Measuring Entrainment of Cohesive Particles

Measuring Entrainment of Cohesive ParticlesUROP Summer 2015Jack HuettelHaley Manchester

The ProjectCollect and analyze data on Geldarts type A cohesive particles.Determine radial flux profiles and overall entrainment in the CFB for various: gas velocitiesparticle diameters (monodisperse only)bed weights (8 kg this summer)

Circulating Fluidized Bed (CFB)

Methods for Measuring FluxShadowgraphy AnalysisThe camera takes two pictures very rapidly. The software then uses the two frames to determine the each particles instantaneous velocity.

Using the recorded velocities, we can determine the flux through that radial position in the column

Methods for Measuring Flux (cont.)Local Flux ProbeThis probe can be inserted through the column wall, and be used to measure local flux at a radial position in the column.

Total Entrainment MeasurementThe butterfly valves in the standpipe allow us to measure the total entrainment through our CFB.32

Particle Loss from Gas OutletWe observed a large number of particles shooting out the gas outlet of our CFB.

This indicated that the system was not circulating properly, and particles were constantly being lost while the bed was in use.

This means the bed weight was changing, and would lead to invalid entrainment measurements.

Solution First, we examined the whole CFB for gas leaks using snoop, and made sure it was airtight.

We realized it could be a problem with the cyclones.

Eventually got the bed to recirulate properly using only one group B cyclone.

Group AGroup B

The switch of cyclones resulted in much more efficient entrainment. Allowed us to run at a higher gas velocity streamers became present.

Standpipe BuildupThe working cyclone circulated particles effectively, but particles began to buildup in the standpipe

WHY?Hypothesis: the particle size resulted in tighter packing in the standpipe. The standpipe/column connection was horizontal Pressure drop from standpipe to column base was not large enough to recirculate particles.

Solution: Vacuum out particles and redistribute into column

ZOOM lower section Horizontal section of pipe

Flux ProbeGOAL:To obtain data that offered a correlation between gas velocity, particle size, and height/radial position in the column to local flux measurements.

Compare to Shadowgraphy analysis data at various heights and radial postions.

In order to obtain valid results we needed to determine necessary gas flow rates in and out of the probe to ensure equal stream velocities into and out of the probe.

HOWEVER

Unable to control gas flow rate in/out of the probe with any sort of precision.

controllable valve

When we opened the valve an appropriate amount, no significant mass of particles could be measuredHOWEVERWhen we took the valve off to let air flow freely, we observed thisWHY?Hypothesis: Particle size particles tend to follow gas stream if some gas went around the probe inlet, so did the particles

Shadowgraphy AnalysisThe camera itself was a challenge to take crisp, in-focus pictures with.

When we did get nice pictures the software had difficulty analyzing them accurately.

Frame # 1

Frame # 2

Analyzed

Not Moving?

Flux calculations from Shadowgraphy AnalysisWe were able to get a couple decent image/analysis pairings -> computed a flux value:

Values depend on velocity, initial position, chosen time lapse (dt).

Determining an appropriate time lapse:

Find average velocity of particles (2 ways)Using avg vertical velocity, determine time needed (dt) for a particle at the bottom of the frame to reach the threshold/mid level height.We used dt = .229 seconds

Effect of Time Lapse (dt)*Yh = 5.525 (midline)

*If statements determine positive and negative flux based on particles crossing Yh