Three Principles for Installing Your First Fume Collector
Most welding & metal fab operations outgrow their first fume collector. Here are 3 basic principles to help you choose your first fume collection system.
By Tom Miller, Donaldson Company and Jay Smith, Air Separation Technologies
Outgrowing Initial Ventilation Systems
It’s almost inevitable that welding and metal fabrication operations will eventually outgrow the ventilation systems they start with. Many welding shops begin as smaller enterprises that expand with time, requiring the installation of new booths, additional work-shifts, or new technologies such as laser cutting. Any of these can lead to an increase in dust and fumes, which can overwhelm smaller exhaust systems that might have been adequate at the beginning.
Knowing When to Upgrade
If your operation is experiencing noticeably dirty air, it may be time for a system upgrade. When it comes time to add or upgrade your plant ventilation systems, there are a few basic principles to follow to ensure the best results for your facility.
Exploring a Real-World Example
Let’s examine these principles through the experience of one fabrication shop in southern Ontario.
Challenges Faced by this Manufacturer
First, honestly evaluate your shop conditions, listing all the challenges you see, both inside and outside the building. The Ontario shop manufactures extensions for forklifts as their primary product but also takes on smaller fabrication projects as well. Their work is primarily with carbon steel, which produces a fine, dense fume. They had grown to five welding stations running two shifts and had recently added two laser cutters.
Encroaching Residential Community
Although the shop is located in an industrial area, a nearby residential community is growing and beginning to encroach on their location. The facility was venting smoke and fumes directly to the exterior with exhaust fans. The situation posed a concern to local residents, and potentially bordered on violation of local air quality regulations.
Current System Not Keeping Up
Inside the building, conditions were also smoky—not just in the fabricating area, but in the front business office as well. The fabricator utilized a system of make-up ventilation air, but an archaic system of hoods, ducts, and exhaust fans was unable to exhaust the dirty air fast enough to maintain proper indoor air quality.
Disuse Due to Inconvenience
In addition, a poorly designed system of source-capture arms, intended to collect fumes from each workstation, sat idle because they were inconvenient for workers to use. Beyond a workplace safety issue, the accumulating iron dust also threatened fine machinery components including electrical panels.
Solutions for Reducing Emmisions
Think holistically about a solution. The owner in Ontario decided to take preemptive action to reduce emissions and improve worker health and safety. He called a consultant at Air Separation Technologies (AST), the Ontario distributor for Donaldson dust collectors in his area to help devise a best-in-class solution for his industrial ventilation concerns. Together, they worked to develop a comprehensive air-quality package. To ensure the best results, they followed these basic principles that are important for all fast-growing metals shops who are working to improve their plant air quality.
Principle 1: Address All Fume Sources
It may be tempting to blame excessive fumes on the most recent process equipment additions (such as the shop’s two new laser cutters) and ventilate only those newer sources. Isolating fume sources is difficult, however, particularly in older facilities; and ignoring other sources of air contaminants in your air-quality assessment will render partial results. If a dust collector is warranted by any one part of the process, it is usually more cost-effective to tie other fume generating sources into the same system.
Ensure Metals are Non-reactive When Combined
It’s important to note that collecting contaminants from multiple sources is possible only if the metals being processed are non-reactive when combined. Aluminum and iron oxide form a combustible combination, for example, and their dust must be segregated to avoid combustion events.
Responsibility to Conduct PHA & DHA
The process owner is responsible for conducting a complete process hazard analysis (PHA), which also includes a dust hazard analysis (DHA) to determine the combustibility of the dust(s) produced by their processes. The DHA will inform your industrial ventilation consultant regarding best practices for system design and equipment selections. In the case of the southern Ontario fabricator, all of their fabrication processes involved only carbon steel, so the weld fume and laser dust were compatible, and fume from both processes could be collected by a single dust collector without concern for reactivity.
Principle 2: Balanced User-Friendly System
Establishing proper capture and convey velocities for a given contaminant is key to proper system design. Weld fume can be captured at velocities as low as 100 ft./min., and conveyed through ducting at velocities as low as 2,500 to 3,000 ft./min. The size and type of source capture arms previously utilized at the subject facility dictated minimum airflows of 800 cubic feet per minute (CFM), but a velocity test of their existing system revealed a weak draw of only 200 CFM per arm. That is just 25% of required capture airflow, which accounted for much of the fugitive dust challenging their air quality.
To design a balanced system with adequate collection capacity, the consulting firm devised a system of flexible capture hoods configured to move up and down, rotate 360 degrees, and extend up to 12 feet in any direction. This maneuverability would permit workers to adjust the hoods as they moved around large parts or follow the work as it moved within the fabrication process.
Addition of New Laser Tables
Laser tables were then added to the system design, and AST engineers created drawings of the proposed system that included 3D renderings of the final ducting layout, and the new dust collector and fan, which would be located at the plant exterior. (See Illustrations 1 and 2.)
Principle 3: Choose the Appropriate Collector & Filters
Equally as critical as hood and ducting design is the selection and sizing of the system dust collector and fan. Fine submicronic dust such as welding and laser fume present a challenging situation for dust collectors and the filter media they utilize. It’s important to understand these challenges to ensure collector selection will result in a system that provides excellent filtration efficiency, in combination with long filter life and low energy consumption. Common filter media are typically unable to meet this ambitious demand.
Understanding the challenge, the consultant recommended a Donaldson Downflo® Evolution
(DFE) cartridge style dust collector, Model #DFE 3-18, equipped with Ultra-Web SB filter media. The Ultra-Web SB filter selected is flame-retardant and utilizes a nanofiber filtration technology that allows fine dust to collect on the surface, instead of the depth, of the filter media, so it pulses off more easily with compressed air. Ultra-Web filters are considered the first choice in the filtration industry when handling challenging, thermally generated dust like weld and laser fume, due to their ability to provide both high efficiency and long life.
Principle 4: Ensure You Get Support
Proper operation and maintenance of your dust collection systems is also critical to system performance. Once the system was installed in the Ontario shop, the consultant reviewed the installation with the owner and trained the owner’s team on critical system features, including monitoring of pressure drop and fan performance.
The Results
The new ventilation system at the Ontario metalworker made a dramatic difference in the quality of air both inside and outside the facility. The owner is surprised by the 150 pounds of dust collecting in the disposal container every three weeks—evidence of the volume of contaminants previously escaping into the environment. Workers understand the benefits and are enthusiastically employing the extended source capture arms to collect more fumes at their source. One year after installation, the original Ultra-Web filters are still providing excellent filtration benefits, to help create a safe and healthy work environment for this owner, who is pleased with the DFE’s ease of maintenance and its long-lasting filters.
Summary
Sooner or later, control of fumes and dust will be a challenge most metals shops face. When the problem warrants a dust collector, it pays to address the entire facility and obtain professional help designing a solution. Today’s ventilation needs go beyond what most “handymen” are capable of providing. Teaming up with a qualified ventilation designer is important in getting a new system that will be cost-effective and serve the business for many years to come.
AST Canada has been helping clients find solutions for their unique Dust, Mist & Fume Collection needs for more than 40 years.
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