Code of practice for design and construction of steel chimneys, Part 1: Mechanical aspects

IS 6533 Part 1: Scope & Key Specifications

• Scope (Clause 1.1):
  Covers mechanical aspects of steel chimneys including design, construction, maintenance, inspection, lining, draft calculations, pollutant dispersion, and ash disposal.

• Efflux Velocity Recommendations (Table B-1, Clause 1.3):

• Key Notes:

  • Use of weather cowls restricting vertical plume motion is discouraged.
  • Special cowls allowing vertical gas flow while preventing rain ingress may be allowed.
  • Diameter at stack exit (D) is critical in draft and dispersion formulas.

• Limitations (Clause B-2.1):
  Formulas apply primarily to tall stacks with plume free from interference by nearby tall buildings.

Summary Diagram of Efflux Velocity by System

graph LR
A[Natural Draft] -->|6 m/s| V1
B[Forced Draft] -->|≤20 m: 6 m/s| V2a
B -->|20-45 m: 9 m/s| V2b
B -->|>45 m: 12 m/s| V2c
C[Induced Draft] -->|7.5 m/s| V3
D[Other Waste Gases] -->|15 m/s| V4
E[Thermal Power Plants] -->|25 m/s| V5

Use these velocities as minimum efflux speeds for pollution control and aerodynamic efficiency in chimney design.

IS 6533 Part 1: General Considerations and Compliance

Key Specifications & Tables

1. Minimum Efflux Velocities (Clause 1.3, Table B-1.3)

Note: Avoid weather cowls that restrict vertical plume motion. Special cowls may be used only if they allow vertical gas flow at recommended velocities.

2. Design Considerations (Clause 8.3)

• Design and construction must ensure plume rise free from interference by nearby tall buildings.
• Applies mainly to tall stacks (Clause 2.1).

3. Limitations of Formula (Annex C, Clause 10.1)

• Formula applicability is limited to tall stacks with free plume rise.
• Nearby structures or atmospheric conditions causing interference invalidate the formula.

Summary Diagram: Stack Efflux Velocity by System

barChart
    title Efflux Velocity (m/s) by Stack System
    x-axis System
    y-axis Velocity (m/s)
    "Natural draft" : 6
    "Forced draft ≤20m" : 6
    "Forced draft 20-45m" : 9
    "Forced draft >45m" : 12
    "Induced draft" : 7.5
    "Other gases" : 15
    "Thermal power plants" : 25

Use these values and considerations to ensure compliance with IS 6533 Part 1 for stack design and construction.

IS 6533 Part 1: Terminology and Definitions – Key Points

• Clause 4.0 specifies that terminology from Clauses 4.1 to 4.21 applies; other definitions refer to Part 2 (structural aspects).
• Key parameters used in formulas (Clause 6.3.1) include:

• Draft loss and friction factors are fundamental for mechanical design and airflow calculations.
• Parameter D is specifically defined as the stack diameter at chimney exit (Clause 1.1).
• The standard separates mechanical aspects (Part 1) from structural aspects (Part 2).

Typical draft loss formula (conceptual):

[ \Delta P = f \frac{l}{D} \frac{\rho V^2}{2} + \text{other losses} ]

where:

• ( \Delta P ) = draft loss (Pa or mm water column)
• ( f ) = friction factor
• ( l ) = duct length (m)
• ( D ) = diameter (m)
• ( \rho ) = gas density (kg/m³)
• ( V ) = gas velocity (m/s)

Summary diagram of parameters:

flowchart LR
    A[Chimney Height (H)] --> B[Draft Loss (da, de, dx)]
    B --> C[Friction Factor (f)]
    C --> D[Velocity (V, V1, V2)]
    D --> E[Diameter (D, D1)]
    E --> F[Length of duct (l)]

**Use

IS 6533 Part 1: Classification & Selection of Steel Chimneys

Key Points from Clauses 5.2 & 5.3

• Selection depends on:

  • Draft required by the plant
  • Fuel type & boiler design
  • Flue gas temperature and velocity
  • Ambient conditions (temperature, pressure)
  • Construction type (lined/unlined)
  • Natural or mechanical draft
  • Horizontal flue length and turn-down ratio

• Basic dimensions: Height (H) and diameter (D) at chimney exit are critical.

Table: Recommended Height to Diameter Ratio (Clause 5.3.3)

• Note: 'x' denotes commonly used dimensions.

Important Formula

• D = Diameter of stack at chimney exit (m) — used in draft and dispersion calculations.

Summary Diagram

flowchart TD
    A[Plant Requirements] --> B[Draft Required]
    A --> C[Fuel & Boiler Design]
    A --> D[Ambient Conditions]
    B & C & D --> E[Select Chimney Diameter (D) & Height (H)]
    E --> F[Refer Table 1 for H/D ratio]
    F --> G[Decide Lined or Unlined]
    G --> H[Final Chimney Design]

Use IS 6533 Part 1 Table 1 as guideline for nominal dimensions and consider site-specific factors for final selection.

IS 6533 Part 1: Key Formulas, Tables & Specifications for Chimney Calculations

1. Legends & Parameters (Clause 6.3.1)

2. Minimum Efflux Velocities (Table from Clause 1.3)

3. Chimney Height Recommendation (Clause 5.3.5)

• Chimney height ≥ 5 m taller than tallest building within 150 m radius (unless other regulations apply).

4. Important Notes

• Formulae apply for tall stacks with plume free from interference by nearby tall buildings (Clause 2.1).
• Avoid weather cowls that restrict vertical plume motion; use special cowls if rainwater entry is a concern.

5. Typical Formula for Draft Losses (General form)

[ \Delta P = f \frac{l}{D} \frac{\rho V^2}{2} + \text{other losses (local, entry, exit)} \

Height of Chimney & Aerodynamic Considerations (IS 6533 Part 1)

1. Minimum Height of Chimney:

• Chimney height H must exceed the height of turbulent air layers caused by nearby buildings.

• Buildings classified as:

  • Narrow Building: ( B < 2.5 H_B )
  • Wide Building: ( B > 2.5 H_B )

• Building orientation types (downwind direction):

  • Type 1: Independent Narrow Building (no obstruction within (6 H_B))
  • Type 2: Independent Wide Building (no obstruction within (4 H_B))
  • Type 3: Narrow Building behind another building at distance (X), (H_B < X < 10 H_B)
  • Type 4: Wide Building behind another building at distance (X), (H_B < X < 8 H_B)

2. Aerodynamic Shadow:

• Chimney height should consider the aerodynamic shadow effect caused by buildings, ensuring plume rises above turbulent zones.

3. Key Parameters:

Recommended Height to Diameter Ratio for Steel Chimneys (Table 1 excerpt)

Note: 'x' denotes commonly used dimensions.

Draft Losses and Flow Parameters (Clause 6.3.1)

• Draft losses ((d_a, d_e, d_x)) in mm water column.
• Friction factor (f), chimney height (H), duct length (l), diameter (D).
• Gas velocity (V), (V_1), and friction coefficient (K_j) influence design

IS 6533 Part 1: Lining Materials & Thermal Expansion

Key Specifications for Lining Materials

• Thermal Conductivity: ≤ 0.23 W/(m·K)
• Bulk Density: ≥ 700 kg/m³
• Cold Crushing Strength: As per manufacturer's specs or relevant clauses

Thermal Expansion Design (Clause 8.3.2)

• Linings (refractory & acid resistant) divided into sections of ~6 m height.
• Each section supported by internal steel ring fixed to chimney shell.
• Expansion space left above each section, filled with refractory fibre/mineral wool (pliable, non-combustible).
• For low-expansion materials (e.g., diatomaceous earth bricks), section height may be greater; small chimneys may have lining up to top without sections.
• Upper lining ends ~one shell diameter below chimney top, finished with dense firebrick and weather-protected.

Thermal Expansion Considerations

• Coefficient of thermal expansion is low for specified bricks.
• Bricks must be dried slowly and stored dry due to high water absorption.
• Design must allow for reheat shrinkage and temperature range up to ~870°C.

Summary Table: Sectioning & Expansion

flowchart TB
    A[Lining divided into sections (~6m)] --> B[Each section supported by steel ring]
    B --> C[Expansion space above each section]
    C --> D[Filled with refractory fibre or mineral wool]
    D --> E[Allows thermal expansion & shrinkage]
    F[Low-expansion bricks] --> G[Sections may be larger or none]
    G --> H[Top lining ends below chimney top by shell diameter]
    H --> I[Finished with dense firebrick & weather protection]

This ensures durability and accommodates thermal movements in chimney linings per IS 6533 Part

IS 6533 Part 1: Insulation and Exterior Protection Key Points

1. Heat Loss (U) Values for Insulation Materials (Clause 9.1, Table 9.2)

• Purpose: Maintain steel shell temperature above acid dew point.
• Factors: Insulation effectiveness, flue gas velocity, inlet temperature.

2. Aluminium Cladding (Clause 9.2)

• Used for high thermal reflectivity.
• Steel shell exterior coated with heat-resistant aluminium paint (see Part 2, Clause 13).
• Cladding diameter used for wind load calculations; steel shell diameter for section modulus.

3. Insulating Refractory Bricks (Clause 8.2.2)

IS 6533 Part 1 — Ash Disposal Systems: Key Points

1. Ash Collection & Disposal Types

• Small boilers: Ash quantity is small; simple disposal.
• Medium/large boilers: Require dedicated ash disposal systems.

2. Ash Disposal System Components (Clause 2.2.1)

• Hopper with automatic gate: Opens on reaching set ash weight/volume.
• Disposal methods: Mechanical, pneumatic, or hydraulic.

3. Hydraulic Ash Disposal (Clause 2.2.4)

• Water flushes ash into the main disposal system.
• Design: 50 mm GI pipe with 10 mm Ø nozzles spaced 150 mm apart (Fig. 6).
• Automatic regulating gate controls ash flow (Fig. 7).

4. Chimney Lining Support (Clause 9.5.5)

• Liners on open frames must be insulated and weather-protected.

Summary Table: Ash Disposal System Types

Diagram: Hydraulic Ash Disposal System

flowchart TD
    A[Combustion Chamber] --> B[Hopper with Automatic Gate]
    B --> C[Water Flush via GI Pipe with Nozzles]
    C --> D[Main Ash Disposal System]
    D --> E[Disposal Pit or Further Handling]

References:

• IS 6533 Part 1:1989, Clauses 1.1, 2.2.1, 2.2.4, 9.5.5
• Figures 6 & 7 for hydraulic ash disposal details.

Influence of Aerodynamic Shadow on Chimney Height (IS 6533 Part 1, Clause 7.2 & Annex A)

Key Definitions:

• B: Width of building in wind direction (m)
• H₃ (Hₛ in some clauses): Height of building obstructing wind (m)
• X: Distance between buildings or obstruction (m)
• H: Calculated chimney height (m)
• H₀: Height of downwind obstruction/building (m)
• Hₛ: Height of aerodynamic shadow (m)

Building Types & Conditions:

Aerodynamic Shadow Height (Hₛ) Formulas:

• Type 1: Hₛ = H₀ (height of obstruction)
• Type 2:
  [ H_s = 0.36 \times B + 1.7 \times H_0 ]
• Types 3 & 4:
  [ H_s = 0.36 \times (B + X) + H_0 ]

Design Criterion:

• Chimney height (H) must satisfy:
  [ H > H_s ]

This ensures the chimney plume rises above the turbulent aerodynamic shadow zone caused by nearby buildings.

Summary Diagram (Building Orientation & Shadow):

flowchart LR
    A[Wind Direction] --> B(Building 1)
    B --> C{Building Type}
    C -->|Type 1| D[Independent Narrow Building]
    C -->

Key Formulas and Specifications for Dispersion of Pollutants and Stack Height (IS 6533 Part 1):

1. Stack Height Formula

For relatively flat terrain and effluent temperature ≈ atmospheric temperature:

[ H = \left(\frac{M \times F}{A}\right)^{1/3} ]

Where:

• H = Calculated stack height (m)
• M = Mass emission rate of pollutant (g/s)
• F = Dimensionless precipitation coefficient
  • Gases: F = 1
  • Dust (with >90% collection efficiency): F = 2
• A = Temperature gradient coefficient (responsible for plume mixing)
  • Tropical zone: A = 280
  • Semi-tropical zone: A = 240

2. Recommended Minimum Efflux Velocities (Table B-1)

3. Important Notes

• Weather cowls restricting vertical plume motion are not recommended.
• For multiple nearby stacks, increase H to ensure combined ground-level pollutant concentration meets air quality standards.

flowchart LR
    A[Emission Rate (M)] --> B[Calculate H using formula]
    C[Atmospheric Conditions (A)] --> B
    D[Precipitation Coefficient (F)] --> B
    B --> E[Stack Height (H)]
    E --> F[Ensure Efflux Velocity per Table B-1]
    F --> G[Design Stack for Dispersion]

This approach ensures compliance with air quality norms by optimizing stack height and efflux velocity for effective pollutant dispersion.

IS 6533 Part 1 (Mechanical Aspects) - Key Revisions, Formulas & Tables

1. Parameter Definition Update (Clause 1.1, B-1.1)

• D = Diameter of stack at the exit of the chimney (in meters).

2. Draft Losses and Flow Parameters (Clause 6.3.1)

3. Recommended Minimum Efflux Velocities (Clause 1.3, Table B-1.3)

Note: Avoid weather cowls that restrict vertical plume motion; special cowls allowed if vertical velocity is maintained.

4. Basic Draft Loss Formula (Example)

[ \Delta P = f \frac{l}{D} \frac{\rho V^2}{2} + \sum K_j \frac{\rho V^2}{2} ]

• Where (\Delta P