An Investigation into the Oxyturbine Power Cycles with 100% CO2 Capture and Zero NOx emission

The world is facing serious issues related to global warming due to the massive use of fossil fuel sources. Global warming coupled with growing energy demand causes environmental concern. Carbon capture and storage (CCS) are promising technologies for achieving shortly to medium-term solution Green House Gas GHG emission reduction goals. The development of CCS for fossil fuel power generation can reduce carbon dioxide emission and produce electricity with lower capital cost (Capex), operating cost (Opex) in comparison with other renewable energies in the short and medium-term while reducing exergy destruction and increasing efficiency.

Oxy-fuel combustion technology is an effective way to increase the CO2 capture ability of oxy-fuel combustion power plants. Also, its advantages in contrast to other CCS technologies include low fuel consumption, near-zero CO2 emission, high combustion efficiency, flue gas volume reduction, and fewer nitrogen oxides (NOx) formation. In this technology, the air is replaced with nearly pure oxygen as an oxidiser. The combustion exhaust is mainly the composition of CO2 and H2O. Then CO2 can be separated from the water through lower-cost technologies such as the water condensation technology, which has lower power consumption. In this thesis, the major proposed oxy-combustion gas turbine power cycles (Oxyturbine cycles) have been investigated and compared by means of process simulation and techno-economic evaluation.

The investigated cycles in chapter 2 are SCOC-CC, COOPERATE Cycle, MATIANT, E-MATIANT, CC_MATIANT, Graz cycle, S-Graz cycle, Modified GRAZ, AZEP 85%, AZEP 100%, ZEITMOP Cycle, COOLCEP-S Cycle, Novel O2/CO2, NetPower, CES. These cycles were modelled with Aspen Plus based on the available cycle data from literature; then, parametric studies are performed after modelling validations. In this PhD thesis, a review of the Air Separation Unit (ASU) and the CO2 Compression and Purification Unit (CPU) are presented. The Technology Readiness Level (TRL), Sensitivities and pilot industrial demonstration for oxycombustion power cycle have also been studied.

In chapter 3, the methodology of the thesis and oxy-combustion cycles of process modelling is indicated. Also, the theories and thermodynamic formulas including mass, energy and exergy balances of Oxy combustion cycle were determined in the MATLAB code to calculate thermodynamic parameters in order to evaluate these cycles; the MATLAB codes are developed to link with Aspen Plus software to simulate the Oxy-fuel power cycle processes with the input data. In this chapter, techno-economic formulas were determined to calculate LCOE for oxy-combustion cycles.

In chapter 4, the exergy destruction in each component of the oxy-combustion power cycle is studied. Results indicate that the exergy destruction in combustion is more than other components and the heat exchanger is the second component with the highest exergy destruction; hence improving these two components are very important to reduce total exergy destruction.

In chapter 5, the Sensitivity and exergy analysis of the Semi-Closed Oxy-fuel Combustion Combined Cycle (SCOC-CC) and E-MATIANT are investigated in detail. TIT and efficiency of SCOC-CC cycle with respect to COP and fuel flowrate was drawn, and also a 3D plot of exergy destruction and TIT were indicated in this section. The Efficiency vs working flowrate for E-MATIANT was determined, and it indicates the maximum turbine efficiency is 46.9% at 290 kg/s based on the available technology for the E-MATIANT cycle.

In chapter 6, the sensitivity and exergy analysis of COOPERATE cycle is determined, and the sensitivity of the Efficiency vs working flowrate for COOPERATE cycle was plotted. Also, a pie chart for exergy destruction of equipment is determined. The exergy analysis indicates that the total exergy destruction in the COOPERATE cycle is minimum at 318 kg/s working flowrates; it is verified that the exergy efficiency and energy efficiency are maximum at this working flowrate.

In chapter 7, the simulation results of the NetPower cycle showed that the efficiency increases up to 1% with 2.5 oC reduction of ΔTmin in constant Combustion Outlet Temperature (COT) and constant recycled flow rates; however, the efficiency increases faster in constant flow rate compared to the constant COT. Also, NetPower cycle simulation indicates that COT and heat exchanger have a critical role in NetPower cycle performance and overall efficiency.

In chapter 8, the results of the TIT sensitivity for the S-CES cycle and the NetPower cycle indicates that the slope of cycle efficiency was higher in the NetPower cycle, which could be explained by the higher impact that the TIT produced in the turbine and the main heat exchanger for the NetPower cycle.

At the end, exergoeconomic, Techno-economic, Technology Readiness Level (TRL) and parametric comparison in Oxyturbine Power cycles are indicated in chapter 9 and the Radar chart for comparison of the oxy-combustion cycles were determined and the results were discussed more depth in this capture. Furthermore, Technoeconomic analysis was conducted according to the oxy-combustion modelling and included performance, cost rate, Levelised Cost of Electricity (LCOE). The oxycombustion cycles parameters were compared by means of TIT, TOT, CO2/kWh, COP, Exergy, Thermal efficiency, Technology Readiness Level (TRL) bar diagrams and Multi-Criteria Decision Analysis (MCDA) with radar diagrams are provided to choose the best possible Oxyturbine cycles.

This PhD research provides a benchmark for comparing the oxy-combustion gas turbine power cycles and drew a road map for the development of these cycles for low carbon, high efficiency and low-cost energy in soon future.