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Compressed air energy storage (CAES) could play an important role in balancing electricity supply and demand when linked with fluctuating wind power. This study aims to investigate design and operation of a CAES system for wind power at design and off-design conditions through process simulation. Improved steady-state models for compressors, turbines and the CAES system for wind power were developed in Aspen Plus ® and validated. A pseudo-dynamic model for cavern was developed in Excel. Compressor and turbine characteristic curves were used in model development for process analysis. In the off-design analysis, it was found that the CAES system for wind power at variable shaft speed mode utilise more excess wind energy (49.25MWh), store more compressed air (51.55×10 3 kg), generate more electricity (76.00MWh) and provide longer discharging time than that at constant shaft speed mode. Economic evaluation based on levelized cost of electricity (LCOE) was performed using Aspen Process Economic Analyser ® , it was found that LCOE for the CAES system for wind power at variable shaft speed mode is lower than that at constant shaft speed mode. Research presented in this paper hopes to shed light on design and operation of the CAES system for wind power and cost reduction.

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Large amount of waste heat is available for recovery in industrial processes worldwide. However, significant proportion (up to 50%) of this thermal energy is released directly to the environment. Application of waste heat to power (WHP) technologies can increase the energy efficiency and cut CO2 emissions from these facilities. Steam Rankine cycle (SRC) and organic Rankine cycle (ORC) are commonly deployed for this purpose. The main drawback of SRC and ORC is the high irreversibility in the heat exchangers. In addition, ORC has limited temperature range and low efficiency while SRC has a large footprint. Supercritical CO2 (sCO2) power cycle is considered an attractive option, which provides better matching of waste heat temperature in the main heater (i.e. low irreversibility). It offers compact design, improved performance and it is applicable to a wide range of waste heat source temperature. The conditions of industrial waste heat sources are highly variable due to continuous fluctuations in the operation of the process. This is likely to significantly affect the dynamic performance and operation of the sCO2 power cycle. In this work, dynamic model in Matlab/Simulink was developed to assess the dynamic performance and control of the sCO2 power cycle for waste heat recovery from cement industry. The case of waste heat at 380 0 C utilized to deliver 5 MWe of power was considered. Steady state simulation was performed to determine the design point values. Open loop simulation was performed to show the inherent dynamic response to step change in the temperature of the waste heat. The dynamic performance and control of the system under varying exhaust gas flow rate between 100% and 50% of the design value were studied. Similar study was done for varying exhaust gas temperature between 380 0 C and 300 0 C. The results showed that the thermal efficiency of proposed single recuperator recompression sCO2 is about 33%. Stable operation of the system can achieved by using cooling water control and throttle valve to maintain constant precooler outlet condition. Dynamic simulation result showed that it is best to allow the turbine inlet temperature to vary according to the fluctuation in the waste heat source. These findings indicated that dynamic modelling and simulation of WHP system could contribute to understanding of the behaviour and control system development under fluctuating waste heat source conditions.

Power generation from coal-fired power plants represents a major source of CO2 emission into the atmosphere. Efficiency improvement and integration of carbon capture and storage (CCS) facilities have been recommended for reducing the amount of CO2 emissions. The focus of this work was to evaluate the thermodynamic performance of s-CO2 Brayton cycles coupled to coal-fired furnace and integrated with 90% post-combustion CO2 capture. The modification of the s-CO2 power plant for effective utilisation of the sensible heat in the flue gas was examined. Three bottoming s-CO2 cycle layouts were investigated, which included a newly proposed single recuperator recompression cycle. The performances of the coal-fired s-CO2 power plant with and without carbon capture were compared. Results for a 290 bar and 593 0 C power cycle without CO2 capture showed that the configuration with single recuperator recompression cycle as bottoming cycle has the highest plant net efficiency of 42.96% (Higher Heating Value). Without CO2 capture, the efficiencies of the coal-fired s-CO2 cycle plants were about 3.34-3.86% higher than the steam plant and about 0.68-1.31% higher with CO2 capture. The findings so far underscored the promising potential of cascaded s-CO2 power cycles for coal-fired power plant application.