A bubbling fluidized bed (BFB) boiler is a boiler that can also handle fuels that are difficult to pulverize or less combustible. The fuel is introduced into a mixture of sand flowing at high temperatures, allowing the fuel to be efficiently combusted.

We are going to use the Kunii-Levenspiel bubbling-bed model to describe reactions in fluidized beds. In this model the reactant gas enters the bottom of the bed and flows up the reactor in the form of bubbles.

10.2 Bubbling Fluidized Bed Combustion

Fluidized beds are used as a technical process which has the ability to promote high levels of contact between gases and solids. Extremely high surface area contact between fluid and solid per unit bed volume. High relative velocities between the fluid and the dispersed solid phase.

Fluidized-bed boilers are the most common type of boiler recommended for biomass fuel, which is burned within a hot bed of inert particles, typically sand. The fuel-particle mix is suspended by an upward flow of combustion air within the bed. As velocities increase the gas/solid mix exhibits fluid-like properties.

The boiler activates a mixture of particles and gas to improve combustion reaction. Moreover, the fluid sand and fuel issuing out of the furnace are collected in a cyclone and recirculated into the furnace again, thereby improving combustion efficiency.

Fluidized-bed reactors (FBR) are the most popular reactor configurations employed for reactions involving solid reactants. In the FBR, a fluidization medium (gas or liquid) is passed through the bed of solid reactants at high enough velocities to suspend the solid and cause it to behave like a fluid.

4. How is the temperature maintained in a bubbling fluidized bed? Explanation: A bubbling fluidized bed gasifier applies inlet from the bottom and moves the bed of fine-grained materials. The temperature is maintained by manipulating the ratio of biomass and gasification agent.

1.3 Bubbling fluidized-bed gasifier. This type of gasifier is characterized by the bubbling of bed material and solid fuel by flowing gas through it when the gas velocity is sufficiently high.

Fluidized bed incinerators are used both the industrial and sewage sludge incineration processes. The principle of fluidization is the process where a granular material in a solid state is turned into a fluid-like state by passing a fluid (liquid or gas) through it.

Fluidized bed boilers are used in pulp and paper mills and sawmills to produce high pressure steam and electric power, particularly in Europe and North America.

Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels. In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.)

As air flow is increased above the minimum fluidization velocity, the bed may exhibit behaviors ranging from smooth fluidization to bubbling fluidization to dilute fluidization in which powder can be transported by the air stream. Smooth fluidization is desirable for optimal performance in the powder coating process.

The bed is composed primarily of a refractory and incombustible material, often sand, to which coal particles are added via feeders located above or to the side of the bed. In a typical BFB, only 5% or less of the bed is coal while the remainder is the inert bed material.

Bubbling fluidized beds are composed by a grid air-distribution at the bottom of the reactor to allow a good uniformity of the oxidant agent in the biomass particles avoiding thermal gradients along the radius of the reactor. The pyrolysis of biomass starts in the bed reactor thanks to the high thermal exchange with the oxidant agent.

In a typical BFB, only 5% or less of the bed is coal while the remainder is the inert bed material. In order to keep the bed in a liquidized state, high-pressure air (the primary combustion air) is introduced through the bottom of the bed and there may also be further air inlets in the sides of the chamber providing secondary combustion air.