This article presents the effects of the application of the passive method of flue gas purification from mercury compounds emitted during combustion. The research was carried out on a fluidized bed installation using coal. The dry method of acid gas pollutants reduction was applied during the combustion with the use of 9 modified sodium sorbents. They were fed into a gas jet of 573 K in two molar ratios (sodium contained in the sorbent to the sulphur contained in the fuel). The mercury emission level into the atmosphere was determined based on the mercury content in the solid substrates of the combustion process (in the fuel and the sorbent) and the solid products (fly ash and bottom waste). The combustion process was accompanied by mercury emission 14.7 μgHg/m3. During the removal of acid pollutants from fumes, a decrease in mercury concentration was achieved. The degree of the mercury reduction depended on the type the sorbent used, the manner of modification and the molar ratio in which they were fed into the installation (2 Na/S = 0.5; 2.1). Each time, the more the sorbent was fed into the installation, the bigger the reduction of the mercury emission level. Among the unmodified sorbents, the lowest emission level was achieved for the raw bicarbonate – 3.7 μgHg/m3. For baking soda it was 9.7 μgHg/m3. The application of mechanically modified compounds based on baking soda resulted in the reduction of the Hg emission in fumes up to 2.5–2.6 μgHg/m3. The determined mercury concentration levels in the gases during the purification of the fumes were compared with the accepted Hg emissions contained in the BAT conclusions for large combustion plants. As for all of the existing and newly built plants with a heat capacity below 300 MW, satisfactory effects would be achieved by the use of mechanically modified sorbents in the molar concentration of 2 Na/S = 2.1.