The electrification of industrial furnaces may be desirable to lower carbon dioxide emission, provided that electricity is produced using “green” sources. Electrical heating elements are available in a variety of shapes, materials, and sizes, which can be used to design an electrical furnace where the tubes are not necessarily arranged in 1 or 2 rows close to the wall as in a traditional fuel furnace.
This work presents some design solutions for a small cylindrical furnace, using vertical tubes for the process fluid and vertical Tubothal® cylindrical heaters of the same length. The basic layout recalls that of a hive: the tubes are placed at the corners of a hexagon, with the electrical heater at the center: replicating this hexagonal pattern, tubes and heaters take up all the section of the furnace. Radiant heat is mutually exchanged between each element (tube, heating device and refractory lining) and all the other elements in sight, being a function of the absolute temperature, and the geometry and the location of each couple of elements. Depending on the flow arrangement of the process fluid, each tube may be at different temperature, and the same is true for each heater, depending on their different location inside the furnace. Accordingly, the problem involves a great number of variables and heat transfer equations, and a Matlab code was arranged to determine temperatures and heat exchanged by each element. The feasibility of the proposed arrangements was assessed by comparing temperatures and power outputs of Tubothal® heating elements with the manufacturer data; it is interesting to notice that, for all tested configurations, refractory lining was found to provide around 50% of the heat globally supplied to the process fluid.