Characteristics of gas back-mixing in micro fluidized bed

Micro fluidized bed (MFB) has been applied to isothermal differential analysis of gas-solid reactions (1), and the fluidized gas and gas product passing through the MFBR is expected to be plug flow. Literature shows that the gas flow is close to plug flow and in low axial gas back-mixing when the gas Peclet number (Pe) is over 50 (2). This work devoted to investigating the effects of inner bed diameter (D), superficial gas velocity (Ug) and static particle bed height (Hs) on axial gas back-mixing in MFB and to distinguishing the conditions for the MFB operation. The experiments of axial gas back-mixing testing are conducted by tracer-gas method in a fluidized bed using air as the fluidized gas and helium as the tracer gas. Fluid catalytic crack (FCC) catalyst particles (Geldart A particles) are selected as the fluidized agent. The mean residence time (), Pe and axial diffusion coefficient (Da,g) of gas are calculated to determine the state of gas flow in MFB. Pe generally decreases with the increase of D and the maximum Pe decreases from 200 to 40 when D increases from 5 to 50 mm as shown in Fig 1. When D of fluidized bed was below 15 mm (i.e. 5 and 10 mm), Pe increased observably from 20 to 200 with the increase of Ug from 10 to 65 times of the calculated minimum fluidization velocity (Umf), but Hs had little effect on it. When D was over 15 mm (15-50 mm), Pe first increased and then decreased to be constant as Ug increased. The higher Hs would lead to lower constant Pe. The suitable operating range and parameters leading to Pe above 50 can be obtained from three-dimensional diagram in which coordinate axis was non-dimensional shown in Fig.2. The empirical equations were further developed to predict the Pe in MFB from the major operating parameters. Please click Additional Files below to see the full abstract

CHARACTERISTICS AND KINETICS OF BIOMASS PYLOLYSIS IN A MICRO FLUIDIZED BED REACTOR

A Micro Fluidized Bed Reactor (MFBR) was developed to enable on-line pulse feeding and isothermal differential reaction of particle reactant. Application of the MFBR to biomass pyrolysis demonstrated that the resulting globe kinetics parameters were 11.77 kJ/mol and 1.45 s-1 on the gas release characteristics, respectively

PERFORMANCE COMPARISON OF SYNGAS METHANATION ON FLUIDIZED AND FIXED BED REACTORS

The performance was compared on Syngas Completely Methanation at atmospheric pressure on fluidized and fixed bed reactors. From space-time yield of CH4, coke content and hot spots of bed temperature, fluidized bed technology was demonstrated to be more applicable to Syngas Completely Methanation. Characterization results showed that different carbon deposition forms were presented on the two operation modes

Hydrodynamics and local mass transfer characterization under gas–liquid–liquid slug flow in a rectangular microchannel

Gas-liquid-liquid three-phase slug flow was generated in a glass microreactor with rectangular microchannel, where aqueous slugs were distinguished by relative positions to air bubbles and organic droplets. Oxygen from bubbles reacted with resazurin in slugs, leading to prominent color changes, which was used to quantify mass transfer performance. The development of slug length indicated a film flow through the corner between bubbles and the channel wall, where the aqueous phase was saturated with oxygen transferred from bubble body. This film flow results in the highest equivalent oxygen concentration within the slug led by a bubble and followed by a droplet. The three-phase slug flow subregime with alternate bubble and droplet was found to benefit the overall mass transfer performance most. These results provide insights into a precise manipulation of gas-liquid-liquid slug flow in microreactors and the relevant mass transfer behavior thereof

Star formation in the centre of NGC 1808 as observed by ALMA

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 85.69 and 99.02 GHz continuum emission and H42$\alpha$ and H40$\alpha$ lines emission from the central 1~kpc of NGC 1808. These forms of emission are tracers of photoionizing stars but unaffected by dust obscuration that we use to test the applicability of other commonly star formation metrics. An analysis of the spectral energy distributions shows that free-free emission contributes about 60 to 90 per cent of the continuum emission in the 85-100 GHz frequency range, dependent on the region. The star formation rate (SFR) derived from the ALMA free-free emission is $3.1\pm0.3$~M$_\odot$~yr$^{-1}$. This is comparable to the SFRs measured from the infrared emission, mainly because most of the bolometric energy from the heavily obscured region is emitted as infrared emission. The radio 1.5~GHz emission yields a SFR 25 per cent lower than the ALMA value, probably because of the diffusion of the electrons producing the synchrotron emission beyond the star-forming regions. The SFRs measured from the extinction-corrected H$\alpha$ line emission are about 40 to 65 per cent of the SFR derived from the ALMA data, likely because this metric was not calibrated for high extinction regions. Some SFRs based on extinction-corrected ultraviolet emission are similar to those from ALMA and infrared data, but given that the ultraviolet terms in the extinction correction equations are very small, these metrics seem inappropriate to apply to this dusty starburst.Comment: 18 pages, 7 figures, 10 tables, accepted for publication in MNRA

The Size-Mass Relation of Post-Starburst Galaxies in the Local Universe

We present a study of the size--mass relation for local post-starburst (PSB) galaxies at $z\lesssim0.33$ selected from the Sloan Digital Sky Survey Data Release 8. We find that PSB galaxies with stellar mass ($M_*$) at $10^9~M_{\odot}<M_*<10^{12}~M_{\odot}$ have their galaxy size smaller than or comparable with those of quiescent galaxies (QGs). After controlling redshift and stellar mass, the sizes of PSBs are $\sim 13\%$ smaller on average than those of QGs, such differences become larger and significant towards the low-$M_*$ end, especially at $10^{9.5}~M_{\odot} \lesssim M_*\lesssim 10^{10.5}~M_{\odot}$ where PSBs can be on average $\sim 19\%$ smaller than QGs. In comparison with predictions of possible PSB evolutionary pathways from cosmological simulations, we suggest that a fast quenching of star formation following a short-lived starburst event (might be induced by major merger) should be the dominated pathway of our PSB sample. Furthermore, by cross-matching with group catalogs, we confirm that local PSBs at $M_*\lesssim10^{10}~M_{\odot}$ are more clustered than more massive ones. PSBs resided in groups are found to be slightly larger in galaxy size and more disk-like compared to field PSBs, which is qualitatively consistent with and thus hints the environment-driven fast quenching pathway for group PSBs. Taken together, our results support multiple evolutionary pathways for local PSB galaxies: while massive PSBs are thought of as products of fast quenching following a major merger-induced starburst, environment-induced fast quenching should play a role in the evolution of less massive PSBs, especially at $M_*\lesssim 10^{10}~M_{\odot}$.Comment: 16 pages, 7 figures; accepted for publication in Ap

BASIC STUDY FOR COAL MOISTURE CONTROL INTEGRATING PNEUMATIC CLASSIFICATION TECHNIQUE

A technique of coal moisture control integrating pneumatic classification with flue gas as heating medium was put forward. With this technique, refined coal moisture control can be realized accompanying classification in one process, and considerable high-quality energy can be saved in coking and milling procedure. In this paper, coal classification and moisture control behaviors was investigated at different conditions. Based on experimental results, the basic parameters for the technique were worked out accordingly

Pyrolysis characteristics of waste tire particles in fixed-bed reactor with internals

This study investigated the characteristics of pyrolysis for waste tire particles in the newly developed fixed-bed reactor with internals that are a central gas collection channel mounted inside reactor. And a few metallic plates vertically welded on the internal wall of the reactors and extending to the region closing their central gas collection pipe walls. Experiments were conducted in two laboratory fixed bed reactors with or without the internals. The results shown that employing internals produced more light oil at externally heating temperatures above 700 °C due to the inhibited secondary reactions in the reactor. The oil from the reactor with internals contained more aliphatic hydrocarbons and fewer aromatic hydrocarbons, leading to its higher H/C atomic ratios as for crude petroleum oil. The char yield was relatively stable for two beds and showed the higher heating values (HHVs) of about 23 MJ/kg. The gaseous product of pyrolysis mainly consisted of H2 and CH4, but the use of internals led to less pyrolysis gas through its promotion of oil production. Keywords: Pyrolysis, Waste tire, Fixed bed, Internals, Secondary reaction