Javier Bilbao

Solid cross-flow into the spout and particle trajectories in conical spouted beds

The trajectories of the particles in conical spouted beds are determined from the vertical component of velocity measured by means of an optical fibre probe and from the horizontal component of velocity calculated by solving the mass conservation equations for the solid in differential volume elements in spout and annular zones. From the experimental measurement of particle flow rate along the spout, the solid cross-flow rate from the annulus into the spout is determined. The effect of the operating variables on the solid circulation rate along the spout and on the vigorousness of the regime, which is characterized by the value of the average cycle time of the particles, is analysed by carrying out the operation with different values of the geometric factors of the contactor (angle and gas inlet diameter) and of the operating conditions (particle diameter, stagnant bed height and gas velocity).

Pressure drop in conical spouted beds

Abstract The limitations of the few correlations in the literature for the design of conical spouted beds and the non-validity of these conventional correlations proposed for cylindrical spouted beds have been proven. Consequently, original hydrodynamic correlations for spouting and jet spouting, corresponding to conical contactors, have been proposed for the calculation of the maximum pressure drop and of the pressure drop in stable operational conditions. The hydrodynamic study has been carried out with different geometries of the contactor—inlet system (different angles and diameters of inlet) and with solids of different particle sizes, densities and shape factors, so that the correlations obtained are of general applicability.

Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon.

The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500°C. Extraction with Na2CO3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800°C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365m(2)g(-1) at the end of 15min.

Effect of operating conditions on solid velocity in the spout, annulus and fountain of spouted beds

An optical fiber probe has been used to study the effect of operating conditions (base angle, gas inlet diameter, stagnant bed height, particle diameter and gas velocity) on particle velocity in the three zones of spouted beds: spout, annulus and fountain. The experimental results prove the validity of the equation of Epstein and Grace (1984) for prediction of the vertical component of particle velocity in the spout by establishing the relationship of the parameter of this equation with operating conditions. It also been proven that the equation of Mathur and Epstein (1974) is valid for predicting particle velocity in the fountain core. From the values of vertical components (experimental) and horizontal components (calculated) of particle velocity, maps of velocity vector throughout the bed have been drawn and zones of preferential solid cross-flow into the spout have been determined.

Deactivation by coke of a catalyst based on a SAPO-34 in the transformation of methanol into olefins

When methanol is converted to olefins on a SAPO-34 catalyst between 350 and 425°C, there is a rapid initial formation of coke, followed by a slower rate of coke deposition. The rate of coke formation decreases with increasing temperature, and with progression through the catalyst bed. The coke completely blocks the internal channels of the SAPO-34 crystals and subsequently blocks the mesopores (intercrystalline and those of the bentonite). Coke deposition mainly blocks sites of acidic strength above 175 kJ/mol. The presence of water in the feed lessens coke formation, either by converting Lewis to Bronsted sites or by competing for surface sites with coke precursors.

New reactor in jet spouted bed regime for catalytic polymerizations

Abstract The hydrodynamic features, suitable for catalytic polymerization in the gaseous phase, of a new reactor in the jet spouting regime have been studied. This regime is reached by expansion of conical spouted beds. The application of the jet spouted bed as a reactor in catalytic polymerizations implies the treatment of sticky solids with a wide particle size distribution, even of catalyst particles of reduced size (less than 1 mm diameter), which are not habitually treated in conventional spouted beds. The jet spouted bed has a high stability and reduced segregation together with a great capacity for continuous operation of the solids. In a pilot-plant scale unit, the following original aspects of the gas-solid contact have been studied: the design factors for stable operation (contactor angle, ratio between the inlet diameter and the base diameter of the contactor, ratio between the inlet diameter and the particle diameter); the hydrodynamics (correlations for the calculation of the minimum velocity, of the stable operation pressure drop and of the maximum pressure drop); the proposal of a disperse plug flow model for the gas in the reactor, and the subsequent calculation of the dispersion coefficient. The behaviour of the jet spouted bed as a reactor in the polymerization of benzyl alcohol has been studied in an automated laboratory unit where the effect of the residence time of the catalyst and the alcohol concentration in the feed have been analysed.

Catalyst deactivation by coking in the MTG process in fixed and fluidized bed reactors

Abstract The validity of a kinetic model for describing the deactivation of a catalyst based on a HZSM5 zeolite has been studied by carrying out reaction in fixed and fluidized bed reactors. The kinetic model takes into account that activity is dependent on the concentration of the lumps of oxygenates, of light olefins and of the remaining products and shows that coke formation capability follows this order. The difference between the deactivation kinetic constants calculated for the fixed and fluidized bed reactors is explained by the effect of the steam produced in the reaction, where coke stripping attenuates deactivation. Future improvements in the deactivation kinetic model must take into account coke stripping by the steam produced in the reaction.

Relationship between surface acidity and activity of catalysts in the transformation of methanol into hydrocarbons

The effect of Si/A1 ratio of HZSM5 zeolite-based catalysts on surface acidity and on selectivity in the transformation of methanol into hydrocarbons has been studied. The acidic strength distribution (measured by combining the differential scanning calorimetry and the chromatographic analysis) and the total acidity (measured by calorimetry and temperature programmed desorption), using ammonia and tert-butylamine, have been studied as acidity measurements. The nature of the acidic sites has been determined by FTIR analysis of both the surface OH groups and the interaction of Bronsted and Lewis sites with pyridine. The increase in light olefin selectivity and the decrease in methanol conversion with increasing Si/Al ratio are a consequence of the kinetic scheme of the reaction, which has steps in series, and can be explained by the decrease in total acidity. The same acidic sites are responsible for the formation of light olefins and for the transformation of these olefins into higher hydrocarbons.

Expansion of spouted beds in conical contactors

Abstract The expansion of conical spouted beds has been studied on a wide experimental base (using contactors of different geometries and solids of different diameters and sphericities). The correlation obtained for calculating the global voidage from the operation conditions is of a more general application than those previously proposed in the literature, which are generally centred on the study of voidage in the spout. The global incipient voidages are delimited for both stable regimes corresponding to two voidage ranges: spouting and jet spouting. While the correlation for calculation of expansion can be applied for the calculation of global minimum jet spouting voidage, a correlation is proposed for the calculation of the global minimum spouting voidage. This equation is applicable in a wide range of operation conditions.

Kinetics of scrap tyre pyrolysis under vacuum conditions.

Scrap tyre pyrolysis under vacuum is attractive because it allows easier product condensation and control of composition (gas, liquid and solid). With the aim of determining the effect of vacuum on the pyrolysis kinetics, a study has been carried out in thermobalance. Two data analysis methods have been used in the kinetic study: (i) the treatment of experimental data of weight loss and (ii) the deconvolution of DTG (differential thermogravimetry) curve. The former allows for distinguishing the pyrolysis of the three main components (volatile components, natural rubber and styrene-butadiene rubber) according to three successive steps. The latter method identifies the kinetics for the pyrolysis of individual components by means of DTG curve deconvolution. The effect of vacuum in the process is significant. The values of activation energy for the pyrolysis of individual components of easier devolatilization (volatiles and NR) are lower for pyrolysis under vacuum with a reduction of 12K in the reaction starting temperature. The kinetic constant at 503K for devolatilization of volatile additives at 0.25atm is 1.7 times higher than that at 1atm, and that corresponding to styrene-butadiene rubber at 723K is 2.8 times higher. Vacuum enhances the volatilization and internal diffusion of products in the pyrolysis process, which contributes to attenuating the secondary reactions of the repolymerization and carbonization of these products on the surface of the char (carbon black). The higher quality of carbon black is interesting for process viability. The large-scale implementation of this process in continuous mode requires a comparison to be made between the economic advantages of using a vacuum and the energy costs, which will be lower when the technologies used for pyrolysis require a lower ratio between reactor volume and scrap tyre flow rate.