Nitrogen dioxide is one of the most dangerous air pollutants, because its high concentration in air can be directly harmful to human health. It is also responsible for photochemical smog and acid rains. One of the most commonly used techniques to tackle this problem in large combustion plants is selective catalytic reduction (SCR). Commercial SCR installations are often equipped with a V₂O₅−WO₃/TiO₂ catalyst. In power plants which utilize a solid fuel boiler, catalysts are exposed to unfavorable conditions. In the paper, factors responsible for deactivation of such a catalyst are comprehensively reviewed where different types of deactivation mechanism, like mechanical, chemical or thermal mechanisms, are separately described. The paper presents the impact of sulfur trioxide and ammonia slip on the catalyst deactivation as well as the problem of ammonium bisulfate formation. The latter is one of the crucial factors influencing the loss of catalytic activity. The majority of issues with fast catalyst deactivation occur when the catalyst work in off-design conditions, in particular in too high or too low temperatures.

Coal fired power plant are still responsible for vast amount of electricity and heat production in Poland in 2019. Increasing number of units is equipped with SCR reactors in order to mitigate NOx emission. Older units have been designed to work in a base load operation· however increasing number of intermittent energy sources on the market· forces power plant owners to operate such units in reduced load for significant number of hours in a year. Most of parameters in coal-fired boiler would change in reduced load operation· particularly flue gas parameters. That would affect the formation of ammonia bisulfate (NH4HSO4) as well as operation of SCR reactors in the boiler. The NH4HSO4 formation is highly undesired as it can plug the catalyst or heating surfaces in the boiler. To investigate this phenomenon· the NH4HSO4 formation was comprehensively studied. Moreover· reduced load operation of boiler in a medium size CHP plant was simulated· using computer modelling tools. Obtained parameters were used to analyse· how different flue gas parameters affect NH4HSO4 formation and what consequences does it have for boiler operation. In particular, effect related with operation of SCR reactors equipped with V2O5-WO3/TiO2 catalyst was deeply studied.

Large coal-fired power plants were typically designed as a base load units. Any changes in load level, as well as start-up time, are noticeably slow on that kind of units. However, in order to adapt to changing market conditions with increasing number of renewable energy sources, coal-fired power plants need to improve their flexibility. In the paper, 200 MWe class unit has been taken into consideration. During the test campaign, a minimum safe load of the unit was decreased from 60 to 40%. Paper presents results of a model that was made using Ebsilon®Professional software. The simulation model is comprised of boiler and turbine part of the power unit. Obtained results were validated using measurements collected from the test campaign. Parameters important from the technical and economical point of view were investigated. Results revealed that simulation model can be utilised successfully to scrutinise coal-fired units under off-design operation conditions. As the outcome of the performed analysis, a number of issues related to low load operation of the coal-fired unit are presented and discussed. Paper indicates sensitive areas that need to be addressed when operation in decreased safe load is considered. Finally, overall potential for flexibility improvement for 200 MWe class coal-fired units has been evaluated.

Polish energy market is comprised of numerous aged 200 MW_e coal units. In order to work in changing market conditions - with growing number of renewable energy sources as well as new supercritical coal power plants - these units will be forced to work with extended flexibility. It results in ability to change load level faster and to extend their designed load range. It is both challenge for turbine and boiler part of the power plant, designed to work as the base load unit. Study presented in the article was performed in order to analyse behaviour of one 225 MW_e coal unit, working in extended load range (from 90 – 225 MW_e), by using Ebsilon®Professional software. The major goal of study, was to verify crucial operation parameters in the load range below designed technical minimum (90-135 MW_e). Two models – turbine part and boiler part - were prepared and validated, using reliable data from test campaign performed in-situ. In this article, the boiler behaviour is comprehensively described with indication of issues that must be addressed when considering boiler operation in load range below its technical minimum.