No abstract

This paper presents a 3-D CFD modelling of flow and heterogeneous reactions in catalytic converters. The pressure and velocity fields in the catalytic converters are calculated by the state of the art modelling technique for the flow resistance of catalyst substrate. A surface reaction model is applied to predict the performance of a three-way Pt/Rh catalyst. A reaction mechanism with detailed catalytic surface reactions for the 3-way catalyst is applied. The novelty of this approach is the use of a surface chemistry solver coupled with a 3-D CFD code in the entire computational domain of the catalyst substrate that allows flow distribution for complex configurations to be accounted for. The concentrations of the gas species and the site species are obtained. A comparison between the simulation results and the experimental data of a three-way catalyst was made.

Oxidation catalyst performances are studied under HCCI (Homogeneous Charge Compression Ignition) and SI (Spark ignited) conditions using a model gas reactor and with natural gas fuelled HCCI and SI engines. The characteristic emissions of HCCI engines are high levels of CO and hydrocarbons, and temperatures as low as 120°C. Conventional oxidation catalysts typically light off at around 200°C, well above these temperatures. The oxidation catalyst for a HCCI engine is required to be active at low temperature, and be durable. Test results will be shown for bench-scale experiments for a series of catalyst formulations. Some catalyst formulations show excellent performance. The HCCI-tailored catalyst exhibits complete conversion of CO under HCCI engine emission conditions with various loads. Under SI conditions, high conversion efficiencies are observed for methane and non-methane hydrocarbons.

Palladium-based catalyst can be employed for natural gas exhaust clean up due to its high activity for light hydrocarbon oxidation. Unfortunately, trace amounts of sulfur in the natural gas feed severely deactivate the catalyst. In this paper, SO 2 adsorption over a monolithic Pd/Al 2 O 3 oxidation catalyst is monitored in a time-resolved manner in the presence of 100 ppm SO 2 under simulated aging conditions of a natural gas engine, which is correlated with the oxidation activity for CO and hydrocarbons such as CH 4 , C 2 H 6 and C 3 H 8. The SO 2 adsorption is saturated in 0.5 h at 400°C and 100,000 h-1. The molar ratio of adsorbed SO 2 and Pd is about 2/1, indicating SO 2 molecules adsorbed, or transferred to the Al 2 O 3 support. The oxidation activity gets stabilized upon saturation of sulfur adsorption, and the hydrocarbon oxidation activity cannot recover even when 100 ppm SO 2 is completely removed from the stream. The light-off temperatures (T 50) of hydrocarbons shift 50-100°C higher after SO 2 poisoning. When the gas stream was switched to the fuel-rich mode, 15% of the adsorbed SO 2 molecules were released from the poisoned catalyst at 400°C. No H 2 S was detected in the outlet stream in the reducing atmosphere. Only traces of SO 2 molecules were detected when the regenerating temperature increased to 550°C. The poisoned Pd catalyst was reactivated to some degree, but suffered from a significant deactivation in 30 min even in the absence of SO 2 , regardless of regenerating temperature. The results revealed the existence of reversible and irreversible sulfur in the reducing atmosphere. A mechanism of sulfur poisoning and regeneration is proposed.

A DCL oxidation catalyst for exhaust-gas cleaning has been field tested on a Wa¨rtsila¨ 50 series dual-fuel engine during 5000 hours of continuous operation in an end-user power plant application. The engine has been designed for continuous operation on natural gas (NG), light fuel oil (LFO) as well as heavy fuel oil (HFO), thus giving the consumer a wide variety of fuelling options. All three fuels were used at some point during the 5000 hours field trial. These fuels have different properties such as differing levels of sulphur and ash contents that affect the abatement efficiencies of the oxidation catalyst. A detailed study was performed to understand the effect of different fuels, lube oil poisoning and long running hours on the abatement performance of the oxidation catalyst. The oxidation catalyst was equipped with sample cores that were exchanged during scheduled engine maintenance periods. This allowed parallel field and laboratory evaluation of the emissions abatement and the quantity of lube oil deposits on the catalyst at successive intervals of engine running hours. We will show that the combination of the dual fuel engine and the oxidation catalyst is very robust, even for the different fuels, and it gives low emissions.