MINNTAC AGGLOMERATOR 

SULFUR BALANCE 

Coleraine Minerals Research Laboratory 

June 21, 1994 

Natural Resources Research Institute 

University of Minnesota, Duluth 

5013 Miller Trunk Highway 

Duluth, MN 55811 

By: Un~ .c f" John 'Engser Scientist 

Approved by:~~~L~ .:> Ro y L. Bleif ss 

Assistant Director 
1 

I 

TABLE OF CONTENTS 

INTRODUCTION ..................................................... 1 

TEST PROGRAM AND PROCEDURES ...................................... 1 

Sampling .................................................... 1 

Analytical Procedures ....................................... 2 

Sulfur Balance .............................................. 2 

DISCUSSION OF RESULTS ............................................ 3 

Acid Pellet Production Tests ................................ 3 

Natural Gas Line 6 Test .................................. 4 

Natural Gas Line 4 Tests ................................. 4 

Wood-Natural Gas Line 4 Tests ............................ 4 

Fluxed Pellet Production Tests .............................. 5 

Natural Gas Test ......................................... 5 

Coal-Natural Gas Tests ................................... 5 

Induration Sulfur Sources ................................... 6 

Green Ball Sulfur ........................................ 6 

Fuel Sulfur .............................................. 7 

Pellet Sulfur ............................................... 7 

Sulfur Removal by the Scrubber .............................. 8 

Atmospheric Sulfur Emissions ................................ 8 

CONCLUSIONS ...................................................... 9 
Number 

1 

2 

3 

4 

5 

6 

7 

Number 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

List of Tables 

Title 

Minntac Taconite Pellet Induration Sulfur Balance. ~nntac Taconite Pellet Induration Sulfur Balance. 

~nntac Agglomerator Samples - Fluxed Pellet Production. 

Minntac Agglomerator Samples - Acid Pellet Production. 

Sulfur Sources in Green Balls - Fluxed Pellet Production. 

Sulfur Sources in Green Balls - Acid Pellet Production. 

Minntac Agglomerator Feed Rates, Recycle Rates, 

Production Rates and Fuel Usage Rates. 

List of Figures 

Title 

Sulfur Balance Acid Pellet Production Line 6 Nov 3, 1993 

Sulfur Balance Acid Pellet Production Line 4 Mar 30, 1994 

Sulfur Balance Acid Pellet Production Line 4 April 12, 1994 

Sulfur Balance Acid Pellet Production Line 4 April 13, 1994 

Sulfur Balance Acid Pellet Production Line 4 April 1, 1994 

Sulfur Balance Acid Pellet Production Line 4 April 4, 1994 

Sulfur Balance Acid Pellet Production Line 4 April 11, 1994 

Sulfur Balance Fluxed Pellet Production Line 6 Mar 11, 1994 

Sulfur Balance Fluxed Pellet Production Line 6 Mar 15, 1994 

Sulfur Balance Fluxed Pellet Production Line 6 Mar 16, 1994 
INTRODUCTION 

The production of sulfur dioxide during the induration of taconite pellets is an 

environmental concern. The sulfur is introduced into the firing process through the 

taconite concentrate, the fluxstone, the bentonite clay, the water in the green balls, and 

the fuel. Mr L. Salmela of USX-Minntac, requested that the University of Minnesota -

Coleraine Minerals Research Laboratory (CMRL) perform induration-sulfur balances 

during the production of fluxed pellets and acid pellets while natural gas, coal and wood 

were being used as the induration fuels. 

TEST PROGRAM AND PROCEDURES 

The scope of the program involved sampling and analysis of all the feed streams entering 

the induration process. It also involved sampling and analysis of the emission (waste) 

gas and water streams exiting the induration process and the final pellet product. The 

feed streams that were sampled during acid pellet production included taconite green 

balls, fuel (coal or wood), filtrate water, scrubber feed water and bentonite clay. Feed 

streams sampled during fluxed pellet production included taconite green balls, fuel (coal 

or wood), filtrate water, scrubber feed water, bentonite clay and fluxstone slurry. Samples 

of the scrubber exit water were taken during each test. The waste gas entering the 

scrubber and the waste gas exiting the scrubber were continuously analyzed for sulfur 

dioxide, oxygen, carbon dioxide and carbon monoxide using CMRL's self contained 

emission monitoring trailer. Minntac personnel performed pitot-traverse tests to determine 

the emission gas flows for each test. The natural-gas fuel was not sampled or analyzed. 

The two recycle streams that are present in the process are the green ball recycle and 

the chip regrind recycle. The green ball recycle stream was not sampled. This recycle 

stream is removed from the feed before any volatilization or oxidation of the sulfur can 

take place and therefore should contain the same quantity of sulfur as the green balls. 

The chip regrind recycle was sampled and analyzed. Chip regrind pellets are pellets that 

have been dried and partially fired in the preheat zone and therefore, could contain a 

different amount of sulfur than the green balls. 

Sampling. All of the green ball, chip regrind, fluxstone slurry, bentonite, water, pellet, and 

fuel samples were grab samples. The emission gas sampling and analysis was perform 

by the analytical instrumentation in the analytical trailer. Analytical readings were taken 

and recorded by a computer every 3 minutes. The emission gas was pumped into the 

gas analysis trailer through a 200 foot long heated umbilical cord. The temperature of 

the umbilical cord was maintained at 180 degrees Fahrenheit so that moisture would not 

condense during the transfer of the emission gas to the analytical instruments. When the 

emission gas entered the analytical trailer, it was split into 2 gas streams. One stream 

was diluted 1 in 10 and analyzed for sulfur dioxide; the second gas stream was dried and 

1 

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analyzed for oxygen, carbon dioxide and carbon monoxide. The em1ss1on gas that 

entered the scrubber was analyzed for moisture on four separate occasions to ensure 

that the calculated moisture that was being used for molecular weight calculations was 

correct. Emission gas flow measurements were performed by Minntac personnel using 

standard pilot-traverse techniques. 

The recycle rate of the green ball recycle stream was taken from the computer readouts 

of belt scales. This number was usually 7 to 9 percent of the feed value. The recycle 

rate of chip regrind was estimated by timing the quantity that fell off the chip regrind belt 

into a bucket and then weighing that quantity. 

Scrubber water flow rates were determined from the water pump settings. 

Analytical Procedures. The analysis of the sulfur in the wood and coal was performed 

on a Dohrmann DX-20A with a T-631 Sulfur Cell. In this system. the sulfur is oxidized 

in a oxygen stream at 1000 degrees Celsius. The off gas is bubbled into an iodide-iodate 

solution and the quantity of sulfur dioxide in the gas stream is measured 

potentiometrically. NIST Certified Coal Standard 1632b was run with each set of 

samples. 

The sulfur analysis of the water samples was performed on a Fison Inductively Coupled' 

Plasma (ICP) Spectrometer Model 3410 using standard ICP procedures. The samples 

were oxidized with hydrogen peroxide addition and acidified with nitric acid prior to 

analysis. Sodium sulfate, reagent grade. was dissolved in dilute nitric acid. This solution 

was used as the standard stock solution. 

The sulfur analysis of the green ball samples. the chip regrind samples, and the pellet 

samples was performed by using an oxidizing-acid dissolution and then analyzing the 

resultant solution on the Model 3410 ICP using standard ICP procedures. Certified 

standards were run with each set of samples. 

The oxygen analysis was performed with an infrared analyzer on the dried portion of the 

emission gas stream. The carbon dioxide and carbon monoxide analyses were 

performed with a dual C02 - CO infrared analyzer on the dried portion of the emission 

gas stream. The sulfur dioxide analysis was performed with an ultraviolet instrument. 

The gas that entered the sulfur dioxide analyzer was a 1 in 10 dilution of the original gas 

that entered the analytical trailer. The dilution was performed to ensure that no moisture 

and therefore, no sulfur dioxide was lost. Certified gas obtained from Matheson Gas 

Products was used to calibrate each analytical instrument. 

Sulfur Balance. The total quantity of sulfur (pounds/hour) that entered the induration 

process was determined from the sulfur analysis of the green balls, the green ball feed 

rate, the sulfur analysis of the fuel, and the fuel usage rate. The natural gas contained 

an insignificant amount of sulfur. The amount of sulfur (pounds/hour) that was recycled 

2 
was determined from the sulfur analysis of the green balls, the green ball recycle rate, 

the sulfur analysis of the chip regrind, and the chip regrind recycle rate. The recycled 

sulfur was subtracted from the total quantity of sulfur that entered the induration process. 

This difference was the total sulfur (pounds/hour) available for oxidation during induration. 

The concentration of sulfur dioxide (ppm) in the emission gas stream that entered the 

scrubber was measured in the analytical trailer. The total quantity of ott gas that exited 

the induration process was determined by performing pilot-traverse tests. The molecular 

weight of the emission gas was calculated from the gas analysis. By using the pilottraverse test data, the molecular weight of the emission gas and the sulfur dioxide 

concentration, the total quantity of sulfur (pounds/hour) that exited the induration process 

was determined. The amount of sulfur that remained in the pellet product was 

determined by subtracting the amount of sulfur that exited with the emission gas prior to 

the scrubber from the quantity of sulfur available for oxidation. The quantity of sulfur in 

the pellet product was verified by sulfur analysis of the pellet product. 

The amount of sulfur (pounds/hour) that entered the atmosphere (scrubber exit gas) was 

calculated from the pilot-traverse data, the calculated molecular weight of the emission 

gas stream, and the sulfur dioxide concentration (ppm) of the emission gas stream that 

exited the scrubber. The sulfur dioxide concentration of the emission gas was measured 

in the analytical trailer. The sulfur dioxide concentration of the emission gas was verified 

by scrubber water sampling. The verification of the sulfur dioxide concentration in the 

emission gas stream was performed by calculation using the scrubber flow rate data, the 

scrubber inlet water sulfur analysis and the scrubber exit water sulfur analysis. 

The sulfur content of the green ball, bentonite clay, fluxstone, and process water were 

determine by chemical analysis. The sulfur in the taconite concentrate was determined 

by subtracting the sulfur concentration of the fluxstone, bentonite clay and water from the 

total sulfur in the green ball. The sulfur concentration in the taconite concentrate could 

not be obtained by direct sulfur analysis because residual sulfur from the water remained 

with the concentrate when the concentrate sample was filtered and dried. The residual 

sulfur from the water would then erroneously be analyzed as sulfur in the taconite 

concentrate. 

DISCUSSION OF RESULTS 

Acid Pellet Production Tests 

Seven tests were performed during acid pellet production. Four tests were run while 

natural gas was being used as the indurating fuel and three tests were run when wood 

and natural gas were being used in combination as the fuel. 

3 
Natural Gas Line 6 Test. The first test was performed during November of 1993 on 

agglomerator line 6. The emission gas that entered the scrubber was sampled on 

November 3rd and the emission gas that exited the scrubber was sampled on November 

4th. The waste gas flows increased slightly from the 3rd to the 4th. No solid samples 

or water samples were taken during this test and the quantity of sulfur in the green balls 

was calculated from the gas analysis and recycle data. The green ball feed rate was 510 

long tons per hour. The scrubber removed 26 percent of the sulfur from the emission gas 

stream. The test data are given in Tables 1 and 2. The feed rates and recycle rates are 

given in Table 7. The sulfur balance for this test is illustrated in Figure 1. The amount 

of sulfur that entered the kiln was 120 pounds per hour and the amount of sulfur emitted 

to the atmosphere was 43 pounds per hour. Fifteen pounds of sulfur per hour was 

removed by the scrubber. 

Natural Gas Line 4 Tests. The remainder of the natural gas tests were performed on 

agglomerator line 4. The line 4 tests were run on March 30. 1994, April 12, 1994 and 

April 13, 1994. The test data are given in Tables 1 and 2. The feed rates and recycle 

rates are listed in Table 7. The green ball feed rates ranged from 480 long tons per hour 

to 605 long tons per hour. The amount of sulfur that entered the kiln ranged from 126 

pounds per hour to 142 pounds per hour. The scrubber removed from 46 percent to 60 

percent of the sulfur from the emission gas stream. The amount of sulfur emitted to the 

atmosphere during these tests ranged from 45 pounds per hour to 59 pounds per hour. 

These three tests are illustrated in Figures 2, 3 and 4. 

The line 4 scrubber is more efficient in removing sulfur from the emission gas stream than 

is the line 6 scrubber. The line 4 scrubber removes approximately twice as much sulfur 

as the line 6 scrubber. There are two obvious reasons for this increased efficiency. First, 

the line 4 scrubber has a higher scrubber-water flow rate than the line 6 scrubber, 3400 

gallons per minute and 2650 gallons per minute respectively. Second, the line 4 scrubber 

was installed at a later date and has a slightly different des1gn. 

Wood-Natural Gas Line 4 Tests. Three tests were performed when wood was being 

used in combination with natural gas as the indurating fuel. These wood-gas tests were 

run on April 1, 1994, April 4, 1994, and April 11, 1994. Two tests were run with 25 

percent of the heat input coming from wood and one test was run with 40 percent of the 

heat input coming from wood. The green ball feed rate ranged from 440 long tons per 

hour to 605 long tons per hour. Feed rates and recycle rates are given in Table 7. The 

quantity of sulfur that entered the kiln ranged from 137 pounds per hour to 195 pounds 

per hour. The scrubber removed from 57.2 percent to 76.5 percent of the sulfur from the 

emission gas stream. The total amount of sulfur that was emitted to the atmosphere 

during these three tests ranged from 28 pounds per hour to 43 pounds per hour. The 

data for these tests are given in Tables 1 and 2. The tests are illustrated in Figures 5, 

6, and 7. 

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The scrubber data indicate that when 25 percent wood was used, the scrubber removed 

approximately 60 percent of the sulfur. When the wood was increased to 40 percent of 

the indurating fuel, the scrubber removed about 76 percent of the sulfur. This increased 

scrubbing efficiency is probably due to the chemistry of the wood ash. Wood ash is 

usually high in calcium oxide, which will react with the sulfur dioxide in the emission gas 

stream forming calcium sulfite. The resulting calcium sulfite will then be removed by the 

scrubber. Other oxides in the wood ash will also react with the sulfur dioxide forming 

water soluble sulfites. 

The line 4 scrubber removed an average of 52 percent of the sulfur when all of the fuel 

was natural gas. The average sulfur removal increased to 65 percent when wood-natural 

gas was the fuel. 

The average sulfur analysis for the wood is given in Table 4. The quantity of sulfur 

introduced into the process by the wood was 2 to 4 pounds per hour. This is less than 

3 percent of the total sulfur that entered the induration process. 

Fluxed Pellet Production Tests 

Three tests were run during fluxed pellet production on line 6, one with natural gas as the 

fuel and two with coal-natural gas in combination as the fuel. During the coal-natural gas 

tests, all of the kiln fuel was coal and all of the preheat fuel was natural gas. 

Natural Gas Test. The fluxed pellet test with natural gas as the fuel was run on 

March 11, 1994. The test data are listed in Tables 1 and 2. The feed rates and recycle 

rates are given in Table 7. The green ball feed rate was 550 long tons per hour. The 

total amount of sulfur that reported to the induration process was 163 pounds per hour. 

The line 6 scrubber removed 50 percent of the sulfur from the emission gas stream. The 

amount of sulfur that was discharged to the atmosphere was 46 pounds per hour. The 

sulfur balance is illustrated in Figure 8. 

As mentioned earlier, the line 6 scrubber removed 26 percent of the sulfur during acid 

pellet production with natural gas as the indurating fuel. This increased to 50 percent 

removal during fluxed pellet production. This increase in scrubber efficiency is probably 

due to the reaction that occurs between the sulfur dioxide and alkaline oxides that are 

present in the induration dust. The sulfur dioxide in the emission gas reacts with these 

oxides forming calcium sulfite and magnesium sulfite which are then removed by the 

scrubber. The calcium oxide dust also aids in neutralizing the hydronium ion 

concentration of the scrubber water. thus increasing the solubility of the sulfur dioxide in 

the water. 

Coal-Natural Gas Tests. Two fluxed pellet tests with coal-natural gas as the fuel were 

performed on line 6. The tests were run on March 15, 1994 and March 16, 1994. The 

green ball feed rate for both tests was 550 long tons per hour. The feed rates and 

5 
recycle rates are given in Table 7. The total amount of sulfur that reported to the 

induration process was 224 and 230 pounds per hour lor the two tests. The line 6 

scrubber removed about 50 percent of the sulfur from the emission gas stream during 

both of these fluxed pellet tests. The average quantity of sulfur that was discharged to 

the atmosphere during the March 15 test was 81 pounds per hour. During the March 16 

test, the average amount of sulfur that was discharged into the atmosphere was 85 

pounds per hour. The data lor these two tests are given in Tables 1 and 2. The March 

15 and 16 tests are illustrated in Figures 9 and 10 respectively. 

The sulfur analysis of the coal is given in Table 3. The quantity of sulfur contributed to 

the process by the coal was 67 pounds per hour. This was about 30 percent of the total 

induration sulfur. 

Induration Sulfur Sources. 

The two main sources of sulfur that entered the induration process were the sulfur from 

the green ball feed and the sulfur from the fuel. 

Green Ball Sulfur. The sulfur in the green balls was the major source of sulfur that 

entered the induration process. When natural gas was the fuel, the green balls 

contributed essentially all of the sulfur that entered the process. During wood firing, the 

green balls contributed about 97 percent of the sulfur. The green balls contributed about 

70 percent of the sulfur to the indurating process when coal was the fuel. 

The sulfur in the acid green balls came from the acid taconite concentrate, the bentonite 

clay and the process water. The amount of sulfur that was contributed by each of these 

constituents is given in Table 5. The quantity of sulfur lor each constituent that is listed 

in Table 5 has been calculated from the analyses of the water and bentonite that are 

found in Tables 3 and 4. The average sulfur concentration in the acid taconite 

concentrate was 0.009 percent. 

The sources of sulfur in the fluxed green ball were the flotation taconite concentrate, the 

bentonite clay, the process water and the lluxstone. The contribution from each of these 

constituents is listed in Table 5. The percent sulfur that was contributed by each 

component was calculated from the analyses of the water. bentonite and fluxstone that 

are listed in Tables 3 and 4. The flotation taconite concentrate contained an average of 

0.007 percent sulfur. 

The main difference between the acid taconite concentrate and flotation taconite 

concentrate was the amount of silica (Si02) that the two concentrates contained. The 

acid concentrate was about 5 percent silica and the flotation concentrate was 

approximately 4 percent silica. Apparently, when the quantity of silica in the taconite 

concentrate was decreased from 5 percent to 4 percent. the amount of sulfur in the 

taconite concentrate was decreased from 0.009 percent to 0.007 percent. However, 

6 
when fluxed pellets were produced, approximately 8 percent fluxstone was added to the 

concentrate. Since the fluxstone contained about 0.05 percent sulfur, the total amount 

of sulfur in the fluxed green balls was about 0.002 percent higher than the sulfur was in 

the acid green balls. 

In the future, the sulfur contribution from the process water in the green ball will continue 

to increase. Taconite contains a small amount of iron pyrite. During the taconite 

processing, the pyrite reports to the tailings and is pumped to the tailing· basin. In the 

basin, the pyritic sulfur oxidizes and hydrates to form sulfuric acid. This acid is 

neutralized by calcium carbonate and magnesium carbonate that are also found in the 

taconite tailings. This oxidation and neutralization is constantly occurring and therefore, 

the concentration of sulfur as sulfate ion in the Minntac process water will increase. The 

concentration of sulfur in Minntac water is increasing at an average rate of 15 parts per 

million of sulfur per year. At this rate, the quantity of sulfur in the green ball will increase 

by about 0.00015 percent per year. This is probably insignificant when compared to the 

variability of the sulfur in the bentonite, fluxstone and concentrate. 

Fuel Sulfur. The amount of sulfur that entered the induration process from natural 

gas was extremely small when compared to the quantity that entered with wood or coal. 

The sulfur analysis of the four wood samples that were taken are found in Table 4. The 

average sulfur analysis of the wood was 0.059 percent. The total sulfur contribution from 

the wood if 100 percent of the induration fuel was wood. would be less than 8 pounds of 

sulfur per hour. This is less than 7 percent of the total sulfur input. 

The sulfur analysis of the two coal samples that were taken are listed in Table 3. The 

average sulfur of the coal was 0. 77 percent. The total sulfur contribution from the coal 

when coal was the only fuel being used in the kiln was 67 pounds per hour. 

This was about 30 percent of the total sulfur input. If the sulfur in the coal was 1 percent, 

the sulfur contribution of the coal would be about 90 pounds per hour. This would be 

about 36 percent of the total sulfur input if the green ball feed rate was 550 long tons per 

hour. 

Pellet Sulfur 

The average calculated percent sulfur in the acid pellet product was 0.003 percent. The 

analyzed average sulfur in the acid pellet product was 0.004 percent. 

The calculated quantity of sulfur in the fluxed pellet product was 0.005 percent. The 

analyzed average sulfur was 0.005 percent. 

These calculated and analyzed sulfur quantities agree very well, which is a good 

confirmation that the sulfur balances are correct. 

7 
Sulfur Removal by the Scrubber 

Two methods were used to determine the rate at which sulfur was removed from the 

emission gas stream. One method determined the sulfur removal rate by using the 

difference between the gas analyses into and out of the scrubber; the other method 

determined the sulfur removal rate by using the difference between the water analyses 

into and out of the scrubber. The gas samples were analyzed every three minutes, while 

the water samples were daily grab samples. The sulfur removal rates for each test using 

both methods of calculation are given in Table 1. The calculated sulfur removal rates 

from both methods are in close agreement. The largest difference between the two 

methods was seen on April 13, 1994. For this date, the average sulfur removal rate of 

the scrubber calculated from the gas analysis was 59.2 pounds of sulfur per hour and the 

rate calculated from the water analysis was 68 pounds of sulfur per hour. This difference 

is within the statistical limits of the test as indicated by the following calculations. The 

standard deviation of the sulfur dioxide analysis into the scrubber was 3.8 ppm. By 

adding the standard deviation (3.8) to the average scrubber inlet gas analysis (47.9) the 

resultant inlet sulfur dioxide concentration is 51.7 ppm. This would result in 126.0 pounds 

of sulfur per hour entering the scrubber and 68.5 pounds of sulfur per hour leaving the 

scrubber. This indicates that the 68 pounds of sulfur per hour that was calculated from 

the water analysis is within 1 standard deviation of the rate that was calculated from the 

gas analysis. 

Atmospheric Sulfur Emissions 

The quantity of sulfur that was discharged to the atmosphere during the 4 acid pellet 

natural gas tests. ranged from 34.8 pounds of sulfur per hour to 57.5 pounds of sulfur per 

hour. The average was 47.1 pounds per hour. During the one fluxed pellet natural gas 

test. 45.5 pounds of sulfur per hour was emitted. The sulfur emitted to the atmosphere 

during the acid pellet test on line 6 was 43.5 pounds of sulfur per hour and during the line 

6 fluxed pellet test the sulfur discharged to the atmosphere was 45.5 pounds per hour. 

During the two coal-fluxed pellet tests, the quantity of sulfur that was released to the 

atmosphere that can be contributed to the fluxed green balls was 50.4 pounds per hour 

and 49.2 pounds per hour. These results indicate that there was approximately the same 

amount of sulfur released to the atmosphere during both acid pellet production and fluxed 

pellet production. Slightly more sulfur entered the induration process dunng fluxed pellet 

proClUction than dunng acid pellet production, however. due to the lime dust that was 

present in the emiss1on gas during fluxed pellet production, the scrubbers removed more 

sulfur than they did during acid pellet production. When coal was used as a fuel rather 

than natural gas for fluxed pellet production, the total amount of sulfur discharged to the 

atmosphere increased by about 80 percent because of the fuel contribution. When wood 

was used as a fuel rather than natural gas, the quantity of sulfur that was discharged to 

the atmosphere decreased by an average of 15 percent. 

8 
CONCLUSIONS 

1. During the production of fluxed pellets, the Minntac line 6 scrubber removed twice 

as much sulfur from the emission gas stream as it did during acid pellet 

production. 

2. When both lines 4 and 6 were producing acid pellets, the line 4 scrubber removed 

about twice as much sulfur from the emission gas stream as the line 6 scrubber. 

3. When 40 percent wood and 60 percent natural gas were used in combination as 

the indurating fuel rather than 100 percent natural gas, the amount of sulfur 

emitted to the atmosphere was decreased by 40 percent. 

4. The green ball constituents contributed from 70 to 1 00 percent of the sulfur that 

entered the induration process. 

5. When coal was being used as the kiln fuel, the coal contributed about 30 percent 

of the sulfur that entered the induration process. 

6. When wood was being used as the kiln fuel, it contributed less than 3 percent of 

the sulfur that entered the induration process. 

7_ Fifty to sixty percent of the sulfur that was in the green ball was contributed by the 

taconite concentrate. 

8. The discharge rate per hour of sulfur into the atmosphere during fluxed pellet 

production and acid pellet production appeared to be about the same when natural 

gas was the indurating fuel. 

9 
Feed Waste 

Rate Fuel Fuel Pellet Test Gas 

line l Ton/hr Type Ratio Type Date lbs/min 

6 510 Gas 100 Acid 11/3/93 28,560 

6 510 Gas 100 Acid 11/4/93 30,360 

4 560 Gas 100 Acid 3/30/94 33,453 

4 560 Gas 100 Acid 3/30/94 33,453 

4 605 Gas 100 Acid 4/12!94 42,500 

4 605 Gas 100 Acid 4/12!94 42,500 

4 480 Gas 100 Acid 4/13/94 35,225 

4 480 Gas 100 Acid 4/13/94 35,225 

4 440 Gas/Yood 75!25 Acid 4/1!94 34,214 

4 440 Gas/llood 75/25 Acid 4/1/94 34,214 

4 540 Gas/Yood 75!25 Acid 4/4/94 35,590 

4 540 Gas/Wood 75/25 Acid 4/4/94 35,590 

4 605 Gas/Yood 60/40 Acid 4/11/94 41,680 

4 605 Gas/Yood 60/40 Acid 4/11/94 41,680 

6 550 Gas 100 Flux 3/11/94 28,500 

6 550 Gas 100 Flux 3/11/94 28,500 

6 550 Coal/Gas 61/39 Flux 3/15/94 32,680 

6 550 Coal/Gas 61/39 Flux 3/15/94 32,680 

6 550 Coal/Gas 59/41 Flux 3/16/94 31,500 

6 550 Coal/Gas 59/41 Flux 3/16/94 31,500 

Table 1 

Minntac Taconite Pellets 

Induration Sulfur Balance 

From Gas 

Analysis Avg Wet Standard Molecular Sa""le Average 

502 Cone. Deviation Yeight Point Sulfur 

ppm S02, ppm of Gas lbs/hr 

29.7 4.4 27.70 Scrub In 58.8 

20.7 3.9 27.72 Scrub Out 43.5 

37.1 2.9 27.72 Scrub In 86.0 

15.0 1.5 27.72 Scrub Out 34.8 

33.2 5. 1 27.74 Scrub In 97.7 

17.8 2.0 27.74 Scrub Out 52.4 

47.9 3.8 27.76 Scrub In 116.7 

23.6 2.2 27.76 Scrub Out 57.5 

48.2 4.7 27.76 Scrub In 114.0 

18.1 2.9 27.76 scrub out 42.8 

46.1 3.8 27.75 Scrub In 113.5 

19.7 1.2 27.75 Scrub Out 48.5 

41.8 2.1 27.77 Scrub In 120.5 

9.8 0.9 27.77 Scrub Out 28.3 

46.8 5.0 27.90 Scrub In 91.8 

23.2 2.1 27.90 Scrub Out 45.5 

73.7 4.1 27.96 Scrub In 165.4 

36.3 4.9 27.96 Scrub Out 81.5 

77.4 3.6 27.95 Scrub In 167.5 

39.2 4.0 27.95 Scrub Out 84.8 

.............. ~ 

From Gas From Water 

Analysis Analyzed Analysis 

Average s Sulfur in Scrubber Sulfur in 

in Scrubber Scrubber Flow Scrubber 

Water lbs/hr Water, ppm GPH Yater( lb/hr) 

15.3 No Sarrple 2650 N/A 

No Sample 

51.2 165 3400 56 

198 

45.3 165 3400 54 

197 

59.2 169 3400 68 

209 

71.2 163 3400 73 

206 

65.0 166 3400 70 

207 

92.2 162 3400 93 

217 

46.3 No Sample 2650 N/A 

83.9 161 3000 84 

217 

82.7 158 3000 78 

210 
........... 

Table 2 

Minntac Taconite Pellets 

Induration Sulfur Balance 

Green Ball 

Feed Average Sulfur Sulfur in Sulfur in Sulfur Sulfur in Pellets % Sulfur Rate Fuel Fuel Pellet Test %sulfur into Kiln GB Recycle Chip Reg in Fuel Pel Lets Produced in Pel Lets line LTon/hr Type Ratio Type Date in Greenball lbs/hr lbs/hr lbs/hr lbs/hr lbs/hr lton/hr Calculated 

6 510 Gas 100 Acid 11/3/93 0.0115* 120 11 4 0 47 418 0.005 6 510 Gas 100 Acid 11!4/93 

4 560 Gas 100 Acid 3/30/94 0.0110 126 11 2 0 27 464 0.003 4 560 Gas 100 Acid 3/30/94 

4 605 Gas 100 Acid 4112/94 0.0110 136 12 2 0 24 500 0.002 4 605 Gas 100 Acid 4/12/94 

4 480 Gas 100 Acid 4/13/94 0.0145 142 10 1 0 14 408 0.002 4 480 Gas 100 Acid 4/13/94 

4 440 Gas/Wood 75/25 Acid 4/1/94 0.0150 135 8 1 2 14 380 0.002 4 440 Gas/Uood 75!25 Acid 4/1/94 

4 540 Gas/Wood 75/25 Acid 4/4/94 0.0135 149 10 2 2 26 460 0.003 4 540 Gas/Wood 75!25 Acid 4/4/94 

4 605 Gas/Uood 60/40 Acid 4111/94 0.0155 191 12 2 4 61 518 0.005 4 605 Gas/Wood 60/40 Acid 4111/94 

Average Calculated Pellet Sulfur for Acid Pellets= 0.003 

6 550 Gas 100 Flux 3/11/94 0.0145 163 15 5 0 52 433 0.005 

6 550 Gas 100 Flux 3/11/94 

6 550 Coal/Gas 61/39 Flux 3/15/94 0.0140 157 14 5 67 40 432 0.004 

6 550 Coal/Gas 61/39 Flux 3/15/94 

6 550 Coal/Gas 59/41 Flux 3/16/94 0.0145 163 15 5 67 43 432 0.004 

6 550 Coal/Gas 59/41 Flux 3116/94 

Average Calculated Pellet Sulfur for Fluxed Pellets= 0.005 

* - No green ball samples taken. This number was calculated from the gas analysis. 
Table 3 

Minntac Agglomerator Samples 

Fluxed Pellet Production 

% ppm Average Std 

Sample Description Sulfur Sulfur Sulfur Dev 

Coal 0.76 0.77 0.0~0 

0.78 

Bentonite 0.25 0.30 0.050 

0. 35 

Fluxstone 0.056 0.050 0.0098 

0.039 

0.062 

0.04~ 

Pellet Product 0.004 0.005 0.0005 

0.005 

0.005 

Chip Regrind 0.0~~ 0.0~3 0.00~7 

0.0~5 

0.0~4 

Concentrate Thickener Water ~64 ~64 4 

~60 

~69 
Sample Description 

Wood 

Bentonite 

Pellet Product 

Chip Regrind 

Table 4 

Minntac Agglomerator Samples 

Acid Pellet Production 

% ppm Average 

Sulfur Sulfur sulfur 

0.067 0.059 

0.075 

0.043 

0.049 

0.36 0.33 

0.30 

0.005 0.004 

0.004 

0.003 

0.003 

0.004 

0.014 0.018 

0.019 

0.014 

0.015 

0.028 

Concentrate Thickener Water 167 181 

184 

190 

180 

182 

Std 

Dev 

0.013 

0.03 

0.0007 

0.0053 

8 
........... ,. ... 

Table 5 

Sulfur Sources in Green Balls 

Minntac Agglomerator Samples 

Fluxed Pellet Production 

Average Bentonite Minimun Maxi nun Minimun Maxirrun *MiniiTlllll *Maxi nun Minirrun Maxi nun 

Test %Sulfur X Sulfur % Range % s from % s from % s from % s from % S from % S from % S from X s from 

line Date in Greenball in Greenball Moisture (lb/LTon) Bent. Bent. Yater Water Fluxstone Fluxstone Tac. Cone. Tac. Cone. 

6 3/11/94 0.0145 0.014 8.89 12 to 18 0.00124 0.00326 0.00138 0.00161 0.00240 0.00560 0.00402 0.00948 

6 3/11/94 0.015 9.15 

6 3/15/94 0.0140 0.013 9.26 12 to 18 0.00124 0.00326 0.00138 0.00161 0.00240 0.00560 0.00352 0.00898 

6 3/15/94 0.015 9.11 

6 3/16/94 0.0145 0.013 9.06 12 to 18 0.00124 0.00326 0.00138 0.00161 0.00240 0.00560 0.00402 0.00948 

6 3/16/94 0.016 9.25 

Average X Sulfur in green ball from taconite concentrate= 0.007 

The Maximum and Minimum numbers are calculated from the average analyses + or - 2 times the standard deviation. 

*All fluxstone calculations were based on an addition rate of 8 %. 
Table 6 

Sulfur Sources in Green Balls 

Minntac Agglomerator Samples 

Acid Pellet Production 

General 

Average Bentonite Minimlln Maxinun Mininun Maxi HUn Mininun Maxi nun 

Test X Sulfur %Sulfur % Range % s from % s from % s from % s from % s from % s from 

line Date in Greenbelt in Greenbelt Moisture (lbs/LTon) Bentonite Bentonite Water Water lac. Cone. Tac. Cone. 

6 11/3/93 0.0115 • No Saq:>le No Sanple 12 to 18 0.00124 0.00326 0.00138 0.00161 0.00662 0.00888 

6 11/3/93 

4 3/30/94 0.0110 0.011 8.85 12 to 18 0.00124 0.00326 0.00145 0.00189 0.00585 0.00832 

4 3/30/94 0.011 8.92 

4 4/12!94 0.0110 0.01 8.88 12 to 18 0.00124 0.00326 0.00145 0.00189 0.00585 0.00832 

4 4/12!94 0.012 8.96 

4 4/13/94 0.0145 0.014 9.36 12 to 18 0.00124 0.00326 0.00145 0.00189 0.00935 0.01182 

4 4/13/94 0.015 9.38 

4 4/1/94 0.0150 0.016 9.35 12 to 18 0.00124 0.00326 0.00145 0.00189 0.00985 0.01232 

4 4/1/94 0.014 9.25 

4 4/4/94 0.0135 0.013 9.16 12 to 18 0.00124 0.00326 0.00145 0.00189 0.00835 0.01082 

4 4/4/94 0.014 9.22 

4 4/11/94 0.0155 0.015 9.35 12 to 18 0.00124 0.00326 0.00145 0.00189 0.01035 0.01282 

4 4111/94 0.016 9.39 

Average% Sulfur in green ball from Taconite Concentrate= 0.009 

*No green ball samples were taken. This is a calculated number based on the gas analysis. 

The calculated minimums and maximums are based on line 6 water analyses 

The Maximum and Minimum numbers are calculated from the average analyses + or - 2 times the standard deviation. 
Test 

Line Date 

6 11/3/93 

4 3/30/94 

4 4/12/94 

4 4/13/94 

4 4/1/94 

4 4/4/94 

4 4/11/94 

6 3/11/94 

6 3/15/94 

6 3/16/94 

Table 7 

Minntac Agglomerator 

Feed Rates, Recycle Rates, 

Production Rates, and Fuel Usage Rates 

Green Ball Pellets Green Ball Chip Reg. 

Feed Rate Produced Recycle Recycle 

LTonfhr Lton/hr LTonfhr LTon/hr 

510 418 46 14 

560 464 50 7 

605 500 55 8 

480 408 34 3 

440 380 25 3 

540 460 36 5 

605 518 38 5 

550 433 50 15 

550 432 50 15 

550 432 50 15 

Fuel 

Used 

MMBtujhr 

153 

142 

137 

106 

109 

129 

158 

205 

231 

220 
Sulfur Balance 

., 

Green Balls 

120 lbs S/hour 

--

Greenball Recycle 

11 lbs S/hour 

Chip Regrind Recycle 

4 lbs S/hour 

Figure 1 

Acid 

Line 

Nov. 

Off Gas 

43 lbs S/hour 

- Scrubber Water 

15 lbs S/hour 

Pellets 

47 lbs S/hour 

Fuel In - Nat. Gas 

0 lbs S/hour 

Pellets 

6 Step 3 

3, 1993 

---
Sulfur Balance 

' 

Green Balls 

126 lbs S/hour 

-- Greenball Recycle 

11 lbs 5/hour 

Chip Regrind Recycle 

2 lbs S/hour 

Figure 2 

Off Gas 

35 lbs S/hour 

... Scrubber Water - 51 lbs S/hour 

. 

Pellets 

27 lbs S/hour 

Fuel In - Nat. Gas 

0 lbs S/hour 

Acid Pellets 

Line 4 Step 2 

Mar. 30, 1994 

-... 
1 

Sulfur Balance 

r 

Green Balls 

136 lbs S/hour 

.. 

---

Greenball Recycle 

12 lbs S/hour 

Chip Regrind Recycle 

21bs S/hour 

Figure 3 

j~ 

Off Gas 

53 lbs S/hour 

Scrubber ~ Water - 45 lbs S/hour 

j ll Pellets 

24 lbs S/hour 

Fuel In- Nat. Gas 

0 lbs S/hour 

. Ac1d Pellets 

Line 4 Step 2 

April 12, 1994 

.. 
Sulfur Balance 

,., 

Green Balls 

142 lbs S/hour 

... 

--

Greenball Recycle 

1 0 lbs S/hour 

Chip Regrind Recycle 

1 lb S/hour 

Figure 4 

J~ 

Off Gas 

58 lbs S/hour 

. 

.. Scrubber Water 

59 lbs S/hour 

j~ Pellets 

14 lbs S/hour 

Fuel in- Nat. Gas 

0 lbs S/hour 

. Ac1d Pellets 

Line 4 Step 2 

April 13, 1994 

• 

... 
Sulfur Balance 

Green Balls 

135 lbs S/hour 

-

-

Greenball Recycle 

8 lbs S/hour 

Chip Regrind Recycle 

1 lb S/hour 

Figure 5 

Off Gas 

43 lbs S/hour 

... 

.. Scrubber Water 

71 lbs S/hour 

Pellets 

14 lbs S/hour 

Fuel In - Gas/Wood 

2 lbs S/hour 

Acid Pellets 

Line 4 Step 2 

April 1, 1994 

.. 
1 

Sulfur Balance 

Green Balls 

149 lbs S/hour 

--

--

Greenball Recycle 

10 lbs S/hour 

Chip Regrind Recycle 

2 lbs S/hour 

Figure 6 

Off Gas 

48 lbs S/hour 

.. 

. Scrubber Water 

65 lbs S/hour 

Pellets 

26 lbs S/hour 

Fuel In - Gas/Wood 

2 lbs 5/hour 

Acid Pellets 

Line 4 Step 2 

April 4, 1994 

• 

... 
1 

Sulfur Balance 

• 

Green Balls 

191 lbs S/hour 

.. 

-

--

Greenball Recycle 

12 lbs S/hour 

Chip Regrind Recycle 

21bs S/hour 

Figure 7 

j~ 

Off Gas 

28 lbs S/hour 

.. Scrubber Water - 92 lbs S/hour 

• a Pellets 

61 lbs S(hour 

Fuel In- Wood/Gas 

41bs S/hour 

. Ac1d Pellets 

Line 4 Step 2 

April 11 , 1994 

... 

. 
Sulfur Balance 

11r 

Green Balls 

163 lbs S/hour 

--

-

Greenball Recycle 

15 lbs S/hour 

Chip Regrind Recycle 

Sibs S/hour 

Figure 8 

Off Gas 

45 lbs S/hour 

... Scrubber Water - 46 ibs S/hour 

•• Pellets 

52 lbs S/hour 

Fuel In- Nat. Gas 

0 lbs S/hour 

Fluxed Pellets 

Line 6 Step 3 

Mar. 11 , 1994 

-
Sulfur Balance 

Green Balls 

157 lbs S/hour 

-.. 

--

Greenball Recycle 

14 ibs S/hour 

Chip Regrind Recycle 

Sibs S/hour 

Figure 9 

Off Gas 

81 lbs S/hour 

... 

... Scrubber Water 

84 lbs S/hour 

Fuel in Coal/Gas 

67 ibs S/hour 

Pellets 

40 lbs S/hour 

Fluxed Pellets 

Line 6 Step 3 

Mar. 15, 1994 

--
, 

Sulfur Balance 

r 

Green Balls 

163 lbs S/hour 

--

--

Greenball Recycle 

15 lbs S/hour 

Chip Regrind Recycle 

Sibs S/hour 

Figure 10 

.I Ill 

Off Gas 

85 lbs S/hour 

... 

... Scrubber Water 

82 lbs S/hour 

ll Pellets 

43 lbs S/hour 

Fuel in- Coal/Gas 

67 lbs S/hour 

Fluxed Pellets 

Line 6 Step 3 

Mar. 16, 1994 

-• -