James C. F. Wang

In situ particle size measurements using a two-color laser scattering technique

We have developed a technique using light scattered from individual particles in the near-forward direction to measure particle size in the range of 10-200 microm. This technique uses the Mie scattering theory to relate the measured light intensity to particle size based on calibration techniques employing pinholes and water droplets of known size. We have applied a unique two-color optical arrangement to minimize the edge effect which can cause incorrect size measurements for particles that pass through the edge of the laser beam focal volume. In this paper we describe our experimental technique and the results of size measurements obtained with this technique for water droplets and pulverized coal particles.

Particle size measurements using an optical variable-frequency-grid technique

A fringe visibility method for sizing particles 10 microm and larger has been developed. As the image of a particle scans across a variable frequency grid, the transmitted light signal oscillates with varying visibility. The visibility goes through a null at a well-defined point where the particle diameter approximates the local grid spacing. Several optical arrangements implementing the variable frequency grid technique have been tested. Using classified alumina and pulverized coal particles we obtained good agreement between size distributions measured by this technique and those from a commercial off-line analyzer. However, our optical arrangement and signal processing techniques require further development to reduce them to practice.

Design criteria and recent developments of optical single particle counters for fossil fuel systems

Optical methods for particle size distribution measurements in practical high temperature environments are approaching feasibility and offer significant advantages over conventional sampling methods. The present paper begins by summarizing user requirements for research and on-line particle measurements in fossil fuel systems. The principles of single particle counter (SPC) design are outlined followed by a discussion of practical instrument design constraints. Three instrument design concepts currently being developed at Sandia are then discussed. An overview of these current methods and other instrument designs is presented with particular emphasis on capabilities to meet user ojectives. Validation and long term testing of these new concepts is considered to be the final important step in achieving user acceptance of in situ optical counters.

A New Real-Time Isokinetic Dust Mass Monitoring System

A new real-time dust mass monitor has been developed by combining an automatic isokinetic sampling probe with a tapered element oscillating microbalance (TEOM). Fly ash from a room temperature wind tunnel is sampled through the isokinetic sampler and collected on an astroquartz mat filter in the TEOM detector. The filter is first excited and oscillated at low frequency (about 200 Hz). As the particles deposit on the filter, the mass increase of the filter is reflected in a frequency reduction which yields the collected particle mass directly in real time. The TEOM detector normally has a high mass resolution (10−9 g) and wide dynamic range (1055–1066). It is desensitized for high particle loading applications. Good agreement has been obtained between the mass collected through the isokinetic sampling system and the weight loss of the dust feeder, in real time. The body of information presented in this paper is directed to those concerned with particle emission and control in fossil fuel combustion systems.

Real-time total mass analysis of particulate in the stack of an industrial power plant

A real-time particulate mass monitor has been developed for operation in stack gas environments. It provides mass measurements of sampled particles in real time (response time less than a few seconds) without diluting or cooling the sampled gas. Measurement biases of the type encountered in conventional physical sampling techniques are minimised. The performance of a system prototype has been tested in the laboratory and in the flue gas of a coal-fired power plant. Preliminary test results and operational experience with the prototype are reported.

Recent development of a real-time particulate mass sampling system for high temperature applications☆

Abstract We have successfully completed laboratory tests which demonstrate the feasibility of utilizing a new real-time sampling system for particulate loading measurements in gas flows above 900°C. Measurements were obtained every 2–5 s for periods of up to 1 h with accuracies of better than 5% with respect to conventional batch sampling measurements. Measurements were made at particle mass loading of up to 4.59 g per actual cubic meter and at gas temperatures of up to 970°C. Automatic self-cleaning of the particle mass detector inside the sampling system was also demonstrated. On the basis of the test results, we are convinced that this new particle mass sampling system can provide, for the first time, critical real-time information on particulate mass loading inside conventional and advanced combustion systems.

A Real-Time Particle Monitor for Mass and Size Fraction Measurements in a Pressurized Fluidized-Bed Combustor Exhaust

We have developed a new particulate mass analyzer and have demonstrated its real-time measuring capability in an actual pressurized fluidized-bed combustor environment. The analyzer incorporates a set of cyclones, each with its own microbalance. During measurements, the temperature and pressure of the sampled gas were kept at the process-stream conditions. With this system, particle mass-loading and size-fraction measurements have for the first time been obtained in real time downstream from a high-temperature electrostatic precipitator. The resulting particle size-fraction data and simultaneous measurements of particle total mass-loading upstream and downstream from the precipitator contributed to better assessment of the performance of the precipitator under various operating conditions.