Fluidized Bed Boilers

Fluidized Bed Boilers

Clean Combustion * Coal to Natural Gas * Emissions Abatement  * Fuel Switching * Selective Catalytic Reduction


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Fluidized Bed Boilers

What are Fluidized Bed Boilers?

Fluidized Bed Boiler 



In a fluidized bed boiler, upward blowing jets of air suspend burning coal (or biomass) allowing it to mix with limestone that absorbs the sulfur pollutants.

In the typical, older coal-fired boilers, coal is crushed into very fine particles (called pulverized coal) which is then blown into the boiler, and ignited.  Other types of coal-fired boilers locate the burning coal on grates.

In a "fluidized bed boiler," crushed coal particles "float" inside the boiler with the coal being  "suspended" on upward-blowing jets of air. The red-hot mass of "floating" coal is referred to as the "bed." The floating coal on its bed, bubbles and tumbles around like the boiling lava inside a volcano. Scientists call this process and the floating coal as being "fluidized." This is how the term, "fluidized bed boiler" came about.

Why does a "fluidized bed boiler" burn coal cleaner?

First of all, a fluidized bed boiler burns coal cleaner due to the "tumbling" action which allows limestone to be mixed in with the coal.  

Limestone acts as a sulfur "sponge" in that the sulfur absorbs sulfur pollutants. As the coal burns in a fluidized bed boiler, it releases sulfur. And just as rapidly, the limestone tumbling around beside the coal captures the sulfur. A chemical reaction occurs, and the sulfur gases are changed into a dry powder that can be removed from the boiler. (This dry powder called calcium sulfate can be processed into the wallboard we use for building walls inside our houses.)

The second reason a fluidized bed boiler burns cleaner than other types of boilers is that a fluidized bed boiler burns "cooler" at about 1,400 degrees F.  The older coal-fired boilers that fluidized bed boilers are now replacing operate at temperatures nearly over twice that - at 3,000 degrees F.! 

Nitrogen Oxides (NOx) form when a fuel burns hot enough to break apart the nitrogen molecules in the air which causes nitrogen atoms to join with oxygen atoms.  However, 1,400 degrees isn't hot enough for this to happen, so very little NOx forms in a fluidized bed boiler.

The result is that a fluidized bed boiler can burn very dirty coal and remove 90% or more of the sulfur and nitrogen pollutants while the coal is burning.  Fluidized bed boilers can also burn just about anything else wood, ground-up railroad ties, and nearly every type of biomass or biomass feedstock.

Fluidized bed boilers are operating or being built that are 10 to 20 times larger than the small unit built almost 20 years ago at Georgetown University. There are more than 300 of these boilers around this country and the world. The Clean Coal Technology Program helped test these boilers in Colorado, in Ohio and most recently, in Florida.

A new type of fluidized bed boiler makes a major improvement in the basic system. It encases the entire boiler inside a large pressure vessel, much like the pressure cooker used in homes for canning fruits and vegetables except the ones used in power plants are the size of a small house!

Burning coal in a fluidized bed boiler produces a high-pressure stream of combustion gases that can spin a gas turbine to make electricity, then boil water for a steam turbine two sources of electricity from the same fuel!

Fluidized bed boilers are more efficient in generating power from coal.  In fact, future boilers using this system will be able to generate 50% more electricity from coal than a regular power plant from the same amount of coal. That's like getting 3 units of power when you used to get only 2.

Because it uses less fuel to produce the same amount of power, a more efficient "pressurized fluidized bed boiler" will reduce the amount of carbon dioxide emissions (one of the six greenhouse gas emissions needing to be reduced) released from coal fired power plants.

"Fluidized bed boilers" are one of the newest ways to burn coal cleanly. But there is another new way that doesn't actually burn the coal at all. 


Fluidized Bed Boilers

Clean Combustion * Coal to Natural Gas * Emissions Abatement  * Fuel Switching * Selective Catalytic Reduction








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Fluidized Bed Boilers




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