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NEFCO Dual Launder/ Baffle Study

NEFCO Dual Launder/ Baffle Study.

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NEFCO Dual Launder/ Baffle Study

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  1. NEFCO Dual Launder/ Baffle Study Many clarifiers feature a launder positioned away from the tank wall with weirs on both sides. The intent is to maximize the weir length in the clarifier. However, this configuration often suffers the effects of density currents that carry lighter solids upward and deposit them in the space between the tank wall and the trough or drive the solids to the trough itself. This study was designed to determine how effective the SB2.0 Density Current Baffle was in reducing solids when used with this clarifier configuration, and shows that the baffle reduced solids by more than 30% in all cases. 1

  2. NEFCO Dual Launder Modeling Three different configurations were studied • Setup One (120.0 ft diameter clarifier, dual weir set 5.0 ft from wall) • Setup Two (120.0 ft diameter clarifier, dual weir set 10.0 ft from wall) • Setup Three (100.0 ft diameter clarifier, dual weir set 12.0 ft from wall) 2

  3. Setup One 5 ft 3 ft 2 ft 20 ft Sludge Blanket 3 ft 120 ft 3 Not to Scale

  4. Setup One – Without Baffle Flow Pattern (colored by speed, red is fast) Treatment Flow Rate = 8.5 mgd These views depict a 2D cross section representation of the flow within the clarifier, from the center to the outer tank wall. In this case, the density current proceeds unimpeded across the top of the blanket, carrying solids up the tank wall and depositing them in the space between the tank wall and the outer weir of the launder. 4

  5. Setup One – Density Current Baffle Density Current Baffle Design Vertical Position of the Baffle 5

  6. Setup One – With Baffle Short-Circuiting current is deflected Treatment Flow Rate = 8.5 mgd Density Current gets Underneath of Baffle Flow Pattern (colored by speed, red is fast) In this case, the baffle intercepts the short-circuiting current and redirects the current and solids away from the launder and into the main volume of the clarifier 6

  7. Setup One – With and Without Baffle Higher Solids Concentration Greater Approach Flow Speeds Flow Pattern (colored by density, red is high) Just as in the velocity plot, solids fill the space between the tank and outer weir. In this case the baffle has diverted the current and reduced the solids concentration at the launder. 7

  8. Setup Two 10 ft 3 ft 2 ft 20 ft Sludge Blanket 3 ft 120 ft 8 Not to Scale

  9. Setup Two – Without Baffle Treatment Flow Rate = 8.5 mgd Flow Pattern (colored by speed, red is fast) Again, the current rises unimpeded into the space around the launder. The speed of the current in the vicinity of the launder is still high. Note the width of the current as it rises up the tank wall. This explains why NEFCO’s SB 2.0 Baffle is designed with a larger horizontal projection than the original Stamford Baffle. 9

  10. Setup Two – Density Current Baffle Density Current Baffle Configuration Vertical Position of the Baffle 10

  11. Setup Two – With Baffle Flow speeds around launders are less Treatment Flow Rate = 8.5 mgd Density Current gets Underneath of Baffle Flow Pattern (colored by speed, red is fast) Here again, the baffle has intercepted and redirected the current away from the launder. 11

  12. Setup Two – With and Without Baffle Higher solids concentration Greater approach flow speeds Flow is directed towards launder, but its speed is less near launders Note the difference in solids concentration at the launder in the two images Flow Pattern (colored by density, red is high) 12

  13. Setup Three 12 ft 3 ft 2 ft 18 ft Sludge Blanket 3 ft 100 ft 13 Not to Scale

  14. Setup Three – Without Baffle Flow Pattern (colored by speed, red is fast) Treatment Flow Rate = 6.0 mgd 14

  15. Setup Three – Density Current Baffle Density Current Baffle Configuration Vertical Position of the Baffle 15

  16. Setup Three – With Baffle Speed of short-circuiting current is less with baffle in place Treatment Flow Rate = 6.0 mgd Density Current gets underneath of baffle Flow Pattern (colored by speed, red is fast) 16

  17. Setup Three – With and Without Baffle Higher solids concentration Greater approach flow speeds Flow is directed towards launder, but its speed is comparatively low Flow Pattern (colored by density, red is high) The difference in the solids concentration at the the launder is striking. 17

  18. CONCLUSIONS • A “classic” density current forms in each of the cases and rides along the top of the sludge blanket. • Without the baffle, the density current rises unimpeded and the solids concentration increases in the area between the tank wall and the launder • The SB 2.0 Density Current Baffle effectively disrupts the short-circuiting current and redirects it. • Depending on the position of the launder, the baffle may cause the current to flow toward the launder, but speed is greatly reduced. • For the operating conditions studied, TSS is reduced by 30% or more.

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