Simulation of biogas co-combustion in CFB boiler: Combustion analysis using the CPFD method

Abstract

CFB boilers exhibit broad fuel adaptability. Multi-fuel co-combustion can be implemented without altering the boiler's main structure, enabling the exploration of additional fuel utilization methods. This study assesses the feasibility of biogas co-combustion in CFB boilers. In this study, the computational particle fluid dynamics (CPFD) method was used to simulate a 130 t/h biomass CFB boiler. The impact of varying proportions of biogas on combustion characteristics and NO emissions in the CFB boiler was systematically analyzed. The results indicate that the fluid velocity in the furnace remains relatively unaffected before and after co-combustion, the flow rate varied from 3 to 5 m/s for all cases. With an increase in the proportion of biogas co-combustion, the temperature inside the furnace rises. However, maintaining the biogas co-combustion ratio below 20 % keeps the temperature within a reasonable range. Beyond this threshold, particularly at a 30 % biogas co-combustion ratio, localized time-averaged temperatures in the furnace exceed 1300K, and the coking risk increases. Additionally, co-combusting biogas decreases fuel nitrogen levels and alters oxygen distribution, thereby impeding NOx formation. This results in a 14.3 % reduction in NO emissions at a 20 % co-combustion ratio and a 24.6 % reduction at a 30 % co-combustion ratio. This paper's research provides a valuable reference for co-combustion of gases in CFB boilers.

Keywords

• Circulating fluidized bed
• Computational particle fluid dynamics
• Co-combustion
• Biogas
• Biomass