1. Liquid Fuel Burners Oils may be burnt in two ways  it is vaporized before ignition so that it burns like a gas (vaporising burners)  it is converted into droplets which are injected into hot air so that they evaporate while burning (atomising burners)

2. Liquid Fuel Burners Atomising burners: On industrial scale, most commonly used burners are atomising burners  Oil is heated to low viscosity and atomised (i)Mechanically by means of a rotating disc or cup with a uniform droplet size (50 microns) (ii)By a high pressure ejection from a fine orifice which gives a conical spray

3. Types of Atomising Oil Burners There are three types which differ on the principal of atomising  Pressure Jet Atomising Burners  Blast Atomising Burners  Rotary Atomising Burners

4. Pressure Jet Atomising Burners  Oil enters the circular swirl chamber through tangentially spaced slots  Oil will rotate in the chamber around the air  The rotating mass is passed through an orifice resulting in the formation of spray of drops  The viscosity should be 70 Redwood I seconds for small nozzles and 100 Redwood I seconds for large nozzles

6.  These burners have low operating cost and most widely used  These type of burners have limited turndown ratio  Turndown ratio can be increased by design modifications e.g. by increasing the number of tangential slots

7. Blast Atomising Burners  These burners use air or steam to atomize the oil  Oil flow through a central tube at a controlled rate mixed with mixed with air as it emerges from the tube  Depending upon the pressure they may be classified as Low pressure, Medium pressure or high pressure  Depending upon the mixing system they may be classified as inside-mix type or outside-mix type

8. Blast Atomising Burners  High pressure burners have high turndown ratio (10:1)  Inside-mix type commonly provide more eficiency

9. Blast Atomising Burners

10. Rotary Atomising Burners  These burners have a centeral stationary fuel line which delivers the oil to the inner surface of rotating hollow cup  The cup is rotated at 3600- 10,000 rpm  Centrifugal force causes the oil to flow towards the brim of the cup in the form of thin film which disintegrates into small droplets  A fan attached to the rotating shaft provides primary air  These burners can be used for more viscous fuels  Low viscosity may cause the oil to slip within the cup resulting in low atomizing efficiency  These burners can have high turn down ratio but low capacity

11. Rotary Atomising Burners

12. Adiabatic Flame Temperature  For adiabatic flame temperature following assumptions are made  No heat loss to the surroundings  Combustion is complete  No thermal dissociation  A reference/datum temperature is selected

13. Adiabatic Flame Temperature Adiabatic flame Fuel oxident diluent Combustion products

14. Adiabatic Flame Temperature  A fuel gas containing 20 % CO and 80 % N2 is burned with 150 % excess air (both air and gas being at 25 C). Calculate the theoretical flame temperaure of the gas.  Following data is available

15. CO2O2N2CO Av. Sp. Heat kcal/mole K 12.107.907.55- Heat of formation at 25 C kcal/kg mole -94052-26412

16. Material Balance Basis: 100 kg moles of fuel gas Material entering Kg moles Materials leaving Kg moles CO N2 O2 CO2 20 80 + 174.05 25 - 80 +174.05 15 20 total299.05289.05 Energy Balance: assuming reference temp. 25 C Heat of reaction = -94052 –(-26412)= -67640 kcal / kg mole Heat produced by combustion = 20 x -67640 = -1352800

17. Cp kcal / kg mole K Amount kg mole mCp dT CO212.102020x12.10xdT O27.90157.90 x 15 x dT N27.55174.057.55 x 174.05 x dT Total=1674.58 dT 1674.58(Tf -298)= 1352800 Tf= 832.8 C

18. Adiabatic Flame Temperature NCV+∆h f +A∆H a =V∆H fg +q d + q l A= air supplied m3/m3 fuel V=flue gases produced m3/m3 of fuel ∆H f =enthalpy of fuel above reference temperature ∆H fg =tf. C pfg(0-tf) –t r C pfg(0-tr) T f =(NCV+∆h f +A∆H a -q d – q l +V. t r C pfg(0-tr) )/ V. C pfg(0-tf)

19. Adiabatic Flame Temperature Calculate the theoretical flame temperature for a fuel gas under the following conditions: (i)Both fuel and theoretical air are at 15 C (ii)50 % excess air at 15 C and fuel gas at 15 C (iii)Theoretical air at 60 C and gas at 400 C (iv)Theoretical oxygen at 15 C and fuel gas at 15 C Data: Fuel gas: CO : 22% CO2 : 18% H2 : 2% N2 : 58% NCV: 719 kcal/m3 Mean sp. Heat of fuel gas at 600 C= 0.342 kcal/m3 C