Fabric Filter Baghouse Troubleshooting Case Studies
Troubleshooting Case Studies
Specialty Rock Products Manufacturer
Food Industry - Granulated Sugar
Supplier of the Air Pollution Control System
Client Specialty Rock Products Manufacturer
The objective of the evaluation was to inspect the condition of each system, determine system gas volume, balance each system, and make recommendations for system improvement. The ETS approach to meet these objectives was to firstly, arrive at a complete understanding of the manufacturing process operation, the dust collector system design, and how they interrelate. This was established by interviewing key plant personnel and reviewing all available process information, system design drawings, and information on the dust collectors and system fans. The next step was to conduct a visual inspection of each system, including the hoods and associated dampers and their respective settings, ductwork, dust collectors and fans; in conjunction with this inspection we measured gas flow and static pressures at key junctures along the ductwork path and compared them with original design values. There exercises yielded the following conclusions:
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.
Client Food Industry - Granulated Sugar
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.
Client Supplier of the Air Pollution Control System
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:
The recommendations for future installations included:
The client implemented most of the recommendations and contracted ETS to consult on the future installations which were in the design stage.
Client Electric Utility
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.
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