Characterization of loop seal in a complex circulating fluidized bed system

Loop seal is widely used in circulating fluidized bed systems to transport solids from high pressure reactor to low pressure reactor. It also found applications in complex systems with multiple reactors. The functions of the loop seal include circulating solids between reactors with desired solids flow rate, preventing gas leak from either reactor, and providing pressure balance for the proper operation of the system. The proper design and sizing of the loop seal are necessary so that the operation of loop seal is not to disturb the desired, independent operation of the reactors. Despite its extensive applications, the systematic, experimental studies that characterize the loop seal operation in the complex reactor systems are limited. Among the available studies, the particles used are mainly Geldart group A and group B particles. Little is conducted on experiments with Geldart Group D particles. This paper examines the operation of solids through a loop seal in a complex circulating fluidized bed system using Geldart group D particles. The circulating fluidized bed has two reactors whose operational conditions are controlled independently, with a loop seal placed between them. Besides the loop seal and the two reactors, the CFB system also includes a riser, a cyclone, a solids receiver, and standpipes. The solids inlet in the supply chamber of the loop seal is connected to the bottom of the standpipe, while the solids outlet in the return chamber is connected to the solids inlet of a dense phase fluidized bed reactor. A gas outlet with a valve and a gas flowmeter is designed to be located at the top of the return chamber to control the gas flow rate flowing into the fluidized bed reactor downstream the loop seal. The rectangular supply chamber has a dimension of 25 mm x 75 mm x 150 mm and the square return chamber is 75 mm × 75 mm × 300 mm. The pressure profile of the system is recorded using differential pressure gauges and pressure gauges are installed throughout the system. The solids circulation rate of the system is measured using a solids bypassing system connected between the bottom of the system and the top of the standpipe. Effects of operating parameters, such as supply chamber gas flow rate, return chamber fluidization velocity, and gas flow rate from the gas outlet of return chamber, on the operation of the circulating fluidized bed system, including the solids circulation rate and the system pressure balance are also analyzed and discussed

Hydrodynamics of chemical looping combustion systems: Effects of reactor design parameters

Chemical looping combustion (CLC) has been considered a transformational technology for the carbon dioxide (CO2) capture in power plants. Extensive research has been conducted on the selection and preparation of oxygen carrier (OC) materials, their production and characterization, CLC process development, and reactor system demonstrations from bench to pilot scales. Different configurations of CLC system have been proposed and tested, such as interconnected circulating fluidized bed (CFB) reactor systems, CFB with counter-current moving bed reactor systems, and fixed bed reactor systems. Despite considerable research efforts on the development of CLC systems, the analysis of the effects of hydrodynamic characteristics of OC particles, such as particle size, density and support content, on the design and operation of the CLC system is still lacking. Further, major operational parameters that continue to be in need of exploration include the control of the solids circulation rate of the system, pressure balance and profile of the system, and the gas sealing from the interconnected reactors. This study examines the inter-relationships between the hydrodynamics and kinetics characteristics of the OC particles and the operating conditions of the reactors, along with the reaction and heat management of the system. The design principle that is applied to sizing the reactor system is developed. Parametric effects on the system performance due to the variation of particle parameters, reactor size, system pressure, and operating conditions are simulated and analyzed

ECVT Imaging of 3-D Flow Structures and Solids Concentration Distributions in a Riser and a Bend of a Gas-Solid Circulating Fluidized Bed

Experimental studies using electrical capacitance volume tomography (ECVT) are conducted to examine gas-solid flows in a riser and a bend of a 0.05 m (2 in) ID gas-solid circulating fluidized bed (CFB) system. The quantitative measurements using ECVT are made that illustrate a three-dimensional symmetric core-annulus structure in the riser and a non-centro-symmetric core-annulus structure in the bend. Results on the volume solids holdup distributions in the riser and in the bend at various operating conditions are also obtained

Modeling on Heterogeneous Structure in Acceleration Regime of Gas-Solid Riser Flows

Recent measurement of solid concentration in gas-solid riser flows by Electric Capacitance Tomography (ECT) reveals a strong heterogeneous structure, typically represented by a core-annulus-wall zone pattern. In this paper we present a mechanistic model in which the formation of the heterogeneous structure is due to the radial migration of solid flow from the wall toward center as well as due to the non-uniform acceleration of solids across the cross-section near the bottom of the riser. Firstly we present the general governing equations and discuss problem closure; then a simplified model with one-way flow coupling between the wall region and the core-annulus region is proposed to simulate the formation and development process of heterogeneous flow structures in the riser. Typical results of the three-zone flow structure along the riser are illustrated, which include the axial distributions of solids concentration and phase velocities in each zone, in addition to the pressure distributions. The model is also validated against the ECT measurements

Female media use behavior and agreement with publicly promoted agenda-specific health messages.

This study set out to explore the relationship between female media use behavior and agreement with agenda-specific publicly promoted health messages. A random digit dial telephone cross-sectional survey was conducted using a nationally representative sample of female residents aged 25 and over. Respondents' agreement with health messages was measured by a six-item Health Information Scale (HIS). Data were analyzed using chi-square tests and multiple logistic regression. This survey achieved a response rate of 86% (n = 1074). In this study the longest duration of daily television news watching (OR = 2.32), high self-efficacy (OR = 1.56), and greater attention to medical and health news (OR = 5.41) were all correlates of greater agreement with the selected health messages. Surprisingly, Internet use was not significant in the final model. Many women that public health interventions need to be targeting are not receptive to health information that can be accessed through Internet searches. However, they may be more readily targeted by television campaigns. Agenda-specific public health campaigns aiming to empower women to serve as nodes of information transmission and achieve efficient trickle down through the family unit might do better to invest more heavily in television promotion

EFFECT OF BACKPACK ON SELECTED GAIT PARAMETERS OF PRIMARY SCHOOL CHilDREN

The purpose of this study was to compare the effects of a backpack load of 15% body weight (BW) on selected gait parameters of primary school children. Ten participants were recruited from primary school (age: 10.3 ± 0.48 yrs; hI: 141.3 ± 0 .41 cm; mass: 38.1 ± 6.1 kg). A JVC 9800 (60 hz) video camera synchronized with an AMTI force plate (1200 Hz) were used to collect data. A repeated measure t-test (p < 0.05) was used for group comparisons. The backpack load did not affect either the proportionate time of the stance phase, swing phase, or the magnitude of selected vertical and anterioposterior ground reaction force parameters. However, the 15% backpack load did cause a significant increase in proportionate double leg support time

General Versus Spinal Anesthesia: Which is a Risk Factor for Octogenarian Hip Fracture Repair Patients?

SummaryBackgroundMost studies have shown no difference between the two types of anesthesia administered to hip fracture patients. This study compared postoperative morbidity and mortality in octogenarian patients who received either general or spinal anesthesia for hip fracture repair.MethodsWe retrospectively analyzed the hospital records of 335 octogenarian patients who received hip fracture repair in our teaching hospital between 2002 and 2006. A total of 167 and 168 patients received general and spinal anesthesia, respectively. Morbidity, mortality, and intraoperative and preoperative variables were compared between groups.ResultsThere were no mortality differences between spinal and general anesthesia groups. However, the overall morbidity was greater in the general anesthesia group than in the spinal anesthesia group (21/167 [12.6%] vs. 9/168 [5.4%]; p = 0.02). Respiratory system-related morbidity was also higher in the general anesthesia group than in the spinal anesthesia group (11/167 [6.6%] vs. 3/168 [1.8%]; p = 0.03). Logistic regression analysis revealed two significant predictors of postoperative morbidity: anesthesia type (general; odds ratio, 2.39) and preexisting respiratory diseases (odds ratio, 3.38).ConclusionGeneral anesthesia increased the risk of postoperative morbidity in octogenarian patients after hip fracture repair, and patients with preexisting respiratory diseases were especially vulnerable. Spinal anesthesia is strongly recommended in such individuals

The novel ZIP4 regulation and its role in ovarian cancer

Our RNAseq analyses revealed that ZIP4 is a top gene up-regulated in more aggressive ovarian cancer cells. ZIP4's role in cancer stem cells has not been reported in any type of cancer. In addition, the role and regulation of ZIP4, a zinc transporter, have been studied in the context of extracellular zinc transporting. Factors other than zinc with ZIP4 regulatory effects are essentially unknown. ZIP4 expression and its regulation in epithelial ovarian cancer cells was assessed by immunoblotting, quantitative PCR, or immunohistochemistry staining in human ovarian tissues. Cancer stem cell-related activities were examined to evaluate the role of ZIP4 in human high-grade serous ovarian cancer cells in vitro and in vivo. RNAi and CRISPR techniques were used to knockdown or knockout ZIP4 and related genes. Ovarian cancer tissues overexpressed ZIP4 when compared with normal and benign tissues. ZIP4 knockout significantly reduced several cancer stem cell-related activities in EOC cells, including proliferation, anoikis-resistance, colony-formation, spheroid-formation, drug-resistance, and side-population in vitro. ZIP4-expressing side-population highly expressed known CSC markers ALDH1 and OCT4. ZIP4 knockout dramatically reduced tumorigenesis and ZIP4 overexpression increased tumorigenesis in vivo. In addition, the ZIP4-expressing side-population had the tumor initiating activity. Moreover, the oncolipid lysophosphatic acid effectively up-regulated ZIP4 expression via the nuclear receptor peroxisome proliferator-activated receptor gamma and lysophosphatic acid 's promoting effects in cancer stem cell-related activities in HGSOC cells was at least partially mediated by ZIP4 in an extracellular zinc-independent manner. Our critical data imply that ZIP4 is a new and important cancer stem cell regulator in ovarian cancer. Our data also provide an innovative interpretation for the apparent disconnection between low levels of zinc and up-regulation of ZIP4 in ovarian cancer tissues

Electrical Capacitance Volume Tomography for the Packed Bed Reactor ISS Flight Experiment

Fixed packed bed reactors are compact, require minimum power and maintenance to operate, and are highly reliable. These features make this technology a highly desirable unit operation for long duration life support systems in space. NASA is developing an ISS experiment to address this technology with particular focus on water reclamation and air revitalization. Earlier research and development efforts funded by NASA have resulted in two hydrodynamic models which require validation with appropriate instrumentation in an extended microgravity environment. To validate these models, the instantaneous distribution of the gas and liquid phases must be measured.Electrical Capacitance Volume Tomography (ECVT) is a non-invasive imaging technology recently developed for multi-phase flow applications. It is based on distributing flexible capacitance plates on the peripheral of a flow column and collecting real-time measurements of inter-electrode capacitances. Capacitance measurements here are directly related to dielectric constant distribution, a physical property that is also related to material distribution in the imaging domain. Reconstruction algorithms are employed to map volume images of dielectric distribution in the imaging domain, which is in turn related to phase distribution. ECVT is suitable for imaging interacting materials of different dielectric constants, typical in multi-phase flow systems. ECVT is being used extensively for measuring flow variables in various gas-liquid and gas-solid flow systems. Recent application of ECVT include flows in risers and exit regions of circulating fluidized beds, gas-liquid and gas-solid bubble columns, trickle beds, and slurry bubble columns. ECVT is also used to validate flow models and CFD simulations. The technology is uniquely qualified for imaging phase concentrations in packed bed reactors for the ISS flight experiments as it exhibits favorable features of compact size, low profile sensors, high imaging speed, and flexibility to fit around columns of various shapes and sizes. ECVT is also safer than other commonly used imaging modalities as it operates in the range of low frequencies (1 MHz) and does not radiate radioactive energy. In this effort, ECVT is being used to image flow parameters in a packed bed reactor for an ISS flight experiment