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Title: A thermodynamic and economic simulation modelling study of utilizing low-temperature sources to power absorption and organic rankine cycles
Author: Masheiti , Salah A. A.
Awarding Body: University of Newcastle Upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2011
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Global economic and social development has lead to the growth in demand for electrical power. The amount of greenhouse gases emitted into the atmosphere, which leads to climate change, is increasing considerably. It is therefore expected of people to reduce their energy consumption to reduce the amount of fossil fuels as a source of energy and also the search is on for improving efficiency of conventional power generation and for renewable and sustainable energy sources which are environmentally friendly. One of the new renewable energy sources of great interest is geothermal energy which can be considered as the most clean and sustainable energy that can be exploited in a wide variety of locations. The urgent need for reducing global warming and the recent increase in the cost and uncertainty of future conventional energy supplies are making low-temperature geothermal resources very attractive as an alternative energy source. These resources are starting to attract significant interest, as lower temperature water resources are common in many countries and new technologies are beginning to appear that allow theses resources to be developed commercially. Currently, the main worldwide direct uses for low-temperature geothermal resources are in the domestic sphere for space heating, bathing, in agriculture for heating greenhouses, and numerous industrial applications. The absorption refrigerator, such as the single/half effect lithium bromide water mixture (LiBr/HzO) absorption refrigeration has been developed as a new method for capturing significantly more heat from low-temperature geothermal resources. This holds promise for producing virtually pollution-free cooling effects. Organic Rankin cycles (ORC) have also been considered for generating electrical power from these energy sources. Remote communities, in arid zones, such as Waddan city in Libya, which have close by four readily available high potential low-grade temperature geothermal resources could greatly benefit from the development of this technology. Such resources located in desert areas are very attractive energy sources for absorption cooling and ORC electrical power generation. The utilization of these resources would solve numerous local social and economic problems, raise living standards and also share the worlds concerns about global warming (by producing green energy even on a small-scale basis). The work described in this thesis is an attempt at developing a thermodynamic and economic model of the geothermal resource at Waddan city based on the local climate conditions and social and economic factors. The presence of natural gas fields near Waddan City close to the geothermal resources also allows the development of integrated energy systems using all the natural resources available to be considered. Five models have been evaluated and simulated using the commercially available software package IPSEpro. The first three models were designed to provide cooling from the geothermal resource and evaluated the choice of absorption refrigerator for this duty. The chillers considered in turn were a water-cooled single effect chiller, an air-cooled single effect chiller and a water-cooled half effect LiBr-HzO absorption chiller. The fourth model was based upon a standalone organic Rankine cycle (ORC), also driven by the geothermal resource to produce electricity. The fifth model utilised the natural gas and geothermal resources combining a simple gas turbine to generate electrical power, a water-cooled half effect chiller for inlet air cooling of the gas turbine and an organic Rankin cycle using R-245fa refrigerant. This was designed to produce electricity and also district heating. The absorption models were validated thermodynamically using a relevant Duhring chart, empirical equations and similar results available in the literature. The organic Rankine cycle models were successfully plotted on relevant thermodynamic T-S diagrams and approved by a leading European manufacturer of ORC units, Tuboden®. The results from the simulation have revealed that the low-temperature geothermal resources at Waddan city could be successfully utilized to power three different stand- alone absorption cycles. The highest cooling capacity of the chilled water that could be supplied to the community was from the water-cooled half effect absorption chiller at 5°C and 4516 kW refrigeration capacity. This capacity was approximately double that of the single effect chillers because the half effect chillier absorbs more heat than the single effect cycles. In addition the stand-alone half effect chillier was found to be directly economically viable, while stand-alone single effect chillers were not economically viable unless they were heavily subsidised or combined with the district hot water supply at least in the winter. The parametric study has shown that the most important independent parameter that could have the greatest effect on the performance of other dependent parameters of the chillier cycles was the coolant temperature. The results obtained of the stand-alone organic Rankine cycle model have shown that this geothermal resource could also used to power an ORC unit using refrigerant R-245fa to produce 350 kW of electrical power at an efficiency of 4.0%. This is useful to meet some of the power demands of the community. This model was found not to be viable economically to produce electricity all year round when the selling price of the electricity is fixed and in line with the subsidized Libyan government selling price of 0.02 £/kWhr. However if the model is used to generate electricity only during spring, summer and autumn and to produce district heating energy in the winter, this model is then economically feasible. The developed combined system could provide Waddan city and surrounded villages with their full electrical demand of 100 MW in an uninterrupted and stable way and also supply district heating and hot water if required. The simulated results show that the output power and thermal efficiency of the combined cycles were improved by 5% and 1.5% respectively compared to the stand alone gas turbine with a reduction in the carbon emissions of 55.7% (291 g/kWh instead of 649 g/kWh). Adding district heating to the electrical energy raised the Energy Utilization Factor to 55.1 %.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available