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Design of Steel Bins (Silos) for storage of Sulphur Bulk Materials for IOCL Panipat Refinery

PMC: Engineers India Limited 

Introduction: 

A bulk storage silo is a storage solution for storing and discharging large amounts of industrial powder materials. Poisson & Youngs Engineering was tasked to evaluate the design of a 550 Mton sulfur silo supplied to IOCL Panipat refinery. The silo is subjected to Bin flow loads, wind, and seismic loads as per IS 9178, IS 875 Part 3, IS1893 Part 3, and design qualification as per IS 800 2007 & API 620.

Objective:

  1. To perform Pre-bid Engineering and calculate the plate thickness of the Silo.   

  2. To develop a 3D CAD model using Solidworks.

  3. To calculate the Bin loads for the Initial and Flow conditions as per IS 9178 - Criteria for Design of Steel Bins for Storage of Bulk Materials - Part 3: Bins Designed for Mass Flow and Funnel Flow

  4. To calculate wind loads as per IS 875  -  Part 3

  5. To calculate the seismic load as per IS 1893 - Part 4

  6. To perform FEA calculation using ANSYS software

  7. To simulate different loading scenarios and analyze the stress distribution.

  8. To validate and qualify the Silo design as per API 620 & IS 800 2007.

Methodology

Model Development

  • Geometry: The 3D CAD model of the Silo was created using Solidworks, focusing on capturing all critical features such as Leg supports, Shell thickness, Roof, and Hopper.

  • Meshing: The CAD model was imported into ANSYS Workbench, where it was discretized into finite elements. Higher-order hexahedral elements were used to balance accuracy and computational efficiency.

 

Material Properties

  • The cylinder and hopper are made of SA240 Gr 304 plates. The structural members like the legs & support members are made of IS 2062 material.

  • Material properties such as Young's modulus, Poisson's ratio, and yield strength were sourced from ASME.

 

Loading Scenario

The design qualification of the soli was performed using Finite Element Analysis for the following conditions.

  • Self-weight

  • live load

  • Bin wall pressure (Initial and Mass Flow Conditions) as per IS 9187 Part 3

  • material loads

  • wind loads as per IS 875 Part 3

  • seismic loads as per IS 1893 Part 4

  • Lifting loads

  • Hydrostatic load during testing.

Load Combinations:

  • DL + Material Load + Live Load 

  • DL + (Material Load + Bin Load)

  • DL + Wind Load in 45-225° 

  • DL + (Material Load + Bin Load) + Wind Load 45-225°

  • DL + (Material Load + Bin Load) + Seismic Load 45-225°

  • DL + Safety Pressure Load 

Simulation and Analysis

  • Simulations were run using ANSYS Mechanical Workbench & APDL.

Bin wall Pressure:

The stored material exerts distributed pressure along the height of the silo. The calculation to estimate the pressure distribution was provided in IS 9178 parts 1 to 3. Two cases, Initial pressure, and Flow pressure conditions are considered in designing the Silo.  

The frictional stress Th & Tw are tangential to the surface and vary along the height of the hopper. ANSYS APDL macro is developed to mimic this scenario.

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Wind Loads:

The wind loads are considered as per IS 875 Part 3. The design wind pressure is applied as per clause 7.3.3.7, which varies along the periphery of the cylinder as shown below.  

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Seismic Load Calculation:

The seismic loads are considered per IS 1893: Part 4: 2015 Criteria for Earthquake Resistant Design of Structures Part 4 Industrial Structures. The spectral accelerations are considered as per the site condition

FEA Results

The FEA stress analysis provided valuable insights into the structural behavior of silos under different loading conditions. The study confirmed that the current design is safe and design is qualified as per API 620. The following checks are performed in qualifying the design.

Plate thickness evaluation:

As per API 620, the maximum allowable Tensile and Compressive stress are determined based on the Latitudinal & meridional direction unit forces. Using APDL macro, the stress state for the entire shell domain was captured and checked with the respective allowable limits.

Design Optimization:

The region at the shell-leg interface is critical due to the high-stress concentration. Further design optimization is performed in a sub-model level, to redistribute the stress in the region with minimum material.

Compression Ring Calculation:

The top and bottom compression rings are not only subjected to high compressive loads but also bending loads from the support legs. Through FEA, the strength and buckling mode of failure are evaluated and qualified as per API 620.  

Design of support structure:

The support structure such as the legs, stiffener rings, and roof structure is designed and qualified as per IS 800 2007, The numerical data from the FEA is used to perform analytical calculations. Further Weld strength calculations are performed and checked as per IS 800 2007.

Erection scenario:

From shop fabrication, testing, and erection, the silo is subjected to various lifting and transportation loads. These conditions are checked through FEA and the structural integrity is ensured at all stages.

Conclusion

The FEA stress analysis successfully validated the structural integrity of the 550 Mton Silo designs The design calculations were checked by Engineers India Limited, and proceeded to the fabrication process. The project demonstrated the effectiveness of FEA as a tool for identifying potential issues and guiding design improvements.

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