Enhance the heat transfer in a heat treatment furnace through improving the combustion process in the radiation tubes

• Main Author: Elmabrouk, Elmabrouk Mohamed
• Published: University of Sheffield 2011
• Subjects: 621.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555511

Radiation tube burner systems are widely used as in-direct heating systems in heat treatment furnaces. Saving energy through improving the combustion and heat transfer process in the radiation tubes has become a pressing issue in the heat treatment industry over the last few years. The material structure during the process of heat treatment is predominantly determined by the temperature. The heat treatment processes usually require an even temperature distribution inside the furnace over a long duration to achieve the desired material properties. Due to the rising energy costs and the environmental concerns regarding the combustion emissions, reducing energy consumption has become a significant area of concern for the industry. This research is aimed at improving the combustion process in the radiation tubes to enhance the heat transfer to the heat treatment chamber, therefore achieving the objective of making energy savings. As a measure of improving the energy efficiency in the heat treatment furnace, Single End Radiant Tube burners (SET) were used to replace Vtube combustion systems. The energy efficiencies of the SET and V-tube combustion systems were experimentally verified in two full-scale working furnaces. This project carried out a quantitative analysis of the combustion and heat transfer processes in the radiation tubes and the heating chamber using Computational Fluid Dynamics (CFD) simulations. One of the main objectives of the project was to optimize the design of the furnace heating system with the aid of validated CFD simulations. Experimental data obtained in the full-scale working furnaces were used for the validation of the CFD simulations and to provide the boundary conditions for the CFD cases. Experimental instruments were installed in two heat treatment furnaces to measure the fuel flow rates in the radiation tubes, their surface temperatures and the temperature distribution inside the heat treatment furnaces. The fuel flow rates were used to determine the energy efficiencies of the heat systems and the fuel inlet conditions for the CFD cases. The measurements of the outer surface temperatures of the radiation tubes were used to determine an average temperature as the boundary conditions for CFD simulations of the combustion process inside the SET burner. The temperature distributions inside the furnace heating chamber were examined by measuring the temperature at specific points using a thermocouple matrix. This temperature measurement provided data to validate the CFD simulations of heat transfer inside the furnace heating chamber. Three series of CFD simulations were carried out in this project. The cases in the first series of CFD simulations were based on the SET burner. The flow mixing, combustion and heat transfer process in the SET burner were analyzed in the baseline CFD case, and the influence of radiation models on the CFD simulations were investigated. The design parameters, such as the effect of the burner diameter, were also verified in the baseline CFD studies. Using the baseline case as a reference, a numerical study was carried out to explore the applications of advanced combustion technologies, such as high temperature air combustion (HiT AC) and two-stage combustion with preheated air in the SET. The results of the CFD simulations were used to determine the heat flux rates through the SET burner wall into the heating chamber, which were used as the boundary conditions for the CFD simulations of the heating chamber in the second series of CFD cases. A good agreement was found between the numerically predicted temperatures at specified points inside the furnace heating chamber and the experimentally measured temperatures at the same points. This demonstrated that the heat flux rates from the SET burners can be applied in CFD-aided design to optimize the operational conditions of similar or super-size furnaces with confidence. Finally, a case study of CFD-aided design was carried out in the third series of CFD simulations of the heat transfer process inside the super-size furnace chamber. CFD simulations were used to verify if six SET burners are sufficient to provide the required temperature distribution inside the chamber and provide optimum locations for the SET burners.