TECHNOLOGIES FOR UTILIZATION OF ACIDIC CONDENSATE FROM FLUE GASES. PRE-TREATMENT, DECARBONIZATION AND SUBSEQUENT USE

Abstract

In recent years, Ukraine has actively modernized gas boiler equipment, particularly within programs aimed at increasing energy efficiency and reducing harmful emissions. Traditional boilers with an efficiency of up to 85 % are being replacing with modern condensing boilers with efficiencies of 95–98 %, along with advanced burners, automation, and safety systems. The acidic condensate of flue gases produced in modernized boilers is a relatively clean liquid, comparable in quality to distilled water but with a high content of carbon dioxide. However, many central and regional boiler houses, especially in smaller Ukrainian cities, still operate using outdated equipment due to limited investment and wartime destruction. For example, boiler systems in Mykolaiv, Kyiv, and Zhytomyr have been severely damaged by shelling, complicating their restoration and modernization.
According to the Ministry of Energy, as of autumn 2023, Ukraine required around 370 modular boiler houses to restore heating services, highlighting the importance of replacing outdated systems. Although natural gas is consider a relatively clean fuel, the condensate resulting from its combustion using outdated equipment may still contain pollutants, including carbon dioxide (CO₂), nitrogen oxides (NOx), and iron oxides. CO₂ forms weak carbonic acid (H₂CO₃) in aqueous environments, lowering the condensate's pH to about 4. Nitrogen oxides form at combustion temperatures above 1200–1300 °C, primarily as nitric oxide (NO) and nitrogen dioxide (NO₂), while iron oxides appear due to corrosion of steel components in the equipment.
Modern systems reduce or eliminate these pollutants, but many heat and power facilities still need modernization. Therefore, the development of technology and equipment for condensate purification is essential. This study focuses on creating a comprehensive purification system to remove three main contaminants – carbon dioxide, nitrogen oxides, and iron-containing. This allows the water quality to approach that of distilled water, making it suitable for using as feedwater for boilers or in electrolysers.
The analyses shows that purified condensate can reused in boiler systems, for equipment rinsing, humidification, solution preparation, fire safety systems, and as a water source for hydrogen production through electrolysis. Efficient reuse of condensate increases overall energy efficiency and reduces environmental impact.
The study proposes a multi-stage treatment process: removal of iron oxides using an electromagnetic filter; decarbonization using a non-reagent neutralizer; and NOx removal through ammonium nitrate formation followed by membrane separation. Experimental research on a lab-scale model confirmed the effectiveness of the proposed system. Statistical analysis and standard testing methods been applied to validate results which confirming that the treated condensate meets quality standards for reuse in electrolysis and boiler applications.