In the 21st century, millions of researches are carrying out all over the world, to advance our civilization, to find answers to our queries and problems as well as to improve our life standard. However, some solutions we have developed to tackle one problem causes another problem and put our life in a cause and effect paradox. Climate change, environmental pollution, and resource depletion are some of the results of the paradox. In our present-day world where a few controls most of the world's wealth, those problems bear the biggest challenge to the people whose life depends on the small-scale agriculture. Thus, reducing our wastes, finding alternative energy fuels & chemicals, and developing CO2 free technologies and processes are the goals of this research.
Spent coffee grounds (SCG) is one of the major wastes in the coffee industries and considering coffee is the second-largest traded commodity next to petroleum as well as the second popular drink (next to water), there is a huge potential of the waste resource coming from this industry from all directions of our planet. Hence, by carrying out elemental analysis and calorific value measurement, the SCG elemental composition was nearly 50% and 7% C and H2 respectively and has about 20.7 MJ/kg net calorific value. These results indicate the potential of SCG as an alternative fuel and a chemical looping gasification procedure in CO2 and steam gasification medium in a semi-fluidized bed batch reactor, using iron ore as an oxygen carrier (OC) was developed.
To understand the thermal decomposition, the physical and structural properties of the SCG and OC, the TGA, SEM, and XRD analyses were carried out. Moreover, the crystal and morphological characteristics of the OC were studied before and after the reduction of the iron-ore in the fluidized bed reactor. The gasification product gases were also analyzed using NDIR and GC machines, hence the carbon conversion, heating value, and cold gas efficiency of the process were determined accordingly.
CO, CO2, CH4, H2, C2H4, and char were the main products of the chemical looping process. When the SCG was gasified by the OC, some char was left mixed with the OC on the reactor bed and the iron ore didn’t fully reduce due to the low density of the SCG, which suspended above the bed. However, adding steam and CO2 gasification medium improved the reactivity of the char and 100% of carbon conversion, and reasonable LHV and cold gas efficiency improvement was achieved at a higher CO2/B molar ratio, 1 kg/kg OC/B ratio and 0.27 S/B molar ratio. In general, the chemical looping process showed the highest performance of solid fuel to gaseous fuel conversion in the steam and CO2 mixed atmosphere than using it in CO2 or steam medium separately.
The post-reduction XRD and SEM-EDX analysis of iron ore (hematite) showed the diffusion of some alkali metals such as Mg, K, and Ca in the partially reduced iron ore (magnetite). From the XRF analysis of the SCG ash and reduced iron ore, more or less similar concentrations of alkali metals were identified. As a result of the diffusions of these alkali metals, the crystal structure of the reduced iron ore showed a slight shift to the right.

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