The results of pilot plant investigations of simultaneous removal of NO x , SO 2 and Hg from flue gas with ozone as the oxidizing agent and the spray tower absorber with NaOH solution as the absorbent have been presented. Flue gas was delivered into the pilot plant at the flow rate of 200 m 3 /h from the coal fired OP-430 boiler. The effectiveness of NO x removal was over 95% when the molar ratio O 3 /NO reached 2.0. Sulfur dioxide was practically completely washed out from flue gas in the absorber at the liquid-to-gas ratio 7.5 dm 3 /m 3 . The effectiveness of Hg removal in the studied system was approximately 80%. It was pointed out that CO concentration in flue gas could considerably increase the ozone consumption. The effect of carbon dioxide in flue gas on the chemistry of absorption due to hydroxides conversion into carbonates and bicarbonates was noticed.

As a result of the large limestone deposits available in Poland, the low cost of reagent acquisition for the largescale technological use and relatively well-documented processes of flue gas desulfurization (FGD) technologies based on limestone sorbent slurry, wet scrubbing desulfurization is a method of choice in Poland for flue gas treatment in energy production facilities, including power plants and industrial systems. The efficiency of FGD using the above method depends on several technological and kinetic parameters, particularly on the pH value of the sorbent (i.e., ground limestone suspended in water). Consequently, many studies in Poland and abroad address the impact of various parameters on the pH value of the sorbent suspension, such as the average diameter of sorbent particles (related to the limestone pulverization degree), sorbent quality (in terms of pure calcium carbonate [CaCO 3 ] content of the sorbent material), stoichiometric surfeit of CaCO 3 in relation to sulfur dioxide (SO 2 ) absorbed from flue gas circulating in the absorption node, time of absorption slurry retention in the absorber tank, chlorine ion concentration in sorbent slurry, and concentration of dissolved metal salts (Na, K, Mg, Fe, Al, and others). This study discusses the results of laboratory-scale tests conducted to establish the effect of the above parameters on the pH value of limestone slurry circulating in the SO 2 absorption node. On the basis of the test results, a correlation equation was postulated to help maintain the desirable pH value at the design phase of the wet FGD process. The postulated equation displays good coincidence between calculated pH values and those obtained using laboratory measurements.

The results of laboratory scale research have been presented on the effects of ozonation of carrier gas containing NOx and SO2 on by-products trapped in Dreschel washers with solution of sodium hydroxide. The controlling parameter in this process was the ozonation intensity determined by the molar ratio O3/NOx. The measured by-products in a scrubber were 2 3 SO ,  2 4 SO ,  2 NO , and  3NO  ions. It has been shown that ozonation of flue gas favours oidation of nitrites to nitrates and sulfites to sulfates in alkaline solution. Some of these results were confirmed in a pilot scale studies. Pilot plant was located in Wroclaw CHP (Combined Heat and Power), which provided flue gas for testing at a rate of 200 m 3 /h from the OP-430 boiler. Exhaust gases were ozonized and captured simultaneously with SO2. Sodium hydroxide was used in a pilot scale as an absorbent.

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The results of laboratory scale research have been presented on the effects of ozonation of carrier gas containing NOx and SO2 on by-products trapped in Dreschel washers with solution of sodium hydroxide. The controlling parameter in this process was the ozonation intensity determined by the molar ratio O3/NOx. The measured by-products in a scrubber were 2 3 SO ,  2 4 SO ,  2 NO , and  3NO  ions. It has been shown that ozonation of flue gas favours oidation of nitrites to nitrates and sulfites to sulfates in alkaline solution. Some of these results were confirmed in a pilot scale studies. Pilot plant was located in Wroclaw CHP (Combined Heat and Power), which provided flue gas for testing at a rate of 200 m 3 /h from the OP-430 boiler. Exhaust gases were ozonized and captured simultaneously with SO2. Sodium hydroxide was used in a pilot scale as an absorbent.