What are the types of CFBC Boiler

 CFBC technology:

 

Coal was the main fuel in power plant and cost of coal was very cheap before 80s in India. I have seen the power plant used the coal of GCV 4000kcal/kg to 5000kcal/kg. But gradually as the industries grow up,  the demand for various grades of coal are increased and cost of generation is becoming the predominant factor. Secondly the supply of high grade coal also comes down due to depletion of coal in mines. So need of the usage of lower grade of coal arises, First AFBC technology and later on CFBC technology of Boiler are developed to use the lower grade of coal  from 2200Kcal//kg to 3000Kcal//Kg of GCV. What are the other benefits of CFBC technology?

1.       High combustion efficiency: as high as 98%

2.       Wide range of fuel can be used: lower grade of fuel i.e sponge iron kiln reject (dolochar )GCV as low as 1000 kcal/kg can be used with mixing with higher grade of coal , coal mill reject from PF fired plant, lignite, RDF, Biomass, wood chips etc.

3.       High moisture content in fuel:  around 20%

4.       High percentage of fines(-1mm) in fuel can be used:  around 50%

5.       Low un burnt in ash : around 2%

6.       High thermal efficiency:  around 87%

7.       Lower SOx and NOx emission

As per manufacturer different types of Boiler are available:

1.       Hot Cyclone:   The flue gas temperature at the cyclone separator is more than 800Deg.C, this is three pass boiler.  Develped by GE Alstom , Lurgi  (Doosan Lentjes) Supplier- BHEL:  GE Alstom, Wixy- Donfang Chinese supplier

2.       Cold Cyclone: The flue gas temperature at the cyclone is around 400 Deg.C, Developed by  Circo fluid SG Supplier: M/S ThyssenKrupp

3.       Compact Separator Cyclone:  The cyclone is steam cooled and the part of the pressure parts  , developed by Foster Wheeler. Supplier: IJT

4.       U-beam Technology: Higher size of particles are separated by U-beam, developed by Babcock Wilcox , Supplier : Thermax

5.       Recent interest:  Scale up, Oxy-fuel  oxygen rich, calcium chemical looping CO2 capture

Hot Cyclone

Cold Cyclone

Compact Separator

U- Beam 

Difference in Cold Cyclone and Hot Cyclone

Sl No	Description	Cold Cyclone	Hot Cyclone
1	Boiler Design	Tower Type	Two pass
2	First Pass	Mostly heating surface	Mostly heating surface in second pass
3	Total Heating Surface	Lower	Higher
4	Fluidising velocity	3.5- 4.5m/s	4.5 to 7 m/s
5	Auxiliary Power	16 kw//mwh	26kw//mwh
6	Cyclone Temperature	400-450 deg.C	850-900 deg.C
7	Cyclone size	Smaller	Larger
8	Cyclone Refractory	50mm castable	600mm refractory bricks and castable
9	Total Refractory	Smaller	Higher by 4-5times

 

Working Principle:

Bed material i.e sand or crushed refractory (<3mm) are used in furnace , Primary Air is supplied  by PA fan to fluidise the bed , to help in combustion, sealing air to feeders, convey the coal to furnace. Pr is around 1100-1400mmwc

Secondary Air  is supplied though SA Fans to provide excess air in different levels of furnace to create turbulence , control overboard temperature, and air for oil  burner . Pr is maintained around 560 to 700mmwc.

Wall Seal Blower:  Supply air to loop seal with pr of 5000-6000mmwc to maintain the fluidization .

ID Fan: Maintain the draft in the furnace.

Start up Burner or Hot gas generator is used for start up of the boiler.