role of emulsified fuel in reducing waste heat, nox and mill-scale in steel reheating furnace
DESCRIPTION
Emulsified Fuel consists of anywhere between 5-20% water embedded in 5-10 micron sized droplets inside the Fuel. In a process known as secondary Atomization, once the Emulsified Fuel is sprayed inside the furnace by the burner the extreme heat of the flame and furnace instantly vaporizes the water, expanding their volume by 1700 times, which rips apart the host Fuel droplet into hundreds of smaller droplets with thousands of times more surface area.TRANSCRIPT
Role of Emulsified Fuel in reducing Waste Heat, NOx and Mill-scale in Steel Reheating Furnace
In any normal combustion process involving atmospheric Air, Oxygen is reduced along with the Fuel to create Heat and Light and produces the following gasses:
C02+H20 + N2+NOx.
The first two gasses are beneficial for spreading heat as the thermal conductivity and radiance of CO2 and H2O(water in the form of steam) are much higher than that of air because they are 3-atomic gases with ability to take part in heat transfer by radiation. However, the latter two gasses namely Nitrogen and Nitrogen Oxides are detrimental for the heating process as they are actually cooling gasses that don’t give up thermal energy easily.
Unfortunately, air contains only 21% oxygen; the remaining 79% is practically Nitrogen. This gas does not play any positive role in combustion, but still gets heated up, consuming extra fuel and ultimately just vents off the heat through the stack as Nitrogen Ballast and NOx, creating unnecessary waste heat, energy losses and pollutants.Thus, in order to optimize the combustion process and improve the heat distribution and thermal transfer from flame to load, it is necessary to curtail the role of Nitrogen as much as possible to reduce waste heat creation and at the same time curtail NOx formation, which is a notorious greenhouse gas.
How Emulsified Fuel helps reduce Waste Heat and NOx
Emulsified Fuel consists of anywhere between 5-20% water embedded in 5-10 micron sized droplets inside the Fuel. In a process known as secondary Atomization, once the Emulsified Fuel is sprayed inside the furnace by the burner the extreme heat of the flame and furnace instantly vaporizes the water, expanding their volume by 1700 times, which rips apart the host Fuel droplet into hundreds of smaller droplets with thousands of times more surface area. This results in the complete combustion of the fuel and the water gets partly disassociated to create SynGas or Water Gas (as result of the combination of the freed Hydrogen with Carbon) and partly converted into superheated steam. This volume of superheated steam, released inside the Furnace acts as a thermal storage battery, which first soaks in the surrounding heat, equalizes it, eliminating hot-spots and then discharges by radiation quickly within the furnace. It thus displaces the traditional role of Nitrogen as Thermal Ballast and at the same time due to the controlled peak temperatures reduces the formation of NOx gasses that are usually formed at flame temperatures above 1300 degrees Celsius. And as most of the Thermal load is discharged within the Furnace area, the exhaust gasses are significantly lower in temperature and waste Heat generation is significantly reduced.
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How Emulsified Fuels helps reduce Ferrous Scale in Steel Reheating Furnaces
Ferrous scale is a waste product of the steel industry consisting of various Ferric Oxides namely FeO and Fe2O3, generated during Ingot or Billet re-heating or when these are rolled into different profiles. These scales comprise the upper coating of metal, which fall off in layers ranging from a few centimeters to a few millimeters in length and thickness. In an average steel re-heating and rolling operation the quantum of mill-scale generated is on average about 3% though it can go even as high as 7%.
There are again two kinds of mill-scale, i.e, the primary scales and secondary scales. The Primary mill-scales are formed inside the re-heating furnaces due the prolonged exposure of the Steel Ingots to high temperatures and Oxygen. The secondary ones are those scales which fall off during the rolling process. Usage of Emulsified Fuel in the steel reheating process drastically reduces primary mills-scale generation. This is because the mill-scale formation takes place in more or less the same conditions that generate NOx, i.e., due to prolonged exposure to Oxygen and temperatures of 1300 degrees and higher.
The complete combustion of Fuel droplets of Emulsified Fuel reduces most of the Oxygen in the air due to complete combustion leaving very little for the purpose of oxidizing either Nitrogen or the Metal. Secondly, the super-heated-steam released by the Emulsified Fuel Combustion ensures that the flame’s peak temperatures doesnt exceed 1300 degrees. And thirdly, the large volume of superheated steam also acts like a flux insulating the heated metal from direct contact with the oxygen. Hence, in place of 30-40 cm long peels of 1-2 mm thickness falling off from Ingots and Billets during the reheating process, after converting to Emulsified Fuel , the negligible amount of mill-scale generated gets physical properties of tiny flakes with thickness not exceeding .06 mm. In a trial made on a 100 Ton per day rebar mill, it was seen that after converting to Emulsified Fuel, the amount of burning loss and mill-scale fell from 3.5 % to 1.6 %.
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