Pellet as a Technological Nutrient within the Circular Economy Model: Comparative Analysis of Combustion Efficiency and CO and NOx Emissions for Pellets from Olive and Almond Trees
Abstract
:1. Introduction
2. Results and Discussion
2.1. Physicochemical Analysis
2.2. CO and NOx Emissions
2.3. Combustion Efficiency
3. Materials and Methods
3.1. Physicochemical Characterization of Fuels
3.2. Description of BIO System Equipment
3.3. Experimental Procedure
- Initial fuel filling and turning-on of the BIO System burner by means of a hot-air igniter oriented towards the fuel pile (Figure 9). During this first stage, primary and secondary air fans are switched on, so there is a high excess of air in the chamber.
- The BIO System burner is fed with new particles of biomass. The operating times for the screw feeder are 3 s in ON position and 20 s in OFF position. During this stage, there is a gradual increase of CO in flue gases, which corresponds to a slow progressive rise in the flow of the biomass introduced into the chamber until the mass flow necessary to obtain the nominal power of the experimental system (165 kW) is reached. In the case of the BIO System burner, the mass flow is within the range of 35 kg·h−1 and 40 kg·h−1. There is a soft start-up of the system in this way.
- Combustion stabilization with screw feeder times of 3/20 s. A stable situation is reached after several minutes when the combustion is maintained with only the heat contribution of the biomass (there is no need to use the hot-air igniter). In this regard, the total air flow needed is a key parameter to ensure the correct operation of the system and a stable combustion process. In this case, total air flow presents a value ranging between 290 m3·h−1 and 300 m3·h−1, with an excess of air fluctuating between 60% and 80%.
- Rise in fuel load. When the combustion process and resulting power are in steady conditions, such conditions are kept for as long as data collection lasts in order to compare the emissions obtained for each of the partial loads until they reach nominal power.
- Turning-off of the BIO System burner. The biomass feeding system is switched off whereas primary and secondary air fans are on, so that any remaining material that may remain in the burner is consumed.
3.4. Analysis of CO and NOx Emissions
3.5. Combustion Efficiency
- Non-burnt solid losses, Qn−b,s, have not been quantified, as the operating time under stable conditions was not long enough to obtain a representative value for each power range studied. Consequently, no non-burnt solid losses have been assumed.
- As the ash content of the fuel was lower than 3% (Table 2), the value of Qsa, which refers to sensitive heat losses in ash, has not been considered, since those losses are considered to be practically insignificant.
- For this calculation, the following constants were used: 11.8421 m3·h−1 for water volumetric flow and 4.185 kJ·kg−1·°C−1 for water specific heat.
4. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Parameter | Type of Pellet | |
---|---|---|
Almond Tree | Olive Tree | |
Diameter (mm) | 6 | 6 |
Length (mm) | 10–31 | 10–24 |
Bulk density (kg·m−3) | 620 | 650 |
Parameter | Type of Pellet | |||||
---|---|---|---|---|---|---|
Almond Tree | Olive Tree | |||||
Stabilized sample | Dry sample | Received sample | Stabilized sample | Dry sample | Received sample | |
Immediate Analysis (% weight) | ||||||
Moisture | 4.53 ± 0.04 | 0.00 ± 0.00 | 3.18 ± 0.03 | 4.40 ± 0.05 | 0.00 ± 0.00 | 2.93 ± 0.03 |
Ash | 2.62 ± 0.36 | 2.74 ± 0.37 | 2.66 ± 0.36 | 2.54 ± 0.39 | 2.66 ± 0.41 | 2.58 ± 0.40 |
Volatile matter | 75.73 ± 1.85 | 79.32 ± 1.93 | 76.80 ± 1.87 | 77.26 ± 1.98 | 80.82 ± 2.07 | 78.45 ± 2.01 |
Fixed carbon | 17.12 ± 0.42 | 17.94 ± 0.44 | 17.36 ± 0.42 | 15.80 ± 0.40 | 16.52 ± 0.42 | 16.04 ± 0.41 |
Elemental Analysis (% weight) | ||||||
Carbon | 45.27 ± 1.11 | 47.42 ± 1.16 | 45.91 ± 1.12 | 45.20 ± 1.16 | 47.28 ± 1.21 | 45.90 ± 1.18 |
Hydrogen 1 | 5.66 ± 0.05 | 5.40 ± 0.05 | 5.58 ± 0.05 | 5.80 ± 0.07 | 5.55 ± 0.06 | 5.72 ± 0.07 |
Nitrogen | 0.49 ± 0.07 | 0.51 ± 0.07 | 0.50 ± 0.07 | 0.48 ± 0.07 | 0.50 ± 0.08 | 0.49 ± 0.08 |
Sulfur | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 |
Heating Value (kcal·kg−1) | ||||||
Upper heating value | 4369 | 4576 | 4431 | 4373 | 4574 | 4440 |
Lower heating value | 4048 | 4295 | 4122 | 4046 | 4285 | 4126 |
Other Properties | ||||||
Energy density (MJ·m−3) | 11,146 | 11,658 | ||||
Air-fuel ratiostoichiometric | 4.751 | 4.711 | ||||
Adiabatic temperature of the flame (°C) | 2308 | 2293 |
Type of Pellet | Nominal Power (kW) | Emissions | |||
---|---|---|---|---|---|
CO (ppm at 6% O2) | CO (ppm at 13% O2) | NOx (ppm at 6% O2) | NOx (ppm at 13% O2) | ||
Almond tree | 150 | 225.3 | 119.5 | 365.8 | 259.4 |
Olive tree | 165 | 351.6 | 186.4 | 333.2 | 236.3 |
Parameter | Fuel | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Pellet from Olive Tree | Pellet from Almond Tree | |||||||||||
Operation Parameters | ||||||||||||
Operation time (s) | 2 | 3 | 4 | 5 | 6 | 7 | 2 | 3 | 4 | 5 | 6 | 7 |
Shutdown time (s) | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
Delta temperature (°C) | 4.7 | 6.7 | 8.7 | 10.3 | 11.9 | 13.1 | 4.1 | 6.2 | 8.0 | 9.7 | 11.1 | 12.1 |
Power (kW) | 64.5 | 91.8 | 120.2 | 141.4 | 164.2 | 180.5 | 56.3 | 85.2 | 110.3 | 134.1 | 152.6 | 166.1 |
Partial load (%) | 39 | 56 | 73 | 86 | 99 | 109 | 34 | 52 | 67 | 81 | 92 | 100 |
Gas Emission | ||||||||||||
Oxygen concentration (%) | 16.7 | 14.5 | 12.1 | 10.4 | 8.4 | 6.7 | 17.2 | 15.5 | 13.3 | 11.5 | 9.5 | 8.0 |
CO (ppm at 6% O2) | 5634.8 | 1558.8 | 977.1 | 429.5 | 351.6 | 3248.6 | 6275.0 | 2589.0 | 865.5 | 387.9 | 225.3 | 3542.6 |
CO (ppm at 13% O2) | 2987.6 | 826.5 | 518.1 | 227.7 | 186.4 | 1722.4 | 3327.0 | 1372.7 | 458.9 | 205.7 | 119.5 | 1878.3 |
NOx (ppm at 6% O2) | 382.3 | 397.2 | 363.4 | 369.8 | 333.2 | 251.0 | 457.4 | 463.1 | 388.4 | 378.0 | 365.8 | 356.9 |
NOx (ppm at 13% O2) | 271.1 | 281.7 | 257.7 | 262.2 | 236.3 | 178.0 | 324.4 | 328.4 | 275.4 | 268.1 | 259.4 | 253.1 |
Combustion Efficiency | ||||||||||||
Gas temperature (°C) | 140.5 | 148.4 | 173.5 | 192.6 | 211.2 | 221.2 | 128.2 | 152.6 | 177.6 | 192.9 | 211.2 | 224.5 |
Combustion efficiency (%) | 76.7 | 84.2 | 86.2 | 87.0 | 87.7 | 84.9 | 76.5 | 81.0 | 84.2 | 85.9 | 86.3 | 84.7 |
Combustion efficiency 1 (%) | 79.9 | 87.2 | 90.4 | 92.0 | 93.1 | 89.8 | 78.0 | 85.0 | 89.4 | 91.4 | 92.1 | 90.2 |
Air flow (m3·h−1) | 397.9 | 340.4 | 315.4 | 309.6 | 293.7 | 417.4 | 375.9 | 383.8 | 339.2 | 327.6 | 299.7 | 371.4 |
Excess of air (%) | 386.7 | 223.3 | 135.1 | 97.9 | 62.0 | 100.9 | 441.6 | 283.2 | 171.6 | 120.2 | 78.9 | 101.5 |
Fuel flow (kg·h−1) | 17.6 | 22.0 | 28.1 | 32.8 | 37.8 | 42.8 | 15.0 | 21.0 | 26.0 | 31.0 | 35.0 | 37.9 |
Radiation and convection losses (%) | 2.6 | 1.8 | 1.4 | 1.2 | 1.0 | 1.0 | 2.9 | 1.9 | 1.5 | 1.2 | 1.1 | 1.0 |
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Molina-Moreno, V.; Leyva-Díaz, J.C.; Sánchez-Molina, J. Pellet as a Technological Nutrient within the Circular Economy Model: Comparative Analysis of Combustion Efficiency and CO and NOx Emissions for Pellets from Olive and Almond Trees. Energies 2016, 9, 777. https://doi.org/10.3390/en9100777
Molina-Moreno V, Leyva-Díaz JC, Sánchez-Molina J. Pellet as a Technological Nutrient within the Circular Economy Model: Comparative Analysis of Combustion Efficiency and CO and NOx Emissions for Pellets from Olive and Almond Trees. Energies. 2016; 9(10):777. https://doi.org/10.3390/en9100777
Chicago/Turabian StyleMolina-Moreno, Valentín, Juan Carlos Leyva-Díaz, and Jorge Sánchez-Molina. 2016. "Pellet as a Technological Nutrient within the Circular Economy Model: Comparative Analysis of Combustion Efficiency and CO and NOx Emissions for Pellets from Olive and Almond Trees" Energies 9, no. 10: 777. https://doi.org/10.3390/en9100777