Clay Boswell Station Unit 4, a 535 MW coal fired station owned by Minnesota Power, planned to retrofit a new SO2 removal system, and needed design through flow modeling to ensure successful operation of the system. Alden used a scaled physical flow model to simulate coal ash deposition in the connecting ductwork and distribution manifold of the planned emissions control system. A modification to the manifold ductwork and new internal flow controls were developed to mitigate areas of ash piling. The plant installed the recommended flow controls and has experienced no major ash piling.

Work Performed

Alden developed a scaled physical model of the planned emissions control system and associated ductwork. The model used velocity inlet profiles based on field data to improve the accuracy of simulations. Initial tests identified one area in particular where high levels of ash deposition were observed in the distribution manifold. Duct modifications and flow control designs were investigated to mitigate the deposition. The final design eliminated the ash deposition.


After several months of operation with the recommendations implemented, plant personnel conducted a walkdown of the system and confirmed that the ductwork and distribution manifold were free of ash piling.

Project Highlights

  • The testing simulated ash transport and deposition in a scaled cold flow model
  • A cost-effective design for the DFGD inlet ducting system was provided
  • Plant feedback after operation confirmed the recommendations were effective