Effect of design on the stability and control of fixed bed catalytic reactors with heat feedback. 1. Concepts

Abstract

1Frohning, C. D.; Kolbel, H.; Ralek, M.; Rottig, W.; Schnur, F.; Schulz, H. I n "Chemierohstoffe aus Kohle"; Falbe, J., Ed.; 0. Thieme Verlag: Stuttgart, Huff, G. A. Chem. Eng. Sci. 198la, 36, 790. Satterfiekl, C. N.; Huff, G. A. Ind. Eng. Chem. Process Des. Dev. to be published, 1981b. Schlesinger, M.; Benson, H.; Murphy, E.; Storch, H. H. Ind. Eng. Chem. 1954, 46, 1322. Schumpe. A.; Serpemen, Y.; Deckwer, W.-D. Ger. Chem. Eng. 1979, 2 , 234, 267. Shah, Y. T.; Deckwer, W.-D. Chapter 6 in "Scaleup in the Chemical Process Industries"; Kabel, R.; Bisio, A., Ed.; Wiley: New York, to be published, 1982. Suganuma, T.; Yamanishi, T. Kagaku Kogaku 1966, 30, 1136. Szeri, A.; Shah, Y. T.; Madgavkar, A. Chem. Eng. Sci. 1976, 31, 225. Tareeff, M. ColloidJ. USSR 1940, 6 , 545; cited in Chem. Eng. 1957, 64(3), 273. Villadsen, J. V.; Michelsen, M. L. "Solution of Differential Equation Models by Polymonlal Approximation"; Prentice-Hall: Englewood Cliffs, N.J., 1978. Zaidi, A.; Louisi, A.; Ralek, M.; Deckwer, W.-D. Ger. Chem. Eng. 1979, 2 , 94.This paper discusses the linear and nonlinear stability analysis of a fixed bed catalytic reactor with heat exchange between the feed and product streams, with special emphasis on cases which are open loop unstable. Our approach, which uses classical frequency response techniques, contains the implicit assumption that the designer should evaluate the effect of the overall design on stability. The paper shows how at this stage, with only limited information about the process, he can determine the minimum information required for this evaluation. The method outlined clearly pinpoints where the stability problems exist because the effects of each unit operation on the system stability are evaluated independently.This work reports a kinetic study on the gasiflcation of Brazilian mineral coal with steam using a thermobalance.The coal is a high ash content (>50 wt %) subbituminous, run of mine coal (Charqueadas). Isothermal runs were made at temperatures between 800 and 1000 O C and at atmospheric pressure, using -14 +20 mesh Tyler size particles. The coal was devolatilized before the gasification. Initially, the influence of the particle size of coal and the flow of steam were studied in order to determine if diffusive effects are important. For certain conditions these effects are negligible and chemical reaction is the rate controlling step. The experimental results are well descrlbed by the unreacted core model above 850 O C and by the continuous model below this temperature. The gaseous products were determined at different times and temperatures and contained essentially H, , CO, and CO, .Comparison of the present results with other data published shows that this coal is highly reactive.

Analysis of instability in an industrial ammonia reactor

“…However, eventually the temperature wave moves through the reactor, and the outlet temperature eventually increases. Such inverse response characteristics are well known for chemical reactors (e.g., Silverstein and Shinnar, 1982).…”

“…Fixed-bed reactors are discussed extensively in the survey of Schmitz (1975), and also in Ray (1972), Gilles (1976), Eigenberger (19851, and J4rgensen (1986). Silverstein and Shinnar (1982) discuss the stability of heat-integrated fixed-bed reactor. Other works on dynamics and control of fixed-bed reactors include Foss (1966, 1968), Vakil et al (19731, Wallmann andFoss (1979, 19811, Foss et al (19801, Gusciora andFoss (19891, andEigenberger andSchuler (1989).…”

Design considerations for tubular reactors with highly exothermic reactions

“…While it is possible to operate a single CSTR by feedback stabilization, this is not advisable for a multitube reactor. The problem of designing a system such that it is robust and easy to control vs. relying on advanced control methods for stabilization is one that often appears in practice (Shinnar, 1986;Silverstein and Shinnar, 1982). Regretfully, very often the problem of the impact of design on controllability is not sufficiently recognized both in practice and in the literature.…”

Tracer experiments and RTD's in heterogeneous reactor analysis and design

“…Exotic dynamics found in a pilot reactor that derive from this coupling may disappear in a large reactor which has higher flow rates. Silverstein and Shinnar (1982) discuss how one can test for this with an inert tracer having fluid phase and macropore diffusion properties similar to those of the reactants.…”