MFM : Secondary combustion chamber

Introduction

The purpose of a secondary combustion chamber in an incineration unit is to prevent the release of certain chemicals emitted by the incinerator from entering the atmosphere. One method of doing so is to raise the gases to such a temperature in the presence of oxygen, as will destroy the chemicals by pyrolysis and/or oxidation/combustion.

The thermal design task is to calculate the field distribution of gas mixture composition and temperature.

The combustion chamber chosen for the present computations retains all major features of real-life industrial equipment: rectangular shape of 920x2100x2400 mm; inlet of primary gas mixture at the bottom; high temperature burner product mixture input at the chamber wall; injection of secondary air through ports in the other; and secondary combustion product discharge at the top.

Chamber walls are supposed to be well insulated. The low conductivity plate is located on the supports inside a chamber with the aim to provide the flow recirculations resulting in the increase of residence time for carbon monoxide of primary gas mixture to be burned out.

The movement of combustion products is dominated by buoyancy. Combustion of CO on the grounds of both single- and multi-fluid Extended SCRS models are included and non-uniform buoyancy forces are allowed to affect both the mean flow and fluctuating dispersion.

Results

The plots show the flow distribution, mixture composition as represented by the model, gas temperature and velocity within the combustion chamber and at the outlet.

Pictures are as follows :

• Combustion chamber geometry.
• Flow distribution: streamlines.
• Velocity vectors at the west outer wall.
• Velocity vectors at the middle plane.
• Velocity vectors at the burner product inlet wall.
• Velocity vectors at secondary air inlet wall.
• Velocity vectors at the cross section through burner products and primary inlets.
• Temperature at different planes of the chamber
• Mass fractions of carbon monoxide, CO.
• Mass fractions of carbon dioxide, CO2.
• Mass fractions of water vapour, H2O.
• Mass fractions of nytrogen, N2.
• Mass fractions of oxygen, O2.
• Isosurface of 5m/s velocity magnitude.
• Isosurface of 1400K temperature.

Comparison with observations.

What	Experiment	Single-fluid	MFMT
Temperature, C	1034	1350	1068
Water vapour, %	14.4	14.0	14.2
Carbon dioxide, %	12.7	9.5	15.6
Oxygen, %	7.3	11.9	6.7
Nytrogen, %	65.6	70.5	63.3

Click here for more details about ESCRS combustion model.

Click here for more details about SCRS+MFM combustion model.