US3147106A

US3147106A - Use of lined passivation chamber in an iron powder passivating process

Info

Publication number: US3147106A
Application number: US101222A
Authority: US
Inventors: Clarence A Johnson; Volk William
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1961-04-06
Filing date: 1961-04-06
Publication date: 1964-09-01
Anticipated expiration: 1981-09-01

Description

p 1, 1964 c. A. JOHNSON ETAL 3,147,106

USE OF LINED PASSIVATION CHAMBER IN AN IRON POWDER PASSIVATING PROCESS Filed April 6, 1961 0 MM &

IN VEN TOR S Clarence A. Johnson Wf/l/am Ko/lr United States Patent 3,147,106 USE OF LINED PASSIVATION CHAMBER IN AN IRON POWDER PASSIVATING PROCESS Clarence A. Johnson and William Volk, Princeton, NJ.,

assignors to Hydrocarbon Research, Inc., New York,

N.Y., a corporation of New Jersey Filed Apr. 6, 1961, Ser. No. 101,222 Claims. (Cl. 75-.5)

This invention relates particularly to a process for the reduction of pyrophoricity of iron powder, and the apparatus in which such iron powders may be passivated.

In the Keith et al. Patent 2,900,246, a process is described for the reduction of iron oxide by the passage of hydrogen gas through a bed of the iron oxide at a rate to cause mobility or fluidization of the bed. This is normally carried out at about 750-950 F. and at a pressure of 350600 p.s.i.g.

It has been found, however, that due to the purity and the fineness of the iron powder, which is normally such that all of it will go through a 20 mesh screen, and at least 20% of which will go through 325 mesh screen, the powder is pyrophoric. In other words, on exposure to air at atmospheric temperatures, there is a tendency of the powder to reoxidize and such reoxidation generates such heat that the mass may be converted into a combustible mixture unless it is adequately cooled, passivated, or retained in a non-oxidizing atmosphere.

It has been suggested that if the iron powder is heated to a temperature in the order of 1200-1600 F. in the presence of an inert gas such as nitrogen for a period of time in the order of a half hour, the surface is so changed as to render the iron non-pyrophoric and suitable for permanent storage, or use in powder metallurgy, or for other purposes.

It has been found, however, that at the temperature necessary to render the iron powder non-pyrophoric there is a tendency for a substantial amount of the powder to adhere to the passivation chamber, and this is a loss not only of material but in the cost of removing the agglomerated particles from the passivation chamber;

The object of the invention is to provide an improved form of apparatus and improved process steps for the passivation of finely divided normally pyrophoric iron powder whereby such material is rendered nonpyrophoric.

Further objects and advantages of the invention will appear from the following description of a preferred form of embodiment thereof, and as more particularly shown on the attached drawing which is illustrative of the invention, and in which FIGURE 1 is a schematic view of an iron ore reduction apparatus and passivation chamber.

FIGURE 2 is a cross section taken along the line 2-2 of FIGURE 1.

FIGURE 3 is a substantially central vertical section, with parts in elevation, of a modified form of passivation chamber.

In accordance with the Keith et a1. patent hereinabove set forth, iron ore may be reduced to a high purity iron powder by direct reduction, preferably in the presence of hydrogen. The ore in hopper is transferred by line 12 under the influence of a suitable gas such as hydrogen to the reducing reactor 14 which may have a plurality of

separate ore beds

14a, 14b, and 140. These beds are suitably interconnected by downcomers 16 and control valves for the controlled downflow of the ore. A reducing gas such as hydrogen is introduced to the bottom of the reactor through line 18 as described in the Stotler Patent 2,805,144 under such conditions of temperature and velocity as to accomplish a fluidized contact with the ore. The oxygen removed from the ore 3,147,106 Patented Sept. '1, 1964 goes upward through the respective beds and thence overhead through line 20. The reduced ore is ultimately removed from reactor 14 through line 22.

The iron powder is of the order of size in which all passes through a 20 mesh Tyler screen with at least 50% passing through a 100 mesh screen and usually at least 20% will pass through a 325 mesh screen. The iron oxide is in the order of -98% reduced (oxygen removed) and is highly pyrophoric. In accordance with the invention, this pyrophoric iron powder is discharged into a passivation chamber generally indicated at 24 which may have an inert gas inlet at 26 and an outlet at 28. Nitrogen gas is the preferable inert gas. Nitrogen gas or other inert gas is passed through the passivator 24 to exclude any air or other oxidizing gas.

The passivation chamber 24 is suitably heated as for example by gas flames schematically indicated at 30 with the temperature controlled to the desired extent. The gas inlet is at 31 and the products of combustion discharge at 32. In a particular operation the temperature was controlled within the range of l2001600 F. and preferably as near 1400 F. as the controls would permit.

The passivation chamber 24 in FIGURE 1 is adapted to be inclined with respect to the horizontal plane and rotated as a kiln through motor 33. The powder tends to flow to the lower portion of the passivator from which it is continually removed as at 34. It is then cooled at 36 before it enters storage hopper 38. The cycle of passage of the are through the passivation chamber is approximately thirty minutes.

Passivation is usually considered complete when the powder can be stored in moist air up to about 500 F., or it oxidizes at a rate of less than 0.0007 gram of oxygen per minute/ grams in boiling water.

The liner or wall 40 for the passivation chamber as shown in FIGURE 2 must be appropriate for the particular iron powder as magnetite powder reacts somewhat diflerently from a powder from ore which was primarily hematite. In some cases reduced mill scale operated even differently.

The following table indicates the temperature conditions within the passivation chamber 24 with respect to the different types of ore and the type of lining and the effectiveness of such liners with respect to adhesion:

Hematite. Magnetite Mill Soale Hematite I do l 00 Graphite N0 adhesion.

Cerium Oxide (coat- Magnetite... 1,6001,700 F. Mill Sca1e 1,600l,700 F Hematite. 2 000 F M agnetite- 1\/Iill Soale 1 60 o. Adhered. No adhesion.

Alundum Stainless Steel Pyroceram in el Titanium Cast Iron Platinum Tantalum posed. No adhesion. Adhered (3 out of 4 samples). Zirconium decomposed. No adhesion. Adhesion. No adhesion. Adhesion.

Carborundnm Zirconium 1,6001,700 1,s0o-1,700 Magnetite 1,600 F Mill Scale 1,e00 F Zirconia (coating) Tungsten It will be apparent that graphite is entirely safe as a liner regardless of the ore treated.

Cerium oxide shows adhesion at 1800 F. but will be usually satisfactory as normal passivation temperatures need not go so high.

Alundum which is a pure aluminum oxide (A1 is a border-line material and must be restricted to ores that can be treated below 1600 P.

All other materials show some adhesion or material disintegration at 1600 F. with some of the reduced ores.

Graphite is available in building blocks and other structural forms, and can readily be fabricated into lining material for passivation equipment.

With a suitable liner such as graphite we avoid the need for expensive stainless steel vessels for a typical carbon steel vessel suitably lined will have an unusually long life.

The linings may be applied in various manners as in the nature of separate brick or sheets or in some cases as for example zirconia, alundum or cerium oxide may be sprayed on the surface.

While the passivation chamber is shown in the nature of a kiln, it has been found that passivation may be accomplished in a vertical chamber. This is more clearly shown in FIGURE 3 in which the passivation chamber 42 is adapted to receive iron powder through th inlet 44 from which it will drop down onto the screen 46. An inert gas entering at the bottom through line 48 will tend to fiuidize the powder, such gas being discharged at 50 Heat for the passivation is by means of hot inert gases such as flue gases that enter serpentine heat exchanger 52 at 54 and discharge at 56. This tube may be of graphite or graphite coated and thus prevent any sticking or agglomeration of the iron powder and in addition it will assure a uniform fluidization of the powder in the necessary large scale passivation chamber, The passivation chamber may also be lined with a suitable lining as hereinbefore described.

While we have shown and described preferred forms of embodiment of our invention, we are aware that modifications may be made thereto which are within the scope and spirit thereof as set forth in the claims appended hereinafter.

We claim:

1. The method of passivation of a finely divided pyrophoric iron powder reduced from metallic oxides from the group consisting of mill scale, hematite and magnetite which comprises the steps of flowing the reduced material through a reaction zone, maintaining said zone at a temperature of at least 1200 F. and not to exceed about 2000 F., flowing said reduced material through the reaction zone in contact only with a surface material from the group consisting of graphite, cerium oxide, Alundum and Carborundum, and withdrawing said finely divided reduced material from said zone as a powder after approximately thirty (30) minutes when its response to oxidation is such that it can be safely handled and stored in moist air at temperatures in the range of 400 F. to 500 F.

2. The method of passivation as claimed in claim 1 wherein the reduced metallic oxide is from the group consisting of divided magnetite and finely divided mill scale and the temperature of passivation in the reaction chamber is in the order of 1600 F. to 1700 F., and the surface material is from the group consisting of graphite, cerium oxide, Carborundum and Alundum.

3. A passivation chamber for the passivation of a reduced ore from the group consisting of hematite, magnetite, and mill scale in a finely divided and normally pyrophoric condition, said chamber having a reduced ore inlet, a reduced ore outlet, and a wall between said inlet and said outlet, means to heat said ore to a temperature in the range of 1200 F. to 2000 F. to render said reduced ore non-pyrophoric, the wall of said chamber being surfaced with a non-agglomerating coating from the group consisting of graphite, cerium oxide, Alundum and Carborundum, said ore heating means including a graphite heat exchange coil within said chamber, and means to pass a heating gas through said coil.

4. A passivation chamber for the passivation of a reduced ore in a finely divided and normally pyrophoric condition, said chamber having a reduced ore inlet, a reduced ore outlet and a wall between said inlet and said outlet, means to heat said wall to a temperature in excess of 1400 F. and below a temperature to fuse said reduced ore to render said reduced ore non-pyrophoric, said wall being provided with a non-agglomerating coating of the class of graphite, cerium oxide, Alundum, and Carborundum.

5. A passivation chamber as claimed in claim 4 inclined with respect to the horizontal plane, and means to rotate said chamber about the axis of said inclination.

References Cited in the file of this patent UNITED STATES PATENTS 1,452,627 Thornhill Apr. 24, 1923 2,603,561 Swann July 15, 1952 2,875,035 Graham et al Feb. 24, 1959

Claims

1. THE METHOD OF PASSIVATION OF A FINELY DIVIDED PYROPHORIC IRON POWDER REDUCED FROM METALLIC OXIDES FROM THE GROUP CONSISTING OF MILL SCALE, HEMATITE AND MAGNETITE WHICH COMPRISES THE STEPS OF FLOWING THE REDUCED MATERIAL THROUGH A REACTION ZONE, MAINTAINING SAID ZONE AT A TEMPERATURE OF AT ELAST 1200*F. AND NOT TO EXCEED ABOUT 2000*F., FLOWING SAID REDUCED MATERIAL THROUGH THE REACTION ZONE IN CONTACT ONLY WITH A SURFACE MATERIAL FROM THE GROUP CONSISTING OF GRAPHITE, CERIUM OXIDE, ALUNDUM AND CARBORUNDUM, AND WITHDRAWING SAID FINELY DIVIDED REDUCED MATERIAL FROM SAID ZONE AS A POWDER AFTER APPROXIMATELY THIRTY (30) MINTUES WHEN ITS RESPONSE TO OXIDATION IS SUCH THAT IT CAN BE SAFELY HANDLED AND STORED IN MOIST AIR AT A TEMPERATURES IN THE RANGE OF 400F. TO 500*F.