Experimental Study of the Viability of Low-Grade Biofuels in Small-Scale Appliances
Abstract
:1. Introduction
2. Methodology
2.1. Fuel
2.1.1. Chemical Characterization
2.1.2. Raw Input Materials
2.2. Description of the Facility
2.3. Experimental Methodology
3. Results and Discussion
3.1. Chemical Properties
3.2. Physical Properties
3.3. Stability of the Facility
3.4. Plant Repeatability
3.5. Combustion Parameters
3.6. Particulate Emissions
3.7. Fouling and Slagging
4. Conclusions
- The test duration is directly related to the ash content in the fuel. The ash is accumulated in the bed after combustion. If very high temperatures are reached, part of the ash melts and forms slag, which worsens the combustion, causing instabilities and unwanted downtime. The test duration without transitory periods for the reference fuel (wp) was 180 min. However, this value was reduced to 40 and 45 min for lp100 and bp, respectively. For lp25, the duration was 90 min.
- In the study of the operating limits of each fuel, the best results for the non-commercial pellets were obtained for lp25, since the primary airflow needed to support combustion is relatively low for high fuel consumption. Furthermore, worse conditions were observed for the 100% leaf pellet, whose combustion required larger amounts of primary air to be employed, obtaining considerably low power values. Its high ash content led to a large accumulation of ash in the bed, which worsens combustion. In addition, a directly proportional relationship was found between the amount of primary air and fuel consumption.
- The particulate matter emission ranges were determined for the three new pellets. The concentration for wp was between 17.5 and 18 mg/Nm3 in this facility. The concentrations for bp, lp100 and lp25 were between 257 and 325 mg/Nm3, 17 and 43 mg/Nm3 and 22 and 53 mg/Nm3, respectively. The particle-size distribution is unimodal for all cases except bp, in which it is mixed. However, all particles are smaller than 1 μm. The size of the particles increases with the amount of primary air, because an entrainment phenomenon occurred in the bed. The mass size distribution peak was located between 30 and 470 nm for bp and in the range of 30 to 300 nm for lp100 and lp25.
- The fouling rates were similar to that obtained for wp. In all cases, independently of the used parameters, the fouling rate was located between 4.1 and 26.4 mg/Nm3. Related to this factor, all fuels were shown to have a good behavior.
- Slagging residues were present to a greater extent for lp100, associated with the high ash content of the fuel. There are two kinds of slag: sintered deposition and grate ash. The first is not practically volatile, while the presence of volatile matter is notable in the second.
- A priori, under the tested conditions, bp and lp100 do not seem to be good choices for commercialization. However, lp25 is not a bad alternative, although its commercialization necessitates the use of additives to improve the fuel quality.
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
ṁ1" | Primary air mass flow (kg/m2s) |
ṁ2" | Secondary air mass flow (kg/m2s) |
ṁf" | Fuel burning rate (kg/m2s) |
ṁair" | Total air mass flow (ṁ1" + ṁ2") (kg/m2s) |
Tg | Gas temperature (°C) |
Tin | Water inlet temperature (°C) |
fc | Unconfined yield strength (kPa) |
ffc | Flow index |
Greek Symbols | |
δe | Effective angle of internal friction (°) |
σ1 | Major consolidation stress (kPa) |
ρb | Bulk density (kg/m3) |
Ф | Angle of wall friction (°) |
λ | Air-exceed ratio |
ψ1 | Primary airflow (%) |
ψ2 | Secondary airflow (%) |
ψ | Air staging ratio ( %Primary air/%secondary air ) |
Abbreviation | |
bp | Barley pellet |
DLPI | Dekati Low Pressure Impactor |
lp25 | Pellet with 25% leaf–75% wood |
lp100 | Leaf pellet |
PM | Particulate matter |
wp | Wood pellet |
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Proximate Analysis 1 (%) | ||||
wp | bp | lp100 | lp25 | |
Moisture 2 | 7.33 | 6.92 | 7.74 | 9.79 |
Volatile | 68.02 | 63.06 | 56.58 | 59.54 |
Char | 24.10 | 21.62 | 22.71 | 23.42 |
Ash | 0.55 | 8.39 | 12.97 | 7.26 |
Elemental Analysis 3 (%) | ||||
C | 48.99 | 44.69 | 44.14 | 45.65 |
H | 6.45 | 6.03 | 5.55 | 6.35 |
N | 0.23 | 0.55 | 1.12 | 0.61 |
O 4 | 43.73 | 39.72 | 35.14 | 39.35 |
S 5 | - | - | - | - |
Ash Analysis (wt % of Dry Ash) | ||||
Na2O | 0.71 | 0.03 | 0.01 | 0.49 |
MgO | 9.45 | 1.62 | 0.60 | 3.80 |
Al2O3 | 12.23 | 0.46 | 0.70 | 8.56 |
SiO2 | 22.79 | 68.21 | 49.74 | 39.12 |
P2O5 | 3.05 | 1.24 | 0.53 | 2.74 |
SO3 | 6.68 | 2.78 | 0.69 | 2.42 |
Cl | 1.41 | 0.74 | 0.11 | 0.61 |
K2O | 16.63 | 13.98 | 1.43 | 8.95 |
CaO | 22.48 | 10.67 | 43.93 | 28.58 |
TiO2 | 0.58 | 0.02 | 0.19 | 0.42 |
Cr2O3 | - | - | - | 0.02 |
MnO | 1.38 | 0.04 | 0.55 | 0.41 |
Fe2O3 | 2.23 | 0.18 | 1.41 | 3.50 |
NiO | - | - | - | 0.01 |
ZnO | 0.26 | 0.01 | 0.08 | 0.11 |
Rb2O | - | - | - | 0.00 |
SrO | 0.13 | 0.03 | 0.05 | 0.07 |
ZrO2 | - | - | - | 0.01 |
BaO | - | - | - | 0.16 |
Fouling Index | ||||
Alkali index | 0.05 | 0.67 | 0.11 | 0.39 |
Base-acid ratio B/A | 1.45 | 0.39 | 0.94 | 0.94 |
Slagging ratio SR | 40.02 | 84.54 | 51.99 | 52.15 |
Fouling ratio FU | 25.08 | 5.40 | 1.34 | 8.90 |
Flow Index | ffc < 1 | 1 < ffc < 2 | 2 < ffc < 4 | 4 < ffc < 10 | ffc > 10 |
---|---|---|---|---|---|
Flowability | Hardened (not flowing) | Very cohesive | Cohesive | Easy flowing | Free flowing |
Raw Material | ρb (kg∙m−3) | δe (°) | ffc (-) | Ф (°) |
---|---|---|---|---|
bp | 148 | 27.0 | 27.3 | 13.1 |
lp100 | 245 | 43.1 | 13.4 | 9.6 |
lp25 | 221 | 45.0 | 10.7 | 14.8 |
wp | 204 | 46.7 | 6.6 | 13.3 |
Total Duration (min) | Ignition (min) | Stability (min) | Shut Own (min) | |
---|---|---|---|---|
Pine pellet | 240 | 45 | 180 | 15 |
Barley pellet | 105 | 45 | 45 | 15 |
Leaf pellet 100% | 100 | 45 | 40 | 15 |
Leaf pellet 25% | 150 | 45 | 90 | 15 |
Relative Deviation (%) | ||
---|---|---|
Combustion parameters | Burning rate (kg/m2s) | 17.82 |
Gas temperature (°C) | 6.81 | |
Fouling | Deposited mass (g/m2h) | 10.04 |
Attached mass (g/m2h) | 13.00 | |
Total mass (g/m2h) | 6.90 | |
Particulate matter | Particulate matter (mg/Nm3) | 4.13 |
Gaseous emissions | O2 measured (%) | 1.70 |
CO (ppm) | 8.24 | |
NOx (ppm) | 5.77 | |
CO2 (%) | 3.69 |
Fuel | Test ID | ψ (%) |
---|---|---|
wp | 1, 3, 5 | 20 |
2, 4, 6 | 30 | |
bp | 7 | 50 |
8 | 60 | |
9 | 70 | |
lf25 | 10 | 20 |
11 | 40 | |
12 | 60 | |
lf100 | 15 | 30 |
13, 16 | 50 | |
14, 17 | 70 | |
18 | 90 |
Fuel Type | wp ref | References | wp | bp | lp100 | lp25 |
---|---|---|---|---|---|---|
PM (mg/Nm3) | 13–34 | [27,28,30,31] | 17.5–18 | 257–325 | 17–43 | 22–53 |
Particle-size distribution | Unimodal and bimodal | [28] | Unimodal | Mixed | Unimodal | Unimodal |
Particle-size peak (nm) | 30–300 | [30,32] | 30–100 | 30–470 | 30-300 | 30–300 |
Conc. peak (mg/Nm3) | 28–240 | [31,32] | 20–35 | 120–140 | 20–27 | 8–31 |
Fouling (g/m2h) | 7–28 | [13] | 6.3–14.4 | 18.5–24.3 | 6.9–26.4 | 4.1–15.3 |
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Regueiro, A.; Jezerská, L.; Patiño, D.; Pérez-Orozco, R.; Nečas, J.; Žídek, M. Experimental Study of the Viability of Low-Grade Biofuels in Small-Scale Appliances. Sustainability 2017, 9, 1823. https://doi.org/10.3390/su9101823
Regueiro A, Jezerská L, Patiño D, Pérez-Orozco R, Nečas J, Žídek M. Experimental Study of the Viability of Low-Grade Biofuels in Small-Scale Appliances. Sustainability. 2017; 9(10):1823. https://doi.org/10.3390/su9101823
Chicago/Turabian StyleRegueiro, Araceli, Lucie Jezerská, David Patiño, Raquel Pérez-Orozco, Jan Nečas, and Martin Žídek. 2017. "Experimental Study of the Viability of Low-Grade Biofuels in Small-Scale Appliances" Sustainability 9, no. 10: 1823. https://doi.org/10.3390/su9101823