# SOCIETYOF MININGENGINEERS PREPRINT NUMBER

OF 

# AIME

CALLERNO.0,LITTLETON,COLORADO80127



## LOW ENERGY CONCEPT FOR STRAIGHT-GRATE PELLETIZING PROCESS



## K. H. Boss

W. Hastik

A. Kilian

H. Walden

Lurgie Chemie und Huttentechnik Federal Republic of Germany

For presentation at 

## the SME-AIHE Annual Meeting Atlanta, Georgia

- March 6-10, 1983 83-85



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## PREPRINTAVAILABILITYLISTISPUBLISHEDPERIODICALLYIN MININGENGINEERING

### 83-85

Low· 

### Energy Concept for Straight-Grate
1

### PelletizingProcess I



### K. H. Boss W. Hastik A. Kilian H. Walden

ERRATA



### Page 6 - Figure 2, bottompart, the legend for volume and temperature of direct-recup. airwas exchanged. 83-85

firing temperature on the entire fuel consumption will.be demonstratedby the example of a pelletizing plant.which produces blast furnace pellets ofhematite orewith a basicity of 0.7 at an oil consumption of 26.2 1/tof pellets. Asimulation of this plant (1) resulted in a theoretical heat requirement that corresponded to

an oil input 23.3 1/t of pellets. The difference of 2.9 is to be ascribed to losses not recorded in the model and, moreover, the calculationswere based on an ideal center zone of the pelletbed. Proposals for simplification and improvement of the gas flow pattern (without changing the firing zone) resulted in a theoretical oil consumption of 21.7 1/tof pellets or, considering the losses, 24.6 1/t. Based on this already simplified firing pattern of this plant, the effect of a combustion gas temperature changewas now investigated. In the preheating zone of the plant, the temperature climbs from 380 to 1320°C within 240 seconds. The tested firing patterns are**sho~m** inFigure 1. The coolingwas always led to the same discharge temperature in the layer center and considered in the output computation. The influence of the various temperatures of combustion in the range of 1220 to 1380°C on the fuel consumption and output is shown in Figure 2. Raising the firing temperature shortens the firing time and reduces thus the needed gas volume to the extent that the enthalpy of the hot
gas entering into the firing zone falls despite

a higher temperature. The lower gas requirement permits that the cooling zone to be provided for direct recuperation can be shorter, which causes the direct recuperation temperature to rise (Figure 2, bottom). This reduces the heat requirement in the preheating zone which, in turn, leads to further reduction of the total heat requirement. The most important results of the simulation, such as the preheating and firing time, gas volumes for firing and direct recuperation, the output and oil consumption are summarized inTable 1. The model computations indicate that the fuel consumption declines when higher combustion gas temperatures are applied. The combustion gas temperature canbe raised only to a certain limit beyond which the quality of finished pellets would begin to suffer. Particular attentionmust in this context be paid to the decomposition of the iron oxide and to slagging. The stated capacity increase at higher firing temperatures is a consequence of the reduced firing times and canbe realized only when the
process zones are newly divided up. In existing plants with an established zone division and at increased combustion gas temperatures instead of increased output, it would be possible to work with less suctionwhich would result in a lower consumption of electric energy in addition to a lower fuel requirement.

Alternative Patterns for Drying and Preheating

Slow preheating is known to increase the exhaust gas losses and, hence, the heat requirement. The preheating speed is therefore always chosen at the highest level permitted by the dried pellets. The preheating speed in the tested plant is already very high at approx. 60C/sec(360°C/ min). For comparison, an arrangement without pre-Synopsis

Inmodern iron pelletizing plants fuel consumptionhas been optimized to such an extent that onlyminor savings can be expected in the future. Inspite of this fact, different process parameters**~ere** studied**~ith** a mathematical model and firing tests. The influence on fuel consumption and productivity**~as** established. Furthermore, the adoption of simplified firing patterns**~as** investigated, in particular for coal firing. In**vie~** ofhigh costs of oil and natural gas, only substitutionof these fuels by coal can substantially reduce production costs. In existing plants partial replacement of oil and gas canbe achievedby addition of coal to the iron ore feed and by firing the pellets with pulverized coal. Two systems havebeen developed for the LurgiDravo travelling grate process which enables coal
to completely replace oil or gas. This paper describes in the first part the potentials for fuel savings available in the Lurgi-Dravo process. In the second part, different techniques for the use of coal as fuel in iron or pelletizingplants and inparticular the recently developed Lurgi Multistage Coal Injection and Combustion Process (LHC) are discussed. Combined with the LMC process, a**~ide** variety of iron ores and coals

- also with high ash contents

- can be used in the Lurgi-Dravo travelling grate process.
Investigation of Fuel Savings

Pellet Drying

In most pelletizing plants, drying is performed in cwo stages, the first one being an updraft drying zone in**~hich** the**lo~ermost** pellets

are predried andheated to avoid condensation in the lower layers during subsequent**do~draft** drying. This complicated gas**flo~** was first studied by means of model computations in an effort to simplify the gas pattern. Thus, it was possible to demonstrate that simple**do~draft** drying is possible under the following condidons: (a) feeding the green pellets warm (approx. 40-600C), for instance after dry grinding

or preheating, (b) performing the**do~draft** drying with a temperature profile suitable for the entering hot gases. In the second instance, a very simple firing pattern is obtained that sets in from the top alreadywith the preheating**~hen** the drying front has progressed to about bed center. How energy consumption and output are affected is evident from examples that will laterbe discussed in detail.

Pellet Firing

For pellet firing, the hot air from the cooling zone is returned directly into the firing zone (direct recuperation) and is there

- by combustion of oil, gas or coal

- heated to the temperature needed for the firing. For an effective heat transfer to the pellets, the combustion
gas temperature must be higher than the necessary indurating temperature. The influence of the 83-85

firing temperature on the entire fuel consumption**~ill** be demonstratedby the example of a pelletizingplant**~hich** produces blast furnace pellets ofhematite ore with a basicity of 0.7 at an oil consureption of 26.2 1/tof pellets. Asimulation of this plant (I) resulted in a theoretical heat requirement that corresponded to

an oil input·23.3 1/tof pellets. The difference of 2.9 is to be ascribed to losses not recorded in the model and, moreover, the calculations**~ere** based on an ideal center zone of the pelletbed. Proposals for simplification and improvement of the gas**flo~** pattern**(~ithout** changing the firing zone) resulted in a theoretical oil consumption of 21.7 1/t of pellets or, considering the losses, 24.6 1/t. Based on this already simplified firing pattern of this plant, the effect of a combustion gas temperature change**~as** now investigated. In the preheating zone of the plant, the temperature climbs from 380 to !320°C within 240 seconds. The tested firing patterns are shown inFigure !. The coolingwas**al~ays** led to the same discharge temperature in the layer center and considered in the output computation. The influence of the various temperatures of combustion in the range of 1220 to 1380°C on the fuel consumption and output is**sho~** inFigure 2. Raising the firing temperature shortens the firing time and reduces thus the needed gas volume to the extent that the enthalpy of the hot
gas entering into the firing zone falls despite

a higher temperature. The lower gas requirement permits that the cooling zone to be provided for direct recuperation can be shorter, which causes the direct recuperation temperature to rise (Figure 2, bottom). This reduces the heat requirement in the preheating zone which, in turn, leads to further reduction of the total heat requirement. The most important results of the simulation, such as the preheating and firing time, gas volumes for firing and direct recuperation, the output and oil consumption are summarized inTable I. The model computations indicate that the fuel consumption declines when higher combustion gas temperatures are applied. The combustion gas temperature can be raised only to a certain limit beyond which the quality of finished pellets would begin to suffer. Particular attentionmust in this context be paid to the decomposition of the iron oxide and to slaggingThe stated capacity increase at higher firing temperatures is a consequence of the reduced firing times and can be realized only when the
process zones are newly divided up. In existing plants with an established zone division and at increased combustion gas temperatures instead of increased output, it would be possible to work with less suctionwhich would result in a lower consumption of electric energy in addition to a lower fuel requirement.

Alternative Patterns for Drying and Preheating

Slow preheating is**kno~** to increase the exhaust gas losses and, hence, the heat requirement. The preheating speed is therefore always chosen at the highest level permitted by the dried pellets. The preheating speed in the tested plant is already very high at approx. 60C/sec(360°C/ min). For comparison,**~n** arrangement without pre-heating zone was testedwith the model, i.e. the downdraft drying is followed immediatelyby the firing zone with 13200C firing temperature (Figure I, Pattern 2). Thus itwas possible to achieve a capacity increase of approximately 5.6%, but the oil consumption increased also by about 3.3%. In this instance it is a disadvantage that the entire hot gas requirement must be satisfied by the direct recuperationwhereas a slightly slowerpreheating speedwould permit to cover the requirement partly out of the wind box recuperation. Theoretically, itwould be possible to try omitting the downdraft drying of the previous example and to startwith the firing immediately after the updraft drying (Figure I, Pattern 3). Thus, ifpermittedby the pellets, the output couldbe raised by 11.4% but the energy consumptionwould then climb, too. This show.s that

- although the hot gas quantity introduced into the 38ooc downdraft drying is utilized only with

a very poor efficiency

- some energy canbe saved in the actual firing, because the pellets need only to be heated from 380°C to firing temperature by means of the hot combustion gas. Both firing patterns, 4 a and 4 b (Figure I)

were started immediately in downdraft operation without updraft drying. The green pellets of the top layer are initially exposed only to approx. JOOOC drying temperature (Figure I, Pattern 4 a) in order to minimize the condensation in the lower pellet layers as much as possible. After drying the upper layers, the gas temperature is raised to 380°C within three minutes according
to a temperature profile. This is followed by the usual firing pattern.. By means of this very simple firing pattern and with a slight increase of the energy consumption, the output can be improvedby approx. 4.3 %at an increasedwaste gas rate. If the available waste gas is to be utilized,

a second down-draft drying zone with 3800C can be provided (Pattern 4b). Energy savings of
I liter of oil per tonne of finished pellets could thus be achieved at the same output. The
most important advantage of this firing pattern is the simplicity of gas flow which is particularly well-suited for a changeover to coal firing.

The Substitution of Oil and Gas by Coal

Coal Addition to Pellet Feed

Before the present come-back of coal as a substitute for oil or gas, it would be recalled that coal was being added as the primary or secondary fuel component even during the early days of pelletizing, some 25 years ago. In October 1956, Cleveland Cliffs Iron Co. started up a travelling grate plant at Ishpeming, Michigan, USA,treating flotation concentrates from specular hematite ores. The whole operation, except for ignition, was carried out in up-draft gas flow. Solid fuel, mostly anthracite or coke breeze at a rate of about 4

- 5 

### 7., was charged in layers onto the surface of greenpellets. The final product consisted of pellets and a certain amount of pellet sinter (2). In October 1955, Reserve Mining Co. commis2 83-85

sioned a travelling grate plant at Silver Bay, Minnesota, USA, inwhich the fuel supply consisted of anthracite (10

- IS 7.) and oil (85-**907.)(3~**One year later, the travelling grate plant of INCO inCopper Cliff, Ontario, Canada, commenced its pelletproduction (4). The only fuel source of this plantwas oil. After the successful operationof this plant, all travelling grate plants were for two decades designed exclusively for oil ornatural gas firing. The main reasons for the decision to use oil and gas were the rather low costs for these fuels at that time, their easy handling properties and the rising product quality requirements. Nowadays, coal addition as a partial replacement of oil or gas is againbeing seriously considered and has been introduced inmany travelling grate plants already. Coal prices are in
many regions attractive evenwhen the costly handling of the materials is taken into account. Extensive investigations were carried out to determine the correct procedure of coal addition. In this respect the primary concernwas themaintenance of pellet quality which should
not deteriorate by the addition of coal. Detailed studies of coal addition are described in the work of B. Hutter (5). Up to 2 %of coals of different reactivity

were added to five different ores ground to the fineness required for green ball formation. The pellet diameter was uniformly 10

- !2 mm. Neither the green nor the dried pellet strength changed in comparisonwith that of pellets without coal addition. However, itwas noticed that the crushing strengthof indurated pellets decreased**wi-!i~** coal addition (as Cfix) of more than

### 0.5 %**~o\** magnetite pellets and the resistance to

### abras~on diminished with coal addition (Cfix) of above: I %. On the other hand, it was possible to considerably raise the capacity of the pelletizing travelling grate for hematite pellets. Therefore, the negative and positive influences are to be considered and outweighed for each particular case. Figure 3 shows the influence of increasing coal additions to hematite andmagnetite pellets. In the case of hematite, the strength rises up to about 0.5% coal addition (as Cfix). The strength then decreases but is still sufficient
up to 

### 1.5 %coal addition. This influence is explained by partial reduction of hematite to magnetite and subsequent incomplete reoxidation ofmagnetite to hematite. Higher coal additions
may even result in a further reduction towards the formation of wuestite which, within the time available, does not reoxidize again and forms fayalite with the silica present. Several plants are currently operatedwith coal addition into the iron ore feed. Hoogovens
at Ijumiden, Netherlands, add coke breeze**in~** quantities of about 1.0% (as Cfix) to the iron

oremix in the blending yards. The coke breeze is thus ground together with the ore mix in closed-circuit dry grinding mills. The ore mix consists of magnetite and hematite type ores invarying ratios. Plant experience shows that the coke breeze can partly compensate for the oxidation heat of the magnetite. Coal addition is also practised in the pelletizing plants in Brazil where charcoal is used as the fuel source.The SIDBEC plant in Canada replaces part of the total fuel by sub-bituminous coal. As a result of the serious fuel oil shortage therewere considerations of designing pellet plants for the use ofmultiple-type fuels in order to counteract the situation in future. Basedon such considerations, ourNorth-American partner, Dravo Corporation inPittsburgh, Pa., received 2 orders for pellet plants with the request to design the plants for the use of natural
gas, for No. 2 and 6 fuel oil as well as for pulverized coal. Both these plants are located in the center of theMesabi Range inMinnesota, USA, and one is owned by the HibbingTaconite Company andwas started up in 

### 1976, whereas the other belongs to the Inland Steel Company and commenced production in 

### 1977. The request of the clients for such multifuel-type pellet plants resulted in a significant change from the so far well-provenLurgiDravo straight grate pelletizing system. Extensive research and industrial-scale test work was done before the final design of these plants started. The diagrams in Figures 4 and 5 illustrate the difference between the new and the conventional system. Figure 4 shows the conventional system in which cold air for cooling the pellets is forced up-streamin the cooling zone through the charge. The hot air,recuperated during cooling, is collected in a header arranged above the hood. The hood is sealed against the moving pallets, thus allowing to develop an over-pressure in the

cooling hood. With the help of this over-pressure the hot air collected in the first cooling hood is introduced via ducts and downcommers into combustion chambers arranged horizontally in the sidewalls of the preheating and firing hood. Burners located in the,center of these combustion chambers heat to the required temperature. The hot air collected in the second cooling hood is, by the up-draft drying fan, conveyed to thewindboxes of the updraft drying hood for partial drying of the pellets. The air leaving the charge with very low temperature is discharged through the stack into the atmosphere by an exhaust fan arranged above this zone. The downdraft drying, preheating and firing zones are operated in the downstream direction. All windboxes of these zones are connected to the windbox exhaust and recuperation fans. Tll'e recuperation fan is connected to the windbox in the downdraft firing zone and therefore handles gases with high temperature. The windbox exhaust fan connected to the downdraft drying and preheating zone handles gases of low temperature which cannot be reused in the
process and are therefore led off to the stack also. This traditional systemworks with natural
gas, fuel oil and in one particular case with a combination of coke oven and blast furnace gas. Figure 5 shows the systemdeveloped for multiple-fuel-type usage. Basically the entire process fan arrangement is the same as in the conventional arrangement. The main difference is that no combustion chambers are provided in the vertical walls of the respective hoods in the preheating and firing zones. The provison of several such combustion chambers would create unnecessary complications when pulverized coal

were used as fuel. Two ormore vertical! ar3 83-85

ranged combustion chambers are provided for a combustion of pulverized coal ornatural gas or fuel oil adjacent to the firing zone. When using pulverized coal, part of thehot air from the second cooling zone is used in the combustion systemof the coal burnerwhich is located at the top of the combustion chamber. The product of**co~bustion** resulting from firing of pulverized coal is mixed with the hot air from the first cooling zone in the combustion chamber and directed into the burnerhood through a horizontal duct. This new system is now in operation in the HibbingTaconite plantwhere, due to specific commercial conditions, only natural gas had been used. The Inland Steel plant had been using pulverized coal over extended periods of time. At the present moment this plant is again using natural gas due to a very substantial cost advantage offeredby the national gas company. The operation of the Inland Steel coal fuel plant has been described in greater detail in other publications 

### (6). It canbe stated that the developed system has been a complete success with the specific ore and pellet quality requirements using a low-ash coal which was possible with a relatively straight-forJard temperature profile and firing pattern.

LMC Process for High-Ash Coal

Further investigations were continued by Lurgi in order to extend the scope of applicability of the process to the use of a wider range of ores and concentrates and particularly of coals, including high-ash coals. Itwas observed in the case of oil-fired plants that fine ore dust particles from pellets entrained in'the recuperated air caused liquid slag formation in the combustion chambers. The slag build-up led to flame deviations and to subsequent refractory failures. In the case of coal firing, an increase in the slag-formationwas anticipated. This was confirmed by detailed observations, during coalfired operation of industrial plants (7) in Sep.- Oct. 1981. An analysis into the causes of the slagging problems in the conventional pelletizing furnaces led to the following conclusions: Low-oxygen, high-temperature regions in flames caused the Fe203 to decompose to FeO which forms low-melting eutectics with Sio2 and Alz03 (at approx. I IOO'OC). Furthermore, due to the high air preheat temperature (800

- I 000°C) there are extremely high local temperatures in extended flame areas corresponding to adiabatic temperatures of up to 2 500 oc. By entrainment of excess air the combustion products are finally cooled down to about I 300 oc, the pelletizingprocess temperature. The retention time of slag particles passing through the high-temperature flame areas is too short for them to reoxidize or cool down and solidify the slag impinging onto the refractory. As a result of the analysis of slagging problems, the following technological and economical preconditions were imposed in order to achieve satisfactory operationwith high-ash coal as fuel:-!.**Technolo~ical Desi~n**  

### Requirements:

The temperature level of the combustionprocess has to be decreased drastically to prevent**refracto~;** 

### problems from liquid slag formation. The local fuel concentration during coal combustion shouldbe as low as possiblewith longest retention times for coal and ash particles in the 02-rich atmosphere to avoid Fe203 decomposition and build-up of low-melting ore/ash eutectics. Coal flames using pulverized coal in the conventional sense shouldbe largely avoided due to thehigh intensityof combustion resulting in high local flame temperatures.

II. E:onomic Requirements: 4



### The coals should be cheap, which are generally high-ash coals. Aminimumof coal preparation operations, e.g. grinding. Flexibility in the use of different solid fuel types as well as in combinationwith solid, liquid or gaseous fuels. In the final development of the**L~C** 

### process, the above criteria have found full application. The most significant features of this process
are: multi-stage·coal injection, multi-stage coal combustion using direct air/gas flowwithin the furnace, aerodynamic size separationof coal.

Multi-Stage Coal Injection

As demonstrated in Figure 6, the coal injection takes place through the sidewalls above the pellet bed, extendedover the first cooling zone. The extensive distribution of the coal across the pelletbed and across the total first cooling zone breaks the "burner" down into an infinite number of "individual burners" '..Tith "individual coal grain combustion". The pellet bed
acts as an air distributor, equalizing the air flow to the individual coal grains by 

### the flow resistance of the pet-lets in the range of 50 mbar. This multi-stage injection ensures low local fuel concentration, one of the preconditions for high-ash coal firingmentioned before. Furthermore, the amount of coal injected through the individual injection points is adjusted according to the temperature and velocity profile of the cooling zone and the required process gas temperature in the preheating and firing zone.**~ulti-Stage** 

### Coal Combustion

Figure i 

### illustrates the principles of single andmulti-stage combustion. In conventional combustion chambers, the combustion of fuel takes place under near-stoichiometric conditions, producing extremely high temperatures of the combustion products. By further entrainment of

excess air, these products are cooled down to the process temperature lev·el of abour l300°C. This**te~perature** 

### evolution is shown in the figure for"single-stage" combustion. The process temperature is approached"fromabove" passing the hatchured "critical slagging area". 

### 83-85

The contrary is illustrated in the second

curve for "multi-stage" combustion, Here, the final process temperature is approached "from below" in infinite combustion stages arranged

one after the other. The critical slagging area is not touched. The temperature-level of thecombustion process is lowered drastically, thus matching another preconditionmentioned before for high-ash coal firing. As also illustrated in Figure 7, multi-stage combustion requires a longer distance to complete combustion, since it proceeds with an essentially lower particle temperature and a

coarser coal size range. The longer distances, however, are availableby using the direct flow pattern, from the cooling directed to the firing
zone, as shown before in Figure 6, Thus, the available distances are on the average about 10 times longer than in conventional "singlestage" combustion chambers. These distances permit the utilization of the ''aerodynamic size separation effect" for coal distribution. This important effect allows the final realization of themulti-stage combustion principle because it spreads the combustion from

a two-dimensional in a three-dimensional combustion as illustrated in theFigure 8. The aerodynamic effect is createdby the lifting forces acting onto the coal particles by the cooling air leaving the pelletbed. Depending on the coal size range, i.e. 0-10

### mm, and on the final balance of forces, three types of combustion canbe distinguished.

Type I: Bed Combustion

which takes place on top of the pelletbed for a coal particle size range (dp<:dgr)-w,hich is not lifted by the air streamwith the velocity
WJ 

### prevailing inside the top layer of the P,ellets. dSJ is the diameterof the floating particle for the air velocity WJ. 

### If the coal to be used leaves a fixed ash structure, a high percentage of this ashwill be transported to the pellet discharge without creating any slagging problems. In industrial plants a certain percentage of coal combustion can be performed this way. The retention time available for combustion

can be calculated by the point of injection and the strand speed. The coal combustion should be completed before entering the second cooling zone.
Type II: 

### Fluidized Bed Combustion

refers to a coal particle size range (ds2:>

### dp

### <dg1) which is liftedby forces cor- responding to air velocity WJ 

### but balanced for the lower velocityw2 above the pelletbed. The particle retention time for combustion here is infinite in theory, but in practise limited by the slowmovement of this particle size
range directed to the firing zone. This movement is createdby the change in airflow from the vertical direction, leaving the top of the pelletbed, to the horizontal direction in the transitionpoint from cooling to firing zone.
Type III: In-Flight Combustion

refers to the particle size range (O<dp<ds2) which is liftedby the force of air correspondingto the air velocityw2. As also illustrated in the above figure the
very small coal particles (dp-o) will follow the airflow patternmore precisely and faster (t min) than coarser particles (dp-ds2) whichneed more time (tmax) tobe accelerated from the initial particle velocity zero to the final velocity. Retention time, acceleration, speed and location of coal particles canbe calculated approximately on thebasis of a mathematicalmodel (8) simulating the elliptical flow pattern. The principles of the multi-stage coal injection and combustionprocess LMC can also be applied in steps to existing straight-grate pelletizingplants. With this concept, used as

a first step at the Ferteco pelletizingplant inBrazil, remarkable fuel oil savingswere achievedwith comparable low capital investment.

Conclusion

The model calculations for energy savings by process optimizationwith the straight-grate plants have pointed out the possibilites for
cost reduction. In existing plants, these possibilities are rather limited in comparisonwith those providedby using relatively cheap coal in place of other, more expensive, fuels. In addition to the admixture of coal into the pellet feed, it is primarily the direct use of lowergrade, high-ash coal bywhich the costs for pellet induration canbe cut substantially. First results achievedwith a new combustion system for coal withhighashcontent and unfavorable ash melting behavior are encouraging. The expenditure for coal handling is also low due
to the preferred coal size range of about 0-10mm. The new coal firing system for straight-grate pellet plants offers, thus, the currentlymost advantageous means of reducing the fuel costs also in existing plants at a relatively low capital investment. Concieved as a multi-fuel system, it offers the necessary flexibility for adaption to the fluctuating conditions of resources and market.

References

1. Cappel, F., Hastik, W., MUller, B., and Pfaff, E., 1982, "Entwicklungen zur optimalen Brennstoffnutzung bei der Herstellung

von Eisenerzpellets auf demWanderrost," (Developments for Optimum Fuel Utilization inProduction of Iron Ore Pellets on the Travelling Grate), Stahl und Eisen, Vol. 102 No. 5, pp.207-212.

2. Violetta, D.C., 1958, "Updraft Pelletizing of SpecularHematite Concentrates", J. of Metals, No. 10, pp. 118-121.

3. Haley, K. M., Apuli, W.E., 1962, "Pelletizing

on a Horizontal GrateMachine, Agglomeration," d. Wepper, W.A., New York, Interscience, pp. 931-964.

4. Quenean, P., Bracken, E. H., and Kelly, D., 1958 "Highgrade Iron Ore at Copper Cliff, Ontario, "J. of Metals, No. 10 (8), pp. 527-532. 5 83-85

S. HUtter, B., 1977, "Die Herstellung gebrannter Eisenerzpellets aus GrUnpellets mit geringer Brennstoffbeimischung, "(The Production of Indurated Iron Ore Pellets from GreenPellets withLow Fuel Admixture), Doctoral Dissertation, Aachen, RheinlandWestfalen: Technische Hochschule Aachen (1977)

6. Leighton, G. P., De Klaver, M. A. 

### A., 1975, "Coal Firing of Dravo-Lurgi Travelling Grates," presented atMinnesota Section, 48thAnnual Meeting AIME, Jan. 1975.

7. Queiroga, I. M., et. al., 1982, "Fuel Oil Reduction at CVRD Pelletizing Plants", presented at SME-AIME Annual Meeting, Dallas, Texas, Feb. 14-18.

8. Hein, B. C., 1982, "Ein Beitrag zur Berechnung der Laufbahnen von einzelnen Kohlepartikeln inPelletbrennofen, Theorie und Ergebnisse", (A Contribution on the Calculation of Trajectories of Individual Coal Particles inPellet Indurating Furnaces, Theory and Results). Unpublished Report, Lurgi Frankfurt, Jan. 4.

Authors' Biograuhies

*Boss, K. H., Chemical Engineer, Fachhochschule Frankfurt, Group Manager in Research Center, Lurgi Chemie und HUttentechnik GmbH, Frankfurt am Main.

**Hastik, W., Mathematical Engineer, Dipl. Ing.

Technische Hochschule Darmstadt, Development DepartmentManager for Process Computation Lurgi Chemie und HUttentechnik GmbH, Frankfurt am Main

***Kilian, A., Civil Engineer, Dipl. Ing., Technische Hochschule Karlsruhe, Manager Combustion Department Central Engineering Division, Lurgi Chemie und Htittentechnik GmbH, Frankfurt am Main

 walden, H., Metallurgist, Dipl. Ing., Dr. Ing., Technische Hochschule Aachen, Senior Manager, Prokurist and Asst. Director of Research Center, Lurgi Chemie und Htittentechnik GmbH, Frankfurt am Main.6



### Figure 1. Investigated firing** pat~erns**

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### on**3t=eng~h** 

### and prcductivit7 of fired**?ellet~** 

### 83-857

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### Figure 7. Comparison single-multi combustion principles

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## :'·.I: ".::**;=:.~~IZE!J** 91::::1 

### @_-**~ d~** 

## 2**~**dp < C51**~--~~--~** ==_,**~ ~** 

TYPE;n

..,N

...=L!GMT''**::;~eUS7iCN** 0 <'dp < d,,**~:" :::CLi~G**  -"IP

T'tP=:S CF 

### liC"' 1 •1

### '1>=1 COAL**CC~BUSTJCN** ! C-- I**~** -,



### Figure 8. Types of coal**co~ustion** 

### BJ-859 83-85

firing Pattern 110. I 2 3 4 

# i

a 

## I b c d e f

# ~ a b 

### :

Firing Temper•ture 'C 1220

# I 1230 1260 1290 1320 1350 1320 1320 1320 1320



## - Preheating and Flring

# I I

Time s 1372

# I 1285 1137 1054 998 9se 927 892 937 983 10IS



## ------ Gas volume rn'/kg 1.94 1.es I.70 1.61 1.55 I.50 I.47 1.33 I.41 I.55 I.5I Pellets 

## I
'---



## ------

# --- i-



## ---- Direct Recup.air

Air volume rn'/kg 1.7R 1.69 I.54 1.45 I.39 1.J4 1.31 1.JJ 1.41 I.38 I.39 Pellets I I



## ------------ Temperature 

### oc 71D

# ~5~ 932 960 984 1007 978 g49 959

# I 960



## ----------·
25.2 1 Oil Consumption 1/t Pel- 34.2 31.8 27.9 25.9 24.6 23.8 23.2 25.4 28.7 23.6 lets 

## J 

# 3. ------------ Firing Capacity t 85.6 92.4 96.8 100 102.4

# i 104.4 105.6 111.4 110 99.7/

---

____ i

---

3 4**Firin~** patterns**accordln~** to F1gure 1

Table I l!esults of Plant s1mulation