Boiler

     Erosion is caused in second pass of coal fired boilers due to impingement of high velocity ash particles on boiler tubes near sidewalls and rear / front wall. MWI is involved in designing Erosion control devices (ECD’s) using CFD to reduce erosion.

AIM

      Aim of the activity is to design erosion control devices to prevent the boiler tube erosion due to impingement of high velocity ash particles. ECD’s will reduce the localized erosion, in second pass of boiler, Screen tubes and to some extent to re-heater tubes.

OBJECTIVES

Objectives of the erosion control scheme are follows:

  • to reduce localized erosion.
  • to reduce tube leakages (breakdown).
  • to reduce replacement of tubes in annual shutdown.
  • to increase life of boiler tubes.

EROSION CONTROL DEVICES (ECD)

     ECD’s are designed to protect the boiler tube from erosion due to impingement of high velocity ash particles. The C.A.V.T. data, visual inspection and CFD analysis results are used to optimize the design of ECD’s to get the best results. Erosion control is made up of screen of various sizes and Configuration to reduce occurrence of highly localized erosion in the second pass of boiler. It is normally observed, erosion is concentrated in some area of boiler. ECDs distribute the erosion from localized area. Shielding is used as a supporting for ECD. The life of ECD is normally 4 to 5 years. Screens are designed to take the erosion & reduce erosion of tubes. However for every shutdown we recommend CAVT for further improvement in flow profile, material required for the same will be around 20% of installed ECDs. CFD technique helps to visualize the effect of ECD on the gas flow and makes it easier to try number of combinations in limited time. The erosions control devices with optimal results are finalized and manufacturing is done accordingly.

   

 

     In the project of Singrauli boiler, which was suffering heavy tube failure rate due to tube erosion, C.A.V.T. was performed and erosion control scheme recommended. Following are the comparisons of flow profiles at various locations:

Existing Flow Profile (Drum Boiler)

Modified Flow Profile (Drum Boiler)

Figure 3: Velocity Profile Before Modification