Patent Publication Number: US-2013228073-A1

Title: Methods and apparatuses for cooling and scrubbing diesel exhaust gases on a ship

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to methods and apparatuses for scrubbing diesel exhaust gases, and more particularly relates to scrubbing methods and apparatuses that first cool the exhaust gases in a scrubbing vessel. 
     BACKGROUND 
     As is well known, the combustion of hydrocarbon-containing fuels, such as diesel, results in exhaust gases containing sulfur compounds including sulfur dioxide. Further, the presence of sulfur dioxide in the atmosphere has been linked to the formation of acid rain. Due to the ecological damage resulting from acid rain, various government standards have been established to reduce or prevent the emission of sulfur dioxide. 
     While land-based combustion plants have utilized a variety of methods to reduce or eliminate the emission of sulfur dioxide, many of these methods are inappropriate for shipboard plants. For instance, land-based scrubbing apparatuses largely can be designed and implemented without, or with little, concern regarding footprint size. However, there is an overriding interest in minimizing the footprint of ship-based scrubbers and other power and exhaust systems. Further, there is an interest in optimizing fuel and exhaust processing systems on ships. 
     In light of the above, the present disclosure provides a method and apparatus for scrubbing exhaust gases on a ship with a reduced footprint. Further, the present disclosure provides a method and apparatus for quenching exhaust gases to saturation temperatures to improve mass transfer during scrubbing. Also, the present disclosure provides a method and apparatus for scrubbing cooled exhaust gases to reduce the cost of downstream equipment. Furthermore, the present disclosure provides a method and apparatus for scrubbing exhaust gases that exhibits a reduced pressure drop on the diesel engine. Alternative or additional features and characteristics of the methods and apparatuses will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     BRIEF SUMMARY 
     Methods and apparatuses for scrubbing diesel exhaust gases produced on a ship are provided. In accordance with one exemplary embodiment, a method for scrubbing diesel exhaust gases on a ship includes providing a scrubber vessel formed with a quench zone, a scrubbing zone, and a riser. Water is passed through the scrubbing zone and into the quench zone. The exhaust gases are delivered to the quench zone through the riser and enter the quench zone at a temperature of about 175° C. to about 340° C. The method includes cooling the exhaust gases to a temperature of about 60° C. to about 70° C. in the quench zone by contacting the exhaust gases with the water. The cooled exhaust gases are then scrubbed in the scrubbing zone. 
     In another embodiment, a method for scrubbing diesel exhaust gases produced on a ship includes flowing the exhaust gases from a diesel engine to a scrubber vessel. The exhaust gases are introduced to a chamber within the scrubber vessel and have a temperature of about 175° C. to about 340° C. Then the exhaust gases are cooled to a temperature of about 60° C. to about 70° C. Thereafter, the cooled exhaust gases are scrubbed. 
     In accordance with another exemplary embodiment, an apparatus for scrubbing diesel exhaust gases produced on a ship is provided. The apparatus includes a scrubber vessel formed with a quench zone, a scrubbing zone, and a riser. Further, a duct is configured to deliver the exhaust gases through the riser and into the quench zone at a temperature of about 175° C. to about 340° C. The apparatus includes a means for cooling the exhaust gases to about 60° C. to about 70° C. in the quench zone. Also, the apparatus includes a means for scrubbing the cooled exhaust gases in the scrubbing zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a schematic view of an apparatus for scrubbing exhaust gases on a ship in accordance with exemplary embodiments; 
         FIG. 2  is a cross sectional view of a scrubber vessel for use in the apparatus of claim  1  in accordance with exemplary embodiments; 
         FIG. 3  is a cross sectional view of an alternate scrubber vessel for use in the apparatus of claim  1  in accordance with exemplary embodiments; and 
         FIG. 4  is a perspective view of water stream in the alternate scrubber vessel of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the methods and apparatuses for scrubbing exhaust gases on a ship as claimed herein. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     As detailed below, the methods and apparatuses for scrubbing exhaust gases on a ship utilize a scrubber vessel that houses both a quench or cooling zone and a scrubbing zone. As a result, the footprint for cooling and scrubbing apparatuses is reduced. Further, the footprint of ducts connecting such apparatuses is eliminated. 
     In  FIG. 1 , a scrubbing apparatus is shown and generally designated  10 . The scrubbing apparatus is located on a ship  12  and includes a diesel engine  14 , scrubber vessel  16  and secondary basin  18 . The diesel engine  14  creates a stream of exhaust gases  22  that are delivered to the scrubber vessel  16  through a duct  24 . Scrubbed gases  26  exit the scrubber vessel  16  as shown. While the exemplary scrubber vessel  16  may incorporate any of a variety of means for scrubbing exhaust gases, it is contemplated herein that water, as well as other components to enhance the scrubbing process, is used in the scrubbing process. As shown, water  32  - which may be, for example, sea water—exits the scrubber vessel  16  and flows to the secondary basin  18 . The secondary basin  18  is positioned below the scrubber vessel  16  such that water  32  will flow from the scrubber vessel  16  to the secondary basin due to gravity. As shown, the apparatus  10  includes a pump  36  to pump recycled water  38  to the scrubber vessel  16  for reuse in the scrubbing process. 
     Referring now to  FIG. 2 , the structure and connections of scrubber vessel  16  may be more specifically explained. As shown, the scrubber vessel  16  has a top end  42  and a bottom end  44 . The bottom end  44  is formed with an inlet  46  in communication with the duct  24  to receive the exhaust gases  22  from the diesel engine  14 . The top end  42  is formed with an outlet  48  through which the scrubbed gases  26  may exit the scrubber vessel  16 . 
     The scrubber vessel  16  defines a chamber  52 . A barrier  54  bounds an inlet zone  56  in the chamber  52  at the bottom end  44  of the vessel  16 . Risers  58  pass through the barrier  54  and extend to openings  60  that are positioned in a quench zone  62 . While two risers  58  are illustrated, the vessel  16  can be provided with six, eight, or more risers  58  as desired. As shown, the quench zone  62  is bounded by the barrier  54  and a vapor-liquid contact mechanism  64 . The exemplary quench zone  62  includes splash or diffusion plates  66 . Each plate  66  is positioned at a riser opening  60  to provide a selected flow path to diffuse the flow of exhaust gases  22  into the quench zone  62 . Further, the plates  66  block or inhibit falling water drops  68  from entering the risers  58 . Typically, any water droplets  68  that enter the risers  58  are atomized and carried back into the quench zone  62  by the flow of exhaust gases  22 . The exemplary vessel  16  is further provided with baffles  72  that inhibit movement of any water collected on the barrier  54 . 
     As shown, the vessel  16  is formed with a water outlet  74  adjacent the barrier  54 . Water  32  landing on the barrier  54  flows out of the outlet  74  to the secondary basin  18 . As a result, water does not rise to the level of the riser openings  60  and does not backflow into the risers  58  toward the engine  14 . Such backflow is prevented even in rocking conditions experienced by the ship  12  on rough seas. As noted in  FIG. 1 , the water  32  received in the secondary basin  18  may be pumped and recycled to the top end  42  of the vessel  16  for reuse in the scrubbing process. 
     When the exhaust gases  22  enter the quench zone  62 , they are typically at a temperature of about 175° C. to about 340° C. (about 350° F. to about 650° F.). Further, the velocity of the exhaust gases  22  from the engine to the vessel  16  is typically in the range of about 2000 feet/minute (ft/min) to about 5000 ft/min. In the quench zone  62 , the velocity of the exhaust gases  22  is typically about 2500 ft/min to about 7000 ft/min. The pressure drop of the exhaust gases  22  exiting the diesel engine  14  is typically about 5 inches of water (inH2O) to about 10 inH2O and the pressure drop of the exhaust gases  22  after passing through the plates in the quench zone  62  is about 2 inH2O to about 7 inH2O. Upon impact with the water droplets  68 , the exhaust gases atomize the droplets  68  into smaller drops, thereby increasing the surface area of the water. The water cools the exhaust gases  22  to a temperature of about 60° C. to about 70° C. (about 140° F. to about 160° F.), such as about 65° C. (about 150° F.) which is at or near the saturation temperature of the exhaust gases. The water further absorbs sound energy from the exhaust gases  22 . In exemplary embodiments, the water removes particulates from the exhaust gases  22 . 
     As shown, the cooled exhaust gases  82  flow from the quench zone  62  into the scrubbing zone  83 . The cooled exhaust gases  82  flow in the same direction (upward in  FIG. 2 ) as the flow of the exhaust gases  22  into the inlet zone  56  and quench zone  62 . The vapor-liquid contact mechanism  64  scrubs the cooled exhaust gases  82 . Mass transfer properties during the scrubbing process are improved due to the reduced temperature of the cooled exhaust gases  82 . Specifically, saturating the gases  82  improves mass transfer by reducing the gas volume and by preventing evaporation at the liquid-gas interface that would otherwise reduce mass transfer from the vapor to the liquid. An exemplary vapor-liquid contact mechanism  64  is a packed bed, with plastic or metal packing It is noted that due to the improved mass transfer properties, a wider variety of packings may be used to sufficiently scrub the cooled exhaust gases  82 . After scrubbing, the scrubbed gases  26  exit the vessel  16  through the outlet  48 . 
     Referring to  FIG. 3 , an alternate arrangement is illustrated. As shown, the exhaust gases  22  enter the vessel  16  through a horizontal inlet  46 . The exhaust gases  22  pass through the inlet zone  56  and horizontal risers  58  into the quench zone  62 . In the quench zone  62 , water streams  84  are directed at the plates  66  with sufficient velocity to form a layer  86  of water extending radially away from the plates  66 . This is shown more clearly in  FIG. 4 . In  FIG. 4 , the exemplary water stream  84  is directed at the disk-shaped plate  66  by a tube  88 . As the water stream  84  contacts the plate  66 , it forms into a layer  86  of water. The layer of water  86  flows out past the edge of the plate  66  in the direction of radial arrows  90 . 
     Referring back to  FIG. 3 , the exhaust gases  22  entering the quench zone  62  are diffused by the plate  66  and pass through the layer  86  of water. Upon impact with the water  86 , the exhaust gases  22  atomize the water  86  into small droplets. As in the vessel  16  of  FIG. 2 , the exhaust gases  22  are cooled, such as from about 175° C. to about 340° C. to near the gases&#39; saturation temperature, such as about 60° C. to about 70° C., for example, about 65° C. The cooled exhaust gases  82  then pass into the vapor-liquid contact mechanism  64  in the scrubbing zone  83 . Water exits the vessel  16  through water outlet  74 . As shown, the exiting water  92  may be recycled to a pump  94  and pumped for reuse in the quench zone  62 , or recycled to the pump  36  (shown in  FIG. 1 ), and reused in the vapor-liquid contact mechanism  64 , as indicated by arrow  96 . 
     While the particular methods and apparatuses for scrubbing diesel exhaust gases on a ship as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of exemplary embodiments and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.