 1459-1468, 2019 [8] Talum, d. d., Tovarniška cesta 10, SI-2325 Kidričevo, Slovenija, Available: http://www.talum.si/ (10.07.2020) [9] Ecoinvent Database, Available: https://www.ecoinvent.org/database/database.html, (10.07.2020) [10] Eurostat, https://ec.europa.eu/eurostat, Available: (10.07.2020) [11] D. J. Gielen, A. W. N. Van Dril: The basic material industry and its energy use, Prospects for the Dutch energy intensive industry, ECN-C-97-019 [12] S. H. Farjana, N. Huda N, M. A. Mahmud: Impacts of aluminum production: A cradle to gate investigation using life-cycle assessment, Science of the Total Environment, Vol. 663, p.p. 958-970, 2019 JET 25 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 [13] U.S. Energy Requirements for Aluminum Production, Industrial Technologies. Program Energy Efficiency and Renewable Energy U.S. Department of Energy, 2007 [14] Calculation of fuel consumption per mile for various ship types and ice conditions in past, present and in future, Arctic Climate Change, Economy and Society, 2014) [15] ARSO, http://www.arso.gov.si/vreme/napovedi%20in%20podatki/vreme avt.html, Available: (10.07.2020) 26 JET im Journal of JET v°lume 13 (2020) p.p. 27-36 Issue 2, September 2020 Type of article 1.01 Technology www.fe.um.si/en/jet.html A REVIEW OF THE USE OF RANKINE CYCLE SYSTEMS FOR HYDROGEN PRODUCTION PREGLED SISTEMOV Z RANKINOVIM PROCESOM ZA PROIZVODNJO VODIKA Urška Novosel1R, Jurij Avsec1 Keywords: Rankine cycle, hydrogen production, electrolysis, thermochemical process Abstract The vast majority of steam power plants in the world are based on the Rankine cycle. It is a well-known, trustworthy process that uses water or water vapour as a working medium, which supplies heat from various primary energy sources: fossil fuels, renewable energy sources (solar energy, energy from wood biomass, etc.) or a combination of both. With the Rankine cycle, energy sources other than electricity can be produced, which can be used as the primary energy source for various applications. The present article focuses on the production of hydrogen in addition to electricity; therefore, two energy sources are obtained from the same system with a few modifications of the existing power plant for further exploitation. There are several processes for hydrogen production using the Rankine cycle; in the present article, two processes are focused on: using part of the electricity produced and obtaining hydrogen by electrolysis of water or using part of high quality steam (basically heat energy) in combination with electricity and obtaining hydrogen by a thermochemical copper-chlorine process. Each of these processes has its advantages and disadvantages, which are presented in the present article with an example model of a power plant. Povzetek Velika večina elektrarn na svetu, ki uporabljajo parni proces za proizvodnjo električne energije, temelji na Rankinovem procesu. Gre za dobro znan zanesljiv proces, ki kot delovni medij največkrat uporablja R Corresponding author: Urška Novosel, University of Maribor, Faculty of Energy Technology, Hočevarjev trg 1, SI-8270 Krško, Slovenia, Tel.: +386 7 6202 213, E-mail address: urska.novosel@um.si 1 University of Maribor, Faculty of Energy Technology, Hočevarjev trg 1, SI-8270 Krško, Slovenia JET 27 Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 vodo oz. vodno paro, kateri lahko dovajamo toploto iz različnih primarnih virov energije - fosilna goriva, obnovljivi viri energije (sončna energija, energija iz lesne biomase ipd.) ali pa kombinacija obojih. S pomočjo Rankinovega procesa lahko proizvajamo tudi druge vire energije, razen električne energije, ki jih nato uporabimo kot primarni vir energije za različne aplikacije. Članek se fokusira na proizvodnjo vodika poleg električne energije, kar pomeni, da iz istega sistema pridobimo dva vira energije za nadaljnje izkoriščanje, s čimer z nekaj modifikacijami izkoristimo obstoječe elektroenergetsko postrojenje za več namenov. Obstaja več procesov za pridobivanje vodika s pomočjo Rankinovega procesa, toda v članku se bomo osredotočili na dva procesa, in sicer lahko uporabimo del proizvedene električne energije in vodik pridobivamo z elektrolizo vode, lahko pa uporabimo tudi del visokokakovostne pare (v bistvu toplotno energijo) v kombinaciji z električno energijo in vodik pridobivamo s termokemičnim baker-klorovim procesom. Vsak od omenjenih procesov ima svoje prednosti in slabosti, ki bodo predstavljene v članku na konkretnem primeru modela elektrarne. 1 INTRODUCTION According to various forecasts, energy demand will strongly increase in the coming decades, so it makes sense to make the best of existing systems, especially through the optimization and production of clean energy sources. Hydrogen is certainly a clean source of energy (besides electricity) and highly applicable in several sectors, mainly in industry and transport. Throughout the world, about 80% of electricity is generated from fossil fuels and nuclear energy, [1]. These power plants mostly use the Rankine cycle as a process to convert primary energy source to electricity and possibly heat. The aforementioned products of the Rankine cycle can be used to produce hydrogen by electrolysis (using solely by electricity) or by a thermochemical copper-chlorine (Cu-Cl) cycle (using heat and electricity). However, an even greater change for the better would be if the Rankine cycle used renewable energy sources as a primary energy source. The present article deals with a model of a conventional steam power plant, in which part of the generated electricity and heat is used to produce hydrogen. The article contains an example of thermodynamic calculation and a comparison of two different cases. 2 RANKINE CYCLE AND HYDROGEN PRODUCTION The process model is a Rankine cycle power plant, in which two different processes were taken into consideration. First, we remodelled a steam power plant to a cogeneration plant (adding process heater in the cycle), since the heat is required for the Cu-Cl cycle to produce hydrogen, [2], (see Fig. 1). For the second case, we made no changes in the Rankine cycle, since only electricity is required for the hydrogen production by electrolysis, [3], (see Fig. 2). In both cases, the operating conditions are steady, and the process operates throughout the year (8,760 hours). 28 JET Vi review of the useof Rankinecycle systemsforhydrogen production Figure 1: Seyfioo nynlo producing hydrogen by Ce-CI peonott Figure 2: Seyfioo cyclo producing hydrogen by olonCrolctit Input data for the steam before entering the turbine are 8 MPa and 600 °C, and the mass flow rate is 50 kg/s. Pressure drops and heat losses are disregarded. Steam leaves the process heater and the condenser as a saturated liquid. The isentropic efficiency of the turbine is 80%; the pumps are isentropic. In the first case, when producing hydrogen by the Cu-Cl process, 30% of the steam is extracted from the turbine at 5.5 MPa for process heating. As in [2], the maximum temperature required for the Cu-Cl cycle is 530 °C (see Fig. 3); therefore, the steam cannot expand to pressure lower than 5.5 MPa (temperature of the steam in state 2 (see Fig. 1) is 543 °C) before entering the process heater. Another 70% of the steam continues to expand to 5 kPa in the condenser. In the second case, when producing hydrogen by electrolysis, the entire mass flow of the steam is expanded in the turbine from 80 MPa to 5 kPa in the condenser. JET 29 UrskaNovosel,Jurij Avsec JET Vol. 13 (2020) Issue 2 2.1 Thermochemical Cu-Cl cycle In the copper-chlorine cycle, water is split into hydrogen and oxygen through intermediate Cu-Cl compounds. The maximum temperature in the cycle is 530 °C. The schematic of a Cu-Cl cycle is in Fig. 3, [4]. The chemical reactions of the four steps in the Cu-Cl cycle with the temperature range are, [5]: 2CuCl(aq) + 2HCl(aq) ^ H2(g) + 2CuCl2(aq) 90 °C CuCl2(aq) ^ CuCl2(s) 150 °C 2CuCl2(s) + H2O(g) ^ CuO-CuCl2(s) + 2HCl(g) 400 °C CuO^CuCl2(s) ^ 2CuCl(l) + y2O2(g) 500 °C Figure 3: Schematic af a Co-Cl cycle The Cu-Cl cycle requires heat and electricity for hydrogen production. It has higher conversion efficiency than electrolysis and many other advantages over other methods for hydrogen production, including lower maximum temperature than other thermochemical cycles, [2]. Energy requirements for the process, used as input data for the calculation, are shown in Fig. 4, [6]. 30 JET Vi review of the useof Rankinecycle systemsforhydrogen production Heat: 220MJ/kg H2 (87.5% of total energy} Electricity input: 31.3MJ/kgH2 29.8% of total energy, (34.1% of total heat) high grade heat. 530°C 32.6% of total energy, (37.3% of total heat) low grade heat, <80°C 25.1% of total energy, (28.7% of total heat) mediun grade heat, 375°C ^^^ 375°C Jj^ 530°C 12.5% of total energy, electrolysis o Water, 9kg 25°C Cu-CI cycle Exothermic process Assume only 50% is reusedHeat process Hydrogen lkg 25°C O Oxygen 8kg, 25°C Figure 4: Eoorgc roquiromaoCt for cho Ce-CI nynlo We also took into consideration the amount of energy required to compress hydrogen; thus, the overall energy requirements for the production of 1 kg of hydrogen by Cu-Cl cycle are 220 MJ of heat and 31.3 MJ of electricity and for the compression 15 kWh of electricity, [6]. 2.2 Electrolysis Electrolysis is a chemical process by means of which the reduction and oxidation of chemical compounds are made using a direct electric current to drive a chemical reaction. The electrolysis of water (also called water splitting) is a process by which water is decomposed into hydrogen and oxygen using a minimum electrical voltage of 1.229 V, [3]. The chemical reaction is: 2H2O0 ^ 2Hz(g) + O2(g) In thermodynamic terms, the total enthalpy required to decompose water into hydrogen and oxygen is given by Eq. (2.1): AH = AG + TAS (2.1) In Eq. (2.1), AH is the reaction enthalpy, under standard conditions it is AH0=-285.83 kJ/mol, AG is the difference in Gibbs free energy (required electricity) and TAS is the amount of heat absorbed from the environment, [3]. Also, in this case, we took into consideration the amount of energy required to compress hydrogen; thus, the overall energy requirements for the production of 1 kg of hydrogen by electrolysis are 55 kWh of electricity for hydrogen production and 15 kWh of electricity for its compression. JET 31 Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 3 THERMODYNAMIC ANALYSIS We made calculations for each of the cases mentioned above at the specified conditions. The process in Fig. 1 is also drawn in the T-s diagram and is shown in Fig. 5. In Table 1, all input data, pressures, and enthalpies at various steam states are collected for the case. When producing hydrogen by the Cu-Cl process, the rates of process heat supply and heat input, as well as the power produced, are given by Eq. (2.2), (2.3) and (2.4), [7]: Steam enters the turbine at state 1, 30% of steam is extracted from the turbine at state 2 for process heating; another 70% of steam expands further to state 5. Steam enters the condenser, where it is condensed at a constant pressure to state 6 and then pumped to state 7. After the process heater, the steam is saturated liquid (state 3) and then pumped to state 4. Both steam fractions enter the mixing chamber and leave it at state 8 (see Fig. 1 and 5). Qph = 0.3mi(h2-h3) Qin = ml(h1-M Wt = 0.3m1(h1-h2) + 0.7ml(h2 - h5) (2.2) (2.3) (2.4) 1 6 5 Specific entropy, s Figure 5: T-u diagram Rankine cycle with praceuu heater 32 JET Vi review of the useof Rankinecycle systemsforhydrogen production Table 1: Input data, pressures and enthalpies for Rankine cycle with Cu-Cl process Steam Mass flow rate Pressure Enthalpy state [kg/s] [MPa] [kJ/kg] 1 50 8 3642.38 2 15 5.5 3530.69 3 15 5.5 1185.09 4 15 8 1188.35 5 35 0.005 2427.33 6 35 0.005 137.75 7 35 8 145.79 8 50 8 458.56 In the second case, we have a basic Rankine cycle process without a process heater (see Fig. 2). The process is also drawn in the T-s diagram and is shown in Fig. 6. In Table 2, all input data, pressures, and enthalpies at various steam states are collected for that case. When producing hydrogen by electrolysis, the rate of heat input and the power produced are expressed in Eq. (2.5) and (2.6), [7]: Qin = m(hi-hj (2.5) Wt = m(h1-h2) (2.6) Steam enters the turbine at state 1, and leaves it at state 2, then enters the condenser where it is condensed at a constant pressure to state 3 (saturated liquid) and pumped to state 4. Specific entropy, s Figure 6: T-t diagram Seyfioo nynlo JET 33 Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Table 2: Input data, pressures and enthalpies for Rankine cycle with electrolysis Steam Mass flow rate Pressure Enthalpy state [kg/s] [MPa] [kJ/kg] 1 50 8 3642.38 2 50 0.005 2441.24 3 50 0.005 137.75 4 50 8 145.79 For both cases, we calculated efficiencies. The Rankine cycle with a process heater is basically a cogeneration plant; the efficiency for this process is also called the "utilization factor", [7], and can be calculated by means of Eq. (2.7); the thermodynamic efficiency for the second case is written in Eq. (2.8). The power of the pumps is almost negligible, so this was not taken into consideration. = ^ (2.7) nTD = W (2.8) 4 RESULTS AND DISCUSSION When producing hydrogen by the Cu-Cl process, heat and electricity are required, so the Rankine cycle is used not only for electricity production but also for heat (process heating unit), resulting in lower turbine power output. With this cogeneration plant, the rate of process heat is 35.18 MW, and turbine power output is 44.2 MW. The rate of heat input in the boiler is 159.19 MW. Thus, the utilization factor, which was calculated with Eq. (2.7), is 50%. The rate of process heat is the input data to calculate the amount of hydrogen produced by the Cu-Cl process. The system operates 8,760 hours per year, so the available heat is 308,177 MWh. This heat energy is enough to produce 5,043 tons of hydrogen per year or 13.82 tons of hydrogen per day. Then how much electricity is available per year and how much electricity is needed to produce 13.82 tons of hydrogen per day were calculated. Per year, 387,192 MWh of electricity is available; the amount of electricity required for the production and compression of 13.82 tons of hydrogen is 119,489 MWh, which means we use about 30.9% of generated electricity. In a second case, producing hydrogen by electrolysis solely with electricity is required. With the basic Rankine cycle power plant, the turbine power output is 60.1 MW. The rate of heat input in the boiler is 174.83 MW. Thus the thermodynamic efficiency, which was calculated with Eq. (2.8), is 34.4%. For an extreme case, which is impossible in practice, when all of the electricity generated in the Rankine cycle power plant is used for the hydrogen production and compression, the amount of produced hydrogen has been calculated. Per year 526,476 MWh of electricity is available, which is enough to produce 7,521 tons of hydrogen per year or 20.6 tons of hydrogen per day. If the same percentage of electricity as in the previous case (30.9% of generated electricity) is used, the 34 JET Vi review of the useof Rankinecycle systemsforhydrogen production amount of produced hydrogen would be 2,324 tons of hydrogen per year or 6.37 tons of hydrogen per day. Thermodynamic results for both cases are shown in Table 3. Table 3: CelneleCioo roteWt RC + Cu-Cl process RC + electrolysis qph [mw] 35.18 / Qin [MW] 159.19 174.83 Wt [MW] 44.2 60.1 eu/nTD 0.50 0.344 100 % of electricity H2 produced 13.82 20.6 [t/day] 30.9 % of electricity 6.37 The calculation results show that a higher amount of hydrogen is produced by the Rankine cycle with a process heater for the Cu-Cl process; since the use of 100% of generated electricity is not realistic, the power supply must always be provided, but there may be a surplus of generated electricity, which can be used for other purposes, such as hydrogen production. If only 30.9% of electricity generated is used, more than half as much hydrogen as in the first case can be produced. Perhaps it makes sense to use also heat, not only electricity but also for hydrogen production, since the electricity is more widely used for many other applications and is easily convertible into other forms of energy. 5 CONCLUSION The present article shows that it makes more sense to produce hydrogen by Cu-Cl process when a Rankine cycle power plant is the source of heat and electricity to drive a hydrogen production process. The article also gives many cues for future work, such as increased efficiency with modifications of the Rankine cycle; adding reheating or regeneration. It would be interesting to make an exergy and economic analysis and then compare results. However, more accurate results would be obtained by building a dynamic model for the chosen hydrogen production process. References [1] International Energy Agency: ElonCricWc royoreCioy by toerno. Available: https://www.iea.org/data-and-statistics (15. 6. 2020) [2] Z. L. Wang, G. F. Naterer: Grooyhoeto get reduction io oil tends upgrading eod oxCrenCioo oporeCioot eich chormonhominel hcgroroo progenCioo, International Journal of Hydrogen Energy, Vol. 35, Iss. 21, p.p. 11816 - 11828, 2010 [3] D. A. J. Rand, R. M. Dell: Hygroroy Eoorrc, RSC Publishing, 2008 JET 35 Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 [4] (F. F. Naterer, S. Suppiah, L. Stolberg, M. Lewis, Z. Wang, M. A. Rosen, I. Dincer. K. Gabriel, A. Odukoya, E. Secnik, E. B. Easton, V. Papangelakis: Progress in thermochemical hydrogen production with the copper-chloeine cycle, International Journal of Hydrog en Energy, Vol. 40, I ss. 19, p .p. 6283-6295, 20 15 [5] N. Naterer, SI. Suppiah, M. Lewis, K. Gaeriel, I. Dincer, M. A. Rosen, M. Fowler, G. Rizvi, E. b. Easton, B. M/1. Ikeda, Ml. Hi. Kaye, L. Lu, I. Pioro, P. Spekkens, P. Tremaine, J. Mostaghimi, J. Avsec, J. Jiang: Recent Canadian advancers in nealeaa-based hydrogen production and the theomochemlcal Cu-CI cycle, International Journal of Hydrog en Energy, Veil. 34-, I ss. 7, p.p. 2901-2917, 2009 [6] J. Avsec, U. Novosel. Z. Wang: Themeoeconomic analysis of combined aolar theamal power plant with hydrogen production process. Proceedings c>f ICCE 2016. Ottawa: !nternational Academy of Energy, Minerals and Materials, p .p. 673-73, 20 16 [7] Y. A. Çengel, MA. Ao Bo:es: gheomodynamics: An Engineering Approach, Eighth edition, McGraw-Hill Education, 2015. Nomenclature; (Symbols) h, H G T s, S Q m W e n (Symbol meaning) enthalpy Gibbs free en ergy temperature entropy heahteraattreate mass flow rate power utilization factor efficiency 36 JET im Journal of JET v°lume 13 (2020) p.p. 37-44 Issue 2, September 2020 Type of article 1.01 Technology www.fe.um.si/en/jet.html REVERSIBLE PUMP-TURBINES -A STUDY OF PUMPING MODE OFF-DESIGN CONDITIONS REVERZIBILNE TURBINE-ČRPALKE -ANALIZA NESTACIONARNIH POJAVOV V ČRPALNEM REŽIMU OBRATOVANJA Uroš JešeR, Aleš Skotak1 Keywords: Pump-Turbine, Rotating stall, Cavitation, Pumping mode instabilities Abstract The role of pumped storage power plants (PSP) in electrical grid systems has been changing in recent years. Demands for switching from pumping to generating mode are becoming increasingly frequent. Moreover, the operating ranges of the reversible pump-turbines used in PSP systems are becoming wider in order to use the PSP as a regulator and a stabilizer of the electrical grid. The primary challenges in the development of pump-turbines are the hydraulic instabilities that occur in pumping and generating modes. The present paper focuses on partial load pumping mode instabilities, such as cavitation and rotating stall. Modern tools, such as CFD, are used for the analysis of the phenomena along with conventional experimental approaches. Rotating stall has been investigated in hydraulic laboratory experimentally and reproduced numerically using commercial CFD code. Three rotating stall cells with a rotational frequency of 2.5% of nominal pump-turbine frequency have been identified. Cavitat-ing vortices related to rotating stall were found in the guide vanes region. Both phenomena indicate highly unstable and potentially dangerous operating conditions that need to be investigated in detail. Understanding the causes for the instabilities will lead to an improved pump-turbine design that will enable safer, more flexible and more reliable operating with fewer unwanted instabilities. R Corresponding author: Uroš Ješe, PhD, Litostroj Power d.o.o., Litostrojska 50, 1000 Ljubljana, Slovenia, uros.jese@litostrojpower.eu 1 Aleš Skotak, PhD, Full time: Litostroj Engineering a.s., Čapkova 2357/5, 678 01 Blansko, Czech Republic, ales.skotak@litostrojpower.com JET 37 UrošJeše,Aleš Skotak JETVoi. 13 (2020) Issu e 2 Povzetek Vloga črpalnih hidroelektrarn v električnih omrežjih se v zadnjih letih spreminja. Zahteve po prehodu s črpalnega v turbinski režim in nazaj postajajo vse pogostejše. Območja obratovanja reverzibilnih črpalk-turbin se ob tem širijo, saj se črpalne hidroelektrarne uporabljajo kot regulator in stabilizator električnega omrežja. Glavni izzivi pri razvoju reverzibilnih črpalk-turbin so hidravlične nestabilnosti, ki se pojavijo v črpalnem in turbinskem režimu. Članek se osredotoča na nestabilnosti v črpanem režimu pri delnih obremenitvah, kot sta kavitacija in vrteče zastojne celice. Sodobna orodja, kot računska dinamika tekočin (CFD), se uporabljajo za analizo pojavov kot dodatek klasičnim eksperimentalnim pristopom. Vrteče zastojne celice so bile eksperimentalno raziskane v hidravličnem laboratoriju ter numerično reproducirane s komercialnim CFD programom. Odkrite so bile tri zastojne celice s frekvenco vrtenja 2.5 % nazivne frekvence črpalke-turbine. V območju vodilnih lopat so bili opaženi kavitacijski vrtinci povezani z zastojnimi celicami. Oba pojava kažeta na zelo nestabilno in potencialno nevarno obratovanje, ki ga je potrebno podrobno raziskati. Razumevanje vzrokov za nestabilnosti bo pripeljalo do izboljšane zasnove črpalke-turbine, ki bo omogočila varnejše, prožnejše in zanesljivejše obratovanje z manj neželenimi nestabilnostmi. 1 INTRODUCTION The market for pumped storage power plants (PSP) is growing every year. The main reason is the increasing number of weather-conditioned sources of energy, such as wind and solar power plants. To provide a reliable electrical grid, power plants that can balance the differences between demand and supply of electricity must be included. A PSP with reversible Francis runner that has a wide operating range and enables a fast transition from the generating to the pumping mode is highly suitable for this task. Besides new PSP projects, refurbishments of the pump-turbine runners represent an important part of the market. The development process of a new pump-turbine runner is related to several major challenges. The customer demands and final goals of the development process are the operation of the pump-turbine from zero to maximum output in the generating mode and non-restricted operation in the pumping mode. To achieve that, the whole operating range should be free of hydraulic instabilities. An additional reason for the refurbishment is frequently the improvement of the total efficiency of the cycle. The development of the new runner with the expected reliability and performance must be supported by effective cooperation among hydraulic and mechanical designers and by the application of precise manufacturing technology. Both generating and pumping mode instabilities have been analysed during this study in order to prepare the new runner design for a 2x325 MW pump storage powerplant in Dlouhe Strane in the Czech Republic, which will be able to operate from 0-100% output power, [1]. The main instability in the generating mode is considered the S-shaped curve close to the runaway operating point. It has been studied numerically and experimentally by various researchers, [2, 3, 4, 5, 6]. In contrast, cavitation and rotating stall are considered to be the main hydraulic instabilities in the pumping mode operation. Cavitation in the pumping mode regime mostly occurs at the impeller leading edge, where local pressure drops to vaporization pressure. However, in combination with the phenomenon called rotating stall, it is possible that the cavitation also occurs in the high-pressure distributor region. 38 JET Reveru/Wle Pump-Turbines-AStudyofPumping ModeOff-DesignConditions Rotating stall is a phenomenon present at partial load operation and was first investigated for the compressor applications, [7]. In recent years, the problem became highly relevant in the field of pump-turbines, which lead to several studies, [8, 9, 10]. The rotating stall is sometimes related to the positive slope of the performance curve also called hump zone, [11], which is an unstable and potentially dangerous operating region. Fig. 1 shows typical pump-turbine characteristics for pumping regime in a non-dimensional form (O - flow rate coefficient, ^ -specific energy coefficient, w - rotational speed, Ws - rotating stall rotational speed). If present, it can lead to uncontrollable changing of the discharge through the machine and consequently strong vibrations. The intensity of the rotating stall in pump-turbines can vary. As shown several times, experimentally and numerically, [8, 11, 12], changing discharge and guide vane opening angle can lead into a different number of the stalled cells and a different rotating stall frequency. Various shapes of rotating stall influence pressure fluctuations, radial forces acting on the impeller as well as guide vanes vibrations related to the torque fluctuations. If the rotating stall is very intense, the appearance of the cavitating vortex is possible in the distributor region. Operating under the described conditions should be completely avoided. However, rotating stall can be present even if the slope on the performance curve is negative. unstable stable —> 4> Figure 1: Pumping mode operating range with distributor hump and related rotating stall Rotating stall has been investigated experimentally and numerically in order to propose a hydraulic design that would be free of instabilities and would satisfy very demanding criteria of non-restricting operation. 2 EXPERIMENT Experimental measurements took place in Litostroj Engineering hydraulic laboratory, [12]. Additional to the standard performance measurement, eight (8) pressure sensors have been distributed around vaneless space between the impeller and the guide vanes. The rotational speed of the model pump-turbine has been set to n = 1400 min-1. Even though the whole range of guide vane openings has been measured, one constant guide vane opening a0 = 20 mm is presented and analysed in the paper. The guide vane channel and vaneless space have been JET 39 UrosJese, Ales Skotak JETVoi. 13 (2020) Issu e 2 observed during the measurements by installing Plexiglas window in the distributor region. The goal of the experimental setup was to measure low-frequency pressure pulsations in pumping and generating mode. Measurements have been done for the entire part load regime, however, for the analysis, operating points at the best efficiency point (BEP) Q = Qbep and at Q = 0.65 Qbep have been chosen and will be presented. Fig. 2 shows pressure fields around the distributor at Q = 0.65 QBEP. Three pressure cells are formed and are rotating around the distributor with governing frequency f = 0.59 Hz, which corresponds to around 2.5 % of the pump-turbine rotation frequency. The relationship between pressure fields and velocity contours obtained by CFD and presented on Fig. 4 have been discussed in detail by [10] together with governing mechanisms of rotating stall on different pump-turbine geometry and indicate the presence of the rotating stall. In contrast, the flow has been stable with no pressure pulsations at the Q = QBEP. The level of low-frequency pressure oscillations has been presented in [13] and reached ±15 % of the average pressure level around the distributor. Figure 2: Pressure fields around the distributor at Q = 0.65QBEP at different time steps Occasionally, during the pressure measurements at Q = 0.65 QBEP, cavitating vortexes have been observed in the distributor between the guide vanes, as seen in Fig. 3. Sometimes, there was one vortex, attached to the suction side of the guide vane (Fig 3, left). At some other instances, the phenomenon has been observed as several separated, smaller cavitating vortices, as seen in Fig. 3, right. In both cases, the vortices occur only for a short time. It should be pointed out that the cavitation in the distributor region is highly unusual due to very high pressure in the surrounding. 40 JET flei/ers/b/ePump-Turbines—A StudyofPump/ng ModeOff-DesignConditions Figure 3: Cavitating vortices in the distributor region 3 NUMERICAL ANALYSIS Fnr the Sinw analysis, numerical Sinw cimulatine (Computational Flui— Dynamics) software is enwa—ayc the most common tool. It ucec a set of Navier-Stokec equatinec to compute the transport of mass ae— momentum ie all parts of the computational —omaie. Commercial software has beee use— for the simulation. Transient simulations were performed ie the premises of Litostroj Eepieeeriep a.s. by using URANS equations ae— turbuleece mo—el base— oe the k-e mo—el. Choosing the appropriate turbuleece mo—el is essential for the successful repro—uctioe of complex phenomena, such as rotating stall. It shoul— be a robust mo—el to eeable convergence with wall functions that eeable exact pre—ictioe of first flow separation oe the gui—e vanes. Phe time step correspond to 2° of the impeller revolution, which has beee prove— by [8] ae— [10] to be a goo— compromise betweee quality of results ae— computational cost. Aroue— 20 revolutions of the impeller have beee simulate—. Boue—ary coe—itioes are very important for the stability of the simulations. Moreover, ie some cases, they also have a significant ieflueece oe the obtaiee— results, especially at eoe-optimal flow coe—itioes, such as part loa—. Ie our case, constant mass flow rate Q has always beee set at the ielet of the —omaie ae— at the outlet of the —omaie, static pressure ps has beee impose—. A no-slip coe—itioe has beee applie— oe the soli— walls. Phe meshing of the —omaies has beee —oee using commercial software, using structure— ae— uestructure— mesh. Phe total mesh contains aroue— 10 million cells; special attention has beee put ieto meshing the —istributor region, since this woul— be the place where the rotating stall occurs. Dimensionle^ criteria y+ that ie—icates mesh quality close to the walls has reache— meae values aroue— y+ = 10 ie all parts of the —omaie. Uestea—y CFD analysis has beee focuse— oe the rotating stall parameters ae— relate— phenomena. Operating points at Q = 0.65 QBEP have beee chosee for the comparison to the experiment. Three regions with high velocity have beee foue— (Fig. 4 - right) ie betweee three cells of blocke— —ischarge, which correspond to the experimental fie—iegs. Separation zoee regions perio—ically appeare— ae— —^appeare— at the gui—e vanes surfaces (Fig. 4 - left) ae— JET 41 UrošJeše,A!eš Skotak JETVoi. 13 ) Issu e 2 caused backflow from stay vanes and even spiral case region. A detailed description of the complex rotating stall origins is given in [11]. Numerical rotating stall frequencies have been estimated to 0.5 Hz. Since the frequencies of the rotating stall are very low, more impeller revolutions should be simulated for more accurate frequency prediction. However, we can say that the phenomenon has been accurately described by using CFD and simple k-e based f Velocity Meridional ¿«p 8.000e+000 M&Êf ^ ® 7.20