Design of Ammonia Synthesis Reactor

Converter Design. Design of ammonia synthesis reactors is not just the calculation of the required catalyst volume other parameters have to be considered, too, and for... 

Fundamental data for design of ammonia synthesis reactor... 

Figure 8. Designs of ammonia synthesis converters (a) Principle of the autothermal ammonia synthesis reactor (b) Radial flow converter with capacities of 1,800 tpd (c) Horizontal three-bed converter and detail of the catalyst cartridge. (Source Walas, M. S., Chemical Process Equipment, Selection and Design, Butterworth Series in Chemical Engineering, 1988.)...

Knowledge of the reaction kinetics is important for designing industrial ammonia synthesis reactors, for determining the optimal operating conditions, and for computer control of ammonia plants. This means predicting the technical dependence on operating variables of the rate of formation of ammonia in an integral catalyst volume element of a converter. 

Figure 17.21. Some recent designs of ammonia synthesis converters, (a) Principle of the autothermal ammonia synthesis reactor. Flow is downwards along the wall to keep it cool, up through tubes imbedded in the catalyst, down through the catalyst, through the effluent-influent exchanger and out. (b) Radial flow converter with capacities to l tons/day Haldor Topsoe Co., Hellerup, Denmark), (c) Horizontal three-bed converter and detail of the catalyst cartridge. Without the exchanger the dimensions are 8 x 85 ft, pressure 170 atm, capacity to 2000 tons/day (Pullman Kellogg), (d) Vessel sketch, typical temperature profile and typical data of the ICI quench-type converter. The process gas follows a path like that of part (a) of this figure. Quench is supplied at two points (Imperial Chemical Industries).

In mathematical models for design, simulation, and/or optimization of ammonia synthesis reactors, the normal principles for reactor calculations are, of course, applied. Reference is made to [463-465]. A general purpose computer... 

Ammonia synthesis reactor. The shaded area contains the catalyst. [Adapted, with permission, from Murase et al., Optimal Thermal Design of an Auto-thermal Ammonia Synthesis Reactor, Ind Eng Chem Process Des Dev 9 504 (1970). Copyright, American Chemical Society.]... 

Murase, Akira, Roberts, Howard L., and Converse, Alvin O., Optimal thermal design of an autothermal ammonia synthesis reactor, l EC Proc. Des. Dev. 9(4), 503 (1970). 

It will be convenient to divide this section more formally than the others, according to the following scheme. Under Sec. 9.7.1 we discuss the genera form of the equations when the wall temperature is constant and illustrate this by considering an endothermic cracking reaction. Under Sec. 9,7.2 we shall consider cocurrent and countercurrent cooled reactors and use the ammonia synthesis reactor as an illustration. These correspond to the two subcases of the third type of design problem mentioned in Sec. 9.5. 

One of the most innovative designs of the ammonia synthesis reactor is from the Haldor-Topspe company. We give in Figure 0.2 the flow cross-sectional view of one of the earlier designs of the so-called radial flow reactor (US Patent 3 372 988, filed September 18, 1964) and ask you to figure out the answers to the following questions ... 

The catalysts for ammonia synthesis are porous particles with weenie and interlaced micro-pores. The active sites playing the role of surface catalysis are distributed on the internal surfaces formed by these micro-pores. The internal surface area of ammonia synthesis after reduction is about 10m -g -15m -g , and the external surface area is only 0.1 m g F So, the surface area playing the role of surface catalysis mainly is internal surface. The equivalent diameter of catalyst particles used in industrial ammonia reactor is between 1.5 mm and 13 mm, and the inhibition effect of diflfusion should be considered in real ammonia synthesis rates. When designing industrial reactor, the resistance of external diffusion can be neglected by increasing contact between gas flow and external sm-face of catalysts. The catalytic reaction processes for ammonia synthesis pertain to considerable internal diffusion process in most cases. 

Dybkjaer, I. Design of Ammonia and Methanol Synthesis Reactors. This course. 

Let us - after these rather extensive introductory remarks -turn to the specific problems encountered in design of ammonia and methanol synthesis reactors. We shall not endeavour to treat all of the above mentioned aspects, but mainly concentrate on the initial steps and on the basis of this illustrate how the various principal types of reactors can be applied in these syntheses. We shall discuss the reaction kinetics for the reactions and the calculation of reactor performance and some of the problems encountered in the calculation of reactor performance. The mathematical procedure used for the computer calculations is discussed by Christiansen and Jarvan W in a separate presentation in this volume. 

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