OCR Text |
Show demonstration is needed, smaller package-type boilers have been used. Pressures in these tests are approximately atmospheric. In trace metal deposition studies, different types of fuels have been used including petroleum residual fuels, coal-derived liquids, jet and turbine fuels, and distillate and residual fuels doped with trace metal compounds. The objectives of most of these experiments have been to measure the deposition rate, corrosion rate, and effects of fuel additives. In addition, many other combustion studies have also been conducted to evaluate the combustion and emission characteristics of different fuels. The formation of aerosols and deposits from the combustion of residual and synthetic fuels distinguishes itself from other particulate systems by its complex chemical nature and high temperatures. Mechanisms of particle formation and deposition can vary significantly depending on the trace elements, the combustion characteristics of the fuel, the type of combustor, and the combustion and operating conditions. The vapor pressure of a trace element compound in fuel determines whether that element can vaporize before oxidation. Thus, the nonvolatile compounds, upon the evaporation and combustion of volatile matter from an atomized fuel droplet, can shrink to form the "residual" aerosol particles. This is similar to the formation of residual ash particles from combustion of coal particles (Flagan and Friedlander, 1978; Damle et al., 1982). Light distillate fuels usually do not contain non-volatile compounds, however, residual fuels contain ash that can not vaporize under combustion conditions. Therefore the combustion of residual fuels are expected to result in residual aerosols. A simple 1.5.12 |