After assisting the client in addressing these problems, ETS conducted a program to flow balance each system.  After completing the system balancing, we provided a schematic with adjusted (measured) design flows, static pressure measurements, system fan amps, and dust collector data along with the properly adjusted damper settings for each balanced system.  This is to be used by plant as a reference for future balancing and system maintenance activities.

As a result of this program the client has significantly increase cartridge life thus reducing replacement costs, has a cleaner atmosphere in the process operation area, and is more vigilant in his approach to inspecting and maintaining his system to insure proper operation. 

Dust Collection System Evaluation

Client      Food Industry - Granulated Sugar
Description      ETS was hired by an international supplier of granulated sugar to evaluate the dust collector systems servicing the granulated packaging and bulk and truck loading operations at the client’s facility in the eastern region of the United States.  The reported problems for each system included reduced gas flow at the capture hoods and high differential pressure (dP) across the baghouse.  In addition the client expressed concerns over the inability to operate the systems on a consistent basis due to plugging of the filter elements.  Included in the ETS scope of work was a review of the system design and operational practices and a comparison with current industry experience and accepted designs and practices.  In addition ETS was requested to provide preliminary designs and specifications of any recommended system hardware upgrades including belt pickups, dust capture hoods, transfer ducts, main ductwork, baghouses, and fans. The client’s engineering group would then use the preliminary design as a basis for the final detailed system design.  The initial task in the ETS effort was to review the design calculations and specifications of the present systems along with any available operation and maintenance records.  This task was necessary so that we could have a complete understanding of the nature of each systems problems and the specifics of the hardware involved.  

A detailed on-site inspection of each system was then conducted.  Included in this inspection were gas flow measurements at several points along the duct system.  It was found during this inspection that all of the long horizontal duct runs were plugged.  The plugging caused reduced gas flow throughout the ductwork resulting in ineffective dust capture at the hoods.  A comparison of the actual versus design flow data indicated there were several inconsistencies; in some cases the problems were caused by improper damper settings or ineffective maintenance procedures, while in some instances the problems were caused by poor design practices such as improper location of bucket elevator discharge pick-ups or inadequate hood capture velocity.  In addition the bags in each dust collector inspected were found to be severely plugged.

ETS concluded that the granulated sugar being transported in the ducts posed an unusual problem in that it was a heavy, moist material requiring higher transport velocities than what is typically required for industrial applications.  Velocity in the duct and the hood face (capture) velocity had to be balanced.  Higher than the required capture velocity in the hood will entrain product (that we do not want to collect) along with the lighter dust material that we do want to collect.  On the other hand, lower than appropriately designed duct velocities will allow the collected dust to settle in the ductwork causing dust buildup and subsequent blockage. 

ETS developed several system design options, all of which included revised hooding and ductwork specifications along with all pertinent velocity/volume and static pressure calculations.  We also recommended and provided a specification for a replacement fabric.  This material offered superior cake release characteristics to the fabric being used and should alleviate the problems of clogging and fabric blinding, thus offering significant payback in baghouse availability, reduced maintenance, reduced baghouse pressure drop, and increased bag life.

Troubleshooting - Premature Bag Failure at Midwestern Power Generation Station

Client      Supplier of the Air Pollution Control System
Description       ETS, Inc. was retained by a leading operating equipment manufacturer (OEM) to consult on the issue of potential bag wear at OEM's pulse jet baghouse located at a Midwestern power plant.  The subject baghouse was of long bag design, had a two section cage design, and employed high pressure low volume (HPLV) pulse cleaning.  The client had indicated that there was significant bag to bag contact and it was their contention that this was the cause of a higher than expected failure rate.

ETS personnel reviewed technical information provided to them and inspected the unit.  The ETS inspection determined that there was a significant amount of bag to bag contact; probably resulting from tube sheet deflection, bent cages, and imperfect cage installation.  It is further noted that bag to bag contact does not necessarily result in premature bag wear and failure.  Industry experience has been relatively positive regarding premature bag wear as long as bag "bumpers" and low gas velocities are employed.  The client's design employed both of these considerations at the subject facility.

Based on their findings, ETS provided recommendations for the subject station and separate recommendations for future units.  Among the recommendations for the subject site were:

1. Document a detailed bag and cage installation procedure.

2. Establish a bag wear monitoring program.

3. Consider a cage alternative test program.

The recommendations for future installations included:

1. Lower the vertical (can) velocity to less than 400 fpm net.

2. Establish a cage improvement program with cage manufacturers.

3. Document a more detailed procedure for bag and cage packing, shipping, on site handling & storage.

4. Develop a detailed in-house bag and cage specification.

5. Review the design of the tube sheet.

6. Monitor HPLV cleaning effectiveness versus bag length.

The client implemented most of the recommendations and contracted ETS to consult on the future installations which were in the design stage.

Baghouse Troubleshooting - Premature Bag Failure

Client      Electric Utility
Description       ETS was retained to conduct an assessment of the baghouses at three of the client's electrical generating plants to determine the causes of premature bag failure at two of these facilities and to make corrective recommendations.  The baghouse systems at all three plants were similar in that they were of the same design, and provided by the same supplier.

In each case the baghouse was preceded in-line by a lime spray drier for SO₂ removal.  Two of the plants had previously retrofitted their baghouse hoppers to lower the can velocity and improve flow distribution in an attempt to lower the operating pressure drop and reduce the potential for bag wear.  The modifications were slightly different in design and the resulting impact on bag life and pressure drop differed.  One of the facilities exhibited both reduced pressure drop and increased bag life as a result of the modification.  Baghouse operation at this facility was not considered to be a problem and was included in the ETS evaluation to provide insight and a basis for acceptable performance.  The design change at the second facility, while alleviating the pressure drop concerns, had little positive effect on bag life.  Bag life in some sections of this baghouse was less than one month.  Because the bag life problem was so severe at this facility, it was decided this is where ETS should focus on initially (problem site #1).  The other problem site (#2) had not made any modifications to the original hopper design.  This facility continued to suffer from the dual problem of unacceptable bag and high pressure drop.

ETS conducted a site visit at problem site #1 and inspected the baghouses.  We also interviewed key plant personnel and gathered relevant design and operational and maintenance information.  A subsequent review of the inspection report and information was conducted and a limited number of failed bags were inspected and tested.  The results  of these exercises indicated the following; (1) bag failure was due to erosion and was almost exclusively in the bottom section of the bags; (2) the pattern of failure was that a few rows close to the bag module inlets was where most of the failure occurred; (3) the system was operating a higher than design gas volume; (4) calculations of vertical flow velocity indicated that the can velocity was significantly higher than what is considered recommended design practice.

ETS concluded that the underlying cause of the bag failure was an uneven distribution of the gas.  This maldistribution results in very high localized velocities which rapidly erodes the bags.  We suspected that further modification to the existing (modified) hopper design, incorporating an improved baffle design, would probably solve the maldistribution and thus the bag wear.  Because the issue of gas distribution design is more of an empirical art rather than a true science, we recommended a flow model analysis should be conducted to both firm up the nature of the existing gas distribution problem, and to optimize the baffle design. 

The client authorized ETS to conduct the flow model, and the results of the study correlated very well with our previous conclusions regarding distribution and failure patterns.  The modeling also provided valuable input to the baffle design and a level of certainty that the re-design would alleviate the problem.  The modifications were made and the system has since experienced significantly  improved bag life and much lower operating costs.  As a result of the success of this project, ETS was commissioned to address the second problem site, as well as provide bag/cage drawings and fabric specifications for all three locations.