David Brooks

Process Engineer

Hibbing Taconite

2012 PEMS work

Quick summary of NOx predictive equations for Lines 1, 2, & 3 based off 2007 & 2010 30 hour NOx stack

tests . Predicted values are in “ ppm dry ”

.

For each furnace, stack test hourly data was combined and entered into Minitab statistical software.

2007 data was entered on its own sheet. 2010 data was entered on its own sheet. Both data sets then

were combined into another sheet. Another sheet was bui lt off all data (as needed) , but was scrubbed

to remove points where probes were plugged or calibrations where being.

Accompanying the stack data, hourly averaged process data was included from the OSI PI historian.

Educated guesses were used to determine the process variables to include. Education and research says

that temperatures and air flow are the main contributors to NOx generation. Scrubbing water and

scrubber pressures are not part of the creation and would do little to remove or predict emission s.

It was chosen that only the highest emitting stack was to be predicted (stack 1 in data ). The other three

stacks were to be predicted off stack 1. The other three stacks seemed to follow a ratio, but did not

always stay constant. All the stacks share a common header so there should be a relationship.

Once stack test data and process data were combined, best subset regressions were run to find the

process variables with the highest correlation and/or effect on NOx emissions.

Overall summary:

Stack 1 wa s predicted reasonably well.

Stacks 2, 3, & 4 predicted off Stack 1 (actual) matched results reasonably well.

Time spent on analysis was stopped once the state decided they d idn’t want to look at the data, and

wanted to proceed with 4 CEMS. W eighting by factor , operating ranges, affect of ppm prediction failure

against total lb/hr, etc. were not explored.

The plan is to add 2012 30 hour stack test data to the existing data to increase the predictive equations’

accuracy.

Results for predicting the highes t emitting stack (Stack 1) compared to stack test data ar e listed in the

following table.

Note: it was found later that DDD hood pressure was not needed in the equations. The penalty to

remove it is a couple tenths in the R squared value.

Intercept DDD

Hood

Pressure Firing

Zone

Pressure Hood 18

Temp South

Inlet

Temp South

Trans

Temp

Line 1

- 453.635 10.92298

- 47.4743 0.105587

- 0.01072 0.126841 86.8% R 2

Line 2

- 889.545 14.08401 50.08297 0.049291

- 0.00216 0.430814 94.1% R 2

Line 3

- 351.206 7.089283

- 8.40658 0.070475 0.045536 0.086557 81.1% R 2The following graphs compare the PPM (dry) prediction to stack test results (Stack 1)

.Using the highest emitting stack (stack 1) , the other three stacks on each furnace were predicted.

Line 1 stack predictions

Stack 2 = 0.277417 + 0.87507 * Stack 1

Stack 3 = 7.37861 + 0.560859 *Stack 1

Stack 4 = 4.20415 + 0.46492 *Stack 1Line 2 stack predictions

Stack 2 = 3.20504 + 0.804379 * S tack 1

Stack 3 =

- 11.8109 + 0.622549 * S tack 1

Stack 4 =

- 8.47991 + 0.484465 * S tack 1Line 3 Stack Predictions

Stack 2 = 6.55725 + 0.745857 * Stack 1

Stack 3 = 15.3618 + 0.368988 * Stack 1

Stack 4 = 11.7028 + 0.238778 * Stack 1