Experiments have been performed on cleaning up gas discharges in a plant consisting of two series-connected cyclones of the same type that differ in diameter in cylindrical parts. A graph is given for the fractional composition of the dust coming for removal in the first and second removal stages.One operation in preparing sand for casting use is drying it in a horizontal single-pass drying drum. The usual designs have drums with diameter up to 2-2.5 m, length up to 15 m, and throughput up to 20 tons/h with parallel motion of oven gases and the material to be dried. The drying agent is flue gas formed by burning natural gas.The flue gases leaving the output chamber from the drum contain dust. The flow of solid particles is characterized by the specific loss per unit mass of sand and the volume flow rate of the gas, which are respectively specified in kg/ton and m 3 /ton of sand treated in the drum.Specific discharge parameters are known for drying drums for sand in various processes (casting, glass production, ceramics, and so on):• mean mass of dust released on drying sand 3.0-7.8 kg/ton; • minimal volume of gas leaving the discharge chamber 1.1-1.3 thousand m 3 /ton; and • dust concentration in the gas going to the cleaning system 2.7-6.0 g/m 3 . The outgoing gases are at about 160-200°C, with water contents varying rather widely (53-360 g/m 3 ) in accordance with the wetness of the sand and the drying specifications. The following is the fractional composition of the dust in the gases at the outlet from the unloading chamber:Fraction size (particle diameter d p ), µm Up to 5 5-10 10-20 20-30 >30 Fraction content, % 6.5-9.5 11.0-15.5 17.3-20.0 11.0-12.0 43-54The average median particle size d m = 28 µm, dispersion of the distribution b m = 4.15. The discharge characteristics are very much dependent on the initial properties of the sand, the specifications for the dried material, the parameters of the drying technology, and so on, so in each particular case, before the method of cleaning the gas discharges is chosen, an analysis should be performed to establish the required degree of cleaning. In Russian practice, this is determined by the maximum permissible discharge (MPD) of pollutant for a particular source on the basis of its position, discharge height, background concentrations of similar substances, wind pattern, and so on.We have analyzed the available information on the MPD for many similar sources of discharge at various engineering plants and organizations manufacturing building materials, from which we conclude that the MPD is attained if the concentration of solid particles in the discharged gases does not exceed 60 mg/m 3 , i.e., a discharge of about 0.246 g/sec, with a discharge height of about 20 m [1].