Case story


Power plant



Belman has designed, manufactured and supplied seven sets of precision engineered Coal Dust Expansion Bellows to a Power Plant in the USA. The bellows are supplied with a refractory lining for installation on the pulverized fuel ducts of the boilers.


The Client Requirements

The power plant was equipped with a supercritical single pass boiler, which is fueled with a mixture of air and pulverized coal dust. The air/coal supply duct required a solution to accommodate movements but which could also be insulated to prevent heat loss. Further, it was important to find a solution which prevented coal dust emissions being released into the atmosphere, which could occur if the process was prematurely shut down. The previously installed solution was not performing optimally and presented a health and safety risk due to the unwanted coal dust emissions. With this in mind, Belman worked closely with the client to expertly design the Coal Dust Expansion Bellows which could remedy the situation.


The Belman Solution

Belman used its considerable experience and engineering capabilities on Coal Dust Expansion Bellows and combined this with the smart use of tools, such as ANSYS Inventor, Rohr2 and others. Utilizing this skill set Belman made a proposal for the optimal design of the Coal Dust Expansion Bellows for the Power plant. In this case it consisted of an Expansion Joint incorporating a flanged pipe section between two Angular Expansion Joints. Two Angular Expansion Joints acting together can work in the same way as a Universal Expansion Joint by absorbing movements simultaneously in several planes. This solution was selected as the boilers tended towards movement in all 3 planes. Additionally, all the expansion joints were designed in accordance with their position in the system to increase the working efficiency and extend their life cycles. Finally, yet equally important, the new design solution prevented the emission of unwanted coal dust. The media in the fuel ducts is a mixture of air with pulverized coal dust, this lead to the requirement for the special insulation of the expansion joints. Coal dust is extremely abrasive and can backfill in the bellows of the expansion joints. For that reason, the expansion joints were designed with a refractory lining to prevent the erosion of the inner lining. Ceramic wool was further installed around the bellow. Additional insulation using special braided hose was also incorporated to provide further protection against the aggressive medium. The coal dust expansion bellows were coated with a primer which is a two-ingredient ethyl-zinc-silicate grey paint and further coated with a grey single ingredient matrix paint. This special paint coating provides improved protection against corrosion to the coal dust expansion bellows. This type of ethyl-zinc-silicate primer can provide protection for many years.


The top engineered Coal Dust Expansion Bellows have the following design parameters:

Dimension: DN 600 • Length: 3115 mm • Medium: Air with coal dust • Design temperature: 400°C • Design pressure: 0,3 barG • AX: +/-187 mm • LA: +137/-0 mm • AN: +/-3°• Bellows: 1.4541 • Flanges: 1.0038 • Design code: EJMA


  • Short on-time delivery
  • Coal dust emissions are now prevented between the mill and the burner, this helps to reduce pollution and lessen the environmental impact of the plant.
  • Increased operational efficiency and an extended life working life reduce the operating costs and downtime.
  • Reliability of the Expansion Joint designed to work under the operating parameters
  • Increased working efficiency and lengthened life cycle reduce operating costs and downtime.
  • Benefit from the considerable know-how of an experienced manufacturer

TECHNICAL information

  • Technical information on  Angular Expansion Joints is available in the Expansion Joint Catalogue
    page 29 -30
  • Installation examples of Angular Expansion Joints are available in the Expansion Joint Catalogue
    pages 68 -73


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Expansion Joints for coal dust engineered to eliminate coal dust emissions between mills and burners!


Read this interesting case story describing how we developed this remarkable Expansion Joint for the client.


In this case story you can see photos of installed Coal Dust Expansion Joints in a power plant.