Development of an Efficient Modelling Approach for Fin-Type Heat-Exchangers in Self-Recuperative Burners

Self-recuperative burners are a common solution for efficient combustion systems in industrial furnaces. Due to the geometric complexity of the recuperators, a detailed CFD simulation is computationally expensive and not feasible for simulation models of burner-integrated systems such as radiant tubes. Especially in the FSI studies of radiant tubes, the temperature of the radiant tube surrounding the burner is decisive for the final results. The exclusion of the recuperator from the simulation models introduces significant uncertainties in the simulations results. The presented paper describes an innovative, efficient approach to model a fin-type recuperator in which the recuperator is geometrically reduced. The resulting acceleration of the numerical simulation makes a fully dynamic modelling of the recuperator in a radiant tube simulation possible. Specifically designed source terms are used to model pressure loss and heat transfer inside the recuperator to match results obtained with a detailed simulation model. The results show deviations in total heat transfer of less than 1.3% with a 98.5% reduction of numerical mesh size. The computational savings enable comprehensive modelling of air preheat for radiant tube simulations and accurately replicate flow and temperature profiles in the recuperator.

Improvement of Radiant Heat Efficiency of the Radiant Tube Used for Continuous Annealing Line by Application of Additive Manufacturing Technology

This study presents the application of additive manufacturing (AM) technology to a W-type INCONEL radiant tube (RT) used to improve its radiant heat efficiency. Appropriate dimensions of honeycomb structure were determined from finite element (FE) analysis and the resulting increase in radiant heat was computed. The honeycomb patterns on the RT surfaces were printed using the directed energy deposition (DED) method. Radiant heat efficiency of a prototype RT with a honeycomb pattern printed was examined in a pilot furnace emulating the continuous annealing line (CAL). Finally, soundness of the prototype RT was tested on-site on the actual the CAL of No. 3 CGL in POSCO Gwangyang Steel Works. The results revealed that partial FE analysis, which predicts the amount of radiant heat by partially modeling the RT structure rather than modeling the entire RT structure, is suitable for overcoming the limitation of the computer memory capacity and calculating the design parameters of honeycomb patterns. The DED is suitable for printing honeycomb patterns on RT with large and curved surfaces. The average amount of gas consumed to maintain 780 °C and 880 °C for 1440 min was reduced by 10.42% and 12.31%, respectively. There were no cracks and no gas leaks on the RT surface in an annual inspection over three years.

Influence of Surroundings on Radiant Tube Lifetime in Indirect-Fired Vertical Strip Annealing Furnaces

The effects of surrounding radiation—emanating from radiation exchange with neighboring partners in indirect-fired vertical strip annealing furnaces, such as the other radiant tubes, the passing strip, and the enclosing furnace chamber—on the radiant tube lifetime were studied. In-house developed and validated numerical models were used to calculate the thermomechanical behavior, especially creep deformations and the corresponding stresses as lifetime indicating parameters. Different setups of recirculating P-type radiant tubes were investigated, including a reference case of an isolated tube. The investigations could be broadly classified into the study of the effects of different tube arrangements, burner operations (synchronous/asynchronous on/off firing), and changes of strip parameters (width/temperature). Results showed higher creep deformation of the central radiant tube in the setup with three tubes arranged horizontally in a row compared to three tubes stacked in a vertical column, even though the respective characteristic temperature values in a firing cycle were similar. Furthermore, the cases with asynchronous burner firing resulted in lower creep rates than other cases, where the burners were operating in synchronous on/off firing modes. In addition, the change of strip width had a higher impact on radiant tube lifetime compared to locally changing strip temperatures across the furnace. Alternating temperatures, caused by burner operation or process changes, such as change of strip’s speed or cross-section, and local temperature gradients were observed to be the main factors influencing the tube’s service life.

Practical thermal model for a radiant tubes annealing furnace

Modeling of vertical radiant tube annealing furnaces has proven to be one of the best tools to improve the performance of a galvanizing line. However, there is a lack of a practical model able to consider the temperature and status of the radiant tubes, which are key elements in the capacity of the furnace. The model proposed divides the furnace in several segments and compares the radiated heat, that is exchanged between the radiant tubes and the strip, and the heat required to increase the temperature of the mass flow on the strip. This comparison is represented as an implicit equation where the strip‘s temperature is obtained by iteration. The model is validated calculating the final temperature of more than five hundred coils divided in four different steel families. The 90% of the calculated temperatures are within a 2% deviation range compared to the measured temperatures. This model combines good accuracy in the results with low computational times, allowing the simulation of hundreds of coils in a few minutes.

Evaluasi Material Radiant Tube Heater Di Unit Refinery Menggunakan Metode Teknik Replika Dan Kekerasan

Tulisan ini dibahas tentang evaluasi materialradianttube refinery heateryang telah beroperasi selama ± 15 tahun dengan metode teknik replika dan uji kekerasan. Secara visual, tube yang merupakan spesifikasi dari material 1¼Cr-½Mo-Si telah terdegradasi akibat terekspos pada temperatur tinggi dalam waktu yang lama. Evaluasi dilakukan secara analitis untuk mengetahui kondisi aktual tube dan menjamin kehandalan tube terhadap beban operasi yang akan datang.Studi ini dilakukan dengan melakukan pemeriksaan visual, struktur mikro dengan teknik replika dan uji kekerasan material dengan alat uji kekerasan portable. Pengamatan pada radianttubemenunjukkan bahwa struktur mikro material tube berupa fasa ferit dan perlit yang mulai terspheroidisasi,batas butir masih cukup jelas, nilai kekerasan minimum sebesar 127 HB (kekerasan brinnell) yang identik dengan nilai kekuatan tarik sebesar 438 MPa.Analisis kekuatan material dari nilai kekerasan mengindikasikan bahwa material tube masih dalam kriteria spesifikasi standar material 1¼Cr-½Mo-Si, dimana kekuatanstandarnya adalah minimum 415 MPa. Berasarkan analisis struktur mikro dan nilai kekerasan dapat disimpulkan bahwa material tube heater masih layak dan handal untuk difungsikan dalam operasi sesuai kondisi desain.Â