Reactor steady-flow

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Glasser, D., Hildebrandt, D., and Crowe, C. (1987). A geometric approach to steady flow reactors The attainable region and optimization in concentration space. Ind. Eng. Chem. Res., 26, 1803-1810. 

There is a steady flow of publication which contributes theories and information to help in the choice of catalysts, the improvement of their selectivity, or the improvement in reactor utilization through increase in... 

The axial-flow propellers have been operated with a steady flow of 10-15 m3/min/m3 reactor volume. 

Discussion. It is apparent from Table II and Figure 3 that even though the reactor has been subjected to very severe oscillatory conditions where the frequency of oscillation was low with respect to the hold-up time and the amplitudes of the functions large, the MWD s of the resulting polymers differ very little from those produced in the steady-flow steady-state. 

Several age-distribution functions may be used (Danckwerts, 1953), but they are all interrelated. Some are residence-time distributions and some are not. In the discussion to follow in this section and in Section 13.4, we assume steady-flow of a Newtonian, single-phase fluid of constant density through a vessel without chemical reaction. Ultimately, we are interested in the effect of a spread of residence times on the performance of a chemical reactor, but we concentrate on the characterization of flow here. 

Consider the startup of a CSTR for the liquid-phase reaction A products. The reactor is initially filled with feed when steady flow of feed (q) is begun. Determine the time (t)... 

Although there is steady flow of feed, the reactor is in unsteady-state operation during the time t, since the outlet concentration cA (and hence fA) is continuously changing (cA decreasing from cAo, and fA increasing from 0). 

FlameMaster v3.3 A C+ + Computer Program for OD Combustion and ID Laminar Flame Calculations. FlameMaster was developed by H. Pitsch. The code includes homogeneous reactor or plug flow reactors, steady counter-flow diffusion flames with potential flow or plug flow boundary conditions, freely propagating premixed flames, and the steady and unsteady flamelet equations. More information can be obtained from http //www.stanford.edu/group/pitsch/Downloads.htm. 

Reactant A (A R, C o = 26 mol/m ) passes in steady flow through four equal-size mixed flow reactors in series (r otai = 2 min). When steady state is achieved the concentration of A is found to be 11, 5, 2, 1 mol/m in the four units. For this reaction, what must be so as to reduce from... 

Consider a steady-flow chemical reactor of length L through which fluid is flowing at a constant velocity u, and in which material is mixing axially with a dispersion coefficient D. Let an nth-order reaction be occurring. 

The experimental strategy in studying catalytic kinetics usually involves measuring the extent of conversion of gas passing in steady flow through a batch of solids. Any flow pattern can be used, as long as the pattern selected is known if it is not known then the kinetics cannot be found. A batch reactor can also be used. In turn we discuss the following experimental devices ... 

Batch-Solids, Mixed Changing Flow of Fluid (to keep fixed). For steady flow in a mixed reactor we have found... 

Solids of unchanging size, R = 0.3 mm, are reacted with gas in a steady flow bench scale fluidized reactor with the following result. 

The chemical reactor is the unif in which chemical reactions occur. Reactors can be operated in batch (no mass flow into or out of the reactor) or flow modes. Flow reactors operate between hmits of completely unmixed contents (the plug-flow tubular reactor or PFTR) and completely mixed contents (the continuous stirred tank reactor or CSTR). A flow reactor may be operated in steady state (no variables vary with time) or transient modes. The properties of continuous flow reactors wiU be the main subject of this course, and an alternate title of this book could be Continuous Chemical Reactors. The next two chapters will deal with the characteristics of these reactors operated isothermaUy. We can categorize chemical reactors as shown in Figure 2-8. 

The RDT or p(t) is the probability of a molecule residing in the reactor for a time t. This i can be found from a tracer experiment in which we inject a tracer of a nonreacting species (perhaps ink) with concentration C,(t) into a reactor with fluid flowing at a steady flow rate, and we measure its concentration C(t) (perhaps from the absorbance of the ink) as it flows out of the reactor. The flow could be pure solvent, or a reaction could be taking place as long as the tracer does not participate in the reaction. The concentration of the tracer leaving the reactor versus time gives p t) with suitable normalization. 

Next consider the response of a PFTR with steady flow to a pulse injected at f = 0. Wc could obtain this by solving the transient PFTR equation written earher in this chapter, but we can see the solution simply by following the pulse down the reactor. (This is identical to the transformation we made in transforrning the batch reactor equations to the PFTR equations.) The S(0) pulse moves without broadening because we assumed perfect plug flow, so at position z the pulse passes at time z/u and the pulse exits the reactor at time T = L/u. Thus for a perfect PFTR the RTD is given by... 

In addition to the high-pressure assembly, the modified system incorporates a new real-time data collection system coupled with a PC based computer. Experimental parameters, such as the valve firing sequence and the reactor temperature-control program, can be set from the computer. Reactants are introduced through two high-spe pulse valves or two continuous feed valves that are fed by mass flow controllers. In high-speed transient response experiments, the QMS is set at a particular mass value and the intensity variation as a function of time is obtained. In steady-flow experiments. 

Chemical reactions occur homogeneously within the reactor, with the extent of reaction governed by the temperature and composition as well as by the residence time. In steady flow the reacted gases exit the reactor with the same mass-flow rate as they entered. The exit gas state is assumed to be the same as the reactor interior, given as T and Yk ... 

R. Jackson and D. Glasser. A General mixing model for steady flow chemical reactors. Chem. Eng. Commun., 42 17,1985. 

If we operate two one-liter CSTRs in series at steady state, what will be the concentration of substrate leaving the second reactor The flow rate is 0.5 L/min. The inlet substrate concentration is 50 g/L and the enzyme concentration in the two reactors is maintained at the same value all of the time. Is the two-reactor system more efficient than one reactor whose volume is equal to the sum of the two reactors ... 

Figure 2.21 Temperature and species concentration profiles in a reverse-flow reactor (a) flow direction is left to right (b) flow is reversed to be from right to left (c) periodic quasi-steady state [47] (by courtesy of ACS).

Fig. 11.8 Schematic representation of continuous flow reactors of length L, characteristic height H, and steady flow rate, Q.

It is possible to determine the value of N that gives the best fit to the response curve of the actual reactor as described below. Consider a steady flow u m3/sec of fluid in and out of the first reactor volume... 

Consider a steady flow of reactant A to products at constant density through an element of radius r, width 8r, and height 81 in a tubular reactor at isothermal condition. Suppose that radial and axial mass transfer is expressed by Fick s law, with (D and (De)r as effective diffusivities. The rate at which A reacts is (-rA), mol/m3 sec. A material balance on a tubular element of radii r and r + 8r and height 81 is carried out from... 

In the reactor/separation/recycle system, the steady-state values of the reactor-inlet flow rate F, are the intersections of this curve with the horizontal fine representing the net amount of reactant fed in the process. This is given, in a dimensionless form, by F0(l -z4)/(cokV) = (1 — z4)/Da. 

Let us consider a small, positive deviation of the reactor-inlet flow rate, from the steady state B. At the right of point B, the amount of reactant fed in the process is larger than the amount of reactant consumed. Reactant accumulation occurs, leading to a further increase of the recycle and reactor-inlet flow rates hence the steady state B is unstable. This is independent of the dynamics, because the proof is based only on steady-state considerations. 

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