Conical spouted bed

Deoxygenation reactions are catalyzed by acids and the most studied are solid acids such as zeolites and days. Atutxa et al. [61] used a conical spouted bed reactor containing HZSM-5 and Lapas et al. [62] used ZSM-5 and USY zeolites in a circulating fluid bed to study catalytic pyrolysis (400-500 °C). They both observed excessive coke formation on the catalyst, and, compared with non-catalytic pyrolysis, a substantial increase in gaseous products (mainly C02 and CO) and water and a corresponding decrease in the organic liquid and char yield. The obtained liquid product was less corrosive and more stable than pyrolysis oil. 

Atutxa, A., Aguado, R., Gayubo, A.G., Olozar, M., Bilbao, J., Kinetic description of the catalytic pyrolysis of biomass in a conical spouted bed, Energy Fuels, 2005, 19, 765. 

Defluidization modelling of pyrolysis of plastics in a conical spouted bed reactor... 

The evolution of the maximum velocity, z/j (0), with the dimensionless longitudinal position at the axis, p, has a similar tracing for all the systems, the velocity decreases as the longitudinal position at the axis increases, Fig. 4. These velocity profiles are more pronounced than those of conical spouted beds [24]. 

In jet spouted bed regime in conical spouted bed, the gas interstitial velocity at the axis, z/j(0), decreases as the dimensionless longitudinal position at the axis, p, increases be-... 

M. Olazar, M.J. San Jose, A.T. Aguayo, J.M. Arandes, J. Bilbao, Stable operation conditions for gas-solid contact regimes in conical spouted beds, Ind. Eng. Chem. Res. 31 (1992) 1784—1792. 

M.J. San Jose, Operation regimes in conical spouted beds. Stability conditions and hydrodynamics, Ph.D. Dissertation, University of the Basque Country, Bilbao, Spain, 1991. 

Thermal pyrolysis for upgrading plastic wastes is one of the better methods for recycling plastics in terms of its perspectives for industrial implementation. The conical spouted bed reactor proposed in this paper may be a solution to the problems arising in fluidized beds handling sticky solids, as particle agglomeration phenomena, which can cause defluidization. In order to avoid defluidization, experiments have been carried out in batch mode in the temperature range of 450-600 °C. A good performance of the reactor is proven under the conditions of maximum particle stickiness. 

The good behaviour of the conical spouted bed reactor is quantified on the basis of the critical thickness of the fused plastic that may be handled. The critical thickness is the value above which the particles fuse when they collide and is a function of the thickness (viscosity) and of the momentum of the colliding particles. From the hypothesis of the critical thickness model of Arena and Mastellone [12], the following expression has been deduced for the critical thickness for... 

In the fluidized bed, the velocity of the particles is of a few cm s-1 and the critical thickness of the fused plastic is between 4 and 7 mm. A fact that should be taken into account is that, although gas velocity is increased, particle velocity hardly changes because most of the excess gas rises through the bed in the bubble phase. Nevertheless, in the conical spouted bed, particle velocity is increased by raising gas velocity up to the dilute spouted bed, in which bed voidage is uniform (between 0.9 and 0.99) and the particle descent velocity is almost equal to the ascent velocity [9]. 

M.J. San Jose, M. Olazar, S. Alvarez, M.A. Izquierdo, J. Bilbao, Solid cross-flow into the spout and trajectories in conical spouted beds, Chem. Eng. Sci. 53 (1998) 3561-3570. 

R. Aguado, M. Olazar, B. Gaisan, R. Prieto and J. Bilbao, Kinetics of polystyrene pyrolysis in a conical spouted bed reactor. Chemical Engineering Journal, 92, 91-99 (2003). 

Flnidized-bed processes are either bnbbling or internally circulating. The fluidized-bed reactor is very versatile for the pyrolysis of polyolefins. Nevertheless one of the problems with fluidized-bed pyrolysis of post-consumer plastics relates to the stickiness of the sand particles (the fluidization medium) that becomes coated with fused plastic. In order to solve these problems, new reactors have been proposed, snch as the conical spouted bed, the conical rotary reactor, a sphere circnlation reactor and a reactor with mechanical particle stirring. 

Fig. 26. Radial voidage profile in a conical spouted bed (Groltsiker s results, G7, quoted in R4).

Arabioumitia et al. studied the thermal pyrolysis of three different polyolefin plastics (HDPE, LDPE and PP) in a conical spouted bed reactor. Compared to fluidized bed reactor, this technology is highly selective to waxes. This fluidized bed reactor requires low residence times and high heating rates that reduce secondary reactions and increase the yield of primary pyrolysis products (waxes). This is an efficient and great versatile technology for the valorization of polyolefinic... 

M. Arabiourmtia et al.. Characterization of the waxes obtained by the pyrolysis of polyolefin plastics in a conical spouted bed reactor. J. Anal. Appl. Pyrol. 94, 230-237 (2012)... 

Since removal of dry material from the dryer is critical for the hydrodynamic stability of dryers with inert carriers, the preferential configuration is the conical spouted bed as it offers intense motion of the particulate phase, which promotes fracture of the dried coat by interparticle collisions and resulting attrition. Moreover, the conical drying chamber has been shown to result in better energy efficiency than the cylindrical one (Kutsakova et al., 1964). Consequently, most of studies aimed at process modeling have been carried out with conical spouted beds. 

Ohveira WP, Silveira AM, Freire IT. Analysis of the drying of pastes in conical spouted beds. In Rudolph V, Keey RB, eds. Drying 94. Proc. 9 Inti. Drying Symposium (IDS 94), Gold Coast, Austraha, 1994, pp 495-502. 

Pham QT. Behaviour of a conical spouted-bed dryer for animal blood. Can. J. Chem. Eng. 61(6) 426-434, 1983. 

Olazar and his associates (1992, 1993a-c, 1995, 1998) studied the design, operation, and performance of a conical spouted bed and found that the conical spouted bed is especially useful for hard-to-handle solids that are irregular in texture or sticky. A conical spouted bed is depicted in Fig. 3. The conical spouted bed exhibits pronounced axial and radial voidage profiles that are quite different from the cylindrical spouted beds. 

Olazar M, San Jose MJ, Aguayo AT, Arandes JM, BUbao J. Pressure drop in conical spouted beds. Chem Eng J 51 53-60, 1993a. 

Olazar M, San Jose MJ Llamosas R, Alvarez S, BUbao J. Study of local properties in conical spouted beds using an optical fiber probe. Ind Eng Chem Res 34 4033-4039, 1995. 

San Jose MJ, Olazar M, Alvarez S, Bilbao J. Local bed voidage in conical spouted beds. Ind Eng Chem Res 37 2553-2558, 1998. 

Fig. 4.1 (a) Design principle and (c) bed pressuredropofaconventional fluidized bed in comparison with (b) design principle and (d) bed pressure drop of a conical spouted bed. Operating regions of conventional fluidized beds 1, packed bed 2, transition region 3, stable... 

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