The 1989 edition of IS 6533 Part 1 delineates detailed directives for the mechanical design and fabrication of steel chimneys, emphasizing structural soundness, thermal behavior, and ash handling mechanisms. This standard is intended for professionals engaged in the design, selection, and erection of steel chimneys in industrial environments, ensuring adherence to safety, environmental, and functional criteria.
Overview
The 1989 edition of IS 6533 Part 1 delineates detailed directives for the mechanical design and fabrication of steel chimneys, emphasizing structural soundness, thermal behavior, and ash handling mechanisms. This standard is intended for professionals engaged in the design, selection, and erection of steel chimneys in industrial environments, ensuring adherence to safety, environmental, and functional criteria.
Audience
Contents
Structure
This section covers the mechanical facets of steel chimney design including structural design, construction, inspection, lining installation, draft computations, pollutant dispersion assessment, and ash disposal techniques. It outlines recommended minimum efflux velocities for various draft systems, highlighting the importance of stack exit diameter in design calculations and noting restrictions on weather cowls that impede vertical plume flow.
Provides essential specifications including minimum efflux velocities by chimney system type, design principles ensuring plume rise free from nearby building interference, and limitations of applicable formulas mainly for tall stacks. It emphasizes avoiding weather cowls restricting plume movement and includes graphical summaries of velocity requirements.
Defines key terms and parameters used in mechanical design and airflow calculations such as draft losses, friction factors, chimney height, duct dimensions, gas velocities, and friction coefficients. It distinguishes mechanical aspects covered in Part 1 from structural considerations in Part 2.
Details the factors influencing chimney choice including required draft, fuel and boiler characteristics, flue gas properties, ambient conditions, and construction type. Provides recommended height-to-diameter ratios for lined and unlined chimneys and guides designers on selecting appropriate dimensions based on plant needs.
Presents fundamental formulas and tables for calculating draft losses, gas velocities, and chimney dimensions. It includes recommended minimum efflux velocities, chimney height recommendations relative to nearby buildings, and notes on formula applicability conditions.
Discusses minimum chimney height requirements considering turbulent air layers caused by surrounding buildings, categorizing building types and orientations. Explains aerodynamic shadow effects and provides formulas and parameters to determine safe chimney height to ensure effective plume dispersal.
Specifies the properties required for refractory and acid-resistant lining materials, including thermal conductivity, density, and strength. Outlines design practices for sectional lining with internal steel ring supports and expansion gaps filled with insulating material to allow for thermal movements and prevent cracking.
Describes insulation materials such as mineral wool and aluminium cladding, their thermal performance values, and usage guidelines. Discusses protective coatings for steel shells and the role of aluminium cladding in wind load calculations and thermal reflection.
Explains ash collection and disposal approaches for small to large boilers, detailing mechanical, pneumatic, and hydraulic systems. Describes hopper designs with automatic gates and water flushing arrangements for effective ash removal.
Provides detailed definitions and formulas to account for aerodynamic shadows caused by nearby buildings, enabling designers to calculate chimney height that ensures plume clearance above turbulent zones. Includes building classifications and graphic representations of shadow effects.
Presents formulas to compute required stack height for pollutant dispersion based on emission rates, precipitation coefficients, and temperature gradients. Emphasizes minimum efflux velocity requirements and cautions against weather cowls that limit vertical plume release.
Lists key parameter updates and clarifications including stack diameter definitions, draft loss variables, friction factors, and minimum efflux velocity recommendations. Includes revised formulas and notes on avoiding restrictive weather cowls.
Frequently Asked
IS 6533 Part 1 divides steel chimneys into two primary categories: unlined chimneys suitable for gases with lower corrosiveness, and lined chimneys equipped with refractory or acid-resistant linings to protect against hot, aggressive gases. The classification further considers nominal diameters ranging typically from 50 cm to 450 cm and height-to-diameter ratios varying between 15 and 110, depending on lining presence and size. Design factors such as aerodynamic influence and pollutant dispersion also affect classification and sizing.
To accommodate thermal expansion, refractory and acid-resistant linings are sectioned into approximately 6-meter high segments, each supported by internal steel rings affixed to the chimney shell. Expansion gaps above each section are filled with insulating materials like refractory fibre or mineral wool to absorb movement and prevent cracking. Low-expansion materials may permit larger or continuous sections, with the lining terminating about one shell diameter below the chimney top, finished with dense firebrick and weather protection.
Refractory firebricks should have alumina content of 28-32%, withstand temperatures up to 1200°C, possess cold crushing strengths between 2 to 4 N/mm², and maintain low thermal conductivity not exceeding 0.23 W/(m·K). Insulating bricks come in grades rated for 850°C to 1500°C service temperatures, with porosity above 60%, cold crushing strength varying by grade, and bulk densities around 630-1000 kg/m³. Acid resisting bricks require alumina ≥28%, Fe₂O₃ ≤2.5%, low shrinkage on drying and firing, high density, and strength to resist corrosive environments.
For small boilers generating minimal ash, disposal is via a hopper with an automatic gate that empties ash into a pit, utilizing simple mechanical or pneumatic methods. Medium and large boilers necessitate dedicated ash disposal systems, often hydraulic, where water flushes ash through pipes equipped with nozzles into the main disposal system. These systems ensure efficient and automated ash removal tailored to boiler capacity.
Minimum chimney height is influenced by plant draft requirements, boiler fuel type, flue gas temperature and velocity, ambient atmospheric conditions, and the horizontal flue length. Additionally, the chimney must rise above turbulent airflow zones caused by nearby buildings, whose widths and heights are classified to assess aerodynamic shadows. Structural stability per Part 2 is also considered. The height-to-diameter ratio tables and building-related formulas guide designers to ensure effective plume dispersion and compliance with safety norms.
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