OCR Text |
Show Included below are some of the findings of our combustion investigations . Atomization and Spray Formation The key factor to efficient combustion of liquid and slurry fuels is proper fuel atomization with efficient atomizers. Small fuel droplets must be formed prior to the hot combustion reaction zone to ensure rapid release of liquid fuel energy and solid particle ignition. Improper atomization can lead to flame instability, poor energy transfer to boiler sections and low carbon burnout of solid fuel. For highly viscous fuels such as No. 6 oil in PETCOM, gas or twin-fluid atomizers are commonly used to provide efficient atomization over a wide range of burner fuel flow rates. As explained in a previous section, our experiments performed on PETCOM indicated lower combustion with steam atomization. The trends of combustion efficiency with nozzle performance show good correlation with the ideal work available in the atomization fluid as shown in Figure 5-2. The ideal work, on a unit weight of fuel basis, was determined using the following equation for isentropic expansion of the atomizing gas:__. (5-1) This relationship shows that more energy is available for high flow rate, high temperature and high pressure atomizing gases. It also indicates that more work is available in a gas with a low ratio of specific heats and molecular weight. Thus, steam (k = 1.25, MW = 18) is favored over air (k = 1.4, MW = 29), all other conditions being the same. 19-20 Ideal work = W V2 = W V2 + 2gkRT L 2W I ™l L k-1 |