TED-AJ03-618 Consideration about High Efficiency and NO_x Reduction with The Slab Reheating Furnace using Highly Preheated Air Combustion

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NEDO (New Energy and Industrial Technology Development Organization) and JIFMA (Japan Industrial Furnace Manufacturers Association) had done the project of "High Performance Industrial Furnace Development" for the purpose of global warming from 1993 to 2002. The core technology of the highly preheated air combustion method has been applied to a large number of industrial furnaces, and energy saving along with the reduction of NOx emission ahs has consequently been achieved. Recently, we applied regenerative burners that embodied this technology to slab reheating furnaces, and the following items were clarified as a result of evaluation based on operation data obtained from the furnace. 1) The coefficient of overall heat transfer (φcg) calculated from the actual measured temperature of the furnace was 0.95. This is approximately 20% higher than the conventional standard. This is considered to be due to the following reasons. The heat flux distribution on heated material is optimized, because the furnace has the most ideal dimensions obtained from experiments and computational fluid dynamics. The regenerative burner increases the inflow velocity of fuel and preheated air. The high velocity flow increases turbulent energy, thus promoting the mixture of the fuel, air, and waste gas. Moreover, the fuel nozzle and preheated air nozzle arrangement are separated from each other and ideally adjusted, which makes the ignition point of the fuel possible with low-concentration oxygen for combustion. Unreacted oxygen along with fuel is diffused in the furnace. Therefore, it is possible to form a large flame zone by burning the fuel at a distance from the burner. As a result, the temperature distribution in the furnace is made uniform. 2) The temperature deviation of the heated material after rough rolling was 10 degrees C. Compared with conventional furnaces, there has been a 30% improvement. The reason for the considerable improvement in the heat-conducting characteristic of the furnace over the heated material is due to the combustion around the skid beam and post that had been considered a cold wall. 3)The quantity of NOx emission was reduced one-third compared with conventional furnaces. It is known that thermal NOx increases exponentially with a rise in temperature. Generation of the partial high temperature zone is decreased due to low oxygen concentration combustion with dilution by the waste gas. As a result, NOx emission is decreased. The volume ration of intervention substances, such as N_2,H_2O, and CO_2,rises as a result of promoting the mixture of the fuel, oxygen and waste gas. Energy generated from combustion is absorbed by the waste gas in the furnace. Therefore, the local flame temperature is lowered.

TED-AJ03-618 Consideration about High Efficiency and NO_x Reduction with The Slab Reheating Furnace using Highly Preheated Air Combustion

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