US3759698A

US3759698A - Method of blowing reducing gas into a blast furnace

Info

Publication number: US3759698A
Application number: US00876535A
Authority: US
Inventors: K Omori; Y Hara; Mija Iguchi
Original assignee: Fuji Iron and Steel Co Ltd
Current assignee: Fuji Iron and Steel Co Ltd
Priority date: 1968-11-20
Filing date: 1969-11-13
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18
Also published as: DE1958214A1; CA939505A; GB1277606A; DE1958214B2; NL147480B; FR2023710A1; NL6917494A

Abstract

METHOD FOR BLOWING A REDUCING GAS INTO A BLAST FURNACE IN WHICH THE REDUCING GAS IS PRODUCED IN A REDUCING GAS GENERATOR, SUPPLYING GASEOUS MATERIALS INTO THE REDUCING GAS GENERATOR UNDER SPECIFIC CONDITIONS WITH THE TEMPERATURE OF THE PRODUCED GAS CONTROLLED AND THE TEMPERATURECONTROLLED GAS BEING BLOWN IN THE BLAST FURNACE.

Description

Sept. 18, 1973 KAZUO QMQR] EI'AL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE;

Filed Nov. 13, 1969 '7 Sheets-Sheet 1 when the blast furnace has a tendenc of Banging (a) (A) (Q) (A) I I I Z0 Blast furnace Pressure at blow-in opening level V g/cm G) m Gas pressure in JJ reducing gas generator s/curs) Oxygen flow rate 4120 (Nm /H) Steam flow rate da (Nm 7H) v produced ('0 4 R-value of gas /9 produced 7 a INVENTOR 0 1 Z Time(min) Yfl fl fim nan BY Hnsnnm lGlUH J! 8 Dig ATTORNEY l 1973 KAZUO OMORI ETAL 3,759,698

METHOD 0f" BLOW'ING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 15, 1969 7 Sheets-Sheet 2 When blow-in opening has 0 tendency of clogging i 7 Z 6 d) g /fifl Blow-in resistance 4 Pressure in gas generator 4 /cm G) Oxygen flow fflpfi 5 (Nm m) 40W Jana Steam flow /m aw Temperature of Z000 gas produced flu!) /Zaa R-value of gas /fl produced increase of increase of (f unbumt constituents unburnt constituents mcrese of unburnt fl constituentsand danger of explosion overheatmg I l l I 4 Z Time INVENTOR Knzuo 0mm YOSIHRtKI HHRR BY Mnsnnm IGUCIH d4 7 5m ATTORNEY Sept. 18, 1973 KAZUO QMOR] ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 1969 'T Sheets-Sheet 5 19 km) (A) Blast furnace Z9 Pressure ot blow-in openinglevel Gus pressure in reducing gas generator /cm G) (Nm /H) Steam flow rate 0V0 Nm H W K 7 I I Temperature ofgos /7fl/7 produced ("0 ,Zflfl R-volue of 905 g produced a: W

ATTORNEY Sept. 13, 1973 KAZUO OMORI ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 1969 '7 Sheets-Sheet 4.

Blow-in resistance J'fl Pressure in gas enerator 4 Q/cm G) Oxygenflow /flflp /H) Steam flow 700 (N /H) 5 1 Temperaiure of [My gas produced ('6) M00 R-va1ueof gas m MWMWM produced 0 I I I l T INVENTOR lrne KHZU 0 onom yasnmm IIRRH BY hnsnnm legal ATTORNEY p 1973 v KAZUO OMORl E L 3,759,698

METHOD OF BLOWlNG REDUCING GAS lNTO A BLAST FURNACE Filed Nov. 13, 196i) '7 Sheets-Sheet l,

Utility efficiency 0.6 e

of hydrogen Reducing gas Temp Z (natural gas) Flow rate Q/Cm H) Down-stream Pressure/ UP Stream P ressure Critical Pressure flia natural 5 who my 9 ajdfl R/ 004 steam ygen JJZfl Specific heal ratio INVENTOR knzuo 0mm yosmnm umzn nnsanm leucm BY life 1L ATTORNEY Sept. 18, 1973 V KAZUO OMQRI ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 1969 7 Sheets-Sheet 6 INVENTOR KHZUO OMDRI yosumm HnRn BY flnsnnm IGUCHI I 9% 3 21! ATTORNEY Sept. 18, 1973 A KAZUO OMOR] ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 15, 1969 '7 Sheets-Sheet 7 ,L/ INVENTOR A kHZuo 0mm a OSHIBKI "HRH HSHPKI IGUCHI ATTORNEY United States Patent 3,759,698 METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Kazuo Omori, Yoshiaki Hara, and Masaaki Iguchi, Himeji-shi, Japan, assignors to Fuji Iron & Steel Co., Ltd., Tokyo, Japan Filed Nov. 13, 1969, Ser. No. 876,535 Claims priority, application Japan, Nov. 20, 1968, 43/85,013, 43/ 85,014; Feb. 20, 1969, 44/ 12,867, 44/ 12,868, 44/8,845

Int. Cl. C22b /00 US. CI. 75-42 6 Claims ABSTRACT OF THE DISCLOSURE Method for blowing a reducing gas into a blast furnace in which the reducing gas is produced in a reducing gas generator, supplying gaseous materials into the reducing gas generator under specific conditions with the temperature of the produced gas controlled and the temperaturecontrolled gas being blown in the blast furnace.

This invention relates to a method of blowing a reducing gas, produced outside of a blast furnace, into the blast furnace in order to reduce the consumption of coke in the blast furnace and to increase its productivity.

The method of producing reducing gas outside of a blast furnace and blowing the gas into the blast furnace has already been proposed. However, there are many prob lems to be solved in such a method, and accordingly, the method has not yet been commercially worked.

The first problem lies in the fluctuation of the composition and temperature of the gas produced owing to the variation of the furnace pressure of the blast furnace.

Even when the furnace pressure of the blast furnace is constant, the blow-in resistance (the resistance against the blowing of reducing gas into the blast furnace) fluctuates owing to the changes in the particle size and softening condition of the burden near the blow-in opening of the furnace, and also to the stick-to and strip-off of the burden around the blow-in opening. The fluctuation of the blow-in pressure spreads through the reducing gas pipe lines connecting the blow-in opening and the reducing gas generator; and finally, the fluctuation of the pressure of the reducing gas generator takes place. As a result, among the raw materials supplied to the reducing gas generator, i.e., the fuel (solid, liquid, gas), the oxidant (air, oxygen) and steam, the supply of the compressible gaseous raw materials (gaseous fuel, oxidant and steam) fluctuates remarkably, which causes the fluctuation of the composition and temperature of the reducing gas produced.

For instance, when the blow-in resistance to the reducing gas of the blast furnace increases suddenly, while the solid or liquid fuel is supplied constantly through the pump, the supply of the oxidant and steam diminishes; and consequently the unburnt constituents (soot, methane, etc.) increases, and the temperature of the reducing gas generator decreases suddenly.

When the blow-in resistance decreases suddenly, a large quantity of the oxidant and steam is supplied instantaneously, and the fuel burns explosively, which leads sometimes to an explosion. When the characteristics of the flow controlling apparatuses for the raw materials do not coincide with each other, a similar phenomenon may occur with the use of gaseous fuel. Even if the explosion does not occur, since much heat is produced by the excess combustion mentioned above, the temperature of the re ducing gas generator increases; and not only the generator lining but also the burner of the generator are damaged by melting, and consequently the operation of the reducing gas generator becomes difiicult, and it is impossible to blow the reducing gas into a blast furnace.

Owing to the change of the quantity and proportions of the raw materials supplied, the fluctuation of R-value which expresses the reducing power of the gas) and temperature of the reducing gas produced takes place. When such a fluctuating gas is blown into the blast furnace, the reducing condition of the blast furnace, particularly the utilization efiiciency of hydrogen is changed, and the gaspermeability of the furnace is also altered. Due to the change in reducing condition, the behavior of silicon in the pig iron becomes unstable, the descending condition of the burden is disturbed, and the smooth operation of the blast furnace becomes impossible.

The present invention shall be described in detail referring to the attached drawings in which:

FIGS. 1-4 are explanatory drawings showing the relation between the pressure variation in a reducing gas generator and the temperature and R-value of the reducing gas produced. The method of supplying raw materials to the reducing gas generator is referred to by (a) and the furnace condition of the blast furnace is referred to by (b) in FIGS. 1 to 4 as follows:

FIG. 1 (a): controlled by a conventional method, (b): the blast furnace has a tendency of hanging and slipping;

FIG. 2. (a): as in FIG. 1, (b): the blow-in opening of the reducing gas has a tendency of clogging;

FIG. 3 (a): according to the method of this invention, ([1): as inFIG. 1;

FIG. 4 (a): as in FIG. 3; (b): as in FIG. 2;

FIG. 5 is an explanatory drawing showing the relation between the temperature of reducing gas blown-in and the utility efliciency of hydrogen;

FIG. 6 is an explanatory drawing showing the critical pressure ratio in the case of, for example, natural gas used as a gaseous raw material;

FIG. 7 is an explanatory drawing showing the relation between the specific heat ratio and the critical pressure ratio of gaseous raw materials;

FIG. 8 is a flow-sheet of an apparatus used in working the present invention;

FIG. 9 is an explanatory drawing of an example of the apparatus for supplying raw materials, attached to the reducing gas generator of this invention;

FIGS. 10-14 are flow-sheets of examples of a reducing gas blow-in temperature controlling apparatus used in this invention, in which the gas is cooled by mixing with a low temperature reducing gas, where;

FIG. 10 is a flow-sheet using a partial flow of the high temperature reducing gas produced.

FIG. 11 is a flow-sheet using a low temperature reducing gas obtained from a separate source;

FIG. 12 is a flow-sheet using the apparatus in FIG. 10 together with a waste heat boiler;

FIG. 13 is a flow-sheet using the apparatus in FIG. 12 together with a waste heat boiler; and

FIG. 14 is an explanatory drawing showing the crosssection of an example of a rapid cooler used in this invention.

As for the first problem mentioned above, the actual problem in the case of supplying the gaseous raw materials by the usual flow controlling system and supplying heavy oil as the fuel by a constant-volume pump will be described referring to FIG. 1 and FIG. 2.

FIG. 1 shows the fluctuating relationship between the furnace pressure of the blast furnace and the temperature and R-value of the gas produced in the reducing gas generator when the blast furnace has a tendency of hanging and slipping.

As seen from the figure, when the furnace pressure of the blast furnace increases gradually as shown by (a) in the figure at the commencement of hanging, the usual controlling apparatus responds sufliciently, and the supply of gaseous raw materials can be maintained almost constant. However, when the furnace pressure decreases beyond the responsibility of the controlling apparatus as shown by (b) at the time of the slipping, the balance of the supply of the fuel, the combustion promoter and the water vapour is destroyed instantaneously, and the fluctuation of the temperature and R-value of the gas produced takes place. Particularly, once such a sudden change of the temperature takes place, a more serious problem ocours as mentioned below.

FIG. 2 shows the fluctuating relationship between the blow-in resistance and the temperature and R-value of the reducing gas produced at the time when the blow-in opening of the reducing gas has a tendency to clog.

When the temperature of the reducing gas to be blowin is higher than that of the softening point of the burden of the blast furnace, the burden near the blow-in opening is melted partially and becomes sticky, and as a result, it clogs the blow-in opening, and the blow-in resistance increases suddenly Then, the flow of the oxidant and steam decreases suddenly. However, when the sticky block of molten burden leaves from the blow-in opening, the blow-in resistance decreases sharply (d), and consequently, the flow rate of the combustion promoter and steam increases suddenly. When the change of the blow-in resistance is rapid and remarkable, the fluctuation in the supply of gaseous raw materials above-mentioned continues for a while, although the deviation from the preset value diminishes gradually; and consequently, the temperature and R-value of the gas produced fluctuate remarkably.

When the blow-in resistance fluctuates suddenly in this way, the generator operating condition becomes quite dangerous. The unburnt constituents in the gas produced, increase owing to the increase of the blow-in resistance; and, in such a situation, when the supply of the oxidant increases owing to the decrease of the blow-in resistance, a large quantity of the unburnt constituents mentioned above burn explosively. When such a condition is repeated, an explosion takes place; the reducing gas generator is broken, and it may result in a human disaster.

As is obvious from the above explanations, unless the first problem is solved, it is impossible to blow the reducing gas into the blast furnace steadily.

The second problem is that the temperature of the reducing gas, produced economically and efliciently in the reducing gas generator, is generally higher than the operatively acceptable upper limit for blowing the reducing gas into the blast furnace; and moreover, as the acceptable blow-in temperature of reducing gas into the blast furnace changes due to the variety of the raw materials to be charged in the blast furnace, and due to their mixing ratio and the furnace condition, this blow-in temperature should be controlled in correspondence with the acceptable temperature of the blast furnace, while the blow-in temperature of reducing gas into the blast furnace cannot be controlled sufliciently by the cooling with a conventional waste heat boiler.

As for the reducing gas useful for the blast furnace, it is necessary that the R-value is greater than 3, or, for instance, when heavy oil is used as the fuel, the unburnt constituents should be 14% (weight percentage to the carbon in the fuel). When such a reducing gas is produced economically and efliciently, the temperature of the gas produced is usually higher than 1400 C. On the other hand, as seen from the efliciency of the reducing gas blowin based on the utility efiiciency of hydrogen in FIG. 5, it is sufficient if the blow-in temperature is 850 C. or above.

In FIG. 5, the vertical axis represents the utility efliciency of hydrogen, the horizontal axis represents the reducing gas temperature, and their relation is expressed as the curve e. While the utility efficiency of hydrogen decreases remarkably below 850 C., it is nearly constant above 850 C., although increasing slightly. From the standpoint of the heat economy of the blast furnace, it is desirable that the gas temperature is as high as possible. However, the softening temperature of the raw materials to be charged in the blast furnace varies in a range of about 900 C.1200 0, depending upon their types and mixing ratios of burden.

Therefore, when gas with a temperature higher than the softening point of the burden is blown in, the burden near the opening of the injector is melted partially and becomes sticky, which prevents the gas permeability and the normal descending action of the burden in the furnace; and the smooth operation of the blast furnace becomes impossible.

In a conventional waste heat boiler, as the cooling capacity is determined by the cooling area, even if the amount and pressure of the cooling water is controlled, the control of the cooling capacity is practically impossible; and moreover, the cooling capacity fluctuates owing to the deposition and strip-off of the soot in the gas on the cooling surface. Therefore, such a waste heater boiler cannot be used for the fine temperature control as in the present invention, in which a large quantity of the reducing gas of a high temperature is cooled.

The third problem concerns the treatment of the gas of varying temperature and R-value at the startup of the reducing gas generator.

It is necessary to blow a reducing gas of nearly constant temperature and R-value into the blast furnace when its operating condition is constant. The fluctuation of the reducing gas disturbs the furnace condition.

Therefore, a reducing gas of fluctuating temperature and R-value should be treated safely without blowing into the blast furnace directly.

The fourth problem is the handling and treatment of the gas produced in the reducing gas generator when the blowing of the gas into the blast furnace is stopped for a short period.

If the production of the reducing gas in the reducing gas generator is stopped in accordance with the blowdown of the blast furnace for a short time in order to repair the cinder notch or the blast tuyere, various problems arise such as the shut-down of the reducing gas generator, the damage of the refractory lining due to the temperature change, the troubles in the generator operation for shut-down and start-up, the delay of blowing the reducing gas into the blast furnace due to the time necessary for starting operation; and consequently, the production efficiency of the reducing gas and the blow-in efiiciency of the reducing gas into the blast furnace are lowered.

The present invention offers a method for blowing the reducing gas into the blast furnace without the problems mentioned above.

The first object of the present invention is to provide a method of producing a reducing gas outside of the blast furnace and blowing the gas produced into the blast furnace, in which, the raw materials consisting of fuel (solid, liquid, gas), oxidant (air, oxygen) and steam are supplied into the reducing gas generator.

Among these materials the gaseous materials are passed through a flow-control apparatus and supplied to the reducing gas generator thorough its burner. The pressure of the gaseous materials after the flow-control apparatus depends on the pressure of the reducing gas generator and the pressure drop in the burner, and fluctuates as mentioned before. Therefore in the present invention, the pressure of the gaseous materials before passing through the fiow-control apparatus is maintained constant so that the ratio of the pressure downstream of the flowcontrol apparatus to the pressure upstream of the flowcontrol apparatus is not more than the critcical pressure ratio used in the hydro-dynamics, and the gas produced is blown into the blast furnace after the gas temperature is controlled.

The second object of the present invention is to provide a method for controlling the blow-in temperature of reducing gas produced in attaining the first object, in which the gas is cooled by mixing with a low temperature reducing gas.

The third object of the present invention is to provide an apparatus for attaining the first object, comprising a reducing gas generator having means for supplying the raw materials into the reducing gas generator under a constant pressure, means for controlling the reducing gas blow-in temperature, in which a high temperature reducing gas produced is adjusted to a temperature acceptable for the blast furnace condition; means for cutting otf the supply of high temperature reducing gas to the blast furnace and preventing the reverse flow of the gas from the blast furnace; means for blowing the reducing gas into the blast furnace; pipe lines connecting the above means; and branched pipe lines connected to the above pipelines and provided with a rapid cooler and a cut oif valve.

The fourth object of the present invention is to provide another apparatus for attaining the first object, comprising a temperature controlling means for controlling the reducing gas blow-in temperature, in which the gas is cooled by mixing with a low-temperature reducing gas.

The following are the results of various experiments and investigations by the present inventors to solve the four problems mentioned above.

The inventors found that, to solve the first problem, a law of hydro-dynamics hitherto known can be applied.

It has been known that, in passing a compressible gas in a pipe line having a neck, when the up-stream pressure is maintained at a constant value, the ratio of the downstream pressure to that of the up-stream being not more than a critical pressure ratio, the flow velocity at the neck is equal to the sonic velocity, and the flow rate can be maintained constant without being influenced by the fluctuation of the down-stream pressure. The relation is shown in FIG. 6.

In FIG. 6, the vertical axis represents the flow rate (kg./cm. /hr.), the horizontal axis represents the ratio of the down-stream pressure to the up-stream pressure; and by maintaining the up-stream pressure constant, the flow rate changes with varying down-stream pressure are illustrated. It is obvious that, by increasing the up-stream pressure, the flow rate increases as shown by A, B and C. However, in every case, there are two zones; the one (D) in which the flow rate is constant without being influenced by the change in the down-stream pressure under a constant pressure up-stream, and the other (E) in which the flow rate changes. The former zone lies in the range in which the ratio of the down-stream pressure to the up-stream pressure is not more than the critical pressure ratio (a), and the latter zone lies in the range in which said ratio is more than the critical pressure ratio (it).

Now through extensive experiments based on the above law for a process for producing reducing gas constantly free from the influence of the pressure of the blast furnace, the present inventors have found that the only commercially applicable way is to apply the above law to the supply of gaseous materials to a reducing gas generator.

Two types of experiments were conducted by the present inventors using the above law.

In one type of the experiments, the ratio of the downstream pressure to the upstream pressure is maintained in the above-mentioned D zone by providing a neck using an orifice or a pressure controlling valve or the like in the pipe line connecting the reducing gas generator and a reducing gas blow-in opening of the blast furnace. In the other type of experiment, a neck using a flowcontrolling valve, an orifice or a burner nozzle or the like is provided in the pipe-line for supplying gaseous materials to the reducing gas generator to maintain the ratio of the down-stream pressure to the up-stream pressure in the above-mentioned D zone.

In the first type of experiment mentioned above, however, the present inventors found that there are such difliculties that the damage of the neck caused by the hightemperature, and the high-velocity reducing gas flow is too small to continuously maintain the above condition, and further the high-pressure resistant construction of the hot gas pipe-line from the reducing gas generator up to the neck involves such complexity that it prohibits a continuous supply of the reducing gas into the blast furnace, in spite of the advantages that the temperature and R-value of the produced gas, as Well as its volume blown into the blast furnace, can be maintained almost constant.

Whereas, in the latter type of experiment the present inventors found that there are no such difiiculties as met in the first type of experiment, and a constant production of reducing gas in combination with the action of a reducing gas temperature controlling apparatus as mentioned hereinafter enables a continuous blowing of the reducing gas into the blast furnace.

One embodiment of the latter experiment in which the reducing gas is produced by using heavy oil as fuel supplied by a constant-volume pump shall be described referring to FIG. 3 and FIG. 4.

FIG. 3 shows, as FIG. 1, the relation between the variation in the blast furnace pressure and the variation in the temperature and R-value of the produced gas. When the reducing gas is produced maintaining the supply pressure of the gaseous materials such as oxygen and steam supplied into the reducing gas generator at a constant value so that the ratio of the down-stream pressure, to the up-stream pressure is not more than the critical pressure ratio, even if the pressure in the balst furnace rises to such high pressure as under a furnace condition in which there is a tendency of hanging and slipping. As clearly understood from the drawing, when the pressure in the blast furnace varies considerably at the time (a) of commence of hanging and at the time (b) of slipping, thepressure in the reducing gas generator corresponds to this and varies considerably.

On the other hand, the variation in the flow rate of the gaseous materials (oxygen and steam) supplied into the reducing gas generator is negligible so that the variation in the temperature and R-value of the produced gas is also negligible. This produced gas with its temperature con trolled was continuously blown into the blast furnace satisfactorily without any trouble in the production of reducing gas, in the blowing of reducing gas into the blast furnace, as well as in the blast furnace operation.

FIG. 4 shows, as FIG. 2, the relation between the pressure in the blast furnace and the temperature and R-value of the produced gas when the gaseous material is supplied and the reducing gas is produced in a similar way as in FIG. 3 under a furnace condition in which the blow-in opening of the reducing gas has a tendency to clog.

As is clear from the drawing, when the blow-in opening is clogged with a sticky block of the burden, the blow-in resistance rapidly increases and then when the sticky block leaves the blow-in opening, the resistance rapidly decreases, and the pressure in the reducing gas generator corresponds to the above changes and varies considerably.

However, the variation in the filow rate of the gaseous material is very small so that the variation in the temperature and R-value of the reducing gas is negligible and the production of reducing gas and the blowing of reduc- I provides for the first time a novel method which can produce reducing gas of an almost constant temperature and R-value without being influenced by the variation in the pressure in the blast furnace or by the clogging of the blow-in opening.

Critical pressure ratios of various gaseous materials are shown in FIG. 7 in which the critical pressure ratios are shown along the vertical axis and the specific heat ratios are shown along the horizontal axis and the line (f) shows the relation between the critical pressure ratios and the specific heat ratios. As shown, natural gas has a critical pressure ratio of about 0.55, oxygen about 0.53 and water vapour about 0.54.

For controlling the thus produced high-temperature reducing gas having constant temperature and R-value to a temperature most acceptable for a blast furnace, a branch flow of the high-temperature reducing gas produced in the reducing gas generator is cooled to about 40 C. by a rapid cooler as shown in FIG. 14 and forced back to the high-temperature reducing gas, or a low-temperature reducing gas separately obtained is forced into the hightemperature gas.

The present inventors found these methods for controlling the temperature of the high-temperature reducing gas by mixing it with a low-temperature reducing gas is best for controlling quickly and precisely a large amount of high-temperature produced reducing gas.

The temperature control of reducing gas may also be done by cooling the gas with a waste heat boiler, and further controlling the temperature of thus cooled gas by mixing a low-temperature reducing gas as above-mentioned corresponding to the variation in the heating capacity of the boiler and to the temperature variation required by the blast furnace.

Next, in the present invention, in order to assure an efficient and stable production of reducing gas as well as an efiicient and stable blowing of the gas into a blast furnace, a branched pipe-line having a rapid cooler is provided in the reducing gas supply pipe-line so that the reducing gas produced at the starting operation of the gas generator and during the blow down of the blast furnace may be supplied or vented to other applications.

Examples of an apparatus used in experiments and cmbodiments of the present invention shall be explained referring to FIG. 8-FIG. 14.

FIG. 8 shows a flow arrangement of an apparatus for working the present invention, in which 1 is a supplier for supplying raw materials to a reducing gas generator 2. 3 is a pipe-line for supplying the reducing gas into a blast furnace. The pipeline 3 is provided with a temperaturecontrol device 4 for the reducing gas used for cooling the high-temperature reducing gas by mixing it with a lowtemperature reducing gas, a cut-off valve 5 for the high temperature gas, a branched pipeline 8 having a rapid cooler 6 and a cutoff valve 7, and an expansion joint 9.

The supplier 1 is constructed as shown in FIG. 9 in case heavy oil, for example, is used as fuel. 11 is a cracking furnace for heavy oil, 12 is a pipe-line for supplying oxygen, 13 is a pipe-line for supplying heavy oil and 14 is a pipe-line for supplying steam.

Both of the oxygen supply pipe-line 12 and the steam supply pipe-line 14 are provided with a pressure controlling valve 15 activated by a signal from the pressure controller (PIC), and a flow controlling valve 16 activated by a signal from the flow controller (FIC).

Oxygen and steam pass through the pipe-lines 12 and 14 respectively, while heavy oil is pumped by a constantvolume pump 17 and passes through the heavy oil supply pipe-line 13, and all are supplied into the cracking burner 18.

For the production of reducing gas in the heavy oil cracking furnace 11, oxygen and steam are forced into the heavy oil cracking furnace 11 while maintaining the supply pressure up-stream of the flow controlling valve 16 or instead of the valve, an orifice (not shown) or a burner nozzle (not shown) at a constant value so that the ratio of the down-stream pressure to the up-stream pressure is not more than the critical pressure ratio (a) as defined above. In this way the temperature and R-value of the produced gas are maintained constant as shown in FIG. 3 and FIG. 4 irrespective of any variation in the blast furnace pressure or the clogging of the blow-in opening.

Next, the temperature controlling apparatus 4 for the reducing gas used for cooling the high-temperature reducing gas by mixing it with a low-temperature reducing gas shall be described referring to FIG. 10-FIG. 14.

In FIG. 10, part of the high-temperature reducing gas produced in the reducing gas generator 2 is led to a rapid cooler 21 as shown in FIG. 14, in which the gas is cooled and washed by quenching it directly in a cooling water (if necessary a spray cooler 22 may be used for spray-cooling and washing), then lead to a compressor 23 where the gas pressure -is increased, through a flow controlling valve 24 activated by the signal from the temperature controller (TIC), and supplied to the pipe-line 3 to control the temperature of the high-temperature reducing gas.

Thus, it is possible to control the temperature of reducing gas to a pre-set temperature without any trouble such as the variation in cooling capacity, poor controllability of cooling temperature etc. which are often met in using a waste heat boiler.

FIG. 11 shows a modification in which instead of cooling the branch fiow of the high-temperature reducing gas, a low-temperature reducing gas, such as a L.D. convertor gas, raw gas for ammonia-production, a blast furnace gas, a coke oven gas, a petroleum waste gas etc. which are available at room temperature, is used. The above lowtemperature reducing gas supplied separately is stored in a tank 31, and the pressure of the gas is increased by a compressor 23 and then the gas is supplied to the pipeline 3 through a flow controlling valve 24 activated by the signal from the temperature controller (TIC). In this way, same results as in FIG. 10 are obtained.

FIG. 12 and FIG. 13 show respectively another modification of the temperature controlling apparatus for the reducing gas used for cooling the high-temperature reducing gas by mixing it with a low-temperature reducing gas and using a waste-heat boiler 41.

In FIG. 12 a high-temperature gas from the pipe-line on the outlet side of Waste heat boiler 41 passes through a branch pipe-line 42 to a spray-washing cooler 43 Where the gas is cooled, through the compressor 23 and a flow controlling valve 24 activated by the signal from the temperature controller (TIC) and is blown into the pipe-line 3 on the inlet side of the waste-heat boiler to control the temperature of the high-temperature reducing gas.

In FIG. 13, the low-temperature reducing gas supplied separately at room temperatures is stored in the tank 31, passes through the compressor 23 and a flow controlling valve 24 activated by the signal from the temperature controller (TIC) and is blown into the pipe-line 3 on the inlet side of the waste-heat boiler 41 to control the temperature of the high-temperature reducing gas.

The apparatus described referring to FIG. 12 and FIG. 13 produce similar results as the apparatus of FIG. 10 and FIG. 11 overcoming the deficiencies of a waste-heat boiler by controlling the temperature of the reducing gas with a low-temperature reducing gas.

The branch pipe-line 8 provided with the rapid cooler 6 and the cut-off valve 7 shall be described referring to FIG. 8 and FIG. 14. The high-temperature cut-ofif valve 5 is closed and the cut-off 7 is opened at the time of starting operation of the reducing gas generator 2, during the period when the temperature the R-value and the unburnt constituents of the produced reducing gas are not constant or during the period when the produced reducing gas cannot be blown into the blast furnace due to a shorttime blow-down. In this way the produced gas is passed through the rapid cooler 6 where it is cooled and vented to the atmosphere through the vent stack 67 or used as a fuel gas, or recovered and used as a low-temperature gas for controlling the temperature of the high-temperature reducing gas.

The construction of the rapid cooler 6 illustrated in FIG. 8, is shown in FIG. 14 and is similar to that of the cooler 21 shown in FIG. 10.

The coolers 6 in FIG. 8 and 21 in FIG. 10 have a diiferent cooling capacity: the former cools the gas to about 100 C., the latter cools the gas to about 40 C.

The cooler 6 shall be described referring to FIG. 14. The cooler 6 comprises a cooling chamber 61 into which the end 62 of the pipe-line 8 projects, a cylinder 63 is positioned about the end 62 between the end and the chamber 61 and a water-vapour separating plate 68 is provided about the pipe-line 8 above the cylinder 63.

At the lower end of the cooling chamber 61 there is provided a water exhaust pipe 64 having an exhaust flow controlling valve 65 activated by a signal from the liquid level controller (LIC) to control the amount of cooling water poured from the cooling water supply pipe 66 and remaining in the cooling chamber 61.

Examples of the present invention shall be described below.

A low-temperature reducing gas cooled to 40 C. was forced into a high-temperature reducing gas at a flow rate of 14,000 Nmfi/hr. (Nm. means gas volume in the normal state at (3., 1 atm.) using the apparatus of FIG. to control the temperature of the high-temperature gas to 1100" C. On the other hand, a hydrogen-rich raw gas at 30 C. for ammonia production of 30 C. from a separate soruce was forced into a pipe-line on the inlet side of a waste-heat boiler at an average flow rate of about 6000 Nmfi/hr. and cooled in the boiler to a controlled temperature of 1100 C. The gaseous materials of the former method (G) and the later method (F) were blown into a blast furnace of 1600 m Conditions for producing reducing gas:

Blowing conditions:

Blowing position (percent) 20 35 Blowing temperature C 0.).... 1,100 1,100 Blowing rate 36, 000 30,000

Blowing position (percent) means the percentage of the distance between the blast tuyere and the blowing position to the distance between the tuyere and the stockllne.

As a comparative example, a reducing gas produced under the same conditions using a conventional material supplying apparatus was cooled by a waste-heat boiler and blown into a blast furnace of 1600 m. at a blowing position of 20%, a blowing temperature of 1100 and a blowing rate of 15,000 Nm. /hr.

The following table shows results of blast furnace operations using the method (H) of the above comparative example, the inventive methods (F) and (G) and the conventional method (K) in which a reducing gas is not blown into the blast furnace.

F G H K Reducing gas blowing availability (percent) 97. 5 97. 9 23. 8 Reducing gas blowing rate (Nm lt-pig)- 195 196 28 Pig production (t./day) 3,705 3,669 3, 207 3, 218 Coke rate 418 424 485 483 Si content in pig (percent):

X. 0. 674 0. 669 0. 733 0. 661 6 ii). 118 0. 113 0. 163 0. 105

Total time of blowing 1 Reducing gas blowing availability=-X Annual time As understood from the above table, in both of the inventive methods (F) and (G), the reducing gas can be blown continuously during the operation of a blast furnace, and show a remarkable eflfect in increasing the pig production, and reducing the coke rate. While in the comparative method (H), the temperature of the reducing gas is influenced by the pressure in the blast furnace into which the gas is blown, and this variation in temperature cannot be adjusted so that a sticky block of the burden is formed at the blow-in opening, and every time this block sticks to or leaves the openingthe explosive burning as mentioned before takes place repeatedly in the reducing gas generator, thus increasing the danger of explosion. Further, the variation in the temperature of the furnace burden and the variation in the reducing condition are large so that the behavior of the silicon content in the pig varies largely, which causes irregular descending of the furnace burden and frequent hangings and slippings, which in turn causes sudden changes of the pressure in the reducing gas generator, and thus frequent interruption of the blowing of the reducing gas is unavoidable. Thus no improvement in a blast furnace operation can be obtained; no better than the conventional method (K), even worse than it as shown in the above example; particularly the variation in the silicon content of the pig is sharply increased and the blast furnace operation becomes exceedingly unstable.

According to the present invention, a reducing gas having a stable temperature and composition can be produced efliciently and economically in a reducing gas generator connected to a blast furnace, and this produced gas can be blown into the blast furnace at a controlled temperature, thus increasing pig production rate, reducing the coke rate and remarkably enhancing the productivity of a blast furnace.

What is claimed is:

1. A method of blowing a reducing gas produced outside of a blast furnace into the blast furnace in which the inside pressure varies depending on the influence of the blast furnace and/or pressure variations in the reducing gas blowing system, comprising the steps of supplying material including gaseous materials composed of fuel, auxiliary fuel and water vapor into a reducing gas generator, controlling the flow of gaseous materials supplied to the reducing gas generator, introducing the gaseous materials at a constant pressure for passage through the flow control step so that the ratio of the pressure after the gaseous materials have passed through the flow control step to the constant pressure of the gaseous materials introduced for flow through the flow control step is less than the critical pressure ratio, withdrawing the reducing gas from the reducing gas generator and introducing it to the blast furnace, and controlling the temperature of the reducing gas before it is introduced into the blast furnace.

2. A method, as set forth in claim 1, wherein the step of controlling the temperature of the reducing gas includes separating a part of the reducing gas Withdrawn from the reducing gas generator and contacting the separated reducing gas with a lower temperature reducing gas to form a reduced temperature reducing gas and maintaining the reduced temperature reducing gas at a controlled fiow rate and mixing it with the remainder of the reducing gas withdrawn from the reducing gas generator 1 1 to control the temperature at which the reducing gas is introduced into the blast furnace.

3. A method, as set forth in claim 1, wherein the step of controlling the temperature of the reducing gas includes supplying from a separate system at a controlled flow rate a reducing gas at a lower temperature than the reducing gas withdrawn from the reducing gas generator, and mixing the lower temperature reducing gas with the reducing gas from the reducing gas generator for controlling "the blowing temperature of the reducing gas into the blast furnace.

4. A method, as set forth in claim 1', wherein the step i of controlling the temperature of the reducing gas includes cooling in a heat exchanger a part of the reducing gas withdrawn from the reducing gas generator, cooling the other part of the reducing gas withdrawn from the reducing gas generator by contacting it with cooling water to produce a lower temperature reducing gas, and mixing the lower temperature reducing gas in a controlled flow with the reducing gas cooled in the heat exchanger to control the blowing temperature of the reducing gas into the blast furnace.

5. A method, as set forth in claim 1, wherein the step of controlling the temperature of the reducing gas includes cooling the reducing gas withdrawn from the reducing gas generator in a heat exchanger, and mixing a lower temperature reducing gas from a separate system at a controlled rate into the reducing gas cooled in the heat exchanger for controlling the blowing temperature of the reducing gas to the blast furnace.

6. A method, as set forth in claim 1, including the steps of diverting a portion of the reducing gas from its path of flow to the blast furnace, cooling the diverted flow of reducing gas, and discharging the cooled diverted gas to a source other than the blast furnace.

References Cited UNITED STATES PATENTS 2,790,711 4/1957 Sellers et a1 75-42 X 2,577,730 12/1951 Benedict 75-35 3,375,098 3/1968 Marshall 75-35 3,458,307 7/ 1969 Marshall 75-42 3,236,628 2/1966 Bogandy 75-42 3,418,108 12/1968 Von Stroh 75-41 X 3,454,395 7/1969 Von Stroh 75-41 X 2,740,701 4/1956 Tenny 48-191 X 3,210,181 10/1965 Manny 75-41 3,233,987 2/1966 Hepburn 48-191 X 3,193,378 7/1965 Peet 75-35 3,591,364 7/1971 Reynolds 75-35 X FOREIGN PATENTS 985,577 3/1965 Great Britain 75-42 OTHER REFERENCES Dean: Article in Blast Furnace and Steel Plant, May 1961, p. 417.

Bureau of Mines RI. 5621, Melcher et al., 1960, pp. 5-7.

Perry: Chem. Engin. Hdbk., 4th ed., McGraw-Hill, 1963, pp. 5-9 thru 5-12.

L. DEWAYNE RUTLEDGE, Primary Examiner M. J. ANDREWS, Assistant Examiner US. Cl. X.R. 266-28