Costa Rica coffee pulp (broza) gasification. a stochiometric-chemical equilibrium model

The ICAFE (Costa Rica Coffee Institute) and Universidad de Costa Rica are leading organizations researching the application of new technologies for coffee production and utilization coffee by-products. Central to this issue is the demonstration of gasification technology applicable to the coffee waste (broza and cascarilla) about 70wt% of the coffee fruit [1]. To accomplish this, the UCR has established academic collaboration since 2014 with the CREC (Chemical Reactor Engineering Centre) from Western University. The present study, describes a Stoichiometric-Chemical Equilibrium model specifically developed for simulating the gasification of coffee pulp (broza de café) in a down draft gasifier. Results of the model are compared with data from experimental runs developed in a 10 kg/h downflow gasifer unit. Please click Additional Files below to see the full abstract

RADIAL DISTRIBUTION OF PARTICLE CLUSTERS IN A DOWNER REACTOR UNIT

This study investigates the formation of clusters at 11 radial positions in a 2.63 cm ID downer reactor using the CREC-GS-Optiprobes. Cluster properties such as dimensions, drag coefficients and velocity across the downer unit radius are established based on the reported data and a probabilistic based model

Radial Distribution of Particle Clusters in Down Flow Reactors

Particle clustering is of major importance in down flow reactors having a profound influence on some fundamental properties of the flowing suspension such as particle slip velocity. The goal of this study is to provide further evidence to support the formation of clusters using the novel CREC-GS-Optiprobes. This sensor is equipped with GRIN lenses and introduces minimum intrusion effects. Results reported include radial distributions of particle cluster size and velocity under various gas flow superficial velocities and suspension densities. Micro-scale and macro-scale flow structures are advanced on the basis of the reported data

Computational fluid dynamics study of crec riser simulator: mixing patterns

The CREC Riser Simulator Reactor is a novel mini-fluidized reactor. This novel device was invented by de Lasa 1. The applications of this unit has shown to be of great value to establish catalyst performance and kinetic models for a diversity of gas phase catalytic reactions. This has been the case, given that the CREC Riser Simulator is excellent with respect to particle and fluid mixing2. This study establishes using CFD (Computational Fluid Dynamics), the CREC Riser Simulator mixing flow patterns. CFD simulations were developed using the COMSOL Multiphysics® module. Fig.1a reports the geometric characteristics of the CREC Riser Simulator including the impeller, the basket containing the catalyst and the external baffles.The proposed CFD model was validated using experimental data obtained in a basket as shown in Fig.1a. For instance, for an impeller speed of 4000 rpm, the outer annulus experimental gas velocity2 was ~0.9 m/s and the simulated CFD gas velocity2 was ~1.3 m/s. Please click Additional Files below to see the full abstract

Single-Bubble Dynamics in a Dense Phase Fluidized Sand Bed Biomass Gasification Environment

Biomass gasification in fluidized beds is a process of important commercial value. The simulation of these fluidized bed units strongly depends on establishing bubble dynamics in dense phase sand fluidized beds. In these studies, the selected biomass pellet dimensions were 2.7 cm in length and 0.8 cm in diameter. To develop bubble dynamics studies in the present research, a combination of CREC-Optiprobes and a video micro-camera were employed. This was done to record bubble velocity and bubble dimensions in a 200–900 μm particle sand fluidized bed. The effects of biomass pellet concentration on the bubble rise velocity and bubble size and shape were evaluated at conditions close to minimum fluidization. On this basis, a theoretical bubble dynamic model was established. This phenomenologically based model included an adjustable bubble wake parameter, with model predictions providing the bubble chord, bubble frontal ratio, and bubble rising velocity

Hydrogen production using a platinum modified TiO2 photocatalyst and an organic scavenger. Kinetic modeling

This contribution reports the kinetics of the photocatalytic production of hydrogen using a modified DP25 (TiO2)-1 wt% Pt and ethanol as an organic scavenger. This study is carried out in a Photo-CREC water II Reactor with a specially designed H2 collector tank. Experiments are developed under the following conditions: (a) An optimum photocatalyst loading, (b) Near-UV irradiation, (c) An acid pH and (d) Using ethanol as an organic scavenger. This research considers an ‘‘In Series–Parallel” kinetics to describe the photocatalytic conversion of ethanol (the organic scavenger) and of other carbon containing product species. Rate equations considered are of the Langmuir–Hinshelwood type leading to a set of ordinary differential equations. Furthermore, it is observed that hydrogen formation is a near zero order reaction. Regression analyses are used to calculate kinetic parameters with a cross-correlation matrix and 95% confidence intervals

Simulation of a Silicon CVD Spouted Fluidized Bed Reactor: Semi-Batch Operations

A comprehensive multiphase gas-solid mathematical model that successfully describes the batch growth of silicon particles in a chemical vapor deposition (CVD) submerged spouted bed reactor is extended to simulate semi-batch operations with periodic seeds additions and product extractions. This model takes into account the fluidized bed reactor as well as a population balance equation representing particle growth and agglomeration. Experimental data obtained from semi-batch operation in a pilot scale reactor at REC Silicon Inc. are used to evaluate the proposed mathematical model

Photodegradation Efficiencies in a Photo-CREC Water-II Reactor Using Several TiO2 Based Catalysts

This study reports phenol degradation using several TiO2 photocatalysts (DP25, Anatase 1, Hombikat UV-100, Anatase 2) in a Photo-CREC Water-II Reactor. The physicochemical properties of the photocatalysts used, such as crystallinity, superficial area, and pore size dis-tribution are reported. Reactor efficiencies are calculated using both Quantum Yields (QYs) and Photochemical and Thermodynamic Efficiency Factors (PTEFs). This is accomplished using phenol and phenol intermediate photoconversion rates. This allows the determination of hydroxyl radical consumption rates, at every step of the photodegradation process. With these data, and with the absorbed photon rates, energy efficiencies are calculated. It is shown that for the best performing photo catalysts the maximum QYs reach 50 % levels. These favourable photoconversion efficiencies confirm the critical impor-tance of having available highly performing photocata-lysts and photoreactors, such is the case of Photo-CREC Water-II Reactor unit

Photocatalytic hydrogen production using mesoporous TiO2 doped with Pt

A series of mesoporous TiO2 (meso-TiO2) were synthesized using the sol-gel technique. A Pluronic F127 triblock-copolymer, a structure-directing agent, was incorporated as a soft template into the sol-gel. In addition, and during a separate synthesis, the sol-gel was doped with a Pt precursor. Semiconductors were prepared with 1.00 wt.%, 2.50 wt.%, 5.00 wt.% Pt nominal loadings, respectively. They were calcined at 500 ◦C and 550 ◦C following synthesis. Morphological and structural properties were studied by: a) X-ray diffraction, b) UV–vis spectrophotometry, c) N2 adsorption-desorption (BET, BJH), and d) X-ray photoelectron spectroscopy (XPS). Optical band gap values for meso-TiO2 and Pt-meso-TiO2 were cal- culated by Kubelka-Munk (K-M) function coupled with Tauc plot methodology. It was observed that the prepared semiconductors displayed pore sizes in the 10–40 nm range with bimodal distributions. Their photocatalytic activity forhydrogenproductionvia water splitting was established ina Photo-CRECWater- II reactor under near-UV light irradiation. The aqueous solution contained 2% v/v ethanol, employed as a renewable organic scavenger. The prepared semiconductors showed that the mesoporous 2.50 wt.% Pt-TiO2 has the highest photoactivity for hydrogen generation. This suggests the important role played by the loading of platinum as a TiO2 dopant, reducing the optical band gap, increasing electron storage and diminishing, as a result, electron-hole recombination. The measured Quantum Yield (QY), obtained using a rigorous approach, was established for the mesoporous 2.50 wt.% Pt-TiO2 at a promising level of 22.6%

Kinetics of the pollutant photocatalytic conversion in a Photo-CREC-Air Reactor

This research reports the kinetic studies for acetone and acetaldehyde photoconversion in the gas phase utilizing a scaled-up Photo-CREC-Air unit with TiO2. The inclusion of intermediate species in the reaction network is required for the kinetic modeling of a wide range of oxygenate pollutant concentrations. The proposed ‘‘in parallel-series” reaction network encompasses a Langmuir-Hinshelwood (L-H) kinetics including species adsorption and intrinsic reaction parameters. The estimated kinetic parameters provide a successful prediction of various measurable chemical species. It is shown that the proposed kinetic model can be simplified, under low initial model pollutant concentrations. This is critical to avoid model overparameterization. The proposed kinetic model while being restricted to two model pollutants (ace- tone and acetaldehyde) and one specific photoreactor (e.g. 55.1 L Photo-CREC-Air), provides a framework to establish the photodegradation kinetics of other organic species in air, for larger photoreactor scales