Analysis of instability in an industrial ammonia reactor

Morud, John; Skogestad, Sigurd

doi:10.1002/aic.690440414

Cited by 122 publications

(108 citation statements)

References 18 publications

(7 reference statements)

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“…1 which is a simplified version of an actual industrial plant. The reactor configuration is from Morud and Skogestad (1998). The stream table results corresponding to the nominally optimal operating point computed using Aspen TM are given in Table 1.…”

Section: The Ammonia Synthesis Processmentioning

confidence: 99%

Control structure design for the ammonia synthesis process

Araújo

Skogestad

2008

Computers & Chemical Engineering

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110

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a b s t r a c tThis paper discusses the application of the plantwide control design procedure of Skogestad [Skogestad, S. (2004a). Control structure design for complete chemical plants. Computers and Chemical Engineering, 28,[219][220][221][222][223][224][225][226][227][228][229][230][231][232][233][234] to the ammonia synthesis process. Three modes of operation are considered: (I) given feed rate, (IIa) maximum throughput, and (IIb) "optimized" throughput. Two control structures, one for Mode I and another for Mode IIb, are proposed. In Mode I, it is proposed to keep constant purge rate and compressor powers. There is no bottleneck in the process, and thus there is no Mode IIa of operation. In Mode IIb, the compressors are at their maximum capacity and it is proposed to adjust the feed rate such that the inert concentration is constant. The final control structures result in good dynamic performance.

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Section: The Ammonia Synthesis Processmentioning

confidence: 99%

Control structure design for the ammonia synthesis process

Araújo

Skogestad

2008

Computers & Chemical Engineering

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110

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“…5 While some explanations have been proposed, 5 it may also be worthwhile to pursue a study of the hydrodynamic fluctuations in reactors of this kind, so as to learn about the relation between hydrodynamic fluctuations and Hopf bifurcations. This work is a first attempt in this direction, by deriving expressions for the concentration fluctuations in a chemical reaction in a temperature gradient.…”

Section: Introductionmentioning

confidence: 99%

“…6 Despite important efforts, this is still not always understood, however. 5 Nonequilibrium molecular simulations are useful for studies of transport properties, and this gives a second perspective to our analysis. Transport coefficients can be found from boundary-driven nonequilibrium molecular simulations or from equilibrium fluctuations via Green-Kubo relations.…”

Section: Introductionmentioning

confidence: 99%

Concentration fluctuations in nonisothermal reaction-diffusion systems

Zárate

Sengers

Bedeaux

et al. 2007

The Journal of Chemical Physics

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In this paper a simple reaction-diffusion system, namely a binary fluid mixture with an association-dissociation reaction between the two components, is considered. Fluctuations at hydrodynamic spatiotemporal scales when a temperature gradient is present in this chemically reacting system are studied. First, fluctuating hydrodynamics when the system is in global equilibrium ͑isothermal͒ is reviewed. Comparing the two cases, an enhancement of the intensity of concentration fluctuations in the presence of a temperature gradient is predicted. The nonequilibrium concentration fluctuations are spatially long ranged, with an intensity depending on the wave number q. The intensity exhibits a crossover from a ϰq −4 to a ϰq −2 behavior depending on whether the corresponding wavelength is smaller or larger than the penetration depth of the reacting mixture. This opens a possibility to distinguish between diffusion-or activation-controlled regimes of the reaction by measuring these fluctuations. In addition, the possible observation of these fluctuations in nonequilibrium molecular dynamics simulations is considered.

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“…2 For heat integration reasons, two feed-effluent heat exchangers (FEHE) are used. SO 2 conversion is further improved and tail gas emissions are reduced through an intermediate SO 3 absorption step. The absorption of SO x is finalized in the second absorber.…”

Section: Process Descriptionmentioning

confidence: 99%

Optimization studies in sulfuric acid production

Kiss

Bîldea

Verheijen

2006

16th European Symposium on Computer Aided Process Engineering and 9th International Symposium on Process Systems Engineering

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Current legislation imposes tighter restrictions to reduce the impact of process industry on environment. This work presents the dynamic simulation and optimization results for an existing sulfuric acid plant. Operational problems may occur when the process is disturbed due to production rate changes or catalyst deactivation, the non-linear response of the plant leading to sustained oscillations. Since the plant is operated near full capacity, only minor increases in energy production can be achieved. However, the SO x emissions can be significantly reduced by ~40% or more, by optimizing the operating parameters. IntroductionMost sulfuric acid plants are rather old and are facing now additional challenges that aim to maximize the amount of energy produced while reducing the environmental impact. Sulfuric acid is the chemical product manufactured in largest quantity in terms of mass, with about 40 million tons produced annually only in USA. It has a wide range of uses and plays an important role in the production of almost all manufactured goods. Approximately 65% of the H 2 SO 4 produced is used in the production of agricultural fertilizers. This study presents the results of the dynamic simulation and optimization of an existing sulfuric acid plant (PFI -Phosphoric Fertilizers Industry, Greece). Due to the partnership with Process Systems Enterprise Ltd. (PSE), and thanks to its powerful features, gPROMS was selected to perform all simulation tasks.1 The dynamic model developed in this study includes also a graphical user interface (GUI) built in MS Excel, that allows scenario evaluation and operator training. The model has been successfully used for dynamic simulations to evaluate the non-steady-state behavior of the plant and detect changes in product quality, as well as to minimize the total amount of sulfur oxides released in atmosphere. For the major units of the flowsheet, the main equations describing the dynamic model are given using the standard notation. Due to space limitations and model complexity, some modeling details were omitted but they are available upon request. Here we limit to present only the most important results of this study.

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Analysis of instability in an industrial ammonia reactor

Abstract: The starting point for this study was

Cited by 122 publications

References 18 publications

Control structure design for the ammonia synthesis process

Control structure design for the ammonia synthesis process

Concentration fluctuations in nonisothermal reaction-diffusion systems

Optimization studies in sulfuric acid production

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