B2 Smári Guðfinnsson
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GEORG Geothermal Workshop 2016 SESSION B2, Midstream. Presentation title: Feasibility study for utilizing an ORC cycle to cool medium temperature geothermal fluid to appropriate temperature for use at Seltjarnarnes district heating
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B2 Smári Guðfinnsson
- 1. A feasibility study for Seltjarnarnes medium temperature geothermal field Utilizing ORC cycle to cool geothermal fluid for district heating Smári Guðfinnsson Sunna Björg Reynisdóttir
- 3. Well nr. Average well Temperature 2014 Depth Year drilled SN-04 103°C 2.025 m 1972 SN-05 101°C 2.207 m 1981 SN-06 120°C 2.701 m 1985 SN-12 109°C 2.714 m 1994 Production Wells at Seltjarnarnes
- 4. Existing district heating system at Seltjarnarnes Pump District heating T ~35°C 100-120°C SN-04 SN-05 SN-06 SN-12 Buffer tank Pump Return water Geothermal fluid Cooling Water ORC Working fluid Return water
- 5. District heating system with ORC utilization Pump Condenser Turbine Evaporator Preheater Geothermal fluid Cooling Water ORC Working fluid 2 Regenerator 80°C 100-120°C Seawater SN-04 SN-05 SN-06 SN-12 Pump District heating T ~35°C Pump Buffer tank Return water Return water
- 6. Logged data series of 2014 0 20 40 60 80 100 120 1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec Flow[L/s] Date Well flow [L/s] Mixing of return water [L/s]
- 7. ORC power production based on installed capacity 0% 13% 25% 38% 50% 63% 75% 88% 100% 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 Utilizationofinstalledcapacity[%] Powerproduction[kW] Installed capacity [kW] Average production [kW] Average capacity utilization [%]
- 8. Need for increased well flow with ORC installed 0 5 10 15 20 25 30 35 40 45 50 55 60 0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 Increasedwellflow[L/s] Installed ORC capacity [kW] Average increased well flow [L/s] Maximum increased well flow [L/s] Minimum increased well flow [L/s]
- 9. Need for increased well flow with 700 kW ORC installed 0 20 40 60 80 100 120 140 1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec Flow[L/s] Date Well flow in 2014 [L/s] Return water [L/s] Incresed well flow [L/s]
- 10. PRO’s Electricity production – for own use / sold to the grid Better control of water temperature to the end-users Further utilization of lower temperatures – spa/bathing/thermal beach CON’s Increased need for well flow Limited area available for industrial development Grótta – a delicate recreation area Future possibilities
- 11. Any questions Thank you Smári Guðfinnsson Sunna B. Reynisdóttir
Editor's Notes
- Good day, my name is Smári and I come from EFLA consulting engineers and today I will present to you a desktop study we did for the Seltjarnarnes district heating. The study was made to evaluate the feasibility of utilizing an ORC cycle to lower the supply temperature to the district heating network. A Thermodynamic model was built to optimize the size of the ORC cycle and simulate a full year of production with logged data from the year 2014.
- I will start by telling you a little bit about the Seltjarnarnes geothermal area. The town of Seltjarnarnes is located within the capital region of Reykjavík and operates its own district heating system for 4.400 inhabitants. There has been drilled 12 wells at Seltjarnarnes, 5 intended for production but only four wells are connected today.
- The production is shifted between the wells throughout the year but at peak hours during the winter, all of the wells are used at the same time. Each well has its own characteristics but well number six has the highest temperature of 120°C.
- This is a simplified diagram of the existing district heating system at Seltjarnarnes. Hot water is pumped from the four wells to a buffer tank followed by mixing of return water before it is pumped to the pipe network.
- This is the system that was modelled with an ORC cycle added to the system. The hot water from the wells is now cooled down to a more suitable supply temperature, lets say 80°C and the heat is used to generate electricity in the ORC cycle. The set-up allows the well flow to be bypassed past the ORC cycle in case of maintenance or increased demand from the district heating.
- In this graph you can see logged data of the flow in 2014 which was used to model the thermodynamic simulation. The red area shows the flow pumped from the wells and the blue area is the proportion of return water mixed with the well flow. You can see how the heat demand fluctuates throughout the year with seasonal weather changes.
- This graph shows the results from the thermodynamic simulation as the blue line represents the average power production as a function of installed capacity of the ORC cycle. The dotted lines represents the utilization ratio of the installed capacity. For better understanding of the graph, lets say we install a 700 kW ORC cycle then the average production had been 614 kW in 2014 or 88% of the installed capacity. An 800 kW ORC system would have increased the average production to 658 kW but the utilization ratio drops to 82%. It is worth to mention that the simulation was calculated with logged data series from 2014 where lower temperature wells are used more than the high temperature wells. By prioritizing the wells for maximum utilization of the ORC cycle, the power production can be increased and lower temperature wells could be bypassed to minimize the extraction from the wells
- The biggest concern with the project is the increased need for well flow to operate the ORC cycle. This graph shows the increased well flow needed as a function of installed capacity. The blue line shows the average increased well flow over the year and if we taka a look at a 700 kW ORC system again the average increased well flow is 26 L/s.
- The need for mixing of return water will be reduced with colder supply temperature from the ORC system. This graph shows how the proportion of return water, which is the blue color, has decreased in the total flow of supply water. The red color is the logged well flow from 2014 and the green color represents the increase in well flow needed to operate 700 kW system. We could increase the exit temperature from the ORC cycle to increase the proportion of return water but that would affect the power production and utilization ratio. This means that we will have to increase the flow from the wells or choose a smaller capacity of the ORC cycle.
- The district heating of Seltjarnarnes would benefit from the ORC cycle by lowering or eliminating the electricity bill and profit from selling excess electricity to the grid. The downstream flow can be utilized further and increase sustainability, by using the return water and the return cooling water from the ORC. Landmass is very limited at Seltjarnarnes and therefore land for industrial development is not available. Utilizing the downstream flow for spa, bathing or even using the coastline and access to the sea, and setting up a thermal beach could be feasible, rather than the more traditional greenhouse, fish farming or drying, or other traditional industrial use. With ever increasing number of tourists visiting Iceland, this could be a viable option for the town or as a private investment in the near future.