Numerical Study On Complex Heat Transfer In Honeycomb Ceramic Regenerators And Its Coupling With SCR Denitration

A honeycomb ceramic regenerator is an important component of the regenerative combustion system.It can effectively improve the thermal efficiency of industrial furnaces by preheating oxidization air with the waste heat of flue gas.A honeycomb regenerator is involved in the unsteady fluid-solid coupled heat transfer.Besides,as high-temperature flue gas and normal-temperature airflow through solid skeleton in the opposite direction periodically and alternately,the heat transfer inhoneycomb regeneratorsis quite complex.In this paper,the commercial CFD software ANSYS fluent is used to simulate the complex heat transfer of honeycomb regenerators.In order to recover morewaste heat from fluegas,the author present a type of honeycomb regenerator with expansion and contraction channels,and numerical simulation is performed to study the heat transfer enhancementof the new regenerators.On the other hand,it is known that the NOx carried by flue gas is harmful to the environment and selective catalytic reduction(SCR)is a common technology for the NOx reduction of flue gas,thusahoneycomb regenerator is coated by a thin layer of Vanadium catalyst to realize bothenergy recovery and NOx reduction of flue gas.With the consideration that the activity of Vanadium catalyst is closely related to temperature,theSCR denitration model is developed based on FLUENT software and then integratedto the heat transfer model of regenerators,with which the numerical researchis conducted on the complex heat transfer coupled with SCR denitration for the composite honeycomb regenerators.The main contents of current work are listed as below:1)The numerical model of complex heat transfer is established for honeycomb ceramic regenerator via second development of Fluent software;Numerical simulation is performed for the traditional regenerators withstraight channels,and the physical mechanism of regenerative heat transfer is studied;Air preheating temperature,regenerator efficiency and pressure loss,etc.are predicted for honeycomb regenerators with different lengths,with which the regenerator is optimized;The performances of heat transfer and flow resistance of the optimized regenerator are simulated under a variety of flow rates.2)Expansion and contraction square channels are presented to enhance the heat transfer performance of honeycomb regenerator,and the unsteady heat transfer model is established for the new type of regenerators.With the numerical simulation,how theexpansion and contraction channels enhance the heat transfer rate of honeycomb regenerators is studied;The influences of the expansion and contraction angle and pitch(θ and S)on the thermal and hydraulic performances are investigated.3)With the thin catalyst layer treated as a porous medium and the catalytic denitration assumed as a heterogeneous volumetric reaction,a numerical model of SCR denitration is developed for the honeycomb of Vanadium catalyst by activating the species transport model of Fluent;This numerical model is validated by simulating the denitration experiments of honeycomb-like catalyst from literature;Concentration polarization phenomena in both catalyst layer and channel are studied numerically.4)By integrating the SCR denitration model with that of regenerative heat transfer,a numerical model of unsteady heat transfer coupled with NOx reduction is established for the composite regenerators with a thin layer of vanadium catalyst;Numerical simulation of the complex process with heat transfer and SCR denitration coupled is carried out for the new type of composite regenerators,and the influences of the structure and operation parameters on the performances of energy recovery,NOx conversion,etc.are investigated.The present study demonstrates that the structure and operation parameters have a great impact on the flow and heat transfer performances of honeycomb regenerators;Expansion and contraction square channels can improve the thermal performances of traditional honeycomb regenerators;Under the premise of constant S(or θ),the heat transfer and flow resistance performances increase with the increment of θ(or S),and the expansion and contraction square channels can result in an increment of energy recovery ratio of 5% with a small increment of pressure loss;The unsteady heat transfer coupled with SCR denitration in the composite regenerators coated by a thin catalyst layer can be simulated successfully with the current CFD model integrating regenerative heat transfer model and that of SCR denitration.The parameters such as hole edge size and fluid flowrate have a significant influence on the energy recovery ratio,NOx conversion rate,etc.With a reasonable combination of structure and operation parameters,both the recovery of waste heat and the reduction of NOx emission can be realized with the new composite regenerators.