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# SOCIETYOF MINING ENGINEERS

CALLERNO.0,LITTLETON,COLORADO80127 

# PREPRINT NUMBER

86-128

DESIGN AND PERFORMANCE OF THE NATIONAL STEEL PELLET PLANT HIGH TEMPERATURE HEAT RECUPERATION SYSTEM

E. F. Draskovich

National Steel Pellet Company Keewatin, Minnesota

D. J. Englund

M. A. Hanna Research Center Nashwauk, Minnesota

W. C. Dailey

National Steel Pellet Company Keewatin, Minnesota

For presentation at the SME Annual Meeting

New Orleans, Louisiana -March 2-6, 1986



### Permissionisherebygiventopublishwithappropriateacknowledgments,excerptsorsummariesnottoexceedone-fourthoftheentiretextofthepaper. Permissiontoprintin moreextendedformsubsequenttopublicationbytheSociety mustbeobtainedfromtheExecutiveDirectoroftheSocietyofMiningEngineers. IfandwhenthispaperispublishedbytheSocietyofMiningEngineers,itmay embodycertainchangesmadebyagreementbetweentheTechnical Publications Committeeandtheauthor,sothattheforminwhichitappearsisnotnecessarily thatinwhichitmaybepublishedlater. Thesepreprintsareavailableforsale. Mailordersto PREPRINTS,Societyof MiningEngineers,CallerNo.D,Littleton,Colorado80127.

PREPRINTAVAILABILITYLISTISPUBLISHEDPERIODICALLYIN MININGENGINEERINGABSTRACT

In 1984 a high temperature heat recuperation system was installed in the pellet plant of the National Steel Pellet Company located in Keewatin, Minnesota. The system is similar to those of Cleveland Cliffs Empire and U.S. Steel's Minntac operations. It recovers hot process air from the cooler by induced flow, and directs it to an intermediate
zone between the drying and preheat
zones on the grate machine. This system recently underwent further modifications in April 1985, :following initial operation in 1984. The M. A. Hanna Company, which manages the property, developed the design criteria and made the subsequent recommendations for modification through its research facility in Nashwauk, Minnesota.

INTRODUCTION

National Steel Pellet Company (NSPC) is jointly owned by National Steel Corporation and Nippon Kokan Steel Corporation. The plant, located near Keewatin, Minnesota, on the Mesabi Iron Range, commenced operation in 1969. At that time, it consisted of a concentrator with 2.44 Mt/yr capacity (2.4 MM lt/yr) and an Allis Chalmers Grate-Kiln pelletizing system. In 1976, a second Allis Chalmers Grate-Kiln system (Phase II) with 4.06 Mt/yr (4.0 MM lt/yr) pellet capacity was added, and the concen- trator was expanded proportionately. In 1979, the original indurating line
was closed permanently. Today, the plant employs 570 people and has increased its capacity to 4.65 Mt/yr (4.58 MM lt/yr) through modifications made to the indurating system. The plant is managed by M. A. Hanna Company.

M. A. Hanna Company also maintains a Research Center at Nashwauk, Minnesota, for support of its mining concerns. ·Hanna Research Center came into existence in 1929 as a beneficiation lab for the lean ores of the Mesabi Range. Since then, the laboratory has grown to include full support services for the iron mining industry as well as research covering beneficiation of sulfide and oxide ores, treatment of industrial minerals, air and water pollution sampling and analysis, pilot plant testing of industrial processes and upgrading of energy resources. The Research Center has fully equipped chemical and mineralogical laboratories to support its research programs in the aforementioned areas. 1

The NSPC Phase II grate machine was originally designed with two process zones consisting of eight windboxes for drying followed by six windboxes for pellet preheating. The machine had a "dedicated fan" type heat recuperation system. Subsequent operation showed the recuperation fan to be too large, since it frequently pressurized the drying
zone on the grate. In 1980, the fan wheel was removed, and the flow throught the duct was induced by the process waste gas fans which exhaust from the drying zone. Gas flow through this duct was tempered by bleed-in air to maintain a 399"C (750"F) operating temperature.
In 1980, Cleveland Cliffs Iron Company introduced the idea of a high temperature heat recuperation system at their Empire III unit. The high temperature recuperation system recovered process air from the
same zone of the cooler as before, but no longer tempered the flow with bleed-in air. Depending on operating conditions the temperature of this air could reach as high as 815"C (1500"F). This hotter recoup gas was introduced into an intermediate
or secondary drying zone situated between the primary drying and preheat zones on the grate.
In general, this secondary drying zone could be made up from windboxes taken from the last half of the original drying
zone and/or one or two of the preheat zone windboxes. The use of a high temperature heat recuperation system reduces the amount of process air required by utilizing recovered process heat without dilution from ambient air. The advantages as applied to a retrofit such as at NSPC include1:

1. Reduction in fuel consumption through more efficient use of process heat.

2. Reduction in fan power as a result of decreased tempering air and decreased drying load.

3. Increased oxidation of magnetite on the grate resulting in additional heat released to improve fuel consumption and decrease preheat fan power.

### 4. Less magnetite entering the cooler further lowering the cooler air requirements and reducing fan power.
5. More complete recovery of heat from the cooler and less heat lost up the stack.

6. Decreased waste gas fan load as the equivalent drying heat 

### is now moved with less air.

For new plants, such a system can result in the employment of a shorter kiln and fewer or smaller process fans1. Today, variations of this system are in operation at Cleveland Cliff's Empire facility, 

## u.s. Steel's Minntac facility, National Steel Pellet Company and LKAB's KP-79 plant in Sweden.
RESEARCH PROGRAM
The decision to evaluate the application of a high temperature recoup system at National Steel Pellet Company was made in 1981. The scope of the program required definition of:
1. The best windbox split configuration for maximum fuel savings.
2. The impact on indurating capacity using the recommended windbox con- figuration.
Based on the results of the test program, plant personnel would eval-**~.:ate** 

### the economic incentives for installing the proposed system.
The Hanna Research Center performed and evaluated all tests and conditions involved for redesign of the machine. The various grate machine configurations were**si~ulated** 

### using an Allis-Chalmers pot-grate furnace. The furnace is equipped with
a 0.093 m2 (l 

### ft2) grate area and standard instrumentation for controlling and recording gas temperatures, bed differential pressures, process gas oxygen content, and bed temperature profiles. All tests were performed with plant production greenballs, made possible by the proximity of the Research Center to the plant.

Table lists the drying zone configurations that were examined. These zones were defined as a combination of windboxes within the original eight. This new zone division would only be installed above the grate, both primary and secondary drying
zones would exhaust into a common header below the grate. 2



### The major portion of the test program was performed simulating the plant at design capacity of 525 t/hr (517 lt/hr). The process conditions of gas temperature and pressure drop 

### in each zone were determined based
on actual plant data, anticipated conditions, and discussions with Allis Chalmers personnel. Two drying zone temperatures were evaluated at 343

### •c and 398

### •c (650"F & 

### 750"F), in combination with six recoup gas temperatures ranging from 510"C to 649"C (950"F to 1200"F). The preheat inlet gas temperature was held constant at 1037"C (1900"F) in order to limit the number of test variables under consideration.

A series of pot-grate tests were also performed at increased production rates of 5%, 10%, and 15% above the design rate. From these test results, the anticipated increase in throughput would be determined based on bed temperature profiles, mass flow rates of gas, and pellet quality.
A series of pot-grate tests were performed to evaluate each configuration. These tests generated data regarding greenball drying rates, magnetite oxidation rates, and pellet strengths at the end of the grate cycle. Approximately 10 tests were performed for each configuration. If a process gas temperature was changed, a new series of tests was performed, omitting any duplication of tests when possible. The data from these tests yielded temperature profiles of the pellets at three points in the bed, a gas/solids
mass ratio by zone, and all appropriate off-gas temperatures by zone. This information was organized into data files and processed using an energy and
mass balance computer program developed at the Research Center. Table 2 gives a complete listing of the input required· by the program to perform a balance.

The computer program performs a straight forward mass and energy balance on the indurating system based on the grate machine configuration. A complete air, water and heat balance is done around each zone on the grate. The kiln is treated as one zone and the cooler as three zones. Forthese tests, the kiln and cooler conditions remained relatively con- stant.
For the sake of comparison, all balances were performed with an assumed greenball mineral composition of 80% magnetite and 5% iron car- bonate minerals. Where not specifically stated, magnetite content was 80% and carbonate content was 5%.
The program starts with an assumed fuel input into the kiln and proceeds to calculate heat requirements zone by zone on the grate followed by calculations for heat recovered from each of the cooler
zones. The cooler heat is proportioned to three zones based on a solids cooling curve as affected by airflow through the zone, incoming solids temperature, and the amount of magnetite remaining in ·the pellets. Additional constraints are placed on the system to maintain a minimum cooler stack gas temperature and a specified recoup gas temperature.
The balance around the secondary drying zone 

### is completed when the calculated cooler recoup gas flow and heat content match the calculated heat and air requirements in the secondary drying zone. In other words, the required mass of air corning out of the cooler has to carry the requisite amount of heat, thus being at the specified gas temperature. Since the cooling curves varied from test to test, a perfect match was rare.
The program has two methods to achieve a balance. The first is based on satisfying the second drying
zone heat requirement using less cooling air than required (actual recoup gas temp 

### > specified gas temp). In this case, bleed-in air is used to temper the mix to the correct temperature. Secondly, if the recoup gas temperature falls below the specified temperature, the air requirement by the second drying zone is satisfied, but not the heat content. Thus, the correct mass of air is moved through the duct, but with insufficient heat to match the simulated conditions. In this case, the program calculates the additional heat required and labels it as a heat imbalance. As long as this value remains less than 5% of the total system fuel input, the balance is considered an acceptable simulation that can be attained in the plant. Any 3

test condition that produced an imbalance in excess of 5% was considered to have insufficient heat recovered in the cooler to meet the demand of the secondary drying zone. This represents an unattainable plant condition. The 5% limitation is an arbitrarily chosen value. In such cases, the pot-grate series was repeated with 

### a lower recoup gas temperature or a smaller area in the secondary drying zone to achieve balanced conditions.

All told, twenty-two series of tests were carried out in the initial phase of the research program. Only the pertinent ones will be discussed here.

RESULTS OF THE TEST PROGRAM Figure illustrates the effect of the secondary drying
zone size on the predicted fuel savings. As can be seen, fuel savings increased as the size of the zone increased. Figure 2 illustrates the relationship between the required gas/solids
mass ratio and the size of the secondary drying zone. In looking at Figure 2, it can be
seen that waste gas fan capacity would be exceeded when the secon- dary drying zone is increased to four or more windboxes in length. The maximum fan flow limit is indicated by the broken lines. ·Also shown is the maximum flow as measured by plant tests. The measured flow rates were lower than the simulated rates due to leaks in the system that could not be accounted for in the bal-
ance.
With the original design (low temp recoup), the plant operated with a preheat gas/solids ratio in the range of 0.8 to 1.0. Based on the experiences at Empire, it was predicted that when in the modified mode, the gas/solids ratio would drop into the range of 0.5 to 0.7. The excess waste gas fan capacity thus created would be used to induce additional recoup flow.

The Phase II machine design included the use of preheat by-pass ducts. These ducts routed kiln exit gas around the preheat zone to the preheat fans, to boost the preheat off-gas temperature to 399

### •c (750•p).The high temperature recuperation system presented an alternative, the replacement of the preheat by-pass duct with a recoup by-pass duct. This duct would direct hot recoup gas to the preheat fans as a replacement for the preheat by-pass system. This alternative presented a means for more efficient utilization of process heat.
The by-pass heat required could also be minimized by making the secondary drying zone as large as possible. By increasing the size of the secondary drying zone, the resultant temperature of the solids entering the preheat zone also increased, and there was a corresponding decrease in the amount of by-pass heat required to boost off-gas temperature. These factors work in unison to reduce the load on the preheat fans, decreasing their power consumption.

As stated earlier, the incorporation of a secondary drying zone utilizing hotter recoup gas should have increased the extent of magnetite oxidation occurring on the grate. The pot-grate tests indicated a relatively minor improvement in oxidation. Reasons for this trend were not clear, although it was felt that the oxidation rate was dependent on both temperature and time at temperature, and that the combinations of conditions tested did not actually vary enough to affect the oxidation cycle. Figure 3 illustrates the effect of magnetite content on predicted fuel consumption with 5% total iron carbonates present in the concentrate. This figure indicates that the machine, when operating in the low temperature recoup mode, was more sensitive to magnetite content than it would be when modified.
The effects of concentrate carbonates on fuel consumption were also examined. Carbonate levels in the plant typically range from 1 to 3% by weight. For these simulations, 5% represented the maximum level expected with future operation. Figure 4 illustrates the effect of carbonate content on predicted fuel consumption for a concentrate containing 80% magnetite.
The test results indicated a maximum fuel savings when the primary drying zone was reduced to three windboxes. However, the subsequent analysis of airflow distribution on the machine demonstrated that the primary drying zone should contain at least four windboxes. If the secondary drying zone equalled or exceeded five windboxes (primary zone <3WB), the induced flow in the recoupduct became too great for the waste gas fans to4

handle. The research program concluded that an even split in the original drying zone of four windboxes each for the primary and secondary drying zones would reduce fuel consumption by 78 MJ/t (75,000 BTU/lt). The alternate configuration was the 5/3 split. This combination was predicted to yield a fuel savings of 62 MJ/t (60,000 BTU/lt). The prime factor in reaching these recommendations was the amount of air to be moved through the re- coup duct. As will be explained shortly, the 5/3 windbox split
was chosen by the plant personnel.

Based on the decision to use the 5/3 windbox split, a series of pot-grate tests evaluated the anticipated effects on grate capacity. These tests measured airflow and pellet strengths at 5%, 10% and 15% increases in the design capacity. By comparing bed temperature profiles and pellet strengths in conjunction with the fan flow constraints, a maximum 9% in-
crease in capacity was considered possible. This information was then turned over to the plant maintenance and production en- gineers for preparing an economic evaluation of the project.

INSTALLATION OF THE SYSTEM

Plant personnel opted for the 5/3 windbox split after studying the findings. They wanted to be sure that the wastegas fans would be able to handle the predicted airflow through the bed and felt that the 5/3 split offered a more reasonable fan load particularly if production was to be pushed. For either split, a major portion of the original recoup duct would be reused. This prevented an additional cost of $300,000 in material and labor.
The installation commenced
on September 13, 1983, with a 24 hour shutdown to blank off both ends of the recoup duct. The plant was allowed to operate without heat recuperation while ductwork construction progressed. All work that could be performed while the plant operated was completed within a 90 day period. In mid November, the plant went down for scheduled maintenance. At this time, the final tie-ins of ductwork and associated equipment were completed.This system has three stainless steel dampers located in the duct inlets to the grate machine. These dampers serve to block the flow of hot air from the cooler during emergency shut-downs to prevent fires in the grate area. The plant with new recoup system started up in January, 1984 wit!)out problem.
PROCESS OPERATING RESULTS

At the end of the 1984 operating year, a fuel savings of 57 MJ/t (55,000 BTU/lt) had been realized. This sav- ings at the fuel rate of $3.15/GJ ($3.33/MMBTU) equates to $0.180/t ($0.183/1t) and an annual savings of $790,000 at 4.39 Mt/yr (4.322 MM lt/yr). In addition, the plant capacity increased by approximately 327,000 t/yr (322,000 lt/yr) from 4.06 to 4.39 Mt/yr (4.00 to 4.322 MM lt/yr). This resulted in a net savings in production costs of $0.65/t or $2,853,500 at the 4.39 Mt/yr production rate. The total indurating power consumption also dropped by 0.98 KWH/t (1.00 KWH/lt) or $52,300 annually in 1984. Figure 5 illustrates the change in fuel con- sumption by comparing 1983 with 1984 operating,conditions. Because of shutdowns in 1983 and 1984, the months in which start-ups occurred have not been included in the plot. Similarly, Fig. 6 compares average monthly production rates for 1983 and 1984. Using the design capacity of 4.06 Mt/yr as the base, production increased by 8.1% in 1984.

PLANT AIRFLOW SURVEYS

Table 3 illustrates the major points in the process where airflow measurements were taken during operation. The simulation compared remarkably well to the actual plant perfor-
mance in 1984. In most instances, actual flows came within 10% of the predicted values. The simulation differed significantly from the actual operation in predicting the recoup gas temperature. When the plant achieved steady-state conditions, recoup temperatures exceeded 788"C (1450"F) at design throughput. The simulation predicted a maximum of 565

### •c (1050"C) for comparable conditions. Operation of the system in 1984 revealed two important limitations in the process. While the predicted rate of recoup airflow was achieved, inplant tests showed that moving more air could further reduce fuel consumption. These tests were conducted because of
excess available heat in the cooler. Since the existing recoup duct was re- used to lower installation costs and gain approval for the project, the5

duct cross sectional area was fixed. Estimates of pressure**dr~ps** and airflow in the duct pr1or to installation concluded that the duct was sufficient in size to handle the volume flow. However, because of the hotter recoup gas temperature and the larger volume of gas available in the cooler, the duct cross sec- tional area became a limiting factor to. flow, particularly at the higher throughput rates.
Since the duct cross sec- tional area was fixed, the only other means available to increase flow was to increase the pressure differential on the duct. The plant tests mentioned above demonstrated the impact of pres- sure differential on flow and fuel consumption. By doubling the pressure differential from 310 Pa to 620 Pa (1.25 to 2.5 in H20), an approximate 23% in-
crease in gas flow was gained, which decreased fuel consumption by an additional 26 MJ/t (25,000 BTU/lT). Data from these tests are shown in Table 3 under the heading of high suction tests. These tests demonstrated the need to move the maximum amount of air through the recoup duct. It should be noted that production rate significantly affected the pressure differential on the duct. The plant process fans could achieve the 620 Pa differential at design capacity, but as throughput exceeded this rate, the differential decreased.
The second limiting factor
was grate casting temperature. Since the pellet bed was hotter and the preheat zone retention time remained constant, casting temperatures began to climb. The only way to maintain an acceptable casting temperature was to cut back on the preheat fan flow. When this was done, the kiln frequently became dusty. It was thought that this action resulted in excessive amounts of underfired pellets near the bottom of the bed. Process operators chose to limit the recoup gas temperature to 677"C (1250"F) to alleviate this problem. However, to achieve this temperature, additional tempering air was required which displaced air from the cooler forcing larger volumes of air up the cooler stack.

A correct proposalproposal •11as made these situations.

considered making to The thepreheat zone smaller by increDsing the size of the secondary drying zone. The objective was to limit the retention time in the**p~eheat** zone so that the preheat fans could be opened up more without burning up the castings. At the same time, the capacity of the waste gas fans would be increased 7% by changing fan wheels to increase the gas flow through the recoup duct. An increased flow would lower the average recoup gas temperature while recovering more heat from the cooler. Also, since the preheat zone size would be decreased, the primary cooling zone would be scaled down to balance it, limiting flow through the kiln to that required in the preheat zone. This move would shift more heat into the secondary cooling zone which the larger fans
were expected to handle. Pot-grate testwork on this program was carried out in the early spring of 1985.
Five series of pot-grate tests were performed to evaluate the enlargement of the secondary drying
zone. Again, computer simulated heat and mass balances were performed on the pot-grate data. The five series
were comprised of three series at the original design capacity and two series at a higher production level. The wall separating these zones would onlybe moved above the grate. Moving the wall would allow the preheat fans to exhaust either one or two windboxes of the secondary drying zone. The last two test series generated dat-a for heat balances at a 20% production increase from design capacity for both of the proposed windbox splits. This increase was chosen on the basis of plant performance in 1984. It actually represented a maximum feed rate that could be attained in the plant under optimum conditions, but generally not held for more than 24 hours.

1985 TEST RESULTS

Since the decision was made to increase the size of the waste gas fan wheels, the heat and mass balances
were evaluated on the predicted capabilities of the fans. The 5/4/5 windbox configuration was chosen as the better of the two modes tested. The simulations at design capacity indicated that both modes would perform equally well. However, the amount of air required to be moved through the recoup duct increased significantly with each additional windbox in the secondary drying zone. This trend is illustrated in Fig. 7; also shown is the original operating fan flow range for this duct as well
as the predicted maximum limit. 6

These simulations clearly indicated that the 5/5/4 configuration placed too much dependence
on the waste gas fans to exhaust this zone, particularly at high capacity. The simulations predicted a maximum fuel savings of 46.7 MJ/t (45,000 BTU/lt).
Another simulation was car- ried out using a model developed by Dr. Mark Cross, a consultant to the M. A. Hanna Company. This simulation investigated decreasing the size of the primary cooling zone to match air flow in the kiln withthe reduced requirement of the preheat zone. It was concluded that the wall could be moved two windboxes. This move would fit into place with the other modifications that were being recommended. It would shift more air and heat into the secondary cooling zone which would be exhausted into the recoup c1uct by the larger waste gas fans.

In the 1984 high-suction plant tests conducted at low tonnage rates, the differential pressure on the recoup duct was increased from the typical 248 Pa (1 in H20) to 620 Pa (2.5 in H20). These tests were intend-
eo to simulate the effects of the larger fan wheels. They demonstratec1 that fuel consumption could drop by as much as 26 MJ/t (25,000 BTU/lt) c1epending on plant conditions. Figure 8 illustrates the impact of differential pressure on measured flow in the recoup duct. Figure 9 plots the impact of recoup gas flow on overall fuel consumption. this figure includes the results of simulations made in 1981, 1982 and 1985 and the corresponding plant data. It should be noted that modifications were made to the computer program in 1984 in order that the 1985 simulation
more closely approximate the 1984 plant data. However, as can be seen, the plant data for 1985 appears to fall into a region of its own. The reason for this will be explained shortly.
1985 PLANT PERFORMANCE

In April 1985, the plant went down for scheduled mainten-
ance. Special tasks included installing the new waste gas fan wheels, moving the preheat zone baffle wall one windbox into the preheat zone, and moving the primary cooler curtain wall two

### windboxes into the primary cooling
zone.
Plant operation started on April 28, 1985 \'lith the new system. Comparing plant operation in 1985 with 1984 results indicated a fuel savings of 10 MJ/t (9600 BTU/lt) was achieved. This represents a $.0314/t savings or an annual savings of $146,100 at the 4.65 Mt/yr production rate achieved in 1985. This production rate represents an increase of 6% over the 1984 production rate and a 14.5% increase from the design capacity of 4.06 Mt/yr. Power consumption in the pellet plant was reduced by an additional 3.94 KWH/t (4 KWH/lt). The total savings projected for the 1985 production rate was $3,545,000 based on the decrease in fixed costs per ton of pellets.
The predictions for fuel savings indicated a potential for up to 72 MJ/t (70,000 BTU/lt). Airflow surveys made in May and June identified the probable
reason for not fully achieving the predicted fuel savings. Apparently, the cooler wall was moved too far, shifting more heat and air into the secondary cooling zone than could be recovered via the recoup duct. Refering to Table 3, one can note the significant difference in cooler stack flow when comparing the 1985 plant results to the 1985 predicted flow data
or to the 1984 high suction plant test results. Also, one should note the significant increase in the recoup tempering air used to bring the recoup gas temperature to set-point in the recoup duct.

As more tempering air is injected into the recoup duct under a constant flow condition, less air can be recovered from the secondary cooling
zone. Tempering air displaces hot gas from the secondary cooling zone resulting in an increased flow up the cooler stack. This is the reason why the 1985 data shown in Figure 9 did not achieve the predicted fuel savings. Although the total flow in the duct was increased, the amount of heat and air recovered from the cooler decreased. If the tempering air were subtracted from the 1985 plant results in Figure 9 and the data replotted, the 1985 re- sults would be shifted over into the 1984 operating range. Figure 10 illustrates the relationship for airflow under approximately constant pres- sure differential and temperature conditions. The cooler modification made in 1985 resulted in a net decrease in cooler air recovered in the recoup duct when compared to similar operating conditions in 1984. Plans are currently underway to move the cooler 

### 7

wall back one windbox in the hopes of correcting this situation.
CONCLUSIONS
Taken as a whole, using 1983
as the base year, the modifications have:
1. Decreased fuel consumption by 63 11J/t, a decrease of 14% 

### 2. Increased throughput by 589,000 t/yr, a 14.5% increase over the rated capacity. 

### 3. Decreased pellet plant power consumption by 4.92 KWH/t,
a 17.9% decrease.
ACKNOWLEDGEMENTS
The authors wish to acknowledge the contribution of Msrs. G.F. Dolinar, R.D. Frans, J.S. Wakeman, and T.M. Wolke to the program.
REFERENCES
1. Skoronski, G.J. and Woida, L.J., "Recent Design and Improvements in the Grate Kiln System" presented at the SME-AD1E Fall Meeting, Salt Lake City, October, 1983, Preprint No. 83-355

## Table 1

NSPC**He~t** 

## Recuperation Program: Grate Cycle Test Conditions

Windbox Splits Inlet Gas Temp,oC Product 001/002/PH 001)002/PH t/Hr

Base Case

- Original Machine

8 - 0 - 6 398-NA-1038 525 8

- 0 - 6 343-NA-1038 525 8

- 0 - 6 398-NA-1038 593 8 - 0 - 6 343-NA-1038 593

High Temperature Recoup Conditions

3 - 5 - 6 343-565-1038

4 

## - 4 - 6 398-565-1038 4 

## - 4 - 6 343-593-1038 4 - 4 

## - 6 343-538-1038 4 

## - 4 - 6 343-510-1038

5 - 3 - 6 343-621-1038 5 - 3 - 6 343-56.5-1038 5 - 3 - 6 398-565-1038 5 - 3 - 6 398-565-1038 5 - 3 - 6 398-565-1038 5 - 3 - 6 343-538-1038

6 - 2 - 6 

## 343-648-1038 6 - 2 - 6 343-593-1038

001

- first downdraft drying zone 002

- second downdraft drying zone PH

- preheat zone NA

- not appropriate 525

525 525 525 525

525 525 593 572 551 525

525 525 Rate

### 9

Table 2

Data Input Required by SimulationProgram

1. Mass of dry pellets in pot firing.

2. Mass of water contained in pellets.

3. Percent weight magnetite in pellets.

4. Percent weight carbonate in pellets expressed as,

a. percent Ankerite, Ca(FeMg)(C03)2 b. percent Siderite, FeC03

5. Percent weight silicateminerals.

6. Percent of total water removed in each drying zone.
7. Estimated temperature of moisture remaining in pellets after first drying zone.
8. Percent of total magnetite oxidized in each zcne including kiln and cooler.

9. Ambient air humidity, mass water/unit mass dry air.

10. Averaged pellet bed temperature at end of each zone on grate.
11. Averaged off-gas temperature at end of each zone on grate.
12. Inlet gas temperature in each zone on grate.
13. Kiln exit gas temperature (assumed equal to preheat zone inlet gas temp).

14. Estimated solids discharge temperature from kiln.

15. Simulated production rate.
16. Averaged casting temperature by zone on grate.
17. Type of fuel to be used in simulation; i.e, coal, gas or oil.

### 10 Table3
ComoarisonofSimulatedGasFlowwithPlantMeasuredFlows



## *

Kiln



### * 1985Wa11 Locations

Simulated Actual 1984 High Simulated AirflowMeasurement 1984 1984 Suction 1985 (IncludesWaterVaoor) Conditions Operation Ooeration Conditions

T

•

### "l'asteGasFans G/S 1.7082 1.6161 1.7240 1.5396 Kg/Min 14951 14649 15627 13475 

## •c 93 119 130 52
2.PreheatFans G/S 1.0222 0.6946 0.5472 0.7049 Kg/Min 8947 6296 4959 6169 

## ·c 343 388 393 372
3.TotalFlcr.r G/S 0.5391 0.4810 0.5942 0.6470 RecoupDuct Kg/Min 4718 4360 5385 5663 

## ·c 537 788 800 678 

## " RecoupTempering G/S 0 0.0737 0.0399 0 

# ... Air Kg/Min 0 668 361 0
5.RecoupBy-PassAir G/S 0 0.0601 0.0207 0.1025 Kgfttin 0 545 259 897 

## •c 0 788 800 678

6.PrimaryCoolingAir 

### G/S 0.7034 0.5776 0.4944 0.4440 Kg/Min 6156 5235 4482 3886

7.

### SecondaryCoolingAirG/S 0.7740 0.8825 0.7500 0.9003 (IncludingRecoup Kg/Min 6774 7727 6798 7880 TemperingAir)

8.CoolerStack G/S 0.2351 0.3851 0.0888 0.2530 Kg/Min 2057 3490 804 2214 

## •c 270 332 173 293

9.ProouctionRate t/hr 525 544 544 525

G/S Refersto9as:solidsmassratio. 8



### Actual 1985 Operation
1.8239

17624

129
0.7226

6449

388
0.6157

5950

793
0.1550 1497
0.0279 269 793
0.5978

5773
1.0558

10249

0.4199

4056

354

580

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## 70



# 60

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20

10 ProductionRate525.mt/hr RecoupGasTemp538..;565C

## 0~----------------.----------------r--------------~ 

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WindboxesinSecondaryDryingZone .....



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# ..... (/) 

## 0.75



# 0.7

0.65

0.6

ct1

### ~**~'**

## 0.55 0



## ...... (/)

### ~"0 '"d 

## :=: 

## 0.5 d) 

### 0

. () (/) 

### :;j' 

### '"d (/)**~** ct1 

## 0.45 H<.!J



# 0.4

0.35 ProductionRate525mt/hr RecoupGasTemp538-565C

-------- MaxPlantFlowpriortoModification



## 2 

## 3 MaxSimulatedPlantFlow



## 4


## WindboxesinSecondaryDryingZone 5**/~.** 

### ....... N

# FIGURE 3

EFFECTOFMAGNETITEONFUELCONSUMPTION 

# 520

510



# - +) 

# a 500**~** )! 

# 490


# -**~** 0 

# 480 •1"'1 +) 

### p. 

# a 470



# ------- ------- I ..... 

# I w 

## ::;; Ul

### ~ 

# 460 0 ()

1"""1 

# 450 Q) 

## ::;;**~** 

# 440
"0 Q) 

# 430 ...,; 0 ·1"'1 

### "0 

# 420 Q) 

### 1-4 

# n.. 410 --t 

### ProductionRate525mt/hr


# 400 RecoupGasTemp538-565C

I I 

# 75**~** 

# 80 85

PercentWeightMagnetiteinConcentrate

# FIGURE 4

EFFECTOFCARBONATE ONFUELCONSUMPTION 

## 510


# 500



# - -+) 

# 490 

# s**~** 

# 480**~** 

# .._...**~** 

# 470

0 •r-1 

# 460 .j.J 

## Po. 

# s 450

# l



# ----- -------' 1-'

### ~**~** {I) 

# 440 d 0 C) 

# 430
.-4 cl)

### ~ 

## 420 f;L. 

### "d 

## 410 (1) -+) 

### 0 

## 400

...... "d cl) 

# 390 J.c 

## P-e 380

# ~ ProductionRate525mt/hr RecoupGasTemp538-565 

## 370



# . . . 1 3 

# 5 7

PercentWeightCarbonateinConcentrate



# --

# 550 540



# - 530 

# ...., 

# s 520**~** 

# 510**~**



## ........ 

# 500**~** 

# 490 0



# ..... 480 .j.) 

### Ill 

# s 470 ;j 

# 460 Ul 

## Q 

# 450 0 

# u 440

...-1 Q) 

# 430 ::1**~** 

# 420 l>l 

## 410 ...-1 

### ,.d 

## 400 +'**~** 

# 390 0

### ~ 

# 380



# . Q) 

# 370 p. 

# < 360 350



# . JAN 

# FIGURE 5

AVERAGEMONTHLYFUELCONSUMPTION

# ~ 

# : '8**~** (ij 

# i () 

# 8- 

# 1**~**



## FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

0 

# 1984 OperatingMonth 

# + 1983 0 

# 1985 1-' U1

## 450



# - 440
....,>**-~** 

# 430
...._, s:1 

# 420- 0 •1""1 

### +' 

# 410 0

### ~ 

### "d 

# 400 0 

### M 

## Ill 

# 390 +' Q) 

## 380 ...-1



## ...... Q) 

## 370 

# n..**~** 

# 360 

# ...-. 

# ..ct +> 350**~** 0

### ~ 

## 340
Q) 

## 330 ttl)**~** 

### H 

# 320 d> 

## I>**~** 

## 310

300



# . JAN 

# FIGURE 6

AVERAGEMONTHLYPELLETPRODUCTION

FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

0 

# 1984 OperatingMonth 

# + 1983 <> 

# 1985 

# ..... 0'1

## 0.74

0.72



# ...., 0 

## 0.7 

# ::s AI"""\ p.

## ~- 0.68 

# p ' 

# g**~** 

## 0.66 11) '-'

### ~ 0 I

## 0.64**~** 

## ·.;:::

....**~** 

## 0.62

. G)

# ~**~** 0.6

(tj ctJ

## ~ 

## ::2!.

## 0.58**~** C/) 

# .9**~** 

## 0.56**~** 

# 0
ret**~** 

## 0.54
(\.) C/)

...., ctJ

### .~ 

## CJ 

## 0.52 "0 Q) 

## 0.5 Jot**~** 

## 0.48

0.46

I 

## 2 

# FIGURE7

EFFECTOFDRYINGZONE SIZEONGAS FLOW

MaxEstimatedFlowRange withNewFanWheels(1985)



## 3 4OriginalFanWheel FlowRange(1984)

ProductionRate525mt/hr RecoupGasTemp677C



## 5


## WindboxesinSecondaryDryingZone 6 ......

........

# FIGURE 8

RECOUPFLOWVSPRESSUREDIFFERENTIAL**0.6~------------------------------------~~--------~** 

## 0.59

Q) 

## 0.58 b.&

# ~ '"""' 0.57 Q)

# ~**~** 0.56**~** Q)

### ~**~** 

## 0.55 

# rx.c'-'**~ .~**  

# 0.54 

# g**~**'0.53 ()

## ~**~** 

# 0.52
ctS

### ~ 

## 2: 

# 0.51 It! C/) .-1 

### '0 

# 0.5 A-4

# = 'd

## ~

## '0.49 d)

...... 

# 5 C/) 

## 0.48
Cl} ctS 

### It!-

### CJ 

## 0.47 11)

## ~ 

## 0.46
0.45 ProductionRate525mt/hr RecoupGasTemp704-873C 

# 0.44**,_~.---.--.---.---.--.---.---.-~--~--~--~--~~--~--~** 

## 300 

# 340 380 420 

## 460 

# 500 

# 540 580 

# 620

Diff.PressureAcrossRecoupDuct

## CPa) t-> 

### co

# 480 470 460 450



# - 440 +> 

# s 430

# ~**~** 

# ._... 

# 420**~** 

# 410 0 

# :p 400 At 

# s 390 

# p 380 00

### ~ 

### 0 

# 370 C)

r-1 

# 360 4)

### ~ 

# 350**~** 

# 340 330 320 310

I 

# 0.3 ,96**~.b** 

# FIGURE 9

EFFECTOFRECOUPFLOWONFUEL



# 'se,

...19e
11.

# ~lflgh

## 1':



## lleollpG'*" ""'Plieeo,P

.1" 

## ""'Pli7

# o~6.,98~11/'*tlo,a**~**

## ~.

# 'q'o**e~ ~e~** 

# 0~**~~**

# 199**~** ' /Jjlll)t

## 0



# 0.35

# QQ)~**~~**

# ~**II?~~ ~.0**  4.9 

# >o

0.4- "r, 

## <9.> .a()



# 0.45 0.5 lieeollpGea

## 'P:.,.'*t/,9lili/J9e

# ~?'Bac

0.55 0.61985 Simulationswith shortenedPreheatZone RecoupGasTemp732C

## ~**~** 

# 0.65 0.7 Recoup Flowfrom SecondaryCoolingZone Gas/Solids Mass Ratio (Kg/Kg) 

# 0.75 1-' U)

# FIGURE 10

RECOUPTEMPERAIRVS FLOWFROM COOLER 0.19

# --r---------------------L--------,

0.18
0.17

r-. 

## 0.16 Ol

# ~ 0.15 J.t Ol 

# :<**~** 0.14
t..J

# ~**.~** 0.13

...... +"" l-4 

# m d) 

# cc 0.12**~** 

# s**~** 0.11 d) «S

### ~**~** 

## 0.1 PI CJ) 

## :J "0 

## 0.09 0 0 0 

## 008 Q) (J) •

### ~

# ~ 0.07 «S (j 

## 0.06
0.05


## 0.0·1- ProductionRato525mt/hr RecoupGasTemp732C PlantMeasurements 

# & 1985 

# m 1984



## 0.03 

# I I I I I I I I I I I I I
., 

## 0.42 0.44 0.46 0.48 

# 0.5 0.52 RecoupFlowfrom SecondaryCoolingZone 

## Gas/Solids Mass Ratio (Kg/Kg) 0.54 N 0