Combustion System of a Reheating Furnace Jul01

Combustion System of a Reheating Furnace...

Combustion System of a Reheating Furnace The main function of a reheating furnace is to raise the temperature of the semi-finished steels (billets, blooms, slabs or rounds) typically to temperatures between 1000 deg C and 1250 deg C, until it is plastic enough to be rolled to the desired section, size or shape in the hot rolling mill. The reheating furnace must also meet specific requirements and objectives in terms of the heating rates for metallurgical and productivity reasons. In the reheating furnace there is a continuous flow of material which is heated to the desired temperature as it travels through the furnace. Hot rolling operations require high quality reheated semi-finished steels at the lowest possible cost and at the optimal production rate of the rolling mill. The reheating furnaces used for heating the semi-finished steels in a hot rolling mill consume a large quantity of the energy and simultaneously generate large quantity of pollutants. Because of this, there is a necessity to look into the ways for the reduction of energy consumption as well as pollutants and hence the costs. This can be done by improving the fuel efficiency of the reheating furnaces. The combustion system of the reheating furnace has a major influence on both the quality of the reheated semi-finished steel product and on the amount of fuel needed for the reheating. The important expectations from a reheating furnace today are not only to lower the emission of the pollutants and the energy consumption, but also to have the improved high quality of the heated steel product, reliability, uniform temperature, heat flux and safety of the equipment and personnel. All these are the key factors which have considerable effect on the combustion system of the reheating furnace. The three basic things...

Oxy- Fuel Combustion and its Application in Reheating Furnace Jan13

Oxy- Fuel Combustion and its Application in Reheating Furnace...

Oxy- Fuel Combustion and its Application in Reheating Furnace Steel reheating is an energy intensive process requiring uniform temperature distribution within reheating furnaces. Historically, recuperators have been used to preheat combustion air, thereby conserving energy. More recent innovations include oxygen (O2) enrichment and the use of regenerative burners, which provide higher preheat air temperatures than recuperators. These processes have limitations such as equipment deterioration, decreasing energy efficiency over time, high maintenance costs, and increased NOx emissions with increased air preheat temperature, unless special equipment is used. Three things are necessary for the starting and sustenance of combustion. These are fuel, oxygen and sufficient energy for ignition. The efficiency of the combustion process is highest if fuel and oxygen can meet and react without any restrictions. But during heating practice, besides efficient combustion, transfer of heat is also of practical considerations. Normal air used for combustion contains nitrogen (N2) and argon (Ar) besides oxygen. In an air – fuel burner the burner flame contains nitrogen from the combustion air. A significant amount of the fuel energy is used to heat up this nitrogen. The hot nitrogen leaves through the stack, creating energy losses. Hence air does not provide optimum conditions for combustion as well as heat transfer. Heat absorbed by nitrogen either gets wasted or is to be recovered for the purpose of energy conservation. Present day best air- fuel heating system in the reheating furnace need at least 310 M Cal for a ton of steel for achieving the right temperature of the steel product for rolling. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. Introduction of an innovative oxy...

Types of Burners in Reheating Furnaces Jan08

Types of Burners in Reheating Furnaces...

Types of Burners in Reheating Furnaces Presently steel industry is facing major challenges of the continuous reduction of the  environmental emissions while improving the economic viability of the processes. Reheating furnaces due to their high-energy consumption is one area where attention of steel industry is needed. They are important equipment which contribute to the productivity and energy efficiency of the steel plant. Modern reheating furnaces are walking beam furnaces where the beams lift the charge steel material (billets, blooms or slabs) inside the furnace and move it to the next position. The heating is done in these furnaces by direct firing of the fuel both from above and below of the steel charge material, using roof burners (to heat the roof which then radiates the heat to the steel charge material) and/or long flame burners (side walls or/and front wall). Common fuels used in the reheating furnaces are mixed gas of low calorific value (blast furnace gas mixed with the coke oven gas and the converter gas), coke oven gas, heavy oil, low sulphur heavy stock (LSHS), or natural gas. The important  parameters for a reheating furnace includes  the combustion system consisting of the fuel used, supply and the technological condition of the combustion air, the burners and their location for proper heat distribution, preheating of combustion air and fuel gas, waste heat recovery system, air fuel ratio, control of furnace draft, the furnace exhaust system, and furnace parameters measurement and control system.  The furnace combustion system besides supporting the required productivity level of the furnace, ensures efficient utilization of heat input, lower heat losses, efficient recovery of waste heat, minimal damage to the furnace refractories, and lower generation of green house gases specially NOx. The furnace combustion system also ensures a furnace atmosphere...

Main Features of a modern Hot Strip Mill Dec22

Main Features of a modern Hot Strip Mill...

Main Features of a modern Hot Strip Mill The objective of a hot strip mill (HSM) is to reheat and roll thick slabs into thin strip with a wide range of thickness. Because of its huge size and large investment a hot strip mill need to have a life time of several decades. The mill must be capable of meeting the market demands for a wide range of steel grades, in particular, high strength and advanced high strength steels (AHSS) with good cold formability and with superior strip properties. The mill should be able to meet the following requirement High mill availability coupled with high productivity and high yields. Meeting the need of low maintenance. Meeting the need of lower energy consumption. Improved product quality by meeting close thickness and profile tolerances as needed by the modern day customers, through powerful controls and adjustments. These tolerances may be much closer than specified in various international standards. More flexible rolling schedules to ensure short delivery times and economical rolling of smaller lot sizes. For achieving these demanding requirements, many important features are incorporated in the modern conventional hot strip mills. Some of these are described below. Reheating furnace – Modern hot strip mills are equipped with energy efficient walking beam furnaces which are normally computerized controlled. These reheating furnaces uniformly heat the slabs to the target temperatures at the required production rates and without skid marks and without cold spots. These furnaces are capable of receiving cold or hot slabs as the charge material in the furnace. Descalers – Descalers are a must in hot strip mills for attaining good surface quality. Present day descalers employ state of the art nozzle technology with highly effective application of high pressure water (upto 400 bars). Descalers are...

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...