Reactor parallel passage

Because of their low pressure drop, structured reactors in practice dominate the field for treating tail gases. Figure 2 presents the major types of reactor. The monolithic reactor represents the class of real structured catalytic reactors, whereas the parallel-passage reactor and the lateral-flow reactor are based on a structured arrangement of packings with normal catalyst particles. 

Bead-string reactors represent the limit of parallel-passage reactors They contain single-catalyst-particle subunits. Figure 10 gives a schematic representation (25). 

Figure 9 Example of the TLP reactor parallel-passage reactor (PPR). (Adapted from Ref. 24.)...

The parallel-passage reactor (PPR) and the lateral-flow reactor (LF ) are fixed-bed reactors suitable for the treatment of large volumes of gas at relatively low pressure, as are typical for end-of-pipe cleaning of combustion gases and other stack gases. In such applications, a low pressure drop, e.g., below 10 mbar, is generally required, and this demand can be met by these reactors. In addition, resistance to fouling by dust particles in the gas is important in a number of cases, and the PPR is particularly suitable for such cases. 

The parallel-passage reactor was conceived and patented in the late 1960s [1-3] and saw its first application in the Shell flue gas desulfurization process in the early 1970s [4]. The lateral-flow reactor was conceived as a constructional modification of the PPR, and its first application was for NO removal from flue gas of a gas-fired furnace in the early 1990s [5]. 

Figure 1 Schematic drawing of a parallel-passage reactor.

Figure 3 Schematic drawing of parallel-passage reactor with corrugated screen.

IIL FLOW AND TRANSPORT PHENOMENA IN PARALLEL-PASSAGE REACTORS... 

Figure 5 shows friction factors for different parallel-passage reactor modules tested by Calis et al. [7]. Particulars on the geometry of these modules are given in Table 1. 

Figure 11 Parallel-passage reactor with wavy catalyst slabs.

V. BED-FOULING BEHAVIOR WITH SOLIDS-LADEN CAS STREAMS A. Fouling of the Parallel-Passage Reactor... 

A flow scheme of the unit, which features two parallel-passage reactors operated in the swing mode with automatic sequence control and sulfur dioxide absorption/stripping system to smoothen the fluctuating sulfur dioxide stream, is shown in Fig. 28. Figure 29 shows a photograph of the unit. 

The performance of the PPR for NOx removal by the Shell low-temperature NOx reduction has been investigated extensively [20]. In the first commercial application of the Shell process with parallel-passage reactors, flue gases of six ethylene cracker furnaces at Rheinische Olefin Werke at Wesseling, Germany, are treated in a PPR system with 120-m catalyst in total to reduce the nitrogen oxide emissions to about 40 ppm v. Since its successful start-up in April 1990, the unit has performed according to expectations... 

Figure 30 Photograph of parallel-passage reactors for NO removal at Rheinische Olefin Werke at Wesseling, Germany. (Courtesy Shell Research.)...

In addition to and as an alternative for the existing concepts of low-pressure-drop reactors with structured catalyst packings, discussed in the previous chapters, a new concept is proposed in this chapter the bead-string reactor (BSR). The BSR was invented [1] as an alternative for a parallel-passage reactor (PPR) with extremely thin catalyst beds, viz. beds of only one catalyst-particle-diameter width. 

To assess the feasibility of the BSR as a competitor of the monolithic reactor, the parallel-passage reactor, and the lateral-flow reactor, it is necessary to do case studies in which the performance and price of these reactors are compared, for certain applications. To allow such case studies, two tools are needed (1) mathematical models of the reactors that predict the reactor performance, and (2) an optimization routine that, given a mathematical reactor model and a set of process specifications, finds the optimum reactor configuration. Furthermore, data are needed on costs, safety, availability, etc. In this section, five mathematical models of different complexity for the bead-string reactor (BSR) are presented that can be numerically solved on a personal computer within a few hours down to a few minutes. The implementation of the reactor models in an optimization routine, as well as detailed cost analyses of the reactor, are beyond the scope of this text. 

A transfer of this definition of the cross-flow term to the chemical reactor field implies that the so-called cell reactor [26], consisting of thin, porous catalyst plates mounted in a rack like a filter press, should also be of interest to describe here. The same may apply to the great number of different electrochemical filter-press cell reactors [27]. It may be noted that the cell reactor principle is, however, not valid for the so-called parallel-passage reactor [28,29]. In this case the same fluid flows on both sides of the catalyst plates without any need for communication and exchange between the fluids through the plates. The advantage of this reactor is its being dust-proof, since dust present... 

Another example of a reactor with small pressure drop is the parallel-passage reactor for flue gas treatment, which is shown in Fig. 8.6. 

A monolith or parallel passage reactor contains a solid construction with parallel channels, usually with a cross sectional area of a few square mm each. They can be manufactured either by drilling parallel holes in a solid block, or by a ceramic process starting with a pile of layers that look like corrugated cardboard, made of clay, which is then baked. The latter type is used as a carrier for catalysts, and applied where a low gas pressure drop is essential, e.g., in automobile exhaust gas purification. The mass transfer rates in such monoliths can be calculated easily from the equations describing mass (and heat-) transfer in straight tubes, see eqs. (4.24), (4.28) and (4.29). 

When a very high degree of conversion of a liquid phase reactant is desired, and the catalyst has a high selectivity, one of the varieties of the three phase packed bed will generally be preferable. When the conversion in the liquid and in the gas have to be high, the two-phase monolith (parallel passage reactor) can be considered. 

Exothermic gas/solid reactions involving large quantities of gas, such as carbon oxide methanation with recycle of cold product gas for temperature control, can be carried out in a parallel passage reactor in which the reactants flow through narrow empty ch2in-nels between shallow beds of solid reactant or catalyst. 

A model reactor has been built and studied using the methanation of carbon dioxide as the test reaction. Calculation results of a simple mathematical model agree well with the experimental data except at low temperatures. The conversions obtained are sufficiently promising to warrant further exploration of the parallel passage reactor as a tool in SNG production, the more so because exploratory calculations show that operation at higher pressures results in much improved performance. 

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