Abstract:
A method to disrupt a smelt flow including: arranging a shatter jet nozzle assembly to direct a jet of disrupting fluid against the smelt flowing from a recovery boiler to a dissolving tank; supplying the disrupting fluid to the shatter jet nozzle assembly from a first source of disrupting fluid to form the jet directed against the smelt flow while a second source does not provide disrupting fluid to the shatter jet nozzle, and supplying the disrupting fluid from both the first source and the second source flow to the shatter jet nozzle assembly to form the jet of disrupting fluid directed against the smelt flow.

Description:
CROSS RELATED APPLICATION 
     This application claims the benefit of application Ser. No. 61/266,252 filed Dec. 3, 2009, which is incorporated in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a shatter jet nozzle and a method for disrupting the smelt flow from a smelt spout of a recovery boiler. 
     A recovery boiler, such as a soda recovery boiler, is typically used in the chemical recovery of sulfate and other sodium-based substances from pulp manufacturing processes. Organic substances dissolved in the waste liquor during digestion or other pulping processes are combusted in the recovery boiler to melt inorganic compounds, e.g., ash, in the waste liquor and generate steam. The melted inorganic compounds flow as a primarily liquid smelt to the bottom of the recovery boiler. The smelt flows from the bottom of the boiler along one or more cooled smelt spouts to a dissolving tank. In the dissolving tank, the smelt is dissolved by water or weak white liquor to produce soda lye, e.g., green liquor. 
     The hot smelt flow from the spout causes “banging” and explosions when the smelt falls into the cooler liquid in the dissolving tank. The temperature of the smelt is on the order of 750° Celsius (° C.) to 820° C. In contrast, the temperature of the green liquor (or weak white liquor) in the dissolving tank, containing mainly water, is on the order of 70° C. to 100° C. This dramatic temperature difference between the hot smelt flow and the much cooler green liquor contributes to the explosions and banging noises as the smelt hits and is instantly cooled by the green liquor. 
     The intensity of the explosive reactions of the smelt in the dissolving tank may be reduced and controlled by disrupting the smelt flow into small streams, droplets or pieces as the flow leaves the spout and before it hits the liquid in the dissolving tank. It is conventional to disrupt the smelt with jet streams, e.g., steam jets, discharged from nozzles at low or medium pressure steam. These nozzles are referred to as shatter jet nozzles because they shatter the flow of the smelt. 
     The shatter jet nozzle discharges a jet stream at a specific volume and rate designed to break-up the smelt flow expected during normal operation of the recover boiler. The smelt flows at a relatively uniform rate and volumetric flow during normal recovery boiler operation. Conventional shatter jet nozzles direct a jet stream at a rate and volume designed to disrupt the normal uniform rate and flow of smelt. Conventional shatter jet nozzles are coupled to a single steam source that provides a constant flow rate of steam to the nozzles. The rate of steam flow to the nozzle typically cannot be adjusted remotely, and is adjusted at or near the nozzle. 
     Variations can occur in the rate and volume of smelt flowing from a recovery boiler. During normal operation of the recovery boiler, the normal steam jets from the shatter jet nozzles are capable of disrupting the smelt flow and sufficiently reducing explosions in the dissolving tank. However, the recovery boiler may be operated in an upset condition resulting in heavy smelt flows. These heavy smelt flows may not be adequately disrupted by the jets from the shatter jet nozzle and the smelt may cause explosions from which hot smelt droplets may splatter from the tank. These excessive explosions of smelt can result in equipment damage and danger to personnel safety. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A shatter jet nozzle has been developed that discharges jets to breakup a smelt flow at two or more flow rates or pressures. The nozzle is coupled to two or more sources of steam (or other disrupting fluid) that provide the capacity for multiple rates or pressures of the jets. Further, the flow rate or pressure of the jets from the shatter jet nozzle may be manually or remotely controlled by controlling the flow of steam from one of the steam sources, such as by unblocking steam from a second steam source only during heavy smelt flows. By controlling the flow rate or pressure, the jet discharged from the shatter jet nozzle can be adjusted to breakup different rates of smelt flow. For example, the volume or pressure of the jets discharged from the shatter jet nozzle(s) may be increased during heavy smelt flows from the boiler and may be reduced during normal smelt flows. 
     An apparatus has been conceived and is disclosed herein to disrupt smelt flowing from a recovery boiler to a dissolving tank, the apparatus comprising: a shatter jet nozzle assembly arranged to direct a jet of disrupting fluid against the smelt flowing from the recovery boiler to the dissolving tank; a first source of disrupting fluid coupled to the shatter jet nozzle assembly; a second source of disrupting fluid coupled to the shatter jet nozzle assembly, and a valve arranged at or between the second source and the shatter jet nozzle assembly to regulate a flow of the disrupting fluid from the second source to a nozzle in the shatter jet nozzle assembly, wherein the apparatus has a first operating mode in which disrupting fluid from the first source flows through the shatter jet nozzle assembly and forms the jet of disrupting fluid discharged from the nozzle while the valve prevents disrupting fluid from the second source from being discharged from the jet, and a second operating mode in which disrupting fluid from the first and second sources flow through the shatter jet nozzle assembly to form the jet of disrupting fluid while the valve permits disrupting fluid to flow from the second source to the shatter jet nozzle assembly. 
     A method has been conceived and is disclosed herein to disrupt a smelt flow including: arranging a shatter jet nozzle assembly to direct a jet of disrupting fluid against the smelt flowing from a recovery boiler to a dissolving tank; supplying the disrupting fluid to the shatter jet nozzle assembly from a first source of disrupting fluid to form the jet directed against the smelt flow while a second source does not provide disrupting fluid to the shatter jet nozzle, and supplying the disrupting fluid from both the first source and the second source flow to the shatter jet nozzle assembly to form the jet of disrupting fluid directed against the smelt flow. 
     A shatter jet nozzle assembly has been conceived and is disclosed herein forming a jet applied to a smelt flowing from a recovery boiler and into a dissolving tank, the assembly comprising: a first nozzle conduit having a first discharge nozzle directed towards the smelt flow as the flow falls from the recovery boiler to a liquid surface in the dissolving tank, wherein the first nozzle conduit is connectable to a first source of disrupting fluid, wherein the disrupting fluid flows through the first nozzle conduit and from the first discharge nozzle to form a jet directed against the smelt flow, and a second nozzle conduit having a second discharge nozzle directed towards the smelt flow as the flow falls from the recovery boiler to a liquid surface in the dissolving tank, wherein the second nozzle conduit is connectable to a second source of disrupting fluid, wherein the disrupting fluid flows through the second nozzle conduit and from the second discharge nozzle to form a jet directed against the smelt flow, wherein the jet from the first discharge nozzle and the jet from the second discharge nozzle merge prior to the jets impacting the smelt flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a is schematic diagram showing a side view, partially in cross-section, of a smelt hood, smelt spout, an upper portion of a dissolving tank and a shatter jet nozzle discharging a jet to break-up the smelt flow from the spout. 
         FIG. 2  is a schematic diagram showing a front view of the hood, smelt spout, shatter jet nozzle and dissolving tank, wherein  FIG. 2  is a view along line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a side view of an exemplary shatter jet nozzle having concentric passages for multiple flows of disrupting fluid. 
         FIG. 4  is another side view, shown in partial cross section, of the shatter jet nozzle, wherein the view is taken from a ninety degree angle from the view shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the distal end of the nozzle taken along line  5 - 5  in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a lower section of a recovery boiler  10  of a pulp mill. Smelt flows from the bottom of the boiler through an opening  12  and into a smelt spout  14 . The portion of the smelt spout  14  extending outside the wall of the boiler is surrounded by a conventional closed protecting hood  16  comprising an upper hood portion  18  and a lower hood portion  20 . The upper hood portion  18  includes a cover  22 . 
     The hood  16  contains the splash of liquid and smelt as they flow through the spout  14  and contains exhaust gases so that the gases do not discharge directly to the environment. The lower hood portion  20  may be connected to a conventional dissolving tank  24  disposed under the protecting hood  16 . The smelt dissolves into liquid in the tank  24  to produce green liquor. 
     Hot, liquid smelt flows from a boiler opening  12  near the bottom of the recovery boiler to the smelt spout  14 . The smelt flows along a downwardly sloped bottom  26  of the spout  14 , over a free end  28  of the spout, and into the dissolving tank  24 . The smelt flow path as the smelt falls from the free end  28  to the spout to the liquid surface in the tank is indicated by arrows  30 . 
     A jet  32  of steam or other disrupting fluid is directed against the smelt as the smelt flows from the free end  28  of the spout to the tank. The jet  32  disrupts the flow of smelt into droplets, segments the flow or otherwise breaks up the flow such that there is not a uniform stream of smelt entering the tank. The jet  32  is discharged from nozzle  34  of a shatter jet nozzle assembly  36 . 
     The shatter jet nozzle assembly  36  may be attached to an adjustable mounting bracket  37  fixed to the lower portion  20  of the hood  16 . The adjustable mounting bracket allows the shatter jet nozzle assembly to be moveably positioned to direct the jet  32  against the flow of smelt  30 . Optionally, opposite shatter jet nozzle assemblies may be mounted to the lower portion  20  of the hood to project disrupting fluid jets from opposite sides of the smelt flow to enhance the breakup of the smelt flow before the smelt reaches the liquid level in the dissolving tank. 
     During normal operation of the recovery boiler  10 , steam or other disrupting fluid is supplied to the shatter jet nozzle assembly by a first pressurized fluid source  38 , such as a source of low pressure or medium pressure steam. The first pressurized fluid source  38  may a pressurized header of steam or other disrupting fluid. Alternatively, the fluid source  38  may be a conduit with a pump coupled to a tank, such as the dissolving tank  24  of the weak white liquor or green liquor. 
     The first pressurized fluid source  38  may provide fluid, e.g., steam or other gas, to the shatter jet nozzle assembly  36  at a first pressure level. The pressure of the first pressurized fluid source may be selected to be adequate to produce a jet  32  from the shatter jet nozzle  34  sufficient to breakup the smelt flow during normal operation of the recovery boiler. The volume or flow rate of disrupting fluid from the first pressurized fluid source to the nozzle assembly  36  is sufficient to fully supply the shatter jet nozzle assembly with a jet  32  adequate to breakup the flow of smelt during normal boiler operation. 
     A first valve  39  connected to a conduit extending from the first pressurized fluid source  38  to the shatter jet nozzle assembly  36  regulates the flow of disrupting fluid, which may be a low-pressure flow, to the nozzle assembly. The first valve  39  may be remote, e.g., twenty feet distant, from the protective hood  16  or the valve may be proximate to the hood. The first valve  39  may be manually operated or remotely controlled by a solenoid affixed to the valve. The first valve is typically open to a fixed position during operation of the recovery boiler to provide a continuous flow of disrupting fluid to the shatter jet nozzle assembly  36 . 
     A second source  40  of disrupting fluid may also be connected to the shatter jet nozzle assembly  36 . The second source  40  provides disrupting fluid that may be at the same or a higher pressure than the first fluid source. The second source  40  may be disrupting fluid in a pressurized header containing steam or other disrupting fluid. Alternatively, the second source  40  may be provided by a pump which pressurizes disrupting fluid, such as liquor from the dissolving tank or water. 
     The second source  40  provides supplemental disrupting fluid that increases the volume or pressure of the jet  32 , over and above the volume or pressure of the jet  32  when supplied solely from the first pressure source. The high velocity and pressure jet  32  formed by the combine flow of disrupting fluid from the first and second sources  38 ,  40  may be applied to breakup heavy smelt flows that occur during an upset condition in the recovery boiler. 
     A second valve  42  is connected to a conduit extending from the second pressurized fluid source  40  to the shatter jet nozzle assembly  36 . The second valve  42  regulates the flow of disrupting fluid, which may be a high pressure flow, to the nozzle assembly. The second valve  42  may be remote, e.g., twenty feet distant, from the protective hood  16  or the valve may be proximate to the hood. The second valve  42  may be manually operated or remotely controlled by a solenoid affixed to the second valve. The second valve  42  may be opened to allow flow from the second pressurized fluid source  40  only during extraordinary conditions, such as during heavy smelt flows. Because the second valve is remote to the hood or is remotely operable, the second valve may be safely opened after heavy smelt flow begins and explosions are occurring as the smelt flow hits the cool liquor in the dissolving tank  24 . 
       FIGS. 3 to 5  show an exemplary shatter jet nozzle assembly  50  which has a generally cylindrical metallic housing  52  which extends substantially the length of the assembly and provides shielding to protect the assembly from smelt. A distal end of the assembly includes a bell housing  54  (not shown in  FIG. 4 ) that provides a shield to the nozzle end of the assembly. Housed within the housings  52  and  54  are coaxial tubes  56  and  58  that define conduits for the two flows of pressurized disrupting fluid, e.g., steam. 
     A center inlet  60  to a center coaxial tube  56  is coupled to one of the sources of disrupting fluid, such as the first steam source  38 . The center inlet  60  directs disrupting fluid from the first source into the center coaxial tube  56  such that the fluid flows to a center nozzle  62 , which may have an oval shape in cross-section as is shown in  FIG. 5 . 
     A side inlet  64  to the outer coaxial tube  58  is coupled to another source of disrupting fluid, such as the second steam source  40 . The side inlet directs disrupting from the second source through an annular passage between the outer and inner coaxial tubes to an outer nozzle  66  that surrounds the center nozzle  62 . The outer nozzle  66  may have a racetrack shape such as shown in  FIG. 5 . The center nozzle  62  and outer nozzle  66  may be coaxial and have adjacent openings at a common outlet for the nozzle assembly. 
     The length of the nozzle assembly  50  is sufficient to position the nozzles  66 ,  62  adjacent to the flow of smelt from the spout. The nozzle assembly is preferably mounted to the protecting hood  16 , so that the nozzles  66 ,  62  may be turned and positioned properly with respect to the smelt flow. 
     With the nozzle assembly  50  disclosed herein, the breakup of the smelt is more efficient and safer, especially during heavy smelt flows from a recovery boiler. The ability to discharge jets from two nozzles  62 ,  66  in the nozzle assembly  50  reduces the risk of extensive explosions in the dissolving tank and the noise level is reduced in the vicinity of the dissolving tank even during heavy smelt flows. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.