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“COST CUTTING and ENVIRONMENTAL PROTECTION ” are the two words, which have swept across the corporate landscape in the recent years. Fuel being one of the key cost areas has come under close scrutiny. Cutting down on the fuel cost through reconditioning and retrofitting of the utility system or chemical treatment have become popular in the last few years.
Let us explore the possibility of fuel saving and emission control through chemical treatment.
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FUEL OIL: A PERSPECTIVE
Since 1972 the demand for the middle order distillate has been on the rise. Therefore the government world over, have tried to adopt technologies, which would permit them to extract more of the middle order distillate from the residual oil. This has given way to new processes like the Vacuum Distillation, FCC, MBCC, Vis-Breaking and Coking.
In these processes the bigger molecules are broken down into smaller molecules, which have lower boiling point so they qualified as middle order distillate .
Due to this technique the distribution of heavy molecules in the residual fuel oil is increased. Among the heavy molecules are highly polymerized aromatic condensate structures with the C to H ratio of 7 to 8. These molecules are known as asphaltenes.
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The asphaltene molecules are kept in the dispersed phase by the presence of the resin molecules, which help to build bridge between the asphaltene and the oil molecules (refer illustration).
Due to the successive distillation, the resin content in the oil decreases and therefore there is a tendency of asphaltene molecules to agglomerate and form heavier molecules having molecular weight in the range of 2500 to 10000. These heavy molecules settle at the bottom and are referred to as "sludge".
For the treatment of sludge a dispersing agent having a structure similar to the resin molecule is used to break the asphaltene agglomerates and disperse it back into the oil phase.
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COMBUSTION
The fuel oil has to be heated to 110 to 120 degrees centigrade so as to achieve viscosity of 20 Cst at the burner tip. On firing the oil through the nozzle tip, the oil splits into millions of smaller particles. This phenomenon is known as atomization.
After the atomization, the oil comes in intimate contact with the primary and the secondary air. The oil droplets are exposed to very high temperatures and therefore surface vaporization of the oil takes place (refer illustration).
So, in the dynamic model of combustion the oil exists in two phases, the gas phase and the liquid phase.
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In the gas phase if the oil cracks due to the constraints of time, temperature and turbulence, then it leads to the formation of "soot".
Soot is pure carbon and is loose and friable. It is easily removed by mechanical soot blowing.
In the liquid phase if the oil cracks, it leads to the formation of the “cenosphere”.
The cenosphere is largely carbon but has the presence of the sodium vanadates, which bring down the overall melting point of the deposit. Therefore the cenosphere sticks to the heat transfer surface and builds up over a period of time. This significantly reduces the heat transfer and therefore the overall efficiency of the system. |
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CATALYST
It is observed that some metals have the property of oxidizing the cenosphere to carbon dioxide at 35 to 45 PPM concentration level. It also allows the boiler to be operated at reduced excess air. Since the cenosphere build up is kept in check by the additives, the heat transfer surfaces are kept clean and the efficiency of the system is improved.
The additive is in an Organo-metallic form .
Once the additive enters the furnace it oxidizes to give the respective oxides, which actually act as the catalyst. The strength of a catalyst depends on its oxygen releasing power.
Alkaline earth metals show this catalytic property and it increases as we move down the series in the periodic table. These catalysts have shown to give the best results.
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BENEFITS |
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On using the product on a regular basis the following benefits may be observed.
- Significant reduction in the un-burnt in stack.
- Cleaner heat transfer surface.
- Lower excess air operation and therefore reduced stack losses.
- Concomitant saving of 2.5 to 4%.
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