Comparison of Products of Incomplete Combustion of Waste Polystyrene and Styrene in Diffusion Flames and Ethyl Benzene in Fuel-Rich Premixed Flames

This study examined the effects of the mode of combustion of waste polystyrene (PS) on the emissions of products of incomplete combustion (PIC). Typically, combustion of PS in furnaces takes place with diffusion flames forming around devolatilizing chunks (pieces, shreds, pellets, etc.) of the solid polymer. In such flames a broad range of local fuel/air equivalence ratios exist, at any given instant of time. The inner side of a diffusion flame is fuel-rich and the outer side is fuel-lean, making it impossible to assess local conditions. Results are typically reported on the basis of a global equivalence ratio, φglobal, which is calculated based on the total amounts of fuel and air consumed in combustion. To examine the effects of local equivalence ratios, φ, on pollutant emissions, premixed flame combustion is necessary. In this investigation emissions from batch combustion of solid PS pellets in fixed beds, placed inside a horizontal furnace, are compared with emissions from steady-state steady-flow combustion of PS particle clouds (aerosols), inside a vertical furnace. Sampling was conducted at the exits of the furnaces. In addition, effluents from both diffusion and premixed flames of PS precursors are also compared. Liquid styrene is the monomer precursor of polystyrene; it is also the most abundant pyrolyzate. It was burned in batches inside the horizontal furnace. However, because of its unstable, often explosive combustion ethyl-benzene was chosen for the premixed combustion experiments. This choice was based on work conducted elsewhere, which showed that in flames the conversion of ethyl-benzene to styrene is extensive and extremely fast. Ethyl-benzene was pre-vaporized in nitrogen, mixed with oxygen and nitrogen, and burned in a flat flame burner. Fuel-rich conditions (φ = 2.5) were implemented to enhance the product yield. Product sampling was conducted in the luminous region of the premixed flame.

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Numerical Simulation of the Effect of Magnetic Fields on Soot Formation in Laminar Non-Premixed Flames

10.1115/power2021-64859 ◽

2021 ◽

Author(s):

Edison E. Chukwuemeka ◽

Ingmar M. Schoegl

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Volume Fraction ◽

Soot Formation ◽

Premixed Flames ◽

Premixed Flame ◽

Pollutant Emissions ◽

Chemical Mechanism ◽

Computational Domain ◽

The Magnetic Field

Abstract Characteristics of non-premixed flames such as flame height and lift-off height are affected by the presence of magnetic fields due to the paramagnetic properties of some combustion species. However, it is unknown whether magnetic fields can be used to reduce the emission of pollutants in non-premixed flames. In general, pollutant emissions are reduced in combustion systems if the mixing of combustion species is enhanced during the process. Since paramagnetic combustion species such as O2, O, OH, HO2, etc have a preferential motion direction in the presence of magnetic fields, there is a potential to harness this effect of mixing by imposing a magnetic field on the flame. This study seeks to provide some insights on the effect of magnetic field on pollutants generated in a laminar non-premixed flame numerically. The non-premixed flame is simulated using a detailed chemical mechanism for propane-air combustion and a modified Moss-Brookes soot model. To simulate the effect of magnetism on the paramagnetic chemical species, the species paramagnetic susceptibility is computed using the Curie relation. The non-premixed flame is placed at three different locations within the magnetic field. The computation predicted that the amount of average pollutants reduction is dependent on the location of the flames within the magnetic fields with respect to magnetic gradients. The mass weighted average of the soot volume fraction over the computational domain decreased when the non-premixed flame is located at certain locations within the magnetic field of the solenoid with respect to the absence of the magnetic fields, but increases in other locations.

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Radiation effects on combustion and pollutant emissions of high-pressure opposed flow methane/air diffusion flames

Combustion and Flame ◽

10.1016/j.combustflame.2004.12.012 ◽

2005 ◽

Vol 141 (1-2) ◽

pp. 118-130 ◽

Cited By ~ 26

Author(s):

X.L. Zhu ◽

J.P. Gore

Keyword(s):

High Pressure ◽

Radiation Effects ◽

Diffusion Flames ◽

Pollutant Emissions ◽

Opposed Flow ◽

Air Diffusion

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Modelling of a Bluff-Body Stabilised Premixed Flames Close to Blow-Off

Computation ◽

10.3390/computation9040043 ◽

2021 ◽

Vol 9 (4) ◽

pp. 43

Author(s):

Shokri Amzin ◽

Mohd Fairus Mohd Yasin

Keyword(s):

Bluff Body ◽

Fluid Dynamic ◽

Premixed Flames ◽

Pollutant Emissions ◽

Moment Closure ◽

Recirculation Region ◽

Scalar Dissipation ◽

Average Error ◽

Conditional Moment ◽

Lean Premixed

As emission legislation becomes more stringent, the modelling of turbulent lean premixed combustion is becoming an essential tool for designing efficient and environmentally friendly combustion systems. However, to predict emissions, reliable predictive models are required. Among the promising methods capable of predicting pollutant emissions with a long chemical time scale, such as nitrogen oxides (NOx), is conditional moment closure (CMC). However, the practical application of this method to turbulent premixed flames depends on the precision of the conditional scalar dissipation rate,. In this study, an alternative closure for this term is implemented in the RANS-CMC method. The method is validated against the velocity, temperature, and gas composition measurements of lean premixed flames close to blow-off, within the limit of computational fluid dynamic (CFD) capability. Acceptable agreement is achieved between the predicted and measured values near the burner, with an average error of 15%. The model reproduces the flame characteristics; some discrepancies are found within the recirculation region due to significant turbulence intensity.

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A Numerical Simulation of Gas Jet Diffusion Flames Enveloped by a Cascade of Venturis

Volume 2: 19th Computers and Information in Engineering Conference ◽

10.1115/detc99/cie-9046 ◽

1999 ◽

Author(s):

Ala R. Qubbaj ◽

S. R. Gollahalli

Keyword(s):

Diffusion Flames ◽

Co2 Concentration ◽

Reaction Model ◽

Numerical Results ◽

Pollutant Emissions ◽

Gas Jet ◽

University Of Oklahoma ◽

Burner Exit ◽

Baseline Case ◽

O2 Concentration

Abstract “Venturi-cascading” technique has been developed in the Combustion Laboratory at the University of Oklahoma. The goal was to control the pollutant emissions of diffusion flames by modifying the air infusion rate into the flame. The modification was achieved by installing a cascade of venturis around the burning gas jet. The basic idea behind this technique is controlling the stoichiometry of the flame through changing the flow dynamics and rates of mixing in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The thermal and composition fields of the baseline and venturi-cascaded flames were numerically simulated using CFD-ACE+, an advanced computational environment software package. The instantaneous chemistry model was used as the reaction model. The concentration of NO was determined through CFD-POST, a post processing utility program for CFD-ACE+. The numerical results showed that, in the near-burner, mid-flame and far-burner regions, the venturi-cascaded flame had lower temperature by an average of 13%, 19% and 17%, respectively, and lower CO2 concentration by 35%, 37%. and 32%, respectively, than the baseline flame. An opposite trend was noticed for O2 concentration; the cascaded flame has higher O2 concentration by 7%, 26% and 44%, in average values, in the near-burner, mid-flame and far-burner regions, respectively, than in the baseline case. The results also showed that, in the near-burner, mid-flame, and far-burner regions, the venturi-cascaded flame has lower NO concentrations by 89%, 70% and 70%, in average values, respectively, compared to the baseline case. The simulated results were compared with the experimental data. Good agreement was found in the near-burner region. However, the agreement was poor in the downstream regions. The numerical results substantiate the conclusion, which was drawn in the experimental part of this study, that venturi-cascading is a feasible method for controlling the pollutant emissions of a burning gas jet. In addition, the numerical results were useful to interpret the experimental measurements and understand the thermo-chemical processes involved. The results showed that the prompt-NO mechanism plays an important role besides the conventional thermal-NO mechanism.

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Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

10.1115/imece1999-1115 ◽

1999 ◽

Author(s):

Ala R. Qubbaj ◽

S. R. Gollahalli

Keyword(s):

Diffusion Flames ◽

Concentration Field ◽

Laser Induced Fluorescence ◽

Pollutant Emissions ◽

Average Decrease ◽

Burner Exit ◽

Fluorescence Measurements ◽

Air Mixing ◽

Flame Region ◽

Lif Spectroscopy

Abstract “Venturi-cascading” technique is a means to control pollutant emissions of diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33% in NO emission index along with a 24% decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, Laser Induced Fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18%, 24% and 12% in the concentrations of OH, CH and CN radical, respectively, from their baseline values. However, in the mid-flame region, a 40% average increase in OH, from its baseline value, was observed. In this region, CH or CN radicals were not detected. The OH radical, in the downstream locations, was mostly affected by soot rather than by temperature. In addition, prompt-NO mechanism appeared to play a significant role besides the conventional thermal-NO mechanism.

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