Three-phase ebullated bed reactor

The H-Cocd Process, based on H-Oil technology, was developed by Hydrocarbon Research, Inc. (HRI). The heart of the process was a three-phase, ebullated-bed reactor in which catalyst pellets were fluidized by the upward flow of slurry and gas through the reactor. The reactor contained an internal tube for recirculating the reaction mixture to the bottom of the catalyst bed. Catalyst activity in the reactor was maintained by the withdrawal of small quantities of spent catalyst and the addition of fresh catalyst. The addition of a catalyst to the reactor is the main feature which distinguishes the H-Coal Process from the typical process. 

Source Adapted from Deshpande, D.A. et al., Similitude studies in three-phase ebullated bed reactors, in Eastern Oil Shale Symposium, November 17-20, Hyatt Regency, Lexington, KY, 1992. 

FIG. 19-39 Gas-liquid-solid reactors, (a) Three-phase iluidized-bed reactor, b Ebullating bed reactor for hydroliquefaction of coal. (Kampiner in Winnacker-Keuchler, Chemische Technologie, vol. 3, Hanser, 1972, p 252.)... 

In a three-phase fluidized-bed reactor, also called an ebullated bed reactor, the solid catalyst particles are kept in suspension by the gas and the liquid flowing upwards (Figure 4.10.12b). The particles are relatively large (1-5 mm) to keep them from being carried away. Fluidized beds are preferred for strongly exothermic reactions or if the catalyst must be frequently exchanged because of rapid deactivation. 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Reactors with moving solid phase Three-phase fluidized-bed (ebullated-bed) reactor Catalyst particles are fluidized by an upward liquid flow, whereas the gas phase rises in a dispersed bubble regime. A typical application of this reactor is the hydrogenation of residues. 

A related reactor is that for coal liquefaction, which can be carried out in a three-phase slurry bubble column (see Fig. 5). Hydrogen can be supplied at the bottom of a column of downcoming product—oil. The solid coal reactant is blended with the product or carrier oil and fed at the top. The generic process depicted in Fig. 5 is a generalization of the liquefaction reactor in the Exxon Donor Solvent Process. As the gas flow rate increases, the bubbles change from uniformly small to chaotic. In the H-coal process, both the gas and a coal-oil slurry are fed from the bottom in an ebullating-bed reactor. Catalyst solids are fed from the top. This reactor operates as an expanded... 

Ebullated bed processes are offered for license by Axens (IFF) ABB Lummus. In ebullated bed reactors, hydrogen-rich recycle gas bubbles up through a mixture of oil and catalyst particles to provide three-phase turbulent mixing. The reaction envirorunent can be nearly isothermal, which improves product selectivity. At the top of the reactor, catalyst particles are disengaged from the process fluids, which are separated in downstream flash drums. Most of the catalyst goes back to the reactor. Some is withdrawn and replaced with fresh catalyst. 

Multi-environment systems with two flowing phases. These systems are perhaps of most interest in reaction engineering applications since they include the most frequently used multiphase reactors. Gas-liquid bubble columns, ebullated beds, three-phase fluidized beds, gas-lift slurry reactors, trickle-bed reactors, pneumatic transport reactors, etc. fall into this category. Some of the developments presented in Section 6.1.1 can be extended to treat these systems. The multivariable joint p.d.f. has to be defined taking into the account that the system has multiple inlets and outlets, i.e. by following the rules established in Section 3 by the appropriate extension of eqs. (9) and (10). However, this approach has not been presented or used to date. The main reason is that the transforms do not have a readily useable analytical form and are functions of many system... 

---