Transient reactor

Vapor-phase alkylation of benzene by ethene and propene over HY, LaY, and REHY has been studied in a tubular flow reactor. Transient data were obtained. The observed rate of reaction passes through a maximum with time, which results from build-up of product concentration in the zeolite pores coupled with catalyst deactivation. The rate decay is related to aromatic olefin ratio temperature, and olefin type. The observed rate fits a model involving desorption of product from the zeolite crystallites into the gas phase as a rate-limiting step. The activation energy for the desorption term is 16.5 heal/mole, approximately equivalent to the heat of adsorption of ethylbenzene. For low molecular weight alkylates intracrystalline diffusion limitations do not exist. 

With the introduction of micro reactors, transient reactor operations also became of interest for production owing to their low internal reactor volume and thus fast dynamic behavior. In 1999, liauw et al. presented a periodically changing flow to prevent coke development on the catalyst and to remove inhibitory reactants in a micro channel reactor [88], This work was preceded in 1997 by Emig and Seiler, of the same group, who presented a fixed-bed reactor with periodically reversed flow [89]. In 2001, Rouge et al. [27] reported the catalytic dehydration of isopropanol in a micro reactor. 

Oh, Se H., Hegedus, L. L., Baron, K. and Cavendish, J. C., "Carbon Monoxide Oxidation in An Integral Reactor. Transient Response to Concentration Pulses in the Regime of Isothermal Multiplicities" Proc. ISCRE5 ACS Symposium Series 65,... 

To examine the extent of this problem, an eigenvalue analysis was done for many different reactor transient and steady state time profiles. The range of stiffness ratios (absolute value of ratio of largest to smallest eigenvalue, real parts only) observed for the different reactor zones was as follows ... 

Monitor carbon formation during start-up and reactor transients... 

Figure II.8.b-I One-dimensional heterogeneous model with interfacial gradients. Start up of reactor, transient temperature profiles. AT = temperature increase of gas phase above feed value AT = increase of solid temperature above initial value.

Some features of impurities behaviour in the BN-600 reactor primary circuit are observed during reactor transients, such as increase of temperature and power, shut-down/start-up modes of the loops, reactor scram etc. 

LIQUID METAL FAST REACTOR TRANSIENT DESIGN... 

Sinulation (or calculation) of various reactor transients vith a nulti-node multi-group reactor model to determine the spatial distribution of a localized transient ISiese data should shov the minimum nunber of ion chanbers necessary to adequately protect the reactor Hhese runs would also provide a basis for safety assurances necessary before a production test could be authorized ... 

The AHTR appears to have excellent safety attributes. The combined thermal capacity of the graphite core and the molten salt coolant pool offer a large time buffer to reactor transients. The effective transfer of heat to the reactor vessel increases the effectiveness of the RVACS and DRAGS to remove decay heat, and the excellent fission product retention characteristic of molten salt provides an extra barrier to radioactive releases. The low-pressure, chemically nonreactive coolant also greatly reduces the potential for overpressurization of the reactor containment building and provides an important additional barrier for fission product release. The most important design and safety issue with the AHTR may be the performance and reliability of the thermal blanket system, which must maintain the vessel within an acceptable temperature range. 

The analytical tool used in this investigation is the Los Alamos Pajarito Dynamics Code (PAD). This code employs the coupled neutronic-hydrodynamics method in one dimension, with the neutronics provided by DTF-IV transport calculations. Without prior normalization, the PAD code has reproduced the fission energy releases of various reactor transient experiments to within a factor of 2 (Ref. 2). Furthermore, identifying the kinetic energy calculated by the PAD code With explosive energy, experimental results for this tatter quantity have also been reproduced with about the same accuracy. ... 

RETRAN (REactor TRansient ANalysis) is a best-estimate transient thermal-hydraulic analysis computer program (sponsored by EPRI) designed to provide analysis capabilities for BWR and PWR transients, small-break LOCAs, balance-of-plant modeling, and anticipated transients without scram (ATWS). 

The plant conditions considered in the safety analyses for LWRs range from relatively mild events to DBAs and natural events that have potential for serious consequences. The transient or event in an NPP can result due to (1) component and system failures or malfunctions, (2) operator errors, and (3) common-cause internally and externally initiated events. Most of the transient leading away from normal operation are results of imbalance between core heat generation and heat removal from the core. Reactor transients generally are classified based on fhe results of probabilistic studies and engineering judgment, into the four classes of evenfs as shown in Table 22.18. 

In this work our presentation of well-known techniques will be brief since they are thoroughly documented in the literature. Toward the end of this chapter, the TAP approach is introduced, which is not widely known in the industry and incorporates many of the advantages from more commonly used techniques such as flow reactors, transient operation, and MBS. 

The power-operated atmospherie rehef valves provide defence in depth by cooling down the steam generators and the reactor coolant system when the condenser is unavailable. The valves are sized such that the maximum flow at design pressure that would result in an acceptable (by tire analysis) reactor transient if one valve should inadvertently open and remain open (Section 10.3.2.2.3 of Reference 6.1). 

In recent years the nonsteady state mode has been used to an increasing extent because it permits accessing intermediate steps of the overall reaction. Very complete reviews of this topic are presented by Mills and Lerou [1993] and by Keil [2001]. Specific reactors have been developed for transient studies of catalytic reaction schemes and kinetics. One example is the TAP-reactor ( Transient Analysis of Products ) that is linked to a quadrupole mass spectrometer for on line analysis of the response to an inlet pulse of the reactants. The TAP reactor was introduced by Cleaves et al. in 1968 and commercialized in the early nineties. An example of appUcation to the oxidation of o.xylene into phthalic anhydride was published by Creten et al. [1997], to the oxidation of methanol into formaldehyde by Lafyatis et al. [1994], to the oxidation of propylene into acroleine by Creten et al. [1995] and to the catalytic cracking of methylcyclohexane by Fierro et al. [2001], Stopped flow experimentation is another efficient technique for the study of very fast reactions completed in the microsecond range, encountered in protein chemistry, e.g., in relaxation techniques an equilibrium state is perturbed and its recovery is followed on line. Sophisticated commercial equipment has been developed for these techniques. 

Delayed neutrons affect reactor transient response by changing effective cycle time from ... 

Spencer, J. L., R. R. Lunt and S. A. Leshaw. Identification of Micromixing Mechanisms in Flow Reactors Transient Inputs of Reactive Tracers. Ind. Eng. Chem. Fundamentals 19 (1980) 135. 

Carbon Monoxide Oxidation in an Int ral Reactor Transient Response to Concentration Pulses in the R ime of Isothermal Multiplicities... 

During expected operational reactor transients the pressure control mode will not be changed however for rapid or prolonged transients, normal pressure control may be lost temporarily. For the pressure transient encountered during loop startup, a separate, special bank of manually controlled heaters are provided to increase pressurisation rates. 

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