Life cycle assessment of the brayton cycle in a combined cycle hybrid solar central receiver power plant

Le Clus, Jeanne (2011-12)

Final year project 2011

Technical report

ENGLISH ABSTRACT: In the past decade global concern for energy security and the negative environmental impacts caused by fossil fuels has caused the global power industry to become more focused in a search for alternative energy sources and solutions. The need for renewable, sustainable green energy sources to reduce the long term impacts caused by current pollution is becoming evident and unavoidable. A promising solution proposes utilizing energy harnessed from the sun; it is clean, abundant and renewable (Bensebaa, 2010). There are different ways of introducing solar thermal energy into fossil fuel fired power generating plants currently in operation, presenting a partial or complete alternative to reduce or replace the usage of fossil fuels (Popov, 2011). The Department of Mechanical and Mechatronic Engineering at Stellenbosch University is currently involved in the evaluation and development of different solar thermal power generating plants (Ficker, 2011). One of these plants, the model on which this project is based, is a hybrid combined cycle solar central receiver. This model utilizes a combined cycle referred to as the Stellenbosch University Solar Power Thermodynamic (SUNSPOT) cycle. This project addresses the Brayton cycle, the first cycle in the SUNSPOT combined cycle concept. A Life Cycle Assessment (LCA) was chosen as the environmental sustainability technique to determine the impacts which the Brayton cycle will have on the environment. A Gate-to-Grave LCA has been conducted on the Brayton cycle, thus taking the operational life of the cycle as well as the disposal of its components into account. GaBi software has been used as environmental sustainability tool to conduct the LCA. Interpreting the GaBi output showed that the global warming potential (GWP) is the indicator of the most significant environmental impacts of the Brayton cycle, thus the CO2 emissions of the power plant are compared with several fossil fuelled power plants. It became clear that a hybrid solar combined cycle power plant has much lower carbon dioxide emissions than a conventional fossil fuel power plant. Notably, unlike solo solar thermal power plants, the carbon emissions are not small enough to be seen as negligible.

AFRIKAANSE OPSOMMING: Wêreldwye belangstelling in alternatiewe energiebronne en –oplossings het die afgelope dekade dramaties toegeneem namate klimaatsverandering en energiesekerheid toenemend kommer gewek het. Dit het duidelik geword dat daar ‘n wêreldwye behoefte bestaan om die kragnywerheid ten gunste van meer hernubare, volhoubare groen energiebronne te omvorm ten einde die langtermyn impak van die huidige besoedeling te verminder. Energie van die son is skoon, volop en hernubaar (Bensebaa, 2010). Om hierdie redes word dit beskou dat sonenergie ‘n sleutelbydraer tot die energiebehoeftes van die toekoms gaan word (Bensebaa, 2010). Daar is verskillende maniere om sonhitte-energie in te bring in die fossielbrandstof gestookte kragopwekaanlegte wat tans in bedryf is, en dit bied ‘n gedeeltelike of volledige alternatief om die gebruik van fossielbrandstowwe te verminder of vervang. (Popov, 2011). Die Departement Meganiese en Megatroniese Ingenieurswese aan Stellenbosch Universiteit is tans betrokke by die evaluering en ontwikkeling van verskillende sontermiese kragopwekaanlegte (Ficker, 2011). Een van hierdie aanlegte, die model waarop hierdie projek gebaseer word, is ‘n hibriede sentrale sonontvanger. Hierdie model benut ‘n gekombineerde siklus bekend as die Stellenbosch University Solar Power Thermodynamic (SUNSPOT)-siklus. Hierdie projek behandel die Braytonsiklus, die eerste siklus in die SUNSPOT gekombineerdesiklus-konsep. ‘n Lewensiklustaksering (LST) is gekies as tegniek vir omgewingsvolhoubaarheid om te bepaal watter impakte die Braytonsiklus op die omgewing sal hê. ‘n Poort-tot-graf LST is op die Braytonsiklus uitgevoer en sodoende word sowel die bedryfslewe van die siklus as die beskikking van sy komponente in berekening gebring. GaBi-sagteware is gebruik as omgewingsvolhoubaarheids-instrument om die LST uit te voer. Vertolking van die GaBi-uitset toon dat die GWP die aanwyser van die mees betekenisvolle omgewingsimpakte van die Braytonsiklus is, dus word die CO2-vrystellings van die kragaanleg vergelyk met verskeie kragaanlegte wat op fossielbrandstof loop. Dit blyk duidelik dat ‘n hibriede gekombineerdesiklus sonkragaanleg veel laer koolstofdioksiedvrystellings as ‘n konvensionele fossielbrandstof-kragaanleg het. Dit is merkbaar dat die koolstofvrystellings, anders as by solo termiese sonkragaanlegte, nie klein genoeg is om as onbeduidend beskou te word nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/70676
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