Measurement of reaction rates for pulverized fuel combustion in air and oxyfuel atmosphere using a novel fluidized bed reactor setup

- A small-scale, fast fluidized bed reactor (FBR) setup is presented.
- Combustion & gasification kinetics for pulverized coal char are determined.
- The activation energy is nearly identical for N2/O2 and CO2/O2 atmosphere.
- The fastest measured reactions show a 90% carbon conversion time <3 s.
- The results of the FBR compare well with EFR and TGA type systems.

The reaction rate of char from pulverized Columbian coal (Mina Norte) is investigated in synthetic air (N2/O2), oxyfuel atmosphere (CO2/O2) and CO2/N2 using a lab-scale fluidized bed reactor (FBR). Reactor temperatures range from 823 to 1273 K for combustion and 1173 to 1373 K for gasification (Boudouard). The oxygen volume concentration is varied between 15 and 30 vol.%, while gasification is investigated in a mixture of 10-75 vol.% CO2 in nitrogen. Using an nth order Arrhenius approach, activation energies as well as apparent order of reaction are calculated for the combustion and gasification reactions.It is found that the combustion reaction with this particular fuel evolves between +17% (873 K) and +75% (1223 K) faster in N2/O2 than in CO2/O2. The results of Arrhenius fit suggest that activation energy of combustion reaction does not differ significantly between synthetic air (regime I: 120.9 kJ/mol, regime II: 62.9 kJ/mol) and oxyfuel atmosphere (116.6 kJ/mol, 64.3 kJ/mol). Comparing results for oxyfuel and air, a difference of approximately 50 K in the transition temperature from regime I to regime II is observed but this finding is not statistically firm, yet. The apparent order of reaction has been calculated to n=0.72 in air (combustion), n=0.66 in oxyfuel (combustion) and n=0.49 in CO2/N2 (gasification).A comparison with available literature data confirms that the results achieved with the fluidized bed are comparable to the two most common experimental setups used in combustion research: Entrained flow reactors and thermogravimetric analyzers. The experimental setup also represents a novelty in FBR systems, as it quantitatively captures reactions with an apparent 90% carbon conversion timet90 of 3 s, which is a third of the time of comparable setups described in literature.