Fluidised beds Reactor

The difficulty with an approach in which flow and diffusive parameters are assigned to a model is that the assumptions do not conform strictly to the pattern of behaviour in the bed. Furthermore, it is doubtful whether either solid dispersion 

These are generally big empty vessels with or without linings of refractoiy or acid resistant materials with various nozzles for (i) entry of reactants and fluidising media (could be high volume of air), (ii) exit of products, (iii) draining the reactor. 

Provision for demisters, separators for catalyst particles and arresting escape of un-reacted particles should be made. 

Reinforcements should be made at all nozzles by adequately sized pad plates, gussets, etc. Pad plates with vent holes to be welded for side supports. 

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Jones, A.G., Wachi, S. and Delannoy, C.C., 1992b. Precipitation of calcium carbonate in a fluidised bed reactor. In Fluidization VII. Eds. O.E. Potter and D.J. Nicklin, New York Engineering Foundation, pp. 407M14. 

Before MPW is fed into the process, a basic separation of the non-plastic fraction and size reduction is needed. This prepared feedstock is then introduced in the heated fluidised bed reactor which forms the core of the process. The reactor operates at approximately 500 °C in the absence of air. At this temperature, thermal cracking of the plastics occurs. The resulting hydrocarbons vapourise and leave the bed with the fluidising gas. Solid particles, mainly impurities formed from, e.g., stabilisers in plastics, as well as some coke formed in the process mainly accumulate in the bed. Another fraction is blown out with the hot gas and captured in a cyclone. 

The thermal cracking of a light ffaction of mixed plastics waste was carried out in a fluidised bed reactor and the fractions obtained were analysed by elemental analysis, gas chromatography and ashing. The main components of the waste were PE and PP with a small amount of PS and the bed was fluidised by pyrolysis gas, nitrogen or preheated steam. Experiments conducted at different temperatures and residence times were compared by calculating the crack severity for each experiment. The results obtained revealed that the amounts of ethene and propene obtained by pyrolysis with steam were comparable with those obtained using a commercial steam cracker. 

The application of a selective pyrolysis process to the recovery of chemicals from waste PU foam is described. The reaction conditions are controlled so that target products can be collected directly from the waste stream in high yields. Molecular beam mass spectrometry is used in small-scale experiments to analyse the reaction products in real time, enabling the effects of process parameters such as temperature, catalysts and co-reagents to be quickly screened. Fixed bed and fluidised bed reactors are used to provide products for conventional chemical analysis to determine material balances and to test the concept under larger scale conditions. Results are presented for the recycling of PU foams from vehicle seats and refrigerators. 12 refs. 

A stirred-tank model has been proposed, (Daly, 1980), to model the mixing behavior of an air-solid, spouted, fluidised-bed reactor. The central spout is modelled as two tanks in series, the top fountain as a further tank and the down flowing annular region of the bed as 6 equal tanks in series. It is assumed that a constant fraction of the total solids returns from each stage of the annular region into the central two tank region, as depicted below. 

Aniline is manufactured by the hydrogenation of nitrobenzene in a fluidised bed reactor. The reactor operates at 250 °C and 20 bar. The reactor vessel is approximately 3 m diameter and 9 m high. Suggest suitable materials of construction for this reactor. 

The essential features of a fluidised bed reactor is that the solids are held in suspension by the upward flow of the reacting fluid this promotes high mass and heat-transfer rates and good mixing. Heat-transfer coefficients in the order of 200 W/m2oC to jackets and internal coils are typically obtained. The solids may be a catalyst a reactant in fluidised combustion processes or an inert powder, added to promote heat transfer. 

Fluidisation can only be used with relatively small sized particles, <300 gm with gases. A great deal of research and development work has been done on fluidised bed reactors in recent years, but the design and scale up of large diameter reactors is still an uncertain process and design methods are largely empirical. 

The principles of fluidisation processes are covered in Volume 2, Chapter 6. The design of fluidised bed reactors is discussed by Rase (1977). 

CLC consists of two fluidised bed reactors, namely reducer and oxidiser. In the reducer reactor, fuel is fed along with the metal oxide containing oxygen, which is transferred from the metal oxide to the reactor as the combustion occurs (Figure 7). A flue gas containing over 99%v/v of C02 can be obtained by a simply condensation stage because of the fact that the exhaust gas at the reducer outlet is primarily formed by C02 and water vapour. This stream is then sent to further compression and permanent storage. 

Calcium looping consists of two fluidised bed reactors, namely carbonator and calciner. In the... 

Schoutens, G. EL, Guit, R. P., Zieleman, G. J., Luyben, K. C. A. M., and Kossen, N. W. F., A Comparative Study of a Fluidised Bed Reactor and a Gas Lift Loop Reactor for the IBE Process Part I. Reactor Design and Scale Down Approach, J. Chem. Tech. Biotechnol., 36 335 (1986a)... 

The fluidised bed reactor is modelled by considering the component balances for the three nitrogen components (i) and also for dissolved oxygen. For each stage n, the component balance equations have the form... 

Continuous Multicomponent Distillation Column 501 Gas Separation by Membrane Permeation 475 Transport of Heavy Metals in Water and Sediment 565 Residence Time Distribution Studies 381 Nitrification in a Fluidised Bed Reactor 547 Conversion of Nitrobenzene to Aniline 329 Non-Ideal Stirred-Tank Reactor 374 Oscillating Tank Reactor Behaviour 290 Oxidation Reaction in an Aerated Tank 250 Classic Streeter-Phelps Oxygen Sag Curves 569 Auto-Refrigerated Reactor 295 Batch Reactor of Luyben 253 Reversible Reaction with Temperature Effects 305 Reversible Reaction with Variable Heat Capacities 299 Reaction with Integrated Extraction of Inhibitory Product 280... 

Borja, R., Rincon, B., Raposo, R, Dominguez, J.R., Millan, R and Martin, A., Mesophilic anaerobic digestion in a fluidised-bed reactor of wastewater from the production of protein isolates from chickpea flour. Process Biochem., 39 (2004) 1913-1921. 

In Canada, hydrogen production from natural gas via a fluidised bed reactor with hydrogen purification via a selective membrane is under investigation. Also, a methanol micro-reformer which includes an integrated metal membrane purification unit is being developed. 

Wen, C.Y., Flow regimes and flow models for fluidised bed reactors, in Recent advances in the engineering analysis of chemically reacting systems (ed. L. K. Doraiswamy), Wiley Eastern Limited, India, 256-287 (1984)... 

We shall consider, in turn, the various problems which have to be faced when designing isothermal, adiabatic and other non-isothermal tubular reactors, and we shall also briefly discuss fluidised bed reactors. Problems of instability arise when inappropriate operating conditions are chosen and when reactors are started up. A detailed discussion of this latter topic is outside the scope of this chapter but, since reactor instability is undesirable, we shall briefly inspect the problems involved. 

If the solid particles can be maintained in the fluidised state without problems of agglomeration or attrition, the fluidised bed reactor Fig. 1.45c is likely to be preferred. For short contact times at high temperatures the dilute phase transfer line reactor (Fig. 3.37[Pg.187]

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