Effect of Mass Transfer on the Performance of Selective Catalytic Reduction (SCR) Systems

Abstract

Effect of IVIass Transfer on the Performance of Selective Catalytic Reduction (SCR) SystemsThis paper presents a computational investigation of the effect of mass transfer on the performance of selective catalytic reduction (SCR) catalysts, which are employed to reduce NO^ emissions from diesel engines. The paper employs a single-channel based, onedimensiotial, isothermal model. The heterogeneous suiface chemistry is modeled by considering standard and fa.st SCR mechanisms, and the mass transfer rate is described by using a one-dimensional flltn model and dimensionless Sherwood (Sh) number. The paper investigates the effect of Sh numbers on the catalyst conversicm performance at various temperatures and space velocities. The re.iults show that the effect of the Sh number on the SCR catalyst performance is temperature dependent and is more pronounced at high space velocities. In general, higher Sh numbers lead to increased conversion efßciencie.s, [DOlIn this correlation, the dependence of Sh on the parameter (Re dIL) is more pronounced than that suggested by Hawthorns [12]. Journal of Engineering for Gas Turbines and Power

Experimental investigation on the urea injection and mixing module for improving the performance of urea‐SCR in diesel engines

“…Furthermore, it can accelerate the evaporation and decomposition of the droplets, so as to improve the NO X conversion efficiency and inhibit urea crystallization at low temperature . The main role of the mixing module is to produce different scales of turbulence and bulk motion, which can make the urea droplets and exhaust gas mix intensively, with better urea distribution uniformity …”

Analysing the Performance of Ammonia Powertrains in the Marine Environment

“…The SCR is modelled using both the "standard" and "fast" SCR reactions-the two most relevant for an approximation of SCR behaviour. The "standard" reaction reduces NO, and the "fast" reaction reduces NO 2 [34,35,[58][59][60].…”

“…Performance losses due to thermal cycling and catalyst poisoning from residual lube oil in the exhaust are ignored, but these effects could become significant as the SCR ages [62][63][64][65]. This model assumes that the SCR reactions are mass transfer limited because the high temperatures at the engine outlet (720-780 K) often yield mass transfer residence times that are larger than chemical kinetics-driven residence times [34,35,[58][59][60]. The effects of chemical kinetics tend to decrease as temperature increases; however, there is evidence to suggest that at very high temperatures, the effects of chemical kinetics resurface in SCR reactors [64,65].…”

“…This study focuses on SCR devices with V 2 O 5 catalysts. These catalysts are well known and used extensively in the automotive industry; thus, their performance is well documented in the literature and practice [34,35,[58][59][60]. Additional materials such as TiO 2 , WO 3 , or carbon nanotubes could also be used to improve the performance of the SCR over time [66].…”

Experiments on a light duty SCR test exhaust system using ammonia gas to provide data for validation of a CFD model

“…By analogy with heat transfer, the mass transfer coefficients were corrected to allow for higher Sherwood numbers downstream of the channel entrance. A recent paper (13) has attempted to quantify the mass transfer effect. Mass transfer of species between gas and pore phases was modelled within the fluid phase of each computational cell and sources and sinks of species due to reactions were determined within the coding of the scalar source user subroutine.…”