Solids Flux, Velocity and Local Solid Fraction Measurements in a CFB Riser

In this investigation a fiber-optic probe and an extraction solids probe are used to measure particle velocities and solids flux values. These are subsequently used to determine the local solids fractions as a function of radial position in a cold flow circulating fluidized bed (CFCFB) in operation at the National Energy Technology Laboratory (NETL). Measurements were taken under several separate operating conditions ranging from dilute up-flow to core-annular flow to fast fluidization using nominal 800 micron cork particles. The solids properties and test operating conditions were chosen particularly to provide dynamic similitude between the test data and the operation of a high temperature, high pressure gasifier. The data from these conditions is different in many ways from the data developed using more conventional solids (glass, FCC, and sand) at atmospheric conditions. In this paper, the data from the middle of the riser corresponding to a height of nominally 8 m is presented. Average solids fractions are compared to the apparent values based upon the pressure drop and the near wall measurements are compared to LDV generated solids fraction values, showing good agreement with both. Also, the radial profiles tended to be relatively flat with a sharp rise at the wall

Applications of tribology and fracture mechanics to determine wear and impact attrition of particulate solids in CFB systems

In recent years, much attention has been focused on the development of novel technologies for carbon capture and chemicals production that utilize a circulating fluidized bed configuration; examples include chemical looping combustion and circulation of temperature swing adsorbents in a CFB configuration for CO2 capture. A major uncertainty in determining the economic feasibility of these technologies is the required solids makeup rate, which, among other factors, is due to impact and wear attrition at various locations, including standpipes, cyclones, and the gas jets in fluid beds. While correlations have been developed that estimate the attrition rates at these areas, these correlations are dependent on constants that are an unknown function of the solid properties and system. Thus, it is difficult to determine the attrition rate a priori without performing extensive experiments on the materials or scaling up entirely. In this work, the authors apply knowledge of fundamental material properties from fields of tribology (the study of wear) and fracture mechanics to the knowledge of forces and sliding distances determined from hydrodynamic models to develop basic attrition models for novel CFB systems. The equations are derived for common equipment found in CFBs, and the equations are compared to experimental data of attrition in the literature

Operating experience of a 50kwth methane chemical looping reactor

Chemical Looping Combustion (CLC) has the potential to efficiently capture CO2 from the combustion of fossil fuels at an affordable price. CLC is a process that produces a flue gas primarily consisting of CO2 and H2O. The CO2 can be easily separated and captured by condensing the H2O, similar to an oxy-fuel process. Although the process looks promising on paper, the challenge is to make chemical looping a reality by demonstrating that the process can work economically. To help achieve this goal, the US Department of Energy’s (DOE) National Energy Technology Laboratory (NETL), has constructed and tested a 50kWth chemical looping reactor (CLR). The general arrangement of the process consists of a bubbling fluidized bed fuel reactor and a fluidized bed/riser air reactor. Three different metal oxide based oxygen carriers have been successfully tested during week-long test campaigns; a hematite ore, promoted hematite ore, and a manufactured copper based oxygen carrier. These three carriers have demonstrated various levels of performance including conversion of natural gas to CO2 and durability. The goal of these tests is to better understand real process metrics so that appropriate economic analysis can be performed

Measurement of Gas Velocities in the Presence of Solids in the Riser of a Cold Flow Circulating Fluidized Bed

The local gas velocity and the intensity of the gas turbulence in a gas/solid flow are a required measurement in validating the gas and solids flow structure predicted by computational fluid dynamic (CFD) models in fluid bed and transport reactors. The high concentration and velocities of solids, however, make the use of traditional gas velocity measurement devices such as pitot tubes, hot wire anemometers and other such devices difficult. A method of determining these velocities has been devised at the National Energy Technology Laboratory employing tracer gas. The technique developed measures the time average local axial velocity gas component of a gas/solid flow using an injected tracer gas which induces changes in the heat transfer characteristics of the gas mixture. A small amount of helium is injected upstream a known distance from a self-heated thermistor. The thermistor, protected from the solids by means of a filter, is exposed to gases that are continuously extracted from the flow. Changes in the convective heat transfer characteristics of the gas are indicated by voltage variations across a Wheatstone bridge. When pulsed injections of helium are introduced to the riser flow the change in convective heat transfer coefficient of the gas can be rapidly and accurately determined with this instrument. By knowing the separation distance between the helium injection point and the thermistor extraction location as well as the time delay between injection and detection, the gas velocity can easily be calculated. Variations in the measured gas velocities also allow the turbulence intensity of the gas to be estimated

Fundamentals of rotating fluidized beds and application to particle separation

Rotating fluidized beds provide unique opportunities to exploit fluidization under higher particle forces. The centripetal force in a rotating bed is typically on the order of 10 times the force of gravity. Since the force keeping the particles in the unit is larger, the drag force can also be larger, allowing for higher gas velocities. This operating regime provides opportunities for higher mass transfer, heat transfer, gas throughput, and bubble suppression. One application for using a rotating fluidized bed in in Chemical Looping Combustion (CLC). When solid fuels are used, oxygen carrier and ash are mixed in the process. In order to maintain high carbon capture efficiencies and recyclability of the oxygen carrier, the ash needs to be separated from the oxygen carrier. This separation can be done aerodynamically since the oxygen carrier is larger and heavier then the ash. It is theorized that rotating fluidized beds could improve the separation process efficiency and throughput as compared to conventional fluidized beds. A 43cm diameter, 2.5cm thick rotating fluidized bed has been designed and constructed to investigate the application of the rotating fluidized beds to particle separation. A series of experiments have been performed to investigate the separation of glass beads (coal ash analog) from a typical chemical looping oxygen carrier. These experiments demonstrate the use of a rotating fluidized bed for particle separation as well as investigate the operational parameters that influence the efficiency of separation

Defining failed induction of labor

BACKGROUND: While there are well-accepted standards for the diagnosis of arrested active-phase labor, the definition of a "failed" induction of labor remains less certain. One approach to diagnosing a failed induction is based on the duration of the latent phase. However, a standard for the minimum duration that the latent phase of a labor induction should continue, absent acute maternal or fetal indications for cesarean delivery, remains lacking. OBJECTIVE: The objective of this study was to determine the frequency of adverse maternal and perinatal outcomes as a function of the duration of the latent phase among nulliparous women undergoing labor induction. METHODS: This study is based on data from an obstetric cohort of women delivering at 25 U.S. hospitals from 2008-2011. Nulliparous women who had a term singleton gestation in the cephalic presentation were eligible for this analysis if they underwent a labor induction. Consistent with prior studies, the latent phase was determined to begin once cervical ripening had ended, oxytocin was initiated and rupture of membranes (ROM) had occurred, and was determined to end once 5 cm dilation was achieved. The frequencies of cesarean delivery, as well as of adverse maternal (e.g., cesarean delivery, postpartum hemorrhage, chorioamnionitis) and perinatal outcomes (e.g., a composite frequency of either seizures, sepsis, bone or nerve injury, encephalopathy, or death), were compared as a function of the duration of the latent phase (analyzed with time both as a continuous measure and categorized in 3-hour increments). RESULTS: A total of 10,677 women were available for analysis. In the vast majority (96.4%) of women, the active phase had been reached by 15 hours. The longer the duration of a woman's latent phase, the greater her chance of ultimately undergoing a cesarean delivery (P<0.001, for time both as a continuous and categorical independent variable), although more than forty percent of women whose latent phase lasted for 18 or more hours still had a vaginal delivery. Several maternal morbidities, such as postpartum hemorrhage (P < 0.001) and chorioamnionitis (P < 0.001), increased in frequency as the length of latent phase increased. Conversely, the frequencies of most adverse perinatal outcomes were statistically stable over time. CONCLUSION: The large majority of women undergoing labor induction will have entered the active phase by 15 hours after oxytocin has started and rupture of membranes has occurred. Maternal adverse outcomes become statistically more frequent with greater time in the latent phase, although the absolute increase in frequency is relatively small. These data suggest that cesarean delivery should not be undertaken during the latent phase prior to at least 15 hours after oxytocin and rupture of membranes have occurred. The decision to continue labor beyond this point should be individualized, and may take into account factors such as other evidence of labor progress

Gasification processes old and new: a basic review of the major technologies. Energies 2010

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