(33b) Investigation into the Attrition Behaviour of FCC Catalysts

Fluidized bed operations have a key importance in fluid catalytic cracking units. Here the intensive mechanical stress causes attrition and consequently important material loss. The distributor region, the jets and the cyclone are the most common contributors to this phenomenon since attrition of friable particles is most likely to occur at impact points where the impact forces are high. Therefore, attrition can be minimized by minimizing the impact angle θ, and minimising stream velocity.

In this work, the attrition of fluid cracking catalyst is considered in detail with emphasis on the link between single particle properties and bulk attrition behaviour, by studying two different sample types and considering particle-wall impacts. The experiments involve the bench scale centrifugal attrition tester (developed by the Wolfson Centre for Bulk Solids Handling Technology, UK) which simulates a particle-wall impact scenario. This apparatus has more recently been used for the evaluation of particle attrition by impact [1] and comprises a rotating disc surrounded by an array of targets. The particulate samples are fed into the centre of the rotating disc and radially accelerated via the tubes and impacted against the target array. Typically, as the impact velocity and impact angle increase, the level of attrition is also observed to increase. Good correlation was found at high impact velocities/gas velocities considering real conditions found in cyclones.

This paper presents a degradation model for particles in fluidized bed conditions. The model utilises a breakage matrix approach. Where the breakage matrix is empirically-obtained from the centrifugal attrition tester, and transforms the input particle size distribution in fluidizing conditions, to the output particle size distribution after the test. Particle size analysis and particle shape analysis were carried out using Sympatec and Malvern Morphologi G3 respectively.

Regarding the operational capacity of the apparatus, the centrifugal tester allows greater control of particle impact velocity; particle-gas interactions are lower than those of the gas-blast tester and steady state conditions are more readily defined as recently summarised in a review paper [3].

[1] B. Kotzur, M.S. Bradley, R.J. Berry, R.J. Farnish, Influence of Solids Loading Ratio on Particle Attrition within a New Centrifugal Accelerator Impact Tester, in: PARTEC Int. Congr. Part. Technol., 2016.

[2] B.A. Kotzur, M.S.A. Bradley, R.J. Berry, R.J. Farnish, Breakage Characteristics of Granulated Food Products for Prediction of Attrition during Lean-Phase Pneumatic Conveying, Int. J. Food Eng. 12 (2016) 835–850

[3] B.A. Kotzur, R.J. Berry, S. Zigan, P. Garcia-Trinanes, M.S.A. Bradley, Particle attrition mechanisms, their characterisation and application to lean phase pneumatic conveying systems: A Review. (submitted to Powder Technology 05/05/2017)