Transient Reactor Model Research Articles

Transient Effects during Dynamic Operation of a Wall‐Cooled Fixed‐Bed Reactor for CO2Methanation

AbstractThe power‐to‐gas process is an option to transform fluctuating renewable electric energy into methane via water electrolysis and subsequent conversion of H2by methanation with CO2. The dynamic behavior of the methanation reactor may then be a critical aspect. The kinetics of CO2methanation on a Ni‐catalyst were determined under isothermal and stationary conditions. Transient isothermal kinetic experiments showed a fast response of the rate on step changes of the concentrations of H2, CO2; in case of H2O, the response was delayed. Non‐isothermal experiments were conducted in a wall‐cooled fixed‐bed reactor. Temperature profiles were measured and the effect of a changing volumetric flow was studied. The experimental data were compared with simulations by a transient reactor model.

Model based analysis of the effect of 2-ethylphenol addition to n-decane in fluid catalytic cracking over a series of zeolites

The catalytic cracking of n-decane (C10) purely, representing the conventional gasoil feed, and in admixture with 2-ethylphenol (EP), as a model component for HDO bio-oil, is investigated in a fixed-bed reactor over three faujasites. It was observed that EP induces faster deactivation with time-on-stream (TOS), which was more pronounced when materials with low mesoporous surface area were employed. The gasoline selectivity was also shown to increase more steeply with TOS for an EP containing feed. A 5-lump FCC kinetic model, including selective deactivation functions, was developed and incorporated into a transient reactor model to assess the obtained data and account for the observed effects. With the aid of the model, the above trends were rationalized by an increase in the value of the frequency factors, related to the feed conversion into coke and gasoline. The FCC kinetic model was subsequently integrated into a riser reactor model for pilot level simulations, via the extrapolation of the results obtained based on the transient model for the fixed-bed reactor to the steady-state behavior of a riser reactor. In particular, a unique deactivation factor Φ, reflecting catalyst condition, was introduced in the model for the latter reactor to adequately account for the deactivation functions determined making use of the data acquired in the former. Simulation results demonstrate the significance of the first meters of the riser, as well as the effect of operation parameters, i.e, Φ, EP addition in the feed, inlet catalyst-to-oil ratio, on conversion and selectivities.

Efficiency assessment of a two-step thermochemical water-splitting process based on a dynamic process model

Solar hydrogen production via two-step thermochemical redox cycles a promising candidate for green fuel production in the future energy market. In a European consortium, the Hydrosol concept has been developed to split water in such a thermochemical cycle. We developed a transient reactor model in order to predict the upper-limit efficiency of a large-scale process based on the Hydrosol reactor concept. The analysis shows that the state-of-the-art ferrite-based redox material properties need to be improved considerably in order to reach competitive efficiency. The two main properties that need improvement are the reaction kinetics on the one hand and the amount of oxygen that can be incorporated into and released from the redox material on the other hand.

One dimensional steady-state circulating fluidized-bed reactor model for biomass fast pyrolysis

A one dimensional (1-D) steady-state biomass fast pyrolysis reactor model is developed for integration with a biomass pyrolysis plant system model. A state-of-the-art biomass pyrolysis kinetic mechanism is combined with the 1-D Eulerian fluid dynamics and heat transfer description. Simulations are performed for a small scale reactor (0.023kg/s) with four different biomass feedstocks (pine, wheat straw, olive husks, organic fraction of MSW). Results show that biomass particles are heated to pyrolysis temperature of 786K in 0.3s and 99% biomass conversion is reached in 0.9s from entering the reactor. Comparison of pyrolysis products yields against available literature data shows that the employed reaction mechanism generally gives good predictions. However, water yield is under predicted. Fluid dynamics and heat transfer results are compared with averaged results from a 2-D, transient reactor model developed in Multiphase Flow with Interphase eXchanges (MFIX). Comparison of the 1-D and the 2-D model results shows flow patterns and reasonably similar values of flow parameters, with the average relative error between the gas velocities of 10%. The solids velocity predictions from the 1-D model carry a larger error since particle clustering is neglected in the plug flow approximation. The 1-D model is still considered attractive because of a reasonable agreement with the averaged experimental results.

Autothermal Reforming of Gasoline for Fuel Cell Applications: A Transient Reactor Model

A mathematical model for an autothermal reforming (ATR) fuel processor has been developed to study the transient response of the reactor for gasoline reforming. The model was developed with experimental data from temperature profiles along the reactor and product composition (CO2, CO, and H2 formation). Model versus experiment results were compared for three cases: partial oxidation, ATR using steam injection, and ATR using liquid water spray. In addition to analysis capabilities, the developed model is intended to help in the design of a feedback controller aimed at improving the dynamic response time of the system.

Combined thermometric analysis of a series of highly dealuminated USY zeolites

A transient reactor model was used to consolidate and quantify the data of ammonia adsorption microcalorimetry and single ammonia TPD runs, using several members of the commercial CBV series of dealuminated HY zeolites. The model accounts for the competitive re-adsorption of molecules desorbing from multiple sites, using the microcalorimetric data to constrain the desorption energy parameters to physically meaningful values. All TPD profiles were well represented by models consisting of only two or three distinct site types, even though the differential heat plots imply a continuous distribution of sites in the 160-80 kJ/mol range for all catalysts. Increasing dealumination severity is evidenced by a decrease in total site density for sites 100 kJ/mol. While there was no evidence of an enhancement of adsorption strength within the series studied, the range of site strengths available remained the same. There is correspondence between the density of adsites = 100 kJ/mol and the framework Al3+ concentration, although the ratio of these is less than one, even for Si/Al80. The inherent limits in using ammonia adsorption as an acidity probe are briefly mentioned.

Mathematical modelling of the transient behaviour of cstrs with reactive particulates: Part 2 — Application to pyrite pressure oxidation

AbstractA population balance based transient reactor model is applied to a particulate process employed in the hydrometallurgical industry. The process is the pressure oxidation of pyritic concentrates, pertinent to the treatment of refractory gold materials. The chemical reaction system involves first an oxygen gas to aqueous mass transfer step, followed by a chemical reaction on the surface of mineral particles. The chemical reactor stimulated is a multi‐stage continuous autoclave with variable compartment size. The model accounts for recycling oxidized solids, as well as for venting the gas phase. A complex system of partial and non‐linear ordinary differential equations is rendered dimensionless and solved by a method developed previously using the Mathematica® software. The transient response of the reactor to different modes of reactor start‐up, as well as the response to a step change of a key variable, are examined. The validity of the steady‐state solution is assessed by comparing it to previous modelling attempts.