CS204971B2 - Process for manufacturing carbonaceous pellets - Google Patents

Abstract

A novel composite briquette useful in producing iron is made by briquetting a reactive coal calcinate made as described in Work et al. U.S. Pat. Nos. 3,140,241 and 3,140,242, and iron oxide, with a bituminous binder, using proportions to insure at least 50 percent carbon plus hydrogen by weight, then curing the briquettes in the presence of a gas containing at least 5 percent of oxygen at briquette temperature of 450 DEG to 575 DEG F, and then further heating the cured briquettes at 1600 DEG to 1800 DEG F, whereby at least 90 percent of the iron is reduced. The briquette is distinguished by consisting of iron particles embedded and evenly distributed through a uniform solid carbonaceous structure.

Description

The invention relates to a method of producing carbonaceous ferruginous pellets that produces a reactive calcinate sequential catalysed particulate charcoal in the presence of oxygen at a temperature from 121 ° C to 230 ^{Э С} for nekoksované coal or o * d 260 ° C to 426 ° C for coking uihlí, they release a substantial portion dehtotvorných vapor heated intermittently to a temperature between 280 ^and C to 640 ° C for nelkoksované coal or from 426 ° C to 640 ° C for coking coal, at least one fluidized bed to substantially remove all dehtotvorných vapor The coal which has been de-tared is heated to a temperature of from 760 ° C to 982 ° C to reduce the volatile matter content below 5% by weight, while maintaining at least 1% by weight of hydrogen in the reactive calcinate, thus produced highly reactive the calcinate is mixed and pelletized with 12-15% by weight of a bituminous binder and the pellets so produced are fired at temperatures from 232 C to 299 ° C for 80 to 180 minutes in a gas containing 5 to 21% by weight oxygen, the pellets are further heated in a reducing atmosphere to a temperature between 760 ° C to 982 ° C for 10 to 180 minutes for coke pellets, whereupon the pellets are cooled.

Many people in the iron technology industry have been dealing with the problem of direct iron production or possibly increasing the performance of the iron. 2 furnaces while reducing production costs. One such method is the formation of pellets of iron oxide together with the carbonaceous material during subsequent heating so that iron oxide is reduced by the carbonaceous material to iron. Generally, high temperatures are used in the reduction, for example 1260 ° C to 1427 ° C. This process yields high iron pellets, but the savings are insignificant or none compared to conventional iron blast furnace processes.

There has also been a proposal to pellet a material comprised of iron oxide and carbonaceous material for a blast furnace charge to obtain iron from the blast furnace flame dusts. Such processes allow better linkages between iron oxide and carbon and thus facilitate the operation of the blast furnace, but the cost of pelletization is higher than the savings in blast furnace operation, so that such processes have not been introduced to a significant extent in manufacturing practice.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method which overcomes the above-mentioned disadvantages of the prior art and significantly reduces the cost of operating a blast furnace.

The aforementioned drawbacks are overcome by the process for producing the carbonaceous iron-bearing pellets according to the invention, which is based on the fact that it is a mixture. The bituminous binder and reactive calcine are added before pelletizing 40 to 50 wt% of the iron-bearing particles, which reduce to at least 90 wt% during coking of the pellets. metal · iron.

The pellets obtained are suitable for processing either in a cupola furnace or in a blast furnace for iron; contain excess carbon to form part. The heat required to reach the temperature at which iron is melted in the cupola furnace is suitable for blast furnace processing, where it significantly reduces production costs.

The carbonaceous iron pellets produced by the process of the present invention differ from iron containing pellets produced by prior techniques in that they consist of finely dispersed iron particles deposited and uniformly distributed in a carbon structure that is identical in appearance and reactivity to oxygen and wherein the -calcinate-derived carbonaceous solid component cannot be distinguished from the binder-derived carbonaceous component; both carbonaceous components reacted so that they are not recognizable under the microscope and react equally to oxygen.

The present invention is based on an extremely high level. of the reactivity of coal calcinate according to the patent Sp. st. am. 3 140 241 and 3 140 342, which are equivalent to MS. No. 155,126. The calcinate is so reactive that it reduces the iron oxide to iron powder at a temperature in the range of 871 ° C to 982 ° C below the agglomeration temperature of the produced iron, so that the oxide reduction gives iron that has the same relationship to the pellet structure as the original iron oxide powder. The process results in pellets that. they are rigid and can be mechanically manipulated. In addition, the chemical bond between the binder and the kaiclate. which . contributes to the peculiar character of the pellets made from it · is not seriously disturbed, · so · multi-component pellets, as well as pellets without iron, are fired without reflection and are thus usable for processing in cupola furnaces and blast furnaces where they have a significant effect on their performance.

The calcine used in the manufacture of multi-component pellets is obtained by grinding coal, preferably of a lower order than anthracite; the fineness of grinding must correspond to the conditions for fluidization. Coal can be pre-dried or catalysed when heated in the presence of gas either in the fluidized state or in the transport phase · in the presence of oxygen, which may come from coal or gas, to a temperature of at least 126 ° C, releasing substantial a portion of the tar vapor for a period of several seconds during the transport, which lasts 10 to 30 minutes in the fluidized bed to produce particles that are not fusible in the next phase. In the carbonization phase, the catalyzed coal particles are heated in one or more fluid chambers to the temperature at which tar is formed, depending on the type of coal, to 260 ° C to 482 ° C, and for a sufficient time to substantially remove all of the coal. tar-forming fumes. Low temperature treated coal, free from volatile condensable matter, containing. however, the noncondensable volatiles are calcinated at a higher temperature to reduce them. content of volatile. of the substances to a sufficiently low level so that the calcinate can be pelleted without causing the formation of a gas which would disrupt it. pellets, i.e. below 5 wt.% of volatiles, preferably below 3 wt. However, the time a shall be selected. a temperature to form coal having an appropriate characteristic that will react with the binder to form pellets; in order to obtain such reactivity, the resulting calcinate must contain at least 1 wt% hydrogen. This result can be achieved by calcination at a temperature of 760 ° C to 871 ° C after. for 10 to 30 minutes. The highly reactive calcine produced in this way is then cooled with a non-reactive gas before being exposed to air.

In shaping the coke, this calcinate is mixed with a bituminous binder, preferably tar formed by venting tar distilled from coal at the carbonization stage using sufficient binder to properly coat the particles.

The mixture was. forming into pellets which are exposed to heat in the presence of an oxygen-containing gas in a proportion of at least 5 to 21% by weight; in general, the gas is supplied. at a temperature of 204 ° C to induce an exothermic reaction in the pellets, possibly resulting in the binder reacting with the calcine and raising the temperature of the pellets to 288 ° C. When calcined at about 760 degrees Celsius to 871 degrees Celsius, which releases volatile substances, pellets are formed, and the material derived from the binder is not discernible from the material formed from the calcined particles.

A substantial portion of the powder containing. the iron can be introduced into the pellet mixture without it. to decrease the chemical bond between calcine and binder when the treated pellets are sintered at temperatures from 871 ° C to 982 ° C. The hydrogen-carbon component of the pellet then. will be . .reduce iron-bearing .powder. for metal iron. Since the temperature of the iron is well below the melting point, the iron does not melt. and does not even clink, so there is no pellet disruption. The result is a product that remains resistant to abrasion. It can be used to produce iron in a cupola furnace where the combustion of the hydrogen carbonaceous material generates some of the heat needed to melt the iron, or it can be charged into a blast furnace to add iron to the existing product, releasing its hydrogen carbonaceous component as a heat source and iron reducing agent. to the furnace.

The crude pellets after manufacture contain at least 50. % by weight, preferably at least 60% by weight, of a hydrogen carbonate material of the total weight, of which a binder content of 12-25% by weight; calcined 88-75% by weight; the remainder being an iron-containing OD. The material is iron and iron. may be iron ore, that. Yippee. hematite, magnetite or. another. .oxide,

S optionally another iron-containing material. It can be blast furnace dust, which is a mixture of iron oxide, carbonaceous material and ash, it can be Scales made up mostly of iron oxide, it can even be shredded steel scrap that is always oxidized to such an extent that it cannot be remelted without difficulty in the cupola furnace, or it can be any finely divided iron source as the base dust of the oxygen furnace. The iron oxide source is much more massive in volume than the calcined binder, so that the volume ratio of the calcined binder and the iron carrier is always much higher than the weight ratio. However, at the highest content of iron-containing material, 40 to 50% by weight, it is desirable to be within the upper limit of the ratio between binder and calcine in the mixture of raw pellets. The amount of binder in the composition will also depend on the desired resistance.

The crude pellets are treated by exposure to a gas containing 5 to 21 weight percent oxygen, preferably above 15 weight percent. The gas which flows around the pellets are heated to about 204 C ^Q (190 ° C to 232 ° C); the pellets produce an exothermic reaction that raises their internal temperature to 232 degrees Celsius to 299 ° C. In a curing oven, the process of fusing the calcine and binder into a single mass enclosing the iron-containing material is completed in a curing oven in 80-180 minutes.

The treated pellets are then calcined for 10 to 180 minutes, preferably 10 to 30 minutes at a temperature of 871 to 982 ° C, i.e. about 37.8 to 93 ° C higher than that used in coking. The environment used must be free of carbon dioxide, which reacts rapidly with the raw pellets, and contain as little water vapor as possible; it is desirable to use a neutral propane flame.

In order to maintain the temperature in the range of 871 ° C to 982 ° C, the coke oven gas may be supplemented partially or completely with gas from the coke oven chamber which has been cooled and cleared of tar and solids coming from the coke oven chamber. The hot pellets are cooled by passing a portion of the same purified cooling gas through a bed of hot pellets. On microscopic observation, the pellets consist of a monolithic carbonaceous material in which the non-molten iron particles are dispersed in a form that is the same as the original material that was embedded in the original raw pellets. There are no boundary lines between the original calcine and the original binder. The iron particles are embedded in this parent material. Upon oxygenation, the carbonaceous material is burned evenly as if it were a one-component substance.

The iron content of the iron-bearing substance is determined by a conventional method which makes it possible to determine the total iron content, the proportion of iron which is free, in metallic form, or zero volatility, and iron which is divalent or trivalent in the compound. The same method makes it possible to determine free or metallic iron in the same substance. Prior to mixing, heating and coking together with the production of reactive coke, this total iron content of the iron-bearing material may be up to 85% by weight, as is the case with shredded car bodies or zero in the case of untreated ores. In the reduced product, the amount of free or metallic iron in relation to the total iron content is equal to the degree or percentage of reduction. This ratio is always greater than 90% in the pellets produced by the process according to the invention.

The quality of the resulting pellets is measured in practice by two specific characteristics. The first measure is the resistance to crushing, or 'crushability', which is defined by the force required to crush or collapse the sample form, the force being applied between two plates of a hydraulic or mechanical device that are designed to exert force in parallel. In the case of pellets of general shape, this figure shall be expressed as total force and this is specific to the dimensions and shape of the pellets tested. In the case of regular cylinders with a cross-section of 6.5 cm ² between parallel bases, the force required to crush is expressed in a unit of force to 6.5 cm ² .

The second measure is the tendency to produce perceived dust. In this test, four pellets are sealed in a 0.480 dm ³ or 0.969 dm ³ low glass jar with a screw cap and shake the glass. A shaking device, for example a conventional shaking piston machine, is used. This device was set to the highest amplitude during the test. In this test, dry fine particles that are passed through a 325 mesh sieve at 25.4 mm are considered dust. Once the shaking time is over, the glass is removed from the test fixture and opened. Dust that rises classifies the substance as "dusty", "slightly dusty" or "non-irritating to the mucous membranes of the nose and throat". This dust characteristic is also measured in a known manner.

The quality of these reactive molded specimens, which were made of reactive calcine, bituminous binder and iron-containing substances, as measured by these tests, showed that they were 1324 N more resistant in the crushing test and had a dustiness of one third compared to control samples which have been produced without the addition of iron-containing substances.

The invention is further illustrated by the following examples.

Example I

160 g of iron oxide ЕегОз was mixed with 160 g of calcine made from low-carbon coal with a high oxygen content and with 40 g of binder made by venting the tar to calculate a softening point of 66 ° C and parts of the material compressed into an average of 2 8 cm on a laboratory press at a pressure of 135 MPa to form shaped cylinders with a diameter of 2.8 cm and a height of 1.9 cm. These samples were heated in oven 3 by circulating air at 232 ° C for 120 minutes. The treated rollers were fired in a muffle furnace in a non-oxidizing environment of volatile coal and nitrogen at 954 ° C for 30 minutes. After cooling, these rollers did not leave any traces of contact and were essentially dust-free after shaking. Analysis of this material showed the conversion of 92% by weight of oxide to free iron.

They did

A mixture of 20 grams of cut scrap from the car scrap was added to a mixture of raw pellets consisting of 87 grams of bituminous coal calcinate and 13 grams of a binder made from the same source by venting to a softening point of 66 ° C. Scrap from body was strongly oxidized and had an average length of 1.25 cm. This mixture was formed into rollers having a diameter of 2.8 centimeters and a height of 1.9 cm. In the molding process, the cut iron was pulverized and moistened. A sample of the rollers was dissolved in toluene, the calcine and binder were washed. The residue was slightly separated by a strong magnet and analyzed for free and bound or total iron by the methods described above. The rest of the rollers were heated in the air at 232 ° C for 120 minutes. These heated samples were further heated to 927 ° C. for 30 minutes in an environment consisting of nitrogen and volatile coal. Eight such fired rollers were crushed as above. The average crushing pressure was 29.2 MPa. Analyzes for iron before and after volatile leakage showed the following relationships:

Raw rollers before burning

Loose iron

Total iron

Conversion - ratio of free iron to total weight%

% wt.

40%

Fired rollers 95.0 wt. 99.0 wt.

95.9%

The oxidized car scrap used in this case is a material that is very difficult to utilize by known techniques; the method of the present invention represents a very economical way of utilizing this material, which is otherwise primarily a waste material.

Example III

A mixture of 15.3 kg of calcine produced from bituminous coal and 2.7 kg of oxidized bonding tar produced with this calcinate and 4.5 kg of mill scale, crushed for passing through a 0.3 cm diameter orifice, was obtained in a wheel mill and homogenizer at a pellet press with a cylinder diameter of 25 cm. The crude pellets were compressed with a total force of 441,330 N. These pellets were heated in the open air in a 30 cm wide basket oven at a gas temperature of 232 ° C for 120 minutes. They were fired in a vertical shaft furnace with an inner diameter of 22.5 cm and a height of 270 cm at 889 ° C using combustion gas with nitrogen in the absence of oxygen. The heated pellets were held for 30 minutes by passing the furnace at 899 ° C.

The analyzes of these samples after firing are as follows:

with added scales Control

Crushing force 4589.5 N 2647.8 N total power total power Dustiness index 3.0 wt. 7.9 wt. Binder content 13.1 wt. 13.1 wt. Addition scales 20 wt. 0.0 wt. Loose iron *) metal, in the form of an element, etc. 92 wt. - Total iron (in compounds) 99% by weight; - Conversion Rate - Free iron to total 93% Pellet size 3.3X 1X2.2 cm 3.3 x 2.5 x 2.2 cm

*) The pellets were pulverized and the iron was separated by a strong magnet. The magnetic material was analyzed by the methods described above for "free iron" and "total iron",

Claims (1)

OBJECT OF THE INVENTION A process for the production of carbonaceous iron pellets, wherein reactive calcinate is prepared by sequentially catalysing coal particles in the presence of oxygen at a temperature of 121 ° C to 260 ° C for non-coking coal or 260 ° C to 426 ° C for coking coal releasing substantial part of the tar-forming vapors, heated suddenly to a temperature of from 260 ° C to 640 ° C for non-coking coal or from 426 ° C to 640 ° C for coking coal, in at least one fluidized bed to remove substantially all tar-forming vapors, de-tared, heated to a temperature of 760 ° C to 982 ^d C to reduce the volatile matter content below 5% by weight, while retaining at least 1% by weight, of the hydrogen in the reactive calcine, the highly reactive calcine thus produced is mixed and pelletized up to 15% by weight of the bituminous binder and the pellets thus produced are fired at temperatures from 232 ° C to 299 ° C for 80 to 180 minutes in a gas containing 5 to 21 wt. oxygen, the pellets are further heated in a reducing atmosphere to a temperature between 760 degrees Celsius and 982 ° C for 10 to 18Ю minutes to coke the pellets, after which they are cooled, characterized in that the mixture of bituminous binder and reactive calcine is added before pelletizing. up to 50% by weight of iron-bearing particles which are reduced to at least 90% by weight of iron metal during coking of the pellets.