Objective
To understand the flue gas flow and dust flow inside the boiler for finding root causes of severely high rates of erosion inside the Evaporator Tube Banks, and suggest design modifications using CFD to arrive at best solution to the erosion problem without affecting the pressure drop between simulated section.
Design Approach
The evaporator tubes banks in AQC-5 boiler has been observing continuous severe erosion during operation. It is therefore required to understand the flue gas flow and dust flow inside the boiler to find the causes of severely high rates of erosion in the Evaporator Tube Banks. For CFD analysis, the domain between inlet of Evaporator-2 and Outlet of Evaporator-3 have been considered.
The boundary condition of calculated mass flow rate and temperature applied at inlet of domain (inlet of Evaporator-2) and pressure has been applied at outlet of the domain (outlet of Evaporator-3). The evaporator-2 & 3 were mathematically modeled with porous media formulation using provided flow rate & pressure drop in the evaporator -2 & -3 tube bundles along with provided temperature difference.
Conclusion
From simulations, it is concluded that, due to the circular duct between evaporator-2 and evaporator-3, a centrifugal force is naturally observed, due to this centrifugal force a dense concentration of particles are observed near to the wall which is also the region where erosion is observed on the tube banks. Several design modifications are iterated and a continuous baffle kind of arrangement is selected and results predicted that, with this design modification the rate of erosion in the tube banks will be reduced by 60%.
