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

Nonmec Nonmechan hanical ical Contr Control ol of of Solids Solids Flo low w in C in Chemica hemical L l Loop ooping ing Sy Systems stems Ted Knowlton Particulate Solid Research, Inc. NETL 2011 Workshop on Multiphase Flow Science August 16 – 18, 2011 Pittsburgh, PA

Proprietary and Confidential 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 2

Proprietary and Confidential Ch Chem emica ical l Lo Loop oping 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 3

Proprietary and Confidential Ch Chem emica ical l Lo Loop oping 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 4

Proprietary and Confidential Che Chemical mical Lo Loop oping 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 of Understanding About How They Operate  Therefore, Several Basic Principles of Nonmechanical Systems will be Reviewed Before Evaluating Several Different Flow Systems 5

Proprietary and Confidential Nonmec Nonmechanical hanical Solids Solids Flo low De w Devices vices  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” 6

Proprietary and Confidential GELDART'S POWDER CLASSIFICATION (Geldart, D. Powder Technology, 1, 285, 1973) Applies at Ambient Conditions 10,000 5,000 D B 3,000 3 , Kg/m 2,000 1,000 g  A - p  500 C 300 200 100 10 20 50 100 200 500 1,000 2,000 d , Microns p A: Aeratable ( U > U ) Material Has a Significant Deaeration Time (FCC Catalyst) mb mf B: Bubbles Above U ( U = U ) (500-micron Sand) mf mb mf C: Cohesive (Flour, Fly Ash) (Wheat, 2000-micron Polyethylene Pellets) D: Spoutable 7

Proprietary and Confidential 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 8

Proprietary and Confidential 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) 9

Proprietary and Confidential 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 10

Proprietary and Confidential NONMECHA NONMECHANICAL NICAL VALVE VALVE OPERATIO OPERATION  The Most Common Nonmechanical Valve Used to Control Solids Flow is the L-Valve 11

Proprietary and Confidential J-Valve Approximated L-Valve J-Valve The Most Comm mmon No Nonme mechanical Valves 12

Proprietary and Confidential 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 13

Proprietary and Confidential Aeration V solids V gas Solids Flow Through Nonmechanical Valves Because Gas Drags the Solids Around the Constricting Bend 14

Proprietary and Confidential  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. 15

Proprietary and Confidential SOLIDS FLOW RATE, Kg/min Threshold Aeration 3 /min AERATION RATE, m 16

Proprietary and Confidential NONMECHA NONMECHANICAL NICAL VALVE VALVE OPERATIO OPERATION  Where Should Aeration be Added to an L-Valve? 17

Proprietary and Confidential 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 D P  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 18

Proprietary and Confidential 20 Material: Sand (260 microns) 18 Aeration Gas: Nitrogen Solids Flow Rate, Thousands of lb/h Height Above 16 Tap Centerline, in 5 14 24 5 4 18 4 3 12 12 3 2 10 6 2 1 8 0 1 B B 6 4 2 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 L-Valve Aeration Rate, ACFM 19

Proprietary and Confidential Nonmec Nonmechanical hanical Solids Solids Flo low De w Devices vices  Understanding the Operation of Nonmechanical Valves Depends Primarily on Two Things: 1. The Pressure Balance in the System 2. Understanding Packed-Bed Standpipe Operation 20

Proprietary and Confidential Standpipes Standpipes  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 21

Proprietary and Confidential  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 D P Relative Velocity = V r = V s - V g W W   g s V   r   e  e 1 A A p g where: V s & V g are the Interstitial solids and gas velocities, respectively W s & W g 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 D P To Be Generated 22

Proprietary and Confidential P 1 Positive Direction P > P 2 1 is Downward P 2 + Case I Case II Gas Flowing Gas Flowing Upward Downward Relative Relative to Pipe Wall to Pipe Wall V g V g V s V r V s V r V r = V s - V g V r = V s V V r = V s - V - (- ) g g V r = V s + V g 23

Proprietary and Confidential St Standpip andpipes es  The Relationship Between D P/L And V r is Determined By the Fluidization Curve  This Curve is Usually Generated In A Fluidization Column, But It Also Applies In Standpipes 24

Proprietary and Confidential Fluidization Curve - Group B Solids Packed-Bed Fluidized-Bed Region Pressure-Drop-Per-Unit-Length Region (Bubbling) D P/L) mf V mf Relative Velocity 25

Proprietary and Confidential Under derflow ow and and Over Overflow St Standp ndpipes pes OVERFLOW UNDERFLOW 26

Proprietary and Confidential St Standpip andpipes es  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 27

Proprietary and Confidential Oper Operation tion of of F Fluidiz luidized Ov ed Overflo erflow w Standpipe Standpipe P D P UB HEIGHT D P grid H sp D P LB P 2 P P P PRESSURE 1 2 Pressure Profile in Column Pressure Profile in Standpipe P 1 D P UB HEIGHT D P grid H sp D P LB ' P 2 PRESSURE P ' P 1 2 28

Proprietary and Confidential St Standpip andpipes es  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? 29

Proprietary and Confidential HEIGHT P 1 D P grid L P 2 I II D P valve P 1 P 2 P 2 ' PRESSURE Pressure Profile in Column Pressure Profile in Standpipe V V V V s g s g D P/L I V II V r r D P/L 2 D P/L 1 V r V r II I Relative Velocity, V r Underflow Packed-B -Bed Standpipe O Operation 30