City Research Online

Abstract

In recent years, there has been a growing interest in small-scale concentrated solar power (CSP) generation. Among the various thermal engines that can be combined with CSP dishes, Stirling engines have exhibited admirable levels of efficiency. However, they are hindered by their high costs and low reliability, mainly attributed to their technical complexity. Micro gas turbines (MGT) offer improved reliability and the potential for cost reduction. The combination of CSP dishes with MGTs (CSP-MGT systems) which exclusively depend on solar energy, results in multiple start-ups during operations due to intermittent thermal input power. Despite the criticality of this phase, there have been limited studies into the start-up in comparison to growing interest in the CSP-MGTs for small-scale applications. Therefore, this thesis focuses on designing an efficient and safe start-up schedule for CSP-MGTs.

A real-time transient model for CSP-MGT was developed and validated using existing experimental data. MGT components were modelled as lumped volumes or one-dimensional discretisation approach with solving conservation equations of mass, momentum, and energy along with components’ characteristic maps. The electrical model was also developed to be combined with the thermo-mechanical model with a steady-state approach. The transient model effectively simulates the transient performance of a CSP-MGT during start-up by showing a good agreement with experimental measurements. After model validation was accomplished, a tailored start-up sequence for the CSP-MGT was introduced. Unlike conventional fuelled MGTs, CSP-MGTs necessitate a reference speed schedule for their control system during the start-up process. The speed schedule was designed and formulated by a number of parameters, each with an adopted range based on the system constraints. Furthermore, an innovative method was employed to classify the types of start-ups, based on the specific temperature value in the system at the initial moment, rather than the duration after the system’s shutdown.

An optimisation framework for the start-up schedule of the CSP-MGT system has been developed. The objective was to find optimised start-up schedules for efficient and safe operation during this phase. It was revealed that the optimised solutions of the defined objectives showed a 60% reduction compared to the remaining potential solutions. The optimised speed schedules for the CSP-MGT system indicate that a minimum of three steps is necessary for the speed schedule. The determinative parameters of the optimal speed schedules with respect to the safety constraints of the system have been quantified.

The transient analysis of the CSP-MGT on an annual basis has also been done. Having developed a programme structure, the annual net produced energy throughout the year was found. The assessment showed that about 3.5% of the yearly produced energy is used for the motoring mode in the case of using optimal start-up schedules and 7% for the case of using the pre-existing speed schedule.

To conclude, this thesis presents detailed insights into the transient analysis of a CSP-MGT during the start-up phase. This has considered finding a tailored and optimal start-up schedule aimed at ensuring both safety and efficiency of a CSP-MGT along with an annual evaluation.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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