Iron ore reduction method and installation therefor

Abstract

The invention concerns a method for iron reduction to make sponge iron which consists in: depositing a feed of iron ore on a grate and moving the grate so as to cause the feed to pass in at least three different zones; inputting gases, called input gases into one or several zones, including a hot gaseous carbonaceous reducing agent, and forcing said input gases through the ore located on the grate; and capturing the gases resulting from said forced passage, called output gases. The passage of the input gases brings the ore to a temperature ranging between 850° C. and 1300° C.; maintaining said feed at said temperature until an iron ore metallizing rate ranging between 60% and 100% is obtained. The feed deposited on the grate consists of either iron ore calibrated between 5 mm and 40 mm, or iron ore pellets having a diameter ranging between 5 mm and 20 mm, or iron ore granules of size between 2 mm and 10 mm, and the thickness of the deposited layer ranges between 150 mm and 600 mm. The flux of input gases, through the feed deposited on the grate, is directed from up downwards and generally obtained by generating beneath the grate an under-pressure ranging between 500 and 200 of water column. The forced flow of input gases through the feed in at least one processing zone consists at least partly of the output gas captured under the grate, said output gas captured under the grate having been at least subjected to a treatment such as scrubbing, desulphurization, drying, dust extraction, reheating and carbonate removal.

1 . Process for the reduction of iron ore with a view to producing iron sponge, in which a gaseous carbonaceous reducing agent is used, characterised in that a load comprising iron ore is deposited on a grate, in that said grate is displaced in order to move said load into at least 3 separate treatment zones, in that the first zone comprises an operation for the formation of the load on the grate, in that the last comprises an operation of unloading the load comprising reduced iron ore from the grate, in that the intermediate zone or zones comprise operations involving the supply of gaseous fluids, referred to as inlet gases, including a hot gaseous carbonaceous reducing agent, in that said gaseous flux or inlet gases are forced through the load on the grate, in that the above-mentioned intermediate zones comprise operations of collecting the gaseous fluids, referred to as exit gases, resulting from said above-mentioned forced passage, in that said ore is raised in this way to a temperature between 850° C. and 1300° C., and in that said load is kept at this temperature until a metallisation rate of the iron ore present is between 60% and 100%.  
     
     
         2 . Process according to  claim 1 , characterised in that said ore is raised to a temperature between 1050° C. and 1150° C.  
     
     
         3 . Process according to claims  1  or  2 , characterised in that said load is kept at the above-mentioned temperature until a metallisation rate of the iron ore present is between 85% and 95%.  
     
     
         4 . Process according to any of  claims 1  to  3 , characterised in that the load deposited on the grate successively passes through at least one zone in which the temperature of the inlet gas is 450° C.±150° C., at least one zone in which the temperature of the inlet gas is 500° C.±150° C., at least one zone in which the temperature of the inlet gas is 1200° C. 35  150° C., and at least one zone in which the temperature of the inlet gas is 1000° C.±200° C.  
     
     
         5 . Process according to one or more of  claims 1  to  4 , characterised in that the load deposited on the grate in the loading zone comprises ore mainly composed, in terms of volume, of iron ore sized between 5 mm and 40 mm.  
     
     
         6 . Process according to  claim 5 , characterised in that the load deposited on the grate in the loading zone comprises ore mainly composed, in terms of volume, of iron ore sized between 5 and 10 mm.  
     
     
         7 . Process according to one or more of  claims 1  to  6 , characterised in that the load deposited on the grate in the loading zone comprises iron ore pellets with a diameter between 5 mm and 20 mm.  
     
     
         8 . Process according to  claim 7 , characterised in that the load deposited on the grate in the loading zone comprises iron ore pellets with a diameter between 5 mm and 10 mm.  
     
     
         9 . Process according to one or more of  claims 1  to  8 , characterised in that the load deposited on the grate in the loading zone comprises iron ore granules with a size between 2 mm and 10 mm.  
     
     
         10 . Process according to  claim 9 , characterised in that the load deposited on the grate in the loading zone comprises iron ore granules with a size between 4 mm and 7 mm.  
     
     
         11 . Process according to one or more of  claims 1  to  10 , characterised in that a load formed by a layer with a thickness between 150 mm and 600 mm is deposited on the grate.  
     
     
         12 . Process according to  claim 11 , characterised in that a load formed by a layer with a thickness between 300 mm and 500 mm is deposited on the grate.  
     
     
         13 . Process according to any of  claims 1  to  12 , characterised in that a layer, referred to as a protection layer, is deposited on the grate, and in that the load is deposited on said protection layer.  
     
     
         14 . Process according to  claim 13 , characterised in that the protection layer has a thickness between 30 mm and 100 mm.  
     
     
         15 . Process according to  claim 14 , characterised in that the protection layer has a thickness between 40 mm and 60 mm.  
     
     
         16 . Process according to one or more of  claims 13  to  15 , characterised in that the protection layer comprises at least one of the following elements: baked pellets, sized ore that may or may not have been pre-reduced or sized scrap iron, either alone or in combination with one or more of the above-mentioned elements.  
     
     
         17 . Process according to one or more of  claims 13  to  16 , characterised in that the protection layer is made of constituents with a particle size between 5 mm and 40 mm.  
     
     
         18 . Process according to  claim 17 , characterised in that the protection layer is made of constituents with a particle size between 10 mm and 15 mm.  
     
     
         19 . Process according to one or more of  claims 1  to  18 , characterised in that a carbonaceous substance is incorporated into the load deposited on the mobile grate in a proportion between 1 kg and 40 kg of carbon present in said carbonaceous substance per ton of iron ore loaded before reduction.  
     
     
         20 . Process according to  claim 19 , characterised in that the carbonaceous substance is coal.  
     
     
         21 . Process according to  claim 19 , characterised in that the carbonaceous substance is coke dust.  
     
     
         22 . Process according to one or more of  claims 1  to  21 , characterised in that the flux of carbonaceous inlet gases through the load deposited on the grate is directed downwards.  
     
     
         23 . Process according to  claim 22 , characterised in that a vacuum between 500 and 2000 mm water column is created underneath the grate so as to obtain a downward flux of carbonaceous inlet gases through the load deposited on the grate.  
     
     
         24 . Process according to one or more of  claims 1  to  23 , characterised in that the flux of inlet gases forced through the load in at least one treatment zone is formed at least partially by exit gas collected underneath the grate.  
     
     
         25 . Process according to  claim 24 , characterised in that the exit gas collected underneath the grate has undergone at least one treatment, such as a scrubbing, a desulphurisation, a drying, a dust-removal, a reheating or a decarbonation operation.  
     
     
         26 . Process according to one or more of  claims 1  to  25 , characterised in that the flux of inlet gases forced through the load in a zone directly located after the loading zone is formed at least partially by fumes generated by the combustion of exit gas collected underneath the grate.  
     
     
         27 . Process according to  claim 26 , characterised in that the exit gas collected underneath the grate is chosen among the collected exit gases with the lowest reducing potential.  
     
     
         28 . Process according to  claim 26  or  27 , characterised in that the exit gas collected underneath the grate has undergone at least one scrubbing or dust-removal operation.  
     
     
         29 . Process according to any of  claims 1  to  28 , characterised in that hot reducing gas is produced from coal in a gasifier and in that said reducing gas obtained is used to form at least partly the gaseous carbonaceous reducing agent, which is forced through the layer forming the load, which is deposited on the mobile grate.  
     
     
         30 . Process according to  claim 29 , characterised in that the gasifier is supplied either with oxygen-enriched air or tonnage or pure oxygen.  
     
     
         31 . Process according to any of  claims 1  to  30 , characterised in that a hot reducing gas is produced by means of one or more “oxygen/coal” burners in at least one zone for treating the load on the mobile grate, said burners using either oxygenated air, pure oxygen or a mixture of the two, and in that said reducing gas obtained is used to form at least partly the gaseous carbonaceous reducing agent, which is forced through the layer forming the load, which is deposited on the mobile grate.  
     
     
         32 . Process according to  claim 31 , characterised in that the zone in which the reducing gas is produced is a zone in which the temperature of the inlet gas is higher than 800° C.  
     
     
         33 . Process according to  claim 31  or  32 , characterised in that the burners are supplied with pulverised coal.  
     
     
         34 . Process according to one or more of  claims 29  to  33 , characterised in that steam is used to control the temperature of the hot reducing-gas produced in a gasifier or by “oxygen/coal” burners during the formation of the flux of gas forced through the load.  
     
     
         35 . Process according to  claim 34 , characterised in that the steam is generated by a steam boiler, the fuel for which is formed at least partly by gases emerging from the layer forming the load and collected underneath the mobile grate.  
     
     
         36 . Process according to  claim 35 , characterised in that the exit gases collected emerge from one or more zones in which the exit gases are too low in CO to be used as reducing gases and too rich in CO2 to be decarbonated at low cost.  
     
     
         37 . Process according to  claim 36 , characterised in that the exit gases contain concentrations of CO and CO2 in terms of volume on dry gas such that 20%≦% CO <40% and 35≦% CO2<55%.  
     
     
         38 . Process according to one or more of  claims 1  to  37 , characterised in that the displacement speed of the mobile grate is modulated in such a way as to obtain a reduced ore with a metallisation rate between 60% and 100% in the unloading zone.  
     
     
         39 . Process according to one or more of  claims 1  to  37 , characterised in that the vacuum created underneath the mobile grate is modulated in such a way as to obtain a reduced ore having a metallisation rate between 60% and 100% in the unloading zone.  
     
     
         40 . Process according to one or more of  claims 1  to  37 , characterised in that the vacuum created underneath the mobile grate and the displacement speed of said grate are modulated in such a way as to obtain a reduced ore having a metallisation rate between 60% and 100% in the unloading zone.  
     
     
         41 . Process according to one or more of  claims 38  to  40 , characterised in that the displacement speed of the mobile grate and/or the vacuum created underneath the mobile grate are modulated in such a way as to obtain a reduced ore having a metallisation rate between 85% and 95% in the unloading zone.  
     
     
         42 . Process according to one or more of  claims 1  to  41 , characterised in that the DRI obtained on the mobile grate is directly unloaded towards a smelting furnace.  
     
     
         43 . Process according to one or more of  claims 1  to  42 , in which a mobile grate (G) successively passes through a loading zone, four treatment zones and one unloading zone, characterised in that, in the first zone (Z 1 ), referred to as the loading zone, a layer comprising iron ore is deposited on the mobile grate (G) in order to form the load (C) to be reduced, in that the grate (G) is displaced so as to move the load (C), by means of the movement of the mobile grate (G), from the loading zone (Z 1 ) to the unloading zone (Z 6 ), successively passing through the treatment zones (Z 2 ), (Z 3 ), (Z 4 ) and (Z 5 ), in that the temperature of the gaseous flux forced downwards through the load (C) deposited on the mobile grate (G) in zones (Z 2 ) to (Z 5 ) is regulated to 450° C.±150° C. in the case of zone (Z 2 ), 500° C.±150° C. in the case of zone (Z 3 ), 1200° C.±150° C. in the case of zone (Z 4 ) and 1000° C.±200° C. in the case of zone (Z 5 ) respectively, in that the gases emerging underneath the grate (G) from the layer are collected underneath the grate (G) in each of said zones (Z 2 ) to (Z 5 ), and in that at least part of the gases collected from at least one of the zones (Z 2 ) to (Z 5 ) is recycled towards means that control the gaseous fluxes forced through the load.  
     
     
         44 . Process according to  claim 43 , characterised in that a layer comprising iron ore is deposited continuously and in a constant thickness on the mobile grate (G) in the first zone (Z 1 ), referred to as the loading zone, in order to form the load (C) to be reduced.  
     
     
         45 . Process according to  claim 43  or  44 , characterised in that a gaseous flux comprising hot reducing gas formed from the gasification of coal into CO and H2 in the presence of oxygen and steam is forced through the load (C) on the mobile grate (G) in zones (Z 4 ) and (Z 5 ), in that at least part of the gas emerging underneath the grate (G) is collected in zone (Z 3 ), in that it is subjected to a scrubbing treatment, and in that part of it is then directed towards a steam generator, in which the collected gas is used as a fuel, and in that another part is directed towards a combustion chamber supplied with a significant excess of air, in which fumes are generated at a temperature of 450° C.±150° C., in that part of the fumes generated is introduced into zone (Z 2 ), and in that another part of the fumes generated is mixed with exit gases collected in zone (Z 2 ) to obtain a gas at a temperature above the acid dew point, in that the gas obtained is dedusted and then evacuated to atmosphere via a flue, in that at least part of the gas emerging underneath the grate in zone (Z 4 ) is collected, in that it is subjected to scrubbing, and in that it is recycled towards zones (Z 4 ) and (Z 5 ) in order to form at least partly the gaseous flux forced through the layer forming the load (C) in these zones (Z 4 ) and (Z 5 ), in that at least part of the gas emerging underneath the grate in zone (Z 5 ) is collected, in that it is cooled, in that it is dedusted and in that it is used in zone (Z 3 ) to form the gaseous fluid forced through the layer forming the load in said zone (Z 3 ).  
     
     
         46 . Process according to  claim 45 , characterised in that the coal is in a pulverised form.  
     
     
         47 . Process according to  claim 45  or  46 , characterised in that the exit gas collected underneath the grate (G) in zone (Z 3 ) is subjected to a drying operation.  
     
     
         48 . Process according to any of  claims 45  to  47 , characterised in that the exit gas collected underneath the grate (G) in zone (Z 4 ) is subjected to decarbonation before it is recycled towards zones (Z 4 ) and (Z 5 ).  
     
     
         49 . Process according to  claim 45 , characterised in that the exit gas collected underneath the grate (G) in zone (Z 4 ) is subjected to a drying operation.  
     
     
         50 . Process according to any of  claims 45  to  49 , characterised in that the exit gas collected underneath the grate in zone (Z 5 ) is cooled by introducing water into it.  
     
     
         51 . Installation for implementing the process of the present invention in accordance with one or more of  claims 1  to  50 , characterised in that it comprises at least: 
 a grate (G), preferably formed by mobile carriages provided with elements that promote the passage of a gaseous flux, the grate being provided with means for displacing it in the direction of the arrow,  
 means (Ch) for depositing a material on the grate (G),  
 means for defining an atmosphere (A 2 ), preferably a hood (H 2 ),  
 means for defining an atmosphere (A 3 ), preferably a hood (H 3 ),  
 means for defining an atmosphere (A 4 ), preferably a hood (H 4 ),  
 means for defining an atmosphere (A 5 ), preferably a hood (H 5 ),  
 means (DC) for unloading the grate (G) and for transferring the load (C) towards an outlet (S),  
 dedusters (D 1 , D 2 ) for treating a gaseous fluid and protecting the fans,  
 scrubbers (L 1 , L 2 ) of gaseous fluids for removing dust and condensing part of the steam,  
 possibly dryers (not shown) for lowering and controlling the steam content,  
 means (E 1 ) for decarbonating a gaseous fluid,  
 means (P 1 , P 2 , P 3 , P 4 ) for propelling a gaseous fluid,  
 means (R 2 , R 3 , R 4 , R 5 ) located underneath the mobile grate (G) to collect the gases emerging from the load (C) underneath said grate (G),  
 a combustion chamber (R),  
 a steam generator (V),  
 means for supplying (H 2 ) gaseous fluid coming from the combustion chamber (R),  
 means for supplying (H 3 ) gaseous fluid collected by (R 5 ), which is dedusted in (D 2 ) and compressed in (P 4 ),  
 oxy-coal burners (B) mounted in (H 4 ) and (H 5 ),  
 means for introducing pulverised coal (CP), oxygen (O2) and steam (VP) from the steam generator (V) into (H 4 ) and (H 5 ) in order to produce reducing gas from pulverised coal, oxygen and steam,  
 means for supplying (H 4 ) and (H 5 ) with gaseous fluid that is recycled and collected in (R 4 ), then passes into the scrubber (L 2 ), possibly also a dryer, then into the compressor (P 3 ) and finally into the decarbonator (E 1 ),  
 means for guiding the exit gas collected at (H 2 ), mixing it with fumes emerging from (R) and sending the resulting gas towards a deduster (D 1 ), then towards a flue (O) via the compressor (P 1 ),  
 means for guiding the exit gas collected in (R 3 ) so as to send it towards a scrubber (L 1 ), possibly also a dryer, a compressor (P 2 ) and then towards the steam generator (V) or the combustion chamber (R), where it is used as a fuel.  
 
     
     
         52 . Installation according to  claim 51 , characterised in that oxy-coal burners (B) are vertically placed in the roof of the hood (H 4 ) and (H 5 ) of zones (Z 4 ) and (Z 5 ) on a number of lines parallel to one another and parallel to the displacement direction of the grate (G).