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For a 2 million-ton-per-year alumina project in West Kalimantan, Indonesia, Rainbow designed and supplied two 100 m sleeve-type steel chimneys for continuous coal-fired boiler exhaust. Each chimney combines a Q355B load-bearing outer shell with a Q255B + TA2 inner flue. Rainbow’s scope covered engineering design, manufacturing, supply, domestic transportation in China and technical guidance for site installation.
Project Parameter | Specification |
Project | 2 million t/a alumina project |
Location | Sanggau Regency, West Kalimantan, Indonesia |
Application | Continuous coal-fired boiler exhaust |
Quantity | Two chimney systems |
Chimney type | Sleeve-type self-supporting steel chimney |
Height | 100 m each |
Outlet diameter | 4,200 mm inner diameter; 4,500 mm outer diameter |
Outer shell | Q355B steel, 26–10 mm thickness |
Inner flue | Q255B + TA2, 10 + 1.2 mm thickness |
Flue gas temperature | 130°C |
Flue gas flow | 681,200 Nm³/h |
Design service life | Not less than 30 years |
Engineering standard | GB/T 50051-2021, Technical Standard for Chimney Engineering |
The chimneys discharge flue gas from coal-fired boilers operating continuously. The exhaust contains carbon dioxide, nitrogen oxides, SO₂ and particulate matter, with electrostatic dust collection incorporated into the upstream treatment process.
Each industrial boiler chimney had to accommodate a large flue gas flow at 130°C. The gas inlet system uses a side-entry arrangement with two inlet connections. Combined with the 4,200 mm outlet diameter and 100 m chimney height, these operating conditions required coordinated control of shell strength, structural stability, vibration and fabrication tolerances.
The project site has an annual average temperature of 26.96°C, a basic wind pressure of 0.4 kN/m² and Category B terrain roughness. Because the chimneys stand independently without an external tower, the structural design also had to account for wind-induced response and continuous operating loads.
Rainbow adopted a sleeve-type self supporting steel chimney configuration. The outer cylinder carries the principal structural loads, while the separate inner flue conveys the treated exhaust. Separating these functions allowed the structural shell and gas-contact surface to use materials suited to their respective operating requirements.
The outer shell uses Q355B structural steel with plate thicknesses ranging from 26 mm to 10 mm. The inner flue combines a 10 mm Q255B layer with a 1.2 mm TA2 layer. The TA2 gas-contact surface was selected for the exhaust environment, while the carbon-steel layer provides structural support for the inner flue.
The complete industrial steel chimney package includes the outer shell, inner flue, embedded components and a vibration-damping device. Paint-based corrosion protection was applied to the chimney structure.
The inlet and flue system incorporates connection flanges, inlet tees and an inner-flue load-bearing assembly. Working platforms, safety ladders, a spiral staircase and temporary installation platforms provide access during erection, inspection and maintenance.
Flue gas sampling and monitoring devices were integrated for operational testing. Manholes, ash-cleaning openings and drainage components support routine internal maintenance, while the top rain cover, cover plates and water-retaining rings help limit rainwater entry. Aviation obstruction lights and a lightning rod complete the safety configuration for the 100 m structures.
This industrial chimney design brings together large-flow exhaust handling, separate structural and gas-contact layers, vibration control and long-term maintenance access within one self-supporting system.
The two chimneys were prefabricated in the factory and prepared for assembly at the project site in Indonesia. Rainbow completed the engineering design, material supply and fabrication, followed by transportation to the buyer’s designated port in China.
After approval of the general arrangement drawing, the embedded components and anchor bolts for both chimneys were arranged for port delivery within 30 days. The first chimney and its accessories followed within 90 days, with the remaining equipment supplied within 120 days. Manufacturing was carried out in December 2025.
The chimney components were packaged in accordance with applicable Chinese requirements and Indonesian government packaging requirements before sea transportation. Rainbow also assigned site service personnel to provide construction coordination, technical control and installation guidance during assembly.
Both chimney systems were engineered for a design service life of at least 30 years. The warranty period covers two years from acceptance.
The project demonstrates Rainbow’s ability to coordinate the design, heavy steel fabrication, corrosion-resistant inner-flue configuration, export delivery and installation support required for large-diameter industrial chimneys in alumina, metallurgical and other heavy-industry facilities.
