Recently the EPA issued the hydrochloric acid (HCl) steel pickling Maximum
Achievable Control Technology (MACT) standard. The standard requires the following HCl emissions
control: 18 ppmv or less, or 97% efficiency or greater for existing and batch processes; and 6 ppmv or less, or 99% efficiency or greater for new and continuous processes. Storage tank and
loading/unloading exhaust is to be enclosed and routed to the control system. For HCl regeneration plants, HCl emission limits are 25 ppmv for an existing source or12 ppmv for a new source; and Chlorine (Cl2) emission limit of 6 ppmv. EPA estimates that about 80 pickling plants and 10 acid generation plants would be subject to the requirements of this regulation, including demonstration of compliance within 2 years by June 22, 2001.
What all this means is you will need to determine whether or not your facility will be
covered under the MACT standard. In order to make this determination, you must determine the amount of HCl and chlorine gas emissions that is being released into the air at your facility. Ways of measuring releases are actual testing of the air (which is fairly expensive), or by calculating the emissions by approved EPA methods (i.e., emission factor or engineering-sound estimate).
Once emissions are determined and you find your HCl or chlorine emissions to be at or
above the MACT action level of 10 tons per year, various emission control methods may be able to
keep you under the MACT threshold level. These methods include source limitation and off gas
removal. Pollution Prevention (P2) and waste minimization technologies are prevalent and normally
financially viable alternatives in comparison to costly control systems. Several successful P2
options include the fumeless enclosure, acid temperature limit, acid concentration percentage, iron content, or other tighter operation or administrative controls.
If you are unable to bring your HCl gas emissions below the action levels, then you
must comply with the MACT standard. Scrubbers have been widely used as a HCl gas control. HCl gas
is very soluble in water so you can "scrub" the air by contacting the HCl gas with water. Scrubbers can use several methods of collecting the HCl vapors as they come off of the tubs and rod during the pickling process. One method is a push/pull. This method blows air across the top of the tub and pulls the air in from the other side. Another method is pull only. Remember, whichever method you decide to use, it must comply with the MACT standards.
The most popular type of scrubber is the packed tower. The packed tower is a vertical unit
that is packed with various shapes of molded plastic. The plastic bed increases the surface area in the scrubber. Water comes in from the top and as it moves down through the plastic bedding, tiny water droplets are created. These droplets catch the HCl gas as it flows up through the scrubber. Other types of scrubbers include cross-flow or horizontal, and plate or tray. Both of these use the same principle as the packed tower, the difference is in how the HCL gas and water are mixed to get the scrubbing action on the air. The water used in the scrubber is generally in a closed loop with make-up water being added as needed. In a closed loop system, adding caustic to this water can benefit the scrubber operation by neutralizing the water stream. Overflow water from the scrubber will be acidic and therefore must be collected and treated before being released back into the environment.
With today's more and more demanding environmental obligations, we must continually
strive to control our emissions through the use of best available technology, such as, scrubbers or control devices, as they are developed.
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American Wire Producers Association
801 North Fairfax Street, Suite 211
Alexandria, VA 22314-1757
Tel (703) 299-4434 | Fax (703) 299-9233 | E-mail info@awpa.org | Web: www.awpa.org
