Almond Shells and Exhausted Olive Cake as Fuels for Biomass Domestic Boilers: Optimization, Performance and Pollutant Emissions
Abstract
:1. Introduction
2. Materials and Methods
2.1. Raw Material and Characterization
2.2. Experimental Setup and Methodology
2.2.1. Boiler Description
2.2.2. Methodology
2.2.3. Statistical Experimental Design
3. Results and Discussion
3.1. Statistical Results
- Parametric study (stage 1)
- Optimization (stage 2)
3.2. Gaseous and PM Emissions
3.3. Efficiency
4. Conclusions
- -
- The required excess air (around 1.5) for both loads (~55 and ~24 kW) was higher than that typically used for woody biomass.
- -
- The optimal primary/secondary air ratio at nominal load was 20/80 for both fuels. However, this value changed to 50/50 for almond shells at a low load.
- -
- Because of the very significant ash content of exhausted olive cake, a higher grate vibration frequency was required (20 s with respect to the 45 s needed by almond shells).
- -
- The boiler efficiency at the optimum operating conditions was above the minimum value of 77%, required by UNE-EN 303-5 for Class 3 boilers, except in exhausted olive cake at low load.
- -
- Regarding gaseous and particles emission, CO emissions were lower and NOx (mainly related to the fuel-N content) were higher at nominal load for both fuels because of a more complete combustion process. Moreover, PM emissions increased due to fuel particles entraining the flue gas.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Abbreviations
λ | Excess air |
η | Boiler efficiency (%) |
LHV | Lower heating value of the fuel (MJ/kg) |
Tff | Fireplace fume temperature (°C) |
Tcf | Chimney fume temperature (°C) |
Ta | Ambient temperature (°C) |
Ppar | Partial load power (kW) |
Pnom | Nominal load power (kW) |
qa | Sensible heat losses in the flue gas (%) |
qb | Latent heat losses in the flue gas (%) |
qc | Heat losses by unburned matter in the solid residue (%) |
Qa | Sensible heat losses in the flue gas (kJ/kg) |
Qb | Latent heat losses in the flue gas (kJ/kg) |
Qc | Heat losses by unburned matter in the solid residue (kJ/kg) |
C | Carbon content of the fuel (wt.%) |
H | Hydrogen content of the fuel (wt.%) |
N | Nitrogen content of the fuel (wt.%) |
S | Sulphur content of the fuel (wt.%) |
Cl | Chlorine content of the fuel (wt.%) |
Cr | Carbon content of the residue with respect to the mass of fuel (wt.%) |
W | Moisture content of the fuel (wt.%) |
A | Residue passing through the grate (wt.% with respect to the fuel) |
B | Unburned matter present in the waste with respect to the mass of residue (wt.%) |
mash | Ash content of solid residues (kg) |
munb | Unburned matter content of solid residues (kg) |
mb | Total fuel feed to the boiler (kg) |
AS | Almond shells |
EOC | Exhausted olive cake pellet |
PA | Primary air flow (%) |
SA | Secondary air flow (%) |
V | Grate vibration frequency (s) |
PM | Particulate matter (mg/m3) |
DoE | Design of Experiments |
OF | Objective function |
RSM | Response Surface Methodology |
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Almond Shells | Exhausted Olive Cake | |
---|---|---|
Moisture (wt. %, wet basis) | 13.43 | 8.39 |
Bulk density (kg/m3, wet basis) | 398.86 ± 4.99 | 616.96 ± 0.18 |
Proximate analysis (wt.%, dry basis) | ||
Ash | 1.93 ± 0.10 | 8.92 ± 0.41 |
Volatiles | 83.39 ± 4.27 | 80.85 ± 4.33 |
Fixed carbon | 14.68 ± 4.17 | 10.16 ± 3.78 |
Ultimate analysis (wt.%, dry basis) | ||
C | 51.53 ± 0.31 | 50.65 ± 0.20 |
H | 5.18 ± 0.11 | 5.41 ± 0.10 |
N | 0.72 ± 0.15 | 1.30 ± 0.10 |
S | 0.01 ± 0.00 | 0.18 ± 0.01 |
Cl | 0.01 ± 0.01 | 0.32 ± 0.02 |
LHV (MJ/kg, dry basis) | 18.82 ± 0.02 | 19.27 ± 0.12 |
Almond Shells and Exhausted Olive Cake | ||||||||
---|---|---|---|---|---|---|---|---|
λ | 1.2 | 1.5 | 1.2 | 1.5 | 1.5 | 1.5 | 1.2 | 1.2 |
PA/SA | 20/80 | 20/80 | 40/60 | 40/60 | 40/60 | 20/80 | 40/60 | 20/80 |
V (s) | 45 | 20 | 20 | 45 | 45 | 20 | 20 | 45 |
Almond Shells | |||||||
---|---|---|---|---|---|---|---|
55 kW | λ | 1.4 | 1.5 | 1.5 | 1.3 | 1.3 | 1.4 |
PA/SA | 20/80 | 30/70 | 10/90 | 10/90 | 30/70 | 20/80 | |
V (s) | 45 | 45 | 45 | 45 | 45 | 45 | |
24 kW | λ | 1.5 | 1.6 | 1.6 | 1.4 | 1.4 | 1.5 |
PA/SA | 40/60 | 50/50 | 30/70 | 30/70 | 50/50 | 40/60 | |
V (s) | 20 | 20 | 20 | 20 | 20 | 20 |
Almond Shells | Exhausted Olive Cake | |||
---|---|---|---|---|
55 kW | 24 kW | 55 kW | 24 kW | |
λ | 1.5 | 1.6 | 1.5 | 1.5 |
PA/SA | 20/80 | 50/50 | 20/80 | 20/80 |
V (s) | 45 | 20 | 20 | 20 |
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Collado, R.; Monedero, E.; Casero-Alonso, V.M.; Rodríguez-Aragón, L.J.; Hernández, J.J. Almond Shells and Exhausted Olive Cake as Fuels for Biomass Domestic Boilers: Optimization, Performance and Pollutant Emissions. Sustainability 2022, 14, 7271. https://doi.org/10.3390/su14127271
Collado R, Monedero E, Casero-Alonso VM, Rodríguez-Aragón LJ, Hernández JJ. Almond Shells and Exhausted Olive Cake as Fuels for Biomass Domestic Boilers: Optimization, Performance and Pollutant Emissions. Sustainability. 2022; 14(12):7271. https://doi.org/10.3390/su14127271
Chicago/Turabian StyleCollado, Rocío, Esperanza Monedero, Víctor Manuel Casero-Alonso, Licesio J. Rodríguez-Aragón, and Juan José Hernández. 2022. "Almond Shells and Exhausted Olive Cake as Fuels for Biomass Domestic Boilers: Optimization, Performance and Pollutant Emissions" Sustainability 14, no. 12: 7271. https://doi.org/10.3390/su14127271