Mohammad Saghafifar

Comparative analysis of power augmentation in air bottoming cycles

The air bottoming cycle (ABC) is a proposed plant configuration in which the steam turbine bottoming cycle in conventional combined power plants is replaced by another gas turbine cycle. Nevertheless, ABCs relatively low efficiency reduces the likelihood of having an ABC power plant in the near future. In this research work, steam injection in the topping cycle combustion chamber and supplementary firing are recommended to improve ABCs performance. Three different configurations of ABC, including simple ABC, ABC with steam injection, and ABC with supplementary firing, are investigated. A thermo-economic analysis is performed to study the effects of the proposed power augmentation approaches thermodynamically and economically. Moreover, optimisation is carried out with the objective of minimising the total cost of the plant for different configurations. Furthermore, a multi-objective optimisation is performed and the results are presented to further understand the trade-off between higher efficiency and lower operating cost.

Improvement in Spiral Heliostat Field Layout Thermo-Economic Performance by Field Zoning Implementation

Arguably, the most complicated and problematic mathematical formulation for solar collectors belongs to the heliostat field collectors. Consequently, extensive researches are carried out in order to develop several codes capable of providing heliostat field analysis and optimization. Noting that most of the aforementioned heliostat field codes are developed based on the radial-staggered field layout which is arguably the most popular and widely implemented heliostat field configuration in the literature. Nevertheless, a ground-breaking heliostat field layout based on the spiral patterns of phyllotaxis discs is recently proposed. It was argued that the transition between the areas with high and low heliostat field density is not continuous in radial-staggered configuration. In a study by the authors, the spiral and radial-staggered field layouts thermo-economic analyses are compared and the results points to the superiority of the radial-staggered layout. Nevertheless, it is believed that utilizing two design variables might be only sufficient for small number of mirrors. Therefore, more design variables must be implemented to fully control different areas of the field for larger capacity heliostat fields. In this paper, spiral field zoning is proposed and its impact on the spiral heliostat field layout performance is assessed. By dividing the heliostat field into multiple zones, each zone is designed with a set of design variables (two design variables: a and b). Consequently, the impacts heliostat field zoning might have on the field thermo-economic performance are investigated.Copyright

Integration of Pulse Combustion in Air Bottoming Cycle Power Plants

To enhance the air bootoming cycles efficiency (ABC), the integration of pulse combustor in ABC configurations is proposed. Two different configurations for pulse combustor incorporation in ABC are recommended including pulse combustor replacing the topping cycle combustion chamber and pulse combustor integration as a supplementary firing in the bottoming cycle. Sensitivity analysis is performed by controlling different design variables and investigating their effects on both thermal efficiency and net specific work output. Moreover, a detailed thermodynamic optimization is performed to achieve the highest power enhancement resulting from the implementation of pulse combustion for cycle configuration. Integration of pulse combustor in the topping cycle can improve the plant efficiency to 50.8% whereas the maximum possible ABC’s efficiency is about 43.6%. Finally, the integration of a pulse combustor as a supplementary firing in the bottoming cycle would enhance the overall plant efficiency to reach about 41.8%.

Thermoeconomic Comparative Analyses of Different Approaches Used for Specific Carbon Dioxide Emission Reduction in Gas Turbine Power Plants

Multiple reports indicate the considerable rate of growth in world’s energy demands. With the ongoing concerns about climate change and the considerable contribution of power generation industry in carbon dioxide emission, it is necessary to reduce the rate of carbon dioxide emission from power generation systems, immediately. In this chapter, three different approaches for a simple gas turbine power plant carbon dioxide emission reduction are recommended. The proposed methods include inlet air cooling with a mechanical chiller, steam bottoming cycle integration, and hybridization of power plants using heliostat field collector. Steam bottoming cycle implementation reduces the plant-specific CO2 emission by about 212–217 kgCO2/MWh (34–35%). Moreover, it is concluded that inlet air cooling technique manages to achieve improvement in both environmental and economic aspects of the plant even in a small-scale power generation system. Furthermore, hybridization is the most expensive approach considered in this study.

Performance assessment and transient optimization of multi-stage solid desiccant air conditioning systems with building PV/T integration

One of the popular solar air conditioning technologies is desiccant air conditioning. Nonetheless, single stage desiccant air conditioning systems’ coefficient of performance (COP) are relatively low. Therefore, multi-stage solid desiccant air conditioning systems are recommended. In this paper, an integrated double-stage desiccant air conditioning systems and PV/T collector is suggested for hot and humid climates such as the UAE. The results for the PV/T implementation in the double-stage desiccant cooling system are assessed against the PV/T results for a single-stage desiccant air conditioning system. In order to provide a valid comparative evaluation between the single and double stage desiccant air conditioning systems, an identical PV/T module, in terms of dimensions, is incorporated into these systems. The overall required auxiliary air heating is abated by 46.0% from 386.8 MWh to 209.0 MWh by replacing the single stage desiccant air conditioning system with the proposed double stage configuration during June to October. Moreover, the overall averaged solar share during the investigated months for the single and double stage systems are 36.5% and 43.3%.

Selecting a proper design period for heliostat field layout optimization using Campo code

In this paper, different approaches are considered to calculate the cosine factor which is utilized in Campo code to expand the heliostat field layout and maximize its annual thermal output. Furthermore, three heliostat fields containing different number of mirrors are taken into consideration. Cosine factor is determined by considering instantaneous and time-average approaches. For instantaneous method, different design days and design hours are selected. For the time average method, daily time average, monthly time average, seasonally time average, and yearly time averaged cosine factor determinations are considered. Results indicate that instantaneous methods are more appropriate for small scale heliostat field optimization. Consequently, it is proposed to consider the design period as the second design variable to ensure the best outcome. For medium and large scale heliostat fields, selecting an appropriate design period is more important. Therefore, it is more reliable to select one of the recommended time average methods to optimize the field layout. Optimum annual weighted efficiency for heliostat fields (small, medium, and large) containing 350, 1460, and 3450 mirrors are 66.14%, 60.87%, and 54.04%, respectively.