Attrition due to mixing of hot and cold FCC catalyst particles

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 the generation of fine particles, a significant amount of aerosols have been identified in the stack emission of FCCUs. To determine the source of these aerosols, samples of fresh and equilibrium (e-cat) type catalysts were heated up to 600 °C and mixed with cold samples, simulating the thermal shock and particle fracture, which occurs inside an FCCU when catalyst is added. The thermal shock in the experiments produced fine particles and aerosols, which were captured on filters and analyzed using scanning electron microscopy (SEM) imaging and atomic absorption tests. It was found that significant quantities of metal rich aerosols were generated by the thermal shock. This production of fine particles and aerosols is a new phenomenon that can help explain excessive catalyst emissions from operating FCCUs.     

High-temperature attrition of sorbents and a catalyst for sorption-enhanced steam methane reforming in a fluidized bed environment

Mechanical degradation of the solid particles used in sorption-enhanced steam methane reforming (SE-SMR) was investigated in a gas jet attrition apparatus. The performance of a dolomite, a limestone and a commercial reforming catalyst were compared based on the air jet attrition index (AJI). The dolomite showed the poorest resistance to attrition, likely due to the extra pore volume caused by calcination of MgCO₃. The degree of loss of fines from the catalyst was significant, pointing to the need to develop catalysts suited to fluidized bed operation. Co-fluidization of the harder catalyst and the dolomite did not lead to additional attrition of the dolomite.     

Experimental study on the attrition and size distribution of bed material in a recirculating fluidized bed

An experimental study was performed on the attrition of the bed materials in a recirculating fluidized bed (RCFB) using Indian standard (IS) grade I sand (size between 2.0 and 1.0?mm) at ambient conditions. Experiments were performed with superficial air velocity ranging from 7.13 to 9.16?m/s, bed inventory of 7–10?kg, and a spacing of 0.085?m between the jet top and draft tube bottom. The main objective of the study was to investigate the effects of operation time on the attrition and size distribution of sand particles in a RCFB. It was noticed that the prime mode of attrition of bed materials was abrasion, not fragmentation. Reduction in the downcomer bed height was observed with increasing operation time. It indicates that attrition was significant and fines were elutriated out with the fluidizing air. Furthermore, variations in the shape, size, and harmonic diameter of particles were studied with increasing operation time. It has been observed that the coefficient of uniformity and coefficient of curvature showed increasing patterns. It specifies that particles of different size ranges and fines were formed due to attrition of particles. At the end of the operation, it was found that a significant amount of fines was elutriated with fluidizing air from the reactor.     

Factors affecting methanol photocatalytic oxidation and catalyst attrition in a fluidized-bed reactor

A resolution IV fractional factorial experimental design explored the effects of seven factors on both the methanol photocatalytic oxidation (PCO) rate and the catalyst particle size distribution using a fluidized-bed reactor. The seven factors were as follows: calcination temperature, calcination time, grinding order, particle size, vibration amplitude, carrier gas humidity, and fluidization velocity. Decreasing calcination temperature from 726 to 623 K increased the activity of TiO₂/Al₂O₃ catalysts for methanol PCO. Attrition during fluidization liberated small TiO₂ particles from the bulk catalyst and the rate of attrition increased with gas velocity. Attrition was the primary cause of catalyst elutriation and not the presence of fine particles initially present in the bed from catalyst preparation. Increasing humidity caused agglomeration of fine particles, which reduced the amount of catalyst carryover. Removal of fines from the catalyst bed prior to fluidization caused an increase in catalyst attrition until the amount of fines present in the bed was similar to that of a bed in which fines were not removed.     

Fluidized bed combustion of high ash anthracite: Analysis of combustion efficiency and particle size distribution

Fluidized bed combustion of high ash anthracite (HAA) was experimentally studied. The combustor consists of 0.25 m ID bed, and auxiliary equipments for coal feeding, ash removal, lemperature control, etc. Experimental results elucidate main cause of fuel loss to be elutriation of fines (i.e., flyash) containing unburned carbon. However, detailed balances of particle size distribution show majority of carbon in flyash comes from fines contained in the feed instead of attrition of coarse particles. The latter is the main source of flyash for conventional coal. The difference is due to much smaller attrition rate of HAA; feed HAA particles do not shrink much in size by combustion and attrition.     

Improving the attrition resistance of slurry phase heterogeneous catalysts

Slurry phase heterogeneous catalysts for processes such as Fischer–Tropsch (F–T) synthesis must exhibit a high degree of attrition resistance. The precipitated Fe–Cu catalyst used for F–T synthesis is quite weak in its as-prepared state. Spray-drying yields spherical particles which show some improvement in attrition resistance. However, the formation of fines (<5 μm) in this powder shows that it is not suitable as a slurry phase catalyst. In this paper, we report on the use of a silica binder to improve the strength of spray-dried agglomerates. The attrition resistance was measured using ultrasonic fragmentation followed by sedigraph particle size analysis. The attrition strength of the iron oxide catalyst agglomerates was compared to that of a commercial alumina powder, which was used as a reference material. The role of calcination (before or after spray-drying) and the method of silica binder addition (before or after spray-drying) was investigated.     

Simulation of catalyst loss from an industrial fluidized bed reactor on the basis of labscale attrition tests

Attrition of catalyst represents a significant economic penalty due to the necessity to make-up the losses on a continual basis. Designing fluidized bed systems to minimize attrition may sacrifice gas-solid contact efficiency that requires pressure to distribute gases in process vessels uniformly. In this paper, the attrition performance of DuPont's vanadium pyrophosphate oxide catalyst (VPP) used in their commercial Circulating Fluidized Bed (CFB) process to convert n-butane to maleic anhydride has been examined. The analysis is based on simulating the commercial conditions in the individual vessels combined with the physical characteristics of the catalyst determined in the laboratory. The comparison of the catalyst loss rate measured in the industrial plant and the simulation results indicates that the measured values are below the values predicted by the simulation. However, the relative change in the catalyst loss rate with operating time is well described. The simulation allows the quantification of the attrition sources in the process. The simulation results revealed that in the present case over 60% of the catalyst loss originates from attrition in the fluidized beds, whereas only 16% originates from attrition in the cyclones. The simulation is an appropriate tool to investigate the influence of parameter changes. Using the simulation the design parameters and operating conditions can be optimized to minimize the catalyst loss rate in the industrial plant.     

Effects of high temperature and combustion on fluidized material attrition in a fluidized bed

This study investigated the effects of high temperature and combustion conditions on the attrition of fluidized material in a fluidized bed. Silica sand was fluidized in air at an atmospheric pressure between 873 K and 1,073 K. The operating parameters evaluated in investigating the attrition rate of fluidized material included particle size, temperature and both combustion and non-combustion conditions. Experimental results indicated that the total weight of attrition increased with increasing temperature and decreased with increasing particle size. The attrition was higher during the initial fluidization period than the later period, due to the loss of sharp corners and edges of the attrition particles. The initial and final attrition rates during combustion were higher than those in the non-combustion condition, because the heat and thermal shock were produced to increase attrition rate during incineration. Comparing the experimental data with previous correlations, that reveals a significant level of error in the prediction results from existing correlations. This error may occur because the experimental equations neglected the operating temperature and particle size.     

Attrition behavior of fine particles in a fluidized bed with bimodal particles: Influence of particle density and size ratio

To process the solid particulates in fluidized bed and slurry phase reactors, attrition is an inevitable consequence and is therefore one of the preliminary parameters for the catalyst design. In this paper, the mechanical degradation propensity of the zeolite catalysts (particles) was investigated in a bimodal distribution environment using a Gas Jet Attrition — ASTM standard fluidized bed test (D-5757). The experimentation was conducted in order to explore parameters affecting attrition phenomena in a bimodal fluidization. In a bimodal fluidization system, two different types of particles are co-fluidized isothermally. The air jet attrition index (AJI) showed distinct increases in the attrition rate of small particles in a bimodal fluidization environment under standard operating conditions, in comparison with single particle. A series of experiments were conducted using particles of various sizes, with large particles of different densities and sizes. Experimental results suggest that the relative density and particle size ratio have a significant influence on attrition behavior during co-fluidization. Therefore a generalized relationship has been drawn using Gwyn constants; those defined material properties of small particles. Moreover, distinct attrition incremental phenomenon was observed during co-fluidization owing to the change in collision pattern and impact, which was associated with relative particle density and size ratios.     

Attrition studies with catalysts and supports for slurry phase Fischer–Tropsch synthesis

Attrition properties of several oxide supports and precipitated iron-based F–T catalyst (100Fe/3Cu/4K/16SiO₂ in parts by weight) were evaluated using ultrasound irradiation test and stirred tank slurry reactor (STSR) test under non-reactive conditions. Attrition by fracture and erosion of the iron-based catalyst was small in both types of tests and its overall attrition strength was better than that of the alumina and silica supports, which were evaluated under the same conditions. Also, attrition studies with four iron-based F–T catalysts were conducted under reaction conditions in the STSR. Catalyst of similar composition, as that used in non-reactive studies, prepared by spray drying technique had the highest attrition strength among all catalysts tested.     

Attrition of porous glass particles in a fluidised bed

Fluidisation is frequently accompanied by unwanted attrition of the bed material. This paper focuses on the mechanical aspects of fines creation by attrition in fluidised beds supported by multi-orifice distributor plates. The attrition rates of low-density porous glass particles were measured; these particles show abrasive wear behaviour rather than breakage. Positron emission particle tracking (PEPT) was used to follow particle motion in three dimensions within the fluidised bed. For a single orifice distributor with background fluidisation, the attrition rate increased exponentially with increasing orifice gas velocity. For a multi-orifice distributor, however, attrition rates were roughly proportional to excess gas velocity, except near to a critical ratio of particle to orifice diameter; as this ratio approached 2, attrition was observed to increase by an order of magnitude. A method is proposed for estimating attrition rates from a combination of small-scale experimental results and theoretical calculations of distributor jet entrainment rates.     

细颗粒对气固流化床中静电行为的影响

聚合物颗粒粒径和残余催化剂量（又称灰分）不同,会影响颗粒的功函数、接触面积和发生接触时的电荷转移数目等,故粒径和灰分含量不同的同种聚合物颗粒在相互接触时对静电的贡献并不相同,尤其是灰分含量较高的细颗粒对静电的影响至关重要．通过在f150mm的流化床冷模装置中,对聚乙烯颗粒－氮气体系进行流态化实验,分别测量了向含较大聚乙烯颗粒的流化床中添加不同粒径的同种聚乙烯细颗粒后的静电压,发现床内电压与所加细颗粒粒径、细颗粒重量分率及细颗粒中灰分含量密切相关,根据上述现象进而提出了包含颗粒粒径作用项和灰分含量作用项的细颗粒作用因子．在实验条件范围内,作用因子小于1.0的三种细颗粒的加入对床内静电压产生影响甚微．而平均粒径最小同时灰分含量最高的细颗粒加入后对床内静电压影响明显,当其作用因子小于1时,同样不会引起床内静电压的太大改变;且当作用因子小于0.5时,静电压还略有降低;而作用因子一旦大于1,床内静电压显著升高;当作用因子继续升高,静电压又有所下降,但同时由于细颗粒的含量增加,粘壁现象变得非常严重．     

Study on attrition of spherical-shaped Mo/HZSM-5 catalyst for methane dehydro-aromatization in a gas-solid fluidized bed

As a potential methane efficient conversion process,non-oxidative aromatization of methane in fluidized bed requires a catalyst with good attrition resistance,especially in the states of high temperature,long-time rapid movement and chemical reaction.Existing evaluation methods for attrition resistance,such as ASTM D5757 and Jet Cup test,are targeted for fresh catalysts at ambient temperature,which cannot well reflect the real process.In this study,spherical-shaped Mo/HZSM-5 catalyst prepared by dipping and spray drying was placed in a self-made apparatus for attrition testing,in which the catalyst attrition under differ-ent system temperatures,running time and process factors was investigated with percent mass loss (PML),particle size-mass distribution (PSMD) and scanning electron microscope (SEM).Carbon deposition on the catalyst before and after activation,aromatization and regeneration was analyzed by thermogravimetry(TG),and the attrited catalysts were evaluated for methane dehydro-aromatization (MDA).The results show that the surface abrasion and body breakage of catalyst particles occur continuously,with the increase of system temperature and running time,and make the PML rise gradually.The process factors of activation,aromatization and regeneration can cause the catalyst attrition and carbon deposits,which broaden the PSMD in varying degrees,and the carbon-substances on catalysts greatly improve their attrition resistance at high temperature.Catalyst attrition has a certain influence on its catalytic performance,and the main reasons point to particle breakage and fine powder escape.     

Granulation in spouted — attrition and other mechanisms

Experimental measurements of overhead fines from a 150 mm diameter spouted bed granulator are described. When granulating sodium chloride, the main source of overhead fines is attrition rather than spray drying of the overhead spray droplets. Attrition increases with increasing evaporation rate and for a given evaporation rate, pure water feed causes more attrition than does salt solution feed. The existence of an optimum feed rate for minimum fractional loss of solute feed by attrition is demonstrated. Related experiments in a dry spouted bed polydisperse granules show that attrition is size dependent, being lowest for intermediate granule sizes.     

Attrition of spherical electrode carbon particles during batch fluidized combustion

Spherical electrode carbon particles prepared from carbon rods of dry cell batteries have been used to study the attrition behaviour in a bubbling fluidized bed combustor. Experiments have been conducted in a 40 mm I.D. and 1 m high fluidized bed combustor operated at 1 m/s superficial velocity. The bed was operated with nitrogen and with two different oxygen concentrations at 850°C to study the effect of combustion on attrition of these particles. The experimental technique used allowed the time resolution of attrited fines generation, providing detailed curves of attrition rates as a function of time. Attrition rate constants have been evaluated. Results show an enhancement of attrition due to combustion even for spherical, homogeneous and smooth particles.     

石英砂流化床床料磨损的数学模型

针对石英砂流化床床料磨损问题,从磨损的机理出发,基于Fleischer关于摩擦磨损的系统能量平衡理论建立了一种磨损数学模型。磨损细颗粒脱离母体颗粒的磨损破坏条件是依据材料动力破坏的最小能量原理。该模型考虑了床料颗粒在流化床的运行特点和颗粒的物理性质,能够反映流化床床料磨损的一些物理意义,且模型计算结果与实验数据吻合较好。     

The effect of SiO_2 particle size on iron based F–T synthesis catalysts

The effect of particle size of silica, as catalyst binder, on the chemical and mechanical properties of iron based FT catalyst was studied in this work. The samples were characterized using XRD, BET, TEM, FT-IR, and H2-TPR, respectively. The attrition resistance and the FT activity were tested. Si-8–Si-15 catalysts prepared with 8–15 nm silica sol show good attrition resistance(attrition loss b 4%), especially Si-13 with an attrition loss of 1.89%. Hematite appeared in XRD patterns when silica sol above 15 nm is used. TEM micrographs show that no obvious Si O_2 particles appear when silica sol particle with size less than 8 nm was used, but Si O_2 particles coated with small ferrihydrite particles appear when silica sol above 8 nm was used. Si–O–Si vibration peak in FT-IR spectra increases with increasing silica sol size. Samples prepared with silica sol show good stability of FT reactions, and the average molecular weight of FT products increases with the increase of Si O_2 particle.     

Computational fluid dynamics and electrostatic modeling of polymerization fluidized-bed reactors

Electrostatics plays an important role in gas-solid polymerization fluidized-bed reactors. Agglomeration of polymer particles can occur due to either electrostatic and/or thermal effects, and can lead to reactor operability problems if not properly mitigated. In this work a first-principles electrostatic model is developed and coupled with a multi-fluid computational fluid dynamic (CFD) model to understand the effect of electrostatics on the bulk polymer, polymer fines, and catalyst particles. The multi-phase CFD model for gas-solid flow is based on the kinetic theory of granular flows and the frictional theory. The electrostatic model is developed based on a fixed, size-dependent charge for each type of particle (catalyst, polymer fines and polymer). The combined CFD model is first verified using simple test cases and then applied to a pilot-plant-scale polymerization fluidized-bed reactor. The multi-phase CFD model is applied to reproduce qualitative trends in particle segregation and entrainment due to electrostatic charges observed in experiments.     

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

The focus of the research reported herein was to investigate the effects of phase changes, as occur during Fe catalyst activation and Fischer–Tropsch synthesis, on Fe catalyst attrition resistance. Different activation conditions (CO, H₂ or syngas) were applied prior to attrition testing to a selected spray-dried Fe catalyst containing 9.1 wt.% binder SiO₂, which had been shown to have the highest attrition resistance in our early study of calcined catalysts. Although, XRD indicated that different Fe phase compositions resulted in the differently activated catalyst samples, chemical attrition was not observed for any of the samples. The BET surface areas of the activated samples were smaller than that of the calcined precursor but no significant changes in pore volume and particle size were found. The attrition resistances of the differently activated catalyst samples were found to be similar to that of the calcined catalyst for this spray-dried Fe catalyst. Attrition resistance was found previously to be governed by catalyst particle density, which has been shown earlier to relate to the SiO₂ network in catalysts. It is therefore suggested that the type and concentration of SiO₂ that is incorporated during the preparation of spray-dried Fe catalysts have a much more significant impact on catalyst attrition than Fe phase change during activation in the presence of CO, H₂ or H₂+CO.     

Attrition studies with precipitated iron Fischer–Tropsch catalysts under reaction conditions

Iron Fischer–Tropsch (F–T) catalyst particles break-up during reaction in slurry phase reactors by physical attrition, and due to chemical stresses caused by phase transformations. Although chemical attrition is known to be important with iron (Fe) F–T catalysts, there have been no studies of attrition properties of precipitated Fe catalysts under reaction conditions. Here we report on attrition properties of three precipitated Fe catalysts (100 Fe/3–5 Cu/4–6 K/16–25 SiO₂) during F–T synthesis in a stirred tank slurry reactor (STSR). Our results show that after 295–497 h of F–T synthesis with these three catalysts in the STSR, the particle size reduction by fracture was moderate, whereas erosion (generation of particles smaller than 10 m) was small (2.3–2.7). The attrition strength of these catalysts is adequate for use in Slurry bubble column reactors (SBCRs) for F–T synthesis.