Geothermal Energy For Residential Co-Generation

Transcription

1 Geotermal Energy For Residential Co-Generation COROIU Miaela PD student Electrical Engineering Faculty, Tecnical University of Cluj-Napoca, Romania Energy Efficiency Director Energobit S.A. Cluj-Napoca, Romania; prof. CHINDRIS Mircea Electrical Engineering Faculty Tecnical University of Cluj-Napoca, Cluj-Napoca, Romania Abstract Nowadays te environmental pollution is one of te main concerns worldwide going next to te preoccupation to ensure te energy consumption of te modern world continuously increasing. One solution to tis issue is te energy generation using renewable sources, especially considering te classic energy sources being limited and te unfavorable availability forecast for coal, natural gas and oil. Te paper is structured in five capters and addresses a topic related to te exploitation of renewable energy sources to generate eat and power using modern and sustainable solutions in order to reduce te environmental impact by facilitating greenouse emissions savings. Te first capter presents general considerations related to te solutions to generate eat from geotermal energy providing brief information about an existing geotermal system in Oradea, underlines te importance of te main topic and te current concerns. In te second capter are evaluated te geotermal system s performance indicators based on te real energy audit. Te tird capter sows an eco-friendly and financial efficient solution to exploit te geotermal potential for cogeneration of eat and power, being presented te optimized energy balance and new performance indicators. In te fourt capter are given economical appraisal results of te geotermal co-generation investment and te last capter indicates te final conclusions. Romania is one of tose countries aving access to a wide range of renewable energy sources, from wind to solar, geotermal or biomass. Te West side of Romania is enriced wit geotermal deposits and several local commercial operators are providing surveys, explorations for geotermal waters by drilling deep wells. Te geotermal deposits in te Romanian West Plane are located at depts of m, in fissured rocks of calk and dolomite, wit average temperature of water ranging between o C. [1] Considering tese water temperatures, te geotermal waters can be successfully used into a eating centralized system (HCS) to generate eat for residential buildings, social objectives, administrative and commercial buildings, placed in te vicinity of te geotermal water extractions. Suc projects are already in place in Bior county were te eating centralized systems are using te geotermal water as source of primary energy, Beius and Oradea eating systems being representative projects. Te structure of a eating centralized system including te geotermal station and tree termal substations is scematically represented in figure 1. [2] Keywords renewable energy, sustainable energy tecnology, energy efficiency, geotermal energy potential, power, eating, cogeneration, Organic Rankine Cycle, energy performance indicators, GES savings. I. INTRODUCTION Modern world is relying today on electrical energy. Te next-generation tecnologies are built to operate consuming power. It s also notable te significant and continuous growt of world population, determining default steps tat sould be taken to provide termal energy in te form of ot water, eating or air conditioning to ensure decent and convenient living conditions. Moreover, te nature needs our elp to conserve te appropriate environment for living conditions. Tus, te green ouse emission level sould be considerable decreased immediately by introducing clean modern tecnologies wit ig energy performance. Significant reduction of greenouse emissions level is accessible by power generation using renewable energy sources. Fig.1. Scematic representation of te eating and ot water production system 66

2 Te geotermal water, extracted from drilling, is transferring te energy witin a eat excanger to te intermediate agent wic is delivered troug te intermediate agent network to tree termal substations. For te seasons wen te need for eat is exceeding te potential of te geotermal water, a boiler using natural gas is providing te missing energy. Te geotermal station analyzed ere is defined by main parameters, [2] as follow: - maximum termal power: 10,5 MW - geotermal water termal power: 8 MW - termal power from boilers on natural gas: 2,5 MW - II. GEOTHERMAL SYSTEM S PERFORMANCE INDICATORS Te energy audit performed for te system formed by te geotermal station and te intermediate agent network is based on te following measured parameters [3]: - geotermal water flow: 117 m 3 / - geotermal water inlet temperature: 106 o C - geotermal water outlet temperature: 52,3 o C - natural gas was flow: 270 Nm 3 / - Inferior calorific power: kj/nm 3 Te complex energy balance, on a yearly basis, for te system gatering te geotermal station and te intermediate agent network is presented in table 1 and scematically represented in te Sankey diagram sown in figure 2. Table 1. Complex energy balance for te system gatering te geotermal station and te intermediate agent network [3] Fig. 2. Sankey Diagram representing te energy balance of geotermal station and intermediate agent network Based on te complex energy audit, sall be determined te following performance indicators: - system s termal performance: - system s electrical performance: (1) - geotermal station termal performance: intermediate agent network termal performance: (2) (3) (4) - green-ouse gases emissions (GES) level [4]: GES = Q gn * F gn + E * F power = 712,90 t CO 2 (5) Te real energy balance results analysis sows tat te solution of using te geotermal water energy to produce ot water and eating witin a eating centralized systems supplying residential and industrial eat consumers as a very good performance ( ) and an appreciable social impact based on te competitive price for ot water and eat, 67

3 muc lower tan te average prices paid by te consumers across country. Te price competitiveness derives from te lower price of te energy obtained from geotermal water ( ) [2] compared wit te natural gas price burned in te boiler ( ) to produce te similar amount of energy. [5] III. CO-GENERATION SOLUTION FOR A SUPERIOR USE OF GEOTHERMAL ENERGY Te investigations addressed te tecnical possibilities for a superior exploitation of te geotermal energy potential, witout generating a significant negative impact on te operation performance of eating centralized system, neiter on te environment or affecting prices competitiveness. Te solution identified proposes te use of a power generation installation using as primary energy a part of te energy potential of geotermal water. Te proposed power generation installation is based on Organic Rankine Cycle module (ORC) aving penta-fluorpropane (HFC-245fa) as working fluid. Te tecnical advantages resulted by te use of an organic fluid in a Rankine cycle consists in ig efficiency, reduced mecanical stress on turbine due to low speed, elimination of te mecanical losses in speed reducer due to te direct coupled turbine-generator, lack of erosion to turbine s blades due to te lack of liquid droplets in te fluid vapours. [6, 7] In addition to te tecnical benefits tere are benefits in te field of operation and maintenance mentioning simple start/stop procedures, no need for supervisory staff, low noise in operation, ig availability (> 98 ), ig efficiency operation at partial loads, reduced costs of operation/ maintenance (3-5 ours/week), long life cycle. [6, 7] Te principles of Organic Rankine Cycle installation is presented scematically in te figure 3. It is important to note tat T expander is not a turbine but a unit of two blades, similar wit te gas compression system from elix compressors. Te main parameters of an ORC power generation installation suitable to be used witin a geotermal station to co-generate eat and power, consist in: installed power: kw; source of warm: geotermal water wit inlet temperature range of C; inlet eat range kw and flow range 27,4 to 45,4 m 3 /; source of cold: cold water or air wit outlet eat range kW; Considering te data above te average electrical efficiency is µ 7.5. Te installation is caracterized by te following basic parameters: termal power on entry: Qi =725 kw (flow 45 m 3 /) electrical power: P e =50 kw termal power to condensation (air-cooling): Q e =670 kw average own power consumption: P p 8.5 kw (power for operation of circulation pump, fans condenser) Te suggested option to insert te ORC power generation module inside te eating centralized system is represented in figure 4. Te ORC module is placed upstream te geotermal station witin a secondary circuit were a part of te geotermal waters flow directed to te geotermal station is used to provide te primary energy for te ORC installation. Te ORC module generates power, to be delivered into national power grid, and eat delivered in te geotermal station. Fig. 4. Scematic representation of te proposed option to insert te ORC power generation module inside te eating centralized system Fig. 3. Scematic representation of te Organic Rankine Cycle installation. [8] On te basis of energy calculations was estimated tat te proposed installation will produce yearly 378 MW of power, of wic 64 MW represents own power consumption and 314 MW represents te electricity to be delivered to national power grid. Starting wit te energy baseline audit presented in table 1 and considering te influence of te operation of ORC module on te geotermal centralized eating system it was 68

4 calculated te new energy balance on yearly basis in order to appreciate ow te operation of ORC module influence te performance of te geotermal system. Te results of te complex energy audit performed for te centralized geotermal eating systems including te geotermal station and intermediary agent network, in te condition of ORC module in operation, is presented in te Table 2 and scematically represented in Figure 5. Table 2. Complex energy balance for te system gatering geotermal station and te intermediate agent network wit ORC module in operation. [3] Inlet Energies Q at eat transferred by te geotermal water MW ,9 90,7 8 Q gn eat produced by burning natural gas 2686, 4 8,13 SCP caz ga RAI c m Q ac eat combustion air 21,4 0,06 E electrical energy 338,5 1,02 consumed W i total inlet energies ,2 100 Outlet Energies MW Q plates eat 25,7 0,08 excanger s lost eat by convection and radiation Q boilers lost eat by 5,2 0,02 convection and radiation Q lost eat via flue 250,7 0,76 gases, discarged into te cimney Q lost eat troug 1458, 4,41 intermediate agent 7 network Q u useful eat, ceded ,2 in termal substation 8,7 3 E power lost in cables 4,9 0,01 E power lost in 46,7 0,14 engines E u useful power (to 286,9 0,87 te engines trees) w e total outlet energies ,5 7,5 2 w Σ te energy balance 159,7 0,48 error Fig. 5. Sankey Diagram representing te energy balance for te system formed by geotermal station and intermediate agent network wit ORC module in operation. Based on te complex energy audit for te system formed by te geotermal station and intermediate agent network, wit ORC module in operation, sall be determined te new performance indicators: - system s general performance: - system s termal performance: - system s electrical performance: - geotermal station termal performance: - intermediate agent network termal performance: (10) - green-ouse gases emissions (GES) level [4]: GES = Q gn * F gn + E * F power = 779,94 t CO 2 (11) Te performance indicators calculations sows tat te operation of te ORC module installed upstream te geotermal station as no significant influence on te eating (6) (7) (8) (9) 69

5 centralized systems performance, observation tat encourage te development of suc power generation projects were conditions are suitable. Analyzing te performance of te ORC installation te calculations started wit te yearly complex audit. Te complex energy balance, on a yearly basis, only for te ORC module as been drawn up based of te information presented in te tecnical seet of ORC module type S400-ET. Te results are presented in table 3 and scematically represented in a Sankey diagram in figure 6. Table 3. Energy balance for te ORC module installed upstream te geotermal station Inlet Energies MW Q at received eat from geotermal water W i total inlet energies Outlet energies MW Q e eat transferred to 5065, 92,4 cold source 2 1 (evacuated in condenser) E g power lost in 37,8 0,69 generator and internal network E CP power for own consumption 64,3 1,17 E u useful power ( to be 313,7 5,72 delivered in national power grid) W e total outlet energies Fig. 6. Sankey Diagram representing te energy balance of te ORC module. Considering te energy balance presented above it was calculated te performance indicators of te ORC module: - ORC module s electrical performance: (12) - green-ouse gases emissions (GES) savings [4]: dges = E u *F p = 219,9 t CO 2 (13) Te power generated by te ORC installation using geotermal water energy as primary energy is clean energy wit zero greenouse emissions. Te greenouse emissions savings corresponds to te clean power generated by te ORC module and delivered into te national grid wic replaces te same amount of power generated by classic power generation installation. IV. ECONOMIC SUSTAINABILITY Te tecnical evaluation confirmed te utility, te realistic and acievable approac of using ORC module to generate power and eat exploiting te geotermal water as primary energy. Te environmental benefits and minimum costs of operation are strong arguments wen te opportunity of suc investments is promoted. Te economic reality is extremely important for creating te sufficient conditions to implement suc projects and te financial sustainability is decisive. Tus, it was terefore necessary an economic evaluation of te project, calculating te financial performance indicators in order to confirm te project s financial feasibility complementary wit te tecnical feasibility. For te financial performance indicators calculation te economic evaluation treats te initial investment versus revenues and expenses generated after implementation. For te amount of power generation calculations is considered tat te ORC module will be in operation 8000 ours/year, te rest of te yearly ours being used for revisions, preventive and corrective maintenance works. Te ORC module generates 400 MW/year power, of wic 68 MW/year represents te own consumption and te rest of 332 MW/year constituting net power production delivered to te national power grid. Te value of te net power generated and delivered into te national grid, considering te price of power and te corresponding green certificates [9] is estimated at: Vp = Q E x (P E + 2 x P CV ) = euro/year were: P E = 49 euro/mw average power price sold in national grid P CV = 50 euro/mw average green certificates price Q E = 332 MW/year - power generated and sold Te revenues obtained from selling te power, generated and delivered into national grid, are formed by te value of te power sold and te value corresponding te sell of green 70

6 certificates distributed according te regulations, two green certificates for eac MW of power generated and delivered into national grid. Te economical appraisal is based on te following ypotesis: - total investment value: euro - depreciation period: 20 years - service and monitoring costs: 944 euro/year - oter operational costs: 1749 euro/year - bank loan level for 5 years: euro - loan interest: euro/year Te resulting financial performance indicators sow a feasible investment [10]: o Payback period = 5,6 years o IRR= 22 o NPV= euro o Benefit/Cots ratio = 1,93 V. CONCLUSION Prior to making use of a part of te geotermal water energy to produce power, te centralized geotermal eating system s performance indicators sows a ig performance level: - general performance: η e = 94,24 - termal performance: η te = 94,22, - electrical performance: η ee = 84,75. Introducing te ORC module upstream te geotermal station cange sligtly in te sense of reducing te performance as follow: - general performance: η e = 94,1, - termal performance: η te = 94,19, - electrical performance: η ee = 84,76. Te performance reduction level is very small, 0,14 for general performance and for termal performance, but te electric performance is remaining te same. Te performance of te ORC module generating power to be delivered in national power grid, evaluated at η e =5,72 is low due to te relatively low temperature of geotermal water (~ O C). But, from economic considerations, were confirmed te opportunity and feasibility of te superior exploitation of geotermal water potential by co-generating power and eat wit ORC module installed upstream te geotermal station in te conditions wen te power is delivered in te national power grid and benefits of te receipt of green certificate. A parallel tecnical and financial evaluation was performed for tecnical and financial feasibility appraisal in te conditions wen te power generated by ORC module is used for te own consumption and not being delivered into national power grid. Te evaluation aware tat if te power generated by te ORC module will be used for te own consumption of te geotermal eating centralized system, te complex energy balance calculations sows a general performance significantly reduced of ηe= 81,38, meaning 12,86 less tat in baseline situation witout ORC module installed. As a result of present solutions analysis it was identified te opportunity to exploit te geotermal water s energy potential to generate power using an ORC module optimizing te use of power by direct delivery in national power grid and not for self-consumption. REFERENCES [1] C. Roba, "Geotermal penomenon in western Romania," PD tesis, Department of Environmental Science, Babes- Bolyai University, [2] D. Hatiegan, M. Coroiu, D. Nistor, "Complex Energy Balance at Transgex in Oradea", [3] D. Hatiegan, M. Coroiu, " Complex Energy audit at Iosia Nort Geotermal Station", 2013 [4] ttp:// Covenant of Mayors, "Tecnical Annex to te instructions SEAP - Emission factors", 2014 [5] ttp:// [6] ttp:// ations, "Te termodynamic principle - te ORC cycle", Turboden, 2014 [7] ttp:// [8] A. Duvia, R. Bini, H Spanring, "Application of ORC units in te MDF and particleboard sector - general considerations and overview of te experiences of te first in tis industry ORC plant installed at MDF Hallein" 2007 [9] Law no. 23/2014 approving Government Emergency Ordinance no. 57/2013 amending and supplementing Law no. 220/2008 for te system to promote energy production from renewable energy sources, MO 184 / [10] ttp://ec.europa.eu/regional_policy/sources/docgener/guides/cost/ guide2008_eu.pdf, Manual EC ACB ("Guide to Cost - Benefit analysis of investment projects"). 71