Computational Fluid Dynamics for biomass boilers

The Computational Fluid Dynamics (CFD) is a very useful tool to study relevant aspects in the design of a biomass boiler such as the mix between the flue gases from the grate with the secondary and tertiary air, the post-combustion, the evolution of the flue gases temperature along the boiler, the heat transfer, the influence of the fouling, the flue gases pressure loss or the flue gases residence time.

Flue gas residence time

This variable is very important in the design of a biomass/waste boiler since flue gases must remain in the boiler at temperatures above 850ºC at least 2 seconds. Numerical fluid simulation is the only tool that allows an accurate calculation of this variable.

CFD model

nablaDot has developed a CFD model, including a detailed representation of the geometry and a flue gas combustion model. Phenomena such as flue gases flow, turbulence, convective heat transfer, radiation and chemical reaction are simulated with this model. The heat transfer in the tube banks was calculated using a porous media approach.

Results

The performance of the biomass boiler was tested with the CFD model developed, verifying that the requirements regarding residence time, pressure loss and heat transfer were met. In addition, the CFD model was used to analyse several measures to improve the boiler operation, contributing to a quick advance towards its final design.

Other applications

The CFD model developed can be adapted to simulate the flue gases flow in any biomass boiler. Additionally, the model elaborated for the calculation of the residence time, a basic parameter in many industrial designs, can be applied to analyse any industrial process.