Simulation of a Combined Cycle Process with Oxyfuel Combustion and Carbon Capture
Heiska, Ilmo (2016)
2016
Ympäristö- ja energiatekniikan koulutusohjelma
Luonnontieteiden tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2016-12-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201611244772
https://urn.fi/URN:NBN:fi:tty-201611244772
Tiivistelmä
The aim of this thesis was to present a combined cycle process with oxyfuel combustion and carbon capture and to study the process through simulation. Two different cases were used to study the effect of a working fluid with and without argon for the process. The thesis includes studying the concept of a combined cycle process and its basic processes, the simulation of the two cases using Aspen Plus simulation software and the analysis of the results with comparison to a similar process, the Graz Cycle.
The simulation model was built according to a patent application by Dr. Matti Nurmia for a Brayton-Rankine process with carbon capture. Case 1 was used for the process without argon and Case 2 for the process with argon. The model configuration and parameters used for the two cases had only minor differences in order to get as comparable results as possible. The completed model was optimized for both cases using the optimization tool of Aspen Plus.
The simulation results showed that the thermal efficiency of the process was 0.565 for Case 1 and 0.535 for Case 2. The separation of carbon dioxide from the process is more straightforward for Case 1 but for Case 2 the separation of carbon dioxide from a mixture consisting mainly of argon and carbon dioxide requires energy. When the energy required for oxygen supply was estimated for both cases as well as the separation work for Case 2, the net efficiency of the process was determined as 0.539 for Case 1 and 0.506 for Case 2, while the net efficiency for the Graz Cycle was 0.548. The pressure ratio for the main gas turbine in the process was determined as 87.0 in Case 1 and 20.8 in Case 2 which was caused by lower discharge pressure in Case 1 as the main gas turbine inlet pressure was the same for both cases. The discharge pressure for the main gas turbine was determined as 0.230 bar in Case 1 and 0.936 bar in Case 2. The results indicate that the use of argon in such a combined cycle could have major benefits as a lower pressure ratio on one hand and a higher discharge pressure on the other hand should lead to capital cost savings considering the structure of the main gas turbine and the heat recovery steam generator of the process.
Further research on the separation of carbon dioxide from a mixture consisting mainly of argon and carbon dioxide is suggested. A more complete economic analysis of the process and a demo-scale plant are recommended to verify the results and confirm the economic feasibility of the process as well as find out which one of the two simulated cases could provide more cost-effective results in practice.
The simulation model was built according to a patent application by Dr. Matti Nurmia for a Brayton-Rankine process with carbon capture. Case 1 was used for the process without argon and Case 2 for the process with argon. The model configuration and parameters used for the two cases had only minor differences in order to get as comparable results as possible. The completed model was optimized for both cases using the optimization tool of Aspen Plus.
The simulation results showed that the thermal efficiency of the process was 0.565 for Case 1 and 0.535 for Case 2. The separation of carbon dioxide from the process is more straightforward for Case 1 but for Case 2 the separation of carbon dioxide from a mixture consisting mainly of argon and carbon dioxide requires energy. When the energy required for oxygen supply was estimated for both cases as well as the separation work for Case 2, the net efficiency of the process was determined as 0.539 for Case 1 and 0.506 for Case 2, while the net efficiency for the Graz Cycle was 0.548. The pressure ratio for the main gas turbine in the process was determined as 87.0 in Case 1 and 20.8 in Case 2 which was caused by lower discharge pressure in Case 1 as the main gas turbine inlet pressure was the same for both cases. The discharge pressure for the main gas turbine was determined as 0.230 bar in Case 1 and 0.936 bar in Case 2. The results indicate that the use of argon in such a combined cycle could have major benefits as a lower pressure ratio on one hand and a higher discharge pressure on the other hand should lead to capital cost savings considering the structure of the main gas turbine and the heat recovery steam generator of the process.
Further research on the separation of carbon dioxide from a mixture consisting mainly of argon and carbon dioxide is suggested. A more complete economic analysis of the process and a demo-scale plant are recommended to verify the results and confirm the economic feasibility of the process as well as find out which one of the two simulated cases could provide more cost-effective results in practice.