Effect of different concentrations of O₂ under inert and CO₂ atmospheres on the swine manure combustion process

The oxy-fuel combustion of swine manure has been evaluated by thermogravimetric-mass spectrometric analysis. Manure samples showed a two-stage decomposition profile. The first stage is related to devolatilization of the sample and the second stage involved oxidation of the char formed in situ. Replacement of the inert carrier gas by CO₂did not seem to affect the first stage. However, this change in carrier gas delayed the oxidation of the samples during the second stage. This finding is mainly attributed to the slower transfer of thermal energy to the fuels in CO₂/O₂atmospheres. The increase in the oxygen partial pressure in the reaction medium had a marked effect on the oxidation stage by shifting the process to lower temperatures (from 514 to 478 °C and from 525 to 475 °C for Ar/O₂and CO₂/O₂, respectively). The kinetics of the process were evaluated by the integral iso-conversional method of Kissinger–Akahira–Sunose (KAS). The two aforementioned stages were clearly identified as two regions of apparent activation energy were obtained. A similar profile was found for the gaseous products released in the process in both atmospheres, as evidenced by a distribution with two emission peaks, which is consistent with the two combustion regions. However, the formation of light products such as H₂, CO and CH₄was favored on using high proportions of CO₂(∼80 vol.%).