Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/16—Sintering; Agglomerating
  • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/16—Sintering; Agglomerating
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/16—Sintering; Agglomerating
  • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
  • C22B1/205—Sintering; Agglomerating in sintering machines with movable grates regulation of the sintering process
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B21/00—Open or uncovered sintering apparatus; Other heat-treatment apparatus of like construction
  • F27B21/06—Endless-strand sintering machines

Definitions

• the invention relates to a method defined in the preamble of Claim 1.
• the invention further relates to equipment defined in the preamble of Claim 8.
• Continuous strand sintering is used for agglomerating pellets after pelletizing powdery mineral material, improving the strength and reactivity of the pellets.
• the mineral material herein refers to a min- eral, which has similar crystal chemistry properties to those of the oxide group and contains the metal to be recovered, the metal mainly comprising compounds of metal and oxygen.
• the strand sintering furnace 1 shown in Fig. 1 should be mentioned, being divided into several sequential zones I to VII, different temperature conditions prevailing in each one of them.
• the strand sintering equipment includes a perforated conveyor belt 2, which is conveyed as an endless loop around two deflector rolls 3, 4. At the left forward end of the furnace, wet fresh pellets are fed onto the conveyor belt 2 to form a bed with a thickness of a few decimetres.
• the conveyor belt 2 conveys the bed of pellets through the drying I, heating II, sintering III, equalizing IV zones of the sintering furnace and further through sequential cooling zones V, VI, VII.
• the pellets After travelling through the cooling zones, the pellets exit at the far end of the strand sintering equipment in a sintered form.
• the energy contained in the cooling gases at the tail end of the furnace is used for drying, heating, and sintering at the forward end of the furnace, which is why the strand sintering equipment includes overhead circulation gas ducts 5, 6, 30 for implementing the gas circulation mentioned above.
• Burners 7, 8 have been placed in the circulation gas ducts 5 and 6 and are used to increase the temperature of the conducted gas to the sintering temperature needed in the sintering.
• the purpose of the invention is to disclose a method and equipment, which can be used to improve the process according to the known technology so that, in connection with sintering, pre-reduction of the mineral material is provided, whereby at the subsequent stages of the process, no separate pre-reduction equipment is needed before the actual reduction, which takes place in an electric fusion furnace or the like.
• Another purpose of the invention is to disclose a method and equipment, which can be used to re- prise the energy consumption of the process.
• an essentially smooth pellet bed is formed from the pellets onto a sintering base.
• the pellet bed is conveyed through the process zones of different temperatures, including at least the heating/sintering zone and at least one subsequent cooling zone.
• gas is conducted through the pellet bed.
• the gas that is conducted from the cooling zone through the pellet bed is circulated to the heating/sintering zone.
• the method in the method, at least part of the gas that has travelled in the heating/sintering zone through the pellet bed is conducted to the cooling zone.
• the gas composition is rendered reductive for pre-reducing the pellets in the heating/sintering zone.
• the gas composition is measured and the gas composition is altered on the basis of the measurement to keep the composition reductive.
• One advantage of the invention is the fact that, simultaneously with the sintering, pre-reduction of the material can be effected, when a reductive atmosphere is arranged in the sintering furnace, whereby at the subsequent stages of the process, no separate pre-reduction equipment is needed. The actual reduction takes place in the electric fusion furnace or the like.
• the gas composition is measured by defining the carbon monoxide and/or the oxygen content of the gas.
• the gas is heated in the direction of rotation after the cooling zone and before the heating and sintering zones by burning a fuel in the gas, and the gas composition is kept reductive by adjusting the air coefficient of the combustion on the basis of the gas composition meas- ured.
• the gas composition is adjusted by conducting air to the gas in the direction of rotation after the heating/sintering zone and before the cooling zone on the basis of the gas composition measured.
• the gas pressure is adjusted to a predefined level by removing from the gas circulation the excess part of gas that is formed in the process during the combustion of the fuel.
• the gas pressure is defined in the heating/sintering zone, and on the basis of the defined pressure, the excess part of gas is conducted to the atmosphere in the direction of rotation of the gas after the heating and sintering zones and before the cooling zone.
• the gas is rendered reductive by means of a carbonaceous material that is arranged on the surface of the pellet bed and/or among the pellets, and/or inside the pellets.
• the strand sintering equipment includes a strand sintering furnace, which is divided into a number of sequential process zones of different temperature conditions, the zones including at least one heating/sintering zone, wherein the pellets are sintered, and at least one subsequent cooling zone, wherein the sintered pellets are cooled.
• the conveyor belt is directed as an endless loop around a deflector roll and a drive roll for conveying the bed of pellets through the process zones of the strand sintering furnace.
• the conveyor belt is gas permeable.
• An overhead circulation gas duct is located above the conveyor belt for conducting the gas from at least one cooling zone to the heating/sintering zone and onto the bed of pellets.
• a burner is placed in the overhead circulation gas duct to heat the gas that travels in the duct.
• a lower exhaust gas duct is located below the conveyor belt for conducting the gas that exits the heating/sintering zone and has been conducted through the pellet bed and the conveyor belt.
• a blower is arranged in the lower exhaust gas duct to provide a movement of the gas.
• a lower inlet gas duct is located below the conveyor belt for conducting the gas to the cooling zone.
• the strand sintering equipment includes a connecting channel, which provides flow communication from the lower exhaust gas duct to the inlet gas duct to conduct at least part of the gas exiting the heating/sintering zone to the cooling zone.
• the equipment further includes a gas sensor, which is arranged in the connecting channel to detect the gas composition.
• the equipment further includes a leakage air channel, which provides flow communication between the lower exhaust gas duct and the atmosphere.
• the equipment further includes a leakage air valve for opening and closing flow communication in the leakage air channel.
• the equipment includes a control device, which, in order to render the gas composition reductive, is arranged to monitor the gas compositions detected by the gas sensor and, on the basis of that, to control the leakage air valve for controlling the access of air from the atmosphere to the exhaust gas duct for adjusting the oxygen content of the gas, and/or to adjust the combustion air coefficient of the burner for adjusting the carbon monoxide content of the gas.
• a control device which, in order to render the gas composition reductive, is arranged to monitor the gas compositions detected by the gas sensor and, on the basis of that, to control the leakage air valve for controlling the access of air from the atmosphere to the exhaust gas duct for adjusting the oxygen content of the gas, and/or to adjust the combustion air coefficient of the burner for adjusting the carbon monoxide content of the gas.
• the equipment includes a pressure sensor, which is ar- ranged to measure the gas pressure in the heating/sintering zone.
• a pressure reduction channel is arranged after the blower in the flow direction to provide flow communication between the connecting channel and the atmosphere.
• a pressure-controlled valve is arranged in the pressure reduction channel and, controlled by the pressure detected by the pressure sensor, it is arranged to allow gas to exit the connecting channel to reduce the gas pressure to a predefined level.
• the strand sintering equipment includes a heating zone, a sintering zone, a first cooling zone and a second cooling zone, which are separated from each other by walls .
• the control device comprises a gas analyzer that measures the carbon monoxide and/or oxygen content of the gas.
• Fig. 1 shows schematically a strand sintering equipment according to the known technology
• Fig. 2 shows schematically an embodiment of the strand sintering equipment according to the inven- tion.
• Fig. 2 shows a strand sintering furnace 1, which is divided into several sequential zones I to VII, different temperature conditions prevailing in each one of them.
• the zones in this example comprise a drying zone I, a heating zone II, a sintering zone III, an equalizing zone IV, and three cooling zones V, VI, VII.
• the conveyor belt 2 is directed as an endless loop around a deflector roll 3 and a drive roll 4 to convey a bed of pellets through the zones I to VII of the strand sintering device 1.
• the conveyor belt 2 is a perforated steel band, the perforation allowing the gas to pass through.
• wet fresh pellets are fed onto the conveyor belt 2 to form a bed with a thickness of several decimetres.
• the conveyor belt 2 conveys the pellet bed through the drying zone I, heating zone II, and sintering zone III of the furnace to the stabilizing or equalizing zone IV, after which the pellet bed further travels through the sequential first cooling zone V, second cooling zone VI, and third cooling zone VII. After travelling through the cooling zones, the pellets exit the tail end of the strand sintering equipment in a sintered form.
• a first circulation gas duct 5 is arranged above the conveyor belt 2 to conduct gas from the second cooling zone VI to the heating zone II and onto the bed of pellets.
• a first burner 7 is arranged in the first circulation gas duct.
• first exhaust gas duct 9 which receives the gas that comes from the heating zone II and has been directed through the pellet bed and the conveyor belt.
• a first blower 11 is arranged in the first exhaust gas duct 9 to provide a movement of the gas.
• a first inlet gas duct 13 is located below the conveyor belt 2 for conducting the gas to the second cooling zone VI.
• a first connecting channel 15 provides flow communication from the first exhaust gas duct 9 to the first inlet gas duct 13 so that at least part of the gas exiting the heating zone II enters the second cooling zone VI.
• first gas sensor 17 for detecting the gas composition.
• a control device 23 is arranged to monitor the gas compositions detected by the first gas sensor 17 and, on the basis of that, to control 23 the combus- tion air coefficient of the first burner 7 for adjusting the carbon monoxide content of the gas and to control the first leakage air valve 21 to allow air from the atmosphere to enter the first exhaust gas duct 9 for adjusting the oxygen control of the gas.
• a second circulation gas duct 6 above the conveyor belt 2 conducts the gas from the first cooling zone V to the sintering zone III and onto the pellet bed.
• a second burner 8 is arranged in the second circulation gas duct.
• a second exhaust gas duct 10 is located below the conveyor belt for conducting the gas that comes from the sintering zone III and has been conducted through the pellet bed and the conveyor belt.
• a second blower 12 is arranged in the second exhaust gas duct to provide a movement of the gas.
• a second inlet gas duct 14 is located below the conveyor belt for conducting the gas to the first cooling zone V.
• a second connecting channel 16 provides flow communication from the second exhaust gas duct 10 to the second inlet gas duct 14 so that at least part of the gas exiting the sintering zone III enters the first cooling zone V.
• a second gas sensor 18 is arranged in the second connecting channel 16 for detecting the gas composition.
• a second leakage air channel 20 provides flow communication between the second exhaust gas duct 10 and the atmosphere. In the second leakage air channel 20, there is a second leak- age air valve 22 for opening and closing the flow communication.
• a control device 23 is arranged to monitor the gas compositions detected by the second gas sensor 18 and, on the basis of that, to adjust the combustion air coef- ficient of the second burner 8 to adjust the carbon monoxide content of the gas and to control the second leakage air valve 22 to control the entry of air from the atmosphere to the second exhaust gas duct 10 to adjust the oxygen content of the gas.
• the gas composition is rendered reductive for pre- reducing the pellets in the heating/sintering zone, and the gas composition is measured.
• the gas composition is measured by defining the carbon monoxide and/or the oxygen content of the gas.
• the gas composition is altered to keep the composition reductive.
• the gas is heated in the direction of rotation after the cooling zone and before the heating/sintering zone by burning a fuel in the gas, and the gas composition is kept reductive by adjusting the combustion air coefficient on the basis of the gas composition measured.
• the gas composition is adjusted by conducting air to the gas in the direction of rotation after the heating/sintering zone and before the cooling zone on the basis of the gas composition measured.
• the pressure in the closed gas circulations formed according to the invention increases cumulatively, unless the pressure is decreased every now and then.
• the gas pressure is adjusted to a predefined level by removing from the gas circulation a volume of gas that corresponds to the volume of gas generated in the process during the combustion of the fuel. Therefore, the gas pressure is measured in the heating/sintering zone, and on the basis of the pressure defined, the excess portion of gas is conducted to the atmosphere in the direction of rotation of the gas after the heating and sintering zones and before the cooling zone.
• the equipment includes a first pressure sensor 24, which is arranged to measure the gas pressure in the heating zone II .
• a first pressure-controlled valve 28 is arranged in the first pressure reduction channel 26. The first pressure-controlled valve 28 releases gas from the first connecting channel 15, being controlled by the pressure detected by the first pressure sensor 24, to reduce the pressure to a predefined level .
• a second pressure sensor 25 is arranged to measure the gas pressure in the sintering zone III.
• a second pressure-controlled valve 29 is arranged in the second pressure reduction channel 27. The second pressure-controlled valve 29 releases gas from the second connecting channel 16, being controlled by the pressure detected by the second pressure sensor 25, to re-lude the pressure to a predefined level.
• carbonaceous material such as coke
• carbonaceous material can also be arranged on the sur- face of the pellet bed and/or among the pellets and/or inside the pellets.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Engineering & Computer Science (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Tunnel Furnaces (AREA)
• Furnace Details (AREA)

Priority Applications (4)

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Citations (6)

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• 2007
  • 2007-09-06 FI FI20075614A patent/FI119940B/fi active IP Right Grant
• 2008
  • 2008-09-01 BR BRPI0816313A patent/BRPI0816313B8/pt active IP Right Grant
  • 2008-09-01 CN CN2008801124413A patent/CN101835913B/zh active Active
  • 2008-09-01 EA EA201000294A patent/EA016211B1/ru not_active IP Right Cessation
  • 2008-09-01 WO PCT/FI2008/050479 patent/WO2009030809A1/en active Application Filing
• 2010
  • 2010-03-10 ZA ZA2010/01706A patent/ZA201001706B/en unknown

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