Analysis of Low Velocity Dense Phase Pneumatic Conveying System to Extend System Conveying Capability Dr Kenneth Williams Research and Development Manager TUNRA Bulk Solids in association with The Centre for Bulk Solids & Particulate Technologies The University of Newcastle
CONTENTS 3 1. Introduction to dense phase pneumatic conveying 2. Flyash Pneumatic Conveying Systems Standard pipe Bypass Pipe 3. Onsite System Analysis and Improvement 4. Conclusions
Decreasing air mass flow rate DP (Pa) MODES OF PNEUMATIC CONVEYING Direction of material flow Dilute phase flow Moving bed Fluidised dense phase Dune flow Dilute phase flow 5 Lines of constant m s Fluidised dense phase 4 Direction of material flow Dilute phase flow 3 No Flow Pressure Minimum Curve Further optimisation Fluidised dense phase 2 Design Point Direction of material flow 1 0 Fluidised dense phase flow Dilute Phase Under Performance -1 0 5 10 15 m a 20 (kg/s) 25 30 35 40
Bypass Pneumatic Conveying System 6 (b) bypass pipe (a) schematic diagram (c) pressure transducer taps arrangement
Test material 7 Material d p, μm ρ p, kg/m 3 ρ b, kg/m 3 P f, 10-7 m 2 /(Pa s) v mf, mm/s Fly ash 14.65 2093 775 6.55 84.7
High speed camera visualization 8 (a) bypass flutes position (b) moving bed (c) Dune Dune Swirl
Specific energy 9
Specific energy for fly ash 10
Specific energy for fly ash 11
Case Study Ash Disposal - Positive pressure blow tank system System Performance Is it achieving design capacity Is there opportunity to improve capacity using existing system components Analyse existing system: Explore optimisation of conveying cycle Investigate opportunities to increase capacity through: Air supply management Feeding techniques Systematically Implement improvement opportunities
Case Study: Improvement to existing flyash system
Power Station Details Built 1957 4 x 30MW units 1976 upgrade to 2 x 500 MW units Ash Handling System: ESP Collection Positive Pressure Blow-tanks 8 x 1m 3 500 m conveying length 5 (250 mm) 6 (300mm) diameter pipe
Case Study: Improvement to existing flyash system
Pipeline components Straights and bends
Discharge
Final delivery
pressure [kpa] Analysis of current system: Conveying cycle pressure 450 Pressure number Length from start of Location from bend (m) pipeline (m) T1 1.0 1.0 m after blowtank T2 4.4 3.4 m after blowtank T3 7.4 1 m before LR bend T4 11.6 middle of LR bend T5 13.6 1 m after LR bend T6 68.6 1 m before T bend T7 70.9 1 m after T bend 400 350 300 250 200 150 T1 T2 T3 T4 T5 T6 T7 100 50 0-50 0 0.5 1 1.5 count 2 2.5 3 x 10 4
pressure [kpa] pressure [kpa] 450 400 350 300 Analysis of current system: Conveying cycle pressure 250 200 150 100 50 0-50 0 0.5 1 1.5 2 2.5 3 count x 10 4 T1 T2 T3 T4 T5 T6 T7 500 450 Blowtank conveying cycle 400 350 300 250 Estimated time that 90-95% of flyash is removed T1 T2 T3 T4 T5 T6 T7 200 150 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 count
Load cell installation
Pressure [kpa] Load [kg] System Analysis: 20 minutes 500 1000 450 900 400 800 350 700 T1 [kpa] T2 [kpa] 300 600 T3 [kpa] 250 500 T4 [kpa] T5 [kpa] 200 400 T6 [kpa] 150 300 T7 [kpa] load [kg] 100 200 50 100 0 0 0 200 400 600 800 1000 1200 1400 Time [s]
Pressure [kpa] Load [kg] Blow tank discharge fill cycle 500 1000 450 400 350 300 250 blowtank emptying cycle blowtank line valve opened blowtank line valve closed slow fill region blowtank pressure venting region fast fill region 900 800 700 600 500 T1 [kpa] T2 [kpa] T3 [kpa] T4 [kpa] T5 [kpa] 200 150 400 300 T6 [kpa] T7 [kpa] load [kg] 100 200 50 100 0 0 550 600 650 700 750 800 Time [s]
Pressure [kpa] Load [kg] 500 1000 Optimisation Flow rates 450 400 350 300 250 200 150 blowtank emptying cycle blowtank line valve opened blowtank line valve closed slow fill region blowtank pressure venting region fast fill region 900 800 700 600 500 400 300 2 4 T1 [kpa] T2 [kpa] T3 [kpa] T4 [kpa] T5 [kpa] T6 [kpa] T7 [kpa] load [kg] 100 200 50 100 0 0 550 600 650 700 750 800 Time [s] Blowtank Refill Flyash Flow Rates Region [kg/s] [t/hr] Slow refill 1.14 4.09 Fast refill 27.1 97.6 Blowtank Discharge Full 100% of discharge 7.67 27.6 First 90% of discharge 13.13 47.3 Last 10% of discharge 1.62 5.82
Pressure [kpa] Load [kg] Optimisation Flow rates 500 1000 T1 [kpa] load [kg] 450 average discharge = 27.6 t/hr 900 400 350 800 700 start Blow tank weight 300 last 10% of material discharged 600 250 200 150 100 first 90% of material discharged average discharge = 5.82 t/hr 500 400 300 200 90% discharge weight 50 0 average discharge = 47.3 t/hr 550 570 590 610 630 650 670 Time [s] 100 0 final Blow tank weight
Improving initial pressurisation It is clear from the analysis that the current flyash material has a conveying rate below 270 kpa which is well below the current pre-pressurisation setting of 400 kpa. It is recommended that the prepressurisation is reduced to 300 kpa in order to save energy and also to provide a faster prepressurisation time of approximately 5 seconds. This recommendation assumes that the grade of flyash will not vary significantly.
Improving tonnage changeover time between blow tank discharge into the main pipeline is 10 s, which appears to include the pre-pressurisation time. total conveying time was 73 seconds. average cycle time of approximately 83 seconds (or 43 cycles per hour). tonnage rate for the 100% conveying time was 27 t/hr over a 73 second period. effective tonnage rate will be 24 t/hr. The 90% discharge rate occurs over a 41 seconds flow rate of 47 t/hr.
Improving tonnage For the 90% discharge rate and taking into account the extra 10 s for cycle changes a new cycle time of 51 seconds (or 70 cycles per hour) provides an effective discharge rate of 38 t/hr. This effective discharge rate increases output capacity by 58%. Lastly, it is important to note: from a life cycle and maintenance issue, you will also have a 58% increase in the operation of the valves over the same time period. A larger blow tank size would reduce valve cycle rates.
Final improvement 2011-2102 Original Control of feed air into blow-tank 40% air bypass tank into main line 60% air to fluidise ash
Final improvement 2011-2102 Improved Control of feed air into blow-tank 90% air into top of tank 5% air bypass tank into main line Increased effective tonnages 40 45 t/hr (originally 27 t/hr) 5% air to fluidise ash
Summary System Design Determine ash properties Define minimum transport conditions Post installation - Analyse existing system: Explore optimisation of conveying cycle Investigate opportunities to increase capacity through: Air supply management Feeding techniques Systematically Implement improvement opportunities
QUESTIONS?