On the dynamic behavior of the catalytic fixed-bed reactor in the region of multiple steady states—II. The influence of the boundary conditions in the catalyst phase

1972 ◽  
Vol 27 (11) ◽  
pp. 1917-1924 ◽  
Author(s):  
G. Eigenberger
Keyword(s):  
Boundary Conditions ◽  
Dynamic Behavior ◽  
Fixed Bed ◽  
Steady States ◽  
Fixed Bed Reactor ◽  
Multiple Steady States

scholarly journals Ammonia synthesis fundamentals for a model-based HAZOP study

2015 ◽  
Vol 8 (1) ◽  
pp. 5-10 ◽  
Author(s):  
Ján Janošovský ◽  
Juraj Labovský ◽  
Ľudovít Jelemenský
Keyword(s):  
Process Model ◽  
Ammonia Synthesis ◽  
Fixed Bed ◽  
Steady States ◽  
Hazard Identification ◽  
Fixed Bed Reactor ◽  
Multiple Steady States ◽  
Nonlinear Behaviour ◽  
Model Based ◽  
Operation Conditions

Abstract Hazard and operability (HAZOP) analysis is a highly disciplined process hazard analysis (PHA) technique based on the exploration of the effects of process variables deviations. Inconveniences of a conventional HAZOP study are its time-consuming character and high cost. The principal objective of this paper is to present a new methodology for hazard identification of a selected chemical production process. Model-based HAZOP study is a very robust tool for predicting a systems response to deviations from design or operation conditions. An approach based on the mathematical modelling of a process can help to identify sources of hazard that could be overlooked by conventional PHA techniques. A case study focused on the multiple steady states phenomenon in an ammonia synthesis reactor is presented. The process simulation was performed using the Aspen HYSYS v8.4 process modelling environment. Nonlinear behaviour of the investigated fixed-bed reactor system was confirmed by an accident in an industrial ammonia synthesis reactor. The analysed system exhibited the feed temperature and pressure dependence of various operation parameters. This fact indicates the presence of multiple steady states. From the safety analysis point of view, switching between steady states can lead to process hazards.

scholarly journals Dynamic Simulation of Adiabatic Catalytic Fixed-Bed Tubular Reactors: A Simple Approximate Modeling Approach

2014 ◽  
Vol 14 (1) ◽  
pp. 25
Author(s):  
Wiwut Tanthapanichakoon ◽  
Shinichi Koda ◽  
Burin Khemthong
Keyword(s):  
Dynamic Model ◽  
Dynamic Behavior ◽  
Dynamic Simulation ◽  
Flow Rate ◽  
Fixed Bed ◽  
Axial Dispersion ◽  
Fixed Bed Reactor ◽  
Inlet Temperature ◽  
Acetylene Hydrogenation ◽  
Tubular Reactors

Fixed-bed tubular reactors are used widely in chemical process industries, for example, selective hydrogenation of acetylene to ethylene in a naphtha cracking plant. A dynamic model is required when the effect of large fluctuations with time in influent stream (temperature, pressure, flow rate, and/or composition) on the reactor performance is to be investigated or automatically controlled. To predict approximate dynamic behavior of adiabatic selective acetylene hydrogenation reactors, we proposed a simple 1-dimensional model based on residence time distribution (RTD) effect to represent the cases of plug flow without/with axial dispersion. By modeling the nonideal flow regimes as a number of CSTRs (completely stirred tank reactors) in series to give not only equivalent RTD effect but also theoretically the same dynamic behavior in the case of isothermal first-order reactions, the obtained simple dynamic model consists of a set of nonlinear ODEs (ordinary differential equations), which can simultaneously be integrated using Excel VBA (Visual BASIC Applications) and 4th-order Runge-Kutta algorithm. The effects of reactor inlet temperature, axial dispersion, and flow rate deviation on the dynamic behavior of the system were investigated. In addition, comparison of the simulated effects of flow rate deviation was made between two industrial-size reactors.Keywords: Dynamic simulation, 1-D model, Adiabatic reactor, Acetylene hydrogenation, Fixed-bed reactor, Axial dispersion effect

scholarly journals Multiple Steady States in the Photocatalytic Reactor for Colored Compounds Degradation

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3804
Author(s):  
Jakub Szyman
Keyword(s):  
Limit Point ◽  
Light Absorption ◽  
Reaction Rate ◽  
Fixed Bed ◽  
Steady States ◽  
Multiple Steady States ◽  
Photocatalytic Reactor ◽  
Inlet Stream ◽  
Ideal Mixing ◽  
Photocatalytic Reactors

The paper reports the occurrence of multiple steady-state zones in most of the constructions of fixed-bed photocatalytic reactors. Such a phenomenon has not been ever observed in a field of photocatalytic reactors. The simulation has been provided for a common case in a photocatalysis—the degradation of colored compounds. The mathematical model of the photocatalytic reactor with immobilized bed has been stated by a simple ideal mixing model (analogous to the CSTR model). The solution has been continued by the two parameters—the Damköhler number and the absorption coefficient related to the inlet stream concentration. Some branches of steady states include the limit point. The performed two-parametric continuation of the limit point showed the cusp bifurcation point. Besides the numerical simulation, the physical explanation of the observed phenomenon has been provided; the multiple steady-states occurrence is controlled by light absorption–reaction rate junction. When the reaction rate is limited by the light absorption, we can say that a light barrier occurs. The dynamical simulations show that when the process is operated in a field of multiple steady states, the overall reactor efficiency is related to the reactor set-up mode.

MULTIPLE STEADY STATES OF ADIABATIC FIXED-BED REACTORS

1993 ◽  
Vol 126 (1) ◽  
pp. 155-177 ◽  
Author(s):  
RICHARD C. DOUGHERTY ◽  
JOHN R. THYGESON ◽  
RAYMOND HU
Keyword(s):  
Fixed Bed ◽  
Steady States ◽  
Multiple Steady States ◽  
Fixed Bed Reactors
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