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Presentation on CFBC Boilers

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National Productivity Council, Hyderabad, India
National Productivity Council, Hyderabad, India

The document discusses the key benefits and evolution of circulating fluidized bed combustion (CFBC) boiler technology. It provides details on the design and operation of CFBC boilers, including their furnace design, U-beam particle separator system, convection pass, and improved performance from two-stage particle separation. CFBC boilers offer benefits like high combustion efficiency, fuel flexibility, compact design, low emissions, and reduced maintenance costs compared to earlier boiler technologies.

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1

Presentation on CFBC Boilers

2

Key benefits are fuel flexibility, reduced emission and lower bed temperature.

3

Different Versions  Industrial boilers ore developing with gradual change in their design of different parts and to optimize the thermal efficiency, fuel multiplicity and to sustain with environmental norms, with cost effectiveness for installation operation and maintenance.  In our country early fifties and sixties small multi fuel boilers were used for process industries and high pressure coal based boilers were used for power generation.  With decreasing trend of coal heat value boiler was constantly modified to reach the present status of CFBC boiler from previous version of stationary furnaces type chain grate type, spreader stoker type, PF type, AFBC type and CFBC type. CFBC is a new generation coal fired fluidized bed boiler developed since 1950 has the advantage of high efficiency low Sox and Nox. emission and higher turn down ratio.

4

CFBC BOILER  Assume a container with an air supply plenum at the bottom , A distributer plate that promotes even air flow through the bed and an upper chamber filled with sand. If a small quantity of air flow through the distributer plate in to the bed , If it will pass through the voids of an immobile mass of sand. For low velocity the air does not exert much force on sand and they remain in place. This condition is called fixed bed or static bed. By increasing a flow rate ,the air exert greater force on the sand and thereby reduces the contact force between the sand particle caused by gravity. By increasing the air flow further ,a point is reached where the drag force on particle counter balance the gravity force and sand particle become suspended in up flowing air steam. The point where the bed start to behave as a fluid is called the minimum fluidization condition.

5

CFBC BOILER As the air increased further , the bed become less uniform bubbles of air start to form and the bed becomes violent . At this condition bed is in expanded condition, This is called bubbling fluidized bed and this occurs at atmospheric condition. Hence, It is called as Atmospheric Fluidized Bed. As the velocity of air further increased (around 10 m/sec.) a condition is reached where in whole of bed material is in circulation from furnace to a collection chamber (U beam hopper) and back to furnace. Thus resulting in uniform temperature profile throughout the furnace. Because the whole bed is in continuous circulation internally, This type of boiler is called IR- CFBC. (Internal Re-circulating fluidized bed combustion).

6

CFBC BOILER TECHNOLOGY OFFERS  High combustion efficiency  Compact and economical design.  Higher reliability and availability.  Lower maintenance cost.  Reduced erosion.  Fuel flexibility. Gas Velocities  CFBC - 4 - 6 m/sec.  AFBC - 2 - 3 mtr./sec.  PF - 8 - 10 mtr./sec.

7

IMPROVED PERFORMANCE AT REDUCED COST  CFBC boiler design as – Two stage particle separation system.  First - U beam impact separators.  Second – Mechanical dust collector or multi-cyclone dust collector.

8

DESCRIPTION OF CFBC BOILER  CFBC boilers are compact natural circulation ,Top supported ,Single drum unit. The primary and secondary particle separator is an integral part of boiler / furnace and connected to the particle return system.

9

THE BOILER IS COMPRISED OF-  CFB Furnace  U-Beam (Particle separator)  Particle Return System  Convection pass and back end equipment.

10

Internal Recirculation - Circulating Fluidized Bed Boilers

11

CFBC FURNACE  The CFBC furnace construction is of all welded membrane tube panels. Functionally the furnace is divided into three distinct zone . A -Primary zones B - Secondary zone C - Free board zone

12

PRIMARY ZONE  In the primary zone the fuel,sand,recycled material and 50% to 60% of the air for combustion are introduced.  SECONDARY AND FREE BOARD ZONE  In secondary zone the balance of combustion air is introduced.  Combustion is completed in free board zone

13

CFBC BOILER • The combustion air split correspond to the furnace zones . i.e. Primary , lower secondary and upper secondary air flow zone. lower secondary zone – Burner upper secondary zone – OF (Over Fired) • Primary air effects the actual fluidization of bed material and is supplied through a distributor plate at the bottom of the furnace. lower secondary and upper secondary air are supplied through nozzle located on both the front or rear furnace walls at two separate elevations. • The air distribution patterns in the furnace can be adjusted to provide for the best control of Nox (Nitrous Oxide) formation. • In addition to the enclosure walls , water cooled division walls for the entire height of the furnace provides additional heating surface.

14

U-BEAM  Flue gas and solids leaving the furnace passes through a high temperature primary particle collector where nearly all of the solids are separated from the flue gas. A unique feature of boiler is a particle separator made of labyrinth type array of beam having a shape similar to the letter “U”. The U- beam made from stainless steel alloy. Or fiber material for less weight & cost and less erosion. The collector is designed to remove solids from dense gas–solids mixture .the solids impacting the first two rows of beams fall by gravity back down the rear of the furnace .Solids impacting the remaining beams fall by gravity in two particle collector hopper located directly beneath the array of beams and enters the rear furnace through particle return system especially designed for this application.

15

Hot Cyclone CFBC

16

BOILER CONVECTION PASS  The flue gas leaving the particle separator flows in to the boiler convection pass which includes the superheated and economizer banks . The gas velocity in these tube banks is designed specifically to minimize the erosion . Gases enters the air pre heater and then to the secondary particle separator . Gas leaving air heater enters the ESP and then to the stack through ID Fans.

17

U-Beam separators © 2003 The Babcock & Wilcox Company, all rights reserved U-Beam separators 41 2 3Flue Gas & Solid Flow Flue Gas 1. Sidewall membrane panel 2. U-beam - SS309H/ SS310H/RA253MA 3. Seal baffle 4. Refractory

18

U-Beams

19

Internal Recirculation - Circulating Fluidized Bed Boilers

20

Internal Recirculation Circulating Fluidized Bed Boilers  A simplified approach to improved flexibility and reliability  Design Features  High combustion efficiency  Compact, economical design  Higher reliability and availability  Lower maintenance costs  Reduced erosion  Fuel flexibility  Low emissions

21

Why CFBC Boiler ?  CFBC is a Fuel Flexible Technology  Accepts wide range of fuels  Volatile matter - >15 %  Ash - UP TO 60%  Heating value - > 2150 Kcal/kg  Moisture - < 10%  Use of lower rank fuels reduces fuel costs  Fuel flexibility - minimizes fuel supply uncertainties  Ability to burn low cost and waste fuels

22

Steam Flow Circuit  Riser tubes are used to direct the steam water mixture from the outlet headers of each water circuit to the steam drum.  The water steam mixture in drum is separated by cyclone separators and the primary and secondary scrubber arrangement.  The saturated steam leaves the steam drum and enters primary super heater in let header through supply pipes.Steam passes through the primary super heater coils and exits the outlet header.Then steam enters the attemperator header for desuperheating.  The attemperator uses water from the high pressure feed water heater discharge to control the secondary super heater outlet temperature.  From the attemperator the steam flow to the secondary super heater inlet header and to the counter flow secondary super heater bank. Steam leaves the coils and exits from the secondary super heater outlet header. Steam enters the turbine through main steam stop valve and NRV.

23

Flue Gas Path  CFBC boilers are balanced draft combustors. The pressure balance point is at the top of the furnace, ahead of the front row of U beams, The flue gas flow path through is as follows :  Gas carrying with large quantity of bed solids, flow into the in bed U beams, above hopper U beams hot particle collector. The U beams removes most of the solids entrained in gas. The flue gas leaves the U beams and flows through the secondary super heater zone, primary super heater zone, Economizer, primary & secondary air heaters. At the bottom of the air heaters gas enters secondary particle U beams separators which collects the majorities of the remaining solids entrained in gas.  The cleaned gas then passes through ESP for final gas cleaning and stack through ID fans. One stands by ID fanes is provided. Dampers are provided before and after the ID fans for maintenance of fans. With the exception of the U beam and secondary particle collection system below APH, The flue path is identical to what is found conventional Unit.

24

CFBC BOILER 1st Pass Fuel 2nd Pass SH - 1 U Beam Section SH - 2 Bed Ash 3rd Pass Economizer APH ESP Fans Ash Recycle Particle Transfer Hopper PA air

25

IR-CFBC Boiler Reheat

26

IR-CFBC Advantages  High Upper Furnace Heat Transfer Rate and Precise furnace temperature control Result of high efficiency solids collection and solids recycle control from the MDC (Mechanical Dust Collection)  Extended turndown ratio (no oil/gas) 100% to 20% MCR (Maximum Continuous Rating)  Low auxiliary power requirements Due to Low Flue Gas ΔP and no fluidizing blower

27

IR-CFBC Advantages  Fast shut down / cool down 80%+ of Bed material is drained during cooldown. Can shutdown / cool / enter / re-start within a 24 hour period compared to 2 to 3 times longer for competitor CFB designs.  Low Maintenance Costs Less refractory or hot expansion joints, ‘RDZ’ at lower furnace refractory interface, no fluidized sealing system, low furnace exit velocity, low gas velocity in convective heating surfaces,...

28

The B&W IR-CFBC Two-Staged Solids Separation System  Benefits  High overall solid collection efficiency ~ More than 99.7%  Precise furnace temperature control ~ By controlling solid recycle rate from the secondary collector  Extended turndown ratio without use of auxiliary fuel (oil/gas) ~ 100% to 20% MCR  Low auxiliary power requirements compared to competitor cyclone-based CFB technologies ~ 50-100 mm w.c.

29

Thin Cooled Refractory 75% less refractory in IR- CFB compared to hot cyclone CFB

30

Difference Between CFBC & AFBC  CFBC boiler  Flue gas velocity-3.7 to 4.3 m/sec  Over bed feeding  U beam Technology  No bed coil  UBC-Less than 2%  Efficiency high (88%)  Clinker formation chances low  Tube erosion high as compared to AFBC  Ash recycle (unburned heavy particle) system.  Fuel consumption is less as compared to AFBC  AFBC boiler  Flue gas velocity-1.5 to 2.0 m/sec  Under bed feeding  No U beam  bed coil  UBC-Less than 3 to 4%  Efficiency low (84%)  Clinker formation chances high  Tube erosion low as compared to CFBC  No Ash recycle (unburned heavy particle) system.  Fuel consumption is more as compared to CFBC

31

Conclusion  With the changing environmental condition of Raw material availability cost and sustainability of boilers are still under modification stage with the effort of optimizing their efficiency and reducing troubles.  Presently different versions of boiler are being installed by various venders like IJT Foster Wheeler (USA) design with compact separator model, Thyssen Krupp AG Germany Design for cold cyclone model. CVL with water cooled “hot loop” cyclone. Songhai electric Alstom design for cyclone & V type seal, Greensol Hungzhon, Wuxi etc with steam cooled cyclone. In view of operation troubles all boiler designers’ are on the way to compete each other, with best possible designs and constant innovation to become the leader of the market.

32

Presentation on CFBC Boilers

More Related Content

Presentation on CFBC Boilers

  • 2. Key benefits are fuel flexibility, reduced emission and lower bed temperature.
  • 3. Different Versions  Industrial boilers ore developing with gradual change in their design of different parts and to optimize the thermal efficiency, fuel multiplicity and to sustain with environmental norms, with cost effectiveness for installation operation and maintenance.  In our country early fifties and sixties small multi fuel boilers were used for process industries and high pressure coal based boilers were used for power generation.  With decreasing trend of coal heat value boiler was constantly modified to reach the present status of CFBC boiler from previous version of stationary furnaces type chain grate type, spreader stoker type, PF type, AFBC type and CFBC type. CFBC is a new generation coal fired fluidized bed boiler developed since 1950 has the advantage of high efficiency low Sox and Nox. emission and higher turn down ratio.
  • 4. CFBC BOILER  Assume a container with an air supply plenum at the bottom , A distributer plate that promotes even air flow through the bed and an upper chamber filled with sand. If a small quantity of air flow through the distributer plate in to the bed , If it will pass through the voids of an immobile mass of sand. For low velocity the air does not exert much force on sand and they remain in place. This condition is called fixed bed or static bed. By increasing a flow rate ,the air exert greater force on the sand and thereby reduces the contact force between the sand particle caused by gravity. By increasing the air flow further ,a point is reached where the drag force on particle counter balance the gravity force and sand particle become suspended in up flowing air steam. The point where the bed start to behave as a fluid is called the minimum fluidization condition.
  • 5. CFBC BOILER As the air increased further , the bed become less uniform bubbles of air start to form and the bed becomes violent . At this condition bed is in expanded condition, This is called bubbling fluidized bed and this occurs at atmospheric condition. Hence, It is called as Atmospheric Fluidized Bed. As the velocity of air further increased (around 10 m/sec.) a condition is reached where in whole of bed material is in circulation from furnace to a collection chamber (U beam hopper) and back to furnace. Thus resulting in uniform temperature profile throughout the furnace. Because the whole bed is in continuous circulation internally, This type of boiler is called IR- CFBC. (Internal Re-circulating fluidized bed combustion).
  • 6. CFBC BOILER TECHNOLOGY OFFERS  High combustion efficiency  Compact and economical design.  Higher reliability and availability.  Lower maintenance cost.  Reduced erosion.  Fuel flexibility. Gas Velocities  CFBC - 4 - 6 m/sec.  AFBC - 2 - 3 mtr./sec.  PF - 8 - 10 mtr./sec.
  • 7. IMPROVED PERFORMANCE AT REDUCED COST  CFBC boiler design as – Two stage particle separation system.  First - U beam impact separators.  Second – Mechanical dust collector or multi-cyclone dust collector.
  • 8. DESCRIPTION OF CFBC BOILER  CFBC boilers are compact natural circulation ,Top supported ,Single drum unit. The primary and secondary particle separator is an integral part of boiler / furnace and connected to the particle return system.
  • 9. THE BOILER IS COMPRISED OF-  CFB Furnace  U-Beam (Particle separator)  Particle Return System  Convection pass and back end equipment.
  • 10. Internal Recirculation - Circulating Fluidized Bed Boilers
  • 11. CFBC FURNACE  The CFBC furnace construction is of all welded membrane tube panels. Functionally the furnace is divided into three distinct zone . A -Primary zones B - Secondary zone C - Free board zone
  • 12. PRIMARY ZONE  In the primary zone the fuel,sand,recycled material and 50% to 60% of the air for combustion are introduced.  SECONDARY AND FREE BOARD ZONE  In secondary zone the balance of combustion air is introduced.  Combustion is completed in free board zone
  • 13. CFBC BOILER • The combustion air split correspond to the furnace zones . i.e. Primary , lower secondary and upper secondary air flow zone. lower secondary zone – Burner upper secondary zone – OF (Over Fired) • Primary air effects the actual fluidization of bed material and is supplied through a distributor plate at the bottom of the furnace. lower secondary and upper secondary air are supplied through nozzle located on both the front or rear furnace walls at two separate elevations. • The air distribution patterns in the furnace can be adjusted to provide for the best control of Nox (Nitrous Oxide) formation. • In addition to the enclosure walls , water cooled division walls for the entire height of the furnace provides additional heating surface.
  • 14. U-BEAM  Flue gas and solids leaving the furnace passes through a high temperature primary particle collector where nearly all of the solids are separated from the flue gas. A unique feature of boiler is a particle separator made of labyrinth type array of beam having a shape similar to the letter “U”. The U- beam made from stainless steel alloy. Or fiber material for less weight & cost and less erosion. The collector is designed to remove solids from dense gas–solids mixture .the solids impacting the first two rows of beams fall by gravity back down the rear of the furnace .Solids impacting the remaining beams fall by gravity in two particle collector hopper located directly beneath the array of beams and enters the rear furnace through particle return system especially designed for this application.
  • 16. BOILER CONVECTION PASS  The flue gas leaving the particle separator flows in to the boiler convection pass which includes the superheated and economizer banks . The gas velocity in these tube banks is designed specifically to minimize the erosion . Gases enters the air pre heater and then to the secondary particle separator . Gas leaving air heater enters the ESP and then to the stack through ID Fans.
  • 17. U-Beam separators © 2003 The Babcock & Wilcox Company, all rights reserved U-Beam separators 41 2 3Flue Gas & Solid Flow Flue Gas 1. Sidewall membrane panel 2. U-beam - SS309H/ SS310H/RA253MA 3. Seal baffle 4. Refractory
  • 19. Internal Recirculation - Circulating Fluidized Bed Boilers
  • 20. Internal Recirculation Circulating Fluidized Bed Boilers  A simplified approach to improved flexibility and reliability  Design Features  High combustion efficiency  Compact, economical design  Higher reliability and availability  Lower maintenance costs  Reduced erosion  Fuel flexibility  Low emissions
  • 21. Why CFBC Boiler ?  CFBC is a Fuel Flexible Technology  Accepts wide range of fuels  Volatile matter - >15 %  Ash - UP TO 60%  Heating value - > 2150 Kcal/kg  Moisture - < 10%  Use of lower rank fuels reduces fuel costs  Fuel flexibility - minimizes fuel supply uncertainties  Ability to burn low cost and waste fuels
  • 22. Steam Flow Circuit  Riser tubes are used to direct the steam water mixture from the outlet headers of each water circuit to the steam drum.  The water steam mixture in drum is separated by cyclone separators and the primary and secondary scrubber arrangement.  The saturated steam leaves the steam drum and enters primary super heater in let header through supply pipes.Steam passes through the primary super heater coils and exits the outlet header.Then steam enters the attemperator header for desuperheating.  The attemperator uses water from the high pressure feed water heater discharge to control the secondary super heater outlet temperature.  From the attemperator the steam flow to the secondary super heater inlet header and to the counter flow secondary super heater bank. Steam leaves the coils and exits from the secondary super heater outlet header. Steam enters the turbine through main steam stop valve and NRV.
  • 23. Flue Gas Path  CFBC boilers are balanced draft combustors. The pressure balance point is at the top of the furnace, ahead of the front row of U beams, The flue gas flow path through is as follows :  Gas carrying with large quantity of bed solids, flow into the in bed U beams, above hopper U beams hot particle collector. The U beams removes most of the solids entrained in gas. The flue gas leaves the U beams and flows through the secondary super heater zone, primary super heater zone, Economizer, primary & secondary air heaters. At the bottom of the air heaters gas enters secondary particle U beams separators which collects the majorities of the remaining solids entrained in gas.  The cleaned gas then passes through ESP for final gas cleaning and stack through ID fans. One stands by ID fanes is provided. Dampers are provided before and after the ID fans for maintenance of fans. With the exception of the U beam and secondary particle collection system below APH, The flue path is identical to what is found conventional Unit.
  • 24. CFBC BOILER 1st Pass Fuel 2nd Pass SH - 1 U Beam Section SH - 2 Bed Ash 3rd Pass Economizer APH ESP Fans Ash Recycle Particle Transfer Hopper PA air
  • 26. IR-CFBC Advantages  High Upper Furnace Heat Transfer Rate and Precise furnace temperature control Result of high efficiency solids collection and solids recycle control from the MDC (Mechanical Dust Collection)  Extended turndown ratio (no oil/gas) 100% to 20% MCR (Maximum Continuous Rating)  Low auxiliary power requirements Due to Low Flue Gas ΔP and no fluidizing blower
  • 27. IR-CFBC Advantages  Fast shut down / cool down 80%+ of Bed material is drained during cooldown. Can shutdown / cool / enter / re-start within a 24 hour period compared to 2 to 3 times longer for competitor CFB designs.  Low Maintenance Costs Less refractory or hot expansion joints, ‘RDZ’ at lower furnace refractory interface, no fluidized sealing system, low furnace exit velocity, low gas velocity in convective heating surfaces,...
  • 28. The B&W IR-CFBC Two-Staged Solids Separation System  Benefits  High overall solid collection efficiency ~ More than 99.7%  Precise furnace temperature control ~ By controlling solid recycle rate from the secondary collector  Extended turndown ratio without use of auxiliary fuel (oil/gas) ~ 100% to 20% MCR  Low auxiliary power requirements compared to competitor cyclone-based CFB technologies ~ 50-100 mm w.c.
  • 29. Thin Cooled Refractory 75% less refractory in IR- CFB compared to hot cyclone CFB
  • 30. Difference Between CFBC & AFBC  CFBC boiler  Flue gas velocity-3.7 to 4.3 m/sec  Over bed feeding  U beam Technology  No bed coil  UBC-Less than 2%  Efficiency high (88%)  Clinker formation chances low  Tube erosion high as compared to AFBC  Ash recycle (unburned heavy particle) system.  Fuel consumption is less as compared to AFBC  AFBC boiler  Flue gas velocity-1.5 to 2.0 m/sec  Under bed feeding  No U beam  bed coil  UBC-Less than 3 to 4%  Efficiency low (84%)  Clinker formation chances high  Tube erosion low as compared to CFBC  No Ash recycle (unburned heavy particle) system.  Fuel consumption is more as compared to CFBC
  • 31. Conclusion  With the changing environmental condition of Raw material availability cost and sustainability of boilers are still under modification stage with the effort of optimizing their efficiency and reducing troubles.  Presently different versions of boiler are being installed by various venders like IJT Foster Wheeler (USA) design with compact separator model, Thyssen Krupp AG Germany Design for cold cyclone model. CVL with water cooled “hot loop” cyclone. Songhai electric Alstom design for cyclone & V type seal, Greensol Hungzhon, Wuxi etc with steam cooled cyclone. In view of operation troubles all boiler designers’ are on the way to compete each other, with best possible designs and constant innovation to become the leader of the market.