Guidelines for flocculator devices

IS 7208: Scope Summary

• Scope: IS 7208 covers design, materials, and construction of flocculator devices used in water treatment.
• Definitions: Clause 3.0 defines terms relevant to flocculator devices.
• Materials & Painting:
  • Mechanical paddles as per Table 6.1 (Clause 6.2).
  • Primer: Red-oxide (zinc chromate).
  • Painting: One coat primer + minimum 3 coats finishing paint after erection (per IS 1477 Part 1 & 2).
• Referenced Standards:
  • IS 1477 (Parts 1 & 2) for painting ferrous metals.
  • IS 210 for grey iron castings.
  • IS 226 for structural steel.
• Devices Covered:
  • Longitudinal flow flocculators (Type B).
  • Vertical flocculators (Type C).
  • Masonry or R.C.C. construction.

Key Specifications (Summary Table)

Painting Coating System (per IS 1477)

flowchart LR
    A[Flocculator Devices] --> B[Type B: Longitudinal Flow]
    A --> C[Type C: Vertical Flow]
    B & C --> D[Masonry or R.C.C. Structure]
    D --> E[Mechanical Paddles (Table 6.1)]
    E --> F[Primer: Red-oxide]
    F --> G[Finishing Paint: ≥3 coats]

For detailed design formulas and paddle specifications, refer to Clause 6 and Tables within IS 7208 and related

IS 7208: Referenced Indian Standards - Key Points

The standard references several Indian Standards critical for materials and painting in structural applications:

Painting Specification (Clause 6.2)

• Use Red-oxide (zinc chromate) primer.
• Apply 1 coat of primer + at least 3 coats of finishing paint after erection.
• Follow IS 1477 (Part 1 & 2): 1971 for painting practices.

Summary Diagram of Painting Process

flowchart LR
    A[Surface Preparation] --> B[Apply Red-oxide Primer (1 coat)]
    B --> C[Apply Finishing Paint (≥3 coats)]
    C --> D[Completed Protective Coating]

Note: Always verify you have the latest amendments of these IS codes for compliance.

IS 7208 — Definitions & Key Specifications

• Clause 3.0 (Definitions): Establishes terminology used throughout the standard for flocculator devices, ensuring uniform understanding.

• Clause 6.2 (Painting):

  • Primer: Use Red-oxide (Zinc Chromate) primer.
  • Painting: Apply 1 coat of primer + minimum 3 coats of finishing paint after erection.
  • Refer to IS 1477 (Part 1 & 2, 1971) for detailed painting practice of ferrous metals.

• Referenced IS Standards:

  IS No.	Title
  210:1978	Grey iron castings
  226:1975	Structural steel (standard quality)
  1477 (Part 1 & 2):1971	Code of practice for painting ferrous metals
  3930:1979	Flame and induction hardening steels
  4691:1985	Degrees of protection for electrical enclosures

• Design Basis: Velocity gradient criteria used for flocculator design (details not in provided context).

Summary Table: Painting Specification (Clause 6.2)

If you need velocity gradient formulas or design details, please specify.

Design Considerations per IS 7208 (Relevant Extracts)

1. Velocity Gradient (G) for Paddle Flocculators (Clause 3.2):
The velocity gradient, a key design parameter for flocculators, is given by:

[ G = \sqrt{\frac{2 C_D A_p \rho (V_p - V_w)^3}{\mu V}} ]

Where:

• (G) = velocity gradient (s(^{-1}))
• (C_D) = drag coefficient (0.8 to 1.9)
• (A_p) = paddle area (m(^2))
• (\rho) = density of water (kg/m(^3))
• (V_p) = paddle tip velocity (m/s), typically 0.2 to 0.6 m/s
• (V_w) = water velocity near paddle tip (m/s)
• (\mu) = dynamic viscosity of water (kg/m.s)
• (V) = volume of water in flocculator (m(^3))

2. Painting Specifications (Clause 6.2):

• Use red-oxide (zinc chromate) primer.
• Apply one coat of primer and at least three coats of finishing paint after erection.
• Refer IS 1477 (Part 1 & 2) for painting practice.

Summary Table: Velocity Gradient Parameters

flowchart LR
    A[Water Volume (V)] -->|Affected by| B[Velocity Gradient (G)]
    B --> C[Paddle Area (Ap)]
    B --> D[Drag Coefficient (CD)]
    B --> E[Paddle Tip Velocity (Vp)]
    E --> F[Water Velocity near Paddle (Vw)]
    B --> G[Water Density (ρ) & Viscosity (μ)]

Note: For detailed mechanical design

IS 7208: Method of Flocculation - Key Points

• Method: Mechanical flocculation using paddle mixers is the standard in India.
• Detention Time: Recommended between 10 to 30 minutes (Clause 4.1).
• Purpose: To promote aggregation of suspended particles into larger flocs for easier sedimentation.
• Design Guidelines:
  • Flocculator devices should ensure uniform mixing with gentle agitation to avoid breaking flocs.
  • Paddle speed and tank dimensions are designed to achieve the required detention time and velocity gradient.

Key Formula: Detention Time (T)

[ T = \frac{V}{Q} ]

• T = Detention time (min)
• V = Volume of flocculation basin (m³)
• Q = Flow rate (m³/min)

Typical Design Parameters:

flowchart LR
    A[Raw Water Inlet] --> B[Flocculation Basin]
    B -->|Mechanical Mixing with Paddles| C[Flocculated Water]
    C --> D[Sedimentation Basin]

Summary: Use mechanical paddles to gently mix water for 10-30 min, ensuring proper floc formation before sedimentation.

IS 7208 Mechanical Paddles Summary

Types of Mechanical Paddles (Clause 6.1)

• Type A: Transverse paddles across tank width, create barrel roll effect for flocculation.
• Type B: Central longitudinal shaft with paddles rotating perpendicular to flow; requires baffling.
• Type C: Vertical shaft in center with intermeshing paddles, stationary and/or moving.

Key Specifications

Design Guidelines

• Paddle area: 10% to 25% of tank sectional area (Clause 6.1.2)
• Peripheral speed: 0.2 m/s ≤ speed ≤ 0.6 m/s (Clause 6.1.4)

Formula for Peripheral Speed, ( V_p ):

[ V_p = \pi \times D \times N ]

Where:

• ( V_p ) = Peripheral speed (m/s)
• ( D ) = Diameter of paddle rotation (m)
• ( N ) = Rotational speed (rps)

flowchart LR
    A[Type A] -->|Barrel roll effect| Water[Water Flow]
    B[Type B] -->|Longitudinal shaft| Water
    C[Type C] -->|Vertical shaft with intermeshing paddles| Water

This concise summary covers construction types, material specs, and key design parameters for mechanical paddles per IS 7208.

IS 7208: Mechanical Paddles Design & Construction

Types of Mechanical Paddles (Clause 6.1)

• Type A: Transverse paddles across tank width; creates barrel roll effect for flocculation.
• Type B: Central longitudinal shaft with paddles rotating perpendicular to flow; requires baffling.
• Type C: Vertical shaft with intermeshing paddles in center of basin; can have stationary and moving sets.

Key Specifications (Clause 6.1.9)

Design Parameters

• Paddle Area: 10% to 25% of tank sectional area (Clause 6.1.2)
• Paddle Tip Velocity: 0.2 to 0.6 m/s

Velocity Gradient Formula (Clause 3.2)

[ G = \sqrt{\frac{2 M V C_D A_p \rho (V_p - V_w)^3}{\mu V}} ]

Where:

IS 7208 Painting & Corrosion Protection Key Points:

• Primer: Use Red-oxide zinc chromate as primer.
• Coating: Apply 1 coat of primer + at least 3 coats of finishing paint after erection.
• References: Follow IS 1477 (Part 1 & 2) for detailed painting practice:
  • IS 1477 (Part 1): Pretreatment of ferrous metals.
  • IS 1477 (Part 2): Painting of ferrous metals in buildings.

Painting Specification Summary

Additional Notes:

• Proper surface preparation (cleaning, rust removal) is critical before priming.
• Painting after erection ensures protection against environmental corrosion.
• Use compatible paint systems as per IS 1477 to ensure durability.

flowchart LR
    A[Surface Preparation] --> B[Apply Red-oxide Zinc Chromate Primer (1 coat)]
    B --> C[Apply Finishing Paint (min 3 coats)]
    C --> D[Corrosion Protection Achieved]

This ensures long-term durability and corrosion resistance of steel structures per IS 7208.

IS 7208: List of Referred Indian Standards

Key Specifications:

• Painting: Use red-oxide (zinc chromate) primer + 1 coat primer + minimum 3 coats finishing paint after erection (per IS 1477 Parts 1 & 2).
• Materials: Refer IS 210 for grey iron castings, IS 226 for structural steel.
• Electrical Machines: IS 325, IS 4691, IS 6362 cover motors and protection.

Notes:

• All standards are periodically reviewed.
• Use latest amendments for compliance.
• BIS governs licensing and quality control under the BIS Act, 1986.

flowchart LR
    A[IS 7208] --> B[IS 210: Grey Iron Castings]
    A --> C[IS 226: Structural Steel]
    A --> D[IS 1477 Part 1 & 2: Painting]
    A --> E[IS 325: Induction Motors]
    A --> F[IS 4691: Protection of Electrical Machines]
    A --> G[IS 6362: Cooling Methods]

For detailed design or painting procedures, refer to the respective IS documents listed above.