Marquis Crose

Temperature balancing in steam methane reforming furnace via an integrated CFD/data-based optimization approach

Abstract In this work, we introduce a furnace-balancing scheme that generates an optimal furnace-side feed distribution that has the potential to improve the thermal efficiency of a reformer. The furnace-balancing scheme is composed of four major components: data generation, model identification, a model-based furnace-balancing optimizer and a termination checker. Initially, a computational fluid dynamics (CFD) model of an industrial-scale reformer, developed in our previous work, is used for the data generation as the model has been confirmed to simulate the typical transport and chemical reaction phenomena observed during reformer operation, and the CFD simulation data is in good agreement with various sources in literature. Then, we propose a model identification process in which the algorithm is formulated based on the least squares regression method, basic knowledge of radiative heat transfer and the existing furnace-side flow pattern. Subsequently, we propose a model-based furnace-balancing optimizer that is formulated as an optimization problem within which the valve position distribution is the decision variable, and minimizing the sum of the weighted squared deviations of the outer reforming tube wall temperatures from a set-point value for all reforming tubes with a penalty term on the deviation of the valve positions from their fully open positions is the objective function. CFD simulation results provide evidence that the optimized furnace-side feed distribution created by the furnace-balancing scheme can reduce the severity of nonuniformity in the spatial distribution of furnace-side temperature in the combustion chamber even when the reformer is under the influence of common valve-related disturbances.

Communication: Direct determination of triple-point coexistence through cell model simulation

In simulations of fluid-solid coexistence, the solid phase is modeled as a constrained system of Wigner-Seitz cells with one particle per cell. This model, commonly referred to as the constrained cell model, is a limiting case of a more general cell model, which is formed by considering a homogeneous external field that controls the number of particles per cell and, hence, the relative stability of the solid against the fluid phase. The generalized cell model provides a link that connects the disordered, fluid phase with the ordered, solid phase. In the present work, the phase diagram of this model is investigated through multicanonical simulations at constant pressure and histogram reweighting techniques for a system of 256 Lennard-Jones particles. The simulation data are used to obtain an estimate of the triple point of the Lennard-Jones system. The triple-point pressure is found to be higher compared to previous work. The likely explanation for this discrepancy is the highly compressible nature of the gas phase.

Multiscale three-dimensional CFD modeling for PECVD of amorphous silicon thin films

Abstract The development of a three-dimensional, multiscale computational fluid dynamics (CFD) model is presented here which aims to capture the deposition of amorphous silicon thin films via plasma-enhanced chemical vapor deposition (PECVD). The macroscopic reactor scale and the microscopic thin film growth domains which define the multiscale model are linked using a dynamic boundary which is updated at the completion of each time step. A novel parallel processing scheme built around a message passing interface (MPI) structure, in conjunction with a distributed collection of kinetic Monte Carlo algorithms, is applied in order to allow for transient simulations to be conducted using a mesh with greater than 1.5 million cells. Due to the frequent issue of thickness non-uniformity in thin film production, an improved PECVD reactor design is proposed. The resulting geometry is shown to reduce the product offset from  ∼ 25 nm to less than 13 nm using identical deposition parameters.

CFD Modeling of a Pilot-Scale Steam Methane Reforming Furnace

Hydrogen is a required key material for petroleum refineries that convert crude oil into a variety of products with higher economic value, e.g., gasoline. In chemical process plants and petroleum refineries, hydrogen is produced primarily by the steam methane reforming (SMR) process synthesizing hydrogen and carbon oxides from methane and superheated steam in the presence of a nickel-based catalyst network in a steam methane reformer. Traditionally, the optimized and profitable operating conditions of a steam methane reformer are analyzed and determined by on-site parametric study at industrial-scale plants or pilot-scale units, which is an experimental approach, and therefore, it must be conducted by changing process parameters in small increments over a long time period in order to prevent significant production and capital loss. Motivated by the above considerations, the present work focuses on developing a computational fluid dynamics (CFD) model of a pilot-scale steam methane reformer comprised of four industrial-scale reforming reactors, three industrial-scale burners and three flue gas tunnels. The pilot-scale reformer CFD model is developed by analyzing well-established physical phenomena, i.e., the transport of momentum, material and energy, and chemical reactions, i.e., combustion and the SMR process, that take place inside the steam methane reformer. Specifically, the \(P-1\) radiation model, standard \(k-\epsilon \) turbulence model, compressible ideal gas equation of state and finite rate/eddy dissipation (FR/ED) turbulence-chemistry interaction model are adopted to simulate the macroscopic and microscopic events in the reformer. The conditions for the tube-side feed, burner feed and combustion chamber refractory walls are consistent with typical reformer plant data Latham (2008) so that the simulation results generated by the pilot-scale reformer can be validated by the plant data. The simulation results are shown to be in agreement with publicly available plant data reported in the literature and also with the simulation data generated by a well-developed single reforming tube CFD model. Subsequently, the proposed pilot-scale reformer CFD model is employed for a parametric study of the mass flow rate of the burner feed, i.e., a \(20\,\%\) increase from its nominal value. The corresponding simulation results demonstrate the advantages offered by this CFD model for parametric study by showing that with the increased burner feed, the outer reforming tube wall temperature exceeds the maximum allowable temperature; these results were developed quickly with the aid of a CFD model, compared to the timescale on which parametric studies are performed on-site and without the potential for rupture of the reforming tubes during the study.

Steam methane reforming furnace temperature balancing via CFD model-based optimization

In this work, we introduce a furnace balancing algorithm that generates an optimized furnace-side feed distribution that has the potential to improve the thermal efficiency of reformers. The furnace balancing algorithm is composed of three major components: data generation, model identification and a model-based balancing scheme. Initially, we adopt a computational fluid dynamics (CFD) model of an industrial-scale reformer developed in our previous work for the data generation, as this model has been confirmed to simulate the typical transport and chemical reaction phenomena observed during reformer operation, and the CFD simulation data is in good agreement with various sources in literature. Then, we propose a model identification scheme in which the algorithm is formulated based on the least squares regression method and basic knowledge of radiative heat transfer. Subsequently, we create a model-based balancing scheme that is formulated as an optimization problem within which the furnace-side feed distribution is the decision variable, and minimizing the sum of the weighted squared deviations of outer reforming tube wall temperatures from a set-point value for all reforming tubes is used as the objective function. CFD simulation results provide evidence that the optimized furnace-side feed distribution created by the furnace balancing algorithm can reduce the temperature nonuniformity inside the combustion chamber, and therefore, allow the reformer thermal efficiency to be increased without shortening the units service life.