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
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2413—Binding; Briquetting ; Granulating enduration of pellets
• • 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 for hard burning green pellets on a pellet burning machine with hot gases being passed through the pellet bed, the pellets first being dried in a drying zone with the gas flow directed downwards.
• pellet burning machines have - seen in the direction of travel - different treatment zones, namely drying zone, thermal treatment zone and cooling zone. These zones can be subdivided, for example into pre-drying and post-drying zones, heating zone, pre-firing zone, main firing zone, post-firing zone, first and second cooling zones.
• the green pellets made from the material to be agglomerated, aggregates and possibly solid fuel under humidification have a low strength and are therefore carefully loaded onto the traveling grate. In the drying zone, the difficulty then arises that the hot G receives as during the drying of the first layers according to its inlet temperature water, then in the adjacent
• drying as suction drying be carried out as slowly as possible.
• Such a process is known, for example, from GB-PS 690 668, in which drying is carried out with hot gases of approximately 260 ° C. This drying can largely prevent bursting, but not the strong condensation of water in the lower layers.
• DE-PS 10 31 328 it was proposed to carry out drying up to about 300 C by means of an upstream unit, such as a feed bunker or conveyor belt.
• an upstream unit such as a feed bunker or conveyor belt.
• strong condensation cannot be avoided if these moist gases cool down in cold pellet layers.
• the invention is based on the object of avoiding the impermissible over-moistening of layers of the pellet bed and bursting of pellets when drying the green pellets as far as possible and with as little effort as possible.
• This object is achieved according to the invention by drying in a first stage using hot gases at 60-180 ° C. and then increasing the temperature of the hot gases to 280-400 ° C. within 2 to 5 minutes.
• the gas temperature always refers to the entry temperature of the gas into the p ellet bed.
• the time always refers to the start of drying.
• the top layer of the pellet bed is first dried and with an inlet temperature of the gas of 60-180 ° C T-drying front moves into the next layer of the pellet bed.
• the increase in the inlet temperature of the gases after this first stage is regulated in such a way that the gases give off so much heat to the already dried pellets that they always arrive at the drying front at approximately the same temperature as possible. Ideally, this would require a continuous increase in the temperature profile of the gases across the drying zone. However, such a continuous increase is complex in practice, so that a gradual increase is carried out.
• Cooling air or exhaust gas from the combustion zone are generally used as hot gases, which are selected at the appropriate temperature or cooled to the required temperature by mixing with cold air or colder gases.
• the drying zone extends a certain length beyond the point where the hot gases with the highest entry temperature first enter the bed. The usual hard firing then takes place at temperatures from above 1000 ° C to above 1300 ° C.
• a preferred embodiment is that the temperature of the hot gases is increased in several stages. An approximation to a continuous increase in the temperature profile can thus be achieved in a simple manner.
• the number of stages is selected depending on the respective operating conditions in such a way that inadmissible over-moistening of layers of the pellet bed is avoided. This can be determined empirically by tests on a sintering pan, since these results can be transferred to the traveling grate.
• the setting of the temperatures in the individual stages is possible, for example, by arranging a gas hood above the drying zone, which is divided into several sections in the running direction of the traveling grate. A stream of hot gases is introduced into the gas hood and the desired gas temperature is set in the individual sections by controlled addition of colder gases. It is also possible to arrange a common gas hood over the entire moving grate and the one in the second K endeavourease resulting warmed cooling air under the ceiling of the G ashaube to conduct under adjustment of the desired temperatures in the drying step.
• a preferred embodiment consists of drying in the first stage for up to 60 seconds using hot gases at 60-120 ° C., in a second stage up to 120 seconds using hot gases in the range of 120-180 ° C., in a third stage up to 180 sec using hot gases from 180 - 220 ° C and in a final stage using hot gases from 280 - 350 ° C. This gives particularly good results.
• the tests were carried out on a pan with a diameter of 26 cm.
• the green pellets were produced on a pelletizing plate with a moisture content of 8.75% and an average diameter of 12.5 mm, and were placed in a layer height of 30 cm on a 10 cm rust coating from pellets which had already been fired.
• the pan was equipped with a gas hood and a wind box for supplying and discharging the gases.
• the pellets were made from a mixture of iron ore concentrate with the addition of bentonite, olivine and coke breeze and had the following chemical analysis and grain size:
• B was racing shows a pelletizing plant as precisely as possible traced.
• Pressure drying of 4.5 minutes at 350 ° C. gas temperature was started, followed by suction drying of 4 minutes with likewise 350 ° C. gas temperature.
• the firing took place at a temperature of 1320 ° C, then the pellets were cooled to an average drop temperature of 120 ° C.
• the quality characteristics of the pellets produced in this way largely correspond to the values obtained in the trailing operating system.
• the advantages of the invention are that drying without inadmissible over-moistening of pellet layers and without bursting of the pellets is possible in a simple manner only in the suction process.
• the quality of the pellets produced is at least as good as that of the processes using the combined pressure-suction drying.
• the length of the drying zone can be shortened, thereby increasing the throughput of the machine. Good use of the heat of the exhaust gas is possible.

Landscapes

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

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Publications (2)

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Citations (5)

• 1983
  • 1983-02-25 DE DE19833306684 patent/DE3306684A1/de not_active Withdrawn
  • 1983-06-28 IN IN799/CAL/83A patent/IN160995B/en unknown
• 1984
  • 1984-02-03 DE DE8484200152T patent/DE3460581D1/de not_active Expired
  • 1984-02-03 EP EP84200152A patent/EP0118149B1/fr not_active Expired
  • 1984-02-22 BR BR8400801A patent/BR8400801A/pt not_active IP Right Cessation
  • 1984-02-22 MX MX200425A patent/MX160178A/es unknown
  • 1984-02-23 ZA ZA841333A patent/ZA841333B/xx unknown
  • 1984-02-24 AU AU25026/84A patent/AU563419B2/en not_active Ceased

Patent Citations (5)

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