Steel making is an extensive process, right from making the iron to finishing. Traditional methods are also very labor intensive. Though modern methods have evolved considerably, the basic premise of using oxygen to reduce the carbon content in iron remains unchanged.
The first step of steel making involves smelting of iron from the ore in a blast furnace for subsequent processing into steel. The blast furnace is basically a vertical shaft into which the raw material is poured from the top and air preheated in the range of 900-1200 deg C is blown in from the bottom. Rapid combustion helps to convert the raw material to liquid iron in about 6 to 8 hours.
Due to the nature of the application, it is important to maintain high heat levels in the blast furnace and combustion air has to be ‘blasted’ into the shaft at pressures above normal atmospheric pressure. The blast furnace wall pressure is a vital indicator of the profile of different zones in the furnace, and therefore an important parameter to be measured. However, since blast furnaces have a hot, dusty, corrosive and erosive internal environment, conventional systems face frequent choking, which cannot be avoided even with normal nitrogen purging based systems. The application therefore calls for indirect back pressure measurement through differential pressure based purge regulators.
The back pressure technique involves precise flow regulation through differential pressure control across flow meters. When differential pressure across any restriction is controlled and made constant, then flow through the restriction will be constant. In this case, the inlet pressure is controlled by the header PRV and pressure at the flow meter outlet is varying. The back pressure technique gives the benefit of steady flow in momentary choking or pressure fluctuation at outlet.
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