Fluidized Bed Combustion

Fluidized bed combustion (FBC) is a combustion technology used in power plants. Fluidized beds suspend solid fuels in upward-blowing jets of air during the combustion process. The result is a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer. FBC technology was adapted to burn petroleum coke and coal mining waste for power generation in the early 1980s in the US. At that time, US regulations first provided special incentives to the use of renewable fuels and waste fuels. FBC technology spread to other parts of the globe to address specific fuel quality problems. The technology has proved well suited to burning fuels that are difficult to ignite, like petroleum coke and anthracite, low quality fuels like high ash coals and coal mine wastes, and fuels with highly variable heat content, including biomass and mixtures of fuels.

The technology burns fuel at temperatures of 1,400 to 1,700 °F (760 to 930 °C), a range where nitrogen oxide formation is lower than in traditional pulverized coal units. But increasingly strict US regulations have led to the use of ammonia DeNOx systems even on FBCs.

Fluidized-bed combustion evolved from efforts in Germany to control emissions from roasting sulfate ores without the need for external emission controls (such as scrubbers-flue gas desulfurization). The mixing action of the fluidized bed brings the flue gases into contact with a sulfur-absorbing chemical, such as limestone or dolomite. More than 95% of the sulfur pollutants in the fuel can be captured inside the boiler by the sorbent. The sorbent also captures some heavy metals, though not as effectively as do the much cooler wet scrubbers on conventional units.

Commercial FBC units operate at competitive efficiencies, cost less than today's units, and have NO2 and SO2 emissions below levels mandated by Federal standards. FBCs demonstrate different performance characteristics including different locations for erosion on the tubes inside the boiler, uneven temperature distribution if clogs occur in the air inlet of the bed, and long starting times reaching up to 48 hours for problem fuels.

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Oil Shale Industry - Power Generation
... shale as a fuel mostly employ two types of combustion methods ... The traditional method is Pulverized combustion (PC) which is used in the older units of oil shale-fired power plants in Estonia, while the more advanced method is Fluidized bed ... The main FBC technologies are Bubbling fluidized bed combustion (BFBC) and Circulating fluidized bed combustion (CFBC) ...
Fluidized Bed Combustion - Types - PFBC
... also uses a sorbent and jets of air to suspend the mixture of sorbent and burning coal during combustion ... Steam generated from the heat in the fluidized bed is sent to a steam turbine, creating a highly efficient combined cycle system ... The PFBC burns the char to produce steam and to heat combustion air for the gas turbine ...
Overview - Types of Boiler - Fluidized Bed Combustion (FBC) Boiler
... Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits ... The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr ... air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity ...

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