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.

Description:
FIELD OF INVENTION  
       [0001]     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  
       [0002]     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 size. This depends on the boiler geometry as well as operating parameters such combustion air flow, liquor flow rate, injection pressure and temperature.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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.  
         [0006]     For the 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  
       [0007]     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.  
         [0008]     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  
       [0009]      FIG. 1 : Cross section of prior art splash plate nozzle.  
         [0010]      FIG. 2 : Cross section of prior art V-jet nozzle.  
         [0011]      FIG. 3 : Schematic of prior art beer can nozzle.  
         [0012]      FIG. 4 : Cross section of variable orifice beer can.  
         [0013]      FIG. 5A : Bottom view of the discharge end of the variable orifice beer can.  
         [0014]      FIG. 5B : Detail view of roll pin and orifice disk from  FIG. 5A .  
         [0015]      FIG. 6 : Cross section of the variable orifice V-jet.  
         [0016]      FIG. 7 : Another variation for the V-jet nozzle. 
     
    
     DETAILED DESCRIPTION  
       [0017]     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.  
         [0018]      FIGS. 4 &amp; 5  shows 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  52  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 could be cut on the perimeter of the disk. A corresponding flat face would be cut in the nozzle body 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 of the inlet orifice  54 . 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.  
         [0019]      FIG. 6  shows a V-jet nozzle  60  fitted in a manner according to this invention. Fluid enters the nozzle through pipe  61  which is mounted to the inlet orifice  65  on body  62 . Sandwiched in between the pipe  61  and the nozzle body  62  is the orifice insert  63 . Fluid passes from the pipe into the inner cavity  66  and is then ejected through the discharge orifice  64 . The insert has a shoulder  69  which butts up against the shoulder  68  located at the end opposite inlet orifice. In order to keep the specific orientation of the spray from a V-jet insert  63  is free to rotate in side the nozzle body. Once the orientation of the orifice  64  has been finalized the nozzle body is tightened up against the pipe through matching threads on the pipe and nozzle body. A sloped interface  67  between the orifice insert and the pipe ensures the fluid does not leak out of the nozzle body.  
         [0020]      FIG. 7  illustrates another variation of the V-jet nozzle.  
         [0021]     Thus, 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.  
         [0022]     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.