1/9

 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 

Technical Analysis for applying LNB technology to UTAC L2 

Grate Kiln (GK) while minimizing product quality issues 

Background 

Metso, as a designer of grate kiln (GK) indurating technology, was asked to analyze the 

effects of Low NOx Burner (LNB) technology for the UTAC Line 2 GK process facility at United 

Taconite Mine in Eveleth, Minnesota while minimizing pellet quality issues. Metso used 

previously modeled conditions summarized in the March 12, 2014 “Updated Technical 

Analysis for applying LNB technology to UTAC L2 Grate Kiln (GK)” report. Simulation 4 was 

used as the base case for comparison since this had the latest operating conditions for the 

facility while producing quality pellets. 

Two simulations were performed using hi stoich LNB burners while mitigating product quality 

as much as possible. Quality issues are affected by changes to airflow, temperature, and 

pressure. The changes will cause pellet quality issues including, but not limited to, the 

following. 

1. Pellet breakage from increased pressure drop, i.e. increased down forces, across the pellet 

bed. 

2. Pellet breakage from increased drying rate and exploded the pellets from rapid steam 

escape. 

3. Pellet fusing from limited cooling in primary section of cooler. 

To mitigate these issues, current plant operations, as tested during airflow study from April 30, 

2013, were used as a baseline for heat up and cool down profiles and pellet bed pressure 

drops. Minimizing changes from baseline conditions minimizes but does not eliminate pellet 

quality effects. While flow, temperature and pressures, referred to as process variables, can 

be maintained, gas composition cannot. This altered gas composition will affect chemical 

reactions that rely on specific gas compounds and concentrations. Magnetite oxidation, for 

example, relies on oxygen to complete the reaction. This simulation does not explore 

mitigations of pellet quality issues from changes to oxygen levels or other chemical reactions 

within the furnace. 

Almost all of the process air in a GK system is introduced thru the cooler. A small amount of 

air is introduced thru the kiln burner. This process air is then used throughout the system to 

process pellets as efficiently as possible while making quality pellets. For these simulations 

cooling air in primary and secondary cooling was maintained to properly cool the pellets and 

minimize pellet fusing issues. This air was vented to atmosphere where it could not be 

returned to the process. 

Since hi stoich LNB burners require greater airflow (115% stoich), i.e. unheated primary air, 

through the burner compared to current burner designs at 15% stoich, airflow from primary 

cooling to the kiln had to be reduced to maintain airflow thru the kiln and on to the grate 

preheat (PH) zone. The grate receives its process gas from two sources, the kiln and recoup 

gas stream from cooler. These two sources of airflow were maintained. This then allowed the 

drying heat-up rate on the grate to be matched and maintain pellet bed pressures. 
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 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 

The primary cooling air stream was maintained to properly cool the pellets. 100% of this air 

normally enters the kiln, since more air is introduced through the kiln burner for hi stoich 

burner operation, the amount of primary cooling air to kiln was reduced. The remaining 

unused primary cooling air was vented. This air had to be vented and could not be used as 

hot recoup air due to its high temperature. The high temperature would lead to broken or 

exploded pellets from rapid drying. By venting this air it then maintained recoup gas 

temperature. This would ensure drying rate on the grate was maintained as current conditions 

dictate. The vented stream heat was not recovered into the kiln; therefore more energy from 

fuel had to be used to satisfy the process. 

Since more fuel is burned in the kiln, there are more combustion products, (CO2, H2O, N2) in 

the kiln gases. The increase in combustion products reduces the concentration of oxygen 

exiting the kiln and entering the PH zone. For plants processing magnetite ore, this will reduce 

the magnetite oxidation reaction on the grate. The completion of this reaction will then be 

pushed to the cooler. Since this reaction is exothermic, i.e. generates heat, there is less 

reaction heat generated on the grate to heat the pellets, therefore the pellets will discharge 

into the kiln at a lower temperature 

Similarly the reaction heat in the cooler will increase pellet temperature above baseline 

conditions. More cooling air will be required into the cooler to maintain final pellet 

temperature. 

This analysis report can be used in conjunction with the previous analysis dated September 

14, 2012 and March 12, 2014. For references to flow stream numbers in this document 

please refer to attached UTAC L2 process flow diagram and UTAC L2 data tables. For 

reference to zones or equipment in this document refer to UTAC L2 process flow diagram. 
3/9

 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 

Simulations 

Two new simulations 6 and 7 were created: Simulations 1, 2, and 3 were part of the 2012 

report. Simulations 4 and 5 were part of the March 12, 2014 report. 

Simulation Description Conditions 

4 Baseline Updated (April 30, 2013) operating conditions on natural 

gas fuel with 14.0% stoichiometric primary combustion air 

5 115% Stoich Updated operating conditions with 115% stoichiometric 

primary air. 

6 115% Stoich 

Mitigation 1 

Updated operating conditions with 115% stoichiometric 

primary air while mitigating pellet quality issues. 

7 115% Stoich 

Mitigation 2 

Updated operating conditions with 115% stoichiometric 

primary air while mitigating pellet quality issues. 

All engineering simulations were performed using natural gas fuel, maintaining peak pellet 

temperature, and maintaining final product temperature. The total air supplied to the cooler 

was adjusted as needed to maintain final product temperature across all simulations. 

Maintaining these parameters ensures that fuel changes are not due to altered processing 

requirements. This study was designed to isolate the effects to various process parameters 

when applying hi stoich LNB technology to UTAC L2 while minimizing pellet quality 

challenges. 

Simulation 4 conditions were simulated for updated operating conditions. 

Simulation 5 conditions were used to simulate a stoichiometric primary combustion air rate 

representing updated COEN LNB technology while trying to unsuccessfully balance fuel 

requirements and pellet quality issues. 

Simulation 6 conditions were used to simulate hi stoich burner operation while mitigating 

pellet quality issues. The cooler was modeled as though the cooler primary cooling zone was 

broken into 2 sub zones. The first sub zone reports secondary combustion air to kiln. The 

second sub zone is vented to atmosphere. The first sub zone would produce higher air 

temperatures then the second. 

Simulation 7 conditions were used to simulate hi stoich burner operation while mitigating 

pellet quality issues also. The cooler was modeled as though the cooler primary cooling zone 

was maintained as one zone with only a fraction of the mixed air reporting to kiln as 

secondary combustion air. The remaining air not sent to kiln is then vented to atmosphere. 

Since all the primary cooling air is mixed from the entire zone before it is used in the kiln, it 

will produce lower temperature secondary combustion air to the kiln than simulation 6. 
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 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 

Comparison Analysis 

The LNB simulations, while mitigating product quality issues, were compared to the base 

simulation for several key process parameters. NOx emissions values cannot be predicted for 

LNB simulations due to limited information from burner suppliers and would not be accurate 

until full scale demonstration testing. Dust generation is affected by pellet heat up and cool 

down rates. Since heat up and cool down rates are similar to current conditions, dust 

generations from heat up changes should be minimal. Where dust generation needs to be 

analyzed is due to lower pellet discharge temperature into the kiln. The lower pellet 

temperature produces pellets with less strength that can break down in the kiln. Dust 

emissions (stream 8, 12, 55) were not compared for LNB simulations because of the 

uncertainty of sensitivity of the pellets. Further testing is required to determine dust generation. 

Please refer to attached tables and comments. Since most airflow, temperatures, and 

pressures were maintained for the purpose of minimizing pellet quality issues, the main 

conclusion is drastically increased fuel rates, green house gases, and particulate release into 

the atmosphere. 

Conclusions 

The comparison of process parameters shows significant operational and environmental 

impacts as a result of mitigating pellet quality impacts from high stoich LNB installation: 

1. Fuel rate is expected to increase between 212% and 220% (stream 36) when 

incorporating LNB technology at UTAC L2 with 115% stoichiometric air while 

maintaining current pellet quality. The increase in fuel requirements can be justified 

from the increase in system losses, i.e. heat generated and not used to satisfy heat 

requirements of pellets. The increase in system loss is made up in primary cooling 

vent, secondary cooling vent, and slight increase in grate exhaust gas loss. The 

primary cooling vent and secondary cooling vent is included in stream 55. 

2. Because PH gases from the kiln have less oxygen concentration, the oxidation reaction 

will slow down. This shifts more reaction heat to the cooler. In order to maintain the 

same product temperature as current operation more air had to be introduced into the 

cooler. The existing secondary cooling fan is currently operating at 100% capacity. It 

does not have available capacity to supply the volume increase requirements. 

3. The reduced oxidation heat on the grate as described above produces lower pellet 

temperatures leaving the grate and entering the kiln. This lower pellet temperature will 

have to be analyzed to determine if the pellets have sufficient hardness to handle kiln 

mechanical action without causing pellet breakage. 

4. Fuel rate increases will substantially increase green house gases such as CO2 and 

particulate. CO2 will increase 167%. 

5. Cooler vent will increase between 274% and 298%. This will increase the amount of 

particulate into the atmosphere. 

6. The cooler vent is now made up of two streams, partial primary cooling vent and the 

secondary cooling vent. There currently is not a vent connection for primary section of 
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 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 

the cooler. This would require engineering analysis to determine the location and how 

to direct this vent stream to atmosphere. 

It is imperative to fully analyze each GK system when incorporating LNB technology due to the 

large variability in operating parameters associated with system designs due to feed materials, 

product specifications, fuels, and burner configurations. Since Minntac’s reduction data is used 

as the baseline for NOx reduction in EPA’s proposed BART FIP, one must analyze the effects 

from features such as, feed materials chemical heat addition, i.e. hematite vs. magnetite, low 

flux vs. high flux, ported kilns and PH burners to determine the NOx reduction that can be 

achieved in GK systems without these features. 

Attached: 

UTAC L2 process flow diagram 

UTAC L2 Data Table, actual data 

UTAC L2 Data Table, normalized data 
6/9

 August 07, 2014 

Metso Minerals (Pyro Division), 350 Railorad St. Danville, PA, 17821 
Criteria Units No. Simulation 4 Simulation 5 Simulation 6 Simulation 7

Production Rate Lton/hr 57

Fuel Rate BTUg/LTon 36

Primary Combustion Air % of stoich 37

Secondary Combustion Air Temperature (°F) 43

Secondary Air Vol. Flow Rate (ACFM) 43

Grate PH bed air flow SCFM/grate ft2 26

Recoup Gas Temperature (°F) 16

Grate pellet disharge Temperature (°F) 34

Cooler pellet discharge Temperature (°F) 57

Grate pellet oxidation % complete 34

Primary Cooling Air Vol. Flow Rate (ACFM) 40

Primary Cooling Air Pressure (In. H2O) 40

Secondary Cooling Air Vol. Flow Rate (ACFM) 47

Secondary Cooling Air Pressure (In. H2O) 47

DDD Exhaust Gas CO2 (lb/min.) 8

H2O (lb/min.) 8

N2 (lb/min.) 8

O2 (lb/min.) 8

NOx (lb/min.) 8

Dust (lb/min.) 8

Mass Flow Rate (lb/min.) 8

Vol. Flow Rate (SCFM) 8

Vol. Flow Rate (ACFM) 8

Temperature (°F) 8

Heat Content (MBTU/min.) 8

Cooler Stack Gas CO2 (lb/min.) 55

H2O (lb/min.) 55

N2 (lb/min.) 55

O2 (lb/min.) 55

NOx (lb/min.) 55

Dust (lb/min.) 55

Mass Flow Rate (lb/min.) 55

Vol. Flow Rate (SCFM) 55

Vol. Flow Rate (ACFM) 55

Temperature (°F) 55

Heat Content (MBTU/min.) 55
Criteria Units No.

Production Rate Lton/hr 57

Fuel Rate BTUg/LTon 36

Primary Combustion Air % of stoich 37

Secondary Combustion Air Temperature (°F) 43

Secondary Air Vol. Flow Rate (ACFM) 43

Grate PH bed air flow SCFM/grate ft2 26

Recoup Gas Temperature (°F) 16

Grate pellet disharge Temperature (°F) 34

Cooler pellet discharge Temperature (°F) 57

Grate pellet oxidation % complete 34

Primary Cooling Air Vol. Flow Rate (ACFM) 40

Primary Cooling Air Pressure (In. H2O) 40

Secondary Cooling Air Vol. Flow Rate (ACFM) 47

Secondary Cooling Air Pressure (In. H2O) 47

DDD Exhaust Gas CO2 (lb/min.) 8

H2O (lb/min.) 8

N2 (lb/min.) 8

O2 (lb/min.) 8

NOx (lb/min.) 8

Dust (lb/min.) 8

Mass Flow Rate (lb/min.) 8

Vol. Flow Rate (SCFM) 8

Vol. Flow Rate (ACFM) 8

Temperature (°F) 8

Heat Content (MBTU/min.) 8

Cooler Stack Gas CO2 (lb/min.) 55

Simulation 4 Simulation 5 Simulation 6 Simulation 7

1.00 1.00 1.00 1.00

1.00 1.61 2.12 2.25

1.00 8.52 8.52 8.52

0.00 102.81 123.43 0.31

1.00 0.65 0.53 0.48

1.00 0.99 1.00 1.01

0.00 510.09 0.25 6.33

0.00 92.91 -33.27 -20.44

0.00 -3.99 -0.79 -0.12

1.00 1.11 0.88 0.89

1.00 0.62 1.05 1.00

1.00 1.00 1.00 1.00

1.00 1.24 1.11 1.13

1.00 1.00 1.14 1.00

1.00 1.37 1.67 1.75

1.00 1.06 1.12 1.14

1.00 0.96 1.00 0.99

1.00 0.91 0.91 0.91

TBD TBD TBD TBD

TBD TBD TBD TBD

1.00 0.97 1.00 1.00

1.00 0.97 1.01 1.01

1.00 1.01 1.02 1.02

0.00 26.80 5.91 6.69

1.00 1.14 1.05 1.06

1.00 1.00 1.00 1.00

H2O (lb/min.) 55

N2 (lb/min.) 55

O2 (lb/min.) 55

NOx (lb/min.) 55

Dust (lb/min.) 55

Mass Flow Rate (lb/min.) 55

Vol. Flow Rate (SCFM) 55

Vol. Flow Rate (ACFM) 55

Temperature (°F) 55

Heat Content (MBTU/min.) 55

1.00 1.58 1.86 1.97

1.00 1.58 1.86 1.97

1.00 1.58 1.86 1.91

1.00 1.00 1.00 1.00

TBD TBD TBD TBD

1.00 1.57 1.86 1.96

1.00 1.58 1.86 1.96

1.00 1.93 2.74 2.98

0.00 246.41 523.30 575.34

1.00 2.30 3.81 4.16

Note: All values except temperatures have been normalized to base simulation. Temperatures are shown as degrees 

°F change.
Criteria Units No.

Production Rate Lton/hr 57

Fuel Rate BTUg/LTon 36

Primary Combustion Air % of stoich 37

Secondary Combustion Air Temperature (°F) 43

Secondary Air Vol. Flow Rate (ACFM) 43

Grate PH bed air flow SCFM/grate ft2 26

Recoup Gas Temperature (°F) 16

Grate pellet disharge Temperature (°F) 34

Cooler pellet discharge Temperature (°F) 57

Grate pellet oxidation % complete 34

Primary Cooling Air Vol. Flow Rate (ACFM) 40

Primary Cooling Air Pressure (In. H2O) 40

Secondary Cooling Air Vol. Flow Rate (ACFM) 47

Secondary Cooling Air Pressure (In. H2O) 47

DDD Exhaust Gas CO2 (lb/min.) 8

H2O (lb/min.) 8

N2 (lb/min.) 8

O2 (lb/min.) 8

NOx (lb/min.) 8

Dust (lb/min.) 8

Mass Flow Rate (lb/min.) 8

Vol. Flow Rate (SCFM) 8

Vol. Flow Rate (ACFM) 8

Temperature (°F) 8

Heat Content (MBTU/min.) 8

Cooler Stack Gas CO2 (lb/min.) 55

Comments

Fuel rate increases for LNB simulation due to increase in 

unrecovered heat in exhaust gas streams

Primary air rate was adjusted to latest COEN estimates for LNB 

operation

Temperature increased for simulaiton 6 hottest air from 

primary cooling was directed into kiln.

Flow rate decreases due to air is displaced by additional primary 

air requirements for LNB technology.

Grate air flow was maintained

Recoup gas temperature increases greatly. More testing is 

required to determine if pellet quality will be effected.

Pellet temperature slightly less because of less oxidation

Oxidation less on grate because reduced oxygen concentration

Primary Cooling was maintained

Cooler area was adjusted to match pressure.

Volumetric flow rate increases. More cooling required because 

oxidation reaction shiftd to cooler

Cooler area was adjusted to match pressure.

Increased due to increase in fuel rate.

Nox generation values not available from burner supplier

Dust generation is effected by pellet heat up rate. Further 

testing required

Volume increased due to higher temperatures. Fan 

performance must be evaluated.

Temperature increased leading to increase in unrecovered heat 

leaving the system.

Increase in unrecovered heat.

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

H2O (lb/min.) 55

N2 (lb/min.) 55

O2 (lb/min.) 55

NOx (lb/min.) 55

Dust (lb/min.) 55

Mass Flow Rate (lb/min.) 55

Vol. Flow Rate (SCFM) 55

Vol. Flow Rate (ACFM) 55

Temperature (°F) 55

Heat Content (MBTU/min.) 55

primary cooling required to maintain cooler pellet discharge 

temperature.

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

temperature.

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

temperature.

Dust generation is effected by pellet heat up rate. Further 

testing required

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

temperature.

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

temperature.

Air flow rate increased to compensate for reduced air flow to 

primary cooling required to maintain cooler pellet discharge 

temperature.

Temperature increased leading to increase in unrecovered heat 

leaving the system.

Increase in unrecovered heat.

Note: All values except temperatures have been normalized to base simulation. Temperatures are shown as degrees