Development of a flyash concentration measurement method based on light scattering techniques

Flyash free fuel-gas produced by burning coal in a pressurized fluidized bed gasifier is essential for a proper functioning of a power-plant gas turbine. A reliable measurement technique/instrument is required for estimating the particle concentration at locations, such as at the entry and exit of the filter system. Feasibility of optical techniques based on Mie scattering and extinction in order to determine flyash concentration in an exhaust at different flow rates is studied using the experimental setup developed in-house. These optical properties are measured for flyash particles with diameter ranging from 20 to 200 μm along with air flow using a continuous-wave green laser (wavelength around 530 nm). Prototype instrument is designed and a uniform feed rate ranges from 2 to 18 g/min is achieved. Scattered signals at different angles are presented as a function of varying feed rates of flyash particles. Extinction signal as a function of time for different feed rate is also presented. Time-averaged, extinction signal based measurements were also in qualitative agreement with light scattering based measurements. It is also possible to measure extinction signal with different particle sizes and feed-rates, representing variation in flyash concentration.