Catalyst attrition and particle characteristics evolution in a fluidized bed

Butane oxidation to maleic anhydride over vanadium phosphate catalysts

This work is a study of the stability of a batch fluidized bed with a simple model. It is shown that multiple steady states can occur with all catalyst particles at the same temperature, some of these states being unstable. If the initial temperature of all the particles is not the same, a special kind of steady state, in which particles of different temperatures can coexist in the bed, might be obtained. The number of these pathological steady states is not finite, and the conversion obtained may be very different from that obtained by a uniform steady state.The analysis has demonstrated that the initial temperature of the catalyst particles may be a predominate factor in determining the kind of steady state obtained. For the case of uniform catalyst particles, a simple stability analysis has been developed. Several numerical solutions of the transient equations were performed to investigate the possible responses of the system to disturbances of various steady states.

Biomass energy has attracted considerable attention as a renewable and clean energy source that can be stored and transported effectively. A critical component in this context is the fluidized bed, which plays a vital role in biomass energy utilization. An in-depth understanding of the flow characteristics of non-spherical biomass particles within the fluidized bed is essential for improving energy efficiency. This study utilizes a combination of numerical simulations and experimental analysis to explore the flow patterns of biomass particles under eight distinct drag correlations. The investigation covers various flow regimes in the fluidized bed, concentrating on critical parameters such as flow evolution, gas-phase pressure distribution, particle phase velocity vectors, bed pressure drop, particle mixing characteristics, bed expansion height, and the energy-dynamic behavior of the particles. The results indicate that the Ergun resistance model closely matches the experimental data, particularly regarding the flow evolution of the particles. This model shows a more uniform mixing of the particles and greater stability in the magnitude and frequency of pressure fluctuations at the bed surface. This stability is reflected in the average pressure drop, highlighting the enhanced performance of the fluidized bed. Overall, this research sheds light on the intricate dynamics of non-spherical biomass particles in fluidized beds and provides valuable insights for optimizing particle design. By focusing on design enhancements, it is possible to achieve higher combustion efficiency, supporting the broader objective of sustainable energy utilization. In summary, this study emphasizes the significance of precise modeling and understanding of flow characteristics in the fluidized bed, which is crucial for advancing biomass energy technologies.

Particle attrition is a prevalent problem in fluidized beds due to continuous moving of catalyst particles. It is always operated at high temperature either for lab‐ or industrial‐scale fluidized beds. The influence of temperature on the attrition behavior of commercial methanol‐to‐olefins (MTO) and fluid catalytic cracking (FCC) catalysts is analyzed in a three‐orifice lab‐scale fluidized bed device from room temperature to 600 °C. The two catalysts are found to be alike in attrition mode. Both change from a combination of abrasion and fragmentation to main abrasion with increasing temperature, but differ greatly in the variation of attrition index with temperature which may be attributed to the difference of material and particle properties. An empirical correlation of attrition index to attrition temperature for all test samples is proposed.

Fischer-Tropsch (FT) synthesis to convert syngas (CO + H{sub 2}) derived from natural gas or coal to liquid fuels and wax is a well-established technology. For low H{sub 2} to CO ratio syngas produced from CO{sub 2} reforming of natural gas or from gasification of coal, the use of Fe catalysts is attractive because of their high water gas shift activity in addition to their high FT activity. Fe catalysts are also attractive due to their low cost and low methane selectivity. Because of the highly exothermic nature of the FT reaction, there has been a recent move away from fixed-bed reactors toward the development of slurry bubble column reactors (SBCRs) that employ 30 to 90 {micro}m catalyst particles suspended in a waxy liquid for efficient heat removal. However, the use of Fe FT catalysts in an SBCR has been problematic due to severe catalyst attrition resulting in fines that plug the filter employed to separate the catalyst from the waxy product. Fe catalysts can undergo attrition in SBCRs not only due to vigorous movement and collisions but also due to phase changes that occur during activation and reaction. The objectives of this research were to develop a better understanding of the parameters affecting attrition of Fe F-T catalysts suitable for use in SBCRs and to incorporate this understanding into the design of novel Fe catalysts having superior attrition resistance. The catalysts were prepared by co-precipitation, followed by binder addition and spray drying at 250 C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt %. The results show that use of small amounts of precipitated SiO{sub 2} alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO{sub 2} wt% {le} 12 produced fines less than 10 wt% during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than type of SiO{sub 2} incorporated into catalyst has a more critical impact on catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO{sub 2} added to a catalyst give higher particle densities and therefore higher attrition resistances. In order to produce a suitable SBCR catalyst, however, the amount of SiO{sub 2} added has to be optimized to provide adequate surface area, particle density, and attrition resistance. Two of the catalysts with precipitated and binder silica were tested in Texas A&M University's CSTR (Autoclave Engineers). Spray-dried catalysts with compositions 100 Fe/5 Cu/4.2 K/11 (P) SiO{sub 2} and 100 Fe/5 Cu/4.2 K/1.1 (B) SiO{sub 2} have excellent selectivity characteristics (low methane and high C{sub 5}{sup +} yields), but their productivity and stability (deactivation rate) need to be improved. Mechanical integrity (attrition strength) of these two catalysts was markedly dependent upon their morphological features. The attrition strength of the catalyst made out of largely spherical particles (1.1 (B) SiO{sub 2}) was considerably higher than that of the catalyst consisting of irregularly shaped particles (11 (P) SiO{sub 2}).

Attrition resistance of spray-dried iron F–T catalysts: Effect of activation conditions

A modeling approach is presented that is able to handle the most important aspects of industrial fluidized-bed reactors. A particular focus is to describe the relationship between catalyst attrition, solids recovery in the reactor system, and chemical performance of the fluidized-bed reactor. The competing influences of attrition of the catalyst particles and efficiency of the solids recovery lead to the etablishment of a catalyst particle size distribution in the bed inventory, which, in turn, influences via the hydrodynamic characteristics of the fluidized bed and, thereby, the performance of the chemical reactor. The usefulness of this approach is illustrated with model calculations for a fictituous first-order reaction in which the fluidized bed is equipped with different solids recovery systems including one single-stage cyclone, several cyclones in parallel, and two- and three-stage cyclone systems. Model calculations illustrate the importance of a high efficiency of solids recovery to keep the fines in the system which is decisive for a high performance of the reactor. The calculations reveal that it might take months until a quasi-steady state of the bed particle size distribution is obtained.

Fossil hydrogen with reduced [formula omitted] emission: Modeling thermocatalytic decomposition of methane in a fluidized bed of carbon particles

A concept of successive contact mechanism has been introduced to account for the influence of dilute phase catalyst on overall conversion of reaction in fluid beds. A theory has been given, as a simpler version of the proposed model, for an isothermal and irreversible first order reaction. To test the concept, axial distribution of bed density has been measured for small scale fluid beds. Rather freely suspended catalyst particles are observed in the dilute phase in enough amount to contribute to the progress of reaction. The theory has revealed for the progress of reaction that the catalyst particles located in the bubble phase are interchangeable with those suspended in the dilute phase and vice versa.

Super-quadric CFD-DEM simulation of chip-like particles flow in a fluidized bed

The effect of the granulometric composition of microspherical KDI alumina-chromia catalysts on variation of the height and density of a fluidized bed was analyzed during pilot industrial testing at the OAO Nizhnekamskneftekhim iso-butane dehydrogenation plant. It was ascertained that one of the factors determining the acceleration of the cracking reactions was a rise in temperature to 600–610°C in the upper part of the reactor at the level of grid no. 10 due to the reduction of the upper boundary of the fluidized bed as a result of carryover from the reactor-regenerator system of catalyst particles smaller than 20 microns. The formation of a stable fluidized bed on the upper grid of the reactor depends on the content of 20–40 μm particles within the circulating catalyst. In order to compensate for the carryover of the catalyst, it is recommended that the mixture of catalysts accumulated in the first and second electrofilter fields be loaded into the system as well. This load consists of ∼25 wt % of the fraction with particle sizes of 20–40 μm and is as good the initial KDI in terms of catalytic parameters, ensuring stabilization of the fluidized bed height at a level of 52%, lowering of the temperature at the tenth grid of the reactor to 568°C, reduction of the yield of cracking products to 4.0 wt %, a 3% increase in the average daily output of iso-butylene, and a 7% decrease in the consumption of iso-butane. Recovery of the irrevocable carryout of the catalyst from the system and the formation of a stable fluidized bed were achieved by alternating the additional loading of the catalysts from the first and second fields of the electrofilter and the initial KDI with optimized fraction composition at a 4: 1 ratio.

Fluidization characteristics of quartz particles with different sizes are experimentally investigated in a fluidized bed with an inner diameter of 300 mm and height of 8250 mm. Results show that the average solid holdup increases with the increase in superficial gas velocity and the decrease in initial solid holdup in the dense zone of the fluidized bed. The average cross-sectional solid holdup decreases with increasing bed height and superficial gas velocity. The bed expansion coefficient increases with the increase in superficial gas velocity and the decrease in solid holdup. Correlations of average solid holdup, average cross-sectional solid holdup and bed expansion coefficient are also established and discussed. These correlations can provide guidelines for better understanding of the fluidization characteristics.

ANALYSIS OF MICROWAVE ASSISTED FLUIDIZED-BED DRYING OF PARTICULATE PRODUCT WITH A SIMPLIFIED HEAT AND MASS TRANSFER MODEL

Experimental study and modelling of pressurized oxy-coal combustion: Effect of devolatilization conditions on the physical structure and combustion characteristics of char particles

One of the significant processes of the crude oil refining process is the fluid catalytic cracking (FCC) unit. This unit produces olefins and other feedstock for the petrochemical industry as well as high octane gasoline, naphtha, light cycle oil, and heavy cycle oil. Attrition is one of the forms of catalyst deactivation on FCC catalyst which affects its operation, thereby giving rise to a high amount of catalyst makeup to compensate for the losses in this unit. This study investigated the effect of catalyst attrition on a commercial FCC unit through an analysis of its technical data from 4-run operations. The catalyst loss profile was evaluated while the scanning electron microscopy (SEM) showed abrasion as the dominant attrition type in the unit, hence resulting in many catalyst particles being lost as micro fines through elutriation. A simulation study was carried out using ASPEN HYSYS version 8.8 to assess the effects of reduction and increment of fresh catalyst makeup on the product yield while a cost analysis was done to evaluate the economic implication. The results showed that a 2% reduction of the current daily catalyst makeup gave the same yield as that of the reference value. The products also had similar qualities showing that $117,000.00/annum could be saved by a 2% reduction of the current catalyst makeup.