| Currently, selective catalytic reduction (SCR) which is widely used is an important technology to remove nitrogen oxides (NOx) from flue gas. The core part of the SCR system is the catalyst. In general, commercial catalysts are made of V2O5-WO3/TiO2, which directly determines the final denitration efficiency of SCR system in most cases. The cost of commercial catalysts often accounts for 30%-50% of the total SCR system. However, with the continuation of the operation time for commercial catalysts applied in SCR units in coal-fired power plants, a potential catalysts deactivation problem will gradually appear. When deactivated catalysts can’t meet the requirement of the denitration, they have to be replaced. Generally, replacing catalysts are needed every 3-5 years, which not only increases the power plant operation cost but causes environmental pollution. With the improvement of the environmental policy in China, plenty of commercial catalysts are being installed in the thermal power unit, so there will be a lot of deactivated catalysts in future. Therefore, it is necessary to regenerate the deactivated catalysts. In this work, the paper is mainly concerned about the catalyst’deactivation mechanism from a coal-fired power plant. In addition, different renewable liquids are performed to regenerate the deactivated catalysts. The main conclusions are as follows:The effect of NH3/NO molar ratio (0.9-1.1) and gas hourly space velocity (3000 h-1-11 000 h-1) on the fresh and deactivated catalysts’activity were investigated. The NH3/NO molar ratio had a little impact on NOx conversion, while the activity of catalysts declined clearly when gas hourly space velocity (GHSV) was over 5000 h-1. The denitration efficiency of two types of catalysts both reached the maximum, respectively 85% and 52% when NH3/NO was 1.0 and GHSV was 5000 h-1. Chemical and physical characterizations of the catalyst samples were characterized by means of SEM, XRD, BET, XRF, FT-IR, XPS and NH3-TPD, for which the influence of different factors causing catalyst deactivation was explored. According to the result, thermal sintering and salts impurities deposition. XRF results showed that large amounts of K, Fe, S and As are deposited on the surface of the deactivated catalysts, especially As and K, respectively increasing 675% and 444% in contrast with fresh catalysts. BET results showed that the specific surface area of deactivated catalysts significantly reduced 43% by comparison with fresh catalysts. The deposition of poisons and the reduction of specific surface area should be the main reason for catalyst deactivation.The influence of different regeneration liquids including deionized water, H2SO4, (NH4)2SO4 and EDTA combined with H2SO4 on the regeneration of deactivated catalysts were investigated. It was found that, under the common drying methods, the suitable regeneration liquid was EDTA combined with H2SO4. The denitration efficiency of regenerated catalysts reached about 83% which was almost close to that of fresh catalysts.Microwave regeneration was introduced to regenerate the deactivated catalysts. It was found that the denitration activity of the regenerated catalysts which was dried by microwave after washing with EDTA combined with H2SO4 reached 92%, higher than that of regenerated catalysts dried by circulation oven. Compared with deactivated catalysts, the specific surface area of regenerated catalysts by microwave significantly increased by 50%, slightly higher than that of fresh catalyst. |
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