FLUIDISATION BED COMBUSTION (FBC) BOILERS

BY

ISAAC JOHNGUIDE

PROF : XYZ

 

INTRODUCTION

Viable alternative Multiple benefits

compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission

of pollutants SOx and NOx. Fuels

coal, washery rejects, rice husk, bagasse & other agricultural wastes.

Capacity range- 0.5 T/hr to over 100 T/hr.

HISTORY: A NEW WAY TO BURN

0ne afternoon more than a decade ago, a British engineer named Douglas Elliott tapped a bit of coal, ground to crumbs in a kitchen blender, into a tin can mounted on the wall. Below the can was an ordinary small open fireplace – ordinary, that is, at a casual glance.

 

For instead of burning coals, a red- hot bed of sand gently undulated like simmering lava. As the coal trickled out of the can onto the glowing bed below, each crumb exploded into flame with a pop and a blue-white flare. It burned only about two pounds of coal an hour, but the little fireplace glowed fiercely, delivering much more warmth than its size suggested.

 

FLUIDISATION

The operation through which fine solids are transformed into a fluid like state through contact with either a gas or a liquid.

A process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material.

MECHANISM OF FLUIDISED BED COMBUSTION

TYPES OF FLUIDISED BED COMBUSTION BOILERS

There are three basic types of fluidized bed combustion boilers:

1.Atmospheric classic Fluidized Bed Combustion System (AFBC)

2.Atmospheric circulating (fast) Fluidized Bed Combustion system (CFBC)

3.Pressurized Fluidized Bed Combustion System (PFBC)

ATMOSPHERIC FLUIDISED BED COMBUSTION SYSTEM (AFBC)

Crushed coal size 1 – 10 mm Velocity of fluidising air –

1.2 to 3.7 m /sec. Narrow temperature range -

800oC to 850oC. Unit Size-25MWe Thermal Efficiency-30%

GENERAL ARRANGEMENTS OF AFBC BOILERS

AFBC boilers comprise of following systems:

i) Fuel feeding system Under bed pneumatic feeding Over bed feeding

ii) Air Distributoriii) Bed & In-bed heat transfer surfaceiv) Ash handling system

Bottom ash removal Fly ash removal

Many of these are common to all types of FBC boilers

CIRCULATING FLUIDISED BED COMBUSTION SYSTEM (CFBC)

Crushed coal size 6 – 12 mm Velocity of fluidising air –

3.7 to 9 m/sec Solid recycle – 50 to 100 kg per

kg of fuel burnt Unit Size - 250-300MWe Thermal Efficiency-40%

PRESSURISED FLUIDISED BED COMBUSTION SYSTEM (PFBC)

Temperature – 860 C Pressure- 16-18bars Flue gases expanded in

gas turbine Used for cogeneration Unit Size-80MWe Thermal Efficiency-40%

RETROFITTING OF FBC SYSTEMS TO CONVENTIONAL BOILERS

Retrofitting fluidized bed coal fired combustion systems to conventional boilers has been

Carried out successfully both in India and abroad. The important aspects to be considered in retrofit

projects are:a) Water/steam circulation designb) Furnace bottom-grate clearancec) Type of particulate control deviced) Fan capacitye) Availability of space.

COMPARISON BETWEEN STOKER AND FLUIDISED BED COMBUSTION

COMPARISON BETWEEN STOKER AND FLUIDISED BED COMBUSTION 

S.No STROKER FBC

1 TRAVELLING/FIXEDGRATE

 

FLUIDISED BED WITH AIR BOXSYSTEM

 2 BED EVAPORATER IS

NOT APPLICABLE 

BED EVAPORATER WILL BEINTRODUCED

 3 BED SUPER HEATER

IS NOT APPLICABLE 

BED SUPER HEATER SHALLBE INTRODUCED

 4 ONLY OVER BED

FEEDING SYSTEM 

UNDER/OVER BED FEEDINGSYSTEM IS POSSIBLE

 5 BED ASH HOPPER

WITH SUBMERGEBELT CONVEYOR

 

BED ASH DRAIN WITHCOOLER AND PNEUMATIC /MECHANICAL CONVEYING

SYSTEM 6 PRIMARY AIR SYSTEM

NOT APPLICABLE 

PRIMARY AIR SYSTEM ISREQUIRED FOR FUEL

TRANSPORTION IN TO BED 

ADVANTAGES OF FBC BOILERS

1. High Efficiency 2. Reduction in Boiler Size3. Fuel Flexibility4. Ability to Burn Low Grade Fuel5. Ability to Burn Fines6. Pollution Control7. Easier Ash Removal – No Clinker Formation8. No Slagging in the Furnace-No Soot Blowing9. Provisions of Automatic Coal and Ash

Handling System10.High Efficiency of Power Generation

CONCLUSIONS

Decreasing electricity prices and improving environmental protection

Clean energy More flexible than conventional plants Reduced emissions and Improved combustion Research and development is required in order to

improve the FBC technology.

THANK YOU