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Flame for cement kilns kppradeep kumar

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  • 1. Combustion techniques and Coal flame for cement kiln If coal is mixed it is burntPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 2. PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 3. Always to be remembered If coal is mixed it is burnt If flame is wrong everything goes wrong whatever you may do with chemistry or higher heat input through calciner or kiln. The burning zone needs heat and it can be only obtained from well shaped radiant flame.i.e., short, snappy and convergent flame .PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 4. Kinetics of coal combustion in kilns The coal combustion phenomenon takes place in a cement Rotary kiln takes place in four stages.( for normal coal) 1.Heating Heating of coal particles takes place by conduction and convection till ignition takes place is reached. Ignition temperature of bituminous coal = 300 O C lignite = 250 O C anthracite = 400 O C pet coke = 800 O C 2. Devolatilisation Devolatisation process starts after the coal particles attain a temperature of 350 to 400 O C . At this temperature the coal bond structure breaks up to yield carbon monoxide , hydrogen and hydrocarbons.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 5. 3.Volatile burning The volatiles that are formed burn in gas phase and the rate of burning depend upon two factors , the rate at which the volatile mix with air after being emitted from the coal particles and the rate of chemical reaction. 4. Residual char burning The residual char is the solid carbon left after complete devolatilisation. As the reaction progresses the residual char starts to take up 70 to 80 % 0f the total burning time.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 6. heat Volatile matter evolution And burning oxygen Char gasification CO2 and H2O combustion NOX SOX etc charPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 7. Coal combustion processPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 8. Main Processes in Coal Combustion homogeneous coal particle combustion CO2, H2O, … volatiles p-coal, d=30- 70µm heterogeneous combustion CO2, H2O, … char devolatilization tdevolatile=1-5ms tvolatiles=50-100ms tchar=1-2sec tPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 9. Stages of coal combustion Coal particle drying , and then heating-up to the Pyrolysis reaction temperature Heating up to the pyrolysis reaction temperature Pyrolysis of the coal particle to produce non-condensable Volatiles ( gases) , condensable volatiles ( tars) , and carbonaceous char Oxidation of the combustible volatiles ; and finally Char oxidation.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 10. Reburning Excess air homogeneous combustion volatiles CO2, H2O, NO… heterogeneous combustion char CO2, H2O, NO… CHi∙ devolatilization CO2, H2O, N2… CHi∙ + NO ↔ HCN HCN + NO ↔ N2 + …PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 11. Staged Combustion Fuel Rich homogeneous combustion volatiles CO, CO2, H2O, N2… heterogeneous combustion char CO, CO2, H2O, N2… O2 Devolatilizatio n CO2, H2O, N2…PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 12. Combustion time as a function of particle diameter The combustion time , T = K ( D ) 1.5 D = diameter of coal particle K = constant characteristic of coal quality low for bituminous coal high for pet coke That is why we maintain high residue for bitumen coal and low residue for pet coke (pet coke has low volatile) The faster the combustion are gases are removed and replaced by fresh air( hot secondary air), the faster the coal particles burn. To fulfill this precondition , a high relative velocity between Combustion air and coal particles is required. This needs a high flame momentum with high primary air velocity and low % of Primary air.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 13. For bituminous coal For pet coke And anthracitePDF created with pdfFactory Pro trial version www.pdffactory.com
  • 14. Relationship between coal types,compostion and grinding fineness Petcoke < 10 < 1.0 4%< + 0.09 mm 0 %< + 0.2 mmPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 15. 0.5 sec 0.1 Combustion time for a particular coal particle Total combustion time Ignition time Burning time of gases pause Burning time of carbon(char)PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 16. The physical processes influencing pulverized coal combustion • Turbulent/swirling flow of air and coal. • Turbulent/convective/molecular diffusion of gaseous reactants and products. • Convective heat transfer through the gas and between the gas and coal particles. • Radiative heat transfer between the gas and coal particles and between the coal/air mixture and the furnace walls.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 17. COAL COMBUSTION CHARS When coal is combusted in air it burns in a two step process. In the first step gases are driven out of the coal structure leaving behind a carbon char that burns in the second step. These chars play a critical role in combustion in that they must burn up in the reaction zone of the furnace or be carried out of the furnace as unburnt carbon in fly ash. This unburnt carbon represents an inefficiency as well as an economic loss because the energy in the unburnt carbon is not being used. Excess unburnt carbon also destroys the ability of the fly ash to be use as a cement in a variety of applications. In modern combustion systems coal is usually ground into a fine powder (-200 mesh or - 74 micrometers) that features many single maceral particles . This is significant in that the various macerals tend to have different reactivities and therefore burn at different rates. Because the different maceral groups form chars with different morphologies, it is possible to analyze coal combustion chars to gain information about the nature and reactivity of coals being combusted. The vitrinite macrerals form chars that take the form of hollow spheres, centispheres . Semifusinite macerals form centispheres with a lacey or honeycomb structure, and fusinite maceral char come through the combustion process unfused.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 18. Coal Combustion Char Classification Tenuisphere Fused or partially fused hollow spherical or angular char with walls less than 10 micrometers and porosity greater than 85 % Crassisphere Fused to partially fused hollow spherical or angular char with walls thicker than 10 micrometers and porosity greater than 75 % Tenuinetwork Partly fused, thin-wall char with internal network structure and porosity greater than 75% Mesophere Partly fused, thin-wall char with internal network structure and porosity 40-60% Inertoid Unfused particle with a rectangular to irregular shape and low porosity of 5-40% Solid Unfused particle with a rectangular to irregular shape and no porosity Fusinoid Unfused particle resembling fusinite with original plant cell structure Mixed Porous Mixed particle showing both fused and unfused sections with fused porous section dominant Mixed Dense Mixed particle showing both fused and unfused sections with unfused porous section dominant Skeletal Unfused, angular but highly burnt out char, still resembling fusinite Mineraloid Char with over 50% mineral matterPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 19. Smaller, this balloon- like spheres and thinner its walls ,faster the combustion. It is very difficult to form such spheres(ceno spheres) from Pet coke because of low volatile presence.It needs very high energy and longer retention time in ignition zone. Description: The object in the center of the field is a typical tenuisphere. It is characterized by its spheroidal shape, open center, and thin walls. The char forms such hollow spheres , also called Cenospheres before Mixing with with Oxygen to form gases of various oxides.It easily bursts Into micro particles of carbon.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 20. CenospherePDF created with pdfFactory Pro trial version www.pdffactory.com
  • 21. Combustion of char Once the ignition has occurred the critical reactions as far as a good combustion in kiln is concerned are: H + O2 = OH + O C n H m+ O = C n-1 Hm+C O CO + OH = CO2 + H 2CO +O2 +M = 2CO2 + M H2O + O = 2 OH 2C + O2 = 2 COPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 22. Effect of coal properties on combustion Moisture content A moisture content of 1 to 1.5 % in the pulverized coal promotes combustion.In the presence of hydroxyl ions (OH)-, the formation CO and CO2 takes place by chain reaction. on the other hand a higher moisture content increases the thermal Inertia of reacting species , shift the flame and reduces the flame temperature. Volatile matter The volatile rich coal has a high porosity offering a larger space area for combustion hence requiring a lower ignition temperature than volatile less coal ( eg anthracite , pet coke etc).Thus coal rich volatile matter > 30% decomposes with higher rate and promotes faster combustion . Volatile rich coal form small cenospheres with thin walls and decompose faster.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 23. Ash Ash is an inert component of coal and an increase in quantity leads to increase in heating time due to added thermal inertia. Most of the combustible particles of coal will be covered by ash and hence less surface is available for oxygen diffusion. This increases the burning time and the residual char causing an increase in flame length. Overall there is delay in combustion, elongates the flame . If there is a cloud of clinker dust , what will happen? This dust will absorb the radiated heat from flame , reduce the heat flow to the refractory( and coating) and get reheated with more stickiness. Hence optimized cooler airflow with good clinker bed , overall cooler efficient operation will enhance the combustion efficiency.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 24. Effect of coal moisture content on degree of combustion Vs distance from the burner. 0 100 1 90 2 80 Degree of combustion 3 70 Moisture content 4 60 High moisture 5 50 6 40 7 30 Low moisture 8 20 9 10 10 1 2 3 4 5 6 7 8 9 10 0 Distance from burner (m)PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 25. Effect of coal moisture on flame temperature vs distance from burner 1700 1600 Flame temperature , deg . C 1500 Low moisture 1400 High moisture 1300 1200 1100 1000 900 800 1 2 3 4 5 6 7 8 9 10 Distance from burner (m)PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 26. Effect of volatile content on degree of combustion vs distance from burner 100 90 80 Degree of combustion 70 60 low volatilite , 9.8 % 50 40 30 High Volatilite , 38 % 20 10 1 2 3 4 5 6 7 8 9 10 0 Distance from burner (m)PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 27. Effect of secondary air velocity on flame temperature Vs distance from the burner 1800 10 1700 9 Secondary air velocity, m/ s 1600 8 Flame temperature, deg C 1500 7 1400 6 1300 5 1200 1100 4 3 1000 2 900 1 800 1 2 3 4 5 6 7 8 9 10 0 Distance from burner (m)PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 28. Effect of oxygen level on exit gas heat loss Heat loss Kcal In complete Optimum operating range combustion -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 oxygen level in kiln exit , %PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 29. Simulated oxygen content for an ideal flame Oxygen concentration in kilnPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 30. FlamePDF created with pdfFactory Pro trial version www.pdffactory.com
  • 31. Cement kiln flame types Straight flame –essentially external recirculation Type-1 flame Weak internal recirculation external recirculation Type-2 flame Strong internal recirculation external recirculationPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 32. PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 33. Straight flame of single channel burner Straight flame is stabilized ( single pipe burner) by the strength of the external recirculation flow established by the shear forces between the primary and secondary air streams Multi channel burner For multi – annual burners , enhancing the internal recirculation flow patterns can increase the flame stability. This can be accomplished by reducing the momentum of the inner zones while increasing the momentum of the outer air zones , or by mounting a bluff body flame stabilizer in front of the primary stream.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 34. Heat transfer from coal dust flames Flue gases or flame gases respectively pass their heat to the environment mainly by radiation and only to a small degree by conduction and convection. Normally 13 % ( ideal) of the kiln volume is usually filled , therefore major portion of the heat is transferred to kiln refractory lining with kiln feed receiving a relatively a small portion of the total heat volume. Many tried to keep the flame close to charge but it has negative influence as coal may get trapped and cause reducing conditions in the charge which causes reduction of Fe2 O3 and also volatile recycling of alkalis and sulfur.If it is close to charge which is 13 – 18 % , the heat radiated to refractory weakened and causes poor heat exchange.The heat is carried always by the flue gases only to result in high backend temperature. If kiln has stable and optimum coating then then we get the best heat exchange as it acts as the best heat reservoir.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 35. We do positioning of the burner for centering the flame.The positions 1,2,3, 4 and 7are close to the refractory and they are away from the charge. 1 2 3 Positions9 and 8 are close to charge . 4 5 6 Only 5 is close to charge and refractory and this is 7 8 9 best as the flame in this gives the best thermal distribution to do effective burning. Position 8 & 9 is very close to charge if coal is trapped it has serious negative impact.Position 1,4 & 7 is very close to refractory and it can burn the Burner positioning refractory.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 36. Flame positioning towards the charge There is an illusion if the burner is kept just above the charge or Impinges the charge burning is better but it is on the other way. In heat exchange process 85 % of the heat is radiated to refractory and 15 % to the charge. If flame is kept above the flame.( Beyond the plume it is invisible)If we are not careful the char takes more time to burn out and hence it is highly possible the char gets trapped , form local reducing condition , reduce the haematite ( vicious redox cycle), spoils the liquid and increase the recycle of sulfurous cycles. The rules of radiation of solids cannot be applied by the radiation of flames. Monatomic and diatomic gases like N2 and O2 are in the range of infra-red entirely transparent and their radiation equals zero.Therefore , the presence of these gases is only ballast. On the other hand gases with a higher no.of atoms such as H2), CO2 and SO2 develop a considerable thermal radiation due to their absorption bands in the IR range.CO2 radiates more than the others.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 37. The radiation active constituents of the pulverized coal flame are a. The CO2 content of the flame gases b. The H2O content of the flame gases c. C the content of suspended dust in the flame gases The following requirements result in promoting the heat transfer By the gases in the clinkering zone 1. An increase in the flame temperature 2. An increase in the concentration of CO2 3. An increase in kiln diameter ( to have 13 % degree of filling) Thick coating increases the degree of filling , reduces the effective diameter 300 mm thickness is considered as ideal to improve the refractory life as Well as the heat exchange process.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 38. Multi channel burner Traditional burnerPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 39. Function of burner or requisites of a good flame. 1.The burner must be able to burn fuel with a low excess air and with a minimum generation of carbon monoxide , nitrogen Oxides and volatile recycling like SO2 etc. 2 The burner must be able to produce a short, narrow , and strongly radiant flame which is a requisite for good heat transfer from flame to material in the sintering zone of the kiln. 3. The flame formation must be conducive to the formation of a dense . stable coating on the refractory in the burning zone of the kiln as well as a nodular clinker with a low dust content and correctly developed clinker minerals. 4.The burner must use as little primary air possible since primary air is basically false air.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 40. Flame momentum The burner in kiln functions as an injector, the purpose of which is to draw the secondary air coming from the cooler into the flame in order to burn the fuel as near the center of Kiln as possible.The explains why momentum of the burner is deciding factor for the flame formation. Multi channel burner makes a faster entrainment of secondary air than single channel burner.Higher the momentum better the entrainment of secondary air and faster the combustion of fuel. momentum or impulse = % primary air * velocity of primary air for normal coal = 1200 – 1500 % m/s for petcoke > 2500 % m/s Momentum obtained by low primary air % and higher velocity is better than higher primary air % and lower velocityPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 41. Secondary air Velocity= 5 – 6 m/s Ignition This depends on the If the jet has good This depends upon pressure difference momentum Rate of mixing of between secondary it will pull back sec air air region and the flue gases ,causing and coal particles, primary air region. external recirculation. size of, Higher the pressure This is an indication of the fuel particle difference higher Sec,air entrainment into and volatile inner Circulation. the primary air jet.Multi Content and the Channel burners do this injection Job efficiently. This reduces Velocity. the NOX formation.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 42. Secondary air Ejector effect Inside Outside circulation circulation Ejector effect Secondary air Secondary air Recirculated combustion Ignition area taking area gas area Axial outer stream Swirl coal +transport air Swirl inner streamPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 43. PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 44. Different flames Flame at the center Normal flame Flame with low Flame downward Secondary air temp Distorted nozzle Flame upward Flame –poor hood geometry Or distorted nozzlePDF created with pdfFactory Pro trial version www.pdffactory.com
  • 45. Different flames Normal snappy flame forms dense and stable coating Indication of first dam Long , lazy flame With unstable coating To be remembered: if burner pipe is at the center that does not mean flame is in center. Visualizing is the best thing to do and it should be done from right and left peeping holes . If there is a peeping hole just above the burner in the center help us further to center the flame. A good uniform coating is a fairly good criterion for a good flame. Uniform shell temperature around the shell is good indication.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 46. Secondary air velocity Vs flame length Secondary air Velocity influences flame length and shape Higher the secondary air velocity longer is the flame.Here we have to increase the flame momentum by increasing the primary air velocity at the tip Higher the sec.air velocity Lower the hot air pressure region. Hence we have to increase the pressure drop at the tip to pull back more secondary air towards the flame. Coating at the tip , called shark teeth, increases the secondary air velocity and so increases the flame length.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 47. Flame trouble shooting Pulsating flame with CO Peaks at the kiln inlet 1. Fluctuations in coal flow Check the flow promoters.clean the bin as there may be coating formation.check the liners in the cone. Bin dusting pressure should be maintained. Coal flow discharge chute can have coating formation. Un uniform gap between screw flight and casing. Firing pump discharge flaps -counter weight needs adjustment . dedusting for coal feeders device is to be optimum.If FK pump seal is leaking transport air can go inside the pump screw and fluidise the coal , change its bulk density and hence the flow. Pump is a volumetric transport device. 2.insufficient secondary air temperature and flow variation Optimise the clinker bed in cooler and cooling air to recuperate more heat. Reduce the variations in the under grate pressure as well as hood pressure pulsation. If shock blasters are there adjust the time interval to avoid pressurization of hood.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 48. 3. Insufficient transport air velocity or coal injection velocity Check the material /air ratio. It is 4 kg coal/ cu .m air to 6 kgs, cu m. The velocity is 25 to 30 m/s . If it is not so, modify the transport pipe inner dia or increase the transport air volume. Too long transport air pipe. The maximum length is 250 meters. Avoid sharp bends as these bends will cause pressure variations. during lay out itself it should be considered. Check the coarseness of coal.Too coarse coal can settle in the pipe line.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 49. Flame characterised by a long blackcore ( long plume) , increased CO-value at the kiln inlet 1.Too high coal injection velocity. It is normally 25 - 30 m /s Increase the coal pipe annular space at tip to have 25 - 30 m/s tip velocity.Some plants plants run with < 25 m/s also. 2.Insufficient mixing of coal and secondary air( delay in combustion) Low secondary air temperature. Arrest false air ingress through nose ring by cooling fan or false outlet sealing. 3.Coarse coal Check the separator . Increase the fineness.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 50. Flame burning at the burner tip or sometimes coal drops 1.Too low coal injection velocity . This may be due to rotor gap fo blowe has increased or blower filter got choked. If coal pipe got punctured inside the burner coal will mix with primary air flow and damage further. check for wear of the coal injection pipe tip. Monitor filter DP and rotor gap ( blower pressure ) 2. Excessive swirl air Optimize the swirl airPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 51. Flame burning unilaterally 1 .Partial pipe clogging due to foreign matter existing in coal channel Remove the foreign matter. When we do the casting ensure that wet castable mix should not drop into the burner.close the burner by a plate while casting 2. Worn out centering element for coal channel or air channel. Unequal spacing of air flow annular space. Aligning of burner channels so that annular spacing is equal for coal flow pipe as well for primary airflow 3. Coal pipe got punctured inside the burner and the coal flows into primary air flow channels. Change the burner along with coal injection pipe.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 52. As per Pillard, burner needs changes when coal quality changes. Coal property Effect Burner adjustment Volatile Flame shortens and Reduce swirl air, increases Burning zone Increase axial air, Temperature rises move Burner into kiln Grindability Fineness decreases, Increase swirl air, decreases flame lengthens and retract burner temperature drops Heat input drops, Increase swirl air, Heating value Flame lengthens and reduce axial air decreases Sintering Temperature and increase coal drops feedPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 53. Characteristic of Flames with and without recirculation Flame with recirculation Flame without recirculation Fuel / air mixing Good Poor Reducing/ oxidizing Oxidizing conditions exist Reducing condition occur in conditions throughout the flame fuel rich part of the flame and in the area of flame impingement Flame impingement None- recirculating gases Flame impingement occurs protect refractory and product on refractory where jet from direct contact expands to hit the wall( 11- 14 %) Carbon monoxide level CO only produced in High levels of CO produced significant quantities below at oxygen levels as high as 2 0.5 % –4% Heat release pattern Rapid mixing gives high Poor fuel/ air mixing gives flame temperature and good gradual heat release with heat transfer long flame Kiln stability Good flame shape with stable Heat release pattern hat release pattern considerably affected by Gives stable operation changes in secondary air temperature, excess air , fuel quality etc.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 54. Burner swirl number = tangential momentum( N) * characteristic swirl radius(m) Axial momentum(N)*charateristical channel radius(m) Flame temperature (T) = Hv / 1.11A s T = theoretical flame temperature A = combustion air required kg / kg coal Hv = heating value of fuel S = specific heat of combustion gas ( 0.29) Heat flux and combustion intensity Hr = mf C v Where Hr = combustion intensity, kw/ m2 Lf π D mf = fuel flow rate, Kg/ s Cv = net calorific value , kj/ kg Lf = flame length , m D = kiln internal diameter , mPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 55. Swirl coefficient( Swirl number) As per M.A.S/ Burner, I tan .R e.tan Sn = I ax .R e.ax Where Sn = swirl coefficient ( swirl number) I tan = momentum of swirl air in tangential momentum Re.tan = momentum of swirl air in axial direction I ax = equivalent radius of swirl air duct R e.ax = equivalent radius of the axial air ductPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 56. PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 57. Axial index This index refers to the generation of gaseous re-circulations externally to the flame/ It is directly to the aspiration and mixing of secondary air by both primary air and fuel / conveying air streams. The axial index also has some relation to reicirculation at the kiln area and the formation of build-ups at the nose-ring called the so-called “ shark teeth”PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 58. Tangential index: This index refers to re-circulations internally to the flame, Which has influence in the ignition of the particles and flame spread. The tangential index has close relationship With the position and intensity of the first temperature peak In the kiln. Usually , during burner design the dimensions Of the nozzles at the tip are calculated in order to allow The variation of this index inside a predetermined range, depending on the adjustment of the primary air components. So , if the basis of design indicates narrower flames , the burner designer should calculate the tip dimensions to get lower values of tangential index in the burner operational range. On the other hand , if the basis of project indicates that the process would require wide and short flames , then the designer should calculate The burner operational range to present higher tangential indexes.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 59. Turbulence index: This index refers to the position of both temperature peaks in the kiln.During the calculation of the burner tip dimensions the turbulence index is checked to be above a minimum value all over the range of adjustment of the burner. Usually this minimum value is calculated as a function of fuel type , fuel preparation ( moisture and fineness ), secondary air temperature and kiln dimensions.With relationship to that minimum value of the turbulence index it should be pointed out that: • Bituminous coal finely ground ( 90 < 170 ) would require lower turbulence indexes than petroleum coke ground to the same fineness. One system operating with 100 % petroleum coke ground to 90 < 170 would require higher turbulence index than another system operating with the same coke ground to 99 < 170PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 60. Dispersion index: This index refers to the conditions of dispersion of the pulverized fuel cloud in the primary and secondary air streams. the dispersion index is related to the intensity of both Temperature peaks and as consequence , plays a major role in the study of the thermal NOX generation. Some additional factors , not directly related to characteristic dimensionless indexes must be considered during burner design. The first one refers to the secondary air conditions ( temperature , velocity distribution , dust content, etc). The second factor is the burner pipe penetration into the kiln cylinder in view that the length of this penetration has proved To interfere in both kiln performance and clinker quality. Finally , the firing hood geometry has some influence in the flame characteristics as it interferes with secondary air flow patternPDF created with pdfFactory Pro trial version www.pdffactory.com
  • 61. Conclusion After taking account of all considerations above , it is possible to conclude that the combustion plays a major role in the rotary kiln operation , but any improvement in this area should be faced , first of all , as a cooking problem and merely as a firing problem. It must be considered all the predominant Variables of the process and not only those related to the Oxidation of a fuel. Statement by - Peter J Mullinger Adelaide combustion institute Though the burner is very efficient we should know how use it. An experienced man must know how to look into the kiln to have Proper judgment about the flame being formed by the burner.PDF created with pdfFactory Pro trial version www.pdffactory.com
  • 62. Thank you for your kind attentionPDF created with pdfFactory Pro trial version www.pdffactory.com