Abstract:
A hazardous gas abatement system decontaminates an exit gas stream containing global warming gases using an electrical heater and a water scrubber. One or more top flow hazardous gas inlets introduce hazardous gases into a heater compartment. Air or oxygen is introduced into a separate chamber for dynamic oxidation and cooling. The streams are mixed and oxygen reacts with the hazardous gases. Solid particulates from the reaction are removed by a filter in a quick disconnect bottom chamber. Filtered exhaust gases flow upward in an exhaust chamber surrounding the heater compartment and through water spray scrubbers. A cleaning ring mounted on an eccentric rod cleans particles from the outside of the internal heater, and the inside of the external heater. An air cylinder drives the eccentric rod and cleaning ring down and up between the heaters and stores the ring above the gas inlets.

Description:
This application is a division of application Ser. No. 10/796,120 filed Mar. 10, 2004, now U.S. Pat. No. 7,534,399 which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for hazardous gas abatement and emission control. Contaminated gas is decomposed, cleaned and neutralized. The present invention is particularly useful for global warming gases and other hard to decompose gases. These gases may include perflourocarbons (PFCs), tetraflouromethane (CF 4 ), hexaflouroethane (C 2 F 6 ) and many other ozone depleting global warming and greenhouse gases. The present system is also useful for decomposing the exit stream of a semiconductor process by removing gases such as arsine (AsH 3 ) or phosphine (PH 3 ). High temperatures are required to clean, neutralize and decompose these types of gases. 
     Existing systems do not provide adequate heating to effectively cleanse exit gas streams of global warming gases. Previous gas cleaning systems include controlled decomposition/oxidation (CDO) and others. These previous systems suffered from low efficiency in performance and considerable downtime of equipment during maintenance. Industries, such as the semiconductor industry, have a considerable need for gas cleansing systems in order to comply with environmental emissions codes and regulations. 
     In existing gas cleaning systems heaters are used. However, the heaters insufficiently heat all of the gases, and the heaters become fouled and unable to efficiently transfer heat. They also become so burdened with particulate contaminants or reaction products as to interfere with free flow of gases through the cleaning systems. Periodic cleaning of the heaters and the chambers becomes necessary, which requires shutting down of the systems or taking the treatment apparatus off line, resulting in duplicate systems and greater expense. If the systems are not cleaned contaminated gases will be released. 
     Needs exist for improved apparatus and systems for cleaning heater compartments in contaminated gas treatment methods and apparatus. 
     Needs still exist for improved systems for neutralizing, pacifying and cleaning contaminated chemical process exhaust and waste gases. 
     Needs exist for improved systems, which efficiently neutralize chemical process exhaust gas hazardous components and contaminates. The system should ensure complete or substantially complete neutralization and pacification of any out flowing contaminant gas in the gas stream to be neutralized. Needs exist for systems that are simple and inexpensive to build and to operate and that do not require a fuel source to operate. 
     Needs exist for systems that are capable of handling spent process gas streams that have contaminate gas concentrations from trace to substantial amounts in volumes of cubic centimeters to several tens or hundreds of liters per minute. 
     SUMMARY OF THE INVENTION 
     The present invention is a hazardous gas abatement system for reacting global warming, greenhouse and/or ozone depleting gases using an electrical heater and a water scrubber. The present invention provides higher temperatures and increased contact surfaces for decomposing the subject hazardous gases when compared with previous systems. 
     Preferably, but not limited to, one or more, or about one to four top flow hazardous gas inlets introduce hazardous gases into a heater compartment where the toxic gases are heated to approximately 1100° C. The hazardous gases flow into the heater compartment surrounded by an outer heater. An inner heater is positioned with respect to the outer heater to create additional heat and contact surfaces for higher gas temperatures. An air inlet introduces air into the cleaning system separate from the hazardous gases. The air is fed around the outside of an external heater for cooling and dynamic oxidation. After the hazardous gases and the air are heated, the two gas streams flow downward in the apparatus and meet below the heater compartment. Oxygen in the air reacts with the heated hazardous gases. When the gases have reacted, the exit gas stream passes through a filter at the base of the cleaning device for removal of solids. A quick disconnect clamp on the bottom of the cleaning system is used to periodically remove the filter for cleaning and removal of accumulated solids. After passing through the filter, exhaust gases flow upward in a chamber outside the heater compartment and then through water spray scrubbers that cool and scrub the gases. 
     A cleaning ring with an eccentric shaft cleans the entry point of the hazardous gas inlets, the outside of the internal heater, and the inside of the external heater. An air cylinder drives the eccentric shaft up and down between the heaters and along the gas inlets. The cleaner removes particles from the exposed surfaces of the heaters as it moves. The cleaning ring has an inner and outer surface for cleaning the inner heater and outer heater simultaneously. When not in use, the cleaner is positioned above the first and second gas inlets and away from the passage of contaminant gases and oxygen. In addition to cleaning the surfaces of the heaters, the cleaner also cleans the entry points of the gas inlets to prevent buildups. 
     Preferably, but not exclusively, the heater compartment, outer heater and inner heater are cylindrical. The cleaner is annular and coaxial with the outer heater. An operator, offset from a center of the cleaning system, moves the cleaner between the outer surface and the inner heater surfaces. The operator is a reciprocation device extending from an end of the treatment apparatus and a rod extending into the heater compartment and connected eccentrically to the annular cleaner for extending in a space between the heaters as the reciprocating device moves the cleaner. 
     Water sprays are also used for cooling and scrubbing of exhaust gases. A water scrubbing zone is positioned after the filter, but before exhaust gas leaves the apparatus. Moisture may also be introduced in the hazardous gas inlet or heater compartment in the form of steam or water. This addition of moisture reduces contaminants and possible damage to the heater compartment and other components by converting fluorine gas to hydrofluoric acid. 
     The present invention efficiently neutralizes, pacifies and cleans contaminated chemical process exhaust and waste gases and allows for easy cleaning of the heater compartment. The present invention ensures complete or substantially complete neutralization and pacification of any out flowing contaminant gas in the gas stream to be neutralized. The system is also simple and inexpensive to build and to operate. The systems is capable of handling spent process gas streams that have contaminate gas concentrations from trace to substantial amounts in volumes of cubic centimeters to several tens or hundreds of liters per minute. 
     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross sectional view of the hazardous gas abatement system. 
         FIG. 2  is a side view of the hazardous gas abatement system. 
         FIG. 3  is a top view of the cleaning ring with eccentric shaft. 
         FIG. 4  is a top view of the hazardous gas abatement system. 
         FIG. 5  is a top cross sectional view of the hazardous gas abatement system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is a hazardous gas abatement system for reacting global warming, greenhouse and/or ozone depleting gases using an electrical heater and a water scrubber. The present invention ensures complete or substantially complete neutralization and pacification of any out flowing contaminant gas in the gas stream to be neutralized. 
       FIG. 1  is a side cross sectional view of the hazardous gas abatement system  1 . Contaminated gases that are in need of neutralization and pacification are taken from a process stream. The contaminated gases feed into the hazardous gas abatement system  1  through a top flow hazardous gas inlet  3 . The hazardous gas inlet  3  introduces the contaminated gases through an entry point  5  that is attached to a heater compartment  7 . In order to carry out the neutralization and pacification of the contaminated gas, the contaminated gas is heated to temperatures of approximately 1100° C. 
     An air inlet  9  introduces an air stream into the cleaning system  1 . Air is introduced near the top of the abatement system  1 . Both the contaminated gas stream and air stream may be pumped into the abatement system  1  or may be drawn into the system  1  by a slight negative pressure within the vessel. 
     The contaminated gases leave the entry point  5  and move into the top of the heater compartment  7 . Gas flow in the heater compartment  7  is in a generally downward direction. At least one electric heater  11  is located within the heater compartment  7 . A second electric heater  13  may also be present. Walls  15  and other devices control gas flow and provide support for structures within the heater compartment  7 . The contaminated gases flow downward through the heater compartment  7 , between the inner  13  and outer  11  heaters. The use of a second heater  13  creates a second heat source and increases contact surfaces to ensure higher gas temperatures. The electric heaters  11 ,  13  heat the contaminated gases to remove some of the contaminants. 
     After entering the system  1 , the air stream flows downward between the external heater  11  and the heater compartment walls  17 . Dynamic oxidation occurs as the air flows around the external heaters  11  and the insulation on the heater  11  is cooled. The pre-heated air stream exits the region between the external heater  11  and the heater compartment walls  17  through vent  15 . 
     At the base of the heater compartment  7 , the contaminated gases exit the heater compartment  7  and mix with the pre-heated air stream. The two gas streams react to decompose the contaminated gases. At the base of the system  1 , a filter  19  removes reacted solids from the combined gas stream. The filter  19  is periodically removed for maintenance and to clean out accumulated solids by means of a quick disconnect clamp  21  on the bottom of the heater compartment  7 . 
     The filtered exhaust gases flow upward in a chamber  23 , outside the heater compartment  7  and inside the outer wall  25  of the apparatus  1 . Prior to exiting the abatement system  1 , the filtered exhaust gases pass through a system of water spray scrubbers  27  that cool the exit stream and further remove contaminants from the exhaust gas. After being scrubbed by the water sprays  27 , the substantially cleaned exhaust gases are exhausted through an exhaust vent  29 . The exhaust is composed of water vapor, air and cleaned gas. 
       FIG. 2  is an exterior side view of the hazardous gas abatement system  1 .  FIG. 2  also shows components  31 ,  33 ,  35  that are used to secure an air cylinder  37  onto the top  39  of the abatement system  1 . 
       FIG. 3  is a top view of a cleaning ring  41  with an eccentric shaft  43 . The decomposition of the contaminated gases results in the buildup of a solid residue within the heater compartment  7 . The filter  19  captures and collects many of the solid particles created from the process. However, decomposition occur throughout the length of the heater compartment  7 , including along the exposed surfaces of the heaters  11 ,  13 . As a result, solid particles form on the heaters  11 ,  13  and reduce the heating efficiency of the heaters  11 ,  13 . In order for the abatement system  1  to work effectively, the heaters  11 ,  13  must be cleaned frequently to remove solid particles on the heaters. In previous systems, the process needed to be shut down and opened for cleaning. In the present invention, the heaters  11 ,  13  can be cleaned without extended disruptions of the abatement system  1 . 
     In an embodiment of the present invention with one heater, the cleaning ring  41  has an outer surface  45  in close proximity to the internal surface  47  of the heater  11 . The outer surface  45  of the cleaning ring  45  is used to scrape solid particles off the heater  11 . The cleaning ring  41  is positioned above the hazardous gas inlet  5  when the cleaning ring  41  is not in use. This positioning keeps the cleaning ring  41  away from the passage of contaminant gases, preventing solid buildup on the cleaning ring  41  itself and preventing the cleaning ring  41  from disturbing the flow of gases in the heater compartment  7 . 
     During cleaning, the cleaning ring  41  is depressed from its initial position above the gas inlet  3  by the air cylinder  37 . The air cylinder  37  provides force necessary to propel the cleaning ring  41  along the sides of the heater  11  while scraping solid particulates off the heater  11  and down toward the filter  19 . In addition to cleaning the surface of the heater  11 , the cleaning ring  41  also cleans the entry points of the gas inlets  3  to prevent buildups that would stifle the flow of gases. The cleaning ring  41  proceeds down the inner walls  47  of the heater  11  until it reaches a stop  49 . The inner walls  47  of the heater  11  are designed such that the cleaning ring  41  scrapes solid buildup from the entirety of some of the walls  47 , but not all of the walls  47 . Part of the inner walls  47  are tapered  51  and extend below the stop  49  to prevent the cleaning ring  41  from becoming misaligned. When the cleaning process is completed, the air cylinder  37  retracts the cleaning ring  41  to its initial position. 
     In an embodiment of the present invention with multiple heaters  11 ,  13 , a cleaning ring  41  has an inner  53  and outer  45  surface to clean an inner  13  and outer  11  heater of solid particles. The outer surface  45  of the cleaning ring  41  is in proximity to the inner surface  47  of the first heater  11 . The inner surface  53  of the cleaning ring  41  is in proximity to an outer surface  55  of the second heater  13 . The cleaning ring  41  encircles the second heater  13 . The cleaning process with multiple heaters  11 ,  13  is similar to the cleaning process for a single heater  11 . An air cylinder  37  depresses the cleaning ring  41  until reaching a stop  49 . The air cylinder  37  then retracts the cleaning ring  41  to its initial position. The air cylinder  37  acts on the cleaning ring  41  through an offset shaft  43 . 
     The cleaning ring  41  with its eccentric shaft  43  is used to clean the entry point of the gas inlets  3 , the outside of the internal heater  55 , and the inside of the external heater  47 . The cleaning ring  41  removes particles from the heaters&#39;  11 ,  13  exposed surfaces as it moves. The cleaning ring  41  cleans the inner heater  13  and outer heater  11  simultaneously. There is no need to disassemble the abatement system  1  in order to remove solid particles from the heaters  11 ,  13 . 
       FIG. 4  is a top view of the exterior of the hazardous gas abatement system  1 . In a preferred embodiment of the present invention, the heater compartment  7 , outer heater  11  and inner heater  13  may be concentric cylinders. As a result, the cleaning ring  41  is annular and coaxial with the outer heater  11 . An operator  43 , offset from a center of the apparatus  1 , moves the cleaning ring  41  between the outer  55  and the inner  47  heater surfaces. The operator  43  is a reciprocation device extending from an end of the treatment apparatus  1  and a rod extending into the heater compartment  7 . The operator  43  is connected eccentrically to the annular cleaner  41  for extending in a space between the heaters  11 ,  13  as the reciprocating device moves the cleaning ring  41 . The cleaning ring  41  is placed in close proximity to the heater surfaces  47 ,  55  to ensure adequate cleaning, but the cleaning ring  41  is not in contact with these surfaces  47 ,  55 . 
       FIG. 5  is a top cross sectional view of the hazardous gas abatement system  1 . Water sprays  27  are used for cooling and scrubbing of exhaust gases. A water scrubbing zone is positioned after the filter  19 , but before exhausting the gases out of the apparatus  1  via the exhaust duct  29 . The introduction of water into the system helps to further scrub the contaminated gases and cools the exit stream. Moisture may also be introduced in the earlier in the cleaning system  1  in the form of steam or water. Water sprays  27  may be reconfigured to dispense water or steam into the oxygenator  5  as well as the exit flow region  23  after the filter  19 . This addition of moisture in the form of water or steam reduces contaminants in the hazardous gas stream. Moisture also reduces the possible damage to the heater compartment  7  and other components by converting fluorine gas to hydrofluoric acid. Hydrofluoric acid is less damaging to the equipment than fluorine in the gaseous form. 
     The present invention efficiently neutralizes, pacifies and cleans contaminated chemical process exhaust and waste gases and allows for easy cleaning of the heater compartment  7 . The present invention ensures complete or substantially complete neutralization and pacification of any out flowing contaminant gas in the gas stream to be neutralized. The system is also simple and inexpensive to build and to operate and does not require a fuel source to operate. The systems is also capable of handling spent process gas streams that have contaminate gas concentrations from trace to substantial amounts in volumes of cubic centimeters to several tens or hundreds of liters per minute. 
     While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention.