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CA-3174534-C - METHOD AND APPARATUS FOR IMPROVED OPERATION OF CHEMICAL RECOVERY BOILERS

CA3174534CCA 3174534 CCA3174534 CCA 3174534CCA-3174534-C

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.

Inventors

  • Daniel R. Higgins
  • Eugene Sullivan

Assignees

  • SULLIVAN, HIGGINS, AND BRION POWER PLANT ENGINEERING, LLC

Dates

Publication Date
20260505
Application Date
20210304
Priority Date
20200304

Claims (14)

  1. CLAIMS 1. A chemical recovery boiler square or rectangular in plan-form, the chemical recovery boiler including a spout wall with spouts for draining smelt and two walls adjacent to the spout wall and, if rectangular, with longer sides thereof less than three feet longer than shorter sides thereof, with a wall opposite the spout wall having no primary combustion air ports and at least two but no more than seven primary ports on each of the two walls adjacent to the spout wall, in which spacing between individual said primary ports on the two 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. 2. The chemical recovery boiler of Claim 1 in which all said primary ports on a first said wall adjacent to said spout wall are directly opposite said primary ports on a second said wall opposing the first said wall plus or minus three tube pitches.
  3. 3. The chemical recovery boiler of Claim 2 in which a jet of combustion air emanates from each of said primary ports toward an 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. 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 16 Date Re9ue/Date Received 2024-03-07 port opposite the at least one first said primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between the at least one first said primary port and the at least one second said primary port.
  5. 5. The chemical recovery boiler of Claim 4 in which said strong jet/weak jet relationship between the at least one first said primary port and the at least one second said primary port is periodically and automatically reversed.
  6. 6. The chemical recovery boiler of Claim 4 in which said strong jet/weak jet relationship alternates sequentially from port to port along the first said wall of the boiler.
  7. 7. The chemical recovery boiler of Claim 1 in which the number of said primary ports on a first of said two walls adjacent to said spout wall is even and the number of said primary ports on a second of said two walls adjacent to said spout wall is odd.
  8. 8. The chemical recovery boiler of Claim 7 in which the primary ports on said first of said two walls are interlaced with the primary ports on the second of said two walls such that said primary ports on the first of said two walls are centered plus or minus three tube pitches between said primary ports on the second of said two walls.
  9. 9. The chemical recovery boiler of Claim 1 in which black liquor is injected into the boiler from at least two elevations with a first said elevation at least two feet above a primary port 17 Date Re9ue/Date Received 2024-03-07 centerline elevation and no more than 12 feet above a floor of the boiler and at least three feet below a second said elevation.
  10. 10. The chemical recovery boiler of Claim 9 in which the first said elevation is below at least one secondary port elevation.
  11. 11. The chemical recovery boiler of Claim 7 in which black liquor is injected into the boiler from at least two elevations with a first said elevation at least two feet above a primary port centerline elevation and no more than 12 feet above a floor of the boiler and at least three feet below a second said elevation.
  12. 12. The chemical recovery boiler of Claim 11 in which the first said elevation is below at least one secondary port elevation.
  13. 13. The chemical recovery boiler of Claim 8 in which black liquor is injected into the boiler from at least two elevations with a first said elevation at least two feet above a primary port centerline elevation and no more than 12 feet above a floor of the boiler and at least three feet below a second said elevation.
  14. 14. The chemical recovery boiler of Claim 13 in which the first said elevation is below at least one secondary port elevation. 18 Date Re9ue/Date Received 2024-03-07 15. A chemical recovery boiler rectangular in plan-form, the chemical recovery boiler comprising a spout wall including thereon spouts for draining smelt, the chemical recovery boiler including a wall opposite the spout wall having no primary combustion air ports, and the chemical recovery boiler including two walls adjacent to said spout wall and having primary ports thereon, in which spacing between individual said primary ports on the two walls adjacent to said spout wall is not less than the dimension S = 0.13 times the dimension W, the plan-form dimension of the boiler parallel to the direction of an 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 two 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. 16. The chemical recovery boiler of Claim 15 in which all said primary ports on a first said wall adjacent to said spout wall are directly opposite said primary ports on a second said wall opposing the first said wall plus or minus three tube pitches. 17. The chemical recovery boiler of Claim 16 in which a jet of combustion air emanates from each of said primary ports toward an interior of the boiler and the volumetric flow and/or mass flow and/or velocity are controlled automatically and independently for each said port. 18. The chemical recovery boiler of Claim 17 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 19 Date Re9ue/Date Received 2024-03-07 lesser than the volumetric flow and/or mass flow and/ or velocity of at least one second said primary port opposite the at least one first said primary port plus or minus three tube pitches creating a strong jet/weak jet relationship between the at least one first said primary port and the at least one second said primary port. 19. The chemical recovery boiler of Claim 18 in which said strong jet/weak jet relationship between the at least one first said primary port and the at least one second said primary port is periodically and automatically reversed. 20. The chemical recovery boiler of Claim 19 in which said strong jet/weak jet relationship alternates sequentially from port to port along the first said wall of the boiler. 21. The chemical recovery boiler of Claim 15 in which black liquor is injected into the boiler from at least two elevations with a first said elevation at least two feet above a primary port centerline elevation and no more than 12 feet above a floor of the boiler and at least three feet below a second said elevation. 22. The chemical recovery boiler of Claim 21 in which the first said elevation is below at least one secondary port elevation. 23. A method of improving the performance of a chemical recovery boiler, the chemical recovery boiler including a smelt spout wall, a wall opposite the smelt spout wall, and Date Re9ue/Date Received 2024-03-07 two side walls between the smelt spout wall and the wall opposite the smelt spout wall, and the method 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 air ports on each of the two side walls. 24. The method of Claim 23, compnsmg: retrofitting an existing said chemical recovery boiler and in which a 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 a primary air port opening area of an original said chemical recovery boiler being retrofitted. 25. The method of Claim 23 in which the step of blocking essentially all primary air ports openings on the wall opposite the smelt spout wall comprises blocking said 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 side walls. 21 Date Re9ue/Date Received 2024-03-07 26. The method of Claim 23 in which a volumetric flow and/or mass flow and/or velocity of at least a first said primary air port of said two side walls is adjusted to be at least 25% greater or lesser than the volumetric flow and/ or mass flow and/or velocity of at least a second said primary air port of said two side walls opposite the at least first said primary air port plus or minus three tube pitches creating a strong jet/weak jet relationship between the at least first said primary air port and the at least second said primary air port. 27. The method of Claim 26 in which said strong jet/weak jet relationship between the at least first said primary air port and the at least second said primary air port is periodically and automatically reversed. 28. The method 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. 22 Date Re9ue/Date Received 2024-03-07

Description

WO 2021/178687 PCT/0S2021/020904 Method and Apparatus for Improved Operation of Chemical Recovery Boilers Technical Field of the Invention [0001] This description relates to chemical recovery boilers. Background of the Invention [0002] Chemical recovery boilers are well known in the pulp and paper industry as a means to recover spent cooking chemicals and the heating value of the black liquor fuel fired therein. In the Kraft pulping process, wood chips are processed (or cooked) in a digester in which they are subjected to high temperature and pressure in the presence of caustic chemicals. In the digester the lignin binding the wood fibers is dissolved liberating the fibers to be used to make pulp. The Kraft process produces relatively long fibers that are used to manufacture strong paper products and is commonly used in all sorts of packaging. After the wood chips are dissolved the spent cooking chemicals, dissolved lignin, and unsuitable wood fibers are captured, the excess moisture is evaporated, and the resulting black liquor is fired in a recovery boiler. After evaporation, the moisture content of the black liquor typically ranges from 20% to 40% depending on the equipment and operation of the individual mill. The black liquor solids consist of approximately 50% inorganics (spent cooking chemicals) and 50% organic material (lignin and wood fibers). The black liquor is injected into the recovery boiler through one or more atomizing spray nozzles, the residual moisture is evaporated, and the organic material is burned. During the combustion process the spent cooking chemicals are liberated and undergo chemical reduction. The predominant spent cooking chemical in a black liquor recovery boiler is sodium sulfate (Na2SO4) and in the presence of heat and elemental carbon is reduced to sodium sulfide (Na2S). This is an endothermic reaction absorbing heat from the combusting volatiles and char. Reduction efficiency is the ratio of the concentration of the total sulfur in the smelt minus the concentration of sulfate divided by the total sulfur ( on a practical basis this can be expressed as Na2S/(Na2S + Na2SO4)). Reduction efficiencies of 95% or higher can be achieved on well-run recovery boilers. Other types of recovery boilers are used such as soda boilers and red liquor boilers in which different chemical mixtures are used to dissolve the wood chips, but black liquor boilers are the most common type by far. We will limit our discussion to black liquor boilers, but the methods and apparatuses described herein pertain to the other types of chemical recovery boilers that use similar combustion system arrangements as black liquor boilers. 1 WO 2021/178687 PCT/0S2021/020904 [0003] Recovery boilers are typically constructed with a square or rectangular planform in the furnace ( combustion) section, typically from 10 feet to 30 feet or more on a side. The floor and walls of the furnace are constructed from steel boiler tubes in a parallel array seal welded to the adjacent tubes. The floor may be flat or sloping about 5 degrees and the walls are vertical forming a large prismatic enclosure from 30 to 100 feet tall. At the top of the furnace one of the walls (typically the rear wall) of the boiler is bent inward forming a bullnose section that turns the hot combustion gases across the convective heat transfer tubes arrayed at the top of the boiler. The convective sections typically consist of one or more superheaters, a steam generator (generating bank or boiler bank), and one or more economizers. The tubes forming the furnace floor are fed by a header at one edge of the floor and turn vertically to form one of the furnace walls opposite the header. In some boilers one or two centrally located headers feed the floor tubes that then feed into two opposite walls. The other walls are fed by their own headers and the headers are fed boiler feed water via one or more downcomers from a water drum at the bottom of the generating bank in a two-drum boiler, or the steam drum in a single drum boiler. A natural circulation system cools the furnace wall tubes in which the hydraulic head from the cooler and denser boiler feedwater in the downcomers pushes the hotter and less dense water in the furnace wall upwards. Radiation is the dominant heat transfer mechanism in the furnace section of the boiler and most of the saturated steam is generated in the furnace walls. [0004] The black liquor fuel is injected into the furnace at one or more locations on one or more of the furnace walls. Larger recovery boilers may typically use three or more injection nozzles per wall and 10 or more injection nozzles total. All nozzles are typically at a single elevation, generally considered the operating level as the liquor injection requires regular attention by the operators. The nozzle elevation may range typically from 15 to 30 feet above the floor. When the liquor is injected into the boiler it goes through several combustion stages including