US3110584A - Liquid fuel injection in blast furnaces - Google Patents

Description

Nov. 12, 1963 FIGURE-l BLAST AIR H. R. SANDERS, JR., ETAL LIQUID FUEL INJECTION IN BLAST FURNACES FiledOct. 27, 1960 INSIDE OF 2 Sheets-Sheet 1 BLAST FURNACE BLOW PIPE CENTERING Hiram R. Sanders, Jr. John R. Kennedy Herbert F. Schroeder DEVICE 7 Inventors Puten'rA'rrorney Nov. '12, 1963 H. R. SANDERS, JR., ETAL 3,1 0,58

LIQUID FUEL INJECTION IN BLAST FURNACES HHBWFIN HNOWS GHIO'IK] Hiram R. Sanders, Jr. John R. Kennedy Inventors Herbert F. Schroeder By K. (Aw- 7 4 Patent Attorney United States Patent 3,110,584 LIQUID FUEL INJECTION IN BLAST FURNACEE Hiram R. Sanders, Jr., Cranford, John R. Kennedy, Clifton, and Herbert F. Schroeder, Roselle Park, NJ, as-

signors to Esso Research and Engineering Company, a

corporation of Delaware Filed Oct. 27, 196i Ser. No. 65,363 5 Claims. (Cl. 75-42) Suitable fuel for this purpose would include any liquid,

liqueiiable, gaseous or emulsi-fiable hydrocarbon fuel product, such as petroleum-type residual fuel oils; distillate fuel oils derived from crude petroleum by distillation, thermal cracking, catalytic cracking, hydroform ing and the like; crude petroleum; diesel fuels; gas oils; kerosene; gasoline; and petroleum naphthas. For economic reasons, those liquid fuel oils of ASTM Specification D-396-48T will generally be preferred with the residual fuel oils 5 and 6, called Bunker C fuels, being especially preferred. In some geographic areas, circumstances will justify the use of the more volatile liquid petroleum naphtha products other than residual fuel oils.

These fuels will be most suitably utilized by injecting them in conjunction with the heated blast lair either through the tuyeres or near the tuyeres into the lower or bosh portion of the blast furnace, cupola, or other furnace to produce high temperatures and suitable reducing gases.

The injection of hydrocarbon fuels, petroleum fuels, is accompanied by certain critical problems not present in conventional injection systems. The injection apparatus and system employed must be capable of uniformly injecting fuel into the blast furnace over a wide range of how rates. In addition, the injection of oil rnust be such so as to allow preheating of the fuelblast air mixture without combustion to minimize smoke formation, yet promote eflicient use of the fuel. A further problem concerns the injection of fuel in the presence of the high temperatures of the blast air and the raceway. The blast air is normally employed at a temperature of at least above 100 0 F. and, in the case where liquid hydrocarbons are used, a higher blast air temperature up to 2000" F. and even higher is required. The higher blast air temperatures are required :due to the initial endothermic cracking of the fuel, but the higher blast air temperature subjects the liquid fuel to sludging, carbonization, thermal cracking, and coking. The radiant heat of the raceway, about 3000 F. and above, also contributes to the carbonization and coking of the fuel as it is being injected. Excessive carbonization and coking or the formation of clinkers in the injection system or tuyeres as extremely undesirable in that the injection system, by being fully or partially clogged, may create hazardous safety conditions or even upset the furnace operating conditions allowing the furnace to go hot or cold.

It has been discovered that a particularly designed injection system and process is well adapted to meet all the aforesaid problems, and to ensure uniform and satisfactory injection of liquid fuels in blast furnaces. The

particular system and apparatus of the invention con-' cerns a fluid shrouded hollow tube fuel injector wherein the fluid shroud protects the injected petroleum fuel from excessive carbonization and coking, especially at low inparticularly liquid 3,110,584 Patented Nov. 12, 1963 jection rates, e.g. below 6 gallons of fuel/hour. The proper placement of the injection system 'has been found to be quite critical with the distance and position in the blowpipe of the tuyere dependent upon the particular tuyere diameter of the blast furnace. The importance of the aforesaid inventive apparatus and process is made even more surprising in that the use of conventional air atomized injection nozzles has been found to be unsatisfactory at all injection rates at high 600" F.) blast temperature, because of the increased susceptibility to coking of the nozzle passageways and openings. The novel process of the applicants provides a simple and economical manner in which to achieve excellent oil spray distribution and partial combustion at all oil flow rates with a reduction in smoke formation and inhibition of carbonization due to high temperature furnace operating conditions.

The instant invention will be more fully understood by reference to the accompanying drawings wherein:

FIGURE 1 is'a diagrammatioal representation of the inventive fluid shrouded injection apparatus in position within the blast furnace blowpipe.

IGURE 2 is a graphical representation demonstrating the criticality of the distance and position of the injection nozzle from the tuyere opening and tuyere diameter.

Turning now to FIGURE 1 in more detail, there is shown an annular hollow tube fuel injection pipe 5 circunrferentially surrounded by a larger diameter, preferably concentric, hollow tube protective fluid shroud pipe 6. The injection tube is shown axially mounted in the blowpipe and approximately perpendicular with the plane of the circular tuyere opening into the blast furnace. The centering of the slim hollow tubes is accomplished by a wedge-shaped centering device 7 which does not unduly restrict the flow of the preheated blast air and which is capable of maintaining the tubes in position at the temperatures encountered within the tuyere blowpipe. The positioning of the tubes may also be accomplished by suspending the tubes from hooks or eyelets fastened to the top of the blowpipe. The exit nozzle 9 of the injection pipe protrudes slightly ahead of the shroud tube in order to prevent the injected fuel from striking the shroud tube and disrupting the oil spray pattern or plugging up the shroud exit. The distance from the exit nozzle to the tuyere nozzle exit into the blast furnace is shown at the maximum critical position of 2.8 times the tuyere'nozzle exit diameter designated as D The criticality of the exit nozzle position with reference to the D will be demonstrated later by FIGURE 2. Since the inventive fuel injector process to be economical must be,

easily installed and adapted to present blast furnace construction, the use of a centering device as shown to hold the atomizer in the axial position within the blowpipe may be unsuitable or even impossible in some cases. The materials of the blowpipe land nozzle may be such as to preclude the welding or fastening of centering devices; therefore, the fuel injector is shown in dotted lines in the slumped position for use where no centering device is economically feasible or practicable. The slumped position is where the inventive fuel injector is allowed to rest on the lower section or bottom of the tuyere nozzle and/or blowpipe. In this case, the maximum critical distance for proper operation was discovered to be 1. times the tuyere nozzle exit diameter.

The critical maximum distance from the tuyere nozzle exit is based in part on the eccentricity of the tuyere nozzle in relation to the injection pipe exit nozzle. The diameter of the injection and fluid shroud is not critical, but the overall dimension should be small enough so as not to unduly-interfere with the flow of hot blast air through the blowpipe. Outside shroud pipes up to /2 in diameter will not normally interfere with hot blast flow.

In operation, the liquid fuel is injected into the fuel injection pipe as shown. The liquid fuel employed may be any hydrocarbon liquid fuel, but preferably is a petroleum fuel oil, while especially preferred are high viscosity residual fuels such as Bunker C and the like. Where a high viscosity fuel is employed, the viscosity is reduced to enhance the handling of the fuel by preheating the fuel, e.g. a No. 6 fuel, to a temperature of above 110 F. or preferably from 125 F. to 250 F. With higher viscosity-type fuels, higher temperatures must be utilized to bring them to the same ejection viscosity. This residual fuel is then introduced at approximately atmospheric pressures or slightly higher, e.g. 2 to 25 p.s.i.g., at the indicated temperatures than the blast air pressure employed. In some localities where a low viscosity petroleum naphtha fuel is employed, the heating of the fuel is not needed, but injection under a pressure of at least 50 p.s.i.g., or preferably from 50 p.s.i.g. to 200 p.s.i.g., is employed. The higher pressure is beneficial in preventing the volatilization of the naphtha in the injection pipe caused by the high temperature conditions surrounding the injecting pipe, especially at low flow rates, e.g. less than 6 gallons/hour. This tendency to volatilization is also inhibited by the fluid cooling shroud which shields the liquid fuel from some of the high heat operating condition. In some cases, normal temperatures and pressures may be employed, i.e. ambient temperatures and a pressure sufficient to introduce the liquid fuel into the injection pipe. This condition would exist where a high viscosity residual fuel is diluted with a low viscosity naphtha fuel, e.g. dilution of Bunker C with a cracked naphtha. Pressure is employed for the residual and lighter fuels, except naphthas, at the injection pipe inlet to over come the normal pressure drop through the pipe at existing conditions of temperature, flow rate, and the like, i.e. to have the pressure at the nozzle outlet at least equal to the blast air pressure employed. Although other pressures will work, the most practical and economical pressure to be employed at the fuel injection inlet is preferably from 10 to 75 p.s.i.g. above the blast air pressure employed.

The viscosity of liquid fuels (at the nozzle inlet) for proper spray distribution in the inventive apparatus and process should be no greater than 300 SSU, while viscosities not greater than 200 SSU are preferred for the best spray distribution and ease of handling the product. The viscosities may be natural or obtained by temperature control, dilution, employment of additives, or by other well known methods.

The atomization of the liquid fuel into a suitable spray pattern is accomplished by the combined influence of the blast air flowing past the injection pipe nozzle and the pressure and rate of fuel injection. Atomization by the blast air has been found to be preferred to the use of conventional air :atomizing nozzles due to the economics and simplicity of operation. Successful atomization is accomplished by the shearing force created by the differential velocity of the blast air and fuel. Suitable velocity ranges for good atomization range from 300 to 800 ft./sec. for the blast air and from to 50 f-t./sec. for the liquid fuel. As the fuel velocity increases, atomization quality decreases. Preheated blast air or oxygen-enriched blast air (e. g., 21-30% oxygen) is normally introduced through the individual tuyeres and into the bosh section of the blast furnace from a bustle pipe circumferentially surrounding the furnace. Suitable blast air pressures and flow rates for the atomizing purposes of the present invention are those normally utilized in the operation of a blast furnace, for example, a pressure of from 5 to 40 p.s.i.g. and floW rate of 1000 to 8000 s.c.f./m. per tuyere. Oil spray distribution is particularly suitable when the air blast velocity through the tuyere nozzle is greater than 600 ft./sec.

Fuel injection flow rates at the individual tuyeres vary according to furnace conditions, the fuel employed, and other factors, but may range from 1 gallon per hour to 250 gallons per hour. Preferred rates are from 8 to 50 gallons of oil per ton of pig iron produced. Utilization of the inventive fluid shrouded fuel injector renders the plugging of the injection pipe by carbonization, sludging, thermal cracking, and the like of the liquid fuel before emergence from the injection nozzle unlikely at rates above 6 gallons per hour. At lower injection rates, the problems of protecting the fuel from clogging the pipe are more severe and the use of fluid shroud cooling shield is necessary to ensure the best operation of the instant injectors.

, The protective fluid shroud operates by passing a fluid through the preferably annular concentric fluid shroud pipe so as to protect the liquid fuel from the direct effects of excessive blast air and raceway heat. Suitable fluids for this purpose would include carbon monoxide, air, steam, gaseous hydrocarbons, nitrogen, or any chemically inert fluid or any fluid capable of producing a reducing gas at the raceway conditions. The temperature and flow rate of the fluid would be such so as to protect the liquid fuel in the injection pipe at that flow rate from excessive temperatures, for example, temperatures exceeding the threshold cracking or s-ludging temperature. With high viscosity residual fuels, this temperature of the injected fuel should not exceed about 700 F.; while for n-aphthas, the threshold temperature would be much higher. In addition, the fluid selected should be such that in operation or on stoppage of the fuel flow its effect on furnace conditions would be negligible. A suitable and preferred fluid medium is a gas such as air at ambient temperatures of from -150 F. and at pressures of from 2-25 p.s.i.g. The fluid flow rate, e.g. air, depends on the amount of protection required under the circumstances, but should, in general, not exceed about 8/ 10 (-by weight) of the liquid fuel flow rate. Air flow rates of from 5/10 to 8/10 (by weight) of the liquid flow rate are preferred for operations where oil flow is 2 to 5 gallons/hour in 4 ID. pipe, wherein the blast air is 1600 F. and higher. At a cooling air rate of 10 standard cubic feet per minute (s.c.f.m.), the inventive injector will not become plugged at fuel velocities of as low as 0.2 ft./sec. (corresponding to 1 gallon per hour through a 4 LD. fuel injection pipe). As the temperature of the blast air employed increases above 2000 F., the need for the fluid shroud protection at fuel flow rates above 6 gallons/ hour would be created.

Turning now to FIGURE 2, there is shown in graphical form the critical relationship between the formation of smoke and tuyere plugging and the nozzle distance and position. In the apparatus of FIGURE 1, the preferred location of the nozzle is in the blowpipe axial position rather than the slumped peripheral or any intermediate position. The axial position allows for a better fuel spray pattern distribution and better mixing of the air and fuel whereby maximum preheat of the ejected fuel without undesired combustion takes place in the tuyere nozzle. This improved mixing and preheat minimizes the formation of excessive smoke and unburned carbon particles, while promoting more efficient use of the fuel. The distance of the injection exit nozzle is of critical importance in that better mixing of the air-fuel is accomplished the farther away the exit is from the tuyere nozzle exit. Both the location of the injection nozzle and its exit distance from the tuyere are critical, in that a position too close will result in inefficient preheating of the atomized mixture and excessive smoke formation, while an excessive distance will result in the plugging of the tuyere by the impingement of the oil spray on the tuyere nozzle and subsequent carbonizations of the fuel and the formation of clinkers in the tuyere opening. The position of the injection nozzle may be dictated by the construction of the blast furnace, i.e. the suitability of axially centering the nozzle, or by other factors. The distance from the plane of the tuyere nozzle exit diameter is subject to control, and thus can be adjusted within the discovered critical operating limits defined to obtain maximized operating efficiency.

The graphical representation of FIGURE 2 is based on the injection of Bunker C residual fuel oil through an individual tuyere of a blast furnace wherein the fuel flow rate was 10 gallons per hour, at a pressure 10 p.s.i., with a blast air temperature of 1800 E, and a flow rate of 467 s.c.f.m., without the use of a fluid shroud. The injection pipe was approximately A" in diameter with the concentric shroud pipe of /2" in diameter, with a tuyere exit nozzle diameter of about 2 /2".

The diluted smoke number was derived from the standard Bachairaich smoke number by using a lower volume of flue gas. This was necessary, since all the smoke measurements made would regn'ster a dense smoke of 9+ on the Standard Bacharach smoke scale; and, thus, an arbitrary reduction in gas was effected to reduce the smoke number to distinguishable units. Thus, the diluted smoke number merely allows measurement of smoke where it would be at the higher limits or off the conventional smoke index. The diluted smoke number was obtained by diluting the sample gas with ambient air until the smokiest setting was on the Bacharach scale. Then the improvements made on the smoke number by changing the nozzle position were measured.

The ordinate of FlGURE 2 is the diluted smoke number measured as above, while the abscissa is the distance in tuyere exit nozzle diameters from the tip of the injection pipe nozzle to the cente of the tuyere opening. The eccentricity lines indicate the deviation in tuyere exit nozzle diameters of the injection nozzle from the axis of the blowpipe. Thus, the maximum eccentricity represents the injection pipe lying in the slumped position shown in FIGURE 1, while zero eccentricity indicates the nozzle position on the axis of the flowpipe. The extreme criticality of the nozzle distance can readily be seen by reference to FTGURB and to minimize smoke formation, the nozzle of the injection pipe must be located at a distance of from 2.8 to 1.4 tuyere exit nozzle diameters away from the tuyere. With the injection nozzle in the preferred axial position, the optimum distance of 2.8 T would provide for a coking-free operation with reduced smoke formation and good air-fuel mixing. Where a slumped position must be utilized, the preferred distance is 1.4 T while nozzle positions intermediate to these positions would according 1y result in intermediate T distances. From the foregoing, the critical relationship of nozzle distance to tuyere, for proper operation, can be readily ascertained EXAMPLE 1 A Bunker C oil of the characteristics described in Table I was injected into a blast furnace through the inventive apparatus of FIGURE 1.

The oil was injected at a pressure of -20 psi. and a 2. To ensure no tuyere plugging temperature of 185 1*. and at flow rates of 1, 5, 10, and 18 gallons per hour. The use of an air cooling shroud through the annula fluid shroud tube permittedmperation down to a level of 1 gallon per hour of fuel. Without the use of the cooling air shroud, injection flow rates of 6 gallons per hour and less. The injection nozzle had a diameter of A, the concentric fluid shroud pipe a diameter of /2, and the tuyere a diameter of 2 /2. Theoperation of the nozzle in both axial and slumped positions gives satisfactory injection, while operation at 2.8 T and 1.4 T respectively gave optimum performance. Injection of the Bunker C oil by the use of a conventional air atomization nozzle gave unsatisfactory results in that coking and subsequent plugging of the nozzle occurred at both the maximum and minimum flow rates above.

In summary, the inventive apparatus and process is capable of injecting liquid fuel into a blast furnace over a Wide range of flow rates when the injection nozzle is Within critical distance of the tuyere opening without danger of nozzle coking, tuyere plugging, or excessive smoke formation.

What is claimed is: 3

1. in a process for introducing a liquid hydrocarbon fuel from a fuel source into a blast fur-ance through a fuel injection pipe having an inlet and an exit nozzle circumferentially shrouded by an outer conduit of larger diameter, said conduit having an inlet and an outlet, and located within a tuyere b'lowpipe and nozzle having a tuyere exit diameter opening into the furnace, through which tuyere heated blast air and fuel areintroduced into the furnace, said exit nozzle being located at a distance be tween 1.4 and 2.8 times the tuyere exit diameter from the tuyere opening; the process comprising introducing said fuel into the inlet of said fuel injection pipe from said fuel source; injecting said fuel from said exit nozzle at a pressure greater than that of the blast air; and simultaneously passing a cooling fluid through the said outer conduit from inlet to outlet at a flow rate not greater than 0.8 by weight of the liquid flow rate, thereby protecting said fuel before injection from the effects of excessive furnace and blast air heat; atomizing said fuel by the differential velocity between the said blast air and said fuel and introducing said atomized mixture of fuel, blast air, and cooling fluid into said furnace, whereby smoke formation is inhibited and plugging of the fuel injection system and tuyere opening is reduced.

2. A process as claimed in claim 1 wherein said blast air has a temperature greater than 1600 F. and the fuel flow rate is less than 6 gallons per hour.

3. A process as claimed in claim 1 wherein said fuel is residual petroleum fuel oil.

4. A process as claimed in claim 1 wherein said cooling fluid is air at a flow rate of between 0.5 and 0.8 by weight of the liquid flow rate and at a temperature of between 60 and F.

5. A process as claimed in injection is at a distance of 1.4 times ameter from the tuyere opening.

claim 1 wherein said fuel the tuyere exit di- References Cited in the file of this patent UNITED STATES PATENTS 26,037 Great Britain ca--s-, of 1904 severe coking occurs at"

Claims (1)

1. IN A PROCESS FOR INTRODUCING A LIQUID HYDROCARBON FUEL FROM A FUEL SOURCE INTO A BLAST FURANCE THROUGH A FUEL INJECTION PIPE HAVING AN INLET AND AN EXIT NOZZLE CIRCUMFERENTIALLY SHROUNDED BY AN OUTER CONDUIT OF LARGER DIAMETER, SAID CONDUIT HAVING AN INLET AND OUTLET, AND LOCATED WITHIN A TUYERE BLOWPIPE AND NOZZLE HAVING A TUYERE EXIT DIAMETER OPENING INTO THE FURNACE, THROUGH WHICH TUYERE HEATED BLAST AIR AND FUEL ARE INTRODUCED INTO THE FURNACE, SAID EXIT NOZZLE BEING LOCATED AT A DISTANCE BETWEEN 1.4 AND 2.8 TIMES THE TUYERE EXIT DIAMETER FROM THE TUYERE OPENING; THE PROCESS COMPRISING INTRODUCING SAID FUEL INTO THE INLET OF SAID FUEL INJECTION PIPE FROM SAID FUEL SOURCE; INJECTING SAID FUEL FROM SAID EXIT NOZZLE AT A PRESSURE GREATER THAN THAT OF THE BLAST AIR; AND SIMULTANEOUSLY PASSING A COOLING FLUID THROUGH THE SAID OUTER CONDUIT FROM INLET TO OUTLET AT A FLOW RATE NOT GREATER THAN 0.8 BY WEIGHT OF THE LIQUID FLOW RATE, THEREBY PROTECTING SAID FUEL BEFORE INJECTION FROM THE EFFECTS OF EXCES-

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