Abatement: More than Meets the Eye
Abatement systems fall into one of the following categories: thermal/wet, thermal, wet, dry resin bed, plasma, or plasma wet. When someone is looking at what type of abatement system to select for their facility, it is not as simple as looking at what chemistry is being used in the process tool. There are a lot of things that need to be considered when selecting the right abatement system for the application. While the starting chemistry is important in the abatement selection, the byproducts of the chemical reaction(s) occurring in the process tool are just as important as well. However, they are not the only considerations in selecting the right abatement system for the application. One needs to look at the reaction(s) occurring in the abatement system and where those byproducts are ending up. Other things that need to be considered are as follows:
Air and wastewater permit requirements
Air and wastewater regulations
Code requirements
The end user (University/R&D or Industry)
Environmental, Health, and Safety (EH&S) requirements
Greenfield (new build) or brownfield (retrofit, renovation, repurpose) site.
Facility and utility availability
Selecting the wrong abatement system may not remove the targeted chemical species or may require the owner to buy additional equipment to remove a contaminant from the abatement system waste stream. For example, using a thermal/wet system for arsine will yield arsenic oxides, which are water soluble. Wastewater regulations prohibit the presence of arsenic containing compounds in the discharged wastewater stream. Additional equipment will be required to remove the arsenic from the wastewater.
The owner’s EH&S department could be forced into deciding which contaminants are the most important to remove and which ones to let pass through the system. For example, MOCVD process uses a lot of hydrogen gas as well as some extremely dangerous metalorganic sources. The metal portion of the metalorganic material may be highly regulated where the discharge limits are exceedingly small to not allowed. A dry resin scrubber is highly effective against metalorganic materials but does nothing for hydrogen gas. There could potentially be enough exhaust flow in the exhaust system at the point where the process exhaust from the abatement system connects to the exhaust system that the hydrogen concentration is below the 25% of LEL, as required by code.
The facility/site conditions can be a factor with the selection of the abatement system. Things like corridor and/or door heights and widths, floor loading capacity, elevator dimensions and capacity, utility availability can restrict the abatement selection, especially in a renovated facility. A greenfield site has the advantage of the ability to plan for any abatement system that could be added later by considering the abatement system’s dimensions, weight, and facility requirements. Brownfield sites may have restrictions on the extent of changes that can be made to the facility that will limit the abatement system selections due to the system size, weight, and/or facility requirements. For example, an existing building may not have water and/or drains near the area where new abatement systems are planned to go may be limited to dry resin scrubbers, especially if water sources and/or drains cannot be added to the facility.
Some dry resin systems will require a separate exhaust system due to the high static pressure across the system. Careful planning of the exhaust system(s) needs to include the static pressure across the abatement system and the equipment connected to the abatement system(s). High static catastrophic release abatement systems should be placed on their own exhaust system. It will be difficult to balance the exhaust system, not to mention the potential of having high noise areas if high static abatement systems are connected to the same exhaust system as equipment with significantly lower static pressure requirements. Also, it will be difficult to get the required airflow through the high static abatement system when they are connected to the same exhaust system as equipment with significantly lower static pressure requirements.