Characteristics of oil shale pyrolysis in a two-stage fluidized bed

Rapid pyrolysis of oil shale coupled with in-situ upgrading of pyrolysis volatiles over oil shale char was studied in a laboratory two-stage fluidized bed(TSFB) to clarify the shale oil yield and quality and their variations with operating conditions. Rapid pyrolysis of oil shale in fluidized bed(FB) obtained shale oil yield higher than the Fischer Assay oil yield at temperatures of 500-600 ℃. The highest yield was 12.7 wt% at 500 ℃ and was about1.3 times of the Fischer Assay oil yield. The heavy fraction(boiling point 350 ℃) in shale oil at all temperatures from rapid pyrolysis was above 50%. Adding an upper FB of secondary cracking over oil shale char caused the loss of shale oil but improved its quality. Heavy fraction yield decreased significantly and almost disappeared at temperatures above 550 ℃, while the corresponding light fraction(boiling point 350 ℃) yield dramatically increased. In terms of achieving high light fraction yield, the optimal pyrolysis and also secondary cracking temperatures in TSFB were 600 ℃, at which the shale oil yield decreased by 17.74% but its light fraction yield of 7.07 wt% increased by 86.11% in comparison with FB pyrolysis. The light fraction yield was higher than that of Fischer Assay at all cases in TSFB. Thus, a rapid pyrolysis of oil shale combined with volatile upgrading was important for producing high-quality shale oil with high yield as well.     

CSFB applied to fluidized-bed gasification of special fuels

The new version of a comprehensive simulation program of moving and fluidized-beds (CSFB or CSFMB) has been tested against data generated from a gasification unit at the University of California at Davis (UCD), Department of Biological and Agricultural Engineering. The pilot operated at atmospheric pressure under bubbling fluidized-bed and consumed various biomasses as well residues. Air was used as gasifying agent and electrical resistances around the reactor helped heating the reactor during start-up and were kept under low energy discharge during experiments. CSFMB was adapted to allow simulation of such cases as well to several other possibilities of additional heating systems to reactors. The present paper presents the results from cases of almond shells and walnut pruning gasification. Good to reasonable agreement between simulation and operational data have been obtained.     

Multi-stage biomass gasification in Internally Circulating Fluidized-bed Gasifier (ICFG): Test operation of animal-waste-derived biomass and parametric investigation at low temperature

In this study, the design, construction and operation of an Internally Circulating Fluidized-bed Gasifier (ICFG) are introduced in detail. ICFG design provides a multi-stage gasification process, with bed material acting as the medium for char combustion and heat exchange by its internal circulation. And it is used for the steam gasification of animal waste at low temperature in view of producing fuel gas. The effects of pressure balance, pyrolysis temperature, catalytic temperature and steam/feedstock ratio on the gasifier performance (e.g. product gas yield, gas composition, tar content) are also discussed. Hydrogen-rich and low-tar product gas can be produced from the low-calorific feedstock, in the properly designed process together with high-performance catalyst.     

Semi-continuous hydrogen production from catalytic methane decomposition using a fluidized-bed reactor

Non-oxidative, catalytic decomposition of hydrocarbons is an alternative, one-step process to produce pure hydrogen with no production of carbon oxides or higher hydrocarbons. Carbon produced from the decomposition reaction, in the form of potentially valuable carbon nanotubes, remains anchored to the active catalyst sites in a fixed bed. To facilitate periodical removal of this carbon from the reactor and to make hydrogen production continuous, a fluidized-bed reactor was envisioned. The hypothesis that the tumbling and inter-particle collisions of bed material would efficiently separate nanotubes anchored to the active catalyst sites of the bed particles was tested and shown to be invalid. However, a switching mode reaction system for the semi-continuous production of hydrogen and carbon nanotubes by periodic removal and replenishment of the catalytic bed material has been successfully demonstrated.     

流化床中吸附干燥大豆特性研究

在流化状态下种子（大豆）与硅胶能够很好的混合，通过湿含量梯度进行传质，干燥后种子质量显著提高；种子与硅胶粒径不同，便于分离。通过实验比较了在不同混合比和不同流化条件下种子的干燥特性。随着吸附剂的加入，干燥速率明显增大，并且随着风速的提高、硅胶与种子混合比的增大，干燥速率也随之提高。通过试验还表明，采取流化床与固定床动静结合的吸附干燥方式，在节能和产品质量方面有一定的优势。     

Design and performance evaluation of triboelectrostatic separation system for the separation of PVC and PET materials using a fluidized bed tribocharger

A triboelectrostatic separation system using a fluidized-bed tribocharger for the removal of PVC material in the mixture of PVC/PET plastics was designed and evaluated as a function of tribocharger material, air flow rate, electric field strength, and the mixing ratio of two-component mixed plastics. The test system consists of the fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. PVC and PET particles can be imparted negative and positive surface charges, respectively, due to the difference in the work function values of plastics suspended in the fluidized-bed tribocharger, and can be separated by passing them through an external electric field. Experimental results show that separation efficiency is strongly dependent on the tribocharger material, electric field strength and particles mixing ratio. In the optimum conditions of 150l/m air flow rate and 2.6 kV/cm electric field strength, highly concentrated PVC (99.1%) can be recovered with a yield of more than 95% from the mixture of PVC and PET materials for a single stage of processing.     

提高流化床中铁矿粉还原反应速度的研究(Ⅰ)

为探索提高还原反应速度和防止粘结可能的新途径,研究了以流化床还原尾气先对矿粉进行附着碳处理并预热,再进行流态化还原的过程,并运用极差分析方法考察了影响还原速度和粘结的因素主次顺序。实验表明,用矿粉预附着碳后再还原和提高还原压力、还原气线速的方法,能使流化床中铁矿粉的还原速度大大增快并防止粘结,矿粉附着碳量5%,达70%还原度所需的时间仅为8分钟,比不采取附着碳工序的还原时间缩短20分钟左右。影响还原速度和粘结的主要因素分别是矿粉附着碳量和还原温度。     

Preparation of nano-sized tungsten carbide via fluidized bed

Ultrafine or nano-sized of tungsten carbide(WC) is the key material to prepare ultrafine grained cemented carbides. In this paper, nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide(WO_(2.72)) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The relationship between particle sizes and reaction temperatures, residence times, atmospheres has been investigated systematically. In addition, the physical–chemical indexes(such as residual oxygen, total carbon and free carbon) of the products were measured. The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950 °C. As the residence time increased, the particle size decreased gradually,and then increased due to slight sintering. The introduction of hydrogen reduced the carbonization rate, and is not beneficial to obtaining nano-sized WC. Products that satisfy the standard were obtained when WO_(2.72) reacted with CO at 850 °C, 900 °C and 950 °C for 3.0 h, 2.5 h and 2.0 h, respectively. The particle sizes of the three samples calculated from the specific surface area were 46.4 nm, 53.2 nm and 52.1 nm, respectively.     

Crystallization and Drying of Milk Powder in a Multiple-Stage Fluidized Bed Dryer

The rationale of this study has been to use fluidized beds to crystallize amorphous spray-dried skim milk powders with multiple stages of processing at different temperatures and humidities with the aim of rapidly making mostly crystalline powders. This paper discusses the performance of a multiple-stage fluidized bed dryer, and a combination of crystallization of lactose in spray drying at high humidity (lactose nuclei formation) and subsequent fluidized bed drying. Two different combinations of spray dryer and multi-stage fluidized-bed dryer have been suggested to crystallize lactose in skim milk powder. The results show significant improvements in the crystallinity of the powders. Moisture sorption test and X-ray diffraction analysis were used to assess the crystallinity of the powders. The processed powders that were crystallized in a humid-loop spray drying combined with a two-stage fluidized-bed dryer/crystallizer showed 92% improvement in lower amorphicity by processing at different stages of 70°C, 50% RH and 80°C, 50% RH for 15 minutes. The conventionally spray-dried powders that were crystallized in a three-stage fluidized-bed dryer/crystallizer showed 87% improvement in lower amorphicity (less moisture sorption) by processing at different stages of 60°C, 50% RH; 70°C, 40% RH; and 80°C, 40% RH for 20 minutes. The multiple-stage fluidized bed system showed distinctive potential to crystallize lactose significantly in skim milk powder using an industrial-feasible process.     

Egg-shell like structure in dried milk powders

The development of an egg-shell like structure in skim milk powder has been investigated in a stirred fluidized-bed dryer at various temperatures and humidities. The developed particles have crystalline surfaces and amorphous cores. The SEM analysis shows a thin layer of lactose crystals (at the nano-scale) that is formed on the surface of the powder while the XRD analysis shows that the particle cores are still amorphous (egg-shell form), so the surface properties have improved while the bulk desirable properties (of good solubility) have been retained. The resulting powders show better flowability and stability and less cake formation during storage by retaining good rehydration and dissolution times. The nano-coating of milk powders by crystalline lactose from the powder itself and the improvement in stability and flowability could be a worthwhile solution for dairy industries.