Characteristics of reaction and product microstructure during light calcination of magnesite in transport bed

A gas-heating laboratory transport bed was adopted to simulate the industrial transportbed reactor for flash calcination of magnesite, and a method based on TG analysis of a reacted sample was further developed to calculate the decomposition rate or conversion of its containing MgCO₃. The study investigated how the conversion and product reactivity as well as microstructure vary with reaction conditions including temperature, particle size and times of re-calcination for powder magnesite. Magnesite powder (<150 μm) calcination is a quick reaction that reaches 98% decomposition of its containing MgCO₃ in 1—2 s,corroborating the feasibility of magnesite flash-calcination in transport bed reactors. The coloration time given by the citric acid chromogenic method was 17—55 s and 294 s for the obtained products from transport and fixed beds, respectively. This proves the obviously higher activity and thus improved microstructure of the product from transport bed. During the calcination process, the MgO grain size of the product gradually increases, and the surface structure changes from loose and porous to dense and smooth. This structural change can be completed within a few seconds.     

非油炸黄桃脆片的加工工艺

为开发非油炸果蔬脆片产品,本文以黄桃为原料,采用流化-微波-烘焙相结合的生产工艺,以色差、Vc含量、感官评分和脆度等为评价指标,采用单因素实验和正交实验研究流化温度、流化风速、微波功率、微波时间、烘焙温度和时间等因素对黄桃脆片品质的影响,并分别对流化、微波和烘焙阶段进行工艺参数进行优化。试验结果表明:黄桃脆片的最佳生产工艺为流化温度55℃、流化风速300 m3/h;微波功率400 W、微波时间600 s,流化和微波转换时黄桃水分含量约20%;烘焙温度65℃、烘焙时间为35 min。在该工艺下研发的黄桃脆片口味甚佳,色泽较好,感官评分为91分,脆度值为469 g。该研究为非油炸果蔬脆片的加工提供了理论依据,也为果蔬类干制产品的开发拓宽了思路。     

Investigation of fluidized bed behaviour using electrical capacitance tomography

The temporal and cross-sectional distributions of particles in a 127 mm diameter fluidized bed have been obtained using a new generation, high-speed electrical capacitance tomography. Two planes of eight electrodes were used and mounted at 160 and 660 mm from the gas distributor which was a 3 mm thick porous plastic plate (maximum pore size of 50-70 μ m). 3 mm diameter, nearly-spherical polyethylene granules made up the bed. Experiments at sampling frequencies of 200-2000 cross-sections per second and gas superficial velocities from just below the minimum fluidization to 83% above minimum fluidization velocities were used. The time series of the cross-sectional average void fractions have been examined both directly and in amplitude and frequency space. The last two used probability density functions and power spectral densities. The information gathered shows that the fluidized bed was operating in the slugging mode, which is not surprising given the size of the particles. It has been found that an increase in the excess gas velocity above the minimum fluidization velocity resulted in an increase in the mean void fraction, an increase in the length and velocity of the slug bubbles as well as the bed height, and a slight decrease in the slug frequency. The results are presented in a level of detail suitable for comparison with later numerical simulation.     

Fluidization of spherical versus elongated particles: Experimental investigation using magnetic particle tracking

In biomass processing fluidized beds are used to process granular materials where particles typically possess elongated shapes. However, for simplicity, in computer simulations particles are often considered spherical, even though elongated particles experience more complex particle– particle interactions as well as different hydrodynamic forces. The exact effect of these more complex interactions in dense fluidized suspensions is still not well understood. In this study we use the magnetic particle tracking technique to compare the fluidization behavior of spherical particles to that of elongated particles. We found a considerable difference between fluidization behavior of spherical versus elongated particles in the time-averaged particle velocity field as well as in the time-averaged particle rotational velocity profile. Moreover, we studied the effect of fluid velocity and the particle's aspect ratio on the particle's preferred orientation in different parts of the bed, which provides new insight in the fluidization behavior of elongated particles.     

高海拔地区大型循环流化床锅炉特性研究

结合青海盐湖工业股份有限公司供热中心4×480 t/h循环流化床(CFB)锅炉的启动调试,通过理论论证及实际应用,对高海拔地区大型循环流化床锅炉特性进行研究,解决了低气压地区流化床锅炉高负荷工况下频繁结焦问题。给出了流化床锅炉正常运行所要维持的流化风速范围,明确了高海拔地区循环流化床锅炉流化风速计算应选用标态风量,与低海拔地区一致,使得此类技术具备实际可参考性及可操作性,对解决同类型问题有一定的参考价值。     

Production of aromatics by catalytic fast pyrolysis of cellulose in a bubbling fluidized bed reactor

Catalytic fast pyrolysis of cellulose was studied at 500°C using a ZSM‐5 catalyst in a bubbling fluidized bed reactor constructed from a 4.92‐cm ID pipe. Inert gas was fed from below through the distributor plate and from above through a vertical feed tube along with cellulose. Flowing 34% of the total fluidization gas through the feed tube led to the optimal mixing of the pyrolysis vapors into the catalyst bed, which experimentally corresponded to 29.5% carbon aromatic yield. Aromatic yield reached a maximum of 31.6% carbon with increasing gas residence time by changing the catalyst bed height. Increasing the hole‐spacing in the distributor plate was shown to have negligible effect on average bubble diameter and hence did not change the product distribution. Aromatic yields of up to 39.5% carbon were obtained when all studied parameters were optimized. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1320–1335, 2014     

Continuous flow characterization of solid biomass in a reciprocating/rotating scraper tube: An experimental study

The performance of reciprocating/rotating scrapers has been assessed in a visualization study of the continuous flow hydrodynamics of air‐fluidized solid biomass under varying conditions of air flow rate and scraping velocities. A combination of low air flow rates and high scraping velocities results in more uniform flow of both types of biomass investigated. Power consumed by the reciprocating action of the scrapers increases with the scraping velocity but typically represents no more than 20% of the overall power consumption at the highest air flow rate applied. We also demonstrate that rotation of the scrapers superimposed on their reciprocating action gives higher flow rate of biomass and better mixing within the bulk solid compared to reciprocating action alone. The application of the reciprocating/rotating scraper technology described in this study represents a viable step forward in developing a continuous, large‐scale process for the microwave‐assisted decomposition of solid biomass to produce bio‐oils. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3732–3738, 2014     

Improved magnetic particle tracking technique in dense gas fluidized beds

Noninvasive monitoring of multiphase flow is rapidly gaining increased interest. More specifically noninvasive particle tracking techniques have received a lot of attention in recent years to study dense granular flow. However, these techniques are usually quite expensive and require strict safety measures. An improved magnetic particle tracking (MPT) technique for dense granular flow will be presented in this article. The improvements of the analysis technique for MPT will be demonstrated and rigorously tested with a three‐dimensional system and two‐dimensional sensor system. The strengths and limitations of the MPT technique will also be reported. Finally, the results of the MPT are compared with data obtained from a combined particle image velocimetry and digital image analysis technique. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3133–3142, 2014