Flame Momentum

WELCOME TO BURNER TECHNICAL SESSION

AGENDA 

FLAME MOMENTUM



FLAME SHAPING

AGENDA 

FLAME MOMENTUM



FLAME SHAPING

BURNER GENERAL ARRANGEMENT

(1) (2) (3) (4) (5) (6)

Fire hood Burner seal Trolley Ignition gas burner Flexible connector sets Primary air ducting

(7) Valve train (8) Flame safety/control panel (9) Coal transport system (10) Emergency air fan w/motor (11) Primary air fan w/motor (12) Burner set for oil or gas

BURNER DESIGN CONCEPT Primary air inlet Burner trolley

Burner pipe with refractory

Valve for radial air

Valve for axial air

BURNER FRONT END Radial air channel Axial air channel

Coal meal channel

Central air duct

Oil burner lance

INPUT DESIGN DATA          

Ambient pressure (mm Hg) Ambient temperature (C) Kiln production rate (tpd) Firing in kiln (kcal/kg.cl) Fuel Net Calorific value (kcal/kg) Design coefficient coal (1.25) Coal conveying air amount (m³/min) Fuel flow rate (kg/h) Kiln hood width (kiln w.p.h to door front) Pyro PD

CONSTANTS USED IN DESIGN           

Axial air temperature: 80˚C Radial air temperature: 50˚C Coal transport air temperature: 70˚C Central duct air temperature: 50˚C Coal discharge velocity: 30 m/s Coal discharge velocity deviation: ± 2 m/s Max. radial air velocity: 30 m/s Max. axial air duct velocity: 35 m/s Central duct nozzle hole velocity: 20 m/s Refractory thickness: 80mm Refractory density: 2800 kg/m³

CALCULATION Burner capacity, Qmax (Mcal/h) = (Design coefficient x Firing in kiln x kiln production)/24 Burner capacity (MW) = (Qmax (Mcal/h) x 4.1868)/3600 Maximum fuel capacity (kg/h) = (((Kiln production x 1000/24) x Firing in kiln) / Fuel NCV) x Design coefficient

CALCULATION Theoretical air amount, Lmin (Kg/s) = Burner capacity, Qmax (Mcal/s) x kg.air/Mcal (Where 1.39 kg.air/Mcal > 4500 fuel NCV and 1.43 kg.air/Mcal < 4500 fuel NCV) Primary air fan volume (m³/s) = 10% of Theoretical air amount, Lmin / Ambient air density Absorbed power (kW) = Pr. Air flow (m³/sec) x Pressure (mmWG)/102*efficiency

FLAME MOMENTUM

FLAME MOMENTUM The best way of expressing the efficiency of a burner is by the momentum (primary air percentage multiplied by discharge velocity) expressed as %m/s or as n/mw (1 N/MW ≈ 296 %m/s). The higher momentum means that a stronger, wider and shorter flame can be generated.

PRIMARY AIR SPLIT UP - SCHEMATIC

PRIMARY AIR MOMENTUM

Input data: Ambient pressure: Ambient temperature: Stoichiometric combustion airflow: Primary airflow, measured: Primary air pressure at nozzle: Primary air temperature: Isentropic exponent for air: Gas constant for air:

pamb mbar  tamb  C Lmin kg/s mpr    kg/s pN mbar  tpr     C 1,4 R  286,89 J/kgK 

PRIMARY AIR MOMENTUM

Primary air percentage:  L

 p

Nozzle velocity:

c pr  =

=

m  pr   L

´ 100[%]

min

é æ   p amb  ö 2 ÷ ´ R (t  pr  + 273,15)´ ê1 - çç ê è  p amb +  p N   ø÷ -1 êë

Primary air momentum:

-1

ù ú [m / s ] ú úû

G pr  =  L p ´ c pr  % m / s

AIRFLOW CALCULATION

Input data:Nozzle area: AN [mm2] Nozzle coefficient (for 100% axial air, lower with swirl air) : kN 0,95

AIRFLOW CALCULATION

2

æ   p amb  ö æ   p amb  ö ç ÷ y  = ç ( p +  p ) ÷ - çç ( p +  p ) ÷÷  N   ø  N   ø è  amb è  amb k 

Flow function:

k  +1 k 

Primary air flow: m pr  = 10

-4

´  A N  ´ k  N  ´y  ( p amb +  p N  ) ´

2k  k 

´

1

- 1  R (t  pr  + 273,15)

[kg / s ]

PRIMARY AIR MOMENTUM (EXAMPLE) Input data: Kiln production: Ambient pressure: Ambient temperature: Stoichiometric combustion air flow, Lmin: Axial air damper: Radial air damper:  Nozzle coefficient: Primary air pressure at nozzle: Primary air temperature: Air nozzle opening:  Nozzle area: Primary air, measured:

3949 tpd 953 mbar   43 °C 20.21 kg/s 100% open 20% open 0,95 197 mbar   80 °C 35 mm 7281 mm2 134.5 m3/min  2,13 kg/s

PRIMARY AIR PERCENTAGE (EXAMPLE)

       

1, 4 1

2

  1, 4      197   

953 953

  1, 4  0,199   197 

953 953

2 1,4 1 4           132 m pr  10 7281 0,95 0,199 953 197 , kg / s 1,4  1 286,8980  273,15

 L p



1,32 20,21

 100  6,53%

PRIMARY AIR MOMENTUM (EXAMPLE)

Velocity:

c pr 

     2 1,4  286,8980  273,15 1      1,4  1 

953 953

    197 

1, 4 1 1, 4

   193 m / s  

Primary air momentum:

G

 6, 53  1931260 % m /s

FLAME MOMENTUM EFFECT Burner momentum is insufficient to effectively mix the fuel with the secondary air, the heat consumption could be increases. Burner momentum is insufficient and it can give a lazy flame and a bad burn out of the fuel, which can lead to fuel particles in the charge The flame momentum below the recommended range will result in too long a flame, high kiln shell temperature above the burning zone and in the kiln back end as unstable kiln operation with a too long and cold burning zone thereby permitting undesirable clinker crystal growth. A higher momentum can reduce the CO.

NOZZLE MOVEMENT Maximum Position

Minimum “0” Position Adjustments made using hand wheel

Nozzle Flush

Nozzle Retracted

PRIMARY AIR MOMENTUM (Nozzle max. open)

PRIMARY AIR MOMENTUM (Nozzle min. open)

PRIMARY AIR MOMENTUM Fuel gas

~1200 %m/s

Fuel oil

~1200-1500 %m/s

Medium volatiles coal

~1500-1700 %m/s

Anthracite or petcoke

~1600-2100 %m/s

Secondary fuels, up to

~2400 %m/s

Flame Momentum is a practical number in which the flame shape will be optimum for the  particular fuel.

FLAME SHAPING

RADIAL AIR ADJUSTMENT Open - more swirl action gives a recirculation zone resulting in shorter, wider and steadier flame Close - less swirl action, long and relatively thin flame. Increase in radial air will results in a hot zone close to the burner. For nominal operation, radial air damper will be set between 10 - 30 % open. Excessive radial air might influence in coating loss close to the burner.

RADIAL AIR EFFECT

Fuel and primary air

Swirl air Hot secondary air

Internal recirculation zone

External recirculation zone

AXIAL AIR ADJUSTMENT Open - increases axial flow, relatively thinner and steadier flame. Close - decreases axial flow, softer and less intense flame. Closing the axial air will make the flame softer / low momentum and might result in the flame impingement on to the coating. For nominal operation, axial air damper will be set 80 - 100 %open. During startup, if there are fumes of un-burnt fuel (black and co formation) then it signifies either lack of axial air or the combustion air.

AIR NOZZLE ADJUSTMENT Open - rotating the spindle anti-clockwise will increases the nozzle area. If the primary air fan damper control is in auto mode (static pressure), an increase in nozzle area will open the fan damper to maintain the static pressure thereby increasing the flame momentum. Close - decreases in nozzle area will have a reverse effect of the above. For nominal operation, nozzle position will be set between 45 65 % open.