Generally, for combustion in liquid-fueled burners, first it is necessary to convert the fuel into a mixed powder with air in order to increase the level of fuel-oxygen contact which is carried out by the nozzle inliquid fuel burners.
One of the issues usually commonly faced by the plant's experts is the nozzle selection for gas oil burners. (Especially given the importance of optimizing fuel consumption)
The following three factors should be considered for the correct selection of gas oil burner’s nozzles:
- Gas oil flow rate (gallon number determined on each nozzle)
- Gas oil spray angle (angle determined on each nozzle)
- Gasoline spray form (letters B, H, S, ... specified on each nozzle)
Determining the flow rate of gas oil (gallon number determined on each nozzle)
Normally, if the thermal value per liter of gas oil is equal to 8,500 kilocalories and the volume of each gallon is 3.785 liters Therefore, the thermal value of a gallon of gas oil is equivalent to: Kcal 8500 * 3.785 = 32000 Kcal. According to the above, the nozzle number needed for 220000 kcal gas oil burners (so called 5 to 7 burner) should be equal to: 220000/32000=6.8 Us Gal While this number is usually announced to be Us Gal. 3.5 for the above burner. For example, for a torch of 600,000 kcal (two nozzles) should the total nozzle number be 600000/32000 = 18.75 G.P.H? While no torch company offers such number for the above torch nozzle and the correct number is usually about 10 gallons. Why? To answer the above question, you should pay attention to two points:
A) A reduction of 4% of the combustion efficiency per 300 m above sea level
B) Theoretical Normal pressure of 7 bars and the actual pressure of the gas pump of each burner
In the case of row (A) in proportion to the increase in altitude from the sea level due to the decrease in the air density (concentration) and naturally oxygen depletion in the air relative to the air at sea level, the combustion efficiency is reduced and consequently there should be less fuel provided for the torch; Otherwise, because of the lack of needed oxygen, combustion will be carried out with unburned fuel or smoke. On this basis for the city of Tehran, which is about 1500 m above sea level, the combustion efficiency is reduced by about 20% this means a 20% reduction in the amount of fuel consumed and the heat produced.
In the case of the row, it is necessary to mention this explanation that the number of gallons written on each nozzle is based on the normal pressure of 7 bars. This means that the "orifice" of the nozzle at gas oil pressure of 7 bars passes the same amount of fuel as written But since the pressure of the gas oil pump is greater than 7 bars (according to the pump diagram), and at this higher pressure, the orifice of the nozzle passes through higher volume of gas oil.
For example, in the case of 220000 kcal torch, the pressure of the gasoline pump is usually 12 to 14 bars, which requires a smaller nozzle number to be selected.
Accordingly, to select a Gallon number of each torch gas oil nozzle of will first:
- We first divide heating capacity of gas oil burner torch by 32000
- We adjust the above number according to the installation height of the torch from the sea level.
For example, in the case of a 220000 kcal torch, if the torch is supposed to be installed at a point in the country which is 1200 meters above sea level first we calculate the amount of fuel consumed in terms of sea level:
Then, considering that every 300 meters above sea level reduces combustion efficiency of the torch by 4%:
Now, using the following diagram and at the pressure of the diesel pump of 14 bars the correct nozzle number required for a torch of 220,000 Kcal / h installed 1200 m above sea level will be equivalent to a nozzle number of 3.5 or a nozzle 4.
The correct nozzle selection diagram at the pressure of the Gas oil Pump of the torch:
Determining the of the gas oil spray angle (angle determined on the nozzle)
the spray angle in gas oil nozzles is determined according to the length of the boiler. meaning, if the length of the boiler or combustion chamber is high or the number of cast iron boilers blades is more than 10, then the 45 degrees nozzles and if the boiler is short, 60 or 80 degrees nozzles are used. Do not use 30 degrees nozzles for central heating boilers, except as recommended by the boiler manufacturer.
Determination of Gasoline spray form
As you can see in the figure below, dispensing form of gas oil varies according to the type of nozzle chosen and its type of use. Usually, when choose nozzles, S or B shape spraying nozzles are chosen. The gas oil spray form should be conical and have a filled and uniform base surface (S). H, B, etc., can only be used in cases where the manufacturer of the boiler or combustion heater has recommended.
Attention: In order to prevent the entrance of particulate matter and impurities present at liquid fuels into the nozzles and, consequently, changing the amount, angle and the type of fuel spray or even the possible closure of the nozzle liquid nozzle diffusion orifice, it is necessary to install a fuel filter (gas oil filter for the gas oil fuel burner torches and Mazut filters for Mazut burner torches) before entrance of the fuel into the nozzle.