Abstract:
The current invention is device for lowering the air velocity and inherent noise of high-speed air released from a closed system, comprising a straight pipe module with an outer tube and a concentric inner tube creating an annular space therebetween. The inner tube has interior fins at the inlet, which initiate rotation in an airflow directed therethrough, and interior fins at the outlet, which arrest the airflow rotation. Perforations along the length of the inner tube, from inlet fins to outlet fins, permit the release of a turbulent outer zone of the airflow, permitting the high velocity core of the airflow to expand and slow, reducing the noise of the airflow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a noise abatement system for lowering air velocity in a closed system. Specifically, the invention describes a straight pipe module suppressor, with internal vanes, which reduces the velocity of air used in an industrial airblow cleaning operation. 
     2. Description of the Related Art 
     High pressure/high velocity air may be used to clean industrial piping. Reference to cleaning in this application is the process of removing loose and/or lightly adhered debris from piping. The piping to be cleaned may be that which is used in the operation of a power generating plant by providing steam to turbines, in a petrochemical plant to provide stock or product to a process or storage unit, or in any other environment using piping that is typically operated under high pressure and/or high temperature. 
     The piping to be cleaned may be new fabrication, which may nonetheless contain dirt, sand, loose bolts, used welding rods or other non-structural items or debris left from the fabrication process. Alternatively, the piping to be cleaned may already have been in service and in need of cleaning to remove built-up material (usually scaling) on the interior of the piping. Typically, cleaning of piping that has been in service is accomplished by first flushing the line with a chemical flush to loosen the mill scale, which is solubilized into a solution. The line is then rinsed, and the metal neutralized (washed) to remove the solution containing the chemical flush and the soluble scale particles. The remaining loose or lightly adhered insolubles left in the piping are then removed with the high-pressure air. 
     Debris from either new fabrication or scaling can damage downstream equipment, such as a turbine, processing unit or other equipment/systems. For example, high pressure impingement of debris on turbine blades operating at high speed could result in damage or catastrophic failure of the turbine. 
     In a typical pipe cleaning operation, the piping to be cleaned is connected at its upstream end to an air pressurization system, typically a pressure vessel and/or piping, and at its downstream end to a temporary bypass line. The temporary bypass line diverts the high pressure cleaning air away from downstream equipment. 
     In either use of high pressure air for cleaning piping (new or used), the air pressurization system is typically charged to a level sufficient to provide air pressure through the piping 1.2 times the normal operating pressure of the piping. This high pressure air passes through the piping and is discharged along with the debris out of the piping. 
     If the high pressure cleaning air, typically traveling at or above sonic speed through the piping, is released directly to the environment without velocity suppression, the noise is intolerable. It is not unusual for such a release to generate noise levels between 115 dB and 140 dB, which can cause hearing loss to those nearby and structural damage or nuisance several miles away. Further, high pressure air can penetrate the skin of a person exposed to the exhaust airflow. This air penetration through the skin can cause air embolisms in the blood vessels, which can be fatal. Thus an air velocity suppression/reduction system is needed in such environments. 
     Air velocity suppressors for high pressure/high velocity air used to clean piping air are found in the prior art. However, these silencers typically use a baffle system to reduce the velocity of the air. These create unwanted backpressure that reduces the velocity of the air upstream in the cleaning process, thus creating the requirement for higher initial air velocity. 
     Other air velocity/noise suppressors use a muffling device with a closed cap end, and direct all airflow laterally outward through release holes in the sides of the inner and outer pipes of the suppressor. This system is dangerous when used with high velocity/high pressure stream, since sudden blockage of the release holes, as from a large piece of debris, will cause immediate over-pressurization of the suppressor and likely explosion. 
     Air suppressor systems used in low velocity applications, such as mufflers used on internal combustion machines or small scale pneumatic silencers on leaf blowers and the like, are unacceptable in high pressure/high velocity air cleaning systems. These low velocity devices, even if scaled up, are unable to adequately reduce the volume and velocity of high-pressure air being exhausted from the system due to their structural and design limitations. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the objectives of this invention are to provide, inter alia, a new and improved air suppression system that: 
     Does not create undue back pressure; 
     Does not pose a risk of sudden blockage; 
     Reduces high air velocity, including those about sonic speed; 
     Uses standard fabrication components; and 
     Is cost effective. 
     These objectives are addressed by the structure and use of the inventive device. A straight through pipe has air directing internal vanes attached to the interior wall of an inside tube. The walls of the inside tube are perforated to permit airflow separated from the main air stream to escape to a space between the inside tube and the outside tube. These vanes cause the high velocity air to rotate about its directional axis. Laminar resistance of the rotation causes a tail of air to form, moving away from the center or core of the exhaust stream and against the interior wall of the inside tube. The high velocity air being released into the inside tube has an exhaust  15  shape shown in FIGS. 6 and 6A, comprising a outer layer  19  and a core  17 . Outer layer  19  is formed as laminar resistance allows side air to move away from the center of exhaust  15 , while the faster air of core  17  speeds through the center of the inner tube  30 . By directing exhaust  15  to rotate about its linear axis, outer layer  19  is “chewed away” as its air is directed into velocity dampening areas between the inside tube  30  and the outside tube  20  of the invention. As outer layer  19  is removed, it is replaced by air from core  16 , thus decreasing the overall velocity of exhaust  15 . 
     Other objects of the invention will become apparent from time to time throughout the specification hereinafter disclosed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a single inventive noise abatement module. 
     FIG. 2 depicts an inlet view of the single noise abatement module of FIG.  1 . 
     FIG. 3 depicts an outlet view of the single noise abatement module of FIG.  1 . 
     FIG. 4 depicts a side view of either a single inlet vane or outlet vane. 
     FIG. 5 depicts a top view of an inlet vane showing its oblique offset from the axial centerline of the direction of inlet airflow. 
     FIG. 5A depicts a top view of an inlet vane with no offset. 
     FIG. 6 a view of the regions of high velocity air as it travels through the inner tube of FIG. 1, cut at line  6 — 6 . 
     FIG. 6A is a view of the regions of high velocity air as it travels through the inner tube of FIG. 1, cut at line  6 A— 6 A. 
     FIG. 7 depicts the use of multiple noise abatement modules. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention comprises the module shown as noise abatement module  10 , depicted in FIGS. 1,  2  and  3 . Noise abatement module  10  comprises an inside tube  30  that is connected at each end to stubs  24 , which are attached to flanges  40 . Each flange  40  has a flange face  42  and typically flange bolt holes  44  for mating with and bolting to piping and/or other noise abatement modules  10 . Circumferential about inside tube  30  is outside tube  20 , defining annular inside space  33 . Outside tube  20  has outside tube ends  22  that define the inlet and outlet boundaries of inside space  33  between inside tube  30  and outside tube  20 . 
     An insulating material  34  may be position in space  33  between inside tube  30  and outside tube  20 . When used in noise abatement module  10 , insulating material  34  may be supported in place by expanded material  36 . Expanded material  36  is rigid enough to hold insulating material  34  in place in space  33 , yet is flexible to be shaped around insulating material  34  and inside tube  30 , as well as permeable to air. In the exemplary embodiment, the insulating material is a blanket of insulation, typically fiberglass or kaowool. Also in the exemplary embodiment as expanded material  36  is a sheet of wire mesh  34 , wrapped around the insulation blanket  34  to hold the insulating material  34  in place between the inner wall of outside tube  20  and the outer wall of inside tube  30 . 
     The diameters of inside tube  30  and outside tube  20  are any that can accommodate the high velocity airflow to be suppressed. In typical applications of noise abatement module  10  being used to abate noise from industrial pipe and vessel air cleaning, inside tube  30  typically has an inner diameter of 30″ to 38″ (76.2 cm to 96.5 cm), and outside tube  20  typically has an inner diameter of 40″ to 54″ (101.6 cm to 147.2 cm). 
     Inside tube  30  has inside tube perforations  32 , which are typically ⅛″ to ⅜″ (3.2 mm to 15.9 mm) in diameter. In the exemplary embodiment, inside tube perforations  32  are intermediate inlet vanes  50  and outlet vanes  51 . 
     Inlet vanes  50  are attached to the interior wall of inside tube  30  at the air inlet side  27 . In the exemplary embodiment inlet vanes  50  are six in number and circumferentially equally spaced, as shown in FIG.  2 . As shown in FIG. 4, each inlet vane  50  has a vane base  52  and a vane first end  53  and a vane second end  54 . Vane second end  54  is a trailing end as viewed by the airflow past inlet vane  50 . Airflow travels first past first vane end  53 , past the length of inlet vane  50 , and then past vane second end  54 . Vane base  52  is attached to the interior wall of inside tube  30 , typically with a weld. In an exemplary embodiment where inside tube  30  has a 36″ (91.4 cm) inner diameter, vane base  52  is 8″-16″ (20.3 cm to 40.6 cm), vane first end  54  is 1″-3″ (2.5 cm to 7.6 cm) high, and vane second end  53  is less than ½″ (12.7 mm). As shown in FIG. 5, an inside tube centerline  31  is referenced at each inlet vane  50 , which passes through vane first end  53  and runs parallel with the length of inner tube  30  along the inner wall. Each inlet vane  50  is oriented oblique to an inside tube centerline  31 . In the exemplary embodiment an offset angle  35  is 0.5° to 2.0°. Such an angle results in inlet vane offset A being approximately 0.25″ (6.3 mm) where vane base  52  is 12″ (30.5 cm). Each inlet vane  50  is thus offset obliquely to its own inside tube centerline  31  while remaining normal to the interior wall of inside tube  30 , as depicted in FIG.  2 . While inlet vane  50  is shown in FIG. 5 as a straight vane, alternatively inlet vane  50  can have an arcuate shape (not shown) that results in the same amount of inlet vane offset A as described above for a straight vane. 
     Outlet vanes  51  are attached to the interior wall of inside tube  30  at the air outlet side  28 . In the exemplary embodiment outlet vanes  51  are four in number and circumferentially equally spaced as shown in FIG.  3 . An exemplary outlet vane  51  is also depicted in FIG. 4 as having the same shape and dimensions as inlet vane  50  when inlet vane  50  is a straight vane. Referring to FIGS. 3,  5  and  5 A, the key difference between outlet vanes  51  and inlet vanes  50  is that outlet vanes  51  each align along an inside tube centerline  31  with no offset A. Each outlet vane  51  is thus aligned with its own inside tube centerline  31  while remaining normal to the interior wall of inside tube  30 . 
     Referring to FIG. 7, noise abatement module  10  may be used singularly or in conjunction with other noise abatement modules  10  or other systems. For example, noise abatement modules  10  may be aligned in series. Alternatively and additionally, noise abatement modules  10  may include Y-connector  26  to afford parallel alignment as well where the outlet end stub  24  of noise abatement module  10  is joined to the inlet end stub  24  of noise abatement module  10 ′. 
     OPERATION 
     Referring to FIGS. 1,  2 ,  3 ,  6 , and  6 A, noise abatement module  10  is attached to piping or equipment (not shown) from which high pressure air is being exhausted. This is typically accomplished by bolting flange  40  at inlet side  27  to an equipment outlet flange (not shown), thus providing sealed fluid communication between the exhaust air and the interior of noise abatement module  10 . High velocity air enters inside tube  30  through the center opening in flange  40  at inlet side  27 , and is rotated about its linear axis by inlet vanes  50 . This causes outer layer  19  of exhaust  15  to rotate about this linear axis, forcing air into space  33  through inside tube perforations  32 , where it is slowed, and high velocity air from core  17  is allowed to expand and move into outer layer  19 . Thus exhaust  15  is “chewed” until it has less and less high velocity air. 
     When the exhaust air nears air outlet side  28 , it encounters outlet vanes  51 , which stop the rotation of the exhaust air, baffling even more of the exhaust gas outer layer  19 , and further “chewing” away outer layer  19 . Piping between outlet vanes  51  and the exit flange  40 , typically 24″-48″ (61.0 cm to 121.9 cm) long and including stub  24  and/or a portion of inside tube  30 , acts as a buffer zone to allow the exhaust air to stabilize back to its original linear flow direction. 
     When used in either or both series and parallel as shown in FIG. 7, each transition through a noise abatement module  10  results in further decrease in the velocity of the air and its attendant noise. The air is finally exhausted to the atmosphere or additional air directing equipment, such as an upward plenum. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.