US3306238A

US3306238A - Fuel injection system for blast furnaces

Info

Publication number: US3306238A
Application number: US457349A
Authority: US
Inventors: Samuel A Bell; William E Marshall
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1965-05-20
Filing date: 1965-05-20
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

1957 s. A. BELL ETAL FUEL INJECTION SYSTEM FOR BLAST FURNACES 2 Sheets-Sheet 1 Filed May 20, 1965 m3 $1858 53% czufihca 84 motzoz 595 20 1985128 56 VF uozmzmazoo wgmfi XE 6328 ma: 8 $38.58 92m 8 $3358 20 E M36328 m; 2 8.532532 ze mm 350 025525; P

Q azmwmj w QY a Q .2 m :3 9 A W m NW INVENTORS SAMUEL ABELL AND BY WILLIAM E. MARSHALL ATTORN EYS Feb. 28, 1967 A, BELL ETAL 3,306,238

FUEL INJECTION SYSTEM FOR BLAST FURNACES Filed May 20, 1965 2 Sheets-Sheet z [NVENTORS SAMUEL A.BELL AND WILLIAM EMAns ALL BY ATTORNEYS.

United States Patent 3,306,238 FUEL INJECTION SYSTEM FOR BLAST FURNACES Samuel A. Bell and William E. Marshall, Middletown,

Ohio, assignors to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Filed May 20, 1965, Ser. No. 457,349 9 Claims. (Cl. 110-104) This invention relates to a fuel injection system for blast furnaces, and more particularly to a substantially oxygen free system of pulverizing, drying and conveying coal for injection into a blast furnace.

As is old and well known in the art, the blast furnace process consists essentially of charging iron ore, fuel (coke) and flux into the top of the furnace, and blowing heated air into the bottom. In an exemplary operation, on the order of 1.7 tons of ore and iron-bearing materials, 0.7 ton of fuel, 0.4 ton of flux, and 2.5 tons of air are required for each ton of iron produced.

The coke or fuel performs a twofold function; that is, it supplies enough heat to melt the iron and slag and to attain the necessary temperature for metallurgical reactions to take place, and also supplies the reducing agent for the process of removing the oxygen from the iron oxide of the ore.

The use of coke as a fuel is entirely satisfactory from the operational standpoint. However, the production of coke requires special facilities (coke ovens, etc.) and requires the utilization of selected high grade coals. And of course, in certain areas, the supply of such coal and/ or coke is somewhat limited or non-existent.

Blast furnaces require a large amount of fuel, and accordingly, the art has long sought more eflicient and economical fuel supplies for blast furnaces. Over the past twenty years, the primary efforts in the field of blast furnace fuel economy have centered about improvement in the raw materials and heat content of the air blast introduced at the bottom of the furnace.

Other efforts directed to this same problem have attempted the injection of various fuels into the bottom of the blast furnace in close association with the hot blast from the :tuyeres. For example, efforts have been made to inject natural gas, fuel oil, or a slurry consisting essentially of fuel oil and powdered coal. While these systems have in part been successful from the operational standpoint, they often are not the most economical injected fuels.

Accordingly, itis a general object of this invention to provide a more economical fuel injection system for a blast furnace than has heretofore been available.

More specifically, it is an object of this invention to provide a system for injecting powdered coal into a blast furnace.

According to statistics of the United States Bureau of Mines, pulverized coal at rest will spontaneously ignite in an atmosphere containing more than 3.7% oxygen, and will burn explosively in an atmosphere containing more than 6.6% oxygen.

Accordingly, it is a further object of this invention to provide a low oxygen atmosphere in which the coal is pulverized, dried and conveyed.

Finally, and in view of the highly combustible nature of powdered coal, it will be realized that temperatures in the conveying system must be kept relatively low, that is, below approximately 250 F. when air is used for conveying. However, with the low oxygen system of this invention, this temperature is limited only to that at which volatile matter begins to distill in undesirable quantities. (300-500 F. depending on coal composition.)

- As generally indicated above, the fuel will be injected 3,306,238 Patented Feb. 28, 1967 ice at a point in close association with the hot blast to the tuyeres, and it will therefore be apparent that the relatively cool air of the fuel conveying system will directly detract from the heat supplied by the hot blast.

It is therefore still another object of the invention to provide a fuel injection system wherein the coal-air mixture is injected in a relatively dense phase. Preferably, the ratio will be approximately one cubic foot of air (0.08 lb.) per pound of coal. This high ratio of coal to air will effect as small a reduction in the efiiciency of the hot 'blast as is practical.

Still a further object of this invention is to provide a fuel injection system as outlined above, wherein the low oxygen coal pulverizing-drying-conveyin-g atmosphere is, at least in part, recirculated continuously.

Numerous other objects and advantages of the instant invention will become apparent to the skilled worker in the art as this specification proceeds. Reference will be made from time to time to the accompanying schematic drawings, in which:

FIG. 1 shows a schematic diagram of the preferred fuel injection system of this invention.

FIG. 2 shows a schematic diagram of a modified form of the invention.

Briefly considered, this invention contemplates the provision of a suitable supply of air under pressure. Air from this supply is divided into two separate gas systems; a pulverizing-drying-conveying system and an injection system. The conveying system includes means for maintaining the oxygen content of the air below about 3.0%, and a supply of powdered fuel. The powdered fuel is entrained and transported by the low oxygen conveying gas to a cyclone collector, which separates the powdered coal. The powdered coal is continually fed by a rotary feeder, attached to the cyclone collector, into the injection system. The now dense phase coal-gas mixture is injected into the blast furnace by means of the injection system which can utilize air, natural gas, inert gas or the like.

In the preferred form of the invention, the low oxygen conveying gas system recirculates the gas from the cyclone collector back through the rest of the system including the pulverizer. This recirculating portion of the gas conveying system includes a vent to atmosphere, the operation of which is controlled by monitoring the differential pressure existing between the conveying gas system and the injection gas system. That is, the conveying gas system will be operated at a higher pressure than the injection gas system, in order to prevent any backing up of the powdered fuel-injection gas mixture into the recirculating system.

Referring now to FIG. 1, the preferred embodiment of the invention will be described in detail. Air under pressure from a suitable main blower 10 will be supplied to the line 12. The main blower will be of such size and capacity that 11,000 to 13,000 pounds of dry air per hour at a gauge pressure of 20 to 55 p.s.i. will be supplied to the point 18.

At the point 18, the supply of dry air is split into two major components; the component flowing through the conduit 20 supplies the combustion air for the low oxygen conveying gas system briefly mentioned above, while the air in the conduit 22 supplies air through the conduit 24 to the injection air system. The conduit 26 supplies air to seal the pulverizer described hereinafter as is well known in the art.

The conveying gas passes from the conduit 20 into the combustor 28. The combustor 28 is also supplied with a fuel (such as natural gas) through the conduit 30, and with recirculated gas through the conduit 32. In an exemplary operation, 3200 to 3500 pounds of dry'air per hour at a temperature of about 180 F. will be combined with 180 to 200 pounds of natural gas per hour at a temperature of about 70 F. along with 42,000 to 45,000 pounds per hour of recirculated gas at a temperature of about 170 F. in the combustor. Under the above conditions, the combustor 28 will generate from 45,000 to 50,000 pounds of gas per hour at a temperature on the order of 450 F. This inert gas will have a composition of substantially 10.6% carbon dioxide, 2.1% oxygen, and 87.3% nitrogen. This low oxygen conveying gas in the exit conduit 34 will be supplied to the pulverizer 36.

The pulverizer 36 will be supplied with lump coal from the pressurized

coal tanks

38 and 40. It will of course be understood that these coal tanks receive a supply of coal intermittently from a conventional hopper or the like. Coal from the tank 40 will be fed to the pulverizer feeder 42, and thence into the pulverizer 36 where it is ground to the desired degree of fineness in a conventional manner.

The warm low oxygen gas entering the pulverizer through the conduit 34 will then dry and entrain the powdered coal and convey it through the conduit 44 to the cyclone collector 46. It will be understood that this collector serves to separate on the order of 95% of the powdered fuel (coal) from the gas, the powdered coal passing out of the collector through the conduit 48 and into the motor driven rotary valve 50, while the low oxygen conveying gas passes out of the cyclone collector through the conduit 52 to be recirculated as described hereinafter.

The finely powdered coal is then passed through the rotary valve 50 into the conduit 54 of the injection system, wherein it is entrained by injection gas from the conduit 24 noted above. By first pulverizing the coal, and then collecting the finely powdered coal at a separate station, whereupon it may be introduced in measured quantities into a measured quantity of injection gas, the instant invention makes it possible to provide a relatively dense phase gas-fuel mixture, which will then be fed from the conduit 54 to a suitable distributor for injection into the blast furnace.

The conveying gas leaving the collector 46 through the conduit 52 will still contain some finely powdered coal, and as indicated earlier, this conveying gas will be continually recirculated through the system. A portion of the gas in the conduit 52 will be vented to atmosphere through the valve 56 and the vent scrubber 58. The remainder of this gas will pass through the recirculating fan 60, the scrubbing means, including the condensercooler 62, and the separator 64, back into the combustor 28.

It will be noted from the foregoing description that the oxygen content of the conveying gas system is closely controlled and maintained at a relatively low level. This is not true of the injection system which, in the preferred embodiment, also utilizes air. In order, therefore, to prevent a back-up of the fuel-gas mixture of the injection system into the cyclone collector which would decrease its efficiency, it is necessary to operate the conveying system at a somewhat higher pressure than is utilized in the injection system. To this end, the valve 56 in the vent of the recirculating conveying gas system is controlled by a conventional diaphragm which in turn is responsive to the differential pressure as at 68 between the con'veying system and the injection system. The conveying system will be operated at a gauge pressure on the order of 1 to 20 psi. greater than that of the injection system. In the preferred embodiment of the invention, a differential pressure of 15 psi. is maintained. In other words, this arrangement insures that the quantity of combustion products added to the system is substantially equal to the quantity of conveying gas exhausted through the vent 56.

As will be seen from examining the drawings, various conventional controls are employed, both to monitor and control the flow, temperature, and pressure through the various conduits. These assemblies and controls are entirely conventional, and will not be described in detail in this application. It is believed that the operation of these elements will be apparent upon considering the legend and designations on the drawings. By way of example, the supply of components to the combustor 28 will be so regulated in response to the oxygen content monitor 66 so that the oxygen level in the system will be maintained below about 3.0%.

In some cases, it may be necessary to use more than one recirculating conveying gas system in parallel to supply the necessary quantity of coal for a given blast furnace.

FIG. 2 shows diagrammatically a midification of the system described above, wherein the oxygen content of the recirculated conveying gas is maintained at a low level by continuously supplying a non-combustion sustaining gas such as nitrogen to the system. It will readily be seen that the great bulk of the components of the midification of this figure are similar to those described in connection with FIG. 1, and hence similar reference numerals have been used to designate corresponding parts.

In this embodiment, the combustor 28 is replaced substantially by the heater 70. The temperature of the heater 70 may be maintained by, for example, the combustion of a natural gas, but the products of combustion are in no way added to the recirculating gas system as in the foregoing embodiment.

A non-combustion sustaining gas such as nitrogen will be introduced through the conduit 72, so as to pass with the recirculated conveying gas int-o the heater 7 0. In all other respects, this system is substantially identical to that described earlier.

It is believed that the foregoing constitutes a full and complete disclosure of this invention. While is has been described in terms of a preferred embodiment and a modification thereof, no limitations are intended or to be inferred except insofar as expressly set forth in the claims which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A powdered fuel injection system comprising:

(a) means for pulverizing a solid fuel;

(b) powdered fuel collection means;

(c) a low oxygen conveying gas system for transporting pulverized fuel from said pulverizing means to said collection means;

(d) a recirculating means for returning at least a portion of said low oxygen conveying gas from said collection rneans back to said pulverizing means;

(e) water removal means in said recirculating means;

(f) an injection nozzle;

(g) means for feeding fuel from said collection means to said injection nozzle;

(h) a separate injection gas system for said injection nozzle; and

(i) means to maintain the pressure in said conveying system at a level higher than the pressure in said injection system.

2. The fuel injection system claimed in claim 1 wherein said means for recirculating said conveying gas includes a vent to atmosphere, means for monitoring the differential pressure between said conveying gas system and said injection gas system, and means responsive to said differential pressure to control said vent.

3. The fuel injection system claimed in claim 2 wherein said low oxygen conveying gas system includes a supply of dry air and a supply of fuel, means for combining and combusting said fuel and air to produce said low oxygen conveying gas.

4. The fuel injection system claimed in claim 3 wherein said means for recirculating said conveying gas communicates with said means for combining and combusting said fuel and air.

5. The fuel injection system claimed in claim 4 including means for controlling the quantities of fuel and air supplied to said combusting means whereby the quantity of combustion products added to said system is substantially equal to the quantity of said conveying gas exhausted through said vent to atmosphere.

6. The fuel injection system claimed in claim 1 wherein said Water removal means includes gas scrubbing means.

7; The fuel injection system claimed in claim 6 including means for monitoring the oxygen content of said conveying gas, said means being operative to maintain less than substantially 3.0% oxygen in said conveying gas.

8. The fuel injection system claimed in claim 1 wherein said means for recirculating said conveying gas includes means for supplying an inert, non-c-ombustion sustaining gas to said system, and means for controlling said supply 1 whereby to maintain less than substantially 3.0% oxygen in said system.

9. The fuel injection system claimed in claim 8 including indirect heating means for heating said recirculated gas and said inert gas.

References Cited by the Examiner UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner.

Claims

1. A POWDERED FUEL INJECTION SYSTEM COMPRISING: (A) MEANS FOR PULVERIZING A SOLID FUEL; (B) POWDERED FUEL COLLECTION MEANS; (C) A LOW OXYGEN CONVEYING GAS SYSTEM FOR TRANSPORTING PULVERIZED FUEL FROM SAID PULVERIZING MEANS TO SAID COLLECTION MEANS; (D) A RECIRCULATING MEANS FOR RETURNING AT LEAST A PORTION OF SAID LOW OXYGEN CONVEYING GAS FROM SAID COLLECTION MEANS BACK TO SAID PULVERIZING MEANS; (E) WATER REMOVAL MEANS IN SAID RECIRCULATING MEANS; (F) AN INJECTION NOZZLE; (G) MEANS FOR FEEDING FUEL FROM SAID COLLECTION MEANS TO SAID INJECTION NOZZLE; (H) A SEPARATE INJECTION GAS SYSTEM FOR SAID INJECTION NOZZLE; AND