Method and Apparatus for Improved Operation of Chemical Recovery Boilers

Abstract

A chemical recovery boilers is described in which the primary air system is reconfigured to provide aggressive charbed control and improved combustion in the lower furnace. The fewest number of primary air ports are used on two opposing walls to generate powerful air jets that penetrate across the boiler providing physical and thermal stability to the charbed while increasing the heat release and combustion stability in the lower furnace, increasing reduction efficiency, and lowering carryover and emissions. Various embodiments are described including operating strategies and multi-level black liquor injection.

Claims

1. A chemical recovery boiler square or rectangular in plan-form, and if rectangular with the longer sides less than three feet longer than the shorter sides, and whether square or rectangular draining smelt from one spout wall with no primary combustion air ports on the wall opposite the spout wall and at least two but no more than seven primary ports on each of two walls adjacent to the spout wall, in which the spacing between individual said primary ports on the two said walls adjacent to said spout wall is not less than 0.13 times the plan-form dimension of the boiler parallel to said spout wall or three feet, whichever is greater.

2. The chemical recovery boiler of claim 1 in which all said primary ports on a first wall adjacent to said spout wall are directly opposite said primary ports on the wall opposing said first wall plus or minus three tube pitches.

3. The chemical recovery boiler of claim 2 in which a jet of combustion air emanates from each of said primary ports toward the interior of the boiler and the volumetric flow and/or mass flow and/or velocity are controlled automatically and independently for each said port.

4. The chemical recovery boiler of claim 3 in which the volumetric flow and/or mass flow and/or velocity of at least one first said primary port is adjusted to be at least 25% greater or lesser than the volumetric flow and/or mass flow and/or velocity of at least one second said primary port opposite the first said primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between said ports.

5. The chemical recovery boiler of claim 4 in which said strong jet/weak jet relationship between said ports is periodically and automatically reversed.

6. The chemical recovery boiler of claim 4 in which said strong jet/weak jet relationship alternates sequentially from port to port along a first wall of the boiler, said first wall adjacent to the spout wall.

7. A chemical recovery boiler rectangular in plan-form draining smelt from one spout wall with no primary combustion air ports on the wall opposite the spout wall in which the spacing between individual primary ports on two walls adjacent to said spout wall shall not be less than the dimension S=0.13 times the W, the plan-form dimension of the boiler parallel to the direction of the air jet, or three feet, whichever is greater, with at least two said primary ports on each of said two walls adjacent to said spout wall with the maximum number of said primary ports on each of said walls adjacent to said spout wall no more than seven plus N where N=(D−W)/S rounded down to the next whole number and D equals the plan-form dimension of said boiler perpendicular to W.

8. The chemical recovery boiler of claim 7 in which all said primary ports on a first wall adjacent to said spout wall are directly opposite said primary ports on the wall opposing said first wall plus or minus three tube pitches.

9. The chemical recovery boiler of claim 8 in which a jet of combustion air emanates from each of said primary ports toward the interior of the boiler and the volumetric flow and/or mass flow and/or velocity are controlled automatically and independently for each said port.

10. The chemical recovery boiler of claim 9 in which the volumetric flow and/or mass flow and/or velocity of at least one first said primary port is adjusted to be at least 25% greater or lesser than the volumetric flow and/or mass flow and/or velocity of at least one second said primary port opposite the first said primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between said ports.

11. The chemical recovery boiler of claim 10 in which said strong jet/weak jet relationship between said ports is periodically and automatically reversed.

12. The chemical recovery boiler of claim 11 in which said strong jet/weak jet relationship alternates sequentially from port to port along a first wall of the boiler, said first wall adjacent to the spout wall.

13. The chemical recovery boiler of claim 1 in which the number of said primary ports on a first of said walls adjacent to said spout wall is even and the number of said primary ports on the second of said walls adjacent to said spout wall is odd.

14. The chemical recovery boiler of claim 13 in which the said primary ports on said first wall are interlaced with said primary ports on said second wall such that said primary ports on said first wall are centered plus or minus three tube pitches between said primary ports on said second wall.

15. The chemical recovery boiler of claim 1 in which black liquor is injected into the boiler from at least two elevations with the first elevation at least two feet above the primary port centerline elevation and no more than 12 feet above the floor of the boiler and at least three feet below the second elevation.

16. The chemical recovery boiler of claim 15 in which said first elevation is below at least one secondary port elevation.

17. The chemical recovery boiler of claim 7 in which black liquor is injected into the boiler from at least two elevations with the first elevation at least two feet above the primary port centerline elevation and no more than 12 feet above the floor of the boiler and at least three feet below the second elevation.

18. The chemical recovery boiler of claim 17 in which said first elevation is below at least one secondary port elevation.

19. The chemical recovery boiler of claim 13 in which black liquor is injected into the boiler from at least two elevations with the first elevation at least two feet above the primary port centerline elevation and no more than 12 feet above the floor of the boiler and at least three feet below the second elevation.

20. The chemical recovery boiler of claim 19 in which said first elevation is below at least one secondary port elevation.

21. The chemical recovery boiler of claim 14 in which black liquor is injected into the boiler from at least two elevations with the first elevation at least two feet above the primary port centerline elevation and no more than 12 feet above the floor of the boiler and at least three feet below the second elevation.

22. The chemical recovery boiler of claim 21 in which said first elevation is below at least one secondary port elevation.

23. A method of improving the performance of a chemical recovery boiler including a smelt spout wall, a wall opposite the smelt spout wall, and two side walls between the smelt spout wall and the wall opposite the smelt spout wall, comprising; blocking multiple primary air ports openings on the smelt spout wall such that only between two and eight ports in the vicinity of each smelt spout are open; blocking essentially all primary air ports openings on the wall opposite the smelt spout wall; and providing at least two but no more than seven primary side wall air ports on each of the two side walls.

24. The method of claim 23 in which the method of improving the performance of a chemical recovery boiler comprises retrofitting an existing chemical recovery boiler and in which the combined opening area of the at least two but no more than seven primary ports on each of the two side walls is between 80% and 120% of the primary air port opening area of an original chemical recovery boiler being retrofitted.

25. The method of claim 23 in which blocking essentially all primary air ports openings on the wall opposite the smelt spout wall comprising blocking primary air ports openings on the wall opposite the smelt spout wall such that the combined openings of the primary air ports openings on the wall opposite the smelt spout wall include less than 5% of the total area of the at least two but no more than seven primary side wall air ports on each of the two walls side walls.

26. The method of claim 23 in which a volumetric flow and/or mass flow and/or velocity of at least one of the side primary air ports is adjusted to be at least 25% greater or lesser than the volumetric flow and/or mass flow and/or velocity of at least one second primary side air port opposite the first side primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between said ports.

27. The chemical recovery boiler of claim 26 in which said strong jet/weak jet relationship between said side air ports is periodically and automatically reversed.

28. The chemical recovery boiler of claim 26 in which said strong jet/weak jet relationship alternates sequentially from port to port along one of the two side walls of the boiler.

29-33. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more thorough understanding of the present invention, and advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0014] FIG. 1 is a side view of recovery boiler in which tubes and pipes are depicted as single lines;

[0015] FIG. 2 is a partial front view of the boiler of FIG. 1 as viewed along lines A-A;

[0016] FIG. 3 is a sectional view of the boiler in FIG. 1 at the primary port level, the section taken along the section lines B-B and showing a first primary port arrangement; and

[0017] FIG. 4 is a sectional view boiler FIG. 1 taken along the lines B-B at the primary port level showing a different primary port arrangement.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0018] The principals described herein can be used in the construction of new chemical recovery boilers and/or retrofitting existing chemical recovery boilers. The description below is directed to chemical recovery boilers and inherently to a method of making and operating an improved chemical recovery boiler.

[0019] The following description references features in the accompanying figures in which the features are identified by like numbers. FIG. 1 is a side view of recovery boiler in which tubes and pipes are depicted as single lines. FIG. 2 is a partial front view of the same boiler as identified by section lines A-A. FIG. 3 is a plan view of the boiler in FIG. 1 at the primary port level as identified by section lines B-B showing a first primary port arrangement, and FIG. 4 also shows section view B-B but depicts a second primary port arrangement.

[0020] Referring to FIGS. 1 and 2, recovery boiler 1 is an older two-drum type using steam drum 2 and water drum 3. The walls and floor of the boiler are constructed of closely spaced tubes 33 (a few of which are shown) in a vertical parallel array, seal welded together to make an air-tight enclosure. The tube walls are constructed with a uniform pitch between the tubes. Boiler feedwater is fed to steam drum 2, some of which flows down the rear tubes 4 of generating bank 5 to the water drum 3 picking up heat from the flue gases 6 that cross screen 7, superheaters 8-11, generating bank 5, and economizer 12. Flue gases 6 are hotter at the inlet to generating bank 5 therefore the water in front tubes 13 absorbs more heat than the water in rear tubes 4 and a natural circulation is created between steam drum 2 and water drum 3.

[0021] Some of the water in water drum 3 flows down downcomer 14 to headers 15-18. The water in header 15 flows through floor 19 then up rear wall 20, through the bullnose 21, and back to water drum 3. Similarly, the water in header 16 flows through floor 22, up front wall 23, through the roof tubes 24, and back to steam drum 2. Sidewall headers 17 and 18 feed sidewalls 25 and 26 respectively and are relieved by headers at the top (not shown) back to steam drum 2. Radiant heat from the combusting fuel is absorbed by walls 20, 23, 25, and 26 producing steam and setting up a natural circulation system.

[0022] Forced-draft combustion air is fed through primary ports 28, primary air ports 29, secondary ports 38, tertiary ports 39, and quaternary ports 40 if present. Most chemical recovery boilers in operation today have smelt spouts on one wall of the boiler, but some older Combustion Engineering units drain the smelt from two opposing walls. The apparatus described herein is particularly suitable in those boilers that drain smelt from one wall although it can be used on boilers draining smelt from two walls. Smelt spouts 27 are at or slightly above the level of the floor of the boiler whereas the spout wall primary ports 28 and the primary air ports 29 are several feet higher. Around the perimeter of the boiler charbed 30 is below the primary ports but it is still above the height of spout openings 31. At spouts 27 the flowing smelt 32 tends to keep the charbed lower, but it can still be problematic to keep the molten smelt running freely in the spouts. The molten smelt falls into dissolving tank 34 where it is turned into green liquor to be reused.

[0023] It is necessary therefore to have some primary ports 28 in operation in close proximity to the smelt spouts, preferably one to ten ports, more preferably two to eight ports, and most preferably three to five ports centered on each spout. These ports are sized and located similarly to traditional primary ports on the spout wall (in this case front wall 23) and in fact can be reused ports if the boiler has been modified in accordance with this disclosure. On the spout wall (front wall 23) only those few primary ports at each spout are open. On the wall opposite the spouts (on a single spout-wall boiler, in this case rear wall 20) no traditional primary ports are required. Preferably the area of air ports on the wall opposite the spout wall is zero, or less than 50%, less than 25%, less than 10%, less than 5%, or less than 1% of the area of ports on the spout wall. If the boiler has been modified in accordance with this disclosure, the existing ports may be blocked with refractory or some other means, or the port tubes, originally bent to create the openings, can be replaced with straight tubes. On the two walls adjacent (perpendicular) to the spout wall (in this case sidewalls 25 and 26), no traditional primary ports exist. Combustion air ports 29, much larger than traditional primary ports, are present instead. As on the other walls, if the boiler is modified to incorporate this disclosure, the existing primary ports are blocked, replaced with straight tubes, or replaced with new bent tubes creating the new larger port openings. In some embodiment, the primary air ports on the two walls adjacent (perpendicular) to the spout wall provide more than 80% of the primary air port area, with the air ports on the spout wall and the wall opposing the spout wall providing less than 20% of the primary air port area. In some embodiment, the primary air ports on the two walls adjacent (perpendicular) to the spout wall provide more than 90% of the primary air port area, with the air ports on the spout wall and the wall opposing the spout wall providing less than 10% of the primary air port area. In some embodiment, the primary air ports on the two walls adjacent (perpendicular) to the spout wall provide more than 95% of the primary air port area, with the air ports on the spout wall and the wall opposing the spout wall providing less than 5% of the primary air port area.

[0024] Conventional primary port openings on recovery boilers typically range from one inch wide by six inches tall to two inches wide by eleven inches tall. The upper limit is 2-½ inches by 15 inches. The new ports, as part of the present disclosure, will be many fewer and much larger than the original primary ports. For example, if the primary ports on a recovery boiler are 1.5 inches wide by eight inches tall, and there are 80 such ports on the boiler, the total primary port area is 1.5×8×80=960 square inches. With the implementation of the present invention, 90% of the primary ports may be replaced totaling 864 square inches. If eight new ports are installed in their place, each port will have an area of 108 square inches. In that case the new ports may be 6 inches wide by 18 inches tall. The actual dimensions may vary from this example depending on the practical requirements of each system.

[0025] The total area of the primary air ports in a recovery boiler being retrofitted in accordance with this disclosure may be approximately the same as the area of the air ports in the recovery boiler prior to being retrofitted. For example, the total area of the primary air ports in a recovery boiler in accordance with this disclosure may be within plus or minus 40%, plus or minus 30%, plus or minus 20%, plus or minus 10%, or plus or minus 5% of the area of the air ports in the recovery boiler prior to being retrofitted.

[0026] Referring to FIG. 3, the number of primary ports 29 on these two walls is dictated by the size of the boiler and the optimum spacing between the ports. The optimum spacing may be a low as three feet for small boilers and up to seven feet for large boilers. Air jets expand as they flow across a boiler therefore for larger boilers, the air jets travel farther and expand more and must start out farther apart to avoid interference with adjacent or opposing air jets. The minimum horizontal spacing between primary air ports is given by Formula 1: S=0.13*W, adjusted to match the tube pitch or other features of the boiler, where S is the nominal horizontal spacing between ports, and W is the plan-form dimension of the boiler parallel to the direction of the air jets, but shall not be less than 3 feet in any case. Dimension W is from the centerline of one wall to the centerline of the opposite wall. D is the dimension of the boiler perpendicular to W. The maximum number of primary ports on opposing walls 25 and 26 adjacent to spout wall 23 on a square boiler is seven, unless the boiler is over 49 feet on a side, in which case additional ports are added to keep S<7 feet. On rectangular boilers the maximum number of primary air ports on opposing walls 25 and 26 adjacent to spout wall 23 may be greater than seven assuming walls 25 and 26 are longer than walls 20 and 23. It should be noted that a square is a type of rectangle and for our purposes a square boiler is any boiler in which the long sides are less than 3 feet longer than the short sides. These relationships assume the direction of the air jets is orthogonal to the walls on which the air jets originate. All primary air ports are equally spaced +/−0.25*S to allow for variations due to other features on the boiler. Spacing L1 is the distance from spout wall 23 to the first primary air port on adjacent walls 25 and 26, and spacing L2 is the distance from the last primary air port on walls 25 and 26 to wall 20 opposite the spout wall. In general, L1=L2 but this may vary +/−0.25*S or more to accommodate the boiler geometry or other features. L1 and L2 should not be less than 0.75*S as the air jet may be sucked against the adjacent wall by a low pressure zone created by the air jet flowing next to the wall.

[0027] Considering that there are fewer primary air ports on the apparatus described herein than in traditional boilers, the primary air ports must be larger. This not only provides the combustion air needed to satisfy the stoichiometric requirements, but also provides more mass flow per air jet and that improves the penetration of the air jets over the charbed. A feature some of the embodiments of the apparatus described herein is that the fewer but larger primary air ports create stronger air jets that penetrate across the boiler providing the combustion air and physical agitation needed to maintain a stable charbed. Typically, about twenty to forty percent of the total combustion air comes from the primary air ports. Knowing the capacity of the boiler, one can determine the stoichiometric requirements for combustion air and determine the required primary air port area using the equations below. A commonly used formula for determining the velocity of an air jet is given as Formula 2: V=67.3*((Pd)*(T/527)){circumflex over ( )}0.5, where V is the velocity of the jet in feet per second, Pd is the differential pressure across the port opening in inches water column, and T is the temperature of the combustion air in degrees Rankine. The formula for determining the area of each port opening is given as Formula 3: Aip=((Q*X)/(V*Cfl*Cfo-Asp))/2N where Aip=area of the individual primary air ports, Q=the total forced draft combustion air to the boiler, X=the fraction of forced draft combustion air to be injected at the primary level, V=the velocity of the air jet, Cfl is a flow coefficient, Cfo is a coefficient of fouling of the port opening (the port openings on a recovery boiler tend to get fouled with char and frozen smelt from the black liquor), Asp is the combined area of the primary ports on the spout wall, and N is the total number of primary air ports. There are other variables that come into play as well. For example, some of the ports may operate at different velocities or flows or be fitted with port dampers that adjust the effective area of the port opening. This will require adjusting the fixed area of the port opening accordingly.

[0028] A first embodiment pertains to the primary ports, generally considered to be the lowest forced-draft air ports on each wall. We can additionally define the primary ports as those ports that the bottom of which are no more than five feet above the floor of the boiler, and there are no lower forced-draft air ports on that wall, except those that may be stair-stepped following the slope of the floor. Referring to FIGS. 1 and 2, the primary ports 28 on spout wall 23 will be located at an elevation suitable to protect smelt spouts 27 from char bed 30. On side walls 25 and 26, primary air primary ports 29 will be located at an elevation to provide the desired depth of charbed 30. The primary ports in the apparatus described herein are generally all at the same elevation but this is not necessarily so, the elevation may vary from port to port or wall to wall, within the context of the definition above. Some boilers have sloping floors and in that case the ports may be equidistant above the floor but not at the same elevation. In the first embodiment, primary air primary ports 29 are located on two opposing walls 25 and 26 adjacent to spout wall 23, and every port has a corresponding port opening on the opposite wall and aligned within +/− three tube pitches of the opposite port. The number of port openings on each wall is the same and the minimum spacing is determined by Formula 1. The minimum number of primary air ports is two on each wall 25 and 26 and the maximum is seven, unless the boiler is rectangular. For a rectangular boiler, in which walls 25 and 26 are more than 3 feet longer than walls 20 and 23, the number of ports 29 can be increased by one for each additional length S. Each port opening is fitted with a means to control the air flow through the port, by varying the port area or the port pressure or both. For our purposes, the term air flow includes the volumetric flow, mass flow, and/or velocity of the air jet. In the apparatus described herein, the air flow through the port automatically fluctuates on a prescribed basis to alter the air flow and combustion characteristics in the boiler and provide aggressive control of the char bed. For example, referring to FIG. 3, the first port on wall 25 may be set to full flow while the port directly opposite on wall 26 is set to partial flow, the second port on wall 25 is set to partial flow while the opposite port on wall 26 is set to full flow, and so on down the wall. This generates strong jets 35 alternating with weak jets 36 over the char bed. Periodically, in a range of one to twenty minutes, the arrangement is automatically reversed so that the strong jets become weak jets and vice versa. The purpose of this arrangement is to provide a strong jet that penetrates across the boiler to control the top of the charbed but is opposed by the weak jet to prevent the char bed from piling against the opposite wall and prevent black liquor, smelt, and char from blowing into the opposite port opening. The air jets have unequal strengths so that the point of contact is not centered on the boiler. Where the air jets contact, they tend to deflect each other upward. Staggering the points of contact prevents the formation of a core of high vertical velocity in the furnace that pushes the fuel, air, and combustion up in the boiler, and that is detrimental as described previously. Formula 2 describes the square root relationship between the differential pressure and resultant jet velocity. If the jet velocity is controlled on a pressure basis, this means that a large difference in differential pressure is required to obtain a modest difference in velocity. For example, to double the velocity of an air jet, the differential pressure must be quadrupled. If a strong jet/weak jet arrangement is used, the lower flow from the weak jets must be taken into account when determining the required area of each port opening.

[0029] A second embodiment, referring to FIG. 4, has the primary air ports interlaced on opposing walls 25 and 26 adjacent to spout wall 23. In that case the minimum spacing between ports is according to Formula 4: Si=0.26*W and the maximum optimum number of ports 29 on each wall 25 and 26 is three for a square boiler. For a rectangular boiler, in which walls 25 and 26 are more than 3 feet longer than walls 20 and 23, the number of ports 29 can be increased by one for each additional length Si. The nominal distance L3 from the first port on wall 25 to wall 20 should be no less than 0.37*Si, and the nominal distance L4 from the first port on wall 26 to wall 20 should be L3+Si/2. This spaces the air jets out evenly across the boiler with each jet interlaced between two jets on the opposite wall, or between a perpendicular wall and an air jet from the opposite wall. This embodiment has the advantage of being less costly as fewer port openings are required, and the air jets can penetrate completely across the boiler, further reducing the updrafts in the boiler, as the collision between air jets is avoided. With nothing to oppose the air jets, however, the charbed may be piled against the opposite wall to a height that may be problematic. As the air jets travel over the char bed they tend to bend upward (the eventual direction of all of the air) and the ability to aggressively control the charbed is diminished. This embodiment has the advantage of simplicity of design and operation as the periodic reversing of the air jets is not required.

[0030] A third embodiment takes advantage of the aggressive charbed control and improved combustion in the lower furnace offered by the primary air ports. In most black liquor recovery boilers, the majority of the forced-draft combustion air is injected below the liquor spray nozzles. This is for practical reasons as the air is needed to burn the fuel, however, the combustion air and gaseous products of combustion must have somewhere to go and in a recovery boiler that direction is up. By creating a strong jet/weak jet arrangement, or interlacing the air jets, strong local updrafts are minimized and the upward pressure on the fuel droplets is reduced. These arrangements have been used for many years at the secondary, tertiary, and quaternary air level but never before at the primary air level as it was assumed that the myriad traditional primary ports were necessary for smelt drainage and char bed control. The primary forced-draft air flow typically represents around 30% of the total air flow, and the secondary around 40%. Using a strong jet/weak jet arrangement or interlacing the secondary air jets has proven effective to improve the combustion in the lower furnace even though the primary air (almost half of the combustion air in the lower furnace) is not participating and in fact interferes with the secondary air jets. By incorporating the primary air into an aggressive mixing and charbed control system using larger and stronger air jets, optimally arranged, the combustion in the lower furnace is enhanced well beyond what can be done at the secondary level alone. This creates an opportunity to push more fuel to the charbed and more fuel that lands on the bed means less fuel burns in suspension and less carryover. Less carryover means the boiler can run longer between cleanings and/or use less steam for sootblowing, or, most importantly for many mills, the boiler can be run at a higher load rate boosting the production of the mill. Referring to FIG. 1, in the current state of the art, one or more black liquor spray nozzles 36 may be located on one or more walls of the boiler, but they are always at the same elevation. For our purposes we will call this the operating level because the operators typically control the boiler from that level. This embodiment incorporates one or more lower black liquor spray nozzles 37 at an elevation lower than the operating level but at least two feet above the primary port elevation and no more than twelve feet above the bottom of the boiler, and preferably below the injection of the secondary air. By spraying liquor at a lower elevation, the fuel is subjected to less updraft and therefore carryover is reduced, and the fuel is burned in the lower furnace where it belongs. This can only be done with a very strong primary air system.

[0031] Multiple versions of these embodiments can be used. For example, any of the arrangements described above can be implemented in mirror image to that described or depicted in the figures; embodiments can be implemented on a boiler smelting off two opposing walls with the ports on the walls adjacent to the smelt walls; the ports can be located on the smelt wall (or walls) and the wall opposite; there can be an even number of primary air ports on one wall and an odd number on the opposite wall; and the primary air ports can be located on the shorter walls of a rectangular boiler. It can be seen, therefore, that many configurations and variations can be implemented without departing from the spirit of the invention.

[0032] Some embodiments provide a method of improving the performance of a chemical recovery boiler including a smelt spout wall, a wall opposite the smelt spout wall, and two side walls between the smelt spout wall and the wall opposite the smelt spout wall, comprising blocking multiple primary air ports openings on the smelt spout wall such that only between two and eight ports in the vicinity of each smelt spout are open; blocking essentially all primary air ports openings on the wall opposite the smelt spout wall; and providing at least two but no more than seven primary side wall air ports on each of the two walls side walls.

[0033] In some embodiments, the method comprises retrofitting an existing chemical recovery boiler and in which the combined opening area of the at least two but no more than seven primary ports on each of the two side walls is between 80% and 120% of the primary air port opening area of an original chemical recovery boiler being retrofitted.

[0034] In some embodiments, blocking essentially all primary air ports openings on the wall opposite the smelt spout wall comprising blocking primary air ports openings on the wall opposite the smelt spout wall such that the combined openings of the primary air ports openings on the wall opposite the smelt spout wall include less than 5% of the total area of the at least two but no more than seven primary side wall air ports on each of the two walls side walls.

[0035] In some embodiments, a volumetric flow and/or mass flow and/or velocity of at least one of the side primary air ports is adjusted to be at least 25% greater or lesser than the volumetric flow and/or mass flow and/or velocity of at least one second primary side air port opposite the first side primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between said ports.

[0036] In some embodiments, said strong jet/weak jet relationship between said side air ports is periodically and automatically reversed.

[0037] In some embodiments, said strong jet/weak jet relationship alternates sequentially from port to port along one of the two side walls of the boiler.

[0038] Some embodiment provide a method of operating a chemical recovery boiler, the method comprising: injecting air through primary smelt spout air ports positioned in the vicinity of a smelt spout to maintain smelt flow at the smelt spout, the primary smelt spout air ports having a combined total primary spout air port opening area; and injecting primary air through between two and eight side wall primary air ports on each of two side walls intersecting the spout wall, the between two and eight side wall primary air ports having a combined total primary side wall air port opening area, the combined total primary side wall air port opening area including more than 80% of a total primary air port opening area.

[0039] In some embodiments, a total required quantity of primary air injected into the furnace is determined by stoichiometry and in which at least 80% of the total required quantity of primary air injected into the furnace is injected through the side wall primary air ports.

[0040] In some embodiments, less than 10% of the primary air is injected through primary air ports on the wall opposite the smelt spout wall.

[0041] In some embodiments, no primary air is injected through air ports on the wall opposite the spout wall.

[0042] In some embodiments, less than 10% of the primary air is injected through smelt spout air ports.

[0043] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.