OCR Text |
Show 1.0 INTRODUCTION The design of rugged optical instrumentation for in situ measurements in high temperature combustion flows remains a topic of current research interest. Particle loading and size distribution measurements can provide important data for the reliable design of combustion process equipment and control of environmental factors. Examples of current and potential combustion applications include the study of: * Ash formation from pulverized coal * Flyash emissions from fluid bed combustors and gasifiers * Droplet atomization and distribution in spray combustors * Radiative heat transfer * Boiler fouling * Particle deposition in process streams * Soot formation * Ash condensation For these applications and many others, there is a clear need for on-line continuous measurements of mass loading and size distribution. In a series of papers, Holve, et al.^»2»3,4 have described the development of a single particle counter system which addresses a wide range of user needs consistent with both fundamental and practical design constraints. Described below is a prototype system for counting in situ particles in the size range of 0.25-100 microns at number densities up to 10^/m^. It also measures the particle velocity for absolute number density measurements and determines the amount of light extinction for high-number-density particle flows. The system incorporates an in situ alignment procedure that is easy to set up and use in a wide variety of research and industrial environments. The present instrument has been applied to a series of measurements of the number and mass frequency distributions of flyash and pulverized coal obtained in an atmospheric combustion exhaust simulator. Besides demonstrating the capabilities of this instrument, these new results show that the raw pulverized coal contains large numbers of submicron particles, similar to the flyash formed after combustion. Thus, as one example of its application, the counter system offers the potential for quantitatively resolving some aspects of flyash formation mechanisms for coal combustion. 2.0 APPARATUS AND TECHNIQUE Figure 1 is a schematic diagram of this Sandia single-particle counter system. The system shown consists of a transmitter unit on the right-hand side separated from the receiver unit by a 70 cm working space, where the process stream and window access system are located. The transmitter unit consists of a small (5 mw) He-Ne laser followed by a spatial filter-expander and a beam-splitter, together with associated mirrors and lenses 5 |