Fluidized-bed plant

Fluidized bed plants. Some plants use a technology that differs from the scheme shown in Figure 20-3 in that the catalyst moves around with the feed during the reaction rather than staying fixed in the reactor tubes. The design, called fluidized bed technology, uses catalyst in a powdered form that is so mobile that it can be pumped like a liquid or blown like a vapor. 

Elutriation is important in most industrial fluidized beds and is generally thought of as a disadvantage. In addition to the small particles which may be present in the initial particle size distribution, fines may be created in the course of operation by the attrition of bed particles. Elutriated particles usually need to be collected and recovered either because they represent the loss of product particles of a given size, because they must be separated from the exhaust gas for environmental reasons, or because of safety concerns there is a considerable risk of a dust explosion with very fine particles and perhaps especially so with many food particulates. Therefore the fluidized bed plant will require ancillary gas cleaning equipment such as a cyclone, filter or electrostatic precipitator to separate the fines from the gas. The loss of a particular size fraction from the bed may change fluidized bed behaviour and it then becomes important to return the fines to the bed continuously. 

A further example of using chemical fluidized-bed processes is that of plants where fluidizable solids are used as a heat transfer medium. Willing [98] describes the use of this process for the cracking of oil arrears, but fluidized-bed plants are also suitable for catalytic or gas-solid reactions. The easy controllability of the reactor temperature is emphasized by Baranek et al. [7], wherein the heat of reaction can be used by immersed coolers to generate steam. The isothermal behavior, and the possibility of both supplying and removing heat, are further advantages. 

The measurements were carried out at a semi-industrial fluidized-bed plant DN 400. The scheme of the process is illustrated in Fig. 16.4, while the plant itself is illustrated in Fig. 16.5. 

The liquid injection is realized using a two-fluid nozzle (Co. Schlick, type 943, form 3, ring-shaped beam 20°-40°, dnozzie = 2.3 mm). A adjustable hose pump conveys the liquid from a store tank, and compressed air is used for the better spreading of the liquid. The investigations of Henneberg et al. [38, 39] in an industrial fluidized-bed plant showed that high nozzle injection rates may lead to low particle concentrations near the nozzle, and to overspray. 

Ormston, O., Robinson, E., and Buckle, D. Stream Raising Circulating Fluidized Bed Plant, Inst. Energy Symp. ser. (London), 4 (Fluid. Combust. Syst. Appl.), IIA/1-IIA/1/10( 1980). 

Figure 25.13 Fluidized-bed plant for the pyrolysis of PET with a feed rate of 1 kg PET/h [32]. (Reprinted from Polymer Degradation and Stability, Vol. 86, T. Yoshioka et a ., pp. 499, 2004, with permission from Elseveir)...

A Pilot Scale Circulating Fluidized Bed Plant for Orujillo Gasification... 

The fluidized bed plants developed by Kaminsky et al. have been used for the conversion of a variety of plastic mixtures. In a recent work,99 the results obtained in the conversion of two different plastic wastes at temperatures of 638, 690 and 735 °C were reported. The raw mixture consisted mainly of polyolefins (65-79%), polystyrene (4-30%) and polyvinyl chloride (4-5%). The following fractions were derived from the pyrolysis of these materials gases (35 42.9%), oils (41-51.8%), residue (5.8-14.3%) and soot (2.2-5.4%). The gases were mainly methane, ethylene and propylene, with a certain concentration of CO and C02 due to the presence of oxygen in the feed material. At the lowest pyrolysis temperature the oil produced contains a high proportion of... 

In Japan, Mitsubishi Chemical operates a fluidized-bed plant (18,000 tpa) based on butene. 

It may also be noted that a French assessment of the explosibility risk in a rather more potentially hazardous operation of incinerating spent nuclear graphite in a fluidized bed plant has also given a favourable result. It is considered that the procedures adopted for the trepanning of Piles graphite, particularly the controls on temperature and the presence of an inert atmosphere in the vicinity of the cutting operation, effectively eliminate the explosibility risk ... 

Practically all industrial gas-solid fluidized bed reactors operate at temperatures well above ambient, and some, such as those used in the production of polyolefins, also operate at elevated pressures. It is therefore important to know how fluidized beds behave under high temperatures and/or pressures and if possible to predict this behavior from observations made under ambient conditions. The emphasis here will be on those aspects of the subject that are of direct relevance to the design and operation of fluidized bed plant a comprehensive review of the more academic aspects can be found in the review by Yates (1996). 

Examples of some radioactive isotopes used for fluidized bed tracking are shown in Table 7. As discussed e.g., by Seville et al. (1995) and Benton and Parker (1996), the scattering or absorption of the emitted radiation may lead to incorrect determination of tracer position. However, since the scattered rays have lower energy than the correct ones, by removing the scatter data one may avoid this problem. Application of radioactive particles as tracers is relatively easy and inexpensive, even for large fluidized bed plants. However, it may sometimes disturb the flow and definitely requires strict safety regulations during the mea-... 

In open- or once-through fluidized bed plants (Scheme 13.1) [1] fresh air is sucked in, filtered and heated up to the desired process air temperature. While passing through the fluidized bed the heated process air takes up the particle s moisture. Thereafter, the wet process air is exhausted via a filter system. Evaporation rates of up to several hundred kilograms of water or organic solvent per hour can be obtained depending on the size of the apparatus and process conditions (e.g. air or gas flow rate, inlet temperature, product temperature, pressure) [4]. 

Scheme 13.2 Fluidized bed plant ith closed-loop system.

These constructive and control system modifications lead to higher investment costs compared to normal pressure fluidized bed plants. Furthermore the circulating as well as permanent heating and cooling of the inert gas cause rather high operating costs. 

The main feature of this unique technique is the operation of a fluidized bed plant at low vacuum conditions. Inertization is not required due to the operation below the minimum ignition pressure. Compared to closed-loop fluidized bed plants, there are many advantages in terms of economic efficiency, ecology and safety aspects ... 

Commercial operation of the Courtaulds, Ltd., fluidized bed plant commenced in 1960, about 8 years after initiation of development work on the project. It is reported that the plant—code named Landmark—cost 1.7 million (Anon., 1963), A flow diagram of the process is shown in Figure 12-46. Design data and typical operating conditions are listed in Table 12-31. 

The 100 bpd fluidized-bed plant was installed in Wesseling, Germany and be MTG operations in December 1982. The plant lo d 8600 h on-stream, proeessing a total of 6870 ton methanol to gasoline. 

---