Young-Il Lim

CFD simulation with experiments in a dual circulating fluidized bed gasifier

Abstract Gas and particles hydrodynamic behaviors were investigated in a pilot-scale cold-mode riser and a bubbling fluidized bed gasifier by means of experiment and computational fluid dynamics (CFD). Six different experimental sets were conducted in the cold-rig dual fluidized bed (DFB) at different gas velocities in both the riser and the recycle chamber aeration. A two-dimensional (2D) multi-fluid Eulerian model incorporating the kinetic theory of granular flows was applied to identify unsteady-state behaviors of the fluidized bed. The CFD model predicts well the solid circulation rate in the cold-rig DFB for all the six experimental runs. A discrepancy between experiment and simulation is observed in the axial solid holdup along the riser. The simulation results demonstrate that the cold-bed simulation can be used to predict the solid circulation rate for the hot-bed operation of the DFB gasifier.

An optimization strategy for nonlinear simulated moving bed chromatography: Multi-level optimization procedure (MLOP)

This paper presents a multi-level optimization strategy to obtain optimum operating conditions (four flow-rates and cycle time) of nonlinear simulated moving bed chromatography. The multi-level optimization procedure (MLOP) approaches systematically from initialization to optimization with two objective functions (productivity and desorbent consumption), employing the standing wave analysis, the true moving bed (TMB) model and the simulated moving bed (SMB) model. The procedure is constructed on a non-worse solution property advancing level by level and its solution does not mean a global optimum. That is, the lower desorbent consumption under the higher productivity is successively obtained on the basis of the SMB model, as the two SMB-model optimizations are repeated by using a standard SQP (successive quadratic programming) algorithm. This approach takes advantage of the TMB model as well as surmounts shortcomings of the TMB model in the general case of any nonlinear adsorption isotherm using the SMB model. The MLOP is evaluated on two nonlinear SMB cases characterized by i) quasi-linear/non-equilibrium and ii) nonlinear/nonequilibrium model. For the two cases, the MLOP yields a satisfactory solution for high productivity and low desorbent consumption within required purities.

Hierarchical economic potential approach for techno-economic evaluation of bioethanol production from palm empty fruit bunches

A hierarchical four-level approach to determine economic potential (4-level EP) is proposed for preliminary techno-economic analysis of new processes. The 4-level EP includes input/output structure, process flow structure, heat integration (HI), and economic feasibility. Two case studies on a 30.2 t/d (or 12.7 million l/yr) bioethanol plant with and without jet fuel production from palm empty fruit bunches (EFB) were investigated by applying the 4-level EP. The plant flowsheet was established based on experiments in a 0.1t/d pilot plant, including sequential dilute acid and alkali pretreatment, and separate hydrolysis and fermentation (SHF). EP approached a more reliable value through the hierarchical 4-level EP. The heating energy was reduced considerably by HI. The product value was estimated at

Gas−liquid multiphase computational fluid dynamics (CFD) of amine absorption column with structured-packing for CO2 capture

0.8-

Optimal flushing flow rates in para-xylene simulated moving-bed considering geometric factor of dead volume

1.3/kg of equivalent bioethanol. It was suggested through sensitivity analysis that a large plant size, enhanced production yields, and capital cost reduction were necessary for the lignocellulosic bioethanol production to be profitable.

Process modeling and energy consumption of fry-drying and torrefaction of organic solid waste

Abstract The gas−liquid multiphase Eulerian computational fluid dynamics (CFD) model was used to investigate hydrodynamics and CO2 removal efficiency of a pilot-scale amine absorber with structured-packing. The structured-packing was represented by a porous media zone having porous resistance, gas−liquid interfacial drag force, and liquid dispersion force. This study aimed to find a reasonable way to identify four modification factors of the Ergun coefficient that determine the hydrodynamic characteristics of structured-packing. The two modification factors (a and b) for porous resistance were mainly related to the liquid holdup (hL) with respect to the liquid load. The other two factors (c and d) for gas−liquid interfacial drag force depended on the specific wet pressure drop (ΔPwet/L) versus the gas load factor. The hL and ΔPwet/L increased in parallel with the increase of a and c, respectively, while the slopes of hL and ΔPwet/L increased with b and d, respectively.

Multi-scale computational fluid dynamics of impregnation die for thermoplastic carbon fiber prepreg production

The complex geometry of dead volume is often modeled into a simplified geometry, but little attention has been paid to how the simplified geometry of dead volume influences one-dimensional (1D) SMB modeling. This study investigated effects of the geometric factor of dead volume on 7-zone para-xylene (PX) simulated moving-bed (SMB). This work demonstrated that a complex geometry of dead volume can be modeled into a simple geometry by using a geometric factor in the 1D SMB simulations. Optimal flushing flow rates of the PX SMB were found by the parametric study on recovery and purity, employing the geometric factor to a simplified geometry.

Effects of Operating Conditions on Pressure Drop in a Pulse-Jet Bagfilter for Coke Dust

ABSTRACT A commercial fry-drying and torrefaction (FDT) plant for producing bio-solid fuel from 45 ton/d organic sludge with 80% water was proposed. The FDT plant was modeled by a process simulator with the aid of plant data. Two double-effect evaporators were used in series to vaporize water, using heat-carrying oil. Torrefied and pelletized bio-solid was produced at 413 kg/h, comprising 4.4 and 4.8% of water and oil, respectively, and 67% of its mass was used as heat source. The total energy consumption was 1,369 kW, including 93 kW electrical and 1,276 kW thermal energies. The total heat duty was 788 kcal/kg-water.

A NONEQUILIBRIUM ADSORPTION MODEL SATISFYING ELECTRO-NEUTRALITY CONDITION FOR ION-EXCHANGE CHROMATOGRAPHY

A multi-scale computational fluid dynamics (CFD) model of a pultrusion process was proposed for unidirectional carbon fiber (UD-CF) prepreg production. Polyamide 6 (PA6) and polyacrylonitrile-based CF were used as the thermoplastic polymer matrix and reinforcement, respectively. The non-Newtonian viscosity of PA6 was expressed by Carreaus model. A micro-scale CFD model was constructed to obtain a proper resin permeability to CF filaments, while the tow domain was treated as sliding porous media in the macro-scale CFD. The resin velocity profile showed a similar shape to the relative resin amount experimentally measured in the UD-CF prepreg. The uniformity index of the resin velocity (UIv) on the outlet surface was calculated for 45 case studies with several tow speeds and resin flow rates. The tow speed showing a maximum UIv was remarkably well expressed as a linear function of the slip velocity, which is the difference between the tow speed and resin velocity.

Multiscale Simulation Starting at the Molecular Level for Adsorption Process Development

A pilot-scale pulse-jet bagfilter was designed, built, and tested for the effects of four operating conditions (filtration velocity, inlet dust concentration, pulse pressure, and pulse interval time) on the total system pressure drop, using coke dust from a steel mill factory. Four models were used to predict the total pressure drop according to the operating conditions. These model parameters were estimated from the 192 experimental data points. The filtration velocity has been determined to be the most relevant variable affecting the pressure drop. An efficient operating condition considering the four variables is proposed from analysis of the dimensionless group model.