Facility evaluation and system selection
November 15, 2001
The article explains how to carry out a facility and process evaluation and discusses the basics of in-plant air filtration system selection.
Plant managers no longer question whether to use an in-plant air filtration system. Rather, they ask what type of system to use. Multiple collection and filtration system options are available from a variety of manufacturers, and different systems may function equally as well when cleaning in-plant air.
So, where should a metal fabrication facility begin when choosing a system, and how does it know when the correct choice has been made? This article explains how to carry out a facility and process evaluation and discusses the basics of in-plant air filtration system selection.
Companies with metal fabrication operations add air filtration systems to:
The first step when selecting an in-plant air filtration system is to make a facility and process evaluation. This analysis includes observing manufacturing and production operations such as the work process and layout, materials used, and existing exhaust and ventilation systems.
Airborne pollutants should be identified and measured professionally to determine a benchmark for collection and filtration methods for each process.
For welding processes, parameters include the type and amount of wire and metal being used and the weld methods being performed.For cutting operations, considerations include the type of metal being cut, the amount of metal removed from the sheet, the length of processing time, and air requirements.
With a proper and thorough evaluation, a correct air filtration system can be identified with relative accuracy, and calculations can be made to determine the likely end result of the installation, including contaminant collection efficiency levels and system/filter maintenance cycles.
Mechanical arm systems can be positioned close to breathing areas to remove smoke without obstructing lighting or sight lines.
By incorporating the facility and process evaluation results with proper application engineering, an efficient and effective air filtration system can be identified. Welding and cutting applications most often are handled with any of three basic collection methods:
Source capture methods also can be integrated with portable filtration systems, combining the versatility of portable systems with the source capture system's collection efficiency.
Pollutants are not removed from the worker's breathing zone immediately with free-hanging systems, but most free-hanging systems can reduce airborne particulate by 75 to 80 percent.
Vertical orientations, or power booth systems, can be positioned near permanent, or fixed, workstations where large items are worked on (see Figure 3). Power booth systems pull the particulate away from the breathing zone without interfering with the workplace or shop layout.
The collection process and filtration method must be considered together. Typical filtration options for welding and cutting applications include:
Disposable filters are discarded when they are filled with particulate and collection efficiency has dropped noticeably. Renewable cartridge filters are made of materials designed to release particulate during cleaning.
Filter-cleaning systems often have pulsed-air or filter-wrapping configurations (see Figure 4). A filter-cleaning system that combines both pulsed air and filter wrapping may clean the filter to within 10 percent of the system's original pressure differential. Better cleaning extends filter life and overall system operating efficiency. In typical usage and maintenance cycles, filters commonly can stay in place for six to 12 months.
Vee-bag filters, constructed of polyester-type materials, are used for capturing sticky or oily dust that can be generated by coated metals. They usually work at a 95 percent efficiency level.
System selection criteria often are balanced among one-time installation costs, operating costs, and filter costs and labor associated with system maintenance. Maintenance and wear are reduced on a system that exceeds an installation's basic operating requirements. It will operate more efficiently, and the larger system blower will lengthen maintenance cycles; however, initial equipment and system installation costs may be greater.
A system sized to the exact needs of the installation may require more filter maintenance during its useful life but may cost less to install.
Facilities management personnel, in cooperation with their systems provider, must determine their own balance among installation costs, operating efficiency, and maintenance costs when selecting an in-plant air filtration system.