52 nd North Carolina Industrial Ventilation Conference

Transcription

1 Common Ventilation System Failure Modes Troubleshooting Laboratory Raleigh, NC April 2009 Troubleshooting IV Systems AGENDA: 1. Overview why IV systems fail 2. Baseline Deviation Method 3. Pressure Ratio Methods 4. No Baseline Data Available 5. Summary of Methods Key Reference: Industrial Ventilation, A Manual of Recommended Operation and Maintenance, ACGIH, 1st Edition, 2007 MM MM A Change Affects All Parts of System Consider the Whole System MM Problems fall into 2 general categories Duct Network Problem? One spot both high & low SP/Q in other ducts General (plugged or bypassed ducts) Change seen throughout system? Collector high or low differential pressure Exhaust fan problems More than one problem likely with infrequent maintenance MM ALERT Monitoring Provide warning of rapid changes that could potentially hurt IVS performance (ie, fan failure, plastic bag, etc.) Change to long term frequency based on monitoring data and experience Identifying Sudden Failures ALERT: Visual Indication or Automatic Alarms MM Identifying Gradual Failures DEGRADATION Monitoring Establish on-going degradation and trend monitoring of the IVS System to: Identify the places where and when the system routinely begins to degrade, helpful for troubleshooting, and Provide confidence that the ALERT monitoring locations give adequate early warning Change to long term frequency based on monitoring data and experience MM Module MM-1-3 1

2 Visual observations Troubleshooting Approaches Data based troubleshooting approaches Baseline Deviation Method Pressure Ratio Method Equivalent Resistance Method What if there is no Baseline or Design data? Step 1: Visual Observation Contaminants billowing out of the enclosure/hood? Hoods pulling in air? Obvious problems with the hood including exhaust vent/slot clogging, damage to opening? Open or leaking cleanout/inspection doors? Obvious changes to the ventilation system (i.e. additional branches/hoods)? Ductwork damaged (dents, holes, rust)? Ducts cut off and covered with blanking flanges? Dampers/blast gates positions been altered? Unusual sounds? MM MM Identify the Problem Identify the Source Insufficient air at hood(s) Too much or too little air from process Settling out of material in duct (low velocity) Excessive or visible emissions Equipment failure Electric or other controls malfunction Equipment Air Balance Change in the Process Adjustment of Dampers Material Handling Moisture or Heat MM MM Troubleshooting: Baseline Deviation Method Start with Static Pressures Remember Baseline Specifications Airflow: + 10% design Static Pressure: + 20% Baseline For a measured SP, calculate % Baseline: % o f Basel in e = measur ed SP - basel ine SP basel ine SP x 100 For example, ( )/(140) x 100 = % MM MM Module MM-1-3 2

3 Example Problem Data Table Test Point Predicted Static Pressure Problem 1 Measured SP Problem 32 Measured SP A B C D E F G H I J MM Problem # 1 Calculate the % Baseline for all test ports -is the system operating as per predicted SP? Use the example problem data table (from system drawing.) Is it OK? If not, where would you suggest to start looking for the problem? % Baseline = Test Port SP Reading Predicted SP (Reading - Predicted) x 100 Predicted % Baseline or LO? A B C D E F G H I J MM Answers to Example Problem #1 % Baseline = Test Port SP Reading Predicted SP (Reading - Predicted) x 100 Predicted % Baseline or LO? A ( )/2.26x100 = LO B (3.27-4/54)/4.54x100 = LO C ( )/4.87x100 87x100 = LO D ( )/5.64x100 = 28.0 E ( )/5.35x100 = LO F ( )/5.77x100 = 25.0 G ( )/7.35x100 = 26.0 H ( )/7.81x100 = 25.0 I ( )/7.00x100 = 25.0 J ( )/11.83x100 = 21.0 Problem # 1 Graphical analysis: Look at the arrow direction change between port F & ports C & E. A reversal indicates something has happened in that area. MM Fig.7-2: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Why Pressures Switch: to LO (or LO to ) For analysis at a single point, possible : Pressures switch because airflow has changed Fan delivers airflow on its curve that matches available system High Static Pressure, Low Airflow Low Static Pressure, High Airflow GH AIRF OR VELOCITY GH 1. Branch airflow > design due to restrictions in an adjacent duct branch: - Orifice too small? - Blast gate closed too far? - Air bleed blocked? 2. Total system airflow > design: - Fan inlet slide gate open too far? - Fan/Rotoclone speed too high? - Belt pulley diameter? - Fan motor speed? - Filter differential pressure low? - Pressure indicator ok? - Bag cleaning too often? 1. Branch airflow > design due to duct branch < design between duct branch air inlet and test point: - Duct access door - Orifice missing? - Orifice too large? - Blast gate open too far? Look at points F & C/E which fit SP data best? Fig.7-3: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Table 7-4: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Module MM-1-3 3

4 AIRF OR VELOCITY (cont d) GH 1. Branch airflow < design due to restrictions between duct branch air inlet and test point: - Poorly cut flange gasket partially blocking duct? - Orifice too small? - Blast gate closed too far? - Air bleed blocked? 1. Branch airflow < design due to restrictions between the test point and the system fan: - Poorly cut flange gasket partially blocking duct? 2. Openings in other parts of system allow airflow to bypass test point duct branch: - Duct access door - Filter inspection door - Missing orifice? - Blast gate opened too far? 3. Total system airflow < design: - Fan/Rotoclone performance? - Fan rotation incorrect? - Loose belts? - Small pulley diameter? - Wrong fan motor speed? - Filter differential pressure high? - Pressure indicator ok? - Bag cleaning ok? - Moisture, bags blinded? - Fan damper closed too far? Table 7-4: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Recommendations: Walk the system with a system schematic - everything look OK? Take static pressures at all test points and compare to Baseline static pressures. See if there is a part of the system where there is reversal or switch between low values and high values. Take airflows in the area of the switch to locate the problem. MM (cont d) A simple memory aid that some operators have used to quickly evaluate Static Pressure readings when they differ from Baseline is : High static pressure? ( High? Look Low ) -> look low in the system (towards the air inlets) Low static pressure? ( Low? Look High ) -> look high in the system (towards the exhaust fan) Problem # 3 Again, take the data from the drawing, calculate % Baseline, and determine if and where the problem might be. % Baseline = Test Port SP Reading Predicted SP (Reading - Predicted) x 100 Predicted % Baseline or LO? A B C D E F G H I J MM MM Answer to Problem # 3 % Baseline = Test Port SP Reading Predicted SP (Reading - Predicted) x 100 Predicted % Baseline or LO? A ( )/2.26*100 = LO B ( )/4.54*100 = LO C ( )/4.87* = LO D ( )/5.64*100 = LO E ( )/5.35*100 = LO F ( )/5.77*100 = LO G ( )/7.35*100 = LO H ( )/7.81*100 = LO I ( )/7.00*100 = LO J ( )/11.83*100 = LO Problem # 3 Graphical Analysis: Look how all the SP s are low - a system wide problem. Since baghouse differential pressure is not high with a high SP at the fan inlet (J), then the fan is the problem - wrong rotation. MM Fig.7-4: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Module MM-1-3 4

5 For analysis at a single point, possible : GH AIRF OR VELOCITY GH 1. Branch airflow > design due to restrictions in an adjacent duct branch: - Orifice too small? - Blast gate closed too far? - Air bleed blocked? 2. Total system airflow > design: - Fan inlet slide gate open too far? - Fan/Rotoclone speed too high? - Belt pulley diameter? - Fan motor speed? - Filter differential pressure low? - Pressure indicator ok? - Bag cleaning too often? 1. Branch airflow > design due to duct branch < design between duct branch air inlet and test point: - Duct access door - Orifice missing? - Orifice too large? - Blast gate open too far? Why are all SP s low? AIRF OR VELOCITY (cont d) GH 1. Branch airflow < design due to 1. Branch airflow < design due to restrictions between duct branch air restrictions between the test point and inlet and test point: the system fan: - Poorly cut flange gasket partially - Poorly cut flange gasket partially blocking duct? blocking duct? - Orifice too small? 2. Openings in other parts of system allow - Blast gate closed too far? airflow to bypass test point duct branch: - Air bleed blocked? - Duct access door - Filter inspection door - Missing i orifice? - Blast gate opened too far? 3. Total system airflow < design: - Fan/Rotoclone performance? - Fan rotation incorrect? - Loose belts? - Small pulley diameter? - Wrong fan motor speed? - Filter differential pressure high? - Pressure indicator ok? - Bag cleaning ok? - Moisture, bags blinded? - Fan damper closed too far? Table 7-4: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Table 7-4: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Good Baghouse D/P = Low Air Flow? GH DIFFERENTIAL PRESSURE 1. Bag blinding, bridging A. Bag cleaning system B. Dust removal system C. Moisture D. Static electricity 2. High airflow through baghouse A. Fan speed B. Fan throttling damper C. Open inspection doors 3. Bag fabric problem A. Fabric not vendor spec B. Correct fabric for service DIFFERENTIAL PRESSURE 1. Low bag A. Inadequate precoat B. Bags cleaned too often C. Bag installation 2. Low system airflow A. Major pluggage in network B. Fan performance? C. Baghouse bypassing? MM Fans Deliver Air Rotating Backwards! Correct impeller rotation (looking from air inlet end) Even with backwards rotation 50-60% airflow 25% static pressure Correct by reversing two of three electric motor leads MM Example Problem #4 Answer to Example Problem #4 Test Point Measured Baseline Value actual - baseline % of Baseline = x 100 Static Pressure on FDFCD baseline ( )/(1.8) x 100 = +117% ( )/(1.7) x 100 = +124% ( )/(2.3) x 100 = +104% ( )/(2.4) x 100 = +71% ( )/(2.9) x 100 = +59% yes ( )/(3.0) x 100 = +43% ( )/(3.1) x 100 = +42% ( )/(6.2) x 100 = +3% (Figure MM A-1) 29 MM Module MM-1-3 5

6 System Perspective Analysis of Problem 4 (Like closing a blast gate) Troubleshooting: Pressure Ratio Method Fig.7-5: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for Fig. 3-1: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM MM Troubleshooting: Pressure Ratio Method SP end = value measured at the end of the same branch duct as SPh SPend up = average value of SPend in the ducts immediately upstream of this duct SPend dn = value of SPend measured in this duct Resistance can change for many reasons: New partial blockage or change to previous partial blockage due to buildup or removal (e.g., cleaning out settled material). New coating or change to the previous coating Adjustment of a damper (increase if inserted further; reduction if pulled out) Increasing bends in a flexible duct or straighten the flexible duct out Crushing a section of duct or replacement of a crushed section Substitution of a component with a higher or lower Changes to the pathway through the ventilated device to the duct (e.g., adjustments to the cutter height for wood planers). For slot/plenum hoods, changes to the slot opening size. Ch.7: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM MM Changes to System and Changes to BrRatio Changes to System and Changes to End Ratio Parameter SP h /SP end Measure In Same branch Thresh -old If Increase in BrRatio 10% Increased upstream of H, or Reduced between H and End If Decrease in BrRatio Reduced upstream of H, or Increased between H and End Parameter SP endup SP enddn Measure In Upstream duct and reference location Thresh -old If Increase in EndRatio If Decrease in EndRatio 10% Substantial blockage Blockage in submain just upstream of downstream of Up Up Lesser changes could be due to blockage further downstream Table 7-8: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for Table 7-8: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM MM Module MM-1-3 6

7 Changes to System and Changes to Pressure Ratios BrRatio: SP h /SP end, ;Measure In: Same Branch; Threshold: +10% EndRatio: SP Meas.In: Duct Header; Thresh.: +10% SP endup /SP enddn 1 2 A 3 B 4 C 5 D 6 E Plan View Cyclone F G H Change In Ratio Increase Ratio Decrease Duct blockage Duct cleaning New or incr. layer Fan Damper adjust. Pulled out Inserted further Flexible duct Straighten bends Increase bends Example DCS for Pressure Ratio Methods K F G Damaged duct Replace duct Duct crushed Dust collector Lower Higher Airflow change Reduced air More air past point Air path to hood Reduce opening Increase opening MM Elevation Fig. 7-6: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for Cyclon e MM J Pressure Ratio Method Baseline Data Time 1 Time 2 ID Type SPh1 SPend1 SPh2 SPend2 1-B Branch A Branch A Branch A-B Submain C Branch C Branch C-D Submain E Branch B-D Submain D-E Submain E-F Main F-G Collector G-H Fan Inlet Fig. 7-6: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM Branch Pressure Ratio Method Example Time 1 Time 2 SP h SP h ID Ratio Ratio Ratio % Altered? /SP end /SP end Time 1 Time 2 Change 1-B 2.83/ / % Not likely 2-A 1.91/ / / % Likely 3-A 1.91/ / % Not likely 4-C 2.37/ / % Likely 5-C 2.37/ / % Not likely 6-E 3.73/ / % Not likely Table 7-9: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM End Pressure Ratio Method [% change =(T2-T1)/T1] T1)/T1] 1 B D A +30% C +13% % E Plan View -17% Cyclone F -19% G Up ID Time 1 Time 2 Ratios ID A B A/B Avg A/B Avg T 1 T 2 %? Altere d? C-D 4-C 5-C / / / / Likely =0.50 =0.65 B-D 1-B A-B / / / / Not =0.68 =0.67 likely D-E B-D C-D / / / / Not =0.98 =0.98 likely E-F 6-E D-E / / / Likely 5.82 /4.12 =0.89 =0.74 F-G / / Likely =0.58 =0.47 Time 1 Time 2 ID Type SPh1 SPend1 SPh2 SPend2 1-B Branch A Branch A Branch A-B Submain C Branch C Branch C-D Submain E Branch B-D Submain Example Branch & End Pressure Ratios Problem H Fan G-H /-12.2 = /-12.3 = Not likely D-E Submain E-F Main Table 7-10: From American Conference of Governmental Industrial Hygienists (ACGIH ), Industrial Ventilation: A Manual of Recommended Practice for MM F-G Collector G-H Fan Inlet MM Module MM-1-3 7

8 Troubleshooting with No Design or Baseline Data Available Potential Sources of Comparison Information Airflow requirements for each hood & enclosure Adequacy of duct conveying velocities Reasonableness of Air Cleaning Device differential pressure Fan operation on its performance curve Adequacy of fan to deliver total airflow for all hoods through the existing duct network Existing drawings Existing design calculations Recommended approaches such as IVM Permit Applications or Title V submissions Walk through the system to determine the required ventilation at each potential exposure point and estimate the needs of the system MM MM Troubleshooting, No Design Data obvious change? Obvious Damage? Branch blanked off? Before After Duct diameter unchanged after several tie-ins? MM MM Compare to Existing Drawings or Make a System Sketch to Show Hood opening sizes (width and length) Plugged or dirty screens at hood openings Diameter of duct connected to hood Locations of blast gates and gate approximate percent open Lengths and locations of flexible hoses Damaged ducts (dented, holes or other audible airleaks) Angle of branch duct entry into the sub-main or main. Y shapes are recommended practice, not T shapes. Ducts removed and sealed with a blank flange or similar device Ducts added (branches joining main header and duct afterwards does not get larger in diameter for the extra airflow) Sudden expansions or contractions in duct diameter without an addition of a branch to explain it. Air cleaning device differential pressure measuring points Unusual fan sounds Estimate number of duct diameters of straight duct into and out of the fan Visible emissions on the roof by the exhaust stack MM Troubleshooting: No Design Data Available Engineering study to gather system data to assess possible system capability Process problems due to LEV Hood/enclosure airflow estimates Duct network dimensions Collector and fan nameplate information Perform calculations - Industrial Ventilation, A Manual of Recommended Practice for Design Recommend system changes MM Module MM-1-3 8

9 Summary Collector High/Low Differential Pressure Troubleshooting Tables Walk the system to check for obvious changes Has there been recent maintenance on system? Take SP data at strategic test points Use some airflow data to clarify unclear SP data System wide problem or confined to part of duct network? (See Collector Troubleshooting Tables reproduced on last pages of this section.) There can be more than one cause of the problem Fan Lab Identify of 3 different system problems. MM MM Fabric blinding by dust Too high air to cloth? Bag cleaning failure? Process moisture? Dust removal failure? Wrong fabric? Higher airflow? Troubleshooting Fabric Filters Low differential Low bag to airflow New fabric not yet conditioned? Bags cleaned too often? Missing bags? Filter access door open bypassing? MM A. Check bag cleaning system - Compressed air supply: Moisture (drier failure)? Pressure < design ( psi) Pressure indicator ok? In line air filter blockage? Valves positioned incorrectly? Air compressor problem? Blowpipe loose, no air to venturi's? - Control system: Incorrect pulse timer settings? Demand pulse not working? Solenoid valve failure? Diaphragm valve failure? Investigate Increasing DP Trend Bag Blinding? B. Check dust removal system (Filter hopper bridged?) - Outlet opening too small? - Rotary feeder valve failure? Valve not rotating? Valve rotating too slowly? Valve pockets blocked? -Discharge chute blocked? C. Check process sources of moisture - Water gets in through leaks in baghouse housing? - High process moisture in dusty air? D. Check for static electricity cling in baghouse in low humidity climates (< 30% relative humidity) MM Investigate Increasing DP Trend High Airflow through Baghouse? Investigate Decreasing DP Trend A. Check fan speed - Belt pulley diameter? - Motor speed? B. Check fan damper at correct setting C. Duct or baghouse inspection door 1.Low bag to airflow. 2.Low system airflow. A. Inadequate new bag pre-coat (bag conditioning)? B. Bags being cleaned too frequently? C. Missing bags due to incorrect installation? A. Major plugging in duct network? B. Fan performance? - Pulley diameter too small? - Belts slipping/loose? - Wrong motor? - Fan incorrect rotation (check motor hookup)? C. Baghouse clean side inspection door MM MM Module MM-1-3 9

10 Dust buildup on cyclone internal walls? Dust hopper backup? Higher than design airflow? Duct cleanout door Troubleshooting Cyclones Low differential Bypassing Cyclone access door Dust hopper access door Throttling orifice opening too small? Dust buildup on scrubber internal walls? Sludge hopper backup? Higher than design water flow? Higher than design airflow? Troubleshooting Scrubbers Low differential Scrubber water low flow? Bypassing Scrubber access door Sludge hopper access door MM MM Troubleshooting ESP s Low differential Pre-filters dirty? Dust buildup on collecting Duct network plugged? plates? Fan shaft speed low? Bypassing Dust hopper backup? Higher than design airflow? Precipitator access door Dust hopper access door Troubleshooting Adsorbers pressure Low differential pressure Adsorbent media blinding by contaminants? t Bypassing? Adsorbent media breakdown? Higher airflow? Adsorber housing access door open MM MM Biologic media Excessive growth? Sump sludge backup? Excessive water flow? Higher airflow? Troubleshooting Biofilters Low differential pressure Bypassing? Biofilter housing access door Little or no water flow? Excessive solvent flow? Higher airflow? Troubleshooting Gas Scrubbers Low differential pressure Excessive packing media solids buildup? Sump backup blocking packed bed? Fan shaft speed low? Channeling of gas through packed bed? Little or no solvent flow? Bypassing? Scrubber access door Sump access door MM MM Module MM

11 pressure Higher airflow? Troubleshooting Thermal Oxidizers Burner combustion air high? Dampers out of position? Contaminant buildup on internal surfaces? Low differential pressure Combustion air? Damper position? Bypassing? Oxidizer access door MM Module MM