Reactor with two inlets

The case of reactors with two inlets was considered more than ten years ago by Treleaven and Tobgy (60). The BPT model allows an interesting representation of the flow in these reactors (56)(fi-gure 2). This will be useful when micromixing phenomena will be dealt with (next Section). 

Figure 10, Equivalence between the C-D model and the IEM model. Reactor with two inlets having different RTDs equivalent to that of 2 and 6 tanks in series, respectively. Unmixed feedstreams of A and B (equal flowrates), second-order reaction, =8, ...

In the case of a reactor with two inlets, (3-15) still holds in each stream but the mean value C.(X) at a given life expectancy must comprise contributions from both feedstreams 1 and 2. 

Reactor with two inlets having different RTDs (2 and 6 tanks in series). Second order reaction Cgo 8 Aoj Ao 0.5,... 

The classical CRE model for a perfectly macromixed reactor is the continuous stirred tank reactor (CSTR). Thus, to fix our ideas, let us consider a stirred tank with two inlet streams and one outlet stream. The CFD model for this system would compute the flow field inside of the stirred tank given the inlet flow velocities and concentrations, the geometry of the reactor (including baffles and impellers), and the angular velocity of the stirrer. For liquid-phase flow with uniform density, the CFD model for the flow field can be developed independently from the mixing model. For simplicity, we will consider this case. Nevertheless, the SGS models are easily extendable to flows with variable density. 

Catalytic reactions were carried out in the isothermal glass batch reactor installed in a shaker and connected to a gasometrical burette. The reactor was equipped with two inlets one for catalyst, solvent, and substrate, and one for hydrogen feeding. The total volume of fluid phase is 32 mL. Hydrogen consumption was controlled by... 

Figure 7. Top, extension of Spencer and Leshaw s model to the case of a reactor having two inlets (unmixed feedstreams). In the general case, there are four environments (two entering, two leaving). Bottom, when the segregation function only depends on residence time, this representation is also valid (78). Three environment model with three parameters R s = exp(-R t ), ...

Figure 2 Flow pattern inside the reactor, (a) one inlet, (b) two inlets. Figure clearly shows use of two inlets can eliminate presence of dead volume and bypassing of fluids that is present in reactor with one inlet (Chen et al., 2001).

The first reactor has two inlets, vCo mol s of reactant A are fed to the first one from the outside and viCjmol s enter the second one from reactor 2. For substance A, the outlet matter flow of reactor 1 and the inlet matter flow of reactor 2 are equal to (v + vi)Ci mol s. The outlet matter flow of reactor 2 is (v + vi)C2mol s and next is divided between two paths. Its part V]C2mol s returns into reactor 1 and VC2 mol s is fed to the inlet of reactor 3. vCs mol L of substance A is eventually withdrawn from the system. In connection with the above and taking into account relationships (2.6) and (2.7), we can write the equations describing the time-dependent loss of the reactant concentration in the each reactor... 

Fig. 30. Conversions of two reactors with the same kinetics, residence times, and inlet concentrations.

The terms space time and space velocity are antiques of petroleum refining, but have some utility in this example. The space time is defined as F/2, , which is what t would be if the fluid remained at its inlet density. The space time in a tubular reactor with constant cross section is [L/m, ]. The space velocity is the inverse of the space time. The mean residence time, F, is VpjiQp) where p is the average density and pQ is a constant (because the mass flow is constant) that can be evaluated at any point in the reactor. The mean residence time ranges from the space time to two-thirds the space time in a gas-phase tubular reactor when the gas obeys the ideal gas law. 

The two BCs of the TAP reactor model (1) the reactor inlet BC of the idealization of the pulse input to tiie delta function and (2) the assumption of an infinitely large pumping speed at the reactor outlet BC, are discussed. Gleaves et al. [1] first gave a TAP reactor model for extracting rate parameters, which was extended by Zou et al. [6] and Constales et al. [7]. The reactor equation used here is an equivalent form fi om Wang et al. [8] that is written to be also applicable to reactors with a variable cross-sectional area and diffusivity. The reactor model is based on Knudsen flow in a tube, and the reactor equation is the diffusion equation ... 

The silicon chip reactor was compressed between a top plate, for direct observation of the flows, gaskets with punched holes and a base plate with all fluid connections [13,14]. Thermocouples inserted between the two plates were located next to the micro reactor. A third inlet served for reaction quenching by introducing an inert gas such as nitrogen. Generally, heat removal is facilitated by the special reactor arrangement acting as a heat sink. 

There are circumstances when a complex process may involve two competing (i.e., opposing) dynamic effects that have different time constants. One example is the increase in inlet temperature to a tubular catalytic reactor with exothermic kinetics. The initial effect is that the exit temperature will momentarily decrease as increased conversion near the entrance region depletes reactants at the distal, exit end. Given time, however, higher reaction rates lead to a higher exit temperature. 

If AW AW the process of finding a linear-mixture basis can be tedious. Fortunately, however, in practical applications Nm is usually not greater than 2 or 3, and thus it is rarely necessary to search for more than one or two combinations of linearly independent columns for each reference vector. In the rare cases where A m > 3, the linear mixtures are often easy to identify. For example, in a tubular reactor with multiple side-injection streams, the side streams might all have the same inlet concentrations so that c(2) = = c(iVin). The stationary flow calculation would then require only AW = 1 mixture-fraction components to describe mixing between inlet 1 and the Nm — I side streams. In summary, as illustrated in Fig. 5.7, a turbulent reacting flow for which a linear-mixture basis exists can be completely described in terms of a transformed composition vector ipm( defined by... 

Note that, due to the choice of c(1) as the reference vector, the mixture-fraction vector l (third and fourth components of y> ) is null. The first component of the mixture-fraction vector thus describes mixing between the initial contents of the reactor and the two inlet streams, and the second component describes mixing with the second inlet stream. For a stationary flow (0) -> 0, and only one mixture-fraction component ( 2) will be required to describe the flow. Note, however, that if c(0) had been chosen as the reference vector, a similar reduction would not have occurred. As expected, the inlet and initial values of the two reaction-progress variables are null. 

The reactor consisted of two inlets with a serpentine delay section and an additional inlet to perform the addition of the reagent in the second step. Channels were of 150 pm width and 50 pm depth. The amine and sodium nitrite solutions were injected separately at a rate of 3.5 pl/min, and (3-naphtol was added via the third inlet at a flow rate of 7 pl/min (Scheme 31). 

There are many different physical scenarios to be considered. In the first category, we find scenarios that result from gas compression, such as by liquid transfer into a closed reactor or gas inlet from a line connected to the reactor. With such scenarios, two-phase flow is unlikely to occur. Other common physical scenarios are linked to unwanted heating of the reactor contents, either by fire or by inadvertently heating of the reactor by the heating system. In this case, two-phase flow may occur. 

The upper left window shown in Figure 6.41 is the Exploring window. Clicking Flowsheet in the list produces the Contents of Flowsheet window, in which there is an icon with two parallel blue bars, which is labeled Flowsheet. Double-clicking this icon opens the Text Editor shown at the top of Figure 6.42. The equation shown is entered to specify that the PV signal of the temperature controller TCpeak is the temperature T(6) from Lump 6 of the 30-lump reactor model (2 m from the inlet) ... 

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