What is the role of auxiliary burners in a black liquor recovery boiler?

Auxiliary burners in a black liquor recovery boiler play a significant role in maintaining a stable char bed during operation. The char bed is crucial for the effective combustion of the black liquor, which is a byproduct of the kraft process in pulping. By providing additional heat, auxiliary burners help ensure that the char remains ignited and continuously active, facilitating the complete combustion of the black liquor.

This stable char bed contributes to better energy recovery and more efficient operation of the recovery boiler. Maintaining this balance is essential not only for maximizing fuel efficiency but also for minimizing pollutant emissions and preventing operational issues that could arise from an unstable combustion environment.

While other options like increasing pressure, burning off excessive fuel, or cooling down the boiler may seem relevant to combustion processes, they do not directly capture the primary function of auxiliary burners, which is explicitly linked to the stability and efficiency of the char bed during the recovery process.