A Thermodynamic Analysis of Two Competing Mid-Sized Oxyfuel Combustion Combined Cycles

Abstract

A comparative analysis of two mid-sized oxyfuel combustion combined cycles is performed. The two cycles are the semiclosed oxyfuel combustion combined cycle (SCOC-CC) and the Graz cycle. In addition, a reference cycle was established as the basis for the analysis of the oxyfuel combustion cycles. A parametric study was conducted where the pressure ratio and the turbine entry temperature were varied. The layout and the design of the SCOC-CC are considerably simpler than the Graz cycle while it achieves the same net efficiency as the Graz cycle. The fact that the efficiencies for the two cycles are close to identical differs from previously reported work. Earlier studies have reported around a 3% points advantage in efficiency for the Graz cycle, which is attributed to the use of a second bottoming cycle. This additional feature is omitted to make the two cycles more comparable in terms of complexity. The Graz cycle has substantially lower pressure ratio at the optimum efficiency and has much higher power density for the gas turbine than both the reference cycle and the SCOC-CC.

Review of Fuel/Oxidizer-Flexible Combustion in Gas Turbines

“…The current gaseous fuel oxy-combustion concepts based on combined cycle can be categorized into the Graz oxy-combustion cycle and the semi-closed oxy-combustion combined cycle (SCOC-CC). , The Graz cycle employs the use of steam from the steam cycle to cool the combustion chamber and the turbine. A large portion of exhaust gas is recirculated back into the combustion chamber, which contains both steam and CO 2 produced during the combustion . The SCOC-CC, as shown in Figure , differs from the conventional combined cycle in the fact that the gas cycle operates the combustion chamber near stoichiometric conditions and uses pure O 2 as the oxidizer and CO 2 as the coolant instead of air to suppress the excess temperatures.…”

“…Then, cooled flue gas enters the flue gas condenser, where the water vapor is separated from CO 2 . Around 93% of CO 2 is recirculated back to the compressor, and the rest goes to the CO 2 compression unit for capturing, storage, and transportation. , …”

“…A large portion of exhaust gas is recirculated back into the combustion chamber, which contains both steam and CO 2 produced during the combustion. 133 The SCOC-CC, as shown in Figure 21, differs from the conventional combined cycle in the fact that the gas cycle operates the combustion chamber near stoichiometric conditions and uses pure O 2 as the oxidizer and CO 2 as the coolant instead of air to suppress the excess temperatures. This SCOC-CC has five main sections: topping cycle, bottoming cycle, air separation unit, flue gas condenser, and CO 2 compression.…”

Evaluation of Bleed Flow Precooling Influence on the Efficiency of the E-MATIANT Cycle

“…According to the chosen method, the relative coolant mass flow for each vane/blade row is defined as follows (1): where: K cool represents cooling flow factor; B ';lkm nrepresents coefficient depending on the metal and TBC BIOT number; ε 0 represents vane/blade cooling effectiveness, η int represents internal cooling efficiency (it was taken equal to 0.7 in the model); ε f represents film-cooling effectiveness. After determining the cooling flow factor for each vane/blade row of the gas turbine, the polytropic efficiency of the cooling stages is defined as follows (2) [11]:…”

“…Numerous works are devoted to optimization of the SCOC-CC cycle parameters [11][12] and the Allam cycle [13][14]. On the other side, the E-MATIANT structural and parametric optimization aspect did not attract proper attention.…”