Coupling High-Temperature Borehole Thermal Energy Storages (HT-BTES) with existing Combined Heat and Power (CHP) systems is a promising approach to increase energy efficiency of district energy systems through recovery of otherwise wasted heat. This solution is currently being discussed in Sweden by the company Tekniska Verken in Linköping AB, for storing waste heat from their CHP operation in summer in a HT-BTES and to utilize it during peaks in winter. This would increase the flexibility between energy supply and demand in one of their plants. The available supply temperature during charge of the BTES is around 95C. There is, though, still limited experience of HT-BTES operation with just a few installations throughout the world. The aim of this Master´s thesis has been to evaluate a potential system design configuration for effective extraction and storage of waste heat from the Gärstadverket CHP-plants in connection to a HT-BTES. Data from previous operation of the CHP-plants and an existing TRNSYS model, developed at KTH and Bengt Dahlgren AB based on the well-known DST approach (Duct Ground Heat Storage Model), was used as a starting point to the development of a new, more complete model that includes a heat pump. The heat pump model was developed from manufacturer’s data for a non-standard 50 MW heat pump system using R717 as refrigerant. As an additional objective, design and operational experience of already existing HT-BTES installations has been compiled and analyzed. The BTES design were simulated with varied number of boreholes and borehole depth. The system was furthermore simulated with two different borehole heat exchangers (BHEs): double U-pipes and coaxial. Based on the results three optimized designs were found: 1 400 boreholes with double U-pipes and a borehole depth of 300 m, 1 300 boreholes with coaxial BHEs and a borehole depth of 300 m, and a design with 1 500 boreholes and 275 m borehole depth – all three designs with a borehole spacing of 5 m and with loops of 3 boreholes connected in series. The three BTES designs showed similar results with a potential to store around 107 GWh/year and to extract around 93 GWh/year with the use of a GSHP. The resulting discharge temperature from the BTES ranges between 40-60C, and up to 70C in the initial discharge period in the tenth simulation year. Further investigation is though needed regarding if there are any coaxial BHE available on the market that can work with the high temperatures in the BTES. Coupling High-Temperature Borehole Thermal Energy Storages (HT-BTES) with existing Combined Heat and Power (CHP) systems is a promising approach to increase energy efficiency of district energy systems through recovery of otherwise wasted heat. This solution is currently being discussed in Sweden by the company Tekniska Verken in Linköping AB, for storing waste heat from their CHP operation in summer in a HT-BTES and to utilize it during peaks in winter. This would increase the flexibility between energy supply and demand in one of their plants. The available supply temperature during charge of the BTES is around 95C. There is, though, still limited experience of HT-BTES operation with just a few installations throughout the world. The aim of this Master´s thesis has been to evaluate a potential system design configuration for effective extraction and storage of waste heat from the Gärstadverket CHP-plants in connection to a HT-BTES. Data from previous operation of the CHP-plants and an existing TRNSYS model, developed at KTH and Bengt Dahlgren AB based on the well-known DST approach (Duct Ground Heat Storage Model), was used as a starting point to the development of a new, more complete model that includes a heat pump. The heat pump model was developed from manufacturer’s data for a non-standard 50 MW heat pump system using R717 as refrigerant. As an additional objective, design and operational experience of already existing HT-BTES installations has been compiled and analyzed. The BTES design were simulated with varied number of boreholes and borehole depth. The system was furthermore simulated with two different borehole heat exchangers (BHEs): double U-pipes and coaxial. Based on the results three optimized designs were found: 1 400 boreholes with double U-pipes and a borehole depth of 300 m, 1 300 boreholes with coaxial BHEs and a borehole depth of 300 m, and a design with 1 500 boreholes and 275 m borehole depth – all three designs with a borehole spacing of 5 m and with loops of 3 boreholes connected in series. The three BTES designs showed similar results with a potential to store around 107 GWh/year and to extract around 93 GWh/year with the use of a GSHP. The resulting discharge temperature from the BTES ranges between 40-60C, and up to 70C in the initial discharge period in the tenth simulation year. Further investigation is though needed regarding if there are any coaxial BHE available on the market that can work with the high temperatures in the BTES. / Koppling av högtemperatur-borrhålslager (HT-BTES) med befintliga kraftvärmeverk (CHP) är ett lovande tillvägagångssätt för att öka energieffektiviteten i fjärrvärmesystem genom återvinning spillvärme. Denna lösning diskuteras för närvarande i Sverige av Tekniska Verken i Linköping AB, för att lagra spillvärme från kraftvärmeproduktion sommartid i en HT-BTES och utnyttja denna under effekttoppar på vintern. Detta skulle öka flexibiliteten mellan energiförsörjning och efterfrågan i en av deras anläggningar, Gärstadverket. Den tillgängliga framledningstemperaturen under laddning av borrhålslagret är ca 95 ℃. Det finns dock fortfarande begränsad erfarenhet av HT-BTES med bara några få installationer i drift över hela världen. Syftet med detta masterexamensarbete har varit att utvärdera en potentiell systemkonfigurationskonfiguration för effektiv utvinning och lagring av spillvärme från Gärstadverkets kraftvärmeverk kopplat till ett HT-BTES. Data från tidigare drift av kraftvärmeverket och en befintlig TRNSYS-modell, utvecklad hos KTH och Bengt Dahlgren AB baserat på den välkända DST-metoden (Duct Ground Heat Storage Model), användes som utgångspunkt för utvecklingen av en ny, mer komplett modell som inkluderar en värmepumpsmodell. Värmepumpsmodellen utvecklades utifrån data från en värmepumpstillverkare för ett icke-standardiserat 50 MW värmepumpsystem, med R717 som kylmedium. Som ett ytterligare mål har designparametrar och erfarenheter från drift av redan befintliga HT-BTES installationer sammanställts och analyserats. BTES-designen varierades genom simuleringar med olika antal borrhål och borrhålsdjup. Systemet simulerades fortsatt med två olika borrhålsvärmeväxlare (BHE): dubbla U-rör och koaxiala BHE. Baserat på resultaten hittades tre optimerade BTES-geometrier: 1 400 borrhål med dubbla U-rörs BHE och 300 m borrhålsdjup, 1 300 borrhål med koaxiala BHE och 300 m borrhålsdjup samt en design med 1 500 borrhål med dubbla U-rör och ett borrhålsdjup på 275 m – alla tre konfigurationer med ett borrhålsavstånd på 5 m och borrhålsloopar med tre borrhål kopplade i serie. De tre BTES-geometrierna visade liknande resultat med potential att lagra cirka 107 GWh / år och att extrahera runt 93 GWh / år med användning av en värmepump. Den resulterande urladdningstemperaturen från borrhålslagret varierar mellan 40-60 °C och upp till 70 °C i början av urladdningsperioden under det tionde simuleringsåret. Vidare studie krävs dock för att undersöka tillgängligheten av koaxiala BHE på marknaden som kan fungera med de höga temperaturerna i borrhålslagret.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-226160 |
| Date | January 2017 |
| Creators | Malmberg, Malin |
| Publisher | KTH, Tillämpad termodynamik och kylteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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