Developing SCR Plate Catalysts for Sustainable NOx Reduction in High Dust Thermal Power Plants

Abstract

The primary aim of this research is to address NOx emission reductions from high ash/dust environments of coal-driven thermal power plants prevalent in India and other regions using low-grade coal with significant fly ash content. Selective Catalytic Reduction (SCR) plate catalysts are developed for breaking down these gases into non-harmful components by reacting with urea or ammonia. As flue gases carry fly ash particles through SCR plates, abrasion occurs. This study seeks to enhance abrasion resistance while maintaining de-NOx efficiency, as required by regulations. A series of SCR plate catalyst samples with stainless steel wire mesh reinforcements are formulated and assessed via Air-jet erosion and NOx conversion evaluations. The outcomes demonstrate the viability of reinforcing the ceramic catalyst matrix with commercially available wire mesh, maintaining erosion resistance levels. Additionally, this study incorporates findings on utilizing glass fibers as supplementary reinforcement. Furthermore, the process parameters such as reinforcement optimization, firing temperature, the weight percentage of glass fibers, the weight percentage of binders and their composition, and thickness are regulated based on experimental results. These resulting parameters improved erosion resistance by around 30-40%. This research proposes two novel methods for manufacturing catalyst plates to enhance erosion resistance. The abrupt temperature fluctuations in the SCR systems induce thermal shock, thereby impacting erosion resistance. This study analyses the influence of thermal shock on erosion resistance, employing a dedicated experiment. V2O5–TiO2 SCR catalysts represent an effective solution for reducing post-combustion nitrogen oxide (NOx) emissions in thermal power plants. This catalyst suffers severe abrasion due to exposure to fly ash. To address this issue, three plate catalyst samples P1 (Low wt% binder), P2 (Intermediate wt% binder), and P3 (High wt% binder) were prepared. A comprehensive analysis of their NOx conversion efficiency, air jet abrasion rate, abrasion resistance (sand drop test), and bonding strength (plate drop test) was performed. The better-performing P2 plate from abrasion tests was chosen for later characterization study. BET, Mercury Porosimetry, XRD, and SEM were used to investigate the morphology, composition, and surface characteristics of the catalyst. Further, the P2 plates are stacked into a customized air jet abrasion setup where variations in velocity, flow rate, particle diameter, and duration of abrasion, depicting real case scenarios were considered for the experiment. The abrasion rate has followed the abrasion model developed by Iain Finnie. The P2 Plate samples were chosen for the study of thermal stress and its effect on De-NOx efficiency and were calcined at different temperatures ranging from 500◦C to 700◦C, and their De-NOx efficiencies at different flue gas temperatures ranging from 300°C - 450°C were investigated. This increase in the temperature of flue gases had varied catalyst De-NOx efficiencies. The De-NOx Efficiency, Specific Surface area, and Pore Volume decrease as the wt% of the binder and glass fibers in the composition increases. The findings also propose a protocol for comprehensive characterization of the V2O5–TiO2 SCR plate catalyst. As mentioned above, SCR plate catalysts are prone to failure due to the erosive wear of their surface by silica content in the fly ash present in the flue gases. In this study, the erosion rate of SCR catalyst material was obtained both experimentally and numerically by varying parameters such as the velocity of abrading particles, impact angle, and testing temperature. Temperature dependence of the erosion rate was studied by conducting the erosion tests at room temperature and at 350°C, which is the actual working temperature of the SCR product. The Finnie erosion model was used to determine the material scaling coefficient (K) and the velocity exponent (n) empirically, which are required for simulations. CFD simulations were carried out with the exact experimental conditions to determine the erosion rate numerically. From this study, it was observed that the erosion rate increases linearly with the impact angle to a maximum value of 90°. Increasing the velocity of erosive particles was found to cause an exponential increase in the rate of erosion, but this effect does not vary with the temperature. The erosion rate was found to increase even with an increase in temperature; the erosion rate was 25% high at 350°C. Using these erosion characteristic data, the erosion process can be simulated under the same working conditions as the SCR product and the life of the catalyst plates can be predicted. In this work, we explore the manufacturing process of SCR catalyst plates tailored for thermal power plants. Conventional methods are reviewed, highlighting limitations associated with separate extrusion and pressing stages. An innovative approach utilizing inline forming rollers is introduced, offering advantages in continuous production, reduced labor requirements, and enhanced mesh integrity. Further, a pre-treatment process for the SS-304 metal mesh is introduced, involving controlled heat treatment to eliminate sagging and improve adhesion. This modification resulted in straighter catalyst plates eliminating undulations, enhancing gas flow, and results indicating overall performance. Additionally, the post-production activation process for the SCR catalyst plates is investigated, which involves depositing a V₂O₅/PVA solution onto the plate surface via jet spraying, followed by calcination for activation and drying. Optimization of the V₂O₅ loading is discussed, balancing performance requirements with material consumption. Through these advancements in the manufacturing process, the chapter contributes to the development of more efficient, cost-effective, and environmentally sustainable SCR catalyst plates for NOx reduction in thermal power plants. The study also highlights the advantages of forming rollers for improved production efficiency, reduced energy consumption, and minimized material waste. This research demonstrates the potential of customized/designed SCR plate catalysts to reduce NOx emissions in high dust thermal power plants significantly.