CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present disclosure claims the benefit of priority of co-pending U.S. Provisional Patent Application No. 62/648,550, filed on March 27, 2018, and entitled “OXYGEN INJECTION SYSTEM FOR A DIRECT REDUCTION PROCESS,” the contents of which are incorporated in full by reference herein for all purposes.

BACKGROUND

[0002] Referring specifically to FIG. 1, in a conventional direct reduction (DR) process, a heated reducing gas 10, consisting mostly of H2 and CO made by natural gas reforming, (or syngas) is fed into a shaft furnace (SF) through a bustle and tuyere system to reduce iron oxides to metallized iron. Typically, an enrichment hydrocarbon fuel, such as enrichment natural gas (EnNG) 12, and 02 14 are injected into the reducing gas stream 10 before entering the SF. The EnNG 12 acts as a chemical feedstock for in-situ reforming inside the SF, increasing reduction by making more reductant. However, this in-situ reforming consumes a significant amount of heat, which reduces the bed temperature and lowers the kinetics of the reduction reactions in the SF. Combustion of the injected 02 14 with the reducing gas 10 maintains the temperature of the bustle gas at about 900 degrees C or more before entering the SF and compensates for the heat consumed by the in-situ reforming inside the SF.

[0003] Typically, the 02 14 is injected into the conduit 16 used through a single pipe and the EnNG 12 is injected through several pipes laid out circumferentially. These pipes 12,14 are self-cooled by the flowing gas alone, unless water-cooled pipes are used. The 02 14 and EnNG 12 are injected at different locations along the conduit 16 to ensure the stable and safe combustion of the 02 14, as the cooling effect of the EnNG 12 may impair the combustion and/or ignition. An inert gas purge 20 is fluidly coupled to the 02 injection pipe 14. Generally, the single 02 injection pipe 14 incorporates one or two 02 injection nozzles, while the EnNG injection pipe 12 is coupled to a circumferential header 22 that includes four to eight circumferential injection holes, for example.

[0004] In general, this configuration suffers from several important problems:

(1) there is limited turn-down capability of the 02 flow 14 through the injection pipe because the 02 flow rate sufficient for self-cooling must be maintain and the 02 supply cannot be depleted;

(2) only a small number of 02 injection pipes 14 can be used because of this reduced turn-down capability of 02 for each pipe and a smaller number of 02 injection points makes it difficult to distribute the 02 14 uniformly in the resulting bustle gas stream 18;

(3) the duct wall around the 02 injection point can develop a hot spot due to the radiation heat of the 02 flame unless the 02 injection pipe 14 projects far enough through the duct wall - this longer projection potentially causing bending of the 02 injection pipe 14, requiring frequent replacing of the 02 injection pipe 14;

(4) to solve the above problems, a water-cooled 02 injection pipe 14 can be used, but this makes the overall system more complex and expensive, and the water cooling the bustle gas 18 could fail; and

(5) although there is minimal chance of the 02 14 reacting with the EnNG 12 since they are injected at different locations, while the EnNG 12 remains mostly unreacted and tends to lower the bustle gas temperature, the 02 14 reacts mainly with the H2 and CO in the reducing gas stream 10 to decrease the amount of reductant and maximize the temperature rise through full oxidation.

[0005] Thus, an improved 02 and EnNG injection system that solves these problems is needed for DR processes.

SUMMARY

[0006] In various exemplary embodiments, the present disclosure improves the flow rate flexibility for an 02 injection pipe without applying water-cooling. The number of 02 injection points is increased, such that the 02 and EnNG can be distributed more uniformly in the bustle gas stream. Further, the present disclosure makes it possible to safely inject 02 very close to the point of EnNG injection, such that the partial combustion of the EnNG is enhanced and the temperature of the reducing gas entering the SF is reduced as compared to with a full oxidation configuration.

[0007] The present disclosure optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition. This is achieved by:

(1) cooling the 02 injection pipes using EnNG shroud gas in a coaxial EnNG/02 injection configuration;

(2) the turndown capability of the 02 flow rate, or the possible zero 02 flow, for each pipe enabled by (1) enables the number of injection points to be increased, thus distributing 02 more uniformly in the bustle gas stream;

(3) the smaller diameter injection pipe for 02 is located inside the large diameter EnNG shroud gas hole to maintain a much higher gas velocity of 02 than that of EnNG, preventing too much cooling by EnNG in the 02 combustion area and stabilizing the 02 combustion even with the coaxial EnNG/02 injection configuration;

(4) a brick orifice located upstream prevents the flows around the 02/EnNG injection locations from becoming too disturbed - the coaxial EnNG/02 injection configuration with the combination of the brick orifice upstream significantly enhancing the partial combustion of EnNG, generating reducing gas while minimizing the temperature increase of the reducing gas; and

(5) with the above, C deposition may occur around the 02 injection points if the amount of heavies in the EnNG is high or if the EnNG/02 flow ratio is high— dividing the EnNG injection into two locations (one around the 02 injection location and another further downstream) optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition.

[0008] In one exemplary embodiment, the present disclosure provides an oxygen injection system for a direct reduction process, including: a common circumferential gas injection header adapted to be coupled to an oxygen source and an enrichment natural gas source and adapted to deliver oxygen from the oxygen source and enrichment natural gas from the enrichment natural gas source to a reducing gas stream flowing through a conduit axially disposed within the common circumferential gas injection header through a plurality of circumferentially disposed ports to form a bustle gas stream; wherein the common circumferential gas injection header includes a circumferential oxygen injection header adapted to deliver the oxygen from the oxygen source to the reducing gas stream through the plurality of circumferentially disposed ports and a circumferential enrichment natural gas injection header adapted to deliver the enrichment natural gas from the enrichment natural gas source to the reducing gas stream through the plurality of circumferentially disposed ports. The circumferential oxygen injection header and the circumferential enrichment natural gas injection header are axially disposed. Optionally, the circumferential enrichment natural gas injection header is axially disposed within the circumferential oxygen injection header. The circumferential oxygen injection header includes a plurality of circumferentially disposed pipes adapted to be disposed through the circumferential enrichment natural gas injection header and a plurality of circumferentially disposed nozzles coupled to the plurality of circumferentially disposed pipes adapted to be collocated with the plurality of circumferentially disposed ports. The oxygen flow rate through each of the plurality of circumferentially disposed pipes is variable. Optionally, the enrichment gas flow rate through each of the plurality of circumferentially disposed ports is variable. The oxygen injection system further includes an inert gas purge coupled to the oxygen source. The oxygen injection system further includes a brick orifice circumferentially disposed about the conduit upstream of the common circumferential gas injection header. Optionally, the oxygen injection system further includes another circumferential enrichment natural gas injection header disposed about the conduit downstream of the common circumferential gas injection header and adapted to deliver additional enrichment natural gas from the enrichment natural gas source to the reducing gas stream through an additional plurality of circumferentially disposed ports.

[0009] In another exemplary embodiment, the present disclosure provides an oxygen injection method for a direct reduction process, including: providing a common circumferential gas injection header adapted to be coupled to an oxygen source and an enrichment natural gas source and adapted to deliver oxygen from the oxygen source and enrichment natural gas from the enrichment natural gas source to a reducing gas stream flowing through a conduit axially disposed within the common circumferential gas injection header through a plurality of circumferentially disposed ports to form a bustle gas stream; wherein the common circumferential gas injection header includes a circumferential oxygen injection header adapted to deliver the oxygen from the oxygen source to the reducing gas stream through the plurality of circumferentially disposed ports and a circumferential enrichment natural gas injection header adapted to deliver the enrichment natural gas from the enrichment natural gas source to the reducing gas stream through the plurality of circumferentially disposed ports. The circumferential oxygen injection header and the circumferential enrichment natural gas injection header are axially disposed. Optionally, the circumferential enrichment natural gas injection header is axially disposed within the circumferential oxygen injection header. The circumferential oxygen injection header includes a plurality of circumferentially disposed pipes adapted to be disposed through the circumferential enrichment natural gas injection header and a plurality of circumferentially disposed nozzles coupled to the plurality of circumferentially disposed pipes adapted to be collocated with the plurality of circumferentially disposed ports. The oxygen injection method further includes varying an oxygen flow rate through each of the plurality of circumferentially disposed pipes. Optionally, the oxygen injection method further includes varying an enrichment gas flow rate through each of the plurality of circumferentially disposed ports. The oxygen injection method further includes providing an inert gas purge coupled to the oxygen source. The oxygen injection method further includes providing a brick orifice circumferentially disposed about the conduit upstream of the common circumferential gas injection header. Optionally, the oxygen injection method further includes providing another circumferential enrichment natural gas injection header disposed about the conduit downstream of the common circumferential gas injection header and adapted to deliver additional enrichment natural gas from the enrichment natural gas source to the reducing gas stream through an additional plurality of circumferentially disposed ports.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components/method steps, as appropriate, and in which:

[0011] FIG. 1 is a schematic diagram illustrating a conventional 02 and EnNG injection system and method, utilizing separate 02 and EnNG injection points;

[0012] FIG. 2 is a schematic diagram illustrating one exemplary embodiment of the 02 and EnNG system and method of the present disclosure, utilizing common, coaxial 02 and EnNG injection points; and [0013] FIG. 3 is a schematic diagram illustrating another exemplary embodiment of the 02 and EnNG system and method of the present disclosure, utilizing common, coaxial 02 and EnNG injection points, as well as a separate EnNG injection point.

DESCRIPTION OF EMBODIMENTS

[0014] Again, in various exemplary embodiments, the present disclosure improves the flow rate flexibility for an 02 injection pipe without applying water-cooling. The number of 02 injection points is increased, such that the 02 and EnNG can be distributed more uniformly in the bustle gas stream. Further, the present disclosure makes it possible to safely inject 02 very close to the point of EnNG injection, such that the partial combustion of the EnNG is enhanced and the temperature of the reducing gas entering the SF is reduced as compared to with a full oxidation configuration.

[0015] The present disclosure optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition. This is achieved by:

(1) cooling the 02 injection pipes using EnNG shroud gas in a coaxial EnNG/02 injection configuration;

(2) the turndown capability of the 02 flow rate, or the possible zero 02 flow, for each pipe enabled by (1) enables the number of injection points to be increased, thus distributing 02 more uniformly in the bustle gas stream;

(3) the smaller diameter injection pipe for 02 is located inside the large diameter EnNG shroud gas hole to maintain a much higher gas velocity of 02 than that of EnNG, preventing too much cooling by EnNG in the 02 combustion area and stabilizing the 02 combustion even with the coaxial EnNG/02 injection configuration;

(4) a brick orifice located upstream prevents the flows around the 02/EnNG injection locations from becoming too disturbed - the coaxial EnNG/02 injection configuration with the combination of the brick orifice upstream significantly enhancing the partial combustion of EnNG, generating reducing gas while minimizing the temperature increase of the reducing gas; and

(5) with the above, C deposition may occur around the 02 injection points if the amount of heavies in the EnNG is high or if the EnNG/02 flow ratio is high - dividing the EnNG injection into two locations (one around the 02 injection location and another further downstream) optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition.

[0016] Referring now specifically to FIG. 2, in one exemplary embodiment, the common 02 and EnNG injection system 100 of the present disclosure utilizes coaxial 02 14 and EnNG 12 injection at the same location, through a common circumferential injection header 24 disposed around the reducing gas conduit 16, thereby forming bustle gas 18 that is delivered to the SF. The common circumferential injection header 24 includes an outer circumferential 02 injection header 26 and an inner circumferential EnNG injection header 28 that collectively utilize a plurality of common circumferential gas injection ports 30. In this exemplary embodiment, each of the 02 injection pipes 32 is disposed along a radius of the common circumferential injection header 24 through the inner circumferential EnNG injection header 28, and collocated with and protruding through one of the circumferential EnNG injection ports 30. An inert gas purge 20 is coupled to the 02 14 as before.

[0017] Thus, the 02 pipe 32 is cooled by the EnNG shroud gas coming out of the circumferential holes 30 of the EnNG header 28 installed on the bustle gas duct 16. This allows more flexibility and turndown capability (including zero flow) of the 02 flow rate for each 02 injection pipe 32.

[0018] The flexibility of this 02 flow makes it possible to increase the number of 02 and EnNG injection points circumferentially and distributes 02 and EnNG more uniformly in the bustle gas stream 18. Further, it provides the flexibility to stop the 02 flow to some of the 02 injection pipes 32 without removing them from the system 100.

[0019] By applying smaller diameter 02 injection pipes 32 inside the larger diameter EnNG shroud gas hole 30 to maintain higher gas velocity for the 02 than that of the EnNG, stable 02 combustion can be achieved without being influenced by the cooling effect of the EnNG. This makes it possible to safely inject the 02 close to the injection point of the EnNG in the reducing gas duct 16.

[0020] The EnNG shroud gas coming out of the shroud gas hole 30 protects the refractory- lined duct wall around the 02 pipes 32 from the radiation heat of the 02 flame, even though the projection of the 02 pipes 32 from the refractory wall is minimal. Such minimal projection thereby extends the life of the 02 injection pipes 32.

[0021] A brick orifice 34 or the like is disposed upstream of the common circumferential header 24 and prevents turbulent flow around the 02/EnNG injection location. This coaxial 02/EnNG injection configuration coupled with the brick orifice 34 disposed upstream significantly enhances the partial combustion of the EnNG 12.

[0022] Referring now specifically to FIG. 3, in another exemplary embodiment, the common 02 and EnNG injection system 100 of the present disclosure again utilizes coaxial 02 14 and EnNG 12 injection at the same location, through a common circumferential injection header 24 disposed around the reducing gas conduit 16, thereby forming bustle gas 18 that is delivered to the SF. The common circumferential injection header 24 includes an outer circumferential 02 injection header 26 and an inner circumferential EnNG injection header 28 that collectively utilize a plurality of common circumferential gas injection ports 30. In this exemplary embodiment, each of the 02 injection pipes 14 is disposed along a radius of the common circumferential injection header 24 through the inner circumferential EnNG injection header 26, with an 02 nozzle 32 collocated with and protruding through one of the circumferential EnNG injection ports 30. An inert gas purge 20 is coupled to the 02 14 as before.

[0023] Thus, the 02 pipe 14 is cooled by the EnNG shroud gas 12 coming out of the circumferential holes 30 of the EnNG header 28 installed on the bustle gas duct 16. This allows more flexibility and turndown capability (including zero flow) of the 02 flow rate for each 02 injection pipe 14.

[0024] The flexibility of this 02 flow 14 makes it possible to increase the number of 02 and EnNG injection points circumferentially and distributes 02 and EnNG more uniformly in the bustle gas stream 18. Further, it provides the flexibility to stop the 02 flow 14 to some of the 02 injection pipes 14 without removing them from the system 100.

[0025] By applying smaller diameter 02 injection pipes 14 inside the larger diameter EnNG shroud gas hole 30 to maintain higher gas velocity for the 02 than that of the EnNG, stable 02 combustion can be achieved without being influenced by the cooling effect of the EnNG. This makes it possible to safely inject the 02 close to the injection point of the EnNG in the reducing gas duct 16.

[0026] The EnNG shroud gas 12 protects the refractory-lined duct wall around the 02 nozzle 32 from the radiation heat of the 02 flame, even though the projection of the 02 pipe 14 from the refractory wall is minimal. Such minimal projection thereby extends the life of the 02 injection pipe 14.

[0027] Again, a brick orifice 34 or the like is disposed upstream of the common circumferential header 24 and prevents turbulent flow around the 02/EnNG injection location. This coaxial 02/EnNG injection configuration coupled with the brick orifice 34 disposed upstream significantly enhances the partial combustion of the EnNG 12.

[0028] Here, a separate downstream circumferential EnNG injection header 36 is also coupled to the EnNG supply 12 and utilized, injecting the EnNG into the bustle gas stream 18 within the duct 16 through a plurality of separate circumferential EnNG injection ports 38. In the first embodiment, with the 02/EnNG coaxial injection configuration, C deposition may occur around the 02 injection points if the amount of heavies in the EnNG is high or if the EnNG/02 flow ratio is high. Dividing the EnNG injection into two locations (one around the 02 injection location and another at a location downstream) allows to 02/EnNG ratio at the 02 injection location to be optimized to maximize the partial combustion and minimize the C deposition. The optimum ratio is 02/EnNG = 0.5— 1.2, or preferably 0.7 ~ 1.0, on a molar/volume basis.

[0029] Thus, again, the present disclosure improves the flow rate flexibility for an 02 injection pipe without applying water-cooling. The number of 02 injection points is increased, such that the 02 and EnNG can be distributed more uniformly in the bustle gas stream. Further, the present disclosure makes it possible to safely inject 02 very close to the point of EnNG injection, such that the partial combustion of the EnNG is enhanced and the temperature of the reducing gas entering the SF is reduced as compared to with a full oxidation configuration.

[0030] The present disclosure optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition. This is achieved by: (1) cooling the 02 injection pipes using EnNG shroud gas in a coaxial EnNG/02 injection configuration;

(2) the turndown capability of the 02 flow rate, or the possible zero 02 flow, for each pipe enabled by (1) enables the number of injection points to be increased, thus distributing 02 more uniformly in the bustle gas stream;

(3) the smaller diameter injection pipe for 02 is located inside the large diameter EnNG shroud gas hole to maintain a much higher gas velocity of 02 than that of EnNG, preventing too much cooling by EnNG in the 02 combustion area and stabilizing the 02 combustion even with the coaxial EnNG/02 injection configuration;

(4) a brick orifice located upstream prevents the flows around the 02/EnNG injection locations from becoming too disturbed - the coaxial EnNG/02 injection configuration with the combination of the brick orifice upstream significantly enhancing the partial combustion of EnNG, generating reducing gas while minimizing the temperature increase of the reducing gas; and

(5) with the above, C deposition may occur around the 02 injection points if the amount of heavies in the EnNG is high or if the EnNG/02 flow ratio is high - dividing the EnNG injection into two locations (one around the 02 injection location and another further downstream) optimizes the 02/EnNG ratio at the 02 injection location to maximize partial combustion and minimize C deposition.

[0031] Although the present disclosure is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure, are contemplated thereby, and are intended to be covered by the following non-limiting claims for all purposes.