Abstract:
A nozzle for the spraying of black liquor in a recovery boiler has discharge orifice inserts that can be removed and replaced with other inserts, to provide variable spray patterns, by changing the size and/or shape of the orifice of the nozzle, without requiring replacement of the entire nozzle body, to enable fine tuning of the atomization of the spray. Adjustment of the orifice height provides adjustment of the atomization and the spray angle of the discharge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11766030 filed Jun. 20, 2007, and claims priority from U.S. provisional patent application 60805460, filed Jun. 21, 2006. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to nozzles used for the injection and atomization of black liquor that is combusted in a chemical recovery boiler. 
       BACKGROUND OF THE INVENTION 
       [0003]    Black liquor is a fluid that is the by product of the pulping process. This fluid contains both organic and inorganic material resulting from the pulping of wood. Black Liquor is burnt in a special boiler where the heat from the organic matter is used to generate steam and the inorganic matter is reduced to extract the pulping chemicals which are then returned to the pulping process. In order to ensure the proper combustion and chemical recovery the liquor has to be atomized to an optimum droplet size. This depends on the physical properties of the black liquor and boiler geometry as well as operating parameters such combustion air flow, liquor flow rate, injection pressure and temperature. 
         [0004]    In accordance with the prior art, black liquor is sprayed into the boiler through dedicated nozzles.  FIG. 1  is a schematic of the most widely used nozzle, the splash plate  10 . Other nozzles types that have been used are used the V-jet  20  shown in  FIG. 2  and more recently the beer can  30  shown in  FIG. 3 . The latter has come about as a result of new developments in boiler combustion. 
         [0005]    In the case of the splash plate nozzle the black liquor is delivered through the pipe  14  which is mounted to the inlet orifice  11  on the nozzle body  13 . The fluid leaves the nozzle through the discharge orifice  12 . Both the inlet and discharge orifices  11  and  12  are an integral part of the nozzle body  13 . The fluid upon leaving the orifice impacts on the splash plate  15  where it spreads out to form a sheet that eventually breaks up into droplets that burn. 
         [0006]    For the V-jet nozzle  20  the fluid is delivered through pipe  24  which is mounted to the inlet orifice  21  found on the nozzle body  23 . The fluid leaves the nozzle through the discharge orifice  22 . Both the inlet and discharge orifices  21  and  22  are an integral part of the nozzle body  23 . Fluid traveling through the discharge orifice contracts and spreads out like a fan forming a thin sheet that eventually breaks up into droplets that burn. 
         [0007]    For the rotary atomizer/beer can nozzle  30  the fluid is delivered through pipe  34  which is mounted to the inlet orifice  31  found on the nozzle body  33 . The fluid leaves the nozzle through the discharge orifice  32 . Both the inlet and discharge orifices  31  and  32  are an integral part of the nozzle body  33 . Fluid traveling through the inlet orifice  31  travels down a small transition channel  35  and enters the inner cavity  36  of the nozzle body  33  at a point tangential to the cavity wall. The fluid swirls around the cavity and eventually leaves the nozzle body  33  through the discharge orifice  32  found at the bottom of the nozzle body. The fluid leaving the discharge orifice spreads like a cone which eventually breaks up into droplets that burn. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the invention, a nozzle for the spraying of black liquor in a recovery boiler is provided, where the discharge orifice of the nozzle can easily be varied without having to change the entire nozzle. This enables one to fine tune the atomization to the specific combustion setup at that time and place. The orifice height is varied to control the spray angle and characteristics to desired configurations. 
         [0009]    The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1 : Cross section of prior art splash plate nozzle. 
           [0011]      FIG. 2 : Cross section of prior art V-jet nozzle. 
           [0012]      FIG. 3 : Schematic of prior art beer can nozzle. 
           [0013]      FIG. 4 : Cross section of variable orifice beer can. 
           [0014]      FIG. 5A : Bottom view of the discharge end of the variable orifice beer can. 
           [0015]      FIG. 5B : Detail view of roll pin and orifice disk from  FIG. 5A . 
           [0016]      FIG. 6 : Exploded perspective view of variable orifice beer can employing alternative. 
           [0017]      FIG. 7 : Exploded perspective view of another variable orifice beer can employed with variable height orifice insert. 
           [0018]      FIG. 8 : Another perspective view of a beer can nozzle without insert in place. 
           [0019]      FIG. 9 : Views comparing a standard 3/16″ orifice ( 9 A) with a thicker orifice of height E ( 9 B). 
           [0020]      FIG. 10 : Cross section of variable height orifice beer can of  FIG. 7 . 
           [0021]      FIGS. 11 ,  12  and  13 : Views of example spray patterns with different height orifices. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    In order to optimize the combustion and chemical reduction it may be necessary for one to change the orifice size to vary the injection pressure or vary the flow rate. For all of the prior art nozzles above, the discharge orifice is an integral part of the nozzle body which would therefore require one to change the entire nozzle body in order to change the orifice. In another instance it may be necessary to change the orifice due to wear which results in the increase in flow area and/or change in shape. With the nozzle arrangement in accordance with the invention disclosed here one has to only change a single piece that bears the opening for the discharge orifice in order to change the orifice size. 
         [0023]      FIGS. 4 &amp; 5  show the arrangement of a beer can type nozzle  40  in accordance with this invention.  FIG. 4  shows the cross section through the nozzle while  FIG. 5A  shows a view of the bottom end of the nozzle  50  with the details for the variable orifice.  FIG. 5B  gives a more details view of a section of the arrangement in  FIG. 5A . In the case of the beer can nozzle  40  the fluid is delivered through a pipe  41  which is mounted to the inlet orifice  45  found on the nozzle body  42 . According to  FIG. 5A  the fluid entering through  41  travels through the passage  51  and enters the body at the top of the inner cavity  46  of the nozzle while traveling tangent to its wall. The fluid swirls around the inner cavity as illustrated by the path  53  and is finally ejected through the orifice the orifice  44 . The orifice is made by drilling a hole on the orifice disk  43 . Unlike the prior art  30  in  FIG. 3 , this disk is not an integral part of the nozzle body  42 . It is a totally independent component which is placed in a recess at the exit end of the nozzle. When the nozzle is in use the orifice disk faces down. A snap ring  48  prevents it from falling out of the nozzle body. In order to achieve the swirling flow inside the nozzle the discharge orifice should lie rotationally in the quadrant furthest away from the inlet orifice. In order to maintain this position the orifice plate is held securely by pin  49  that has part of its circumference engaged with disk  43  while the remainder engaged with the housing  42 . In liu of the pin a flat face  55  could be cut on the perimeter of the disk  43 ′, as illustrated in  FIG. 6 , a perspective view of an alternative beer can type nozzle body  42 ′ and discharge disk. A corresponding flat face  57  would be cut in the nozzle body  42 ′ as well. In either case, the pin or flat face and the orifice hole are set 180° apart and the lie along the line  52  which is at an angle of 45° from the center line  54  of the inlet orifice. The pin is inserted into a hole in the housing. The depth of the hole is selected such that the pin does not protrude beyond the surface of the disk. It is important to have the pin flush with the outer surface of the disk in order to properly seat the snap ring. While it is possible to hold the disk by cutting a male thread on the edge of the disk corrosion and thread distortion due to heat does not make it very practical. In order to enable one to operate the nozzle in the environment of a chemical recovery boiler while maintaining the ability to change the orifice diameter by swapping out the orifice disk the nozzle housing are made of different materials which have substantially different thermal expansion coefficients. The thermal expansion coefficient of the disk is greater than that of the nozzle housing. The disk diameter and the recess diameter in the nozzle body are carefully controlled so that at room temperature (˜20° C.) a specific gap  47  is maintained between the two of them. The black liquor delivered to the nozzle is in the range of 100-130° C. Therefore at elevated temperatures the disk would expand more than the housing hence closing the gap  47  ensuring a seal of the inner chamber  46 . When the nozzle is taken out of service and the temperature lowered to room temperature the disk will shrink to its original size which in turn will enlarge the clearance between these two components enabling one to swap out the disk thereby changing the orifice diameter. 
         [0024]      FIG. 8  is another perspective view of a beer can type nozzle body, where the flat face portion  57  (or other suitable geometric feature to provide indexing or keying of insert placement) is observable. 
         [0025]    In accordance with the invention, a nozzle arrangement is provided to enable changing of orifice properties to adjust flow and spray pattern without requiring the replacement of the entire nozzle body. This can provide lower cost operation and maintenance, for example. Further, the orifice properties may be changed to provide desired drop sizes and droplet velocities in the spray for optimum combustion in the recovery boiler. 
         [0026]    Varying the height of the orifice insert can provide adjustment and variation to the resulting spray pattern.  FIG. 7  is an exploded perspective view of another variable orifice beer can (viewed from the discharge side) employed with standard orifice insert, wherein the height  102  of insert disk  104  will sit on seat  106  that is formed in the interior of the nozzle body  108 , where the height  110  between the outer edge  112  and the inner face  1114  is the same as the orifice height  102 .  FIG. 9A  shows a cross section of disk  104 , suitably a standard insert disk of minimum thickness. The orifice height  102  is given by the thickness t= 3/16″. The exit diameter G of the orifice is suitably larger than the inlet diameter F, with an inwardly decreasing diameter defined by a bevel to half the thickness of the insert thickness t, whereupon the diameter F continues inwardly (defining a substantially 90 degree angle of the orifice walls) to the inlet face.  FIG. 9B  is the cross section of the variable height orifice disk. This orifice disk that has one end the corresponding features to the disk as shown in  FIG. 9A , having a diameter D 1  together with a cylindrical section having a height E and a diameter D 2 &lt;D 1 , D 2  chosen as slightly less than the diameter C of the beer can interior cavity, to allow for insertion into the cavity. The height E may be varied to provide adjustment of the discharge spray angle and characteristics. The maximum height E is the depth to where the inner face of the orifice disk just reaches position  116  ( FIG. 10 ), where the insert and seat reach the opening of passage  122  from which the supply of the sprayed material will enter the nozzle chamber. By changing the height (or thickness) of the insert disk, the spray angle and characteristics can be changed. The section of diameter D 1  will still fit into the same seating area in the nozzle as the standard disk  102  shown in  FIG. 7 . 
         [0027]      FIG. 10  is a cross section of variable height orifice beer can of  FIG. 7 , fluid entering the nozzle through pipe  118  which is mounted to the inlet orifice  120  found on the nozzle body, travels through the passage  122  and enters the body at the top of the inner cavity of the nozzle while traveling tangent to its wall. The fluid swirls around the inner cavity and is finally ejected through the orifice  124 . The orifice is made by forming a hole on the orifice disk  104 , wherein the hole is beveled to be wider at the output side than at the input side. 
         [0028]    Suitable dimensions in a particular embodiment include: diameter A of body, 3″, height B of body, 3.38″, diameter C of interior body cavity, 2.25″, height D of interior body cavity, 3″, based on the variation of the thickness of the orifice disk the span E can vary from 0″ to 0.45″, diameter F of interior face opening of orifice could range from, 12/32″ to 48/32″, diameter G of exterior face opening of orifice is given typically given by the relation G=F+ 3/16″, diameter H of exterior opening of body, 2.5″. Diameter D 2  is slightly less than the interior diameter C interior body cavity of the beer can nozzle such that the nozzle insert may be fitted into the interior body cavity. 
         [0029]    While in the preferred embodiment, D 2  is chosen as slightly less than but very close to the diameter C of the can interior to allow insertion and removal of the insert, D 2  can be varied such that D 2 &gt;F+sufficient thickness to provide rigidity not collapse in use, up to D 2 =C−fit tolerance. Other nozzles with different sizes are also suitable. The specific dimensions may be varied depending on flow rate desired and fluid viscosity. The outer diameter B of the can should be smaller than the diameter of the opening in the boiler wall so that the can may fit into the boiler without requiring boiler modifications. 
         [0030]    As noted, by controlling the height of the orifice (suitably by controlling the thickness of the insert orifice disk, the spray angle of the discharge spray can be controlled. Suitable values of orifice height and resulting spray angles measured are provided below. 
       EXAMPLES 
       [0031]    A nozzle body in accordance with  FIGS. 7 ,  9 A,  9 B and  10  was mounted in an elevated position with a pressurized water supply provided thereto. The nozzle bodies with varying height orifice insert disks were tested and the resulting spray patterns and spray angles were observed. 
         [0032]    Example 1—orifice height 4.7 mm ( 3/16 inch), orifice diameter 32 mm—spray angle 62 degrees. See  FIG. 11 , a photograph of a resulting spray test. 
         [0033]    Example 2—orifice height 12 m (½ inch), orifice diameter 32 mm—spray angle 60 degrees. The spray cone appears round and well developed. Material within the spray cone appears well balanced and without noticeable weak or heavy zone. See  FIG. 12 , a photograph of a resulting spray test. 
         [0034]    Example 3—orifice height 25 mm (1 inch), orifice diameter 32 mm—spray angle 54 degrees. The spray cone appears round and well developed. Material within the spray cone appears well balanced and without noticeable weak or heavy zone. See  FIG. 13 , a photograph of a resulting spray test. The spray droplets appear to be getting coarser as the spray angle is reduced. The coarser droplets appear to give a more pronounced splash zone on the ground. 
         [0035]    Variation of the orifice height also has an impact on the flow rate, as measured in these examples: 
         [0036]    Example 1—orifice diameter F, 32 mm, height 4.7 mm ( 3/16 inch), at pressure of 138 kPa (20 psig), a flow rate of 24.1 m 3 /h (106 GPM) was measured. 
         [0037]    Example 5—orifice diameter F, 32 mm, height 25.4 mm (1 inch), at pressure of 138 kPa (20 psig), a flow rate of 22.9 m 3 /h (101 GPM) was measured. 
         [0038]    Accordingly, the spray angle may be modified by modifying the height of the orifice through which the spray discharges from the nozzle body. 
         [0039]    While plural embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.