Research Papers: Multiphase Flows

Challenging Paradigms by Optimizing Combustible Dust Separator

[+] Author and Article Information
Wayne Strasser

Fellow ASME
Eastman Chemical Company,
Kingsport, TN 37660
e-mail: strasser@eastman.com

Alex Strasser

Oak Ridge National Lab,
Oak Ridge, TN 37830
e-mail: alexstrasser367@gmail.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 14, 2017; final manuscript received January 9, 2018; published online March 13, 2018. Assoc. Editor: Praveen Ramaprabhu.

J. Fluids Eng 140(7), 071301 (Mar 13, 2018) (12 pages) Paper No: FE-17-1500; doi: 10.1115/1.4039234 History: Received August 14, 2017; Revised January 09, 2018

A computational study was carried out to investigate the effects of internal geometry changes on the likelihood of solids buildup within, and the efficiency of, an industrial dust collector. Combustible solids held up in the unit pose a safety risk. The dust collector serves multiple functions, so the design requires a delicate balance. Particles should be separated from the incoming mixture and collected in the bottom of the unit. This particulate material should freely flow into a high-speed ejector (Mach 0.4) underneath. Gas must also flow freely to the top outlet, but sufficient gas must flow down to the ejector so that its motive gas augments the transport of particles back to the reactor (recirculation). Computational design evaluations included: (1) rod spacing, (2) ledge removal, and (3) rod cover plates. Testing on particle size distribution and density was carried out in-house to provide inputs to the computational fluid dynamics (CFD) model. Rod spacing reduction had a mixed effect on flow distribution. Plates were found to induce a negative effect on recirculation and a mixed effect on combustible solids accumulation. Removal of the ledge, however, offered slightly more recirculation along with completely alleviating stagnant solids accumulation. It is shown that, without consideration of detailed fluid physics, general separator design principals might be misguiding.

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Grahic Jump Location
Fig. 1

Dust collector and ejector control volume. The block containing an “A” will be expanded for mesh explanation later.

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Fig. 2

Base case mesh configuration from section “A” of Fig. 1. Note that the final employed mesh is significantly more refined than this shown.

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Fig. 3

Velocity magnitude contours on a centerline symmetry plane 2D simulation comparing the coarse mesh (left—0.02″ MLS) to a much finer mesh (right—0.005″ MLS). Yellow dashed arrows at the bottom show the general direction of flow near the lower outlet.

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Fig. 4

The effect of MLS on flue gas recirculation to the boiler

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Fig. 5

The effect of MLS on the collector inlet vacuum

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Fig. 6

Mesh of the dust collector bottom and the piping which connects it to the ejector

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Fig. 7

Dust particle diameters including two raw data scans and a Rosin–Rammler distribution fit

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Fig. 8

Velocity magnitude contours on a centerline symmetry plane 2D simulation comparing 0.325″ rod spacing (left) to 0.1″ rod spacing (right)

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Fig. 9

Velocity magnitude contours on a slice of the vessel which is placed at approximately the vertical midpoint

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Fig. 10

Mach number contours in the ejector on the symmetry plane

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Fig. 11

Solids concentration contours on the symmetry plane of the stock system, where blue = 0.0 and red ≥ 0.1 kg/m3

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Fig. 12

Solids concentration contours on the symmetry plane without a floor, where blue = 0.0 and red ≥ 0.1 kg/m3

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Fig. 13

Plate arrangement; there could be up to five plates installed, numbered from top to bottom. Only the complete bottom two are shown here, but only the upper four were considered in this study, leaving the bottom 20% rod area open for flow.

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Fig. 14

Solids concentration contours on the symmetry plane with four equally sized cover plates blocking flow to the top 80% of the rod section, where blue = 0.0 and red ≥ 0.1 kg/m3

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Fig. 15

Effect of plate count on overall collector mass flow

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Fig. 16

Effect of plate count on flue gas recirculation to the boiler

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Fig. 17

Effect of plate count on solids recirculation to the boiler

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Fig. 18

Streamlines colored by residence time (blue = 0.0 s and red ≥ 2 s) with the stock case on the left and the four cover plate case on the right

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Fig. 19

Effect of plate count on the bypassed (carried over the top) solids mean diameter

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Fig. 20

Lateral velocity normalized by terminal velocity for 200 μm particles along the centerline of the rods; positive values are left-aimed, i.e., moving between the rods in the proper direction

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Fig. 21

Velocity contours (top—blue = 0.0 m/s and red ≥ 10 m/s) and local turbulence intensity (bottom—blue = 0.0% and red ≥ 100%) comparing the stock (left) and four-plate (right) cases

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Fig. 22

Vectors of velocity magnitude for the stock case (left) and the four-plate case (right); colors are from blue = 0.0 m/s to red ≥ 1 m/s (left) and ≥ 10 m/s (right)



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