Wednesday, 15 August 2012

Fluidized-bed combustion Technology


Fluidized-bed combustion Technology

Fluidized-bed combustion technologies have some inherent environmental benefits over conventional PF type plants:

• Combustion temperatures are generally lower than those found in typical PF plant. In this regard, lower NOx emissions are achievable without the need for special combustion systems.
• The need for expensive flue gas desulphurization equipment can be avoided by injecting sorbent (e.g. limestone) directly into the fluidised bed boiler. This has the added benefit of fuel flexibility to burn coals with a wide range of sulphur content.

Primarily two types of fluidized bed combustors are in use;

• circulating fluidized-bed combustion (CFB) plant; and

• bubbling fluidized-bed combustion (BFB) plant.

The third pressurised (bubbling or circulating) fluidizedbed combustors (PFBCs) have been excluded from further consideration. Essentially PFBC technology entails passing pressurized hot flue gas through an expander section of a gas turbine before it is then used to raise steam in a conventional boiler. It is our view that a prospective developer would not opt to construct PFBC plant today, or in the near future,

because:

• the higher efficiency of PFBC over CFB does not offset the lower availability caused by the lack of opportunity to carry out online repairs; and
• gas turbine materials have advanced such that the optimum design temperature for the expander inlet is greater than can be achieved by proven hot-gas clean-up in the PFBC plant.

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