Method and apparatus for crushing smelt

Abstract

The smelt breakup device includes an inlet orifice, an outlet orifice, and a fluid path between the inlet orifice and the outlet orifice. A converging-diverging zone is located between the inlet orifice and the outlet orifice. In one exemplary configuration, a first separable section includes the inlet orifice, and a second separable section includes the outlet orifice and a diverging zone of the converging-diverging zone. In some configurations, there may be a second outlet orifice in fluid communication with the inlet orifice. To provide uniformity across the multiple breakup jets, the first outlet orifice can have a cross-sectional dimension, and the second outlet orifice is positioned at a distance from the first outlet orifice that is between about 4 times and about 10 times the cross-sectional dimension.

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 076,665, filed on September 10, 2020, entitled “Method and Apparatus for Grinding Smelt.” U.S. Provisional Application No. 63 / 076,665, filed on September 10, 2020, entitled “Method and Apparatus for Grinding Smelt,” is incorporated herein by reference in its entirety. [Background technology]

[0002] The present invention relates to smelt processing, Kraft wood pulping processes, Kraft wood pulping mills, black liquor recovery processes and apparatus, and related fields.

[0003] The conversion of wood to wood pulp is typically carried out using the kraft process. Wood chips are pulped in a mixture containing water, sodium hydroxide, and sodium sulfide. This mixture, commonly called white liquor, helps separate the cellulose fibers (wood pulp) from the lignin that holds the fibers together. The separated cellulose fibers are then removed, leaving a waste product typically called black liquor.

[0004] The regeneration and reuse of pulping chemicals from black liquor is desirable to control costs associated with the papermaking process. During the recovery process, the black liquor is concentrated into a solution containing approximately 65-80% solids. The concentrated solution is sprayed into the internal volume of a chemical reduction furnace, also called a recovery boiler. The black liquor is burned in the recovery boiler to recover spent pulping chemicals and generate steam and electricity used in various processes. As a result of the combustion, a molten smelt pool, mainly composed of sodium carbonate (Na2CO3) and sodium sulfide (Na2S), is formed at the bottom of the boiler. The molten smelt has a density of approximately 2000 kg / m³. 3The smelt stream has a surface tension of approximately 0.21 N / m and flows continuously from several outlets at a flow rate of approximately 1 L / s per outlet and a temperature of approximately 780-830°C (1440-1530°F) from the boiler. Preferably, the smelt stream is pulverized into small droplets of a few millimeters by a pulverizing jet. [Overview of the project] [Problems that the invention aims to solve]

[0005] The crushed smelt droplets fall into the dissolution tank, where they dissolve in a weak washing solution (recycled water from the caustic plant) to form a green liquor. The interaction between the molten smelt and the green liquor is noisy and violent. In extreme cases, an explosion in the dissolution tank can occur, causing equipment damage, personal injury, and boiler shutdown. Because these extreme cases are undesirable, regulations are becoming increasingly stringent. The development of new and improved smelt nozzles and methods for effective and safe dissolution tank operation is a top priority in pulp mill operations.

[0006] Certain improvements are disclosed in this specification. [Means for solving the problem]

[0007] In some exemplary embodiments disclosed herein as non-limiting examples, a smelt grinding apparatus includes an inlet orifice, an outlet orifice, a fluid path between the inlet and outlet orifices, and a convergence-divergence zone located between the inlet and outlet orifices. In some such embodiments, a first separable section includes the inlet orifice, and a second separable section includes the outlet orifice and the divergence zone of the convergence-divergence zone. In some embodiments, there may be a second outlet orifice in fluid communication with the inlet orifice. In some such embodiments, the first outlet orifice may have a cross-sectional dimension, and the second outlet orifice is located at a distance of about 4 to about 10 times the cross-sectional dimension from the first outlet orifice.

[0008] In some exemplary embodiments disclosed herein as non-limiting examples, a smelt grinding nozzle includes an inlet orifice, an outlet orifice, and a fluid path between the inlet and outlet orifices having a constriction. In some such embodiments, the nozzle includes a first section including the inlet orifice and a second section including the outlet orifice, the first and second sections being fixed together to define the fluid path, and the constriction is defined at the interface between the first and second sections. In some such embodiments, the portion of the fluid path in the second section extends from the interface to the outlet orifice. In some such embodiments, the portion of the fluid path in the first section has a larger diameter than the portion of the fluid path in the second section. In some embodiments, the portion of the fluid path extending from the inlet orifice to the constriction narrows to reach the constriction.

[0009] In some exemplary embodiments disclosed herein as non-limiting examples, the smelt grinding apparatus includes a plurality of smelt grinding nozzles as described in the preceding paragraph. The outlet orifice of the smelt grinding nozzle has a diameter, and the spacing between the outlet orifices of the plurality of smelt grinding nozzles is no more than eight times that diameter.

[0010] In some exemplary embodiments disclosed herein as non-limiting examples, a method for grinding smelt is disclosed. A smelt grinding apparatus is provided, comprising an inlet orifice, an outlet orifice, a fluid path between the inlet and outlet orifices, and a convergence-divergence zone located between the inlet and outlet orifices. A fluid stream is flowed through the fluid path to generate a fluid jet. The fluid jet comes into contact with the smelt stream, converting the smelt stream into ground smelt. The ground smelt is fed into a dissolution tank. In some embodiments, the fluid stream includes steam. In some embodiments, the method further comprises generating the smelt stream by burning black liquor in a recovery boiler using a kraft pulp mill. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 schematically shows a smelt pulverization device that supplies a melting tank. [Figure 2] Figure 2 schematically shows (A) a top view and (B) a side view of the pulverized smelt entering the melting tank. [Figure 3] Figure 3 schematically shows the interaction between smelt and water when (A) the concentration of the pulverized smelt in the inlet region of the smelt tank is low and (B) the concentration of the pulverized smelt in the inlet region is high. <L [Figure 4] Figure 4 schematically shows an enlarged side cross-sectional view of the smelt pulverization nozzle of Figure 1. [Figure 5] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 6] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 7] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 8] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 9] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 10] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 11] Figures 5 to 11 show various flow rate calculations described in this specification. [Figure 12] Figures 12 and 13 schematically show a smelt pulverization nozzle according to another embodiment in (A) a perspective view and (B) a cross-sectional perspective view. [Figure 13] Figures 12 and 13 schematically show a smelt pulverization nozzle according to another embodiment in (A) a perspective view and (B) a cross-sectional perspective view.

Mode for Carrying Out the Invention

[0012] Referring to Figure 1, a smelt crushing device is shown that supplies to a dissolution tank. A smelt stream is generated by burning black liquor in a recovery boiler (not shown) using a kraft pulp mill. A smelt nozzle 10 delivers the smelt stream 12 to a dissolution tank 14 containing a solvent fluid such as water (e.g., a weak cleaning fluid including water recycled from a caustic plant) to form green liquor 16. A grinding jet nozzle 20 (shown in a cross-sectional view in Figure 1 to reveal the internal fluid pathway 22) receives a fluid stream 24, such as steam 24, exemplify this, which flows through the fluid pathway 22, generating a fluid jet 26 that comes into contact with the smelt stream 12, converting the smelt stream 12 into ground smelt 28, which is then fed into the dissolution tank 14. Optionally, the dissolution tank may include an impeller 30, etc., to circulate the green liquor 16 to assist in the processing of the ground smelt 28.

[0013] Numerous studies have been conducted on the safety of dissolution tanks. These studies have shown that droplets of molten smelt often do not explode immediately upon contact with water, but rather remain stable in the water for several seconds before exploding. Furthermore, it has been observed that the explosion of one droplet can trigger the explosion of other nearby droplets, potentially leading to a series of explosions involving multiple droplets. These findings suggest that 1) effective dissolution of smelt in a dissolution tank requires droplet-scale or "mini" smelt-water explosions, and 2) large-scale explosions are caused by one large fragment of molten smelt or numerous small droplets within a narrow, limited area.

[0014] Figure 2 schematically illustrates the interaction between the smelt from the smelt outlet 10 and the water in the dissolution tank 14 from (A) a top view and (B) a side view. The distribution of smelt droplets (i.e., droplets of pulverized smelt 28) and the projected area over which the droplets fall are greatly influenced by the pulverization of the smelt. As the droplets reach the liquid and continue to sink, they form a cylindrical volume 32 of the smelt-green liquid mixture (schematically shown as a rectangular box in part A of Figure 2 and as a circle in part B of Figure 2). An extreme case scenario occurs when all smelt droplets within the boundaries of the control volume 32 explode simultaneously.

[0015] A thermodynamic model based on the Hicks-Menzies principle was developed to calculate the energy released by large smelt-water interactions in the dissolution tank. The results showed that the conversion ratio (CR), which is the ratio of total explosion energy to the available thermal energy stored in the smelt, increases with increasing green liquor temperature and green liquor-to-smelt volume ratio. This means that the design of the pulverization jet needs to be optimized so that droplets of molten smelt are uniformly distributed over a wide area of ​​the green liquor, in order to reduce the likelihood of the dissolution tank exploding.

[0016] The design and grinding methods of smelt grinding jets vary greatly from mill to mill, and there are no clear industry guidelines regarding nozzle design, configuration, and operation. Typically, nozzles are operated with saturated steam (equivalent to 3.5–15.5 bar, 50–225 psig; and 150–250°C, 300–480°F), and the resulting grinding jet is directed either vertically downwards or slightly opposite to the direction of the smelt flow.

[0017] Referring to Figure 3, the interaction between smelt and water is schematically shown in (A) when the concentration of pulverized smelt 28 is low in the smelt inlet region into the green liquid 16 in the dissolution tank 14, and (B) when the concentration of pulverized smelt 28 in the inlet region is high. Figure 3 also schematically shows the smelt outlet 10, smelt stream 12, and pulverizing jet 26, as previously mentioned with reference to Figure 1. Disruptions in the operation of the dissolution tank often occur when the smelt flow exceeds the capacity of the pulverizing jet. Such overflow situations include smelt overflow (a sudden increase in smelt flow) and "jellyroll" smelt. Jellyroll smelt can be caused by the sudden freezing of molten smelt, fallen sediment, or the inclusion of a large amount of unburned coal. This slow-moving, viscous smelt makes pulverizing the smelt 12 more difficult, and once it is removed, the surge of molten smelt behind it can lead to an overflow situation. When this occurs, the smelt flow overwhelms the capacity of the smelt crushing jet, rendering it ineffective. As a result, the molten smelt typically concentrates in the region directly below the outlet, as schematically shown in Figure 3(B), increasing the explosive energy. Therefore, a crushing jet with sufficient crushing energy to handle both the normal smelt flow and the chaotic state is desirable.

[0018] In some cases, the grinding jet 26 can allow some or all of the smelt flow 12 to escape due to changes in the smelt flow characteristics. Therefore, a grinding jet that covers a wide area is also desirable. Furthermore, while smelt grinding should achieve an optimal droplet distribution, there is also a desire to minimize steam consumption in order to reduce operating costs.

[0019] Accordingly, it is recognized herein that it is desirable for a grinding jet nozzle to be able to meet several criteria: i) generating high grinding energy, ii) being able to cover a wide area, and iii) minimizing steam consumption. Disclosed herein are embodiments of a grinding jet nozzle and a method for performing smelt grinding that address these several criteria (e.g., having sufficient grinding energy to handle both flow and disturbed conditions with normal smelt, providing a wide area of ​​coverage, and minimizing steam consumption).

[0020] Referring to Figure 4, an enlarged side cross-sectional view of the grinding jet nozzle 20 of Figure 1 is shown. To improve the intensity of the grinding jet while minimizing steam consumption, the grinding jet nozzle 20 features a converging-diverging (CD) nozzle design. In an exemplary design, the grinding jet nozzle 20 includes an inlet orifice 40, an outlet orifice 42, and an internal fluid path 22 between the inlet orifice 40 and the outlet orifice 42. The outlet orifice 42 has a cross-sectional dimension D o This has a diameter D when the exit orifice 42 has a circular cross-section. o The steam or other working fluid flows from left to right in the orientation of the nozzle 20 shown in Figure 1, as indicated by the “flow” arrows. That is, the steam enters the inlet orifice 40, passes through the fluid path 22, and exits the outlet orifice 42.

[0021] The fluid path 22 has a constriction or throat 44, which divides the fluid path 22 into a convergence zone 46 between the inlet orifice 40 and the throat 44, and a divergence zone 48 between the throat 44 and the outlet orifice 42. The terms “constriction” and “throat” are used interchangeably herein and refer to the constricted portion of the fluid path 22 that separates the convergence zone 46 and the divergence zone 48. Generally, as steam converges within the constriction or throat 44, it flows through the convergence zone 46 at high pressure and low speed; then, as the steam exits the throat 44, it diverges, resulting in steam in the divergence zone 48 being at low pressure and high speed compared to the high pressure and low speed in the convergence zone 46, respectively. The divergence zone 48 extends from the constriction or throat 44 to the outlet orifice 42. The convergence zone 46, i.e., the portion of the fluid path 22 extending from the inlet orifice 40 to the constriction 44, is optionally constricted to reach the constriction 44. However, in other embodiments, it may have a constant lumen diameter (see, for example, Figure 13). The combination of the convergence zone 46, the constriction or throat 44, and the divergence zone 48 is sometimes referred to herein as the convergence-divergence zone located between the inlet orifice 40 and the outlet orifice 42. For the shown steam flow, the convergence zone 46 is upstream of the divergence zone 48; or conversely, the divergence zone 48 is downstream of the convergence zone 46.

[0022] The complex fluid dynamics of the pulverizing jet nozzle 20 allow the steam flow to reach the speed of sound in the throat or constriction 44 and even further at the outlet, i.e., the outlet orifice 42. Outlet diameter D o , the narrowed portion or the throat diameter D of the throat 44 th , divergence zone 48 extension angle A div Factors including nozzle length allow for customization of the grinding jet nozzle 20 for use with various smelt flow characteristics.

[0023] Properly designed throat-outlet orifice area ratio R:

number

[0024] To achieve a wide coverage range, a plurality of outlet orifices 42 can be arranged adjacent to each other to achieve a wider pressure profile. (See, for example, the embodiments of FIGS. 12 and 13 having a single inlet orifice 40 and two outlet orifices 42). The spacing ΔD (see FIGS. 12 and 13) between adjacent outlet orifices 42 is preferably designed to optimize the overall performance. If the spacing ΔD is too small, the required coverage range may not be obtained. On the other hand, if the spacing ΔD is too large, a low-pressure region may occur between adjacent orifices 42.

[0025] Referring to FIG. 6, velocity contours of a single jet (FIG. 6(A)) generated from a CD nozzle having an inlet steam pressure of 150 psig are shown based on two-dimensional asymmetric computational fluid dynamics modeling. This result shows that for this jet, the optimal spacing between adjacent orifices is 8D o (the diameter D of the orifice oThis indicates that the distance must not exceed eight times the inlet vapor pressure. Otherwise, an undesirable low-pressure region may form in the center. Therefore, a convergent-divergent multi-jet nozzle design can produce a jet with both intensity and coverage while minimizing steam consumption. Figure 6(B) shows the velocity contours of a dual jet generated from a CD nozzle at an inlet vapor pressure of 150 psig. This result is 6D o This indicates that the spacing does not create undesirable low-pressure regions.

[0026] To evaluate the performance of the CD multi-jet nozzle, various design parameters were investigated, and conventional porous (non-CD) nozzles were also tested for performance comparison. A summary of the experimental conditions is shown in Table 1.

[0027] [Table 1]

[0028] In the experimental setup used in this study, compressed air was used to simulate steam. A Pitot tube array was placed in front of the nozzle under test to measure the peak impact pressure of the jet. This indicates the intensity of the pulverizing jet. The position of the Pitot tubes can be adjusted in the x, y, and z directions. Changes in the x and y positions generate a jet pressure profile, and changes in the z position change the distance between the nozzle and the Pitot tubes.

[0029] Referring to Figure 6, the nozzle performance of five CD single-jet nozzles with different throat diameters of 1 / 4 inch, 5 / 16 inch, 11 / 32 inch, 3 / 8 inch, and 1 / 2 inch is shown. Figure 6 plots the pressure profiles of the grinding jets at various orifice sizes (distance: 20 inches, pressure: 150 psig). The results show that, in general, the larger the orifice size, the higher the jet intensity. A conventional porous nozzle used for reference has an equivalent orifice diameter of 0.48 inches calculated based on the total opening area, which is slightly smaller than the largest 1 / 2-inch CD nozzle. Due to the greater number of orifices, it covers a wider range than the CD single-jet nozzle, but the intensity is significantly lower than that of a CD nozzle with a similar orifice size.

[0030] Referring to Figures 7 and 8, the effects of the number of nozzles and the spacing between CD orifices were also investigated. Figure 7 shows the pressure profiles of a dual-jet nozzle and a tri-jet nozzle (distance: 20 inches, pressure: 150 psig), and Figure 8 shows the effects of different spacings between orifices (8D o (8 times the diameter) and 16D o Figure 8 shows the pressure profile of a dual jet nozzle. Again, the distance is 20 inches and the pressure is 150 psig. The results show that increasing the number of nozzles produces a wider pressure profile with similar peak impact pressures at the centerline. If the orifices are too far apart, a low-pressure region is formed in the center, reducing the effectiveness of the pulverizing jet.

[0031] Referring to Figure 9, the orifice spacing is the same, but the throat size (D thThe pressure profiles of two different CD dual-jet nozzles are shown, along with the pressure profile of a conventional porous grinding jet nozzle for comparison. This result demonstrates that the convergent-divergent multi-jet nozzle 20 in Figure 4 can outperform the conventional grinding jet nozzle by achieving higher energy and wider coverage while consuming less steam. The comparison of jet pressure profiles from the optimized nozzle and the conventional nozzle shown in Figure 9 is also for a distance of 24 inches and a pressure of 150 psig.

[0032] Referring to Figures 10 and 11, the inlet pressure and distance between the smelt stream and the grinding jet can also affect the performance of the grinding jet. Figure 10 compares the performance of the CD dual jet nozzle at various inlet pressures by plotting the grinding jet pressure profiles at various vapor pressures. Figure 11 compares the performance of the CD dual jet nozzle at various distances from the Pitot tube by plotting the grinding jet profile at various distances from the Pitot tube. The results shown in Figures 10 and 11 indicate that increasing pressure and decreasing distance lead to higher jet intensity and a wider application range.

[0033] In summary, the disclosed grinding jet design (embodied, for example, by the exemplary grinding jet nozzle 20 in Figure 4) improves the effectiveness of smelt grinding and the safety of dissolution tank operation.

[0034] Referring here to Figures 12 and 13, another exemplary grinding jet nozzle 120 employing a convergence-divergence (CD) approach is schematically shown. Figure 12 shows a perspective view of the grinding jet nozzle 120, which is a dual-jet design with two outlet orifices 42, while Figure 13 shows a perspective cross-sectional view of the grinding jet nozzle 120 to reveal the internal fluid path 122. In this embodiment, the nozzle includes a first section 126 in which a convergence zone 46 is formed, and a second section 128 in which a divergence zone 48 is formed. The interface 134 where the first section 126 and the second section 128 are joined outlines a constriction or throat 44. The two sections 126 and 128 are separate parts that can be connected to each other via bolts 140 (as shown) or by other connecting means such as clips, welds, screws, etc. In the exemplary grinding jet nozzle 120 shown in Figures 12 and 13, the first section 126 includes an inlet orifice 40, and the second section 128 includes an outlet orifice 42 (or two outlet orifices 42 in the exemplary two-jet design). The first section 126 and the second section 128 are fixed together to define a fluid path 122 between the inlet orifice 40 and each outlet orifice 42, and the fluid path 122 has a "Y" branch to allow a single inlet orifice 40 to supply steam to both outlet orifices 42, as seen in the cross-sectional view of Figure 13. In this embodiment, a constriction or throat 44 is defined at the interface 134 between the first section 126 and the second section 128. The portion of the fluid path within the second section 128 (i.e., the divergence zone 48) extends from the interface 134 (corresponding to the constriction or throat 44) to the outlet interface 42. As shown in Figure 13, at interface 134, the portion of the fluid path 122 in the first section 126 (i.e., the convergence zone 46) has a larger diameter than the portion of the fluid path 122 in the second section 128 (i.e., the divergence zone 48). The resulting abrupt decrease in the diameter of the fluid path 122 at interface 134 defines a constriction or throat 44.

[0035] In Figure 13, a "Y" branch is employed to supply steam to two outlet orifices 42 along with a single inlet orifice 40, but more generally, the fluid path 122 can include a one-to-N manifold in which a single inlet orifice supplies steam to N outlet orifices.

[0036] The crushing jet nozzle 120 in Figures 12 and 13 allows for on-site adjustment via selective pairs of converging and / or diverging sections 126, 128 having various characteristics, but not limited to, the number of orifices, the cross-sectional shape of the orifices, the cross-sectional area of ​​the orifices, the converging and / or diverging profiles within each section, and the directional output of the outlet orifice.

[0037] The geometric spacing between the outlet orifices 42 allows for widening the steam pattern while maintaining the desired impact pressure profile. In at least one embodiment, the spacing ΔD between the orifice outlets 42 of the dual jet nozzle 120 is 4D o And here D o (D) is the diameter of the orifice exit 42. o (This is shown only in Figure 12). In another embodiment, the spacing ΔD is approximately 4D o ~ in the range of approximately 16D, more preferably approximately 4D o ~about 8D o In some embodiments, the outlet orifices may be of different sizes; for example, the cross-sectional dimensions of the first outlet orifice may be larger than those of the second outlet orifice (the same D for both outlet orifices 42 of the dual jet nozzle 120). o (In Figures 12 and 13, which have this feature, the deformation is not shown.)

[0038] While the above description constitutes preferred embodiments of the present invention, it will be understood that the present invention is easily modifiable, varied, and altered without departing from the appropriate scope and fair meaning of the appended claims.

Claims

1. A first separable section including an entrance orifice; A second separable section including an exit orifice; The fluid path between the inlet orifice and the outlet orifice; and The convergence-divergence zone located between the inlet orifice and the outlet orifice. Includes, A smelt grinding apparatus in which the second separable section includes a divergent zone of the convergent-divergent zone.

2. The apparatus according to claim 1, wherein the convergence zone of the convergence-divergence zone begins with the first separable section.

3. The apparatus according to claim 1, wherein the convergence zone begins at the boundary between the first separable section and the second separable section.

4. The apparatus according to any one of claims 1 to 3, wherein the divergent zone of the convergent-divergent zone has a profile defined by a fluid path in the second separable section.

5. The apparatus according to any one of claims 1 to 3, wherein the convergence zone of the convergence-divergence zone has a profile defined by the fluid path upstream of the divergence zone of the convergence-divergence zone.

6. The apparatus according to any one of claims 1 to 3, wherein the outlet orifice is a first outlet orifice, and the apparatus further includes a second outlet orifice that is in fluid communication with the inlet orifice.

7. The apparatus according to claim 6, wherein the first outlet orifice has a cross-sectional dimension, and the second outlet orifice is located at a distance of 4 to 10 times the cross-sectional dimension from the first outlet orifice.

8. The apparatus according to claim 6, wherein the cross-sectional dimensions of the first outlet orifice are greater than the cross-sectional dimensions of the second outlet orifice.

9. The apparatus according to any one of claims 1 to 3, wherein the convergence and divergence zone includes a constricted portion of the fluid path between the inlet orifice and the outlet orifice.

10. A first separable section including an entrance orifice; A second separable section including an exit orifice; and A fluid path between the inlet orifice and the outlet orifice having a constricted portion. A smelt grinding nozzle, including one.

11. The smelt grinding nozzle according to claim 10, wherein the first separable section and the second separable section are fixed together to define the fluid path, and the constriction is defined at the interface between the first section and the second section.

12. The smelt grinding nozzle according to claim 11, wherein the portion of the fluid path in the second section extends from the interface to the outlet orifice.

13. The smelt grinding nozzle according to claim 12, wherein at the interface, the portion of the fluid path in the first section has a larger diameter than the portion of the fluid path in the second section.

14. The portion of the fluid path extending from the constricted portion to the outlet orifice widens from the constricted portion to the outlet orifice, as described in claim 10.

15. The smelt grinding nozzle according to claim 14, wherein the portion of the fluid path extending from the inlet orifice to the constricted portion is narrowed to reach the constricted portion.

16. A plurality of smelt grinding nozzles as described in claim 10, A smelt grinding apparatus in which the outlet orifice of the smelt grinding nozzle has a diameter, and the distance between the outlet orifices of a plurality of smelt grinding nozzles is 8 times or less the diameter.

17. A smelt grinding apparatus is provided, comprising a first separable section including an inlet orifice, a second separable section including an outlet orifice, a fluid path between the inlet orifice and the outlet orifice, and a convergence-divergence zone located between the inlet orifice and the outlet orifice, wherein the second separable section includes the divergence zone of the convergence-divergence zone; A fluid stream is flowed through the aforementioned fluid path to generate a fluid jet; Bringing the fluid jet into contact with the smelt stream to convert the smelt stream into pulverized smelt; and The pulverized smelt is then put into the dissolution tank. A method for grinding smelt, including the process described above.

18. The method according to claim 17, wherein the fluid stream includes steam.

19. The method according to claim 17, further comprising generating the smelt stream by burning black liquor in a recovery boiler using a Kraft pulp mill.

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