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Interactions, known as the ignition promotion and burnout inhibition, exist during the combustion of blended coals in the air. The oxy-fuel conditions influence these interactions due to the change of the gas physical properties and the gasification reaction. However, little research has focused on the oxy-fuel combustion interactions of blended coals. To investigate the combustion interactions of blended coals in an O2/CO2 atmosphere, experimental and numerical studies of the mixed combustion of less- and more-volatile coals are performed in a drop tube furnace. The results show that the more-volatile coal combustion brings the promotive effect on the devolatilization of the less-volatile coal and the inhibitive effect on the char combustion of the less-volatile coal. Compared with that in the air, the promotive effect is weaker, but the inhibitive effect is stronger in the 21%O2/79%CO2 environment due to the different physical properties of the gases. In the O2/CO2, increasing the oxygen concentration increases the promotive effect but weakens the inhibitive effect owing to the change of the physical properties of gases and the reactivity improvement of the less-volatile coal char. In addition, the promotive and inhibitive effects achieve a level similar to that in the air when the oxygen concentration is increased to approximately 30–35%. Furthermore, the char-CO2 gasification reaction in the O2/CO2 has little impact on the promotive effect but weakens the inhibitive effect. Increasing the reactor wall temperature weakens both the promotive effect and the inhibitive effect.

Gas temperature deviation is a common problem for tangentially fired boilers, affecting the boiler operation safety and the boiler generation efficiency. The gas temperature deviation in the tangentially fired π-type boilers has been well studied. However, the gas temperature deviation in the tangentially fired tower-type boilers has yet to be fully understood. This paper develops insights into the causes and controlling strategies of gas temperature deviation in a 660 MW tangentially fired tower-type boiler with obvious steam temperature deviation by experiment and simulation. Firstly, four upper furnace structures are established to fully reveal the causes of gas temperature deviation. The gas temperature deviation is mainly caused by the flue gas rotation, the heating tubes division, and the suction effect of the induced draft fan. More evident recirculation is observed near the right side than the left side in the platen heater region, resulting in that the flue gas deflects to the left side, and the left side region presents higher temperature. Furthermore, the controlling strategies of gas temperature deviation are studied comprehensively by adjusting SOFA (Separated Over-fire Air) horizontal angle and setting SOFA left–right-side velocity offset. Properly SOFA horizontal angle or enhancing the left-side SOFA velocity may effectively reduce the gas temperature deviation. 34–45° for the SOFA horizontal angle and 1.2 for the SOFA left–right-side velocity ratio are recommended. In the actual operation, offsetting the SOFA left–right-side velocity (i. e. SOFA air damper opening degree: left side—80% and right side—50%) is successfully applied to reduce the re-heated steam temperature deviation from 18 K to 1 K without bringing adverse effects under the low load. These deep insights may provide useful information to control the steam temperature deviation in the platen heater zone.

Maintaining stable combustion is one of the major challenges for microscale combustors. In this study, a novel premixed CH4/air flame micro-combustor combining a flame holder, backward-facing step and preheating channel is developed to enhance the flame anchorage and extend the blow-off limits. The effects of flame holder shape (triangle and rectangle) and height (H = 0.0, 0.5, 1.0, 1.5 and 2.0 mm) on the combustion stability are studied numerically by FLUENT 16.0. The results show that this micro-combustor not only can considerably anchor the flame root owing to flow recirculation but also can further improve CH4 flammability owing to heat recirculation. Compared with the rectangle flame holder, the triangle flame holder achieves the higher blow-off limits owning to the larger recirculation zone and better preheating effect. As the flame holder height increases, (i) the recirculation zone sizes near the flame root decrease, weakening the flame-root anchorage ability, and (ii) the heat recirculation effect becomes stronger, improving CH4 flammability. Under the combined effects of flow recirculation and heat recirculation, the highest flame blow-off limits are attained when H = 0.5 mm. The flame holder with triangle shape and H = 0.5 mm attains the highest flame blow-off limits (10.3 m/s and 6.2 m/s at Φ = 0.7 and 0.5).