US3704088A - Method of restricting oxidation of sponge iron - Google Patents

Abstract

A SYSTEM FOR REDUCING THE OXIDATION OF AGGLORMERATED SPONGE IRON DURING STORAGE OR TRANSIT WHEREIN THE MASS OF IRON IS STORED IN AN ENCLOSURE HAVING A GAS-PERMEABLE BOTTOM AND AIR, NITROGEN-ENRICHED AIR OR NITROGEN TREATED TO REMOVE MOISTURE AND ACIDIC CONSTITUENTS, IS PASSED THROUGH THE MASS AT A PREDETERMINED RATE.

D R A W I N G

Description

METHOD OF RESTRICTING OXIDATION OF SPONGE IRON Filed May 22, 1970 Nov. 28, 1972 H. NAGEL ETAL 2 Sheets-Sheet 1 Y L W E m m H amu wwm m m mtm e mmm mw $3M n m METHOD OF RESTRICTING OXIDATION OF SPONGE IRON Filed May 22, 1970 Nov. 28, 1972 H. NAGEL E AL 2 Sheets-Sheet 2 N GI 28.: g g Q s Q s a s q 5 ME? 7 Horst NAGE L Wilhelm THUWi Horst: GARBE William Henry BAILEY Egon GOEDEKE Rolf DADAZYNSKI INVENTORS.

United States Patent O 3,704,088 METHOD OF RESTRICTING OXIDATION OF SPONGE IRON Horst Nagel, Bergen Enkheim, and Wilhelm Thumm and Horst Garbe, Frankfurt, Germany, William H. Dailey, Cleveland, Ohio, and Egon Goedeke, Frankfurt, and Rolf Dadazynski, Rod an der Weil, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt, Germany, and The Steel Company of Canada Limited, Hamilton, Ontario, Canada Filed May 22, 1970, Ser. No. 39,630 Claims priority, application Germany, May 29, 1969, P 19 27 300.8 Int. Cl. C23f 15/00 US. Cl. 21--2.5 4 Claims ABSTRACT OF THE DISCLOSURE A system for reducing the oxidation of agglomerated sponge iron during storage or transit wherein the mass of iron is stored in an enclosure having a gas-permeable bottom and air, nitrogen-enriched air or nitrogen, treated to remove moisture and acidic constituents, is passed through the mass at a predetermined rate.

FIELD OF THE INVENTION The present invention relates, in general, to a system for reducing the oxidation of iron and more particularly to a system for reducing the oxidation of agglomerated sponge iron during storage or transportation.

BACKGROUND OF THE INVENTION It is known that sponge iron, when piled in a mass, such as it is during storage or transit, can oxidize, particularly in the presence of moisture, causing a rise in temperature of the mass to 80-100 C. or even to the point of ignition, endangering the storage or transit means, e.g. a ships hull.

Heretofore, it has been the practice to prevent oxidation of sponge iron by coating it with anti-corrosive agents, such as oil, paraflin or plastics.

However, these methods do not afford adequate protection, are expensive and leave impurities on the iron.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention to provide a system for reducing or restricting the oxidation of agglomerated sponge iron during storage or transit.

Another object of the invention is to provide a method of limiting oxidation of sponge iron in lump or agglomerated form which is relatively inexpensive and free from the indicated disadvantages.

Still another object of the invention is to provide a system for the purpose described that does not deposit impurities on the iron.

SUMMARY OF THE INVENTION The above mentioned objects, and others which will become apparent hereinafter, are achieved by piling the agglomerated or lump sponge iron mass in an enclosure having a series of gas nozzles formed in the bottom. A gas, such as air, nitrogen, enriched air or nitrogen, is driven through the nozzles and passes through the sponge iron mass, which is gas-permeable or porous.

The rate at which the gas is passed through the mass determines the rise in temperature of the mass, so that a rate can be selected to give virtually no rise in temperature or a rise only to the highest permissible limit.

It has been found that the rate at which the gas should be passed through the mass is about 5-160 cubic meters per square meter-hour, depending on the height of the mass.

Although it has been found that the oxidation rate and resultant temperature rise are primarily dependent on the rate of gas flow, the moisture content of the gas is a major contributing factor in the oxidation of the iron mass. To this end, a dehumidifier is provided to remove moisture constituents present in the gas, prior to passage through the mass. The dehumidifier may drop the temperature of the gas to about 20 C., a heater is provided to bring the gas to about 30 C., the gas being then driven into the enclosure by a blower, at a water-vapor partial pressure as low as possible.

Under certain circumstances, it is advantageous to collect and recycle the gas, in which case, in addition to the dehumidifier, heater and blower used to treat the gas, a lime filter is used to remove any acid constituents which may have been picked by the gas passing through the iron mass. When atmospheric air is employed, even without recirculation, acid constituents such as CO S0 and S0 are removed by this filter.

Because such acid constituents have a strong oxidizing action, this measure further reduces the oxidation of the mass.

The invention is based upon our surprising discovery that in spite of the fact that the oxidation-limiting gas may contain oxygen and eventually bring about more contact of iron surface with oxygen than a static system in which an ambient atmosphere lies in contact with sponge iron, the circulation of the gas through the mass materially limits oxidation. We believe that the degree of oxidation is a function of temperature and, whereas a temperature buildup occurs in the static case, the displacement of the gas through the mass according to the invention prevents such buildup.

It has been found further that any steps which reduce the water vapor pressure in the gas supplied to the enclosed pile bring about a greater reduction in the tendency toward oxidation. Such reduction of the H 0 vapor pressure can be effected by dehumidification using a cooler to bring the temperature of the gas below the dewpoint and condense water therefrom, absorption to remove water without changing the gas temperaure, or heating to reduce the relative humidity. Since a cooler is used to lower the temperature of the gas below the dewpoint, it is apparent that the gas circulated through the iron mass is at a temperature above the dewpoint (at most 45 C. as seen in curves b and d in FIG. 2), and that the water-vapor partial pressure is below that of the dewpoint at the gas temperature used.

Best results are, of course, obtained with minimum oxygen content in the gas stream so that nitrogen or nitrogen-enriched air is used preferably. After the initial passage of air through the mass, however, the oxygen concentration is slightly reduced, thereby enriching it with nitrogen. It is preferred, therefore, to recirculate this gas, abstracting the heat picked up in its passage through the mass.

The rate at which the gas is supplied depends upon DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the invention will become more readily apparent from 3 the following description and specific examples, reference being made to the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of the apparatus according to the invention; and

FIG. 2 is a graph illustrating results of the process according to the invention.

SPECIFIC DESCRIPTION The enclosure 2 shown in FIG. 1 has cylindrical walls 2' and a perforated conical bottom end 2" supporting the sponge-iron mass. A removable lid 3 is provided at the top of enclosure 2 for introducing agglomerated sponge iron therein. The sponge iron forms a gas-permeable mass 1, which can be removed by means of a door 4 provided at the apex of the conical bottom 2".

A series of gas nozzles 5 are provided in an array along the inside walls of the conical bottom 2". The nozzles 5, which introduce a gas such as air, nitrogen-enriched air or nitrogen, into the enclosure 2, are supplied by conduits 5' equipped with regulating valves 5".

The conduits 5' are supplied with warm gas at 30 C. from a heater 6 via a single conduit 6, the heater 6 being supplied by a blower 7.

The blower 7 and heater 6 form part of a recycling system which starts with the introduction of the aforementioned gas into the enclosure 2 via the nozzles 5. The gas is passed through the mass 1 at a rate of 5 to 160 cubic meters per square meter-hour, depending on the height of the piled mass 1. By way of example, if the height of the piled mass is 1 to 3 meters, the required rate is 5 to 40 cubic meters per square meter-hour, preferably 8 to 25 cubic meters per square meter-hour. If the mass height is 3 to 8 meters, the requirement is 10 to 80 or preferably to 50 cubic meters per square meterhour. If the height of the mass exceeds 8 meters, the requirement is 20 to 160 or preferably 40 to 100 cubic meters per square meter-hour.

After the gas passes through the mass 1, it is drawn off at outlet 8 into a dehumidifier 9, where the cooling coil 9 condenses the moisture that the gas picked up passing through mass 1, the liquid condensate being drained through an outlet valve 9" provided at the bottom of dehumidifier 9.

After passing through the dehumidifier 9, the gas, which has been cooled to 20 C., is drawn through conduit 10' into a lime filter 10, where the acid constituents picked up from the mass 1 are removed.

Upon leaving the filter 10, the gas is drawn into the blower 7, completing the cycle.

In FIG. 2, a graph representing some test results is shown.

The time in hours is plotted along the abscissa and the temperature, in the upper region of the iron mass, in degrees centigrade along the ordinate. Percentages recited relate to water content of the gas.

The curve a shows the rise in temperature of the mass when 5% water is present in the still atmosphere and no gas is passed through.

Curve b shows the temperature rise of the mass when 5% water is present and air is passed through at a rate of cubic meters per square meter-hour.

Curve 0 shows the temperature rise of the mass with a 0.19% water content and no air circulation.

The results shown in FIG. 2 were obtained with a vessel of 0.5 meter diameter and 3 meters height using 830 kg. of sponge iron (fresh) for each set of tests.

We claim:

1. A method of preventing oxidation of sponge iron, comprising the steps of piling and enclosing agglomerated sponge iron to form a gas-permeable mass; passing a gas selected from the group consisting of air and nitrogenenriched air through said mass at a rate of 5 to 160 standard cubic meters per square meter-hour, and suflicient to prevent the temperature in said mass from rising above substantially 45C.; and dehumidifying said gas prior to passing it through said mass to maintain the water vapor partial pressure below that of the dewpoint at contact with said mass.

2. A method of preventing oxidation of sponge iron as defined in claim 1, wherein the gas is dehumidified by cooling followed by the step of warming said gas prior to passing it through said mass.

3. A method of preventing oxidation of sponge iron as defined in claim 1, further comprising the steps of:

collecting said gas after passing it through said mass;

recycling said collected gas through said mass, said gas picking up acid constituents upon traversal of said mass; and

deacidifying said gas prior to passing it through said mass.

4. A method of preventing oxidation of sponge iron as defined in claim 1 wherein said gas is passed through said mass at a rate with respect to the height of the mass in accordance with the following table:

Height: Gas-flow rate 1 to 3 meters 5 to 40 m. /m. -hr. (STP) 3 to 8 meters 10 to m. /m. -hr. (STP) 8 meters 20 to m. /m. -hr. (STP) References Cited UNITED STATES PATENTS 2,156,357 5/1939 Simson 2l2.5 UX 2,160,831 6/1939 Colby et a1. 212.5 UX 2,616,780 11/1952 Atkinson et a1. 212.5 3,111,371 11/1963 Bull 212.5 3,188,166 6/1965 Dietz et al. 212.5 3,551,215 12/1970 Claiborne et a1. 75-26 UX 3,562,780 2/1971 Risenberg 75-26 FOREIGN PATENTS 649,735 1/1951 Great Britain 21--2.5

BARRY S. RICHMAN, Primary Examiner US. Cl. X.R. 750.5 R

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