2.4. Operating conditions
The operating conditions for these experiments are shown in
Table 2. The in-bed stoichiometric oxygen ratio (Sb) can be
controlled by changing the ratio of the primary air to FGR in this
study. The secondary gas is preheated to about 200 C in the
combustor outer jacket before pumped into the combustor.
To eliminate the effect of residence time on the combustion
behavior, all of the experiments are conducted at a fixed primary
gas flow rate of 3 Nm3/min and a fixed secondary gas flow rate of
2 Nm3/min, respectively. In this study, the oxygen concentration
data of the flue gas at the outlet of ID fan were detected and
transmitted to the primary gas control system for adjusting the
mixing ratio of the primary air and FGR to maintain the oxygen
content in the primary gas at a set value.
The secondary gas is composed by mixing the secondary air and
nitrogen. The mixing ratio was adjusted according to the set value
of excess oxygen and stoichiometric oxygen of primary gas. In order
to maintain the excess oxygen ratio at a set value, the flow rate of
secondary air decreases and the flow rate of nitrogen increases
when the in-bed stoichiometric oxygen ratio increase.