Low Pressure Membrane Filtration System Operations

Transcription

1 Low Pressure Membrane Filtration System Operations Nick Lucas MISCO Water New Mexico PWO Seminar

2 Agenda Membrane Basics Comparison to Conventional Treatment Systems Drivers & Applications Operations Discussion

3 Low Pressure Membrane Filtration Basics Membrane filtration is a pressure-driven separation process through semi-permeable membrane material with a pore size of less than 1 µm Typically hollow fiber membrane Outside-in flow pattern most common

4 Membranes Provide Physical Barrier Membranes provide physical barrier against: Suspended solids Cryptosporidium Giardia Bacteria Colloids Viruses Does NOT affect: ph/conductivity Dissolved solids Filtrate Cross-section: dirty fiber Crypto on Fiber Surface Diatom on Fiber Surface Dirt on Fiber Surface

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6 Typical Water/Solids Separation Processes

7 Comparison: Conventional & Membranes Conventional Technologies: Clarifiers & Media Filters Chemically assisted separation Sensitive to feed water changes Sensitive to flow changes Treated quality subject to breakthrough Minimal temp effects media filters Large temp effects - clarifiers

8 Treatment Mechanisms Differ Conventional Technologies: Clarifiers & Media Filters Chemically assisted separation Sensitive to feed water changes Sensitive to flow changes Treated quality subject to upsets Minimal temperature effects Membrane Filtration: Physical separation Copes with sudden, short-term feed condition changes Copes with sudden flow changes Stable treated water quality Temperature impacts to production performance

9 Low Pressure Membrane Drivers/Applications Drivers Surface Water Source treatment removal credit Need/Desire for High Effluent Quality Verifiable Pathogen Removal Footprint Considerations High Recovery Requirements Simplicity of Operations High Degree of Automation Flexibility of Operations Start/Stop Ability Applications Surface Water Treatment (multi-process component or direct feed) Groundwater (GUI) Reuse applications Pretreatment to NF/RO

10 Pressure & Submerged Low Pressure Membrane Systems Pressurized: Membrane modules operate in a closed environment. Feed water is pressurized (pump or gravity) through the modules and membrane skid or unit. The modular skid design simplifies installation and operation. Submerged: Membrane modules operate in a open tank, or cell. This configuration allows for visual inspection, simple membrane installation and removal. Feed water enters the cell by gravity and a suction pump draws water through the immersed membrane modules.

11 Wide Range of Flow Applications Small Package Systems Large Component Systems

12 Typical Membrane System Scope of Supply Compressors/Blowers Feed VVV Strainer Feed Pumps Air System Membranes Housings Frame/cells Piping Valves Instruments PLC HMI Master PLC SCADA PLC & I/O Membrane System Scope of Supply.. O.. O.. O.. O.. O.. O.. O.. O.. O.. O.. O.. O CIP System H Heater Tank Recirculation Pumps

13 General Membrane Modes of Operation Normal Filtration Backwash Chemical Cleaning Integrity Testing

14 Normal Filtration Cycle Filtrate Feed stream Feed stream Start Filtration Filtrate Filtrate End Filtration Raw water is pressurized or drawn to the membrane fibers Particles larger than pore size remain on surface Filtrate, is collected in the inside (lumen) of the fibers Water from the fiber bundles (modules) is collected and sent to the next process in the application train Raw/Feed Water

15 Definitions Fouling gradual accumulation of contaminants on a membrane surface or within a porous membrane structure that inhibits the passage of water TMP Transmembrane Pressure pressure drop across membrane fiber measure of membrane fouling/performance Flux throughput of a pressure driven membrane filtration expressed as flow per unit of membrane area [gal/ft 2 *d] way of measuring how hard a system is being run Permeability ability of a membrane barrier to allow fluid passage as flow per unit of membrane area [gal/ft 2 *d*psi]

16 Air Scour Backwash Cycle Primary solids removal mechanism Fully automated process Based on time or volume

17 Chemical Cleaning Chemical/Physical method of fouling control Frequency dependent on flux and backwash interval Common chemicals Sodium Hypochlorite and/or Sodium Hydroxide (or blend) Citric, Sulfuric, Phosphoric or Hydrochloric Acid (or blends) Steps include Filtrate recirculation / Soak / Aeration Maintenance Washes: Typically 45 minute duration / lower chemical concentration / unheated Frequency varies depending on application (daily to weekly per unit) Clean In Place (CIP): Typically once per month / heated Usually dual cleans; 2-3 hours per chemical

18 Integrity Testing Verifies intact barrier Fibers Orings Seals Is more sensitive than particle counters and turbidimeters Can be correlated to a Log Removal Value (LRV) for pathogens 0.3 micron (or greater) per EPA Membrane Filtration Guidance Manual

19 Integrity Testing How it Works Apply Air Decay Rate Low P Flaw Decay Rate High time

20 Integrity Recovery via Bubble Test & Pin Repair Pin Repair is Permanent Squirter Identified Low pressure air applied to leaking module without removal from skid

21 It s All in the Details Spikes Seasonal Trend Monitoring TMP Control Methodology Cleaning Efficiency Integrity B/wash Efficiency Constant Trace Stable, Low Cost, Long Term Performance Conc. Coagulant Feed Conditions Chlorine Regular Maintenance Flexibility Long Term Fouling Recovery Benchmarking Plant Sizing Trials Cleaning Interval Operation Integrity Mgmt Cleaning Schedule

22 Low Pressure Membrane Systems: Shift in Focus from Conventional Treatment CONVENTIONAL Chemical Optimization enhances separation and effluent quality Incoming Feed Changes Can Adversely Impact Effluent Quality Steady state Operation Yields Best Performance Temperature Not Large Impact on Filter Media Performance more impact on Clarification processes MEMBRANE Effluent Largely a Given focus on monitoring membrane performance Incoming Feed Changes Can Adversely Impact Effluent Quantity Flexibility in Operations through Start/Stop Ability ability to cycle units in and out of service quickly Temperature (via viscosity) has large impacts on throughput and level of performance (i.e. permeability, flux)

23 Operations Focus Items FOCUS ITEM Effluent Largely a Given focus on monitoring membrane performance Incoming Feed Changes Can Adversely Impact Effluent Quantity Flexibility in Operations through Start/Stop Ability ability to cycle units in and out of service quickly Temperature (via viscosity) has large impacts on throughput and level of performance (i.e. permeability, flux) RESULTING GENERAL APPROACH Focus on Performance Trends and Cleaning Intervals Data Collection/Monitoring Flexible Use of Backwash and Chemical Cleaning during Challenging Feed Periods Alternate use of units during lower flow periods (shared burden) Automated rotation to reduce downtime, up efficiency Operational plans for colder temperatures when lower throughput expected --- generally coincides with lower demand

24 Data Monitoring generic trend CIP TMP (psi) Operating Time Maintenance Wash

25 Trend Comparison

26 System Flux Selection & Operation Impact of operation at extremes not understood Leaves little room for unexpected conditions Requires frequent use of chemicals More frequent waste handling Long term fouling in this mode is not fully understood Increases operating costs Greater energy usage Greater chemical usage Consider Impact on Eventual Membrane Replacement More susceptible to viscosity effects Operations Standpoint: High flux reduces operational time to meet short-term demand or increases capacity of current infrastructure (i.e. fill short-term gap) adds long term risk more fouling more chemical & More long-term residual fouling More rapid membrane decline Less room for unexpected conditions & membrane replacement cost sooner

27 Flux & Temperature Impact on Performance

28 Membrane System Control System Membrane Control System and HMI/SCADA provides broad oversight Active Warning and Shut Down Alarms HMI Screens Displaying All System Component Operations Data Monitoring & Logging Capabilities Remote Accessibility Membrane system often one component of broader architecture Membrane Controller System Feed tanks Feed Pumps Strainers Membrane Units Filtrate Tanks Pretreatment Posttreatment Bulk Chemicals CIP Equip Compressed Air

29 Low Pressure Membrane System Maintenance Schedule Regular Maintenance Membrane Maintain Chemical Cleaning Interval Integrity Monitoring (Sonic Test Mapping) Regular Maintenance Ancillary Equipment Valve actuator timing/seating Instrumentation Calibration Compressor/Blower (oil filter change) Strainer cleaning Dosing Pump Calibration Long-Term Maintenance Rotating Equipment (pumps, compressors, blowers, etc.) Membrane Repairs O-ring replacements and seals

30 Long Term Equipment Care Membrane Replacement $64,000 Question ---- How long will my membranes last???? Followed By Ultimate Sales Response ---- It depends Factors: Flux, Operational Load, Feed WQ, Chemical Cleaning Regime, Preventative Maintenance Program, Pretreatment Process/Chemistry, Cost/Benefit Evaluation at End of Membrane Life Major Rotating Equipment Feed Pumps, Compressors, Blowers Skids Generally Planned for 30 year wear life Under right maintenance program maybe longer First generation of large scale membrane systems entering third decade of service Repairs/Rehabs can involve proprietary parts, but can add an extra 5-10 years to a long-term piece of equipment

31 Conclusions Paradigm Shift in Operator Focus from Conventional to Membrane Systems Importance of Data Trend Analysis Assessing Long-Term Performance Trade-Offs in Operation (Short Term Benefits vs. Long Term Risks) Various Controls System Oversight Options Short Term Maintenance Requirements Membrane Maintenance Regular Mechanical Ancillary Equipment Upkeep Long Term Maintenance Requirements Integrity Management Rotating Equipment Upkeep Long Term Use Equipment Upkeep

32 Thank You for you Attention Questions????? Nick Lucas