Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor
Abstract
:1. Introduction
2. Materials and Methods
2.1. Fuels
2.2. Description of the Pilot Plant
2.3. Experimental Methodology
3. Results and Discussion
3.1. Plant Stability and Repeatability
3.2. Influence of Air Configuration
3.3. Emissions
4. Conclusions
- The effect of air staging and total airflow in the burning (reaction) rate was analyzed. When low primary airflows are used, similar reaction rates were measured, regardless of whether the plant is working only with primary or air staging. For higher primary airflows, the reaction rate, bed devolatilization and thermal power rise up. Using only primary airflows, the combustion is poorer and the values move closer to the incomplete combustion (sub-stoichiometric regimen) while using air staging the burning rate and gas temperature grew almost proportionally following the char stoichiometric line.
- An increase in the total amount of primary air supplied enhance the burning rate with an almost constant air excess ratio (λ). This ratio varies depending on the air staging, but it normally moves between 1.5 and 2.5.
- Primary air excess ratio (λ1) between 0.4 and 0.55 as well as in-bed stoichiometric ratio (λC) close to one were experimentally measured as a consequence of the continuous oxygen-limited char combustion regime.
- The burning rates measured in this work are much higher when compare with reference data obtained in a batch combustor. The main explanation for this behavior is not only the effect of the air staging that enhances the reaction rate, but also the steady position of the ignition front due to the continuous feeding. In a batch combustor, as the ignition front travels along the tube there is an important heat dissipation. However, in the current facility, the combustion front is always steady in the same place owing to the continuously feeding system, increasing the temperature and thickness of the reaction front.
- The amount of particulate matter collected is a function of the sampling moment due to the ash accumulation in the combustion chamber.
- Particle concentrations between 15 and 75 mg/Nm3 at 6% O2 were recorded with air staging in most of the cases. When only primary air is introduced, the concentration is increased, reaching values of up 360 mg/Nm3.
- The characteristic size obtained for the PM was 0.05–0.1 μm. As with the total concentration, this size does not seem to vary significantly with the air conditions (total airflow or staging ratios). At the very least, the variations are lower than the measurement uncertainty for this study.
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
Primary air mass flow (kg/m2s) | |
Secondary air mass flow (kg/m2s) | |
Total air mass flow ( + ) (kg/m2s) | |
Fuel burning rate (kg/m2s) | |
Char/carbon burning rate (kg/m2s) | |
AFR | Particle air to fuel stoichiometric ratio (kg of dry air per kg of fuel burnt) |
AFRC | Char air to fuel stoichiometric ratio (kg of dry air per kg of carbon burnt) |
Tch | Chimney/Stack gas temperature (°C) |
Tg | Gas temperature (°C) |
Tin | Water inlet temperature (°C) |
Greek Symbols
λ | Air excess (total air-fuel equivalence ratio) |
λ1 | Primary air excess (primary air-fuel equivalence ratio) |
λC | Char air excess (primary air-char equivalence ratio) |
φ | Air staging ratio (/) |
ØPM | Particulate matter representative size (μm) |
Abbreviation
DLPI | Dekati Low Pressure Impactor |
PM | Particulate Matter (mg/Nm3) |
SEM/EDS | Scanning Electron Microscopy/Energy Dispersive Spectroscopy |
wp | wood pellet |
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Proximate Analysis 1 (% Weight) | |||
wp1 | wp2 | wp3 | |
Moisture | 6.85 | 6.60 | 5.81 |
Volatile | 68.50 | 66.65 | 66.46 |
Fixed carbon 2 | 24.24 | 25.75 | 24.60 |
Ash | 0.41 | 1.00 | 3.13 |
Ultimate Analysis 3 (% Weight) | |||
C | 47.43 | 46.23 | 47.71 |
H | 6.22 | 6.29 | 6.17 |
N | 0.14 | 2.55 | 1.95 |
O | 46.21 | 44.93 | 44.17 |
Fuel | Number of Tests | Parameter | Relative Deviation % | Air Staging φ |
---|---|---|---|---|
wp1 | 9 | Burning rate | 6.1 | 20% |
Gas temperature | 9.3 | |||
5 | Burning rate | 4.7 | 15% | |
Gas temperature | 2.7 | |||
5 | Burning rate | 7.6 | 30% | |
Gas temperature | 3.8 | |||
wp2 | 17 | Burning rate | 10.3 | 20% |
Gas temperature | 4.9 | |||
wp3 | 46 | Burning rate | 10.4 | 25% |
Gas temperature | 8.8 |
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Regueiro, A.; Patiño, D.; Porteiro, J.; Granada, E.; Míguez, J.L. Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor. Energies 2016, 9, 940. https://doi.org/10.3390/en9110940
Regueiro A, Patiño D, Porteiro J, Granada E, Míguez JL. Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor. Energies. 2016; 9(11):940. https://doi.org/10.3390/en9110940
Chicago/Turabian StyleRegueiro, Araceli, David Patiño, Jacobo Porteiro, Enrique Granada, and José Luis Míguez. 2016. "Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor" Energies 9, no. 11: 940. https://doi.org/10.3390/en9110940