Shu-Yii Wu

Segregation by size difference in gas fluidized beds

Abstract Binary systems of particles of different size but equal density are fluidized in a 30-cm diameter bed with a perforated plate distributor. This work described the extensive experimentation, and relates the mixing/segregation properties to the visible bubble flow rate, the particle size ratio, and other parameters of minor influence. Experimental data are expressed as mixing index, correlated in terms of the decisive parameters. Comparison with previous empirical equations for the mixing index is also included. The excess gas flow rate required to avoid segregation in a fluidized bed of wide size distribution powders can be calculated from the expression for the mixing index (Eq. (15)).

Hydrogen Production with Immobilized Sewage Sludge in Three-Phase Fluidized-Bed Bioreactors

Municipal sewage sludge was immobilized with a modified alginate gel entrapment method, and the immobilized cells were used to produce hydrogen gas in a three‐phase fluidized bed. The hydrogen‐producing fluidized beds were operated at different liquid velocity (U0) and hydraulic retention time (HRT). The results show that in response to operating liquid velocities, the fluidized‐bed system had three flow regimes, namely, plug flow, slug flow, and free bubbling. Pressure fluctuation analysis was used to analyze the hydrodynamic properties in this three‐phase fluidized bed when it was under a steady‐state production of biogas. With a steady‐state biogas production rate (Ug) of 0.196 mL/s/L, a transition state occurred at a liquid velocity (U0) of 0.85 cm/s. As U0 < 0.85 cm/s, the system was basically a nonhomogeneous fluidized bed, whereas the bed became homogeneous when U0 was higher than 0.85 cm/s. The fluidized bed can be stably carried out at high loading rates (HRT as low as 2 h). Hydrogen fermentation results show that the maximal hydrogen production rate was 0.93 L/h/L and the best yield (YH2/sucrose) was 2.67 mol H2/mol sucrose.

Microbial hydrogen production with immobilized sewage sludge

Municipal sewage sludge was immobilized to produce hydrogen gas under anaerobic conditions. Cell immobilization was essentially achieved by gel entrapment approaches, which were physically or chemically modified by addition of activated carbon (AC), polyurethane (PU), and acrylic latex plus silicone (ALSC). The performance of hydrogen fermentation with a variety of immobilized‐cell systems was assessed to identify the optimal type of immobilized cells for practical uses. With sucrose as the limiting carbon source, hydrogen production was more efficient with the immobilized‐cell system than with the suspended‐cell system, and in both cases the predominant soluble metabolites were butyric acid and acetic acid. Addition of activated carbon into alginate gel (denoted as CA/AC cells) enhanced the hydrogen production rate ( vH2) and substrate‐based yield ( YH2/sucrose) by 70% and 52%, respectively, over the conventional alginate‐immobilized cells. Further supplementation of polyurethane or acrylic latex/silicone increased the mechanical strength and operation stability of the immobilized cells but caused a decrease in the hydrogen production rate. Kinetic studies show that the dependence of specific hydrogen production rates on the concentration of limiting substrate (sucrose) can be described by Michaelis‐Menten model with good agreement. The kinetic analysis suggests that CA/AC cells may contain higher concentration of active biocatalysts for hydrogen production, while PU and ALSC cells had better affinity to the substrate. Acclimation of the immobilized cells led to a remarkable enhancement in vH2 with a 25‐fold increase for CA/AC and ca. 10‐ to 15‐fold increases for PU and ALSC cells. However, the ALSC cells were found to have better durability than PU and CA/AC cells as they allowed stable hydrogen production for over 24 repeated runs.

Elutriation of fines from gas fluidized beds of Geldart A-type powders — effect of adding superfines

Abstract Experimental work on the entrainment of Geldart Group A powders was carried out in a 7.62-cm diameter column fluidized batchwise at velocities between 0.2 and 0.7 m s −1 . Group C powders were added to a number of base Group A powders in proportions which ensured that they remained within Group A. The superfines influenced the elutriation rate constant K i * at a given superficial gas velocity, K i * increased with decreasing particle size and then levelled off below a critical size. This effect results from interparticle adhesion forces. A method is presented for estimating the critical particle size at which adhesion forces become significant compared with gravitational and hydrodynamic forces, with an empirical equation to predict K i * below the critical particle size.

High-Efficiency Hydrogen Production by an Anaerobic, Thermophilic Enrichment Culture From an Icelandic Hot Spring

Dark fermentative hydrogen production from glucose by a thermophilic culture (33HL), enriched from an Icelandic hot spring sediment sample, was studied in two continuous‐flow, completely stirred tank reactors (CSTR1, CSTR2) and in one semi‐continuous, anaerobic sequencing batch reactor (ASBR) at 58°C. The 33HL produced H2 yield (HY) of up to 3.2 mol‐H2/mol‐glucose along with acetate in batch assay. In the CSTR1 with 33HL inoculum, H2 production was unstable. In the ASBR, maintained with 33HL, the H2 production enhanced after the addition of 6 mg/L of FeSO4 · 7H2O resulting in HY up to 2.51 mol‐H2/mol‐glucose (H2 production rate (HPR) of 7.85 mmol/h/L). The H2 production increase was associated with an increase in butyrate production. In the CSTR2, with ASBR inoculum and FeSO4 supplementation, stable, high‐rate H2 production was obtained with HPR up to 45.8 mmol/h/L (1.1 L/h/L) and HY of 1.54 mol‐H2/mol‐glucose. The 33HL batch enrichment was dominated by bacterial strains closely affiliated with Thermobrachium celere (99.8–100%). T. celere affiliated strains, however, did not thrive in the three open system bioreactors. Instead, Thermoanaerobacterium aotearoense (98.5–99.6%) affiliated strains, producing H2 along with butyrate and acetate, dominated the reactor cultures. This culture had higher H2 production efficiency (HY and specific HPR) than reported for mesophilic mixed cultures. Further, the thermophilic culture readily formed granules in CSTR and ASBR systems. In summary, the thermophilic culture as characterized by high H2 production efficiency and ready granulation is considered very promising for H2 fermentation from carbohydrates. Biotechnol. Bioeng. 2008;101: 665–678.

Biohydrogen production in a three-phase fluidized bed bioreactor using sewage sludge immobilized by ethylene-vinyl acetate copolymer.

Ethylene-vinyl acetate (EVA) copolymer was used to immobilize H(2)-producing sewage sludge for H(2) production in a three-phase fluidized bed reactor (FBR). The FBR with an immobilized cell packing ratio of 10% (v/v) and a liquid recycle rate of 5l/min (23% bed expansion) was optimal for dark H(2) fermentation. The performance of the FBR reactor fed with sucrose-based synthetic medium was examined under various sucrose concentration (C(so)) and hydraulic retention time (HRT). The best volumetric H(2) production rate of 1.80+/-0.02 H(2) l/h/l occurred at C(so)=40 g COD/l and 2h HRT, while the optimal H(2) yield (4.26+/-0.04 mol H(2)/mol sucrose) was obtained at C(so)=20 g COD/l and 6h HRT. The H(2) content in the biogas was stably maintained at 40% or above. The primary soluble metabolites were butyric acid and acetic acid, as both products together accounted for 74-83% of total soluble microbial products formed during dark H(2) fermentation.

The Autothermal Pyrolysis of Waste Tires

Abstract The growing amount of rubber waste, such as that from tires and cables, has resulted in serious environmental problems. Since rubber waste is not easily biodegradable even after a long period of landfill treatment, material and energy recovery is the preferable alternative to disposal. The potential offered by waste tire pyrolysis for solving both energy and waste treatment problems is widely recognized. Pyrolysis is one method of inducing thermal decomposition without using any oxidizing agent, or using such a limited supply of the agent that oxidization does not proceed to an appreciable extent. The latter may be described as autothermal pyrolysis and will be studied in the present work. The main objective of this research was to study the operating parameters of autothermal pyrolysis of scrap tires in a laboratory-scale fluidized bed reactor with a 100-cm bed height (10 cm I.D.) and a 100-cm freeboard (25 cm I.D.). Scrap tires were pyrolyzed in a limited oxygen supply, so that the heat for pyr...

The fluidized bed pyrolysis of shredded tyres: the influence of carbon particles, humidity, and temperature on the hydrodynamics

Abstract Ultrafine carbon particles (dsv = 165 nm) are formed from the pyrolysis of shredded tyres in a fluidized bed reactor. The carbon particles affect the hydrodynamic properties of the fluidized bed itself, such as the minimum fluidization velocity Umf, the elutriation rate, etc. This work investigates how humidity and temperature influence the elutriation rate constant K i ∗ of the carbon particles, and how the presence of ultrafine carbon particles in a sand bed influence the minimum fluidization velocity.

Dust Collection Efficiency Analysis in a Two-Dimensional Circulating Granular Bed Filter

Abstract Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 ± 0.24, 21.50 ± 0.11, and 30.51 ± 0.57 g/sec at louver angles of 45°, 30°, and 20°, respectively. Optimal dust collection efficiency peaked with a louver angle of 30°. Average particle sizes of bed material by sieve diameters (μm) of 795 μm had higher dust collection efficiency than the average collector particle size of 1500 μm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.

Optimal Absorbent Evaluation for the CO2 Separating Process by Absorption Loading, Desorption Efficiency, Cost, and Environmental Tolerance

The CO2 absorption capacities of potassium glycinate, potassium sarcosinate (choline, proline), mono-ethanolamine (MEA), and tri-ethanolamine were evaluated to find the optimal absorbent for separating CO2 from gaseous products by a CO2 purification process. The absorption loading, desorption efficiency, cost, and environmental tolerance were assessed to select the optimal absorbent. MEA was found to be the optimum absorbent for separating the CO2 and H2 mixture in gaseous product. The maximum absorption loading rate was 0.77 mol CO2 per mol MEA at temperature of 20°C and absorbent concentration of 2.5 mol/L, whereas desorption efficiency was 90% by heating for 3 h at 130°C. MEA was found to be an optimal absorbent for the purification process of CO2 during gaseous production.