Large Particle Ash (LPA)/Popcorn Ash

Airflow Sciences Corporation has been involved in over 30 projects focused on the modeling and design of devices that capture LPA and protect air preheaters and SCRs from pluggage.

Large Particle Ash.

Large Particle Ash (LPA) that is allowed to travel downstream beyond the economizer hopper can cause pluggage issues in both the air preheater and SCR. This pluggage can cause:

Increased system pressure loss
Large cleaning costs
Forced outages
Reduced efficiency of the catalyst
Accelerated catalyst de-activation
Erosion of the catalyst screen
Heavy flyash buildup that compromises structural integrity

SCR catalyst plugged by Large Particle Ash.

Screen eroded by ash.

Flow Modeling of Economizer Hopper Exit

The economizer hopper exit is the most efficient spot to trap LPA. Baffles and capture screens are the two devices typically used. CFD modeling is critical to the design and placement of both. Without careful modeling and prediction of gas velocities and particle trajectories, baffles will be inefficient and screens can erode quickly. ASC's CFD modeling:

Analyzes which approach will works best: baffles, screens or a combination of both.
Incorporates the proper drag, rebound, and specific gravity features of popcorn ash.
Predicts the percentage of ash capture in the economizer hopper.
Computes trajectories for various particle sizes.
Compares pressure loss versus capture efficiency; modifications are designed to balance maximum capture efficiency with minimal pressure loss.

CFD model of ash flow within the economizer hopper before baffle installation

CFD model of ash flow/capture at economizer exit
prior to the design/installation of baffles.

CFD of ash flow in economizer hopper after baffle installation

CFD model of ash flow/capture at economizer
exit after the design/installation of baffles.

Flow Modeling of Selective Catalytic Reduction (SCR) Equipment

Pre-installation modeling of SCRs includes predictions of carryover of LPA. Several particle sizes simulated (1, 3, 5, 7 mm diameter). Designed to capture 100% of the 5 mm and greater particles while minimizing pressure loss. Design of LPA screens. Evaluate erosion potential and help maximize screen life. Screen pluggage potential is evaluated as well.
Smoke visualization in physical model of an SCR.	Physical model of an SCR.

Field and Laboratory Testing

ASC field testing services provides on-site measurement of LPA flow rates.
ASC's on-site laboratory facility has allowed us to perform extensive experiments to access the aerodynamic characteristics of LPA.

Performing ASTM D197 Fineness Test in our laboratory.