• Journal of Korean Society of Environmental Engineers
• /
• v.29 no.1
• /
• pp.23-30
• /
• 2007

The ultimate objective of this study is to develop oxygen-enriched combustion techniques applicable to the system of practical industrial boiler. To this end the combustion characteristics of lab-scale LNG combustor were investigated as a first step using the method of numerical simulation by analyzing the flame characteristics and pollutant emission behaviour as a function of oxygen enrichment level. Several useful conclusions could be drawn based on this study. First of all, the increase of oxygen enrichment level instead of air caused long and thin flame called laminar flame feature. This was in good agreement with experimental results appeared in open literature and explained by the effect of the decrease of turbulent mixing due to the decrease of absolute amount of oxidizer flow rate by the absence of the nitrogen species. Further, as expected, oxygen enrichment increased the flame temperatures to a significant level together with concentrations of $CO_2$ and $H_2O$ species because of the elimination of the heat sink and dilution effects by the presence of $N_2$ inert gas. However, the increased flame temperature with $O_2$ enriched air showed the high possibility of the generation of thermal $NO_x$ if nitrogen species were present. In order to remedy the problem caused by the oxygen-enriched combustion, the appropriate amount of recirculation $CO_2$ gas was desirable to enhance the turbulent mixing and thereby flame stability and further optimum determination of operational conditions were necessary. For example, the adjustment of burner with swirl angle of $30\sim45^{\circ}$ increased the combustion efficiency of LNG fuel and simultaneously dropped the $NO_x$ formation.

• Journal of Advanced Marine Engineering and Technology
• /
• v.38 no.4
• /
• pp.367-375
• /
• 2014

In numbers of kinds of heat exchanger, the shell-tube heat exchanger is the most commonly used type of heat exchanger in the industry field. In order to improve the thermal performance of the heat exchanger, this study was analyzed heat transfer characteristics according to arrangement of baffle and direction of baffle and bump phase of baffle about shell-tube heat exchanger using appropriate SST (Shear Stress Transport) turbulence model for flow separation and boundary layer analysis. As the boundary condition for CFD (Computational Fluid Dynamics) analysis, the inlet temperature of shell side was constantly 344 K and the variation of the water flow rate was 6, 12, 18 and 24 l/min. As the result of analysis, zigzag baffle arrangement enhances heat transfer rate and pressure drop. Furthermore, in the direction of the baffle, heat transfer rate is more improved with vertical type and angle $45^{\circ}$ type than existing type, and pressure drop was little difference. Also, the bump shape of baffle surface contributes to heat transfer rate and pressure drop improvement due to the increased heat transfer area. Through analysis results, we knew that the increase of the heat transfer was influenced by flow separation, fluid residual time, contact area with the tube, flow rate, swirl and so on.