Waste Heat Recovery Devices...

Waste Heat Recovery Devices  Industrial furnaces are used for carrying out certain processes which requires heat. Heat in the furnace is provided by (i) fuel energy, (ii) chemical energy, (iii) electrical energy or (iv) a combination of these energies. Gases which are generated during the process leaves the furnace at a temperature which is the inside temperature of the furnace and hence have a high sensible heat content. Sometimes the exhaust gases carries some chemical energy, which raises the temperature of exhaust gases further due to post combustion because of this chemical energy. The heat energy contained in the exhaust gases is the waste energy since it gets dumped in the environment. However, it is possible to recover some part of this energy if investments are made in waste heat recovery devices (WHRDs). Methods for waste heat recovery include (i) transferring heat between exhaust gases and combustion air for its preheating, (ii) transferring heat to the load entering furnaces, (iii) generation of steam and electrical power, or (iv) using waste heat with a heat pump for heating or cooling facilities. WHRDs work on the principle of heat exchange. During heat exchange the heat energy of the exhaust gases gets transferred to some other fluid medium. This exchange of heat reduces the temperature of the exhaust gases and simultaneously increases the temperature of the fluid medium. The heated fluid medium is either recycled back to the process or utilized in the production of some utilities such as steam or power etc. The benefits of WHRDs devices are multiple namely (i) economic, (ii) resource (fuel) saving, and (iii) environmental. The benefits of these devices include (i) saving of fuel, (ii) generation of electricity and mechanical work, (iii) reducing cooling needs, (iv) reducing capital investment costs in...

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...

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...