Taeyoung Chae

Experimental study on moisture re-adsorption characteristics of dried coal

Recently, Korean coal-fired power plants have used sub-bituminous coals with moisture and volatile contents higher than design coal of those plants. This causes a decrease in the efficiency of boil...

The Effects of De-humidification and O2 Direct Injection in Oxy-PC Combustion

This study is aimed to derive effects of de-humidification and O2 direct injection in oxy-PC combustion system. Temperature distribution and flue gas composition were observed for various air and oxy-fuel conditions such as effect of various O2 concentration of total oxidant, O2 concentration of primary stream and O2 direct injection through 0-D heat and mass balance calculation and experiments in the oxy-PC combustion system of 0.3 MW scale in KITECH (Korea Institute of Industrial Technology). Flame attachment characteristic related to O2 direct injection was also observed experimentally. We found that FEGT (furnace exit gas temperature) of 100% de-humidification to oxidizer is lower than humidification condition; difference between two conditions is lower than 20°C in all cases. The efficiency changing of combustion was negligible in O2 direct injection. But O2 direct injection should be carefully designed to produce a stable flame.

Numerical Simulations of a Large Scale Oxy-Coal Burner

Oxy-coal combustion is one of promising carbon dioxide capture and storage (CCS) technologies that uses oxygen and recirculated CO2 as an oxidizer instead of air. Due to difference in physical properties between CO2 and N2, the oxy-coal combustion requires development of burner and boiler based on fundamental understanding of the flame shape, temperature, radiation and heat flux. For design of a new oxy-coal combustion system, computational fluid dynamics (CFD) is an essential tool to evaluate detailed combustion characteristics and supplement experimental results. In this study, CFD analysis was performed to understand the combustion characteristics inside a tangential vane swirl type 30 MW coal burner for air-mode and oxy-mode operations. In oxy-mode operations, various compositions of primary and secondary oxidizers were assessed which depended on the recirculation ratio of flue gas. For the simulations, devolatilization of coal and char burnout by O2, CO2 and H2O were predicted with a Lagrangian particle tracking method considering size distribution of pulverized coal and turbulent dispersion. The radiative heat transfer was solved by employing the discrete ordinate method with the weighted sum of gray gases model (WSGGM) optimized for oxy-coal combustion. In the simulation results for oxy-model operation, the reduced swirl strength of secondary oxidizer increased the flame length due to lower specific volume of CO2 than N2. The flame length was also sensitive to the flow rate of primary oxidizer. The oxidizer without N2 that reduces thermal NOx formation makes the NOx lower in oxy-mode than air-mode. The predicted results showed similar trends with measured temperature profiles for various oxidizer compositions. Further numerical investigations are required to improve the burner design combined with more detailed experimental results.

Effect of Combustion Characteristics on Wall Radiative Heat Flux in a 100 MWe Oxy-Coal Combustion Plant

Oxy-coal combustion exhibits different reaction, flow and heat transfer characteristics from air-coal combustion due to different properties of oxidizer and flue gas composition. This study investigated the wall radiative heat flux (WRHF) of air- and oxy-coal combustion in a simple hexahedral furnace and in a 100 MWe single-wall-fired boiler using computational modeling. The hexahedral furnace had similar operation conditions with the boiler, but the coal combustion was ignored by prescribing the gas properties after complete combustion at the inlet. The concentrations of O2 in the oxidizers ranging between 26 and 30% and different flue gas recirculation (FGR) methods were considered in the furnace.