Comparison of Dewatering Technologies
Transcription
Comparison of Dewatering Technologies
HWEA Biosolids: Dewatering Processes and Practices Sustainable Sludge Treatment Systems Presented by: Mack McPherson Mike Elhoff Hawaii Engineering Services Dry Solids! Dewatering of digested sludge >30% w/w Introduction • • • • Centrifuge Design S Screw P Press Design D i Sludge Performance Conclusion History - Centrifuge • Continuously operated screw press: – Pulp and Paper – Other applications with fibrous material involved: e.g. Cardboard compaction What Does Mechanical Liquid-SolidSeparation Mean? Sedimentation Filtration (gravity/pressure) Centrifugal Centrifugal Force Centrifugal force Fz grows with: longer distance r to the rotating axis g speed p higher m: mass; c: centrifugal acceleration : angular speed Fz = m · c c = r ·2 Bowl and Scroll Design Features State-of-the-art rotor design steep bowl cone, d:l = 1:4 deep pond (for large volume) double cone scroll (for intensive compacting) spin element at the end of feed pipe Centrifuge Advancements 1975 •Hydraulic scroll drives allow independent scroll and bowl operation •Eddy current drives allow for differential scroll speed adjustment •Steep cone designs increase capacity •PLC PLC control t l system t allows ll for f fully f ll automatic t ti control t l •VFDs are used on scroll drives but require bowl and scroll linkage due to gear box braking •Independent bowl and scroll gearbox not utilizing braking •Planetary gearbox allows totally independent bowl and scroll operation •Centrifuge can run in either leading or lagging mode •Less energy loss by elimination of braking •Scroll can operate independently at maximum speed for cleanout •Energy recovery and deep pond designs for higher capacity and drier solids 2014 Decanter Drive Systems Hydraulic Scroll Drive Instead stead o of a gea gear bo box there t e e is s a rotating hydraulic motor supplied with pressurized oil via a rotary feedthrough. The differential speed is continuously adjustable The oil pressure is directly proportional to the torque moment in the scroll drive. Independent Bowl & Scroll Variable Speed Dual VFD Dual VFD Control Independent scroll and bowl operation Automatic A t ti and d unattended tt d d operation via torque control Highest efficiency and reliability Small space requirement Dual VFD Control Bowl Drive Bowl VFD Bowl motor Scroll Drive Bowl speed set point Scroll motor Scroll VFD Control loop PLC Dual VFD efficiency Example: energy losses (kw) at scroll drive: Where is the energy primarily lost? 9 8 By braking. 7 6 5 4 High g torque q 3 Normal use 2 1 By belt drive losses at a tremendous circulating power. By poor efficiency of the hydraulic pump and motor. 0 SIMPDRIVE Backdrive Hydraulic 2-Gear EddyBrake By braking and refeeding. Only moderate gearbox losses. Typical Control Panel Interior Flottweg new C-series Centrate Energy Recovery Traditional design New design Centrate is discharged straight into the housing. Centrate is redirected and tangentially discharged into the housing. g Rotational energy of the centrate is lost! Rotational energy is recovered! Advancements in Centrifuge Design • Deep Pond Technology reduces Energy Consumption by 25-30% • Centrate Energy Recovery reduces Consumption by an additional 20% • Dual VFD has lower installed HP and reduces energy consumption by eliminating “braking the bowl” • Optimized Solids Discharge (1-2% added cake solids) Wear S Scroll ll with ith TC tiles til and d ceramic i paste t • Optional: Hard metal wear plates (with backing plate) • Optional: CXL paste on scroll blades Wear Feed Zone Replaceable Wear Protection Solids Discharge Zone showing s o g TC C de deflectors ecto s a and d so solids ds po portt liners es Quality centrifuge - critical features: Central lubrication system Wear protection Field replacable Bowl removal vertical Sound insulated Drive system outside separation area Separate scroll bearing All high grade stainless steel Scroll interchange program Municipal Dewatering Centrifuges Flottweg Model C3E C4E C5E Z6E C7E Z8E Z92 Max. Bowl M B lS Speed d (rpm) ( ) G-Force 4000 3300 3400 3000 3100 3000 3200 3500 2770 3000 2650 3000 2250 2600 Capacity (varies by application) (lbs dry/hour) y ) 750 2500 3500 4000 6000 7000 8000 075 50150 125225 150250 225400 250450 300500 14 18 22 24 27.5 30 36 3800 7000 000 20 5 40 10 Dewatering Range (GPM , typical) Mechanical Bowl Diameter (inch) Machine Weight (lbs typical)) Electrical Motors: Main Drive (HP) Scroll Drive (HP) 12000 20000 20000 35000 50000 75 20 150 30 150 40 200 40 350 60 C4E Type C4E Bowl Speed Bowl Power Scroll Power (SIMP® Drive) Dimensions (mm) RPM HP HP L W H 5000 40 10 3520 1140 1030 History – Screw Press • Screw Press: ancient world – Oil mill: edible oil • • • • Oil seeds Palm fruit Olive Oil Coconut Oil • Screw Press: Biosolids Dewatering – Existing Screw press designs applied from other industries – Modifications M difi ti tto optimize ti i operation ti and d allow ll dewatering of different types of sludge – Special design for sewage sludge dewatering: Inclined… Inclined Screw Press Design Features auger pressure cone pneumatic cylinders filter basket pressure monitoring auger bearing auger drive i d pressurized sludge feed filtrate fil outlet cake discharge • O&M advantages: Screw Press – Labor: unattended operation, high automation level already built in – Dewatering process starts immediately even with empty screw press – Spare p Parts: minimal cost factor – slow turning g device,, minimal number of turning parts – Wear Parts: wiper to clean basket on the inside – located at tip of the auger flight; crucial for sludge with very little or no fibrous material and no self cleaning. No major off site overhaul and inspection like for centrifuges Performance • Screw Press’ Press have proven to be competitive with centrifuges: anaerobically digested sludge Sludge Evaluation and Equipment Selection • Cake Solids: project specific – – – – – Bench B hT Tests t Pilot Tests Scale Up p Basket design: drainage, thickening, dewatering Sludge characteristics Sample Analysis • Dewaterability • Polymer screening • Pilot Go I No Go 40 35 30 cake solids [% DS S] Effect of Volatile Solids % on Dewatering Performance 25 20 15 an WAS blend Log. (an) Power (blend) 10 5 0 40 50 60 70 VSS [%] 80 90 100 Dry Solids vs. % Residue on Ignition(100-%VS) 50 Dry Solids Content [%wt.] 45 Raw- and mixed sludge Raw 40 35 Digested sludge 30 25 20 15 Activated sludge 10 5 0 0 10 20 30 40 50 Residue on ignition [%wt.] 60 70 80 Polymer Use - Demonstration and Pilot Tests Blend # off plants l t 19 WAS 17 Aerobically digested Anaerob. digested 26 29 Polymer Consumption in lbs active / ton DS Avg. Min - Max 15.5 20.3 25.1 31.5 8.1 – 24.9 9.6 - 27.2 8.5 - 40 10 - 75 29.5% 18.2% 19.8% 22.1% 18 - 38% 14 - 24% 14 - 27% 16 - 35% Cake Solids (DS) in % Avg. Min - Max Performance Site tests: cake solids for anaerobically digested sludge • BFP: 14 14.8 8 to 18 18.5 5% • Centrifuge: 22.2 to 23.7 % • Screw Presses: 17.3 to 24.1 % Evaluation Criteria • • • • • Cake Solids Polymer Consumption Wash Water Requirements Energy Consumption O&M costs: – Labor: unattended operation, automation – Spare parts – Wear parts • Indirect O&M costs: – Nutrients N i lload d returned d to treatment plant l – Capture rate – Hauling Costs: highly affected by cake solids Evaluation Screw Press 20 Year LCC Breakout Power Cost 1% Chemical Cost 1% 3% 9% 4% 1% Operating Cost (manpower) Maintenance Cost (parts & labor) Disposal Cost Major Rework 81% Equipment Cost Evaluation $0 Disposal Screw Press 20 Year LCC Breakout Power Cost Chemical Cost 4% 17% Operating Cost (manpower) 8% 0% 3% 47% 21% Maintenance Cost (parts & labor) Major Rework Equipment Cost Cost Per Dewatering Technology Dover, NH Pilot Study (Centrifuge, BFP, and Screw Press) Dewatering Cost Total Disposal Water Electrical Polylmer Operations Labor Maintenance $0 $50,000 $100,000 $150,000 BFP Reference AECOM Pilot Testing Results – Dover, NH $200,000 $250,000 Screw Press $300,000 Centrifuge $350,000 $400,000 $450,000 $500,000 Energy Energy Consumption: the installed HP clearly favor BFP and screw presses at similar throughput • Centrifuge: 37.5 kW (50 hp) • BFP: drive unit 4 kW(5 ( hp) p) • Screw Press: 4 kW (0.5 - 5 hp) Dewatering Technologies Belt Filter Press Centrifuge Belt Filter Press • • • • • • • • Oldest Technology Low to Med Cake Solids High Water Consumption Low to High Polymer Consumption High Operator Attention Low Maintenance Low Electrical Loads Low to Med Capture Rate Inclined Screw Press Centrifuge • • • • • • • • Older Technology Medium to High Cake Solids No Water Consumption Med/High Polymer Consumption Low Operator Attention High Maintenance High Electrical Loads Med to High Capture Rate Screw Press • • • • • • • • Newer Technology Medium to High Cake Solids Low Water Consumption Med/High Polymer Consumption Low Operation Attention Low Maintenance Low Electrical Loads Med to High Capture Rate Energy • Energy gy Consumption: p – Mid size plant: processing 25 ton DS/week centrifuge: 78,000 kWh/yr screw press: 8,000 kWh/yr annual savings: $ 22,400.00 at $0.32/kWh – Large g p plant: p processing g 200 ton DS/week annual savings: $ 180,000.00 at $0.32/kWh Conclusion Overall evaluation needs to be tailored for site specific conditions: treatment plant process and biosolids handling affect the importance of each parameter in the cost analysis Dry Solids! Dewatering of digested sludge >30% w/w