Method and apparatus for determining size and composition of a particulate matter in a fume flow

An apparatus for determining size and composition of a particulate matter in a fume flow produced by a combustion process and conveyed by means of a chimney;

• the apparatus comprising a laser source for projecting a polarized laser light beam through the fume flow in a projection direction transversal to a fume conveying direction, and at least two optical devices for detecting the intensity of the scattered light from the fume flow in a sideward scattering direction and in at least one forward scattering direction;
• each optical device comprising a respective group of lenses for gathering light according to a respective optical axis, a respective light beam separator for separating the gathered light into polarized light components on the planes parallel and orthogonal to the optical axis, and a respective pair of optical detectors for measuring the light intensity of the polarized light components;
• the group of lenses of a first optical device being arranged with the optical axis overlapping the sideward scattering direction, and the group of lenses of the second optical device being arranged with the optical axis overlapping the forward scattering direction;
• the apparatus further comprising a processing unit, which is connected to the optical detectors for receiving the measured light intensities and is configured to determine, for each of said scattering directions, a respective scattered light polarization ratio as a function of the light intensities of the polarized light components measured for the scattering direction, and to determine the size of the particulate matter and the unburnt carbon percentage in the particulate matter as a function of the scattered light polarization ratios determined for said scattering directions.