MECHANICAL DES IGN AND DEVELOPMENT OF MILD COMB US TION B URNER N.H. AB U BAKAR
[email protected] ABSTRA CT This paper discusses the summary design and development of the Moderate and Intense Low o xygen Dilution (MILD) co mbustion burner using Computational Flu id Dynamics (CFD) simulations. This combustion is also known as flameless oxidation (FLOX) and high temperature air co mbustion (HiTAC). The requirement for MILD co mbustion is the oxygen dilution in the oxidant stream and for the mixture temperature to be above the self-ignit ion for the fuel.CFD was used to stimu late preliminary before designs for the burner before the final design was sent for fabrication. So, for the result, we can conclude that the flame can be seen when the oxygen is low, which is 2% co mpare to the conventional combustion, 21%. Fo r further discussion, we want to emphasize about development of a MILD burner for non -premixed open flame. INTRODUCTION The combustion is one of the most important sources of energy. However, the ordinary combustion process causes high pollution emissions and greenhouse gases. Therefore, due to energy needs and pollutions emission, the researchers concentrate on the improvement of co mbustion efficiency, new co mbustion technology and combustion modelling. One of the clean and efficient co mbustion technologies is Moderate and Intense Low oxygen Dilution (MILD). MILD is one of the new and sophisticated technologies that produces lower pollution emission and increases thermal efficiency. This co mbustion is also known as flameless oxidation (FLOX) and high temperature air co mbustion (HiTA C).The requirement for MILD co mbustion is the oxygen dilution in the oxidant stream and for the mixture temperature to be above the self-ignit ion for the fuel. The o xygen dilution and the heating of the oxidizer can be achieved by the use of exhaust gas recirculat ion (EGR). The hot EGR will dilute the o xygen in the o xidant and preheat it. The o xygen content in the fresh air will reduce the dependence on the ratio of the fresh air and EGR. EGR works by recirculation a portion of the exhaust gas back to the combustion chamber. According to his journal, the main purpose is to dilute oxygen and heat mixture. A requirement of M ILD co mbustion is to preheat a mixtu re and dilute the oxygen content in the oxidant. In o rder to achieve this condition, EGR was utilized. For further discussion, we want to emphasize about development of a MILD burner for non-premixed open flame. The burner was design ANSYS Fluent 14.5 to stimulate and predict the behaviour of combustion and flame. At the USQ mechanical workshop, the burner was built. Besides that, combustion has been proven to be a promising co mbustion technology in an industrial application with decreased energy consumption due to the uniformity of its temperature distribution. It is cleaner than traditional combustion due to producing low NOx and CO emissions.
THEORY USED In order to design the mild co mbustion burner, the basics of combustion equation must be used. According M.M. Noor the balanced co mbustion not produce unburned hydrocarbon (UHC) in the exhaust gas. This shows that the combustion process consumes all the fuel. The co mbustion process can be written in a general hydrocarbon stoichiometric co mbustion Cn H m + (n + m/ 4) (O2 + 3.76N2 ) > nCO2 + m/2 H2 0 + 3.76 (n + m/ 4) N2 CFD SIM ULATIONS USED In order to develop the mild co mbustion burner, application of computer simulat ion techniques is used to improve many comp lex processes, including the combustion process. CFD is an important design tool that has been extensively used to explore and design engineering hardware (Baukal, Gershtein, & Li, 2001; Davidson, 2002) including combustion chambers. The MILD co mbustion open furnace was modeled and the flame behavior, temperature distributions, flow velocit ies, turbulent behavior and EGR flo w were analy zed. The early design of the combustion chamber was with 2 EGR and 4 s mall EGR pipes to transport the exhaust gas to mix it with fresh air. This result is in accordance with earlier research shows the main stream o f the exhaust flowing out through the top exhaust pipe. The mo le fraction of methane between are 0 and 0.6 and between 0 and 0.05.
Conclusion To conclude, the simulat ion of the MILD co mbustion was successful in ach ieving a MILD co mbustion regime. The CFD was successfully utilized to develop an open furnace for MILD co mbustion. The combustion has to be enclosed to collect the exhaust gas and utilized to dilute the o xygen in the o xidant stream and, at the same time, increase the oxidant temperature. Four EGR pipes were added to bring down the exhaust gas and mix it with the inlet air. The furnace was equipped with three high-temperature glass windows to monitor and record the flame propagation. The R-type thermocouple was used for the main chamber temperature measurement since it can withstand up to 2040K. A K-type thermocouple that can withstand up to 1645K was used to measure the temperature of the exhaust gas at the exhaust gas pipe on the top of the chamber and in the EGR p ipe. A data acquisition system was used to collect and record the data fro m the thermocouples. The composition of the exhaust gas in the exhaust pipe and EGR pipe was measured using gas analyzers.
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