Reheating furnaces in steel plants Apr13

Reheating furnaces in steel plants...

Reheating furnaces in steel plants In steel plants reheating furnaces are used in hot rolling mills to heat the steel stock (Billets, blooms or slabs) to temperatures of around 1200 deg C which is suitable for plastic deformation of steel and hence for rolling in the mill. The heating process in a reheating furnace is a continuous process where the steel stock is charged at the furnace entrance, heated in the furnace and discharge at the furnace exit. Heat is transferred to the steel stock during its traverse through the furnace mainly by means of convection and radiation from the burner gases and the furnace walls. It is shown in Fig 1.               Fig 1   Heat transfer mechanism in a reheat furnace The charging temperature of the steel stock may range from ambient temperature to 800 deg C. The target exit temperature of the steel stock is governed by the requirement of the process of rolling which is dependent on the rolling speed, stock dimension and steel composition. Steel quality aspects put constraints on temperature gradient and surface temperature. Fuel used in these furnaces can be liquid or gaseous fuel. The main features of a reheating furnace are shown in Fig. 2.   Fig 2     Main feature of a reheating furnace. The size of reheating furnace is usually expressed as the capacity to supply the rolling mill with sufficiently hot steel from the cold stock and is expressed in tons per hour. The energy efficiency of reheating furnace is usually defined as increase of steel stock heat content when heated from 10 deg C to 1200 deg C divided by the fuel energy (latent heat plus sensible heat) used for it. Many design features of the furnace affects...