The present embodiments relate to a device and a method for determining at least one concentration of coal particles in a gas flow flowing through a channel, wherein at least part of the gas flow having coal particles contained therein is measured by at least one microwave sensor and at least one measurement signal characterizing the concentration of the coal particles is provided, wherein an autocorrelation function of the measurement signal is determined and at least one distance value characterizing a distance of a point of the gas flow belonging to the concentration from the microwave sensor is determined in dependence on the autocorrelation function.