Nonmec Nonmechan hanical ical Contr Control ol of of Solids - - PowerPoint PPT Presentation

Nonmec Nonmechan hanical ical Contr Control

• l of
• f Solids

Solids Flo low w in C in Chemica hemical L l Loop

• oping

ing Sy Systems stems

Ted Knowlton Particulate Solid Research, Inc. NETL 2011 Workshop on Multiphase Flow Science

August 16 – 18, 2011 Pittsburgh, PA

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Chemical Chemical Loop Looping ing Syste Systems ms  There are Many Different Types of Chemical Looping

Systems That are Being Developed or Proposed

 All Involve Substantial Flows of Solids Around the

System

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Ch Chem emica ical l Lo Loop

• ping

ing Sy Syst stem ems  Typically, the Temperatures Involved in Chemical

Looping Systems are too High to Easily Use Mechanical Valves for Control

 Therefore, Nonmechanical Means are Being Employed

to Control the Solids Flow Rates Around the Systems

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Ch Chem emica ical l Lo Loop

• ping

ing Sy Syst stem ems  How Are the Solids Being Controlled in These

Systems Using Nonmechanical Means?

 This Depends on the Type of Flow System Used as

Well as the Particle Size Used in the System

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Che Chemical mical Lo Loop

• ping

ing Sys Syste tems ms  To Evaluate the Different Nonmechanical Techniques

it is Necessary to Understand the Principles Behind Nonmechanical Systems – but Often There is a Lack

• f Understanding About How They Operate

 Therefore, Several Basic Principles of Nonmechanical

Systems will be Reviewed Before Evaluating Several Different Flow Systems

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

Nonmechanical Solids Flow Devices Fall Into Two Categories:

• 1. Solids Flow Control Devices (Valves)

Example: L-Valve

• 2. Solids Flow-Through Devices Which

DO NOT CONTROL Solids Flow (They Automatically Pass Solids Through Them) Examples: Loop Seal Automatic “L-Valve”

Nonmec Nonmechanical hanical Solids Solids Flo low De w Devices vices

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10 20 50 100 200 500 1,000 2,000 100 200 300 500 1,000 2,000 3,000 5,000 10,000

d , Microns , Kg/m

GELDART'S POWDER CLASSIFICATION

A B C D

A: Aeratable ( U > U ) B: Bubbles Above U ( U = U ) C: Cohesive D: Spoutable

mb mf mb mf

 

3 p p g

• Material Has a Significant Deaeration Time

Applies at Ambient Conditions (Geldart, D. Powder Technology, 1, 285, 1973) (FCC Catalyst) (500-micron Sand) (Flour, Fly Ash) (Wheat, 2000-micron Polyethylene Pellets)

mf

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Non Nonmec mecha hanica nical l Solids Solids Flow Dev Flow Devices ices  Nonmechanical Valves Used for Control Require

Particle Sizes Greater Than About 100 Microns (Group B or D Materials)

 Nonmechanical Devices in Automatic (Non-Control)

Operation Can be Used With Group A as Well as With Groups B and D

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Non Nonmec mecha hanica nical l Solids Solids Flow Dev Flow Devices ices  Why do Nonmechanical Valves Not Work Well With

Group A Materials?

 This is Because Group A Materials Do Not Defluidize

Instantaneously When Gas is Shut Off to a Fluidized Bed, and They Retain Their Fluidity for a Few Seconds

 Thus, When Group A Solids are Poured Into a

Nonmechanical Valve, the Solids Retain Their Fluidity and Flow Through the Valve Like Water (Uncontrollably)

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NONMEC NONMECHANICAL HANICAL VAL VALVES VES USED USED FOR FOR SOL SOLIDS IDS FL FLOW OW CONTR CONTROL OL



Nonmechanical Valves are Devices That Use Only Aeration Gas in Conjunction With Their Geometrical Shape to Control the Flow Rate of Solids Through Them

• 1. Have no Moving Parts (Other than the Solids)
• 2. Are Very Inexpensive
• 3. Can Feed Solids Into a Dense-Phase or Dilute-Phase

Environment

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NONMECHA NONMECHANICAL NICAL VALVE VALVE OPERATIO OPERATION 

The Most Common Nonmechanical Valve Used to Control Solids Flow is the L-Valve

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The Most Comm mmon No Nonme mechanical Valves

L-Valve J-Valve Approximated J-Valve

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NONMECHA NONMECHANICAL NICAL VALVE VALVE OPERATIO OPERATION 

Solids Flow Rate Through a Nonmechanical Valve is Controlled By the Amount of Aeration Gas That is Added to It

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Solids Flow Through Nonmechanical Valves Because Gas Drags the Solids Around the Constricting Bend

V V

gas solids

Aeration

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 When Aeration Gas is Added to a Nonmechanical

Valve, Solids Do Not Begin to Flow Immediately. There is a Certain Threshold Amount of Aeration Which Must Be Added Before Solids Begin to Flow.

 Solids Flow Through a Nonmechanical Valve

Because of Drag Forces on the Particles Produced By the Aerating Gas.

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AERATION RATE, m

3/min

SOLIDS FLOW RATE, Kg/min Threshold Aeration

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NONMECHA NONMECHANICAL NICAL VALVE VALVE OPERATIO OPERATION 

Where Should Aeration be Added to an L-Valve?

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AER AERATION ATION TAP TAP LOC LOCATION ATION

 Add Aeration to a Nonmechanical Valve as Low in the Standpipe as Possible, But Above the Bend

• 1. Will Give Maximum Standpipe Length
• 2. Minimum Nonmechanical Valve DP

 Both Factors Result in Increasing the Maximum Solids Flow Rate Through the Valve  If Aeration is Added at too Low a Point, However, (especially in an L-valve) Gas Bypassing Results and Solids Flow Control is Not Effective

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0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 4 6 8 10 12 14 16 18 20

L-Valve Aeration Rate, ACFM Solids Flow Rate, Thousands of lb/h

Material: Sand (260 microns) Aeration Gas: Nitrogen B 1 2 3 4 5 Tap Height Above Centerline, in 1 2 3 4 5 24 18 12 6 B

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

Understanding the Operation of Nonmechanical Valves Depends Primarily on Two Things:

• 1. The Pressure Balance in the System
• 2. Understanding Packed-Bed Standpipe

Operation

Nonmec Nonmechanical hanical Solids Solids Flo low De w Devices vices

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 A Standpipe is a Length of Pipe Through Which

Solids Flow by Gravity

 The Primary Purpose of a Standpipe is to Transfer

Solids From a Low Pressure Region to a Higher Pressure Region

Standpipes Standpipes

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 Solids Can Be Transferred From Low to High Pressure in a

Standpipe if Gas Flows Upward Relative To The Solids Thus Generating The Required Sealing DP Relative Velocity = Vr = Vs - Vg

where: Vs & Vg are the Interstitial solids and gas velocities, respectively

Ws & Wg are the mass flows of solids and gas, respectively p and g are the particle and gas densities, respectively e is the solids voidage, and A is the pipe area

 Gas Flowing Upward Relative To The Solids Causes A

Frictional DP To Be Generated

 

A W A 1 W V

g g p s r

e   e   

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P > Case I Case II Gas Flowing Upward to Pipe Wall Gas Flowing Relative to Pipe Wall V V V

g s r

2

Downward Relative Vs Vr V

g

P1 P

1

P

2

Vr = Vs - V

g

Vr = Vs

• V

g

Vr = Vs - V

g

(- ) Vr = Vs + V

g

+

Positive Direction is Downward

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 The Relationship Between DP/L And Vr is Determined

By the Fluidization Curve

 This Curve is Usually Generated In A Fluidization

Column, But It Also Applies In Standpipes

St Standpip andpipes es

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Relative Velocity Pressure-Drop-Per-Unit-Length

P/L)mf

Packed-Bed Region Fluidized-Bed Region (Bubbling)

Vmf D

Fluidization Curve - Group B Solids

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OVERFLOW UNDERFLOW

Under derflow

• w and

and Over Overflow St Standp ndpipes pes

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 Many Standpipes are Fluidized Overflow Standpipes  Operation of These Standpipes is Easy to Understand,

and Non-Control Nonmechanical Devices (Loop Seals, Seal Pots, etc.) Operate with This Type of Standpipe Above Them

St Standpip andpipes es

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DPLB DPUB Hsp D P

grid

P

1

P

2

DPLB DPUB Hsp D P

grid

P

1

P

2

PRESSURE HEIGHT PRESSURE HEIGHT Pressure Profile in Column Pressure Profile in Standpipe

P P P

2

' P'

2

P

1

Oper Operation tion of

• f F

Fluidiz luidized Ov ed Overflo erflow w Standpipe Standpipe

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 However, Nonmechanical Valves (Used to Control the

Solids Flow Rate) MUST Operate With a Packed Bed Underflow Standpipe Above Them

 How Does This Type of Standpipe Operate?

St Standpip andpipes es

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DP

grid HEIGHT PRESSURE

Pressure Profile in Column Pressure Profile in Standpipe

DP/L

Relative Velocity, Vr

DPvalve

Vr Vr

D P/L 2 DP/L 1

Underflow Packed-B

• Bed Standpipe O

Operation

L

P1 P2 P1 P2 P2'

I II

II I

V V V V V V

r r s s g g

II I

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 Gas Can Flow Either Upward or Downward (Relative

to the Pipe Wall) in the Packed Flow Standpipe Above the L-Valve

 The Direction of This Flow Depends on Particle Size

and the DP/L in the Standpipe Above the Valve

Nonmec Nonmechanical hanical Valv alves es for

• r

Solids Solids Flo low Contr w Control

• l

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QT Qext Qsp QT Qsp QT = Qext Qext + Qsp QT = Qext - Qsp Occurs With Small Particle Sizes and/or At High Solids Flow Rates Occurs With Large Particle Sizes and/or At Low Solids Flow Rates Most Common Situation

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 Nonmechanical Valve Operation Also Depends on the

Pressure Balance Around the System

 Not Designing the Pressure Balance Correctly can

Limit Nonmechanical Valve Operation by Affecting the Solids Flow Rate

Nonmec Nonmechanical hanical Valv alves es for

• r

Solids Solids Flo low Contr w Control

• l

Proprietary and Confidential 34 DP

Hopper

Aeration Gas Outlet DP

Standpipe

DPL-Valve DP

Bed

DPPiping DP

Standpipe

+ D PHopper = DP

Bed

+ DPPiping + DPL-Valve

L-Valve System Pressure Balance

DP

Standpipe =

K + DPL-Valve K

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DP/L)mf

V V

r mf

DP/L

Maximum DP/L in Standpipe is:

DP/L)mf

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 There is a Maximum DP/L That the Packed-Bed

Standpipe Can Develop -- (DP/L)mf

 If Increase Solids Flow Rate, L-Valve ΔP

Increases and Standpipe ΔP Increases Until DP/L Reaches (DP/L)mf

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 A Short Standpipe Will Reach Its Maximum DP/L At a

Lower Solids Flow Rate Than a Longer Standpipe

 Therefore, the Maximum Solids Flow Rate Through an

L-Valve Depends on the Length of the Standpipe Above it

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After is Reached, More Aeration Produces Bubbles in the Standpipe, Which Hinder Solids Flow

D P/L)mf

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 Pressure Balance is Critical in Designing a System Containing a Nonmechanical Valve: 1. If the Pressure Balance is Not Correct, the Valve Will Not Operate Correctly

• 2. Example on Next Slide Shows Actual Case of

Someone Designing an L-Valve That Could Have, But Did Not Work

Pressure Balance is Critical

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DPfb + DPsp = DPL-valve + DPriser If DPfb < DPL-valve + DPriser Then Relative Velocity as in 1 Occurs If DPfb > DPL-valve + DPriser Then Relative Velocity as in 2 Occurs

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Combustor Gas Out Cyclone Feed Vessel Conveying Steam

FEEDING A DRYER WITH AN L-VALVE

L-Valve Dilute-Phase Dryer Hot Bed Sand

(FORTUM)

Aeration

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The L-Valve Can be Designed to Prevent System Gas from Exiting the Reactor

V V

g s

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It is also Possible to Prevent Aeration Gas from Entering the Reactor

V V

g s

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NON NON-CONTROL CONTROL (AUTOMAT (AUTOMATIC) IC) NONMEC NONMECHANICAL HANICAL SOL SOLIDS IDS FL FLOW OW DE DEVICE VICES

 Provide a Pressure Seal (In Conjunction

With a Standpipe)

 Operate With an Overflow Fluidized Bed

Standpipe Above Them

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AUTOMA AUTOMATIC TIC NONMEC NONMECHANIC ANICAL AL SOL SOLIDS IDS FL FLOW OW DEV DEVICES ICES

 Do Not Control Solids Flow  Automatically Adjust to Changes in the Solids Flow Rate

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 One of the Most Frequent Applications of

Automatic Nonmechanical Devices is in CFB Systems Where a Loop Seal is Used to Recycle Collected Solids from the Cyclone Back to the CFB

Proprietary and Confidential 47 Secondary Air Air In Cyclone Bed Discharge Primary Air To Superheater Coal-Limestone Feed

Circ rculati ting Fluidized Bed Combustor

Loop Seal Standpipe Riser Dilute Phase Dense Phase

(Foster-Wheeler Type)

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Seal Pot Loop Seal

Fluidizing Gas Fluidizing Gas

Proprietary and Confidential 49 Aeration Dipleg Gas Out External Cyclone L-Valve Fluidizing Gas Fluidized Bed

Solids Out

Proprietary and Confidential 50 W W W Solids Flow Rate W Q H 1

1 A

W > W1

2

W < W

1 3

H 2 Q A Q A H 3 Seal Height

1 2 3

H 1 H 2 H 3

A B C

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Che Chemical mical Lo Loop

• ping

ing Sys Syste tems ms  In the Following Slides, Several Different Types of

Proposed Solids Flow Systems for Chemical Looping are Shown

 The Techniques Used to Control the Solids Flow Rate

Around Each of the Systems Are Different

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CON CONTR TROL OL OF OF NON NONMEC MECHANICAL HANICAL SYS SYSTEMS TEMS

 There are Four Ways to Control the Solids Flow Rate in Nonmechanical Systems: 1. Using a Nonmechanical L-Valve Below a Packed Bed Standpipe 2. Operating the Riser at the Choking Velocity to Control the Solids Flow Rate 3. Using Inventory Control to Change the Level in an Overflow Fluidized Bed Standpipe 4. A Combination of Methods 2 and 3

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Aeration Aeration L-Valve L-Valve Riser 2 Gas Riser 1 Gas Fluid Bed 2 Loop Seal Loop Seal Fluid Bed 1 Cyclone Cyclone

L-Valve Control System

Yazdanpanah et. al., CFB-10 Proc., May 2-5, 2011

dp = 320 microns

Advantage(s): 1. Good Solids Flow Control 2. Do Not Need to Change Inventory for Control Disadvantage(s): 1. Works With B/D Geldart Groups Only Conclusion: Good, Solid Design

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Inventory Control System

Shimizu et. al., CFB-10 Proc., May 2-5, 2011

dp = 150 microns

DPsealpot + DPriser + DPcy = DPSP = HSP*SP

If the Solids Flow Rate Increases, the Pressure Drop Across the Riser Will Increase (if the Gas Velocity in the riser is constant). Therefore, the Solids Level in the Standpipe Must Increase. But, It Cannot Increase for a Constant Inventory in the System. Therefore, Solids MUST be added to the System to Allow the Increased Solids Flow Rate.

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Inventory Control System

Shimizu et. al., CFB-10 Proc., May 2-5, 2011

dp = 150 microns

Advantage(s): 1. Can be Used With Group A Particles Disadvantage(s): 1. At High P Will be Hard to Add and Remove Solids 2. Solids Flow Rate Change Not “Immediate” Conclusion: More Complex and Less Responsive System

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Inventory + Riser Control System

Guio-Perez et. al., CFB-10 Proc., May 2-5, 2011

Loop Seal 3 Loop Seal 1 Cyclone 2 Cyclone 1 Aeration Control Air Riser Loop Seal 2 Aeration Aeration Fuel Air

dp = 161 microns

Advantage(s): 1. Can be Used With Group A Particles Disadvantage(s): 1. At High P Will be Hard to Add and Remove Solids 2. Solids Flow Rate Change Not “Immediate” Conclusion: More Complex and Less Responsive System

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Superficial Gas Velocity, U Riser Pressure Drop Per Unit Length

G = G

1 2

U For Curve 1

ch

2

G = G1

3

G = G

3

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L-Valve Control

The Ohio State University, L.S. Fan and Colleagues

Advantage(s): 1. Good Solids Flow Control 2. Do Not Need to Change Inventory for Control Disadvantage(s): 1. Cannot be Used With Group A Solids Conclusion: Good, Solid Design

Large Group B and Group D Particles

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Riser Control

Chalmers Univ. of Tech.,

• A. Lyngfeldt, 1st Intl Conf
• n Chem Looping, Lyon

March 17-19, 2010

Advantage(s): 1. Can be Used With Group A Particles Disadvantage(s): 1. At High P Will be Hard to Add and Remove Solids 2. Solids Flow Rate Change Not “Immediate” Conclusion: Less Responsive System

Varied

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Thank You! Questions?