1 

### Technical Services, Minnesota Ore Operations 

### Memorandum

Date: April 1 3 , 2012

Subject: Line 6 Biomass Performance Testing on Repaired Kiln Low NOx Burner

During the major repair in March 2012, the Line 6 Low NOx Burner was removed to repair the deformed biomass outer pipe on the burner. When the burner was removed, we also found two holes in the deformed biomass outer pipe. The photo below shows the deformed biomass outer pipe and one of the holes in this pipe. The two holes coin cided with where the pipe supports for this outer pipe were located. After some discussions with Hatch and Coen, it was determined that the pipe supports in the coal annulus were shaped in such a way that the coal was being directed at the biomass outer p ipe causing excessive wear from coal abrasion. To reduce the wear in this area, the new supports installed were modified with a beveled leading edge to direct the coal around the supports and not directly at the biomass outer pipe.

Figure 1: Picture o f Line 6 Burner Prior to Repair

Deformed Biomass Outer Pipe Hole in biomass outer pipe from coal abrasion at supports

Biomass Annulus Atomiz ing Air l2 Coen’s analysis of the deformed biomass pipe concluded that it was inadequately supported within the burner causing the deformation seen above resulting in reduced biomass throughput and plugging issues in the biomas s pipe/annulus . The deformed portion of the biomass outer pipe (~4 ft) was cut off and replaced with a new pipe and three additional supports were added in both the coal and biomass annuluses to properly support the pipe and prevent deformation. The pict ure below shows the repaired burner with the additional three supports in both the coal annulus and the biomass annulus. The original design only had 3 supports 120° apart in each annulus.

Figure 2: Picture of Line 6 Burner After the Repair

Prior to the repair, at biomass feed rates above 150 lbs/min

, we experienced plugging issues in the biomass system which we could n o t confirm were due to the deformed biomass pipe or other burner design or biomass feed system issues

. On April 11, 2012 , biomass testing was performed on the repaired Line 6 Kiln Low NOx Burner to determine if we could achieve the designed biomass feed rate of 300 lbs/min. Two tests were performed to determine the maximum biomass feed rate that could be achieved before plu gging issues occurred. Line 6 was running steady at full production throughout the test period. The fuels burned during the testing were a combination of natural gas and biomass. The biomass burned during the test period was a combination of oat hulls a nd wood. For each test, t he bioma ss blower was started first and allowed to run for a period of time (~5 minutes) with no biomass feed to ensure the line was clear and to get a baseline pipe pressure. The pipe pressure is measured Atomizing Air

Biomass Annulus

Coal Annulus

Combustion Air Annulus

Six additional supports added in coal and biomass annulus 1 2 3

4 5 63 at the feed end of the pipeline and is used to indicate plugging problems in the biomass pipeline/burner annulus. The blower and wood auger are interlocked with this pipe pressure and will kick out if the pipe pressure exceeds 6.5 psi to prevent severe plu gging of the biomass p ipeline. The following is a list of the burner operating parameters that were used and remained constant during the entire test period:

• The burner was in the gas firing position

• Coal was shut off and the primary air fan was running to cool the coal annul us

• Atomizing air was set at 3,000 lbs/hr

• The kiln exit temperature was controlled with natural gas

Figure 3 below is an overview of the entire 2 hr test period showing the relationship between the biomass feed rate , VFD wood auger speed and biomass system pipe pressure. As you can see from the graph below, for each test we sta rted with 50 lbs/min of biomass and increased the feed rate in 50 lb/min increments up to 150 lbs/min. The incremental increase in biomass was reduced to 25 lbs/min above 150 lbs/mi n. At each biomass feed rate, the biomass system was allowed to stabilize before further increases in feed rate s were made

. Figure 3: Line 6 Biomass System Process Data Trend Chart

0 1 2 3 4 5 6 7 8

0 20 40 60 80 100 120 140 160 180 200Wood System Pipe Pressure (PSI)Wood Flow (LBS/MIN)-Wood Auger VFD Speed (%) Line 6 Biomass Testing 4

- 11

- 12

LINE 6 WOOD AUGER VFD SPEED LINE 6 WOOD FLOW (LB/MIN) Line 6 WOOD SYS PIPE PRESS (PSI)

During Test # 1, we ran for an extended time period (34 minutes) at 150 lbs/min due to a 10 minute period in the middle of the run where the pipe pressure was erratic and was varying Start of test #1 End of test #1

Sta rt of test #2 End of test #24 between 3.7 and 5.6 psi. During this time period the auger speed was also steadily increasing to maintain 150 lbs/min of biomass. Talkin g with Hillwood Products, they stated that the increase auger speed was due to a change in the biomass feed composition from mostly oat hulls to an oat hull and wood mixture which changed the density of the biomass feed. After this upset in the system , th e pipe pressures dropped back down around 3.6 psi and stabilized. The feed rate was then increased to 175 lbs/min where it ran relatively stable at 3.9 psi for just over 15 minutes before the pipe pressure spiked up above 6.5 psi and the system kicked out . After restarting the blower twice, we were able to clear the plug in the biomass system. Table 1 and Figure 4 summarize the key process data during test #1.

Table 1: Biomass Test # 1 Summary Data

Biomass Feed Rate Wood System Pipe Pressure Wood Auger VFD Speed Air to Fuel Ratio Setpoint Core Gas Annulus Gas Operating Time at Biomass Feed Rate
lbs/min PSI % % % min:sec

0 2.2 0.0 15 25 75 6:10
50 2.6 7.9 10.5 25 75 11:05
100 3.0 15.5 9 25 75 11:25
150 3.9 32.1 7.5 38 62 34:30
175 3.9 44.6 7.5 38 62 15:05

Figure 4: Biomass Test #1 Process Data Trend Chart

0 1 2 3 4 5 6 7 8

0 20 40 60 80 100 120 140 160 180 200Wood System Pipe Pressure (PSI)Wood Flow (LBS/MIN)-Wood Auger VFD Speed (%) 

### Line 6 Biomass Testing 4

- 11

- 12

- Test #1

LINE 6 WOOD FLOW (LB/MIN) LINE 6 WOOD AUGER VFD SPEED Line 6 WOOD SYS PIPE PRESS (PSI) Erratic pipe
pressures5 A second test was performed to confirm the test results from the first test using the same test procedures as test #1. During the second test, the pipe pressures at 100 lbs/min biomass feed rate were 0.4 psi higher than test #1 (3.4 psi compared to 3.0 psi). When the biomass feed rate was increased to 150 lbs/min, the pipe pressure steadily increased to around 5 psi. Less than 3 minutes after the increase to 150 lbs/min, the pressure spiked over 6.5 psi again causing the blower and wood auger to ki ck out. The blower was restarted and the pipe plug was cleared and no further biomass testing was performed. Table 2 and Figure 5 summarize the key process data during test #2

.

Table 2: Biomass Test # 2 Summary Data

Biomass Feed Rate Wood System Pipe Pressure Wood Auger VFD Speed Air to Fuel Ratio Setpoint Core Gas Annulus Gas Operating Time at Biomass Feed Rate
lbs/min PSI % % % min:sec

0 2.2 0.0 15 25 75 4:35
50 2.6 10.8 10.5 25 75 8:15
100 3.4 25.9 9 25 75 11:00
150 4.5 34.5 7.5 38 62 2:50

Figure 5 : Biomass Test # 2 Proce ss Data Trend Chart

0 1 2 3 4 5 6 7

0 20 40 60 80 100 120 140 160Wood System Pipe Pressure (PSI)Wood Flow (LBS/MIN)-Wood Auger VFD Speed (%) 

### Line 6 Biomass Testing 4

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- Test #2

LINE 6 WOOD FLOW (LB/MIN) LINE 6 WOOD AUGER VFD SPEED Line 6 WOOD SYS PIPE PRESS (PSI)6 

### Conclusions

Comparing the test res ults from April 11 th , 2012 with the repaired biomass annulus to the tests performed in 2011 with the deformed biomass annulus, there was no improvement in biomass throughput with the repaired burne r. Plugging issues in the biomass pipe/burner annulus continue to occur at feed rates of 150

- 175 lb s /min . This leads me to conclude that the deformed biomass annulus was not the root cause of the plugging issues before the burner repair and that further analysis of the existing burner design and the biomass feed system is needed to determine the actual cause of these plugging issues.



### Future Work

No further biomass testing is scheduled until we can inspect the burner and biomass pipeline. During the ne xt minor repair on line 6, we need to inspect the biomass annulus for deformation to ensure the modification made to the biomass annulus were effective. We also need to open up the inspection hatch located where the biomass pipeline connects to the burner to determine if any large biomass or tramp material built up in this area during the previous biomass testing. This is where the 6” biomass pipeline meets the 3⁄4” biomass annulus of the burner, so if we are receiving larger biomass or tramp material from our supplier, this is the area where it would buildup and restrict the flow of biomass to the kiln.

Once we have confirmed there is no tramp material in the biomass pipeline/annulus and the annulus is not deformed, further biomass testing based on analysi s and recommendations from Coen and Hatch will be performed to determine the root cause of the plugging issues. Additional pressure monitoring at various points in the biomass pipeline may be required to pinpoint where the plugging is occurring and to ens ure any future design modifications are effective

. We also plan on testing the burner again with a fine ground oat hull biomass to determine how the type of biomass affects biomass feed rates. From past experience, fine ground oat hulls are the best biom ass material to convey through a pipeline and should therefore indicate the maximum capacity of the biomass system/burner under ideal conditions.