cfb boilers

Download CFB Boilers

Post on 20-Jan-2016

136 views

Category:

Documents

15 download

Embed Size (px)

TRANSCRIPT

  • 1CFB Boiler Design, Operation and Maintenance

    By Pichai Chaibamrung

  • 2Content Day11. Introduction to CFB2. Hydrodynamic of CFB3. Combustion in CFB4. Heat Transfer in CFB5. Basic design of CFB6. Operation7. Maintenance8. Basic Boiler Safety9. Basic CFB control

  • 3Objective To understand the typical arrangement in CFB To understand the basic hydrodynamic of CFB To understand the basic combustion in CFB To understand the basic heat transfer in CFB To understand basic design of CFB To understand theory of cyclone separator

    Know Principle Solve Everything

  • 41. Introduction to CFB1.1 Development of CFB 1.2 Typical equipment of CFB1.3 Advantage of CFB

  • 51.1 Development of CFB 1921, Fritz Winkler, Germany, Coal Gasification 1938, Waren Lewis and Edwin Gilliland, USA, Fluid Catalytic Cracking,

    Fast Fluidized Bed 1960, Douglas Elliott, England, Coal Combustion, BFB 1960s, Ahlstrom Group, Finland, First commercial CFB boiler, 15

    MWth, Peat

  • 61.2 Typical Component of CFB Boiler

  • 71.2 Typical Component of CFB BoilerWind box and grid nozzle

    primary air is fed into wind box. Air is equally distributed on furnace cross section by passing through the grid nozzle. This will help mixing of air and fuel for completed combustion

  • 81.2 Typical Component of CFB BoilerBottom ash drain

    coarse size of ash that is not take away from furnace by fluidizing air will be drain at bottom ash drain port locating on grid nozzle floor by gravity. bottom ash will be cooled and conveyed to silo by cooling conveyor.

  • 91.2 Typical Component of CFB BoilerHP Blower

    supply high pressure air to fluidize bed material in loop seal so that it can overflow to furnace

    Rotameter

    Supplying of HP blower to loop seal

  • 10

    1.2 Typical Component of CFB BoilerCyclone separator

    located after furnace exit and before convective part.use to provide circulation by trapping coarse particle back to the furnace Fluidized boiler without this would be BFB not CFB

  • 11

    1.2 Typical Component of CFB BoilerEvaporative or Superheat Wing Wall

    located on upper zone of furnaceit can be both of evaporative or SH panellower portion covered by erosion resistant materials

  • 12

    1.2 Typical Component of CFB BoilerFuel Feeding system

    solid fuel is fed into the lower zone of furnace through the screw conveyor cooling with combustion air. Number of feeding port depend on the size of boiler

  • 13

    1.2 Typical Component of CFB BoilerRefractory

    refractory is used to protect the pressure part from serious erosion zone such as lower bed, cyclone separator

  • 14

    1.2 Typical Component of CFB BoilerSolid recycle system (Loop seal)

    loop seal is located between dip leg of separator and furnace. Its design physical is similar to furnace which have air box and nozzle to distribute air. Distributed air from HP blower initiate fluidization. Solid behave like a fluid then over flow back to the furnace.

  • 15

    1.2 Typical Component of CFB BoilerKick out

    kick out is referred to interface zone between the end of lower zone refractory and water tube. It is design to protect the erosion by by-passing the interface from falling down bed materials

  • 16

    1.2 Typical Component of CFB BoilerLime stone and sand system

    lime stone is pneumatically feed or gravitational feed into the furnace slightly above fuel feed port. the objective is to reduce SOx emission. Sand is normally fed by gravitation from silo in order to maintain bed pressure. Its flow control by speed of rotary screw.

  • 17

    1.2 Typical Arrangement of CFB Boiler

  • 18

    1.3 Advantage of CFB Boiler Fuel Flexibility

  • 19

    1.3 Advantage of CFB Boiler High Combustion Efficiency

    - Good solid mixing- Low unburned loss by cyclone, fly ash recirculation- Long combustion zone In situ sulfur removal Low nitrogen oxide emission

  • 20

    2. Hydrodynamic in CFB2.1 Regimes of Fluidization2.2 Fast Fluidized Bed2.3 Hydrodynamic Regimes in CFB2.4 Hydrodynamic Structure of Fast Beds

  • 21

    2.1 Regimes of Fluidization Fluidization is defined as the operation through which fine

    solid are transformed into a fluid like state through contact with a gas or liquid.

  • 22

    2.1 Regimes of Fluidization Particle Classification

  • 23

    2.1 Regimes of Fluidization Particle Classification

  • 24

    2.1 Regimes of Fluidization Comparison of Principal Gas-Solid Contacting Processes

  • 25

    2.1 Regimes of Fluidization Packed Bed

    The pressure drop per unit height of a packed beds of a uniformly size particles is correlated as (Ergun,1952)

    Where U is gas flow rate per unit cross section of the bed called Superficial Gas Velocity

  • 26

    2.1 Regimes of Fluidization Bubbling Fluidization Beds

    Minimum fluidization velocity is velocity where the fluid drag is equal to a particles weight less its buoyancy.

  • 27

    2.1 Regimes of Fluidization Bubbling Fluidization Beds

    For B and D particle, the bubble is started when superficial gas is higher than minimum fluidization velocityBut for group A particle the bubble is started when superficial velocity is higher than minimum bubbling velocity

  • 28

    2.1 Regimes of Fluidization Turbulent Beds

    when the superficial is continually increased through a bubbling fluidization bed, the bed start expanding, then the new regime called turbulent bed is started.

  • 29

    2.1 Regimes of Fluidization

  • 30

    2.1 Regimes of Fluidization Terminal Velocity

    Terminal velocity is the particle velocity when the forces acting on particle is equilibrium

  • 31

    2.1 Regimes of Fluidization Freeboard and Furnace Height

    - considered for design heating-surface area- considered for design furnace height- to minimize unburned carbon in bubbling bed - the freeboard heights should be exceed or

    closed to the transport disengaging heights

  • 32

    2.2 Fast Fluidization Definition

  • 33

    2.2 Fast Fluidization Characteristics of Fast Beds

    - non-uniform suspension of slender particle agglomerates or clusters moving up and down in a dilute- excellent mixing are major characteristic- low feed rate, particles are uniformly dispersed in gas stream- high feed rate, particles enter the wake of the other, fluid drag on the leading particle decrease, fall under the gravity until it drops on to trailing particle

  • 34

    2.3 Hydrodynamic regimes in a CFB

    Lower Furnace below SA: Turbulent or bubbling

    fluidized bed

    Furnace Upper SA: Fast Fluidized Bed

    Cyclone Separator :Swirl Flow

    Return leg and lift leg : Pack bed and Bubbling Bed

    Back Pass:Pneumatic Transport

  • 35

    2.4 Hydrodynamic Structure of Fast Beds Axial Voidage Profile

    Bed Density Profile of 135 MWe CFB Boiler (Zhang et al., 2005)

    Secondary air is fed

  • 36

    2.4 Hydrodynamic Structure of Fast Beds Velocity Profile in Fast Fluidized Bed

  • 37

    2.4 Hydrodynamic Structure of Fast Beds Velocity Profile in Fast Fluidized Bed

  • 38

    2.4 Hydrodynamic Structure of Fast Beds Particle Distribution Profile in Fast Fluidized Bed

  • 39

    2.4 Hydrodynamic Structure of Fast Beds Particle Distribution Profile in Fast Fluidized Bed

  • 40

    2.4 Hydrodynamic Structure of Fast Beds Particle Distribution Profile in Fast Fluidized Bed

    Effect of SA injection on particle distribution by M.Koksal and F.Hamdullahpur (2004). The experimental CFB is pilot scale CFB. There are three orientations of SA injection; radial, tangential, and mixed

  • 41

    2.4 Hydrodynamic Structure of Fast Beds Particle Distribution Profile in Fast Fluidized Bed

    No SA, the suspension density is proportional

    l to solid circulation rate

    With SA 20% of PA, the solid particle is hold up

    when compare to no SA

    Increasing SA to 40%does not significant on

    suspension density aboveSA injection point but the low zone is

    denser than low SA ratio

    Increasing solid circulationrate effect to both

    lower and upper zoneof SA injection pointwhich both zone is

    denser than lowsolid circulation rate

  • 42

    2.4 Hydrodynamic Structure of Fast Beds Effects of Circulation Rate on Voidage Profile

    higher solid recirculation rate

  • 43

    2.4 Hydrodynamic Structure of Fast Beds Effects of Circulation Rate on Voidage Profile

    higher solid recirculation rate

    Pressure drop across the L-valve is proportional to solid recirculation rate

  • 44

    2.4 Hydrodynamic Structure of Fast Beds Effect of Particle Size on Suspension Density Profile

    - Fine particle - - > higher suspension density- Higher suspension density - - > higher heat transfer- Higher suspension density - - > lower bed temperature

  • 45

    2.4 Hydrodynamic Structure of Fast Beds Core-Annulus Model

    - the furnace may be spilt into two zones : core and annulus

    Core - Velocity is above superficial velocity- Solid move upward

    Annulus- Velocity is low to negative- Solids move downward

    core

    annulus

  • 46

    2.4 Hydrodynamic Structure of Fast Beds Core-Annulus Model

    core

    annulus

  • 47

    2.4 Hydrodynamic Structure of Fast Beds Core Annulus Model

    - the up-and-down movement solids in the core and annulus sets up an internal circulation- the uniform bed temperature i

Recommended

View more >