APC Technologies, Inc. Case Study
HIGH-EFFICIENCY OIL MIST CONTROL SYSTEM FOR METAL ROLLING MILL
Background
A Fortune 500 aluminum company has a plant that produces, among other products, aluminum sheet for end use in transportation, building and construction, recreation, and other markets. During the production process, large slabs of aluminum are rolled under pressure on hot and cold rolling mills. Lubricants used the rolling process are released due by spray activity and evaporation at the high process temperatures and exhausted from the mills. The evaporated emissions quickly condense to create a submicron oil mist, typically also with a small amount of solid particulate present also. At this plant, this exhaust was controlled by a device that used cyclonic separation as the primary removal mechanism.
The plant had developed a new process that yielded significantly higher throughput for one of the rolling mills. However, this process used greater amounts of lubricant to process the increased amount of metal, and the resulting opacity (i.e., visible emissions) from the stack would exceed the plant’s opacity limit of 10% during this operation. The plant was therefore limited in its productivity because of the emissions level.
Objective
The plant engineering group’s objective was to determine if there was a control system available that would provide: sufficiently efficient find a system to replace the venturi scrubber that:
- Eliminates visible emissions and meets the plant’s 10% opacity requirement;
- Is proven, reliable, and low maintenance, allowing continuous 24/7 operation with no downtime;
- Has sufficiently low capital and operating costs such that the unit would pay for itself quickly by allowing the plant to process more metal through the mill.
Alternatives
Alternatives for fine oil mist control include the following technologies:
- Progressive and deep bed mist control systems;
- Venturi scrubbers;
- Wet ESPs;
- Oxidizers;
- Ultra-High Efficiency Filter (UHF®) system.
Comparison of Alternatives
Progressive and deep bed type mist control systems can provide high-efficiency control of the oil mist, but do not work effectively if any solid particulate matter is also present, which is often the case. The solid particulate blinds the filter (or pre-filters), choking off air and/or causing channeling/bypass or premature change-out of the filter media. These systems also tend to be very expensive.
The venturi scrubber presents multiple problems, mainly very low control efficiency on submicron mist droplets (or conversely requiring a pressure drop on order of 40” w.g. to effectively control submicron sizes, i.e., extremely high energy costs), and also results in a water treatment/disposal issue.
The wet ESP has exceptionally high capital cost and was dismissed because of this.
Catalytic and thermal oxidizers were dismissed as the air stream was dilute and would require very high natural gas costs for the large volume of air.
The UHF® filter system offered a control efficiency of up to 99%, simultaneously removed any solid particulate matter without any operational problem at all, and offered very simple and reliable operation, with no downtime required for filter replacement. It offered these features at much lower capital and operating cost than any other option.
Decision and Result
A 50,000-ACFM UHF® filter unit was selected and installed. The plant is now operating the rolling mill with the new process, resulting in the desired high throughput for the mill. Opacity under this operating condition is zero, as measured by certified testers using EPA Method 9 for Visual Opacity, allowing the plant to comfortably meet its visual opacity limit. Filter usage rate for the unit is extremely low, costing the plant approximately $1,000 per year annualized. The UHF® unit has had no downtime, and the plant is very pleased with the installation, economically and on a performance basis.
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