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Airdusco Engineering & Design Services LLC.

4739 Mendenhall Road South

Memphis, TN 38141

TYPICAL BASELINE ASSESSMENT REPORT

HAMMERMILL DUST COLLECTION SYSTEM

http://www.airdusco.com

Project Documentation: Typical Revision:

Effective Date: 11/2/2016

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Table of Contents Executive Summary ................................................................................................................................................................ 3 Preface .................................................................................................................................................................................... 4 Methodology ............................................................................................................................................................................ 4 Hammermill Dust Collection System ....................................................................................................................................... 5

Equipment ........................................................................................................................................................................... 5

Primary Cyclone .............................................................................................................................................................. 5 Dust Collector .................................................................................................................................................................. 6 Centrifugal Fan ................................................................................................................................................................ 7 Abort Gate ....................................................................................................................................................................... 8 Back-Draft Damper.......................................................................................................................................................... 9 Ductwork ....................................................................................................................................................................... 10 Abort Cyclone ................................................................................................................................................................ 10

Dust Sources and Controls ............................................................................................................................................... 11 Observations ..................................................................................................................................................................... 13 Theoretical vs. Actual Performance .................................................................................................................................. 18

Calculation Parameters ................................................................................................................................................. 18 Theoretical Performance ............................................................................................................................................... 19 Actual Performance ....................................................................................................................................................... 20 Comparison ................................................................................................................................................................... 20

Evaluation .......................................................................................................................................................................... 21 Conclusions ....................................................................................................................................................................... 22 Recommendations ............................................................................................................................................................ 23

Tier 1 Recommendations .............................................................................................................................................. 23 Tier 2 Recommendations .............................................................................................................................................. 24




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Executive Summary 1. The system is operating adequately as observed; however, a slight increase in filter differential

pressure could cause the airflow to decrease, which would drop duct velocities below the minimum conveying velocity of 5,000 FPM.

2. Frequent bag changes are caused by the significantly high air-to-cloth ratio of the filter. 3. Filter discharge and bridging issues can be traced the extremely high interstitial velocity of the filter. 4. The fan is operating at the peak of its performance curve and small changes in static pressure can

cause significant changes in airflow throughout the system.




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Preface

To obtain the information necessary to prepare this report, a site visit was scheduled over two days. The Airdusco EDS personnel present for the site visit was Casey Shockey, P.E. Additionally, other personnel involved in the production of the audit documents were Kevin Cardwell, CFEI, CFPS, Operations Manager, and Adam Lancaster, President of Airdusco EDS, LLC.

Methodology

All velocities presented in this document were calculated and/or interpolated from data gathered in the field, and do not take material loading into account.

All air velocity and volume calculations assume no build-up of product in the duct. All ducts were to have been cleaned before our arrival. Any obstructions were noted.

All velocity pressure and static pressure readings were taken in accordance with industry standards1 and Customer requirements as defined in the documents provided to Airdusco EDS by the customer2. o No material loading was possible in the ducting during measurement. o Material loading would result in either quickly plugging and/or physically damaging the pitot probe.

Material from machines like the hog and planer could produce this type of loading. o Velocity and volume flow measurements with pitot probes are subject to slight error.

Many individual readings were taken (traverses, centerline duct readings, static pressure readings, air temperature readings, etc.) and are used in various places throughout this document. Not every reading is covered in detail, but all were used for calculations. Calculations and measurements have an error tolerance of ± 10% which is typical for dust collection systems. o All readings are listed included as separate files with this report. o For the sake of simplicity, all readings, calculations and statements concerning airflow assume air at

standard conditions3 unless otherwise stated. o The exceptions to this are for systems in which the observed or calculated static pressure is less than

20” water gauge (wg). For these systems, compressibility has to be considered4.

Fan characteristics are obtained by using comparable information from Twin City Fan & Blower and/or The New York Blower Company in some cases. This method is subject to errors and may not give a completely accurate picture of the fan’s actual performance. This process is completed with the best information available.

Readings are taken when the system is not under load and the amperage draws are taken when the system is under load meaning the system is capturing process material. This may affect the results.

Distances measured for Fire Protection Equipment in many cases are taken from ground level, and should be considered to be accurate ± 1’-3’.

All air calculations involving duct neglect the wall thickness.

Published data will be used and cited for all materials where bulk density is necessary. o In all cases, when calculating material volumes, the worst-case published bulk density will be used.

At the customer’s request, this document is not a Process Hazards Analysis.

1 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 3.4; Appendix C. 2 Pitot-Tube-Traverse-Data-Form for Duct Velocity-Flow Rate Determination (13June14).xls; Dust Collection Systems Bid Documents Final.doc; Dust Collection Systems Baseline Guideline (10Jan14).doc. 3 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 3.9. Temperature @ 70°F;

Elevation @ sea level; Air is assumed to be dry; the weight of contaminant is neglected; effects of compressibility are ignored. 4 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 3.11, page 3-12.




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Hammermill Dust Collection System

Equipment

Primary Cyclone

Primary air-material separator (AMS)

Located inside, upstream of the baghouse, inlet at roughly 65’ above grade

Manufacturer: M-E-C Company o Manufacture date: 11/2004 o Model number: CL9-062 o Serial number: N/A o Work order number: S-683-HF o Maintenance personnel indicated 11-12 years in operation o Tangential inlet: 48” x 16” o Single tangential discharge: 24” diameter o High-to-Medium efficiency design with small surge/expansion chamber at the bottom. o Cyclone has two explosion suppression canisters o Cyclone has fire protection deluge system

Figure 1 Primary AMS




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Dust Collector

Secondary air-material separator (AMS)

Located inside, downstream of the cyclone

Manufacturer: MAC Equipment (Now MAC Process) o Manufacture date: 2004 o Model number: 144MCF153 o Serial number: 63829-013-1 o Filter area: 2,204 ft2 o Total airflow to filter: 16,548 CFM o Air-to-cloth ratio: 12.1:1 o Interstitial (rising) velocity: 814 ft/min o Discharge Airlock: MAC FS-10x8

Figure 2 Secondary AMS




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Centrifugal Fan

Primary Air-moving device (AMD)

Located inside, downstream of the baghouse (clean side of baghouse)

Manufacturer: M-E-C Company o Model: 70XH o Inlet diameter 24”. o Motor: 150 BHP, 222 Full Load Amps, 460 Volts, 1785 RPM, 3 Phase. o Customer provided amperage readings: o 160 Amps o Motor sheave 14” diameter o Fan sheave 13.2” diameter o Customer supplied manufacturer’s fan curve and drawing, but it doesn’t match the fans

observed performance or speed. o Approximate fan RPM of 1893 RPM based on sheave sizes; 1860 based on customer-

supplied information. o No nameplate data o Fan performance corresponds well to a Twin City, Model RBO-923.

Figure 3 Primary AMD




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Abort Gate

Hi-Speed Abort Gate

Located inside, upstream from the cyclone and baghouse transfer line.

Abort position routes around cyclone and baghouse to the fan.

Manufacturer: Clarke’s Sheet Metal, Inc. Model CM-24 o Serial number: M24LPXX04963 o Age unknown

Figure 4 Abort Gate




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Back-Draft Damper

Passive back-draft damper

Located inside, between the cyclone and baghouse.

Approximately 38” diameter duct, field measured from the ground.

Manufacturer Clarke’s Sheet Metal, Inc. o Includes explosion vent on top. o Estimate 37” x 37” vent size. o No vendor information available. o Age unknown.

Figure 5 Back-Draft Damper




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Ductwork

Combination of welded and angle ring flange connections.

Abort Cyclone

Secondary air-material separator (AMS)

Located outside, upstream of the fan

Manufacturer: M-E-C Company o Manufacture date: 11/2004 o Model number: FDAR6-D58 o Serial number: N/A o Work order number: S-645-HF o Maintenance personnel indicated 11-12 years in operation o Tangential, round inlet: 24” diameter o Single center discharge: 24” diameter o Medium efficiency design o Cyclone discharges to the ground, inside a vault o Cyclone is unprotected

Figure 6. Abort Cyclone




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Dust Sources and Controls There are two dust sources in this system. The first, is one of two hammermills that is fed from dryers above, see Figure 7. Each hammermill can be isolated via a manual divert valve just upstream of the machines. The air intake of each machine is also equipped with a manual damper, both of which were in the full open position. The hammermill has a blow-through style dust collection hood which pulls air underneath the machine through the path of milled material falling from above. The air/material mixture is routed through a long radius rectangular elbow and then transitioned to square ductwork. This ductwork is joined with the other hammermill at the manual divert valve. The system only supplies dust collection to one hammermill at a time.

The second dust source in this system is a recirculation connection located underneath the baghouse’s rotary valve (see Figure 8). This connection is a 4” diameter line and has an open-air intake. This connection routes to just upstream of the abort gate where it then ties in to the system.

Figure 7 Hammer Mill #2




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Figure 8 Recirculation Dust Collection Point




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Observations

The system was installed around 2004 according the maintenance personnel. The rotary valves in the system are fabricated airlocks with flexible tips. These are well-suited for passing wood chips and dust, but are inadequate for isolation per NFPA standards. The hammermills have air intakes are covered with expanded metal. The recirculation line has an open air inlet. These three points could allow foreign objects to enter the system. If any metallic items were to enter, they could potentially be a source of a spark in the ducting, cyclone, or filter. If an abort were to occur, the foreign object could also pass through the fan, possibly causing fan damage or a spark. Airdusco EDS was told that the filter bags must be changed every 3 months, and that the material in the filter bridges over the airlock. Maintenance personnel indicated that the bridging would typically indicate that is was time to change the filters. There are multiple air leaks in the system. Figure 9 and Figure 10 shows two ports that are open to atmosphere. Figure 11 through Figure 14 show various leaks associated with the fan. These include a missing drain plug, leaks around the inlet flange and the scroll, and significant leaks around the access door. The leakage air decreases the efficiency for the system.

Figure 9 Abort Gate Air Leak

Figure 10 Abort Gate Air Leak




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Figure 11 Fan Housing Leaks




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Figure 12 Fan Housing Leaks




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Figure 13 Missing Drain Plug




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Figure 14 Fan Access Door Air Leaks




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Theoretical vs. Actual Performance Calculation Parameters

Calculations are based upon the Velocity Pressure Method, which is also referred to as Balance by Design or Static Pressure Balance Method. 5

Velocity and Static pressure calculations are based on formulae and factors found in Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition. 6

Hood calculations are based on formulae and factors found in Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition. 7

Balancing calculations are based on formulae found in Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition. 8

System will be evaluated as a worst-case situation.

Assumptions: o All slide gates must be assumed fully open. o Minimum required conveying velocities:

Light dust or material loadings require a minimum duct velocity of 4,500 FPM. Medium dust or material loadings from equipment such as the saws require a

minimum duct velocity of 5,000 FPM. High material loading from equipment such as the planer requires a minimum duct

velocity of 5,500 FPM. o Constant uninterrupted airflow to the hoods at all times. o Theoretical calculations based on airflow only. o No material loading considered. o All hoods remain the same and the routing remains the same.

5 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 5.4, Pages 5-9 through 5-11. 6 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 9, Page 9-28, Figure 9-12. 7 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 9, Page 9-57, Figure 9-a. 8 Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition, Chapter 9.7.1, Formula [9.8]

𝑄𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑 = 𝑄𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙√𝑆𝑃𝐺𝑜𝑣𝑒𝑟𝑛𝑖𝑛𝑔

𝑆𝑃𝐿𝑜𝑤𝑒𝑟 .




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Theoretical Performance

Table 1 Theoretical Performance

Test Point ID Location Airflow (ACFM) Average Velocity (FPM) Static Pressure

(" w.g.)

1 Baghouse Inlet 15700 5000 -15.0

4 Cyclone 15700 5000 -9.0

9 Abort Cyclone 15700 5000 13.0

Table 2 Theoretical Static Pressure

Test Point ID Location Static Pressure

(" w.g.)

5 Fan Inlet -23.0

6 Fan Outlet 13.0

Hammermills produce heavy material loadings due to the operational nature of the equipment. This

dust loading requires a high conveying velocity to reduce accumulations in the ductwork and should maintained at 5,500 FPM according the industry standards. To maintain 5,500 FPM in a 24” diameter duct requires approximately 17,300 SCFM. However, due to the geometry of the hammermill and associated ductwork to the diverter valve this velocity is not feasible. It would result in extremely high conveying velocities, static pressure requirements, and a large brake horsepower demand. Therefore 5,000 FPM will serve as the minimum conveying velocity in the 24” diameter duct. For theoretical calculations the design basis for conveying velocity shall be 5,000 FPM. To maintain 5,000 FPM in a 24” diameter duct requires approximately 15,700 SCFM. This value serves as the minimum airflow requirement for the system to ensure the ductwork is free of accumulations according NFPA standards for combustible dusts.

Theoretical results yielded the values shown above in Table 1 and Table 2. When the hammermill is in operation, free air come from three sources. First is the open slot that runs underneath the unit, second is through the mill itself, and the third source is from the airflow generated by the rotation of the rotor in the mill. Calculations show that roughly 10,000 SCFM enters through air intake and the rest enters or is generated by the mill. The static pressure requirement to reach the cyclone is approximately 9” w.g. No manufacture specifications or drawings were provided for the cyclone and therefore the test measurement were be used for the pressure requirement across the cyclone. This is done by using the fans laws to adjustment the static pressure up based on the theoretical airflow required. The adjustments yield a pressure requirement of 3.7” w.g. at 15,700 SCFM. The cyclone is a high efficiency model and the pressure drop is within the expected range for this type of cyclone. From the cyclone to the baghouse adds approximately 2.25” w.g. When designing dust collection systems worst case value must be used for the pressure requirement across the filter media. The worst situation represents the performance requirement just before the filters blind and need to be changed. The industry accepted value for this application would be 6” w.g. From the baghouse through to the stack requires approximately 15” w.g. The pressure loss includes the system effects of the fan due the ductwork arrangement on the inlet and outlet. It also includes the pressure loss of the silencer, abort cyclone, and stack. Theoretical system requirements were approximately calculated to be 15,700 SCFM at -36” w.g.




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Actual Performance

Table 3 Actual Performance

Test Point ID Location Airflow (ACFM) Average Velocity (FPM) Static Pressure

(" w.g.)

1 Baghouse Inlet 16548 5267 -12.90

4 Cyclone 15501 4934 -8.20

9 Abort Cyclone 15749 5013 12.20

Table 4 Actual Static Pressure

Test Point ID Location Static Pressure

(" w.g.)

2 Cyclone Outlet -12.30

3 Cyclone Inlet -8.70

5 Fan Inlet -17.80

6 Fan Outlet 12.90

7 Hammermill #2 -9.70

8 Hammermill #1 -8.60

Actual performance was measured with the manual divert valve set to hammermill #1 and shown above in Table 3 and Table 4. Both hammermills were running while the system was being measured. The differential pressure across the filter was observed at 0.55’ w.g. from the magnehelic gauge at the base of the unit. This value indicates that the filters are relatively new and clean. The static pressure was measured at the fan inlet and outlet to provide a total system pressure. The fan inlet measured -17.8” w.g. and the fan outlet measured 12.9” w.g. The overall airflow was measured in three different locations and ranged from 15501 ACFM – 16548 ACFM (conveying velocities of 4934 FPM to 5267 FPM, respectively). The lower value was used to represent the worst possible situation for the system. The values are within the accepted tolerance of +/-10%. Field measurements are included separately with this report. The system is providing adequate performance for the hammermills, but any significant changes in differential pressure across the filter will negatively affect performance. Actual system performance was measured to be 15501 ACFM at -30.7” w.g.

Comparison Theoretical results indicate a slightly higher requirement than the actual performance measured by about 14%. The fact that theoretical results are slightly different than the actual performance indicates the overall system design is marginal. Any significant increases in differential pressure will negatively affect the performance of the hammermills. Overall flows are within the expected tolerance of +/- 10%.




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Evaluation

The overall performance appears to be adequate, provided that the filter differential pressure does not rise beyond 1” w.g. The performance is close to the theoretical calculations. The fan curve provided does not match the performance observed. As stated above, a Twin City, model RBA 923 closely represents the performance observed. The fan curve for this fan is shown below in Figure 15. Through inspection of the fan curve, it can be seen that small changes in static pressure will result in significant changes in airflow through the system. If the differential pressure across the baghouse were to rise to 2” w.g., the effect on the system would be a large decrease in airflow as represented by the red lines on the curve below. The system performance would be approximately 10,000 ACFM at 32” w.g. Any further increase static pressure would cause the fan to surge. This would be evident by excessive vibration and noise. Surge can shorten the life of the fan and its components.

Figure 15 RBA 923 Fan Curve

The transfer line underneath the baghouse is underperforming. The available static pressure at the

connection point just upstream of the abort gate is 7.7” w.g. Calculations indicate that the airflow through the 4” diameter line is approximately 425 ACFM which equates to a conveying velocity of 4,870 FPM. The velocity is below the accepted minimum conveying velocity of 5,000 FPM. Although the value is not extremely low, care must be taken to avoid plugging on startup and shut down sequences. The system must purge the line on before the rotary valve starts to feed material.




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The dust collector has two significant issues that are causing the filters to blind prematurely. Filter media in this type of application should last between six to twelve months. As mentioned above, bridging was the key indicator for a bag change. This is most likely due to two key baghouse parameters, interstitial velocity and air-to-cloth.

Interstitial Velocity refers to the upward or rising air velocity in the filter body between the filter cartridges. This parameter is determined by the particle size, aerodynamic particle diameter, etc., of the collected material. If the interstitial velocity is too high, the dust that is cleaned from the filters will not fall down to the hopper. Some of the collected dust will remain aerated in the top section of the filter near the tubesheet and will only settle when the system is shut down. This presents problems with removal of the captured material and in some extreme cases, a baghouse can completely fill with dust due to high rising velocity conditions. No maximum interstitial velocity was supplied from the equipment manufacturer. Calculations indicate that the interstitial velocity is approximately 814 FPM. For wood dusts, the customer requires under 300 FPM for interstitial velocity. It is acceptable to be within approximately 5% of that value in some cases. Some equipment manufactures recommend interstitial velocities below 200 FPM for the same material.

Air-to-cloth ratio refers to the volume of air passing through a square foot of filter medium. Others names for this metric are filtration velocity and penetration velocity. Exceeding the air-to-cloth ratio can cause significant performance problems, which include reduced bag life, poor filter media cleaning, and high-pressure drop across the filter media. Fine dust and powder applications require lower air-to-cloth ratios to avoid re-entrainment of the dust on the bags in most cases. Also, higher dust loadings require lower air-to-cloth ratios. The air-to-cloth ratio of a baghouse is engineered along with the other system engineering considerations. It must be evaluated in all design cases.

The correct air-to-cloth ratio provides the maximum capacity for a given baghouse. For wood dusts with larger particle sizes, the industry accepted air-to-cloth ratio would be approximately 6 to 1. The filter is currently operating with an air-to-cloth 12.1 to 1. This is double the industry accepted value. This situation will cause premature filter blinding and in some cases bag failure.

Conclusions

On the day of observation, the system was performing adequately. The filters were recently changed and the filter media was relatively clean, which made the differential across the baghouse low. When the filter’s differential pressure requirements increase, the system performance will suffer. This situation puts the system in a marginal performance category. Monitoring the filter’s differential pressure is crucial to keeping the system performing at an acceptable level. The future elimination of the abort cyclones will improve the allowable differential pressure across the filter. If this modification is made, the system will be considered satisfactory.




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Recommendations

Tier 1 Recommendations

1) Constant Monitoring

a) Purpose: i) Provide a means of detecting problems in the system, such as plugged lines and/or

unexpected static pressure changes. b) Required actions:

i) Installation of individual differential pressure gauges on the inlet and outlet of the fan. ii) Installation of amp meter to read amperage draw of the fan motor.

c) Result: i) Allows constant monitoring of fan performance. ii) Will establish baseline for a preventive maintenance schedule and allow for continued

preventive maintenance based on measurable parameters and time intervals. iii) Will ensure that the system is always performing at an acceptable level. iv) Low cost installation

2) Install an inlet filter on the transfer line inlet

a) Purpose:

i) Prevention of foreign material that could possible cause a spark from entering the transfer line.

b) Required actions: i) Selection and installation of a 4” low-loss inlet filter for the transfer line.

c) Result: i) Keeps foreign material out of the transfer line ii) Prevents possible spark caused by foreign material in the transfer line.

3) Remove the abort cyclone from the system

a) Purpose: i) Use the static pressure that was required for the cyclone to increase the allowable

differential pressure across the baghouse. b) Required actions:

i) Remove the abort cyclone from the system. c) Result:

i) Lowers the system pressure requirement. ii) Allows the baghouse to operate within the acceptable range of 0 – 6” w.g.




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Tier 2 Recommendations

4) Replace fan with a fan sized for 17,300 cfm @ 36” w.g., with a shallower performance curve. (Note: Cannot be done with the current filter)

a) Purpose:

i) To allow the system to maintain 5,500 fpm (clean air) with the filters blinded, to maintain proper suspension of the material in the ducting.

b) Required actions: i) Select a fan (probably a radial tipped fan or a radial blade with a flatter curve) sized for

the application ii) Implement recommendation 5 or 6 below.

c) Result: i) System is able to maintain proper conveyor velocity under all normal system conditions.

5) Add additional filter to the system

a) Purpose:

i) To reduce the interstitial velocity and the air-to-cloth ratio of the filters. b) Required actions:

i) Select a filter sized to accommodate the total airflow, in conjunction with the existing filter.

ii) Re-route ducting to accommodate the new filter along with the existing one. c) Result:

i) The ability to run a higher overall airflow, much longer filter life and reduced issues with discharging the material from the filter.

6) Replace the existing cyclone and filter with a filter over the metering bin sized for the

increased airflow.

a) Purpose: i) To reduce the interstitial velocity and the air-to-cloth ratio of the filters. ii) Simplify system layout iii) Reduce overall required static pressure

b) Required actions: i) Select a filter sized to accommodate the total airflow. ii) Remove the cyclone and existing filter, install new filter over metering bin. iii) Re-route ducting to accommodate the new filter along.

c) Result: i) The ability to run a higher overall airflow, much longer filter life and reduced issues with

discharging the material from the filter. ii) Reduction in required protection equipment.
