CA1081464A

CA1081464A - Method for generating gases for the reduction of oxide ores, particularly iron ores

Info

Publication number: CA1081464A
Application number: CA255,108A
Authority: CA
Inventors: Kurt Tippmer
Original assignee: Carl Still GmbH and Co KG
Current assignee: Carl Still GmbH and Co KG
Priority date: 1975-06-18
Filing date: 1976-06-17
Publication date: 1980-07-15
Also published as: DE2527097A1; AU1500576A; ZA763573B; MX3649E; AU506529B2; JPS51151691A; BR7603894A; IT1063403B; SE7606935L

Abstract

METHOD FOR GENERATING GASES FOR THE REDUCTION
OF OXIDE ORES, PARTICULARLY IRON ORES
ABSTRACT OF THE DISCLOSURE
In the method, the reduction gases are used in excess relative to the ores to be reduced, a part of the waste gas from the reduction process is re-introduced into the process after cooling thereof, liberation of dust therefrom, and scrubbing of C02 therefrom, another part of the waste gas is discharged and its heat of combustion utilized in the reduction process, and an amount of fresh gas, containing C0 and H2, cor-responding to the amount of spent and discharged waste gas is introduced into the gas circulationcircuit. The fresh gas is produced by partial oxidation, of hydrocarbons of all types, with oxygen and steamand/or carbon dioxide,and carbon black, C0 and sulfur compounds are washed out, and steam is condensed, before the fresh gas is added to the gas circulation circuit.
The mixture of fresh gas and circulating gas is heated to from 800-1000°C by the heat of combustion of the discharged part of the waste gas. As an alternative, the fresh gas is produced by partial oxidation of sulfur-free methane, methane-containing gases, or natural gas and is introduced, without cooling, to the gas circulation circuit. Only the recycled gas, after cooling, dust removal and C02 scrubbing, is heated, prior to mixing with the fresh gas, to from 350-550°C, by the heat of combustion of the discharge part of the waste gas.

Description

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FIELD_AND BACKGROUND OF THE INVENTION
This invention relates to a method for generating gases for the reduction of oxide ores, particularly iron ores containing C0 and H2, and in which the reduction gases are used in excess relative to the ores to be reduced with a part of the waste gas, from the reduction process, being re-introduced into the process a~ter having been cooled, freed of dust, and having C2 scrubbed therefrom, another part of the waste gas is discharged from the gas circulation circuit and its heat of combustion used ln in the reduction process, and an amount of fresh gas, containing C0 and H2, corresponding to the amount of spent and discharged waste gas is introduced into the gas circulation circuit. In particular, the present invention is directed to the production of the fresh gas which is used to replace the waste gas portion discharged from the circuit.
It is known to produce this gas portion by reacting natural gas or methane to carbon monoxide (C0) and hydrogen (H2) for example, by Marincek in "Redox-Rundschau" No. 5, of 1966, pp. 280-290. The reaction is effected continuously or periodically in the presence of catalysts by adding steam or carbon dioxide (I:itschke and Keller in "Erdoel and Kohle", for 1973, pp. 132-139~ and supplying the required reaction heat by indirect heating (Bogdandy in "Stahl und Eisen", No. 82 of 1962, pp. 869-883).
These methods depend on the availability of natural gas or methane of adequate quality, and which are not available in all locations. They also depend on the thermal efficiency of the heating systems and, in addition, because of the high temper-atures to be applied and the composition of the reaction gases, special materials of hi~h resistance are required and which are only available in limited quantities.

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There are also kno~n methods for preparing the reducing gas, where coke, coal, or natural gas are reacted with carbon dioxide and steam using electric power, at 1000C (Stahlhed in "Metals" No. 9 of 1957, pp 246-249).
The unpurified generated gas contains components which interfere with the reduction process, for example sulfur compounds (Archiv. f.d. Eisenhuettenwesen, 1960, No. 5 (May) p~. 271-277) as well as dust and carbon black, and no quality of iron sponge, defined with respect to the sulfur and carbon con-tent, can be produced with these methods.
In another known method for the production of reducing gas, natural gas is partially oxidized with steam in periodically heated furnace ~'Metals" 1959, pp. 315-318). However, .he re-ducing gas produced in this manner has an H -C0 ratio of about 4.6, which is unfavorable for the reduction qf ore, and an uneco-nomical degree of oxidation of more than 8%, and it thus requires a costly preparation before it can be used as a reducin~ gas for ores.
All known methods have in common a very high specific heat consumption, which is 3.3 x 10 to 5.8 x 106 kcal on a natural gas basis, related to one ton of pig iron, of which only a relatively small portion is used for the reduction of the ore.
In yet another method known from the literature ("Redox Rundschau" for 1966, pp. 280-290~, reducing gas is ob-tained by partial oxidation of fuel oil, the fresh gas is mixed with waste gases from the reduction process, and the mixture i9 introduced at various points into the reduction shaft or tower.
The fresh gas is introduced into the reduction process without cooling, unscrubbed and not desulfurized, and thus has its entire content of H2, C0, sulfur compounds, and carbon black. With this method, it is also not possible to obtain a constant quality of iron spony,e.

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SUMMARY OF THE INVENTION
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The objective of the invention is to provide new methods for the production of reducing gases for ores, which are more economical than presently known methods and which assure the parameters and properties required by the reduction process for the production of iron sponge of constant qualitl, such as degree of oxidation, entrance temperature into the re-duction process, H2:C ratio, steam:C02 ratio, and absence of sulfur and carbon black, and in which the entire spectrum of carbon-and-hydrogen-containing substances available in the world can be used.
To solve this problem, in accordance with the inven-tion, the spent gas, discharged from the reduction process, ;s replaced by c fresh gas containing C0 and H2, and which is pro-duced, in a known manner, by partial oxidation of hydrocarbons of all types, for example, naphtha, heavy and light oils, as well as hard coal, soft coal and peat, with oxygen and steam and/or C0, and from which carbon black, C02 and sulfur compounds are washed out, and steam is condensed, before it is added to the reducing gas, with the fresh gas being heated together with the reducing gas to 700-1000C by means of the waste gas portion ` discharged from the gas circulation circuit.
; In accordance with the invention, the basis for the ,~roduction of the fresh gas supply is substantially widened and extended to materials of all types containing carbon and hydrogen, with more than one carbon atom in the molecule, of - an aliphatic or aromatic nature, such as naphtha, fuel oil, burning oil, young and old coal, as well as materials in the preli~inary stage of carbonization, such as peat, for e~ample, as well as so-called recycling substances of the chemical industry, for example scrap plastic. The H2:C0 ratio can be ' ' ' .

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adjusted without any additional expense, by providing a conver-sion stage.
The method can also be ~sed for natural gas and methane. In this case, a particularly hi~h degree of utilization of its heat of combustion cal~. be obtained, for the reduction process itself, by using natural gas that is free of H2S, and removal of carbon black, C02 and sulfur compounds, after partial combustion, is eliminated. It is necessary only to heat the circulated gas portion slightly after the C0 has been washed out, for example to 400C. In accordance with the invention, this heating is effected by means of the waste gas portion dis-charged from the process. By mixing with the gas at about 1400C
from the partial combustion, there is obtained a mixed gas of about 900C which can be introduced directlJ ~nto the reduction furnace with a degree of oxidation of 4% to 6%.
The advantage of the method according to the invention i8 that a major part of the heat of con~ustion, namely 55% to 65%, of the material used for the production of the supplementary gas, is used for the production process. This accounts for the great economy of the method.
The degree of oxidation of the reduction product is determined by the degree to which C02 is washed out of the fresh and circulating gas. The degree of oxidation is defined as the quotient of the volume and mole portions, re~pectively, of C02+H20 Co2+H2 ~ ~co+H2 The sensible heat of the gas from the reduction furnace, which must be cool for its further preparation, is pre- -ferably used for the generation of steam.
If methane or natural gas is used, it is also possible to return a part of the gas, discharged from the process, into ~ - . 1.
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the partial combustion, if this seems expedient for the adj~lst-ment of the degree of oxidation of the circulating gas.
An object of the invention is to provide an improved method for generating gases for the reduction of oxide ores, particularly iron ores containing CO and H2.
Another object of the invention is to provide such a method for producing the reducing gases in a more economical manner and in a manner assuring the parameters and properties required for the reduction process for the production of iron sponge of constant quality.
A further object of the invention is to provide a method for the production of the reducing gases by partial oxidation of hydrocarbons of all types with oxygen and steam and/or C02, with carbon black, C02 and sulfur compounds being washed out and steam condensed before the reducing gas is added to the gas circulation system.
Yet another object of the invention is to provide a novel and improved method for producing the re~ucing gas from natural gas and methane.
For an understanding of the principles of the inven-tion, reference is made to th~ following description of typical embodiments thereof as illustr~ted in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
Fig. 1 is a flow diagram of the invention method utilizing fuel oil and coal; and Fig. 2 is a similar flow diagram for the use of natural gas.
DES~RIPTION OF THE PREFERRED EMBODIMENTS
Referring first to Fig. 1, a fresh gas generator 1 is ; charged, on the one hand, with fuel oil or a coal and water suspension through line 2 and, on the other hand, with oxygen ;- , ' , . .
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through line 3. The oxygen is produced by an air separation plant 4, receivin~ air throu~,h an air compressor 5 and a line 6.
Nitrogen issues from air separation plant 4 through a line 7 and oxygen issues through a line 8 and is co~pressed in oxygen compressor 9 connected to line 3. The fresh gas is removed from generator 1 through line 10 and cooled in waste heat boiler 11, to wash out the C02 and H2. Boiler feed water is fed to waste heat boiler 11 through a line 12, and steam is removed there-from through a line 12a. A part of this steam is added, if nec-essary, through a line 13 to the fuel oil or coal-water suspen-sion in line 2.
The cooled fresh gas enters a scrubber 15 through a line 14, from which the scrubbed gases are dischar~ed through line 16 for further use. The scrubbed fresh gas fro~ scrubber 15 is supplied to a gas mixer 18 through a line 17 and, in gas mixer 18, it is mixed with gas from the reduction process supplied through a line 19 to mixer 18. The mixed gas enters a preheater 21 through a line 20, and is heated, together with gas from a line 22 discharged from the reduction process, to 9~0C. The washed gas is discharged through a line 22a.
The reduction gas is supplied to reduction furnace 24 throùgh a line 23, and, in furnace 24, the reduction gas reduces oxide-containing iron ore to iron sponge. The iron ore i8 supplied to reduction furnace 24 through a hopper 25, and sponge iron i8 removed through a dischar~e 26.
The partly spent reducing gas, laden ~ith ore dust, leaves reduction furnace 24 through a line 27 and is delivered to a preliminary dust arrester 28 from which it is dlscharged throu~,h a line 29. The fine separated ore dust can be returned into the process through known devices. Line 29 supplies the reducing gas to a circulating gas cooler 30 in which the . . I
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reducing gas is cooled, for the wet removal of dust and CO2.Boiler feed water is supplied to gas cooler 30 through a line 30a and steam is discharged from the gas cooler through a line 30b.
The cooled gas is delivered by a line 31 to a wet dust separator 32 to which fresh wash water is delivered through a line 33 and dust-laden wash water is discharged through a line 35. A part of the gas in line 35 is discharged from the process through line 22 to reduce and adjust the inert level, and is used -in the reduction process itself for preheating purposes. Anotherpart of the gas in line 35 is supplied to line 36 through a com-pressor 37. The compressed circulating gas from compressor 37 enters C02 scrubber 39 through line 38, and C02 is discharged through a lire 40. The dust-free scrubbed gas is combined, in mixer 18, with the fresh gas current from line 17.
The flow diagram of Fig. 2 is based on the use of natural gas, which is free of sulfur, and the best procedure is shown in the flow diagram. Due to the elimination of the , :
scrubber, it is not necessary to cool the fresh gas before it is mixed with the circulating gas. Since the cooler 11 and the scrubber 15, in the path of the fresh gas current, are eliminated, the fresh gas is fed from the generator la directly through line lOa to the mixer 18a. Since the fresh gas can be furthermore supplied to mixer 18a with a temperature of about 1400C, and the circulatin~ ~as ~s supplied from line l9 with a temperature of about 400 deg. C, a reheatin8 device in the path of line 20a, between mixer 18a and reduction furnace 24, can be omitted. Further, it is not necessary to preheat the mixture of fresh and circulating gas, and only the circulating gas ~` 30 portion, after the carbon dioxide scrubbing, is to be preheated.
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^` 1081~64 The compressed circulating gas flows off through line 38a. A
portion thereoE passes, through line 41, into carbon dioxide scrubber 39a an~, throu~,h line 42, into-preheater 21a and is directed, preheated to about 400 deg. C and through line l9a, into mixer 18a. The heating gas for preheater 21a is taken from the reduction gas circuit, throu~,h line 43. If needed, for adjusting a favorable gas mixture, a portion of the gas from line 43 may also be branched off through line 44 and supplied to reduction gas generator la.
; 10 In the following, the invention is explained by three examples.
Example 1 .~
The charge is natural gas.
Analysis of the natural gas:
~ ~ N2 + ~Y ~r 5.0% by volu~e ; 2 0.1 " "
CH4 93.9 ~ "

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I Calorific value (Ho) water-free: 8,900 Kcal/~m3 l~i "
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1081~'1 Gas balance for 1000 tons of iron sponge in 24 hours:
% by Vol. Fresh Gas Circulating Reducing Discharged _ Gas Gas Gas C0 + H2 90-70 85.20 87.45 66.80 CH + ~+ N 2 10 12;00 8.00 9.50 C2 1.30 2.30 1.90 20.00 CO + H2-amount Nm3/h 31.000 44.000 75.000 `5.000 Heat balance:
Charge 12,300 Nm3/h natural gas 110 x 106 Kcal _ 6 t/h steam of 5 at. 3 x 106 Kcal 113 x 10 Kcal The amount of the discharged ~as is 5000 Nm3/h C0 ~ ~2.
This results in a degree of utilization for Co & H2 of about 84%.
Heat consumptions and losses are caused by:
Produced iron sponge of 800 deg. C 6.7 x 10 Kcal Cooling of circulating gas 13.6 x 10 "
Removal of C02 15.3 x 10 Reduction 71.0 x 10 Waste gas from preheater4.8 x 10 General heat losses 2.6 x 10 113 x 106 The specific heat consumption, related to the upper calorific value of the charging material, is thus 2.7 x 106 Kcal per ton of iron sponge.
Exa~ple 2 The charge is fuel oi~
Analysis of fuel oil: , C 85.10% by weight ,.
~ 11. 30 ' 2 ' N2 - 08 " "
S 3.50 " " .

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Calorific value (Ho) water-free: 10,400 Kcal/kg Gas balance for 1000 tons of iron sponge in 24 hours:
% by volume Fresh Gas Circulating Reducing Discharged _ Gas Gas Gas 2ar ~ 87.30 92.00 69.80 CH4 + ~ + N2 1.00 4.80 3.00 3.20 C2 1.00 7.00 4.30 23.0 H20 0.50 0.90 0.70 4.00 S . 0.01 - 0.01 '0.01 CO + H2 -Heat bala~ce amount Nm~/h 37.000 38.000 75.000 11.000 Charge 12.8 t/h fuel oil of Ho 10,400 Kcallkg = 133 x 106 Kcal/h.
Discharge per hour 11,000 Nm3 C0 + H2.
The degree of utilization for C0 + H2 is about 70%.
Heat consumption and losses:
Produced iron sponge of 800 deg. C 6.7 x 106 Kcal ; Cooling circulating gas 13.0 x 10 Removing CO2 + H28 17.0 x 106 ~ ~
Recovery of carbon black 12.0 x 106 ~ i Reduction 71.0 x 106 " , -1~1aste gas from preheater 10.0 x 106 ~ j General heat losses 3.3 x 10 133.0 x 106 Kcal/h ; The specific heat consumption related to the upper calor-ific value of the charged material is 3.2 x 106 Kcal per ton of ` iron sponge.
Example 3 The charge is coal.
Analysis of coal:
C 78.5 Z by weight H2 5.4 " "

N 1.4 " "
S 1.2 " "
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1~8~46~ 1 2 8.5 % by weight Ashes 5.0 % by weight Calorific value (llo), water-free : 7800 Kcal/k~, Gas balance for 1000 tons of iron sponge in 24 hours Circulation Reducing Discharged % by vol. Fresh Gas Gas Gas Gas CO + H2 97-50 87.30 92.00 69.80 ¢ ~ CH4 +,~ ~ N2 1.00 4.80 3.00 3.20 2 1.00 7.00 4.30 23.00 H20 0.50 n. so o. 70 .4.00 S 0. 01 - O . 01 O. 01 CO + H2-amount Nm3/h 37.000 38.000 75.000 11.000 Heat balance:
The charge is 18.5 t coal 144.0 x 106 Kcal

3 t/h steam of 5 at.1.5 x 106 -145.5 x 106 Kcal The amount of discharged gas is 11,()00 Nm3/h CO + H2.
The degree of utilization, related toC0 + H2, is thus about 20 70%.
Heat consumptions and losses:
Produced iron sponge of 800 deg. C 6.7 x 106 Kcal Cooling of circulating gas 13.0 x 106 ~
Recovery and preheating 18.0 x 106 "
: Removal o~ C02 ~ H2S~ 22.5 x 10 Reduction 71.0 x 106 Waste gas from preheater lO.0 x 10 General heat losses 4.3 x lO
145 x 106 Kcal The specific heat consumption related to the upper calorific value of the charging material, is 3.5 x 106 Kcal per ton iron sponge.

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Accordingly an object of the present invention is to provide a method of generating gases for the reduction of iron ores to form sponge iron, which gases contain carbon monoxide and hydrogen comprising, producing a fresh gas by partially oxidizing all kinds of materials containing carbon and hydrogen, with oxygen and a gas selected from a group con-sisting of hydrogen and carbon dioxide, cooling the fresh gas using water to produce steam, scrubbing the cooled fresh gas to wash out carbon dioxide and hydrogen, mixing the cooled scrubbed fresh gas with dust free scrubbed gas to produce the reducing gas containing carbon monoxide and hydrogen, pre-heating the reducing gas, combining excess amounts of the reduc-ing gas with the iron ores to produce sponge iron and a gas with ore dust, cooling and removing the dust from the gas and ore dust, the cooling of the gas and ore dust contributing to the preheating of the reducing gas, and scrubbing the dust free gas of carbon dioxide to form the dust free scrubbed gas.
A further object of the present invention is to provide a method of generating gases for the reduction of iron ores, which gases contain carbon monoxide and hydrogen comprising, producing fresh gas by partial oxidation of a gas selected from the group consisting of sulfur-free methane, methane containing gases and natural gas, with oxygen and a gas selected from the group consisting of hydrogen and carbon dioxide, mixing the fresh gas with dust free scrubbed and pre-heated gas, to form the reduction gas containing carbon monoxide and hydrogen, combining excess amounts of the reduction gas with iron ore to produce sponge iron and a gas with ore dust, removing the dust from the gas and cooling and scrubbing the gas of carbon dioxide to form the dust free scrubbed gas.

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While specific embodiments of the invention have been sho~ and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention ~ay be embodied otherwise without departing from such principles.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of generating gases for the reduction of iron ores to form sponge iron, which gases contain carbon monoxide and hydrogen comprising, producing a fresh gas by partially oxidizing all kinds of materials containing carbon and hydrogen, with oxygen and a gas selected from a group con-sisting of hydrogen and carbon dioxide, cooling the fresh gas using water to produce steam, scrubbing the cooled fresh gas to wash out carbon dioxide and hydrogen, mixing the cooled scrubbed fresh gas with dust free scrubbed gas to produce the reducing gas containing carbon monoxide and hydrogen, pre-heating the reducing gas, combining excess amounts of the reduc-ing gas with the iron ores to produce sponge iron and a gas with oredust, cooling and removing the dust from the gas and ore dust, the cooling of the gas and oredust contributing to the preheating of the reducing gas, and scrubbing the dust free gas of carbon dioxide to form the dust free scrubbed gas.

2. A method of generating gases for the reduction of iron ores, which gases contain carbon monoxide and hydrogen comprising, producing fresh gas by partial oxidation of a gas selected from the group consisting of sulfur-free methane, methane containing gases and natural gas, with oxygen and a gas selected from the group consisting of hydrogen and carbon dioxide, mixing the fresh gas with dust free scrubbed and pre-hated gas, to form the reduction gas containing carbon monoxide and hydrogen, combining excess amounts of the reduction gas with iron ore to produce sponge iron and a gas with ore dust, removing the dust from the gas and cooling and scrubbing the gas of carbon dioxide to form the dust free scrubbed gas.