What is a major characteristic of bubbling fluidized bed boilers?

A major characteristic of bubbling fluidized bed boilers is that the bed is in a fluid-like state. This is achieved by forcing air or gas upward through a bed of solid particles, such as sand or ash. The high velocity of the gas causes the particles to become suspended, creating a behavior similar to that of a liquid. This fluidization allows for efficient heat transfer and intimate mixing of fuel and combustion air, resulting in effective combustion processes.

This characteristic greatly enhances the combustion efficiency and enables the boiler to handle a variety of fuels, including low-grade and waste fuels. The fluid-like behavior allows for better temperature control and reduces the formation of nitrogen oxides (NOx) by maintaining lower combustion temperatures compared to traditional combustion methods.

While other options touch on aspects of fluidized bed boilers, they do not capture the essence of the characteristic that defines their operation as prominently as the fluid-like state of the bed does.