FINAL DESIGN PROJECT REPORT - University of...

FINAL DESIGN PROJECT REPORT

Dust Collector 09 Efficiency Improvements for the Nemak Windsor Aluminum Plant

A Formal Report Submitted to the Department of Civil & Environmental Engineering in

Partial Fulfillment of the Requirements for the Course 93-409 Project and Seminar

by Nadia Silvestri

I.D. 981 183 430

University of Windsor

Windsor, Ontario August 12, 2002

Final Project Report: DC 09 Efficiency Improvements Nadia Silvestri I.D.# 981 183 430

3255 Halpin Rd. Windsor, ON N8R 2B3 Phone (519) 735-2209 [email protected] August 12, 2002 Dr. Paul Henshaw Ph.D., P.Eng. Associate Professor, Civil and Environmental Engineering University of Windsor Windsor, ON N9B 3P4 Dear Dr. Henshaw, Please accept this report entitled “Dust Collector 09 Efficiency Improvements” as my submission to partially fulfill my 4th year final project requirements. The following report is intended to describe the purpose and objective of the report, how the analysis was completed, the significance and interpretation of obtained results, and conclusions and recommendations for the Nemak Windsor Aluminum Plant (WAP) based on the results of the analysis. This project has provided me with valuable experience and a greater knowledge of baghouse dust collectors, including the importance of various efficiency parameters including particle size distribution, air-to-cloth ratio, pressure drop, and inlet velocity. Also, this project has enabled me to apply and improve upon skills acquired through the undergraduate curriculum and my previous Co-op work term experiences. The practical experience of writing a technical report should also be an invaluable lesson for future work. It is my desire that this project will contribute to the continuous improvement of the quality, safety, production and business of WAP, as well as aid in environmental protection for years to come. Finally, I would like to thank Annik Roy-Girard, Joe Bondy and Dr. Iris (Xiaohong) Xu for their suggestions and guidance with this report and my project. Sincerely, Nadia Silvestri, ID # 981 183 430

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EXECUTIVE SUMMARY

A baghouse dust collector is an integral component to many industrial processes.

However, some baghouses in operation today were improperly designed from their inception, or

due to process modifications, can not operate at their required efficiency, which may cause

problems. Plant operators and owners of the Nemak Windsor Aluminum Plant (WAP) are faced

with one of three possible decisions concerning their inefficient baghouse: (i) allow the baghouse

to continue operating without modifications, (ii) upgrade the baghouse to a more efficient design

that can take advantage of high efficiency pleated filter cartridges instead of filter bags and

cages, or (iii) make minor design modifications in order to improve the operation of the existing

baghouse.

This report will focus on a combination of #2 and #3 and outline several cost-effective

ways that can have an immediate impact on overall performance, without the need for a full

rebuild of the baghouse. Topics for design modification will include ductwork configuration to

reduce or eliminate re-entrainment of collected particles to the collection system and distribution

of airflow from the inlet ducts located in the hopper. Each of these two parameters can inhibit

overall dust collection effectiveness and must be addressed so that other modifications to the

baghouse will have maximum benefit. The report will also discuss upgrading to higher

performance accessory items such as pleated filter elements. This type of filtering element has

been engineered to overcome original design flaws that lead to short bag life, improper filtering

and/or cleaning, and emissions.

Understanding these options, along with the benefits each offers in terms of time savings,

reduced energy consumption, and filtration enhancement, can enable the decision makers at the

WAP to evaluate solutions to their problem that provide maximum impact at minimal cost.

iii.


TABLE OF CONTENTS

LETTER OF SUBMITTAL EXECUTIVE SUMMARY TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES 1. INTRODUCTION 1.1 Background

1.1.1 Current Air Pollution Control System at WAP 1.1.2 Problem Identification

1.2 Project Scope and Objectives 2. LITERATURE REVIEW 2.1 Air Pollution Control Equipment 2.2 Fabric Filtration Theory: Pulse-Jet Baghouses 2.3 Particulate Collection Parameters 2.3.1 Motion of Suspended Particles 2.3.2 Differential Pressure 2.3.3 Can Velocity 2.3.4 Inlet Design 2.3.5 Air-to-Cloth Ratio 2.3.6 Other Important Parameters 2.4 Design Considerations 3. DUST COLLECTOR 09 EFFICIENCY IMPROVEMENT DESIGN 3.1 Design Process Steps 3.2 Sample Analysis Details and Testing Results 3.3 Design of Modified System 3.3.1 Proposed Design 3.3.1.1 Total Available Filtration Area 3.3.1.2 DC 09 Inlet Design 3.3.2 Performance Expectations 3.3.3 Cost Analysis 3.4 Conclusions and Recommendations ACKNOWLEDGEMENTS REFERENCES APPENDICES Appendix A: DC 09 Inlet Duct Test Summaries Appendix B: Primary Sand System Drawings BIBLIOGRAPHY

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LIST OF FIGURES P

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Figure 1: WAP Process Flow Chart and Exhaust System Figure 2: Bag Changes for DC 09 from 1995 to 2000 Figure 3: Characteristics of Particles and Particles Dispersoids Figure 4: Types of Air Pollution Control Equipment Figure 5: Pulse-Jet Baghouse Cleaning Function Figure 6: Theory of Particle Collection for Surface Filters Figure 7: Ladder Vane Baffling Used to Modify a Poor Baghouse Inlet Design Figure 8: Recommended Screw Conveyor Direction Figure 9: Steps in the Design Process for the DC 09 Efficiency Improvements Project Figure 10: Components of an EPA Method 5 Sampling Train Figure 11: DC 09 Inlet Duct Particle Size Distributions Figure 12: Primary Sand Cooler as a Fluidized Bed

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LIST OF TABLES P

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Table 1: Summary of Particulate Emission Control Techniques Table 2: Some Design Considerations for Baghouse Systems Table 3: Methods of the Ontario Ministry of the Environment Source Testing Code Used for DC 09 Inlet Testing Table 4: Nemak WAP DC 09 Inlet Duct Testing Results

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1. INTRODUCTION

1.1 Background

1.1.1 Current Air Pollution Control System at WAP

A Baghouse is a generic name for Air Pollution Control (APC) equipment that is

designed around the use of engineered fabric filter tubes or envelopes in the dust

capturing, separation or filtering process. Baghouse collectors can be found in virtually

every industry and have been used for industrial dust collection for over 50 years,

providing a full range of solutions from nuisance dust to extremely heavy dust loads. The

Nemak WAP, a facility in the automotive industry that uses state-of-the-art technology to

produce aluminum castings, has several baghouses that service various components of

its processes. Dust collector (DC) 09, which is the topic of this report, is an outdoor

baghouse that operates on a timed-pulse operation as opposed to a reverse air or shaker

system.

Currently, the sand coolers are vented to a Jetair Technologies model 2126-56 pulse

jet baghouse, then to a Buffalo size 805L-25 direct drive exhaust fan and discharged

through an 80 foot stack to atmosphere (Refer to drawing no. 114-ZW-WAP-012, sheet

002 in Appendix B). The actual design volume is 25,000 cfm at 100 F and the air-to-

cloth (A/C) ratio of existing equipment is 5.77/1 (cfm/ft2). Operation of the system results

in the pressure drop across the filter bags rising uncontrollably over a relatively short

period of time. The higher pressure drop limits the flow of exhaust to an undesirable

level reducing the throughput of the sand cooler. Corrective measures have been

undertaken unsuccessfully including the use of expensive Teflon member bags (Aldon

Sheet Metal, 2001).

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1.1.2 Problem Identification

DC 09 processes sand materials from the primary sand cooling system which cools

sand coming directly from the Thermal Sand Removal (TSR) ovens A through C. WAPs

process flow chart and exhaust system is illustrated in Figure 1 on the following page.

Recent changes to the process have introduced fine talc. Talc is used to coat the sand

cores before the liquid metal pouring process to: (i) ensure maximum sand removal, (ii)

decrease roughness, and (iii) increase flow through the aluminum castings. Soon after

the process modifications, the use of talc increased by approximately 45% with the

production of breather cores (these cores have a larger surface area) and a production

volume increase of about 65% (Bondy, 2002). The composition of the fine sand and talc

mixture being collected results in blinding of the filters (blinding refers to fabric blockage

by dust not being discharged by the cleaning mechanism, resulting in a reduced gas flow

due to the increased pressure drop across the filter media), creating a high differential

pressure, reduced capture velocity at the source as well as a decreased filter life (Roy-

Girard, 2002). Other system problems include a high A/C ratio (defined in section 2.3.5)

and an inadequate inlet design for DC 09 which may be largely contributing to re-

entrainment of the collected material, thus increasing the dust loading to the filter bags.

The purpose of the DC 09 efficiency improvement project is to evaluate methods

to improve the efficiency of the DC 09 system, as it currently requires premature filter

changes due to the Plant’s talcing process. The number of complete bag changes (DC

09 contains 184 bags) has increased since process modifications began in 1999. Prior

to the introduction of talc, bag changes were only necessary once every two to three

years. Figure 2 (page 4) demonstrates the increasing trend of required bag changes for

the subject baghouse.

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Sand Receiving Silo

Final Sand Cooling SystemSand Storage Silo DC 6

Core Making North Core Making SouthS2

S3 S4

S1

Glue

Assembly

Liner Glue

Assembly

A C

Liquid Aluminum Pouring System

B

DC 1

PE 2

DC 2

PE 3

PE 4

PE 1

INC.

PE 6

Liquid Treat Unit 2 Liquid Treat Unit 1

Liquid Aluminum (319) Receiver Liquid Aluminum (356) Receiver

TSR A TSR CTSR B

Initial Sand Cooling

DC 4INC.

PE 7

DC 3INC.

PE 5

Sand System

DC 9

PE 11

PE 8

PE 9

PE 12

PE 13

DC 11

DC 7

Shot Blast B

Casting Saw B

Heat Treat

Shot Blast C

Casting Saw A Casting Saw C

Shot Blast A

Finishing Dept. Jet Melter

REVERB MELTER

PE 10

Figure 1: WAP Process Flow Chart and Exhaust System

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4

01234

1995

1996

1997

1998

1999

2000

# of Complete Bag Changes

Figure 2: Bag Changes for DC 09 from 1995 to 2000 1.2 Project Scope and Objectives

The objective of this project is to conduct a theoretical investigation of the cause and

possible solutions to the efficiency problem of DC 09 for the Nemak WAP. This report includes

an evaluation of methods to maximize the efficiency of the subject dust collector by considering

parameters such as, but not limited to, dust collector size, filter media and A/C ratio.

This report is organized as follows:

Chapter 2 provides a brief introduction to each of the major types of particulate control

techniques, theoretical information regarding the pulse-jet type baghouse filtration system,

and design considerations; the reasons why this type of APC device is advantageous over

others are also outlined.

Chapter 3 describes the design process steps used for finding and selecting appropriate

baghouse parts and technology for this specific application. Also included in this chapter is

an interpretation of sample analysis results and a proposed design solution based on an

evaluation of alternatives.


2. LITURATURE REVIEW

2.1 Air Pollution Control Equipment

A preliminary selection of suitable particulate emission control systems is generally based on knowledge of four items: particulate concentration in the system to be cleaned, the size distribution of the particles to be removed, the gas flow rate, and the final allowable particulate emission rate (Flagan and Seinfeld, 1988a).

“Particulate matter (or particulates) are very small-diameter solids or liquids that remain

suspended in exhaust gases and can be discharged in the atmosphere” (Cooper and Alley,

1994a). Materials handling processes, combustion processes or gas conversion reactions in the

atmosphere can form particulate. An important characteristic of suspended particles is the size

distribution of the particles. Figure 3 on the following page illustrates the range of sizes of

common particle dispersoids.

Aside from adverse environmental impacts such as reduced visibility due to smog or

haze, plant damage due to deposition and alteration of local weather, particulates can also affect

human and animal health in several ways. “Particulates in the size range from 0.1 to 10 microns

can penetrate deep into lungs where they are then deposited in the respiratory bronchioles or

alveolar sacs” (Cooper and Alley, 1994b). To continually improve global air quality, every country

needs to enforce the implementation and monitoring of particulate control equipment where

applicable.

APC devices that are often used to control the adverse environmental impact of

particulate matter in the atmosphere consist of:

Settling chambers - gravity

Cyclones - inertial separation Filtration - inertial separation and diffusion Electrostatic precipitators - electrostatic forces Wet Scrubbers - inertial separation and diffusion (Heinsohn and Kabel, 1999a)

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Figure 3: Characteristics of Particles and Particles Dispersoids (Lapple, 1961)

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Settling chambers are simply large chambers that enable particles to settle into a hopper

by gravity. The configuration of a typical settling chamber can be seen in Figure 4(a).

Cyclones remove particulate from a gas stream through a centrifugal force and inertia that

causes the particles to collide with the outer wall and slide to the bottom of the device as depicted

in Figure 4(b). Cleaned gas moves upward in a small inner spiral and exits from the top while

the collected particles exit from the bottom through a rotary valve. The wet scrubber pictured in

Figure 4(c) is an APC device that employs the principles of interception and impaction of dust

particles by droplets of water. There are many types of scrubber designs that are distinguished

according to the liquid contacting mechanism employed.

An electrostatic precipitator (ESP) uses the application of electrostatic forces that act only

on the particles and not on the entire air stream. First, contaminated air flowing between

electrodes is ionized, followed by the charging, migration and collection of the particles on plates

of opposite charges. Finally, the contaminants are removed from the plates by being knocked or

washed off and collected in the bottom of the ESP. The last type of particulate collection

equipment is a fabric filtration unit (baghouse) that operates by forcing dust-laden air through

cloth bags. Air passes through the fabric of the bags, particles accumulate on the cloth while

clean air is exhausted to the atmosphere. Dust is periodically dislodged from the filter bags by

shaking or reversing the airflow in the system. Figure 4(d) illustrates a typical pulse-jet

baghouse. A summary of the above mentioned particulate emission control devices, including

advantages and disadvantages of each type, is presented in Table 1 on page 9.

A baghouse filtration system remains to be the most attractive option for the specific

application of dust removal at WAP based on its versatility, variable size, and the fact that the

collection efficiency is practically independent of the volumetric flow rate (Heinsohn and Kabel,

1999b). “The advantages of fabric filter baghouses clearly outweigh their limitations, as they

currently represent close to 50% of the industrial gas-cleaning market” (Flagan and Seinfeld,

1988b).


(a) (b)

(c) (d)

Figure 4: Types of Air Pollution Control Equipment (a) Settling chamber; (b) Tangential inlet vertical reverse flow cyclone; (c) Venturi scrubber; (d) Pulse-jet baghouse

(Flagan and Seinfeld, 1988c) and (Heinsohn and Kabel, 1999c)

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Table 1: Summary of Particulate Emission Control Techniques Device

Minimum particle size

(um)

Efficiency (%)

(mass basis) Advantages Disadvantages

Gravitational settler

> 50 < 50 Low-pressure loss Simplicity of design and

maintenance

Much space required Low collection efficiency

Cyclone 5 – 25 50 – 90 Simplicity of design and maintenance Little floor space required Dry continuous disposal of

collected dusts Low-to-moderate pressure

loss Handles large particles Handles high dust loadings Temperature independent

Much head room required Low collection efficiency of

small particles Sensitive to variable dust

loadings and flow rates

Wet collectors Spray towers Cyclonic Impingement Venturi

> 10 > 2.5 > 2.5 > 0.5

< 80 < 80 < 80 < 99

Simultaneous gas absorption and particle removal Ability to cool and clean

high- temperature, moisture-laden gases Corrosive gases and mists

can be recovered and neutralized Reduced dust explosion risk Efficiency can be varied

Corrosion, erosion problems Added cost of wastewater

treatment and reclamation Low efficiency on

submicron particles Contamination of effluent

stream by liquid entrainment Freezing problems in cold

weather Reduction in buoyancy and

plume rise Water vapor contributes to

visible plume under some atmospheric conditions

Electrostatic precipitator

< 1 95 – 99 99 + % efficiency obtainable Very small particles can be

collected Particles may be collected

wet or dry Pressure drops and power

requirements are small compared with other high- efficiency collectors Maintenance is nominal

unless corrosive or adhesive materials are handled Few moving parts Can be operated at high

temperatures (573 to 723 K)

Relatively high initial cost Precipitators are sensitive

to variable dust loadings or flow rates Resistivity causes some

material to be economically uncollectable Precautions are required to

safeguard personnel from high voltage Collection efficiencies can

deteriorate gradually and imperceptibly

Fabric filtration < 1 > 99 Dry collection possible Decrease of performance is

noticeable Collection of small particles

possible High efficiencies possible

Sensitivity to filtering velocity High-temperature gases

must be cooled Affected by relative

humidity (condensation) Susceptibility of fabric to

chemical attack (Flagan and Seinfeld, 1988d)

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2.2 Fabric Filtration Theory: Pulse-Jet Baghouse As indicated beforehand, the fabric filtration process consists of three phases. First,

particles collect on individual fibers by inertial separation and diffusion. Then particles

accumulate on previously collected particles, bridging the fibres (this substantially increases the

collection efficiency). Finally, the collected particles form a dust layer, usually referred to as

cake, that acts as a packed bed filter for the incoming particles (Flagan and Seinfeld, 1988e). In

a baghouse unit with high upward velocities, mechanical separation of the fine submicron dust

can occur, creating a dustcake structure that is very dense. A dense dustcake creates a greater

resistance to airflow and higher differential pressures, therefore the dust layer must be dislodged

periodically into the hopper at the bottom of the baghouse to regenerate the fabric bag.

More specifically, in a pulse-jet system baghouse, dust is collected on the outside of the

bags. Compressed air is injected (pulsed) into the top of the bags and travels internally the

length of the bag accelerating and expanding the bag away from its supporting cage. After

expansion of the bag occurs, dustcake is separated from the fabric, falls to the dry dust hopper

and is discharged through a bottom valve. Figure 5 on the following page illustrates the basic

steps for high efficiency particulate collection in a pulse-jet baghouse.

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Figure 5: Pulse-Jet Baghouse Cleaning Function

2.3 Particulate Collection Parameters Cooper and Alley (1994c) stated that “Design and operation of particulate pollution control

equipment require a basic understanding of the characteristics of [the] particles [being collected]

and of the dynamics of [the] particles in fluids”. The significance of the following baghouse

parameters related to WAPs DC 09 efficiency problem will be discussed in this section of the

report:

Motion of suspended particles Differential pressure Can velocity (defined in section 2.2.3) Inlet design A/C ratio; and Other important parameters including bag-to-cage fit and hopper screw conveyor

direction


2.3.1 Motion of Suspended Particles

A suspended particle is constantly and randomly bombarded from all sides by

molecules of the fluid. If the particle is very small, such as the talc in DC 09, the hits it

takes from one side will be stronger than the bumps from the other side, causing it to

jump. These small random jumps are what make up Brownian motion (Encyclopedia

Brittanica, 1968). “[Since]… Brownian motion is more pronounced the smaller the

particle, [it is expected]… that devices based on diffusion as the separation mechanism

will be most effective for small particles” (Flagan and Seinfeld, 1988f).

2.3.2 Differential Pressure

Differential pressure (∆P) represents the difference between static pressures

measured at the inlet and outlet of a component, compartment, or device, or it is the

pressure drop across a component or device located within the gas stream (i.e. between

the dirty and clean sides of filter bags and tubesheets). For the gas stream flowing from

point 1 to point 3 in Figure 6 on the following page, the velocity of flow is relatively

constant because of gas expansion due to pressure drop, therefore the particles of gas

are left behind. Consequently, there is a reduction in pressure as a result of the frictional

resistance to flow through the filter cake and the filter medium. If the dust cake that

accumulates on the filter bags is not adequately removed, the pressure drop across the

system will increase to an excessive amount. This is the problem being experienced in

DC 09.

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1 2 3

Cleaned gas

Fluid Flow

Dirty gas stream

Figure 6: Theory of Particle Collection for Sur(http://even.tamuk.edu/air/courses/5328/sec7/section7/fa

2.3.3 Can Velocity

“Can velocity is the upward air stream speed passing

collector with the filter elements suspended from the

horizontal cross-sectional plane of the collector housing at

Group, 2000a). Can velocities that are too high can cause

is a pulse-jet collector that cleans “on-line” and has its in

case, a large can velocity may be a significant problem.

A solution to the problem of a large can velocity is

pleated filters have more filter area than traditional bags, t

can be reduced, therefore creating more open area for

velocity. Positioning the inlet to a point above the bottom o

solution to a high can velocity.

13

Filter medium

face Filters bric_filters1.htm)

between the filters in a dust

tubesheet, calculated at the

the bottom of the filters” (BHA

high pressure drops. DC 09

lets below the filters. In this

to install pleated filters. Since

he total number of filters used

airflow and reducing the can

f the filters is another possible


2.3.4 Inlet Design

The importance of proper inlet design is extremely significant as it relates to the

operation of a baghouse dust collector. If airflow is directed into the bottom of the hopper

area, this can cause particulate in the hopper to swirl upward and to be re-entrained into

the filter media. When combined with the incoming material, the material re-entrained

from the hopper produces a higher grain loading on the filter bags.

Enlargement of the inlet duct prior to the hopper can reduce the inlet velocities

on entry. Inside the hopper, the installation of “ladder vane” baffling seen in Figure 7

creates a more uniform velocity profile in the hopper. Better distribution of inlet air

minimizes the re-entrainment potential and reduces the amount of material carried to the

filter bag surface. These baffles are inexpensive and easy to install for most baghouse

designs.

Figure 7: Ladder Vane Baffling Used to Modify a Poor Baghouse Inlet Design (BHA Group, 2000b)

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2.3.5 Air-to-Cloth (A/C) Ratio

One of the most important aspects in design that is sometimes overlooked is a

proper A/C ratio. This ratio is an expression that shows how much air volume is being

handled versus how much cloth area is available in the baghouse. More specifically, it is

defined as the ratio between acfm flowing through a filter and the filter area available (ft2).

This can also be thought of as the velocity of the gas passing through the filter in feet per

minute (fpm).

It should be noted that in the metric system the term used is “filtration velocity”

(instead of “air-to-cloth ratio”) and is defined as the relation between the m3/min. of air

flowing through a filter and the m2 of filter area available (BHA Group, 2000c). Typical

A/C ratios and filtration velocities for pulse-jet baghouses are 5.0 to 6.0:1 or 1.52 to 1.83

m3/m2/min. Too high a ratio can contribute to inefficient operation of the baghouse.

2.3.6 Other Important Parameters

Other important parameters that contribute to the proper operation of a baghouse

include bag-to-cage fit and screw conveyor direction. A major cause of failures on pulse-

jet systems is improper fit of the filters to the support cage. For proper performance of

pulse-jet filters, the fit relationship between the bag and the cage is critical.

Consequently, filters that are too loose or too tight will severely limit collection efficiency

and lead to premature failure. A related area is the importance of the proper support

cage to support the filter bag. There are many types of cages in the marketplace,

however, proper care must be taken to ensure that the cage construction will properly

support the filter bag as well as optimize cleaning and efficiencies. Important variables

that should be reviewed include the number of vertical wires used and the type of ring

spacing employed.


Finally, to prevent re-entrainment of the collected hopper dust into the baghouse,

correct trough hopper screw conveyor direction is essential. As the collector loads the

screw conveyor, the material depth in the screw conveyor increases. When the mass of

material is moved toward the dirty inlet (the point of highest velocity in the hopper) it often

becomes airborne and is carried back to the filter bags. This increases the recirculating

load in the collector and creates artificially high pressure drops (BHA Group, 2000d).

Figure 8 illustrates the recommended screw conveyor direction to ensure that the mass

of material collected is moved away from the gas entrance, eliminating the recirculation

of collected material.

Figure 8: Recommended Screw Conveyor Direction (BHA Group, 2000e)

DC 09 currently has two inlets located on one side of the hopper. One inlet is

located near the discharge point, and the other is located on the opposite end of the

hopper. It is very possible that this is a major contributor to the high dust loadings on the

blinded filter bags.

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2.4 Design Considerations Baghouse design typically involves optimization of the filtering velocity in order to balance

capital costs (baghouse size) with operating costs (pressure drop). “Major factors that affect the

selection of the design [filtering velocity] include prior experience with similar dusts, fabric

characteristics, particle characteristics, and gas stream characteristics” (Cooper and Alley,

1994d). Another design consideration that will be discussed in the following text includes

minimization of energy usage.

It is well known that there are many advantages of pulse-jet over reverse-air and shaker

cleaning methods. One such advantage is the tolerance for high filtering velocities that reduce

the net cloth area required, thus reducing the required size of the baghouse and capital costs.

Fabric characteristics are an extremely important consideration when designing a baghouse.

Certain fabrics will only be effective at collecting particles if they are suited for the temperature

and chemical nature of the gas. This parameter will be discussed more in section 3.4.1

(Proposed Design) of the report.

Particle characteristics also dictate the type of fabric to be used in the filtration process.

Specific information pertaining to the particulate matter being collected and gas stream

characteristics in DC 09 is presented in section 3.2 (Sample Analysis Details and Testing

Results) of the report.

Minimization of energy use should also be considered and can be accomplished through

the following:

Better equipment design leading to increased efficiencies

Proper equipment selection for the specific application; and Optimization of equipment operation through frequent evaluation of equipment performance (Cooper and Alley, 1994e)

Since DC 09 was not originally designed to handle the fine talc material that is being processed

through the primary coolers as a result of process modifications, the energy being used to

operate the baghouse is most likely much higher than anticipated. Other design considerations

for baghouse systems are summarized in Table 2 on the following page.

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Table 2: Some Design Considerations for Baghouse Systems Consideration Comments

Temperature and Humidity

Fabrics have different maximum allowable temperatures Operation above these temperatures can rapidly degrade bags Low temperatures can cause condensation of acid and/or blinding of the fabric with wet dust Wet particulate matter can bridge over in hoppers As temperatures increase, both gas viscosity and gas volumetric flow rate increases - both tend to increase pressure drop requirements

Chemical Nature of Gas Different fabrics have different resistances to acids or alkalies

Fire/Explosion Some fabrics are flammable; some dusts are explosive

Bag Arrangement It is important to consider maintenance; arranging bags in

straight rows is better than dense packing Providing walkways every few rows might be a very good investment Spacing of a few inches between bags is sufficient operating clearance

Dust Handling The dust removal rate (mass and volume), conveyor system

(pneumatic tube or screw conveyor), and hopper slope (dust must flow out by gravity) should all be considered

Fan Location A clean-air-side fan (a “pull-through” baghouse) saves on

maintenance of the fan and allows the use of a more efficient fan with backward-curved blades - however, this method requires an airtight structure - furthermore, a stronger structure is generally required

(Cooper and Alley, 1994f)


3. DUST COLLECTOR 09 EFFICIENCY IMPROVEMENT DESIGN

3.1 Design Process Steps

The purpose of this section is to outline the design process steps used to define, evaluate and

recommend a technologically and economically feasible solution to the DC 09 efficiency problem.

Figure 9 illustrates the major steps taken in the design process, followed by a more detailed description.

Preliminary problem definition

Lab analysis

Preliminary data

Final problem definition

Dec. point 1

Alternative 1

Alternative 2

Alternative 3

Alternative 5

S.P.

S.P.

S.P.Alternative 4

Dec. point 2 Final design Preliminary cost

estimatePreliminary

process design

S.P.

Figure 9: Steps in the Design Process for the DC 09 Efficiency Improvements Project (Cooper and Alley, 1994g)

The following discussion relates to the design process steps outlined in Figure 9. The

preliminary problem in the DC 09 baghouse situation is that the system currently requires premature

filter changes due to the Plant’s talcing process. Preliminary data was collected, including process flow

sheets, baghouse drawings, and related literature, in order to familiarize with the process, ductwork and

dust collection systems. Lab analysis to determine particle size distribution (PSD), dirty filter bag

properties, and dust loadings from the inlet duct in DC 09 had previously been conducted by third-party

companies. The preliminary data and lab analysis results were then examined to determine the route

cause of talc entry to DC 09 and the severity of the problem.

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Based on the above design steps a final problem definition was established. The

composition of the sand and talc mixture being collected is such that it is blinding the filters,

creating high differential pressure - limiting the exhaust flow and reducing the throughput of the

sand cooler, reduced capture velocity at the source as well as a decreased filter life. The final

problem definition established the design basis for the project. Research was then conducted on

pulse-jet baghouse filtration systems including several important parameters as discussed

previously in sections 2.2 (Fabric Filtration Theory: Pulse-Jet Baghouses) and 2.3 (Particulate

Collection Parameters) of the report, as well as alternatives to a baghouse for dust collection

purposes.

At decision point 1 (D.P.1), alternative control techniques were evaluated for their

suitability and capability of efficiently collecting the desired particles, and economic feasibility for

the WAP. Alternatives 1 through 5 are discussed below, including their subproblems (S.P.) and

rationale for their dismissal.

Alternative 1: Cyclone as a pre-collector

The low capital cost and nearly maintenance-free operation of a cyclone makes it an

attractive option for particulate removal from a gas stream. An additional benefit to cyclones is

that they can operate at high temperatures, pressures and high dust concentrations. The

implementation of a cyclone as a pre-collector to the pulse-jet baghouse could cause a reduction

in the amount of dusts reaching DC 09 by as much as 80%. However, the remaining dust will

consist of mostly talc and other fine particles, which are more likely to bleed through the fabric.

Also, a denser dust cake on the filter fabric will result, leading to high differential pressures,

consequently not solving the original problem. Disposal of the collected particulate matter would

be the same as what WAP is currently doing for their baghouse operation.

20


Alternative 2: Electrostatic Precipitator (ESP)

ESPs have very high efficiencies, even for very small particles which could make this

alternative an attractive solution. However, subproblems to this alternative include high capital

costs, space constraints and high operating costs at very high efficiencies (which is what WAP is

looking for). Also, ESPs are typically not flexible to operation changes. Considering the amount

of material being processed by the primary sand coolers and exhausted to the pollution control

device ultimately depends on production, this is not a feasible solution to the problem. Disposal

of the collected particulate matter would be the same as what WAP is currently doing for their

baghouse operation.

Alternative 3: Particulate Scrubber

Although there are many advantages of scrubber systems for particulate removal, there

are too many disadvantages related to WAPs process that justify abandonment of this alternative

as a practical solution. First, since the APC device would have to be situated outside due to

space constraints, protection against freezing in the winter months is required with this type of

collection equipment. Second, process temperatures are very high and it is likely that mist would

evaporate instantaneously. Any combination of a scrubber system with the current baghouse

system would not be feasible since moisture is catastrophic for filter bags. Finally, effluent liquid

can create water pollution problems and disposal of waste sludge may be very expensive.

21


22

Alternative 4: Settling chamber as a pre-cleaner

The low capital and operating costs in addition to low pressure drops imply that a settling

chamber would be an appealing option for particulate removal from a gas stream. Settling

chambers, however, typically remove particles with diameters greater than 100 microns, which

does not represent the particle size distribution that the APC device would be required to handle.

Disposal of the collected particulate matter would be the same as what WAP is currently doing for

their baghouse operation.

Alternative 5: Pulse-jet baghouse with design modifications

As previously mentioned in section 2.1, baghouse filtration systems are very versatile

and their collection efficiency is practically independent of the volumetric flow rate (which is highly

variable in WAPs process). Collection of small particles with high efficiencies is generally

observed with this type of APC device, provided it is properly designed for the specific application

it services. By modifying the current baghouse design so that the total available filtration area is

increased, inlet gas stream is evenly distributed among the filter bags, and the collected

particulate is properly removed to avoid re-entrainment, the pressure drop in the system will most

likely decrease. Disposal of the collected particulate matter would be the same as what WAP is

currently doing for their baghouse operation.

Finally, alternative 5 was selected at D.P.1. D.P.2 involves the selection of baghouse

products and preliminary design modifications, which are detailed in section 3.3.1 (Proposed

Design). A preliminary cost estimation and cost savings for WAP are detailed in section 3.3.3

while the recommended final design is presented in the later sections of the report.


3.2 Sample Analysis Details and Testing Results On February 13 and 15, 2001, on-site sampling for total suspended particulate (TSP) and

PSD of the DC 09 inlet air stream was conducted by Dillon Consulting Limited (Dillon). Table 3

outlines the sampling methodology used to obtain the TSP and PSD testing results while Figure

10 illustrates the components of an EPA Method 5 sampling train.

Table 3: Methods of the Ontario Ministry of the Environment Source

Testing Code Used for DC 09 Inlet Testing Method Description

1 Location of sampling site and sampling points

2 Determination of stack gas velocity and volumetric flow rate

3 Determination of molecular weight of dry stack gas

4 Determination of moisture content of stack gases

5 Determination of particulate emission from stationary sources (Dillon, 2001a)

The results of the Method 5 testing and estimated loadings tests performed on the DC 09

inlet duct are summarized in Table 4 on the following page.

Figure 10: Components of an EPA Method 5 Sampling Train (Heinsohn and Kabel, 1999d)

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Table 4: Nemak WAP DC 09 Inlet Duct Testing Results

(Dillon, 2001b) Note: Method 5 Test #1 was performed during abnormal process operating conditions

On March 21, 2001 two samples of ground mineral powder from DC 09 were sent to TSL

Professional Services for analysis to determine percent talc by volume. The submitted samples

were analyzed by Plasma Spectrometer and the results obtained indicated that talc represents

approximately 2% of the weight of dust being collected.

Similarly, in March of 2001, a filter analysis was performed on two dirty jet air filter bags

from DC 09. The filter analysis indicted that the dirty weight was more than double the original

weight of the clean filter bag (16oz/sq.yd) and that even though this weight reduced by 22% after

pulsing, an abundant amount of dust remained on the filters. Also, the measured permeability of

the dirty filter was very low. The results of the analysis indicated that the filters were probably

experiencing the early stages of blinding, shortly after bag changes (Filterfab Inc., 2001).

24


The particle size distributions of the particulate matter in the inlet gas is shown in Figure

11 on the following page. The results from the two PSD tests indicate that the 50% cut

aerodynamic diameter (Dp50) fell in the range of five to six microns. It can also be seen in Figure

11 that two diverse particle streams exist in the inlet gas, thereby indicating a bimodal particulate

distribution. The larger particles are represented by fine grains of sand while the dark, fine dust

(talc) portrays the smaller particulate (Dillon, 2001c). Unfortunately, the flow of sand into the

primary sand coolers is not monitored and is irregularly dependent on production, therefore, no

correlation could be made to the test results. Additional summaries of the DC 09 inlet duct tests

are provided in Appendix B of the report.

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26

Figure 11: DC 09 Inlet Duct Particle Size Distributions (Dillon, 2001d)


3.3 Design of Modified System 3.3.1 Proposed Design

When DC 09 was originally installed, it was not intended to handle very fine,

submicron particles. Process modifications have proven to increase maintenance costs

to continually reduce the high differential pressure exhibited in the current system. The

preceding analysis of the DC 09 collection efficiency problem prescribes the requirement

for a modified baghouse design.

3.3.1.1 Total Available Filtration Area

Filter area should be increased in order to reduce the average dust load

being experienced on each filter bag, to reduce the A/C ratio and to operate at

significantly lower differential pressures. Pleated filter elements provide a simple

retrofit for upgrading existing dust collection systems and improving problem

systems. A pleated filter element is a one-piece pleated product of spun bonded

polyester media and is a direct replacement for traditional filter bags and cages.

This media resists surface penetration of particulate, dramatically increasing

efficiencies while operating at significantly lower differential pressures than felted

or woven materials.

Since the media is pleated and molded into a filter element, it has the

potential of increasing filtration surface area over bags by 100-200+%,

depending on existing bag sizes. The unique spun bonded media used in the

manufacture of pleated filter elements is unlike traditional felt fabric. It has a tight

pore structure and rigid physical properties that allow it to hold a pleat without the

need for supporting backing material. Because of this, as much as three times

more filtration area can be installed in the same tube sheet hole to replace a

conventional bag and cage.

(wysiwyg://138/http://www.stormloader.com/ebjco/pleated.htm)

27


Due to the ability to increase filtration area so dramatically, pleated filter

elements provide a very economical alternative to having to purchase new

equipment or spend significant capital funds. They also provide other substantial

side benefits that make this a very cost effective way to improve the performance

of existing equipment without the need for major changes.

3.3.1.2 DC 09 Inlet Design

Re-entrainment of the collected particles in the hopper should also be

avoided to improve the efficiency of the system. To accomplish this, two design

changes should be implemented. The first modification involves the DC 09 inlet

ducts. The inlet that is currently located close to the discharge point (refer to

drawing no. 114-ZW-WAP-012, sheet 011 in Appendix B) should be relocated to

the opposite end of the hopper. This new configuration will ensure that the mass

of material collected is moved away from the gas entrance, eliminating the

recirculation of collected materials (refer to Figure 8 on page 16).

The proposed design up to this point suggests that both inlet ducts will

now be located on one end (opposite sides) of the baghouse hopper. To prevent

abrasion and exceedingly high dust loadings of the bags closest to the inlets, the

second design modification consists of a ladder vane baffling system, such as

the one illustrated in Figure 7 on page 14, should be installed. Better distribution

of the inlet air stream will also minimize the re-entrainment potential, therefore

reducing the amount of material carried to the filter bag surface. As pointed out

earlier, these baffles are inexpensive and easy to install.

28


3.3.2 Performance Expectations

Improvements can be expected for various particulate collection parameters

once the proposed design modifications are implemented. The A/C ratio will improve as

shown below:

Current Total Cloth Area (ft2) = {[Bag diameter (in.) x π x Bag length (in.)] ÷ 144} x Total No. of bags = {[6 x π x 145] ÷ 144} x 184 = 3,492.40 ft2 Current Net A/C ratio (ft3/min/ft2) = Inlet gas flow rate (acfm) ÷ Total cloth area (ft2) = 23,275 acfm ÷ 3,492.40 ft2

= 6.66 ft3/min/ft2 The average flue gas flow rate based on DC 09 inlet duct testing results (Table 4 on

page 24) is 23,275 acfm (actual cubic feet per minute). Assuming it is desirable to

double the available collection surface area in DC 09 so that annual bag changes are

necessary as opposed to quarterly:

No. of required pleated filter bags = Ac (ft2) ÷ Aper bag

= 2(3,492.40 ft2 ) ÷ 49.2 ft2 per bag = 142 bags The total cloth area of 49.2 ft2 per bag for pleated filters is based on a snap band top filter

that fits in a 6.375 inch hole and is 2 meters long (McConnell, 2002). It should be noted

that 42 less filter bags are required to double the available cloth-collection area.

Modified Total Cloth Area (ft2) = 49.2 ft2 x 142 bags

= 6,986.40 ft2 Modified Net A/C ratio (ft3/min/ft2) = 23,275 acfm ÷ 6,986.40 ft2

= 3.33 ft3/min/ft2

29


3.3.3 Cost Analysis

In addition to energy savings due to lower differential pressures, the cost savings

of the new modified design are significant. Now that the dimensions, materials and

operating parameters of the DC 09 system have been determined, a cost analysis can be

performed to determine the potential cost savings.

If the current operation continues (one year):

Cost ($CAN) = 1 year x No. of bag changes x [(Cost per bag x No. of bags) + labour]

∴ Cost ($CAN) = 1 year x 4 bag changes per year x [($140.40/bag x 184 bags) + $8,500.00] = $ 138,070.40

If the modified design is implemented (one year):

Cost ($CAN) = Cost of ladder vane + Installation + Cost to relocate one inlet duct + (Cost per pleated filter x No. of pleated filter bags) + labour

∴ Cost ($CAN) = $2,500.00 + $10,000.00 + $7,000.00 + ($79.00/bag x 142 bags) + $8,500.00 = $39,218.00

Even including material and installation costs of the new equipment, the first

year’s savings (estimated) will add up to $98,852.40. It should be noted that cost savings

are based on the assumption that the cost of operating DC 09 is approximately the same

for the current and modified design. Each additional year, the cost savings will be

$118,352.40 as calculated below (not including required annual maintenance work on the

equipment itself, only bag change costs):

Cost savings per year = $138,070.40 – 1 bag change/year x [($79.00/ bag x 142 bags) + $8,500.00] = $118,352.40

This means that the Plant could save up to 85.72% the cost they are currently spending

to maintain the DC 09 collection system.

30


31

3.4 Conclusions and Recommendations

On the basis of the testing results obtained from the analysis of the DC 09 system at the

Nemak WAP, it is concluded that the current particulate collection device servicing the primary

sand coolers is neither adequate nor economical for the specific dust collection application. The

following is a summary of the specific conclusions relating to tests conducted on various DC 09

parameters and evaluation of the five particle collection alternatives:

The low permeability of the blinded filter bags in addition to the high differential pressure being experienced is causing the production throughput to be reduced. Particulate loadings are highly variable and unpredictable. A pulse-jet baghouse filtration system remains to be the best option for the specific application of dust removal, particularly due to the fact that it is the only collection device completely independent of volumetric flow rate.

Recommendations:

After evaluating the alternatives, it is believed that the following recommendations are the

most technologically and economically feasible solution to the efficiency problem of DC 09.

1. Increase the total available cloth-collection surface area by replacing the currently used expensive Teflon coated filter bags with pleated filter tubes.

2. Install a ladder vane flow separator at the inlet to reduce re-entrainment of collected particles and enhance settling properties of the finer particulate in the system.

3. Relocate the inlet closest to the hopper discharge valve to the opposite end of the baghouse. This will promote movement of the mass of material collected away from the gas entrance. Greater gas flow and extended bag life is achievable with this recommendation. Screw conveyor wear is also reduced resulting in less maintenance needed on the equipment.

Additional recommendations are made for possible future DC 09 investigations or projects:

1. Preventing pollutants from being produced in the first place is cheaper than removing them from a discharge process gas stream. Therefore, investigate alternatives to talc as a coating for the sand cores. Other possibilities include increasing resin content to fill voids and decrease roughness of the castings, or liquid core wash.

2. Investigate the opportunity and technologies available for removal of the talc from the fluidized bed shown in Figure 11 before it is exhausted to DC 09.

Figure 11: Primary Sand Cooler as a Fluidized Bed


ACKNOWLEDGEMENTS

The author sincerely thanks Dr. Iris Xu for her guidance and assistance

throughout the development of this project. In addition, thanks is extended to Mrs. Annik

Roy-Girard, P. Eng at the Nemak Windsor Aluminum Plant and Mr. Joe Bondy, Ford

Essex Engine Plant, for their continued support and dedication to helping the author

acquire the necessary information to complete this report. The technical assistance and

suggestions of Mr. Pierre Lambert and Mr. Larry McConnell from BHA Group Inc., as

well as Mr. Mike Mahon from Aldon Sheet Metal, is also sincerely appreciated.

32


REFERENCES

BHA Group Inc. (2000) BHA Parts and Services Catalog / Troubleshooting Guide. BHA Group, Inc. Cooper, C. David and Alley, F.C. (1994) Air Pollution Control: A Design Approach. Illinois: Waveland Press, Inc. Flagan, Richard C. and Seinfeld, John H. (1998) Fundamentals of Air Pollution Engineering. New Jersey: Prentice-Hall Inc. Gnyp, Alex W., St. Pierre, Carl C., and Smith, Doug S. (updated by Paul Henshaw) (2002) A Guide to Technical Writing. University of Windsor. Heinsohn, Robert Jennings and Kabel, Robert Lynn (1999) Sources and Control of Air Pollution. New Jersey: Prentice-Hall Inc. Lapple, C.E. (1961) The Size of Common Aerosols. Stanford Research Institute Journal, Vol.5 pp. 322 – 325.

33


34

Bondy, Joe. Nemak W.A.P., personal communication (January – May, 2002) Kitchen, Al. Nemak Engineering Centre (N.E.C.) (January – February, 2002) Mahon, Mike. Aldon Sheet Metal, personal communication (July, 2002) McConnell, Larry. BHA Group Inc., personal communication (July, 2002) Roy-Girard, Annik. Nemak W.A.P., personal communication (January – July, 2002) Waddle, Aaron. BHA Group Inc., personal communication (February, 2002) END NOTES 1. Report: Analysis of Baghouse Requirements (DC-09) by Douglas K.Hook, P.Eng, Advanced Integrated Resources Inc. 2. FILTERFAB Inc. test results by Marty Agnino, Vice President, Plant #2 FILTERFAB QUEBEC 3. Report: Analysis of Baghouse Requirements (DC-09) by Douglas K.Hook, P.Eng, Advanced Integrated Resources Inc.

Pleated air filter bags wysiwyg://138/http://www.stormloader.com/ebjco/pleated.htm MAC Equipment – Cyclone separators and Dust collectors http://www.macequipment.com/prod_cyclones.html Air Cleaning Technologies, Inc. – Baghouse Collectors http://www.aircleaningtech.com/cyclone.html Sly Inc. – TubeJet PulseJet Collectors http://www.slyinc.com/tubejet.htm TAR TEK – Baghouse Monitors, Broken Bag Detectors, Particulate & Mass Monitors http://www.tartek.com/bm910.htm


APPENDIX A

DC 09 Inlet Duct Test Summaries (Dillon Consulting Ltd.)

35


APPENDIX B

Primary Sand System Drawings

Sand System – Primary: DC-09 Drawing Index

Drawing Number Sheet # Description of Drawing 114-ZW-WAP-012/1F103A0016 002 General Arrangement 114-ZW-WAP-012/10103P1050 011 Exhaust Blower & Duct Assembly

44


BIBLIOGRAPHY

BHA Group Inc. (2000) BHA Parts and Services Catalog / Troubleshooting Guide. BHA Group, Inc. Cooper, C. David and Alley, F.C. (1994) Air Pollution Control: A Design Approach. Illinois: Waveland Press, Inc. Flagan, Richard C. and Seinfeld, John H. (1998) Fundamentals of Air Pollution Engineering. New Jersey: Prentice-Hall Inc. Gnyp, Alex W., St. Pierre, Carl C., and Smith, Doug S. (updated by Paul Henshaw) (2002) A Guide to Technical Writing. University of Windsor. Heinsohn, Robert Jennings and Kabel, Robert Lynn (1999) Sources and Control of Air Pollution. New Jersey: Prentice-Hall Inc. Lapple, C.E. (1961) The Size of Common Aerosols. Stanford Research Institute Journal, Vol.5 pp. 322 – 325. Encyclopedia Brittanica, 1968 Report: Analysis of Baghouse Requirements (DC-09) by Douglas K.Hook, P.Eng, Advanced Integrated Resources Inc. Pleated air filter bags wysiwyg://138/http://www.stormloader.com/ebjco/pleated.htm MAC Equipment – Cyclone separators and Dust collectors http://www.macequipment.com/prod_cyclones.html Air Cleaning Technologies, Inc. – Baghouse Collectors http://www.aircleaningtech.com/cyclone.html Sly Inc. – TubeJet PulseJet Collectors http://www.slyinc.com/tubejet.htm TAR TEK – Baghouse Monitors, Broken Bag Detectors, Particulate & Mass Monitors http://www.tartek.com/bm910.htm

47

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