Joshua Matthew Whitcombe

Application of sensitivity analysis to oil refinery emissions

Catalyst emissions from fluidising catalytic cracking units have the potential to impact significantly on the environmental compliance of oil refineries. Traditionally it has been assumed that gas velocity and fine particles significantly impact on emission levels. Through the use of a simple fluidised bed model, sensitivity analysis was conducted to identify the key operating parameters that influence emission rates. It was found that in addition to velocity, density and mid sized particles are the most influential factors for emission rates. Further work is needed to identify how these parameters can be altered during normal operations to reduce catalyst emissions.

Case Study on the Practical Use of Wettable Filters in the Removal of Submicron Particles

Chemical and metallurgical industries frequently generate submicron wet/dry sticky particles. Conventional wet scrubbers, usually Venturi scrubbers, are used in such industries with varying degrees of success. These scrubbers may be capable of removing larger particles, but become inefficient when particle size drops below the one-micron level. The main idea of this project was to utilize a wettable filtration system after the scrubber to achieve a high removal efficiency with a relatively low increase in total pressure drop. The use of wettable filtration allows an equilibrium liquid film to develop on each of the filter fibres (Agranovski et al. [1]). This liquid film than acts as the primary filtration zone, removing particles before they reach the filters surface. The filtered contaminants are then removed from the fibre by a continuous influx of fresh water preventing blockages to the system. The new filtration systems can be incorporated into existing air pollution control systems by utilizing a space inside hollow liquid/air separators commonly used for the baffling of droplets after wet scrubbers. The new wettable filtration system installed at a strip galvanizing plant achieved removal efficiencies of approximately 98.6 % for the total particle loading with a minimal increase in pressure drop.

Utilisation of wet fibrous media for filtration of sticky aerosol particles

The use of a wet filtration process for the removal of submicron sticky particles has been successfully trialed at a commercially operating strip galvanising facility and achieve a removal rate of 98.6% and 98% for total particles and chloride components respectively. These removal rates were achieved at a facility with a long history of producing semi-wet sticky particles, over a wide particle size distribution between 0.01 and 300 μm. The use of a wet filtration system can be seen as a very effective tool to allow existing commercial facilities to augment their existing wet scrubber technology without large capital expense.

Impact of Metal Ridging on the Fluidization Characteristics of FCC Catalyst

Minimum fluidization and bubbling velocities were used to compare the fluidity of FCC catalyst sourced from various refineries. It was found that fluidity characteristics of the catalyst of the same original type change after some period of use in the FCCU. Under closer examination using Scanning Electron Microscopy (SEM), large surface ridging of metal contaminates, was identified on the used catalyst. Mild bubbling attrition tests were conducted, and it was found that all of the catalyst experienced an increase in fluidity. Using total levels of iron, it was discovered that it is the quantity of metal ridging that is important and not the total levels of metals which influence fluidizing characteristics. This work provides insight into what causes changes to fluidizing characteristics inside an operation FCCU.

CATALYST FRACTURE DUE TO THERMAL SHOCK IN FLUIDIZED CATALYTIC CRACKER UNITS

The formation of fines in a fluidized catalytic cracker unit (FCCU) due to catalyst attrition and fracture is a major source of catalyst loss. In addition to standard attrition tests described in the literature, the possibility that thermal conditions could lead to catalyst fracture and fines production has been explored. Samples of fresh and used (equilibrium or e-cat) type catalysts were heated up to 600°C and mixed with cold samples to determine the impact of thermal shock on particle stability. It was found that significant fracture occurs under these conditions, leading to loss of larger catalyst particles in the bed and significant gain in the amount of fine particles. Agglomeration of particles was also evident, in some cases leading to an increase in the quantity of larger particles appearing to be present in the catalyst sample.

FCCU transition-probability model

The adequacy of the use of transition-probability matrices for modelling fluidised catalyst cracker unit emissions was investigated. A number of different-sized matrices that modelled the processes of attrition and agglomeration were used, and it was found that an 8x8 sized matrix provided the best results. The processes of attrition within the matrix were studied, indicating an oscillatory attrition curve, and may suggest a preferred attrition size range. Studies on the effects that the agglomeration parameters had on the model indicated that, as time and the size of the matrix increased, agglomeration became more important. The results of the modelling were compared with laboratory experiments, and indicated very good agreement between the model outputs and the observed emissions.