| OCR Text |
Show Experience has also shown us that many different factors can affect the probability that satisfactory burner flame shapes and other operating variables can be obtained. For suspension firing, the two most important factors are fuel injection momentum and fuel droplet or particle size. If the fuel/transport media momentum can be reduced to less than 10% of the total air register momentum, for most applications flame shape can be controlled solely by changing the aerodynamics of the air register. Similarly if the mass median fuel droplet or particle size is 50u .or-J^ess, these particles will follow the flow stream lines created by the air register. Unfortunately for most real burner systems, these two criteria cannot be met and burner development becomes a complex problem of balancing and matching the fuel injection method to the aerodynamics of the burner air register. The use of a modified dense phase transport system with coal pulverized to a specification of 70 wt % minus 200 mesh (70u) provides a combination that more closely approximates this ideal fuel momentum and size criteria than other conventional fuel injection methods. This advantage means that a greater range of flame shapes should be obtainable with dense phase fuel injection than with liquid fuel or dilute solid fuel injection systems. For process systems where flame size and shape is often of critical importance, this could be the difference between the success and failure of a coal conversion. A second requirement for some process applications is satisfactory rate of change on heat input and turndown. Based on C-E's experience from large scale laboratory testing, it would appear that use of a dense phase fuel supply system with free burning coals will permit load rate changes and burner turndowns that are similar to those now available with oil firing systems. For use with agglomerating coals, finer grinding may be required to achieve turndown levels greater than 4 to 1. 11-25 |
