Biomass Waste Incinerator CFD Simulation

Description

Biomass Waste Incinerator CFD Simulation, ANSYS Fluent Tutorial

Introduction

This study investigates the combustion process of biomass waste in an industrial incinerator using Computational Fluid Dynamics (CFD) analysis. The simulation aims to understand the complex fluid dynamics, heat transfer, and chemical reactions within the incinerator, focusing on achieving uniform combustion on the rubbish surface. By employing advanced models for turbulence, species transport, and combustion, this research provides valuable insights into optimizing waste-to-energy processes and improving the efficiency of biomass incineration systems.

The CFD simulations were conducted using ANSYS Fluent software. The computational domain includes a trapezoidal waste pile, air inlets, fuel inlets, and a cooling system. The geometry designed in ANSYS Design Modeler represents an industrial incinerator with multiple air and fuel inlets and two exhaust gas outlets. Then the geometry is meshed using ANSYS Meshing software, while the total number of elements are 6,893,518.

Methodology

The simulation was set up as a steady-state analysis using a pressure-based solver. The RNG k-ε model with standard wall functions was utilized for turbulence modeling, accounting for the complex flow patterns within the incinerator.

The energy equation was enabled to accurately model heat transfer within the system, which is crucial for capturing the thermal behavior of the combustion process and its impact on the incinerator’s performance.

A species transport model was employed to simulate the combustion process, with two primary reactions defined: CH4 + O2 and H2 + O2. The eddy-dissipation model was activated for turbulence-chemistry interaction, simulating the fast chemistry regime typical in industrial combustion processes.

To represent the continuous generation of combustible gases from the waste, fixed source terms for CO and H2 mass fractions were applied at the rubbish surface boundary condition.

Results

The CFD simulation provided comprehensive insights into the thermal and fluid dynamic behavior of the biomass waste incinerator:

The simulation results show a significant temperature gradient within the incinerator. The outlet chamber temperature (979.38 K) is considerably higher than the cooling outlet temperature (376.59 K), indicating effective heat generation and transfer in the main combustion zone. The average temperature for both outlets combined is 875.82 K, suggesting efficient overall heat recovery.

The velocity magnitude contours reveal complex flow patterns within the incinerator, with maximum velocities reaching 14.72 m/s. These flow patterns play a crucial role in mixing air and fuel, as well as distributing heat throughout the chamber.

The static temperature contours show peak temperatures exceeding 2000 K in the main combustion zone, indicating intense reactions. The temperature distribution on the waste surface varies, with higher temperatures observed near the fuel inlets and in regions of good air-fuel mixing.

The mass fraction contours for CH4 and CO2 provide insights into the combustion process. High concentrations of CH4 are observed near the fuel inlets, while CO2 concentrations increase in the post-combustion zones, indicating the progress of the reaction.

The temperature-colored pathlines illustrate the complex three-dimensional flow within the incinerator. They show how the air and fuel streams interact, mix, and combust, creating recirculation zones that enhance mixing and promote more complete combustion.

The simulation results demonstrate the complex interplay between fluid flow, heat transfer, and chemical reactions in the biomass waste incinerator. The temperature gradients and species distributions highlight areas of efficient combustion as well as potential zones for optimization. The flow patterns revealed by velocity contours and pathlines suggest that careful design of inlet positions and flow rates is crucial for achieving uniform combustion on the rubbish surface.

While the current design shows good overall performance, there is potential for further optimization. Adjusting the positions and flow rates of air and fuel inlets could lead to more uniform temperature distribution on the waste surface, potentially improving combustion efficiency and reducing emissions.