Cement Energy and Environment

shredded and particulate solid fuels into the flame . These injectors are well suited to alternative fuels such as RDF, sawdust, fluff and rice husks (see Figure 3) . Particle size must be small enough to make sure no unburned particles are left to fall into the feedbed. Refractory castables should be Estimating burner momentum thick enough to satisfy campaign requirements but not so thick that the burner pipe starts to restrict secondary airflow into the kiln. Liquid fuel nozzles for waste oils, solvents and other liquids. The nozzle type should provide the degree of nebulisation required for efficient combustion of the fuel. Compressed air nozzles provide good flexibility for handling a wide range of liquid viscosities yet have a good turndown ratio. Cooling plate to allow cooling air flow through the burner and help stabilize the flame. A spare duct should be fitted to allow future use of other alternative fuels. Positioning of high-momentum burners is normally parallel to, and centred on the kiln axis to keep the flame central and reduce the risk of flame impingement. Burner alignment on the kiln centerline allows more time for the complete combustion of difficult fuels and ensures any ash is carried further up the kiln before settling . This reduces the risk of localized reducing conditions, buildups and quality problems. A common parameter for characterizing burner performance is the momentum to thermal load ratio, as N/MW, which relates the axial energy in the burner jet to the thermal load in the burning zone. Although the full calculation process is rather tedious an approximate value for the axial momentum can be obtained from the simplified equation: Axial momentum (N/MW) = Where: %PA X UPA 300 % PA = primary air expressed as a % of the stoichiometric equivalent (Amin) U PA =axial velocity component of the primary air leaving the burner tip (m/s) (Note that transport air is usually disregarded when assessing multichannel burners) How much momentum do you need? Burner momentum requirements depend mainly on the nature and combustibility of the fuels being used. Easily– combusted liquid fuels such as light oils may burn well with a relatively low burner momentum, but momentum requirements are higher for solids and alternative fuels which are hard to burn. While a burner momentum between 2-4N/MW used to be considered adequate for burning most traditional fuels, higher momenta are now being specified as the benefits have become more widely recognized. Most suppliers now provide burners with a momentum of 5 or GN/MW for firing mostly traditional fuels and 8 or 1ON/MW for firing different types of petcoke. For some difficult-to-burn fuels momentum to thermal load ratios in excess of 12 N/MW may be needed to achieve satisfactory combustion at high fuel substitution rates. But it is possible to have too much of a good thing. Excessively high momentum can cause loss of coating, rapid refractory damage, high NOx 21