Patent Publication Number: US-2005142052-A1

Title: Method and apparatus to remove particulates from a gas stream

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to an emission control system to remove particulates from a gas stream and to a method of removing particulates from a gas stream. More particularly, the method includes adding water to the gas stream and subsequently removing water from the gas stream in a condenser, the water removed containing particulates.  
      2. Description of the Prior Art  
      Emission control systems are known. However, previous systems do not operate effectively to remove particulates from a gas stream, or, they are extremely expensive to operate or to construct, or they are inefficient and do not remove a sufficient proportion of the particulates.  
      Settling tanks have been used previously to separate particulates from a gas. Further, it is known to have a wet scrubber that uses water to separate particulates from a gas, but scrubbers either do not remove sufficient particulates or they are expensive and complex to manufacture or operate.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a method of removing particulates from a gas stream by first adding water to the gas stream and subsequently removing water and particulates from the gas stream by condensing the gas stream. It is a further object of the present invention to provide an emission control system for removing particulates from a gas stream where water is added to the gas stream at a first location and subsequently removed in a condensor located at a second location downstream from the first location.  
      A method of removing particulates from a gas stream, the method comprising continuously adding water to the gas stream at a first location, continuously condensing the gas stream to remove water from the gas stream at a second location, the particulates being removed from the gas stream with the water, the second location being downstream from the first location.  
      An emission control system for use with a gas stream containing particulates uses a water supply connected to continuously add water to the gas stream at a fist location. A condensor is located at a second location downstream from the first location. The condensor is connected to operate at a lower temperature that the temperature of the gas stream. The condensor has a drain for water and particulates that are removed from the gas stream. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of the emission control system of the present invention;  
       FIG. 2  is a schematic perspective view of one embodiment of the emission control system;  
       FIG. 3  is a perspective view of one embodiment of a scrubber used in the emission control system;  
       FIG. 4  is a schematic side view of a scrubber; and  
       FIG. 5  is a schematic perspective view of a further embodiment of the emission control system. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT  
      In  FIG. 1 , a gas stream containing particulates enters a humidification zone where water is added. Preferably, the water is added by using spray nozzles. The water is added to saturate the gas stream with water and, preferably, to add sufficient water to not only saturate the gas stream, but to have free water in the gas stream. Downstream from the humidification zone is a cooling/condensation area where the temperature of the gas stream is lowered. Preferably, a condensor is used to lower the temperature of the gas stream, but other devices and methods could be used in place of a condenser to lower the temperature of the gas stream. When the temperature of the gas stream is lowered, water is removed from the gas stream and the water removed contains particulates. Therefore, the particulates are substantially removed from the gas stream along with the water, resulting in a substantially clean gas stream. Preferably, substantially all of the water that is added in the humidification zone is removed in the cooling/condensation area. The greater the amount that the temperature of the gas stream is lowered, the more water that will be removed. Usually, the greater the amount that the temperature is lowered, the greater the expense will be to operate the cooling/condensation area. However, when ambient temperatures are low as they are during the winter in many geographic locations, the temperature of the gas stream can be lowered substantially using ambient air with minimal expense. For some gas streams, it will be desirable to lower the temperature by a sufficient amount to remove more water from the gas stream than the water that was added in the humidification zone. In some applications, it will be desirable to remove less water than the water that was added in the humidification zone. The method and device of the present invention allows a user to control the amount of water added as well as the amount of water removed. In most applications, it will be desirable to remove at least as much water as has been added to the gas stream.  
      In  FIG. 2 , a gas stream  2  has an inlet  4  and an outlet  6 . The gas stream at the inlet  4  contains particulates and the gas stream at the outlet  6  is clean gas. When the expression “clean gas” or similar expressions are used in this application, those expressions should not be interpreted as meaning that the clean gas is entirely free of particulates. The clean gas might still contain some particulates, but will contain fewer particulates than the gas stream contained prior to passing through the emission control system of the present invention. Preferably, the gas stream will contain substantially fewer particulates after passing through the emission control system of the present invention. Water is added to the gas stream at a water inlet  8  located at a first location  10 .  
      A condenser  12  is located at a second location  14 . The second location is downstream from the first location. Preferably, spray nozzles are used at the water inlet to add water to the gas stream so that the water is dispersed throughout the gas stream. Preferably, a sufficient amount of water is added to the gas stream to saturate the gas stream with water. The condensor  12  has a drain  16  whereby water that is removed from the gas stream and particulates that are removed with the water can be drained from the condenser. Between the first location  10  and the second location  14 , there is located a scrubber  18 . The scrubber can be used to add more water to the gas stream and/or to remove some water from the gas stream along with some of the particulates. The scrubber  18  can be a conventional scrubber or it can be a scrubber as described in  FIGS. 3 and 4 . Preferably, the scrubber is a wet scrubber.  
      Referring to  FIGS. 3 and 4  in greater detail, the scrubber  18  has housing  20  with an inlet  22  and an outlet  24 . Within the housing  20 , there is a passage  26 , which extends in more than one direction to the outlet  24 . A cylindrical section  28  of the passage  26  is concentrically mounted in an upper portion of the housing  20 . On a top  31  of the housing  20 , there is mounted a hood  32 . A shaft  34  extends vertically through the housing  20  from the hood  32  to a bottom  36 . The shaft  34  is rotatably mounted in bearings  38 ,  40 . A motor  42  is mounted in a bracket  44 . The motor has a shaft  45  with a pulley  46  mounted thereon. The shaft  34  that extends through the housing  20  has a pulley  48  mounted thereon. Preferably, the motor  42  is an electric motor (the electrical connections are not shown) and a belt  50  connects the pulleys  46 ,  48  so that the motor  42  can rotate the shaft  34 . Beneath a lower edge  52  of the cylindrical section  28 , there is a fan  54  mounted on the shaft  34 . The fan  54  has blades  56  and inner vanes  58 . The inlet  22  is located near the top  31  of the housing  20 . The housing contains an annular baffle  60  that is located between the inlet  22  and the fan  54 . Drains  62  are located in a base  64  of the housing  20 . As is best shown in  FIG. 4 , a plurality of moisturizers  66  (only one of which is shown), which are preferably spray nozzles, is located just upstream from the inlet  22 . The moisturizers  66  add a fine mist to the gas stream  2  just before the gas enters the inlet  22  of the scrubber  18 . When the fan  54  is activated, gas containing particulates is drawn into the inlet  22  and is directed by the shape of the passage  26  and the annular baffle  60  downward and inward. Immediately after passing the baffle  60 , the gas stream  2  strikes the outer blades  56  of the fan  54 . The outer blades  56  are generally flat and lie in a vertical plane and the blades direct the gas outward and downward. Since the gas contains moisture, the blades  56  remove some of the moisture from the gas stream  2  and force it by centrifugal force against an inner wall of the housing  20  where it falls by gravity to the drains  62 . The particulates affix themselves to water droplets in the mist. Therefore, as the moisture is removed, some of the particulate matter is also removed through the drains  62 . After passing downward through the outer blades  56  of the fan  54 , the gas stream is forced inward and upward by the inner vanes  58  of the fan  54  into an interior of the cylindrical section  28 . The vanes  58  are angled to force the gas upward as the fan rotates. The abrupt change in direction causes the gas stream to lose more moisture and the gas stream moves upward through the hood  32  to the outlet  24 . The gas stream  2  then moves on to the condensor (not shown in  FIGS. 3 and 4 ) where the gas is further cleaned. The water that is added through the moisturizers  66  just upstream from the inlet  22  could be added to the gas stream within the scrubber  18 . There are arrows located within the passage  26  to show the flow direction of the gas stream. The scrubber  18  shown in  FIG. 3  is slightly different from the scrubber  18  shown in  FIG. 4 . the motor could be a direct drive with a gear box instead of having a shaft and pulley as shown.  
      The amount of water added to the gas stream is such that a wet environment is created with sufficient free water carried by the gas stream. In other words, the gas stream is preferably more than saturated with water.  
      The fan  54  of the scrubber  18  could have the inner vanes  58  removed and located in a separate fan, either within the scrubber or somewhere else in the gas stream between the inlet  4  and the outlet  6 . With some gas streams, a fan to move the gas stream through the emission control system of the present invention will not be necessary. In other applications, a fan will be required to force the gas stream through the emission control system.  
      In  FIG. 5 , there is shown a perspective view of a further embodiment of an emission control system having a scrubber  18 , which is described in detail in  FIGS. 3 and 4 . The same reference numerals are used in  FIG. 5  to describe the components that are identical to the components of  FIGS. 2, 3  and  4 . Spray nozzles  70  are located before the scrubber  18 . the detailed components of the scrubber  18  shown in  FIG. 5  have not been numbered, but are identical to the components shown in  FIGS. 3 and 4 .  
      Preferably, all of the water that is drained from the emission control system is recovered and is collected in a container (not shown). The water is then connected to a pump and pumped back into the emission control system in the humidification zone. The circulation and re-use of the water reduces the water consumption significantly. By circulating and re-using the water, the concentration of suspended particles in the water will increase. The emission control system of the present invention can be operated continuously, or, intermittently, as required. The water is independently pumped from the container by a second pump to a filter (not shown) and then returned to the system. The recycled water is preferably filtered form time to time to keep the water reasonably clean.  
      The fan and rotor can be one component or separate components. The fan has blades to move the gas through the system. The rotor has vanes to remove water and particulates from the gas stream. the rotor is located in the scrubber. The fan can be located in the scrubber or elsewhere in the system. Preferably, the fan and rotor are one component.  
      The device of the present invention is efficient and cost effective to collect airborne dust particles from many sources of emissions. One source of these emissions is industrial boilers, including those that are burning waste wood and emit airborne ash particles (flyash) in the flue gas from gas stacks.