| Abstract [eng] |
Nitrogen oxides (NOx), according to the Kyoto Protocol, are considered as indirect greenhouse effect compounds, and, together with sulfur oxides, cause acid rain, pose a risk to human health. The use of biofuels in the energy sector is gradually increasing in Lithuania, and although the generation of nitrogen oxides by burning biofuels is a small part of the energy sector's emissions, stricter standards and requirements encourage the introduction of new flue gas purification technologies. Following the entry into force of the EU Directive 2015/2193, the permitted levels of pollutant emissions from combustion of biofuels are tightened. The paper reviews the most commonly applied primary and secondary NOx abatement technologies, based on the literature review, a selective non-catalytic nitrogen oxide removal method was chosen for experimental studies. In order to assess the optimization of the selective non-catalytic NOx removal method, the study was carried out in two stages - in a laboratory using a boiler of 40 kW and in a real 10 MW boiler house. At the first stage of the experimental studies, experiments were carried out using a laboratory boiler stand. During the studies, different concentrations of the selected NOx-reducing reagents were injected into the system and the CO, NOx and O2 concentrations were measured in flue gas. In the second stage, the experiments were carried out in a 10 MW biofuel boiler room, where reagents were injected into the boiler's second burning zone without the boiler reconstruction and the change of the combustion temperature regime. The effectiveness of the NOx removal method was assessed by measuring the NOx and O2 concentrations in the exhaust fumes. In the laboratory tests, the best results (34% removal efficiency) were achieved by using a 2,5% ammonia water solution. In the 10 MW boiler house, the highest NOx removal efficiency (49,7%) was achieved using a 25% ammonia water solution. Based on the results obtained during the research, the optimal process conditions for the use of a selective non-catalytic reduction method for the redection of NOx from the combustion of biomass are presented. By conducting research in a 10 MW boiler house that actually operates, it became clear that there is no need to change the design of existing boilers in order to install the SNCR. Assessing reagents, safeguards and operating costs, it has been found that the system using urea will be more cost effective. |
