Reactor plugging

The methanation reaction is carried out over a catalyst at operating conditions of 503—723 K, 0.1—10 MPa (1—100 atm), and space velocities of 500—25,000 h . Although many catalysts are suitable for effecting the conversion of synthesis gas to methane, nickel-based catalysts are are used almost exclusively for industrial appHcations. Methanation is extremely exothermic (AT/ qq = —214.6 kJ or —51.3 kcal), and heat must be removed efficiently to minimise loss of catalyst activity from metal sintering or reactor plugging by nickel carbide formation. 

The first reactor plugged up irreversibly in the first minutes of operation. A second reactor was made and production started. The polyethylene was dark and stinking but the Navy needed the material. As the war ended, the product was improved when competition started, quality accelerated significantly. Fourteen year after production started, the first pilot-plant was built, since the continuous process was difficult to study in small scale. A few more years later, three polyethylene pilot-plants were running day... 

The work reported here is part of a continuing program on the emulsion polymerization of styrene in a tubular reactor. It is now evident that the reactor construction is of primary importance in avoiding the problem of reactor plugging. The plugging is associated with a wall effect so that both the reactor dimensions and the nature of the wall surface are important. 

In contrast to the Pt catalysts discussed above, Ni based catalysts (i.e., also when supported on ZrO usually form coke at such a rapid rate that most fixed bed reactors are completely blocked after a few minutes time on stream (see Fig. 8) [16], The coke formed with the Ni catalysts is filamentous. The Ni particle remaining at the tip of the filament hardly deactivates as the coke formed on its surface seems to be transported through the metal particle into the carbon fibre, but the drastic increase in volume causes reactor plugging and prevents use of the still active catalyst (see Fig. 8). The TEM photographs indicate that the carbon filaments have similar diameters to those of the Ni particles. 

For continuous reactors, plug-flow designs require smaller volumes and hence smaller inventories than mixed-flow designs for the same conversion, as discussed in Chapter 5. 

It is well known that during liquefaction there is always some amount of material which appears as insoluble, residual solids (65,71). These materials are composed of mixtures of coal-related minerals, unreacted (or partially reacted) macerals and a diverse range of solids that are formed during processing. Practical experience obtained in liquefaction pilot plant operations has frequently shown that these materials are not completely eluted out of reaction vessels. Thus, there is a net accumulation of solids within vessels and fluid transfer lines in the form of agglomerated masses and wall deposits. These materials are often referred to as reactor solids. It is important to understand the phenomena involved in reactor solids retention for several reasons. Firstly, they can be detrimental to the successful operation of a plant because extensive accumulation can lead to reduced conversion, enhanced abrasion rates, poor heat transfer and, in severe cases, reactor plugging. Secondly, some retention of minerals, especially pyrrhotites, may be desirable because of their potential catalytic activity. 

In membrane reactors plugging is an ever-present problem because any membrane is also a good filter. In bubble, drop, emulsion, and trickle bed reactors surface-active agents can cause formidable problems with foaming. Traces of soap in liquid feeds are difficult to avoid, and their result is similar to too much detergent in a washing machine. 

Table 6.1 Systems that are most often simulated by complete mix reactors, plug flow reactors, etc.

Complete mix reactors Plug flow or complete mix reactors in series... 

In the following sections, the solutions of the models as well as examples will be presented for the case of trickle-bed reactors and packed bubble bed reactors. Plug flow and fust-order reaction will be assumed in order to present analytical solutions. Furthermore, the expansion factor is considered to be zero unless otherwise stated. Some solutions for other kinetics will be also given. The reactant A is gas and the B is liquid unless otherwise stated. 

The treatment of PAH-contaminated soil in a reactor environment is basically limited to the use of soil slurry reactors. Conversely, many different bioreactor designs exist for the treatment of water contaminated with PAHs. As reviewed by Grady (1989) and Grady Lim (1980), these include fixed film reactors, plug flow reactors, and a variety of gas-phase systems, to name a few. Given the depth and magnitude of such a topic, for the purposes of this review discussions will be limited to a generic overview of reactor applications for PAH bioremediation. 

Tube reactors Plug-flow for liquid Plug-flow for gas 0.01-2 10-500... 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

A number of innovative polymerization reactors using loop reactors, plug-flow and static mixer reactors, and continuous stirred-tank reactors have been reported. For example, Wilkinson and Geddes (15) describe a 50-liter reactor that has the same capacity as a 5000-gallon batch reactor. Extruders, thin-film evaporators, and other devices designed to provide intense mixing for viscous or unstable materials have also been used as reactors. 

When processing in a set-up with a short, curved flow element (0.3 m long bendt Teflon tube of 0.3 mm inner diameter) between the funnel and straight tubular reactor plugging occurred after only 30 s (see Table 1.10) [53], Hence the insertion of curved flow passages is detrimental, even for only short paths. 

During the laboratory-scale testing of pollutant oxidation under SCWO, the main interference would come from reactor corrosion and reactor plugging. These issues are discussed in detail in the Scale-Up Studies section. 

The accumulation of vanadium as a function of time for catalysts A, B, C and D is shown in Fig. 1. For catalysts B and C, runs were suspended before the final condition (420°C) was reached. The first was taken to regeneration and for the second, an operational problem of reactor plugging ocurred at 410°C. 

Due to its complexity (conversion and separation in the same unit) and because this system has been most widely studied experimentally, CMRs for dehydrogenation (or more generally for equilibrium-restricted reactions) have been the subject of modeling approaches [6, 54-59]. The modeling of CMRs requires mass and energy balances in both feed and permeate sides of the reactor (plug-flow behavior is always assumed) and appropriate boundary conditions. Generally these models fit the experimental data well. 

RP Reactor plugging, FE Feed finished, PP Pump valve plugging... 

A problem encountered when utilizing the AA-GMA pair was that there is a slight reactivity of the carboxylic acid and epoxide functional groups during the continuous bulk polymerization which led to gels and reactor plugging[14]. The success of this approach requires that the functional groups be totally inert inside the polymerization reactor. 

Membrane-enclosed packed-bed reactor. Plug-flow regime at both membrane sides. Isothermal system. No axial or radial diffusion. Mass transfer rate constant all over the membrane. Negligible pressure drop at the catalyst side. 

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