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

Cross-borehole delineation of a conductive ore deposit in a resistive host-experimental design

Journal ArticleThe finite-difference time-domain method is used for high-resolution full-wave analysis of cross-borehole electromagnetic surveys of buried nickel sulfide deposits. The method is validated against analytical methods for simple cases, but is shown to be a valuable tool for analysis of complicated geological structures such as faulted or layered regions. The magnetic fields generated by a wire loop in a borehole near a nickel sulfide deposit are presented for several cases. The full-wave solution is obtained up to 200 MHz, where quasi-static methods would have failed. The dielectric response is included in the solution, and the diffractive nature of the field is observed. The sensitivity of each receiver in a vertical line in the cross borehole is presented and analyzed to provide an optimal weighting for receivers that can be applied to an experimental study

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

Characterization of oil shale pyrolysis by solid heat carrier in moving bed with internals

Oil shale pyrolysis by solid heat carrier in moving bed with internals (MBI) was investigated with the aim to identify the effect of oil shale properties (moisture content and particle size) and heat carrier types on the physicochemical properties and distributions of pyrolysis products. Pyrolysis of oil shale with high moisture content of 10 wt% caused obvious increase in shale oil yield due to the protective effect of steam atmosphere by its reducing secondary reactions and also catalysis action of shale ash. The obtained highest shale oil yield was close to the yield of Fischer Assay. Pyrolyzing dried oil shale produced shale oil containing more light oils (gasoline and diesel) and allowed higher gas yield. Pyrolysis of large size (i.e. &gt;10 mm) oil shale reduced oil yield but increased light oil content due to the required long time for heat transfer and intra-patticle volatile diffusion. Comparing with ceramic balls, shale ash as the heat carrier presented a favorably catalytic effect on cracking and upgrading of shale oil. With increasing pyrolysis temperature from 465 to 525 degrees C, using shale ash greatly raised light oil content by 10.24% (relatively), considerably reduced the content of heteroatomic compounds, and promoted the conversion of aliphatics to aromatics. Shale ash carrier particles enabled better dust removal than ceramic balls did to attain oil product with a dust content below 0.2 wt%. Generally, oil shale pyrolysis using shale ash heat carrier in MBI process has obvious effects of in-situ shale oil upgrading and in-bed dust removal to allow good pyrolysis performance. (C) 2017 Elsevier B.V. All rights reserved.</p

Pyrolysis of Huadian Oil Shale in an Infrared Heating Reactor

Pyrolysis of Huadian oil shale was investigated in a newly designed shallow fixed bed reactor mounted with infrared heating to clarify the pyrolysis behavior at different heating rates and pyrolysis temperatures under minimized secondary reactions to volatiles in an oil shale bed. The maximum shale oil recovery was obtained under the proper conditions of a heating rate of 0.5 degrees C/s, a pyrolysis temperature of about 550 degrees C, a reduced reaction pressure (0.6 atm in this work), and for a single layer oil shale bed. The highest shale oil yield under such conditions was close to 100% of the Fischer Assay oil yield (11.10 wt % of dry basis). For the adopted infrared-heating reactor, increasing the heating, rate decreased the shale oil yield but increased the gas production. The total hydrogen in volatile products including shale oil and pyrolysis gas increased with raising the heating rate, and the total volatile production was higher for the infrared quick heating pyrolysis (heating rate: 25 degrees C/s) than that for the Fischer Assay. The shale oil from the infrared quick heating pyrolysis had also more light fraction. Experiment also found that pyrolyzing the multilayer oil shale bed lowered the shale oil yield in comparison with the pyrolysis of a single-layer material bed. Thus, adopting a single-layer oil shale bed, low infrared heating rates, and reduced reaction pressures obviously suppressed the secondary reactions toward volatiles to have consequently high shale oil yield. High infrared heating rate facilitated volatile and hydrogen production but led to more serious secondary reactions to lower the shale oil yield.</p

Oil shale pyrolysis in indirectly heated fixed bed with metallic plates of heating enhancement

This study is devoted to improving the heating to oil shale particles and in turn the yield and quality of shale oil in fixed bed reactors indirectly heated through use of internals. Metallic heating plates were vertically welded on the reactor wall as heating enhancement internals to provide extra heating surfaces inside the oil shale bed and to increase the high-temperature heating surface area by 35% to 210%. Comparison of heating rate to particles and shale oil yield was made between the reactors without and with the plate internals. Utilizing internals evidently enhanced the heating to oil shale particles and shortened pyrolysis time by 30% to 50%. The shale oil yield increased by 7% to reach 90% of the Fischer Assay oil yield (8.98 wt.%, dry base) when the heating surface area was increased by 70-110%. With increased heating surface area above 110%, the shale oil yield manifested conversely a slight decrease. Nonetheless, the fraction of light oil (boiling point &lt;350 degrees C by analysis in simulation GC) was increased to about 66 wt.% from 60.94 wt.% for the reactor without any heating plate. Characterizing the char samples at different lateral positions of the oil shale bed justified that the flow of gaseous pyrolysis product in the reactor was guided to the vicinity of heat transfer plates to speed up gas exhaust and selective cracking. Consequently, adding heat transfer plates into an indirectly heated reactor would obviously intensify the heating to the oil shale bed and also elevate the pyrolysis oil yield and quality. (C) 2015 Elsevier Ltd. All rights reserved

Distinctive oil shale pyrolysis behavior in indirectly heated fixed bed with internals

Intrinsic characteristics of oil shale pyrolysis in a fixed bed reactor with internals have been investigated in this study. Mounting particularly designed internals in fixed bed reactor improved shale oil production to up to 90% yield by Fischer assay. Comparing particle characteristics at different radial positions of the reactors with and without internals demonstrated that, inside the particle bed with internals, the product flow was regulated to move from the high-temperature zone (outer) to low-temperature zone (center), which reduced the secondary reactions of released volatiles. Terminating oil shale pyrolysis at central particle bed temperatures of 150, 300, 450, and 550 degrees C showed that the contents of vacuum gas oil and heavy oil in the shale oil produced had increased from 9.63 wt% to 53.29 wt%. The volatile contents of particles in the inner layer of the reactor slightly increased in the early stage of pyrolysis and, in turn, decomposed to form pyrolysis products as the temperature was raised. The adsorption or condensation of liquids on the surface of particles gradually increased from the outer region to the central region of the reactor due to the regulated product flow direction and low temperatures in the central zone of the reactor causing heavy components to condense. Increasing the degree of pyrolysis was also found to decrease the alkene, aromatic, and cycloalkane contents in shale oil, but increased those of alkane and heteroatomic compounds. These results demonstrate that adopting internals into oil shale pyrolysis optimized the product flow direction and selectively directed secondary reactions to occur for heavy volatile species only.</p

Pyrolysis in indirectly heated fixed bed with internals: The first application to oil shale

The indirectly heated fixed bed reactor with particularly designed internals has been devised to achieve advanced pyrolysis performance for coal (Energy &amp; Fuels, 28,2014: 236-244). This study extends the application of the reactor to oil shale and thereby solves the problems of low shale oil yield and low heating efficiency to shale particles in conventional fixed beds. The yield and quality of the produced shale oil and the rate heating the oil shale particles were compared for laboratory fixed beds without and with the particularly designed internals. It was shown that the use of internals doubled the efficiency of heating the oil shale inside the reactor from the heated reactor wall. Raising the heating temperature from 600 degrees C to 1000 degrees C increased the shale oil yield from 9.50% to 10.60% in the bed with internals, and reached 84.9% of the oil yield of Fischer assay (12.49 wt.% in dry base). Furthermore, the shale oil maintained its relatively stable aliphatic hydrocarbon content. In the bed without any internals such a temperature rise sharply decreased the shale oil yield from 9.53% to 4.60%. Consequently, the fixed bed with internals would be an advanced reactor also for oil shale pyrolysis, which allows high process efficiency, high oil yield and high oil quality. (C) 2015 Elsevier B.V. All rights reserved.</p

Mechanism of kerogen pyrolysis in terms of chemical structure transformation

This article presents an overview on carbon chemical structure transformation to understand kerogen thermal decomposition based on the chemical structure of kerogen. Formation of kerogen is highlighted to distinguish the typical types of kerogen containing in oil shale and coal. The oil production potential for oil shale and coal is found to little correlate with their organic amounts but to depend on the quality or chemical structure of organic matters. Aliphatic and aromatic carbons in kerogen are correlative with the yield of oil and carbon residue from Fischer Assay retorting, respectively. The aliphatic carbon moieties largely produce oil and gas, while aromatic carbon portion is apt to be converted directly to carbon residue during kerogen pyrolysis process. On this basis, an updated lumped mechanism model is proposed for viewing kerogen pyrolysis and provides a basis for understanding the transformation of carbon chemical structures. Further quantization and analysis conclude that: 1) 10-20% aliphatic carbon leaves in carbon residue as methyl groups and methylene bridges attached to aromatic rings, 2) 45-80% aliphatic carbon is directly distillated into oil, and 3) 15-40% aliphatic carbon is aromatized into aromatic carbon. The aromatization degree of aliphatic carbon varies with secondary reactions and its intrinsic chemical structure (alkyl chains, naphthenic and hydroaromatic hydrocarbons). Thus, the article justifies that primary pyrolysis determines the potentially maximal oil yield according to original carbon chemical structure, while the subsequent secondary reactions should be selective and minimized to determine the final oil yield and quality. (C) 2017 Elsevier Ltd. All rights reserved.</p