Przybylski W. Scientific and technical principles of the use of ammonium compounds to reduce emissions of pollutants in medium capacity boilers ".

The modern environmental protection requirements put the issue of reducing emissions of pollutants and greenhouse gases on the agenda for the development of thermal power industry. A thermal power facility must comply with the principle of High Efficiency and Low Emission in order to be competitive at a time of rapid development of renewable energy sources. For reducing the negative impact on the environment, boiler units must be equipped with systems for cleaning flue gas from pollutants, which are able to ensure compliance with European environmental requirements. To reduce the emission of nitrogen oxides for boilers of medium capacity, it is advisable to use selective non-catalytic reduction as a measure that allows reducing NOx emissions without the construction of special devices and the catalyst use. The use of ammonium compounds will make it possible to combine semi-dry desulfurization systems and selective non-catalytic reduction systems into one complex flue gas purification system. Using ammonia as an environmentally friendly fuel for energy applications will reduce emissions of greenhouse gases and toxic substances. But its use as a fuel faces the following problems: carbon-free ammonia synthesis, ammonia combustion, solving economic and environmental problems. The use of a urea solution instead of an ammonia solution in flue gas desulfurisation technologies will make it possible to significantly simplify the use of this technology in terms of safety and reagent transportation. The use of urea solution for effective binding of sulfur dioxide requires its preliminary thermal hydrolysis. In the process of hydrolysis of urea at the boiling temperature, gaseous ammonia will be formed, which in the process of gas-phase reaction binds about 80% of SO2 at the initial concentration of urea in the solution of 30%. This makes it possible to consider the possibility of gasphase bonding of sulfur dioxide with ammonia without building a semi-dry desulfurisation reactor. Ammonia is an important chemical that is widely used as a nitrogen fertilizer in the agriculture, in chemical and refrigeration technology. The transition to the production of "green" ammonia involves the generation of hydrogen from water using electrolysis technologies with the subsequent application of either Haber-Bosch technology or ammonia generation technologies in electrochemical cells, which are at the stage of research and industrial testing. Since the generation of "green" ammonia is an energy-consuming process, its production can serve as an effective means of regulating the load in the power system. If the current level of ammonia production in Ukraine is maintained at 5 million t/a, its "green" production using Haber-Bosch technology will require about 60 billion kWh of electricity. This would make it possible to completely abandon the generation of electricity at coal-fired thermal power plants in a manoeuvrable mode. Electrolysis production with subsequent production of ammonia will make it possible to utilize the peaks of electricity generation from renewable sources, the capacity of which is growing at a rapid pace, without harming the stability of the frequency and capacity regulation in the power system. Ammonia has a very low laminar burning speed and a long ignition delay due to its high activation energy. To improve the combustion conditions, it is suggested to use an increased oxygen content in the oxidizer or a mixture of ammonia with hydrogen or ammonia with methane. This ensures a 4-time increase in the laminar combustion speed. A mixture of ammonia and hydrogen as a product of incomplete cracking of ammonia is a promising carbon-free fuel for thermal power plants. A power unit with a capacity of 1,000 MW was put into operation with the implementation of joint combustion of coal (80%) and ammonia (20%) in special vortex burners. The production of ammonia can allow to abandon the consumption of coal in the energy sector. Thus, emissions of sulfur dioxide, dust, carbon monoxide and carbon dioxide will disappear. When burning a mixture of fuel and ammonia, emissions of dust, SO2, CO and CO2 will be reduced by the fraction of the fossil fuel replaced by ammonia. The use of ammonium reagents for the removal of pollutants will allow combining the technology of desulfurization and the technology of selective noncatalytic reduction of nitrogen oxides into one complex, making the equipment of the gas cleaning system more compact with the use of one reagent, which is relevant for boiler units of medium capacity. The concept and scheme were developed, and calculations were made of the integrated flue gas cleaning system of the water heating grate boiler WR25 using urea or its 40% solution as a reagent, which will ensure the concentration of sulfur dioxide and nitrogen oxides below the requirements of Directive 2015/2193/EU, which determines the emission limit values for medium combustion plants.