Observation of Flow Regime Transition in a CFB Riser Using an LDV

The solids flow in a circulating fluidized bed (CFB) riser is often described to have a core-annular structure. For a given superficial gas velocity, at the initial introduction of solids into a riser a flow structure of dilute upflow regime exists. Continuing to increase the solids flow in the riser transitions the flow structure to the core-annular flow regime. However, with further increase of solids flow a condition is reached, depending on the superficial gas velocity, where all the solids across the riser cross section flow upwards, even those at the wall. When the solids flux, solids fraction and gas velocity are relatively high, such a condition is described as the dense phase suspense upflow (DSU) regime. In this paper we report our observations of these flow regime transitions by using a laser Doppler velocimeter (LDV) to monitor the upward and downward particle flow velocities at and near the riser wall of the National Energy Technology Laboratory’s 30.4 centimeters diameter CFB cold flow model. The particles were high density polyethylene (PPE) spheres with a Sauter mean diameter of 861 micron and a density of 800 kg/m3. Three superficial gas velocities of 6.55 m/s, 10.67 m/s and 13.72 m/s were used in this study. For the case of superficial gas velocity 6.55 m/s, the experimental data show that the transition from dilute upflow to core-annular flow occurred when the solids flux was about 7 kg/m2-s and the transition from core-annular flow to dense suspension upflow was about 147 kg/m2-s. As the superficial gas velocity was increased to 10.67 m/s the corresponding flow regime transitions were at 34 kg/m2-s and 205 kg/m2-s, respectively. For the case of superficial gas velocity of 13.72 m/s the data showed no distinct transition of flow regimes. The particles were all upflow for the range of solids fluxes from 10 kg/m2-s to 286 kg/m2-s

Flow Regime Study in a High Density Circulating Fluidized Bed Riser with an Abrupt Exit

Flow regime study was conducted in a 0.3 m diameter, 15.5 m height circulating fluidized bed (CFB) riser with an abrupt exit at the National Energy Technology Laboratory of the U. S. Department of Energy. Local particle velocities were measured at various radial positions and riser heights using an optical fiber probe. On-line measurement of solid circulating rate was continuously recorded by the Spiral. Glass beads of mean diameter 61 μm and particle density of 2,500 kg/m3 were used as bed material. The CFB riser was operated at various superficial gas velocities ranging from 3 to 7.6 m/s and solid mass flux from 20 to 550 kg/m2-s. At a constant riser gas velocity, transition from fast fluidization to dense suspension upflow (DSU) regime started at the bottom of the riser with increasing solid flux. Except at comparatively low riser gas velocity and solid flux, the apparent solid holdup at the top exit region was higher than the middle section of the riser. The solid fraction at this top region could be much higher than 7% under high riser gas velocity and solid mass flux. The local particle velocity showed downward flow near the wall at the top of the riser due to its abrupt exit. This abrupt geometry reflected the solids and, therefore, caused solid particles traveling downward along the wall. However, at location below, but near, the top of the riser the local particle velocities were observed flowing upward at the wall. Therefore, DSU was identified in the upper region of the riser with an abrupt exit while the fully developed region, lower in the riser, was still exhibiting core-annular flow structure. Our data were compared with the flow regime boundaries proposed by Kim et al. [1] for distinguishing the dilute pneumatic transport, fast fluidization, and DSU

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

Numerical simulation of the influence of the orifice aperture on the flow around a teeth-shaped obstacle

The sound generated during the production of the sibilant [s] results from the impact of a turbulent jet on the incisors. Several geometric characteristics of the oral tract can affect the properties of the flow-induced noise so that the characterization of the influence of different geometric parameters on the acoustic sources properties allows determining control factors of the noise production. In this study, a simplified vocal tract/teeth geometric model is used to numerically investigate the flow around a teeth-shaped obstacle placed in a channel and to analyze the influence of the aperture at the teeth on the spectral properties of the fluctuating pressure force exerted on the surface of the obstacle, which is at the origin of the dipole sound source. The results obtained for Re = 4000 suggest that the aperture of the constriction formed by the teeth modifies the characteristics of the turbulent jet downstream of the teeth. Thus, the variations of the flow due to the modification of the constriction aperture lead to variations of the spectral properties of the sound source even if the levels predicted are lower than during the production of real sibilant fricative

Solids Fraction Measurement with a Reflective Fiber Optic Probe

A method has been developed to extract solids fraction information from a reflective fiber optic probe. The commercially available reflective fiber optic probe was designed to measure axial particle velocity (both up and down directions). However, the reflected light intensity measured is related to particle size and particle concentration. A light reflection model is used to relate the reflected light intensity to solids fraction. In this model we assume that the reflected light intensity is a fixed fraction, K1, of the total light intensity lost in penetration of a solid layer. Also, the solids fraction is related to particle concentration, N, in the light path, by N = K2 (1- ε), where (1-ε) is the solids fraction. The parameters K1 and K2 are determined through a calibration and curve fitting procedure. This paper describes this procedure and the steps taken to derive the values of K1 and K2. It is proposed that the reflective fiber optic can be used for real time measurement of solids fraction in a circulating fluid bed

Background Radioactivity in the Decorah Fault Region

A known fault site at Decorah, Iowa, was surveyed for indicative variations in surface radioactivity. A portable ionization chamber revealed significant increases in gamma ray intensity at several locations. At one point the radiation level was 70% greater than the background intensity. Measurements repeated one year later verified this pattern. Radiation contours were plotted over an extensive area in the city of Decorah. This map, with other items of supporting evidence, indicated a possible fault strike of approximately N 55° W

Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called “type zero” sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding

HIV Testing of At Risk Patients in a Large Integrated Health Care System

OBJECTIVE: Early identification of HIV infection is critical for patients to receive life-prolonging treatment and risk-reduction counseling. Understanding HIV screening practices and barriers to HIV testing is an important prelude to designing successful HIV screening programs. Our objective was to evaluate current practice patterns for identification of HIV. METHODS: We used a retrospective cohort analysis of 13,991 at-risk patients seen at 4 large Department of Veterans Affairs (VA) health-care systems. We also reviewed 1,100 medical records of tested patients. We assessed HIV testing rates among at-risk patients, the rationale for HIV testing, and predictors of HIV testing and of HIV infection. RESULTS: Of the 13,991 patients at risk for HIV, only 36% had been HIV-tested. The prevalence of HIV ranged from 1% to 20% among tested patients at the 4 sites. Approximately 90% of patients who were tested had a documented reason for testing. CONCLUSION: One-half to two-thirds of patients at risk for HIV had not been tested within our selected VA sites. Among tested patients, the rationale for HIV testing was well documented. Further testing of at-risk patients could clearly benefit patients who have unidentified HIV infection by providing earlier access to life-prolonging therapy