Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
2000-04-19
2001-12-04
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C095S009000, C095S187000, C095S199000, C095S224000, C422S171000
Reexamination Certificate
active
06325983
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to treatment systems for removing nitrogen oxides from process exhaust streams, and more particularly to a gas scrubbing system and method for treating such streams.
BACKGROUND OF THE INVENTION
State and federal laws regulate the discharge of oxides of nitrogen, such as nitrogen monoxide and nitrogen dioxide (collectively referred to herein as NOx), to the atmosphere. Therefore, in processing facilities in which NOx is present in the process exhaust streams, these streams must be treated prior to release into the environment. An example of such a facility is a semiconductor processing facility, and especially a facility involved in the processing of silicon wafers. Some of these process exhaust streams result from the use of nitric acid, such as in etching and cleaning processes, however, the present invention is applicable to treating any process stream containing NOx, regardless of the original source of the NOx.
A variety of treatment mechanisms have been developed to remove NOx from process exhaust streams. For example, one known process is discussed in U.S. Pat. No. 5,637,282, the disclosure of which is hereby incorporated by reference. That system involves removing NOx from a process exhaust stream through scrubbing with an aqueous peroxide solution. While effective, this system requires the processing facility be equipped with suitable handling and storage equipment for hydrogen peroxide. It also requires a considerable flowrate of once-through water, which must be disposed of after use.
SUMMARY OF THE INVENTION
The present invention provides a system and method for cost-effective removal of NOx. The invented system includes a plurality of sequential scrubbing assemblies that receive a process exhaust stream containing a concentration of NOx and collectively reduce the concentration of NOx therein to below a determined threshold. The scrubbing assemblies each include a reverse osmosis assembly that significantly reduces water consumption for the scrubbing process as compared to conventional once-through systems. The system may be operated at an elevated pH to prevent fouling from inhibiting the cost-effective operation of the reverse osmosis assemblies. The system may also include an automated control system adapted to monitor and control the operation of the system.
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Bomber Andrew J.
Boyce Allen R.
Mukhopadhyay Debasish
Alston & Bird LLP
Griffin Steven P.
Medina Maribel
SEH America Inc.
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