Research questions, objectives and delimitations

CSP hybrids seem to be one possible solution for the problems of stand-alone CSP and conventional power plants, since they are capable of lowering the LCOE of CSP tech-nology and provide a technical pathway to reach lower CO2emission level demanded

by the EU and EPSs. However, there are only few operational CSP hybrids. The re-search questions for this thesis originate from this situation:

- What are the state-of-the-art technologies in CSP and conventional power plants?

- Which are the possible integration options available between the CSP and con-ventional power plant technologies?

- How the possible integration options compare to each other?

- What are the process requirements and restrictions, and the achievable thermal parameters for both plants?

- What kind of solar shares can be reached with the hybrid system?

- What are the automatic control strategies and the main control loops of CSP and conventional power plants?

- How the control engineering of the hybrid power plant can be arranged?

- How the system operates at steady state with different solar field and boiler loads?

- How the system operates under transient solar irradiation conditions?

As a conclusion from the research questions, the main objectives of the thesis are:

- Research state-of-the-art technologies in CSP and conventional power plants.

- Comprehensively study the possible integration options between the CSP and conventional power plants.

- Work out process and control engineering for one hybrid plant configuration.

- Develop control mechanisms for the hybrid power plant.

- Demonstrate the operation of the hybrid system under typical boundary condi-tions by means of Advanced Process Simulator (Apros).

- Find challenges, process requirements and restrictions within the hybrid system and future development requirements for the hybrid system.

The results include simulation results of steady-state and transient simulations with the selected and modelled CSP hybrid. Thus, the results include steady state results with different loads of solar field and boiler as well as transient results of the hybrid system under fluctuating solar irradiation conditions. In addition, challenges of the hybrid sys-tem are discussed based on theory and simulations results. Furthermore, possible solu-tions and future development requirements are defined.

The thesis includes many limitations. First of all, the reader of the thesis is assumed to have basic knowledge about power plant and control engineering. Thus, the basics of thermodynamics and control engineering are excluded from the theory, which focuses on the state-of-the-art technologies of CSP and conventional power plants in recent years and in the near future. In addition, CSP plants can use different kinds of collectors and HTFs. In this thesis, the focus is on line-focusing collectors with direct steam

gen-different kinds of combustion technologies. The chosen host power plant scenario in this thesis is conventional steam power plant with atmospheric fluidized bed combus-tion. Thus, any other power plant and combustion technology is excluded. Furthermore, the theoretical and operational experience data of this kind of CSP hybrids is limited, as sufficient research data can only be found from feedwater preheating process arrange-ment, in which the solar field produces preheated feedwater for the steam power plant.

Furthermore, only two CSP hybrids are operational and another one under construction, in which line-focusing collectors with direct steam generation are integrated with con-ventional steam power plants. The operational plants are Liddell Power Station in Aus-tralia (National Renewable Energy Laboratory 2013) and Sundt Solar Boost in Tucson, USA (Tucson Electric Power 2016; Tucson local media 2014). The CSP hybrid under construction is Kogan Creek plant in Australia (CS Energy 2015).

The focus of the thesis is on the development of the process and control engineering of the CSP hybrid plant in order to find challenges and limitations in the process and con-trol engineering of the selected CSP hybrid configuration. In other words, only one CSP hybrid configuration is designed and modelled and economic analyses are excluded from the thesis. Energy analysis is conducted for different hybrid process configurations in order to select one configuration for the CSP hybrid plant. Exergy analysis is exclud-ed, which can be used in later work in order to optimize the operation of the hybrid plant, as energy analysis can be conducted in order to analyse the quality of the process.

For the development of the hybrid configuration, the solar field is designed and mod-elled in order to produce steam with certain steam parameters correspond to the selected hybrid configuration. The thermal power and outlet steam mass flow of the solar field can be altered by changing the size of the solar field or the available DNI level in order to analyse the operation of the hybrid under different loads of the solar field. The opti-mal size of solar field for the hybrid system is not analysed, as it requires information about the location of the hybrid plant, such as the typical consumption curves for elec-tricity and annual variation of the DNI level and weather conditions, which are excluded from this thesis. Furthermore, the simulations are conducted with peak DNI level of the selected location in order to demonstrate the operation of the hybrid plant under peak irradiation conditions. In other words, the hybrid is located in southern Spain and the steady state and transient simulations are conducted on June 21^st at 12.00. a.m. Any oth-er location, season or time are excluded from the thesis. Moreovoth-er, the start-up and shutdown procedures of the CSP hybrid are excluded from this thesis.