Eduardo Garcia*, Hao Liu
Low Carbon Energy and Resources Technologies Research Group, Faculty of Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
Co-combustion of coal and spent coffee grounds blends in a fluidized bed reactor
References[1] Guo, F., Zhong, Z. (2018). Co-combustion of anthracite coal and wood pellets: Thermodynamic analysis, combustion efficiency, pollutant emissions and ash slagging. Environmental Pollution, 239(2018) 21-29.
[2] Sirisomboon, K., Kuprianov, V. (2017). Effects of fuel staging on the NO emission reduction during biomass-biomass co-combustion in a fluidized-bed combustor. Energy and Fuels, 31, 659−671.[3] Reddy, P., Clean coal Technologies – for power generation. CRC press. 2014.
Co-combustion of coal and biomass is quite a promising alternative in the short-term to achieve major reductions in GHG emissionsfrom coal power sector, but it still faces unsolved challenges [1] [2]. A higher biomass ratio than the currently used in mostcommercial applications, 5-10 % (energy basis) [3], means lower GHG emissions. However, higher ratios raise concerns aboutcombustion efficiency, GHG emissions and ash issues. Spent coffee grounds (SCG), a by-product from the coffee industry, has similarheating values to low-rank coals. SCG is available in large quantities, and almost free in every soluble coffee plant and coffee shop.Its use represents a sustainable alternative to the increasing adverse environmental impact of this industrial sector in recent years.
SCG used as a fuel in co-combustion with coal appears as a feasiblesustainable alternative due to the increased combustionperformance in fluidized bed combustion compared to pure coal, andSTW and WP. Nevertheless, the fuel-N in SCG arises as a challengethat need to be addressed by the optimization of operationalconditions. In future the effect of blending ratio on emissions andagglomeration tendency under extended operation time will betested upon different conditions.
Conclusions and Future work
Background
Figure 6. Schematic diagram of the bubbling fluidized bed (BFB)
Preliminary Results
Figure 7. Comparison of emissions (energy basis) from spent coffee grounds (SCG) compared to wheatstraw (STW) and wood (WP), and pure coal (BC); CO2 emissions (a), CO emissions (b), NOx emissions
(c), and efficiency losses due to unburned carbon (UBC) and CO emissions (d).
Related UN sustainable goals
a b
c d
Experimental setupThe 30 kW BFB reactor, 15.4 cm ID and 2 mheight. After initial heating up by the electricheaters, the fuel blends were fed by the screwfeeder to start the combustion and adjusted tomaintain the operational temperature. Blends ofcoal with commercial wheat straw (STW) and wood(WP) pellets were considered for comparison.
Operational conditions:
• Bed material: Silica sand, 0.6 – 1.0 mm• Fuel feeding rate: 2.2 -2.6 kg/h• Bed Height: 20 cm (shallow bed)
• Excess air: 75 – 95 %• Temperature: 900 °C• Operational time: 20 hours
The flue gas composition (CO, CO2, O2 and NOx)was analysed online using flue gas analysers. Theash and used bed particles were collected from thecyclone and reactor at the end of each experiment,respectively.
To investigate the feasibility of co-combustion of spent coffee groundswith coal in a fluidized bed reactor in terms of the mostrepresentative emissions (CO2, CO and NOx), combustionperformance and agglomeration tendency.
Objective
DiscussionCo-combustion experiments of bituminous coal (12-20 mm) and in-house manufactured SCG pellets blended at 40 wt% wereperformed in a BFB. All the blends showed increased combustionperformance compared to pure coal. It is attributed to highervolatile matter from biomass increasing the reactivity of coal.Combustion of blends of coal and SCG pellets showed lower COemissions than the blend with WP, with similar values to the blendwith STW and pure coal. Unlike blends with STW and WP, the blendwith SCG did not show any decrease in NOx emissions incomparison with pure coal combustion. It is attributed to highernitrogen content in SCG compared to the other fuels. No relevantdifference was found among the blends with different biomass fuelsin terms of CO2 emissions. Blends with SCG showed reducedefficiency loss due to CO emissions and unburned carbon comparedto other biomass fuels and pure coal. No evidence of agglomerationwas detected during operation for blends with SCG.
Figure 2. Silica sand
Figure 3. In-house manufactured SCG
pellets
Figure 4. Fuel blend
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Figure 5. Typical profiles: (left) Temperature (right) emissions
Acknowledgement
This work was supported by the Administrative Department of Science, Technology and Innovation of Colombia – COLCIENCIAS and The Newton-Caldas Fund.
73.18
86.75
72.69 71.13
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409
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407
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8.68
6.57
7.85
1.22
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Effi
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loss
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COemmissions
83.4792.86 89.14
95.26
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Heat
Power
Technical approach
Figure 1. Schematic description of energetic use of spent coffee grounds
