MultiScience - XXXI. microCAD International Multidisciplinary Scientific Conference University of Miskolc, Hungary, 20-21 April 2017 ISBN 978-963-358-132-2 DISTRICT HEATING SYSTEM WITH GEOTHERMAL ENERGY USE IN SZEGED, SOUTHERN GREAT PLAIN REGION, HUNGARY 1Zsolt Pinjung 2János Szanyi, 2Balázs Kóbor, 2Tamás Medgyes, 1P-MONT Kft. 6723 Szeged, Rózsa u. 10, [email protected], 2Dept. of Mineralogy Geochemistry and Petrology, University of Szeged, Egyetem u. 2-6. Szeged, H-6722, Hungary, [email protected] ABSTRACT Geothermal energy is widely known for its reliable, weather-independent and renewable energy. Hungary is one of the best places for geothermal energy in Europe, since the earth's crust is significantly thinner beneath Hungary than elsewhere. Geothermal energy is used mostly for heating and supplying baths with thermal water. Our study gives a comprehensive view of geothermal energy utilization for stakeholders and all those interested in the geothermal potential of Hungary and Central-Eastern Europe. INTRODUCTION The geological and hydrogeological conditions of the Pannonian basin are favourable for geothermal energy use: a positive geothermal anomaly occurs with high geothermal gradient. In comparison with the other parts of the continent, the Earth crust is much thinner in Hungary, only 22-26 km. This fact leads to a positive anomaly in the geothermal gradient of approx. 50°C/km with a heat flow of 90–100 mW/m2 (Fig. 1). Fig. 1. Thermal energy content of the Upper Pannonian strata (Dövényi, Horváth 1988) DOI: 10.26649/musci.2017.003 GEOLOGICAL BACKGROUND From the geological point of view, the Carpathian Basin is a large sedimentary basin, the basement, which consists of variously subsided basins and ridges. It was formed by rifting during the late Early and Mid-Miocene time. Extension was controlled by the retreat and roll-back of the subducted lithospheric slab along the Carpathian arc. (Fodor et al., 1999). Two corners, the Bohemian and Moesian promontories, formed gateways towards this open space. At both the northern and southern corners, broad shear zones developed. The initial NE-directed tension was gradually replaced by a later E- to SE-directed tension as a consequence of the progressive termination of subduction roll-back along the arc from the Western Carpathians towards the Southern Carpathians. There is growing evidence that an E-W-oriented short compressional event occurred during the earliest Late Miocene but during most of the Late Miocene extension was renewed. Starting from the latest Miocene, roll-back terminated and a compressional stress field propagated from the Southern Alps gradually into the Pannonian Basin, resulting in Pliocene (?) through Quaternary tectonic inversion of the entire basin system.(Horváth et al., 2006).The thickness of these deposits can reach 5,000 m in the South Great Plain. From geological aspects, it is practical to distinguish the fractured, karstified rocks of the basin's basement from the sediments overburden the basin. Fortunately, the formations related to the basement can be found on the surface as well, in the highland region, so their investigation does not necessarily require deep drillings (Fig. 2). Fig. 2. W-E Geological cross-section [Q:Quarter, Pa2:Upper-Pannonian, Pa1:Lower-Pannonian, PrePa: Pre-Pannonian] The two main depressions of the South Great Plain were formed in the Miocene, the Makó-Hódmezővásárhely depression and the Békés Basin, divided by the Battonya- Pusztaföldvár ridge. A thick layer of porous sediments can be found on this thinned, subsiding basement. The thickest porous aquifer sequences (with a total thickness of 2,500 m overburden layers) deposited in the upper Pannonian period. The sedimentary formation environments vary from those in deep basins through prodelta and delta fronts to delta plains. Fig. 3. Hydrodinamical background (Tóth, Almási 2001) On the bottom of the basin, different metamorphic and carbonaceous rock bodies are located and presenting possibilities for geothermal use. In the basin there are two existing flow rates: an upper, gravity driven flow system and a deeper, overpressured driven system concerning essentially the finer deep sea sediments and underlying formations (Fig. 3). The cause of the high overpressure (up to about 10 MPa above the hydrostatic pressure) is the tectonic compression of the formations. According to the pressure - elevation data, we can define, that the pressure gradient exceeds the hydrostatic pressure in the upper Pannonian sequences too. According to databases, more than 1,400 registered deep wells in Hungary have discovered thermal water, though only 950 are in production.. Some of them are abandoned oil and gas wells, but they also include wells drilled for thermal water exploitation purposes. The currently estimated total production rate from thermal wells, which are mostly used for about 6 months a year, is 84 million m3/year, with a heat content of 15.2 PJ/year. In Csongrád County, where 172 wells are located, all cities have geothermal district heating systems with injection wells. The South Great Plain Region has Hungary’s most important thermal water reservoirs, since the Quaternary and Upper Pannonian aquifer formations are the thickest in this area (Fig. 4). Even though the exploitation of these advantages are far below the potential production level, there are several excellent examples for direct thermal water utilization in Hungary. One optimum solution is the complex utilization of thermal water for energy production and balneological purposes. This is demonstrated by the system in Csongrád County. Another example is the utilization of the produced fluid’s heat in a multi-stage cascade system, and it’s reinjection into the deep reservoir. This is demonstrated by the geothermal cascade system of Makó (Pinjung et al. 2016). Fig. 4. Bottom of the Upper Pannonian layers [m.a.s.l] GEOTHERMAL PROJECT After considering environmental and energy saving aspects, the University of Szeged and the Council of Szeged have decided to use geothermal heat for their district heating systems. The Department of Mineralogy, Petrology and Geochemistry of the University of Szeged applied successfully within the Interreg III programme of the European Regional Development Fund for designing and authorizing a complex system using thermal energy. The use of geothermal energy has a long history in Szeged. The first researches related to thermal water were performed in Szeged in the 1880’s, and the first thermal well was drilled in 1927, but after that, the geothermal energy utilization slowed down. The heat supply systems of the University institutions, public buildings and householdes of Szeged are mainly based on natural gas. Approx. 75% of the estates are supplied from district heating systems, while the remaining part uses gas convectors or individual heating solutions. Fig. 5. Geothermal cascade system in the downtown Fig. 6. Geothermal cascade system in New-Szeged According to the concept, the thermal water has to be produced from the 2,000-m deep wells at two locations (downtown and New-Szeged), with 92-95 ºC water temperature, and it is injected into the underground layers through 2 reinjection wells at each location. The plans were completed by 2008, but the project was not implemented due to the lack of money. A professional investment group was set up, which successfully applied for EU funding for 48% of the total investment costs. According to the updated concept, the two thermal circles supply 80% of the heating of the buildings (clinics, department buildings, dormitories) of the University of Szeged and certain buildings of the Council(the Medical Clinic No. 1 and the Szeged Swimming Pool). The University of Szeged has approximately 30,000 students and is the town’s largest thermal energy consumer, so the largest emitter of pollutants. The construction of the system has been completed; six wells have been drilled, pipelines have laid down, heating circuits in the buildings as well, the heating centres are refurbished, and both systems started operation last year. (Fig. 5., 6.) The two systems are substituting a quantity of natural gas of 2,900,000 m3/year with a capacity of 8.9 MWth, and reduce the emission of CO2 by approximately 5,900 t,. The total costs of the project, including the six wells, pipelines, new heating stations, reach 10.8 million euros. The expected operating costs of the system reach 473,000 €/year. The project has a payback period of 13.5 years, which is reduced to 7 years due to the non-refundable grant. Thanks to this, our University reached 19th place on the World Ranking List of the “Green University”. Most of the geothermal systems in Csongrád County, e.g. in Csongrád, Makó, Mórahalom and Kistelek are operating similarly to the University systems, described above. These projects are relatively quickly recoverable and environmentally friendly investments. The District Heating Company of Szeged provides heat and domestic hot water to 28,000 households and around 400 public institutions, with 24 individually controlled boiler houses in Szeged (pop. 170,000). The total installed capacity is more than 110 MW. This system needs renovation, in every aspect. Bringing down heat distribution losses, optimizing control, intelligent metering, combining renewables, waste heat etc. are aims that would resonate with the using of geothermal energy. Thanks to the good geothermal potential, and the huge heating market, Szeged would be one of the best example of geothermal energy utilization in Hungary. The optimal use of thermal water in a cascade system can be described in the following way: In case of the production of 150°C thermal fluid, the first stage in an ideal geothermal cascade system is the electric power generation. The second level consumers in the cascade system are calibrated to a temperature difference of 90/70°C. In the next stage, the fluid is used with a temperature difference of 70/45°C, which is suitable for greenhouses or domestic hot water production.