How many combustion zones are specified for black liquor boilers?

In black liquor boilers, the design typically includes three combustion zones to optimize the combustion process and ensure efficient energy recovery from the black liquor produced in the pulping industry's chemical process. These three zones are crucial for effectively managing combustion under varying conditions, including temperature and airflow.

The first zone is the primary combustion zone, where the initial combustion of the black liquor occurs. In this zone, the concentrated organic materials in the liquor begin to burn off. The second zone is often referred to as the secondary combustion zone, wherein additional air is introduced to ensure complete combustion, helping to convert unburned gases and improve overall efficiency. The third zone serves as the burnout zone, which is designed to ensure that any remaining solid particles and gases are fully combusted before leaving the boiler, thereby minimizing emissions and maximizing energy extraction.

This multizone approach is essential in managing the complex combustion characteristics of black liquor, which can be quite different from more straightforward fuel sources. Each combustion zone plays a vital role in ensuring that the boiler operates at optimal performance while adhering to environmental regulations.