FFeebbrruuaarryy 22000077 ✦✦ 2277

V & M Star of Vallourec & MannesmannTubes is a steelmaking facility with a 95-

ton electric arc furnace, a ladle metallurgicalfurnace and a 3-strand rounds caster. Largeamounts of electrical and chemical energy areused to melt scrap metal in the electric arc fur-nace. More electrical energy is used to refineand achieve the desired steel temperatures atthe ladle metallurgical furnace before it issent to the caster. Molten steel must have suf-ficient superheat to fully cast through atundish without interruptions due to skullingof cold steel in the ladle or the tundish.

Microporous insulation has been used foryears in many shops to reduce shell tempera-tures and steel temperature loss in ladles.Microporous insulation had never been usedat V & M Star. It was believed that the samemicroporous insulation could reduce temper-ature loss and energy costs if it were used ineach step of the steelmaking process.

BBaacckkggrroouunnddElectric Arc Furnace — The electric arc fur-nace at V & M Star is a 20-foot-diameter FuchsAC-EBT. Its refractory sidewall working liningis constructed with 18-inch-thick magnesia-carbon brick. The sidewall backup lining inthe melting area of the furnace consists of 3-inch-thick fired magnesia brick, while the side-wall backup lining in the sump area of the fur-nace consists of a 3/4-inch-thick layer of mag-nesia-based dry vibratable. Maximum furnacesidewall shell temperatures range is 525–884°F in the melting area and 590–899°F inthe sump area.

Ladles — V & M Star has a fleet of nine 95-tonround ladles with one bottom stir plug ineach. Their refractory working linings are con-structed with 6-inch-thick magnesia-carbon inthe slagline, 6-inch-thick resin-bondeddolomite in the barrel, and 9- to 12-inch-thickprecast alumina in the bottom. The backuplinings are 70 percent alumina castable 3 inch-es thick in the sidewalls and 6 inches thick inthe bottoms. The maximum ladle shell tem-

perature range is 680–879°F in the slag lines,635–740°F in the barrels and 345–633°F in thebottoms.

Tundishes — V & M Star has a fleet of 10 3-strand tundishes. They are capable of casting8.75-, 10.5- or 11.25-inch-diameter rounds.

Their refractory working linings are a 3/4-inch-thick layer of resin-bonded magnesia dryvibratable. Their backup linings are 70 per-cent alumina castable 4 inches thick in thesidewalls and 5 inches thick in the bottom. A1/4-inch thick layer of ceramic fiber paperinsulation is installed against the steel shell.No shell temperatures were measured beforethe start of this program.

Microporous Insulation — Microporous insu-lation acts as a barrier to all three mechanismsof heat transfer: conduction, convection andradiation. Microporous insulation is formedlargely from amorphous silica particles with alow intrinsic thermal conductivity. It is 90 per-cent void space and uses very fine particles,5–25 nanometers in diameter, to increase thepath length of solid conduction across thematerial. Insulation with a large percentage ofvoid space must also minimize heat conduc-tion by gases. This can be done by ensuringthat a gas molecule undergoes a maximumnumber of collisions with solid surfaces withinthe insulation instead of with other gas mole-cules. Microporous insulation has a very smallpore size that minimizes thermal conductivity.

Gaseous convection is easily eliminated as aheat transfer mechanism through all commoninsulation materials by making the average

Energy Savings at V&M StarWith Microporous Insulation

V & M Star realized meltshop energy savings via

microporous insulation in its EAF, ladles and

tundishes. Power consumption was less as molten steel

heat loss was reduced. Microporous insulation also

reduced EAF, ladle and tundish shell temperatures.

Authors

SShhaawwnn RR.. EElllliiootttt,, meltshop project/maintenance engineer, MMiikkee BBllaanneerr,, casting/refractory general supervisor, andWWiilllliiaamm KKeeppkkoo,, casting team leader, V & M Star of Vallourec & Mannesmann Tubes, Youngstown, Ohio(selliott@vmstar.com, mblaner@vmstar.com, bkepko@vmstar.com); and JJ.. RRoobbeerrtt DDoottyy (pictured), IMACRO Inc.,Northfield Center, Ohio (rdotyimacro@cs.com)

THIS ARTICLE IS AVAILABLE ONLINE AT WWW.AIST.ORG FOR 30 DAYS FOLLOWING PUBLICATION.

2288 ✦✦ IIrroonn && SStteeeell TTeecchhnnoollooggyy

void space in the structure small enough thatconvection currents cannot form. Micro-porous insulation has extremely small voidsand no convection heat loss.

The microporous insulation used for thisprogram contains a thermally stable metaloxide opacifier of a controlled particle sizedistribution. The particle diameter is sized tobe about the same as the wavelength of theincident radiation. The opacifier particlesscatter infrared radiation that would passthrough other insulating materials, and soreduces the transmission of heat by radiationto the lowest possible level.1

IInnssuullaattiinngg LLaaddlleessLadle No. 9 was lined with 0.20-inch-thickmicroporous insulation against the inside steelshell in the bottom and sidewalls in lateFebruary 2005. Ladle No. 3 was relined in lateMarch 2005 without microporous insulation.The temperatures and energy used to processthe most commonly produced grade of steel inthese two ladles were compared through theend of 2005 to quantify the energy savings pro-vided by the microporous insulation. All otherladles in the fleet were insulated with microp-orous insulation when they were completelyrelined between April and October 2005.

Ladle No. 9 With Microporous Insulation Average Monthly Molten Steel Temperatures and LMFEnergy UsedMMoonntthh NNoo.. ooff EEAAFF ttaapp tteemmpp.. LLMMFF eexxiitt tteemmpp.. %% LLMMFF LLMMFF kkWWhh// MMaaxx.. ccaasstteerr EExxiitt LLMMFF –– mmaaxx..iinn 22000055 hheeaattss ((°°FF)) ((°°FF)) ppoowweerr--oonn ttiimmee sstteeeell ttoonn tteemmpp.. ((°°FF)) ccaasstteerr tteemmpp.. ((°°FF))

March 29 3,067.8 2,838.5 27.3 28.68 2,800.9 37.7

April 17 3,072.0 2,838.4 31.8 33.81 2,792.3 46.1

May 27 3,053.6 2,844.5 32.0 32.74 2,798.4 46.1

June 33 3,041.9 2,840.1 34.9 35.35 2,791.6 48.5

July 41 3,059.4 2,834.1 31.8 32.44 2,792.6 41.5

August 23 3,042.0 2,834.7 31.4 31.48 2,795.3 39.4

September 12 3,076.6 2,833.1 26.7 26.49 2,787.1 46.0

October 25 3,053.2 2,838.9 28.8 28.89 2,792.2 46.6

November 30 3,065.6 2,834.6 29.1 30.10 2,793.4 41.2

December 6 3,083.0 2,838.8 26.3 27.06 2,793.5 45.3

Average 243 3,058.2 2,837.6 30.6 31.41 2,794.1 43.4

Table 1

Ladle No. 3 Without Insulation Average Monthly Molten Steel Temperatures and LMF Energy UsedMMoonntthh NNoo.. ooff EEAAFF ttaapp tteemmpp.. LLMMFF eexxiitt tteemmpp.. %% LLMMFF LLMMFF kkWWhh// MMaaxx.. ccaasstteerr EExxiitt LLMMFF –– mmaaxx..iinn 22000055 hheeaattss ((°°FF)) ((°°FF)) ppoowweerr--oonn ttiimmee sstteeeell ttoonn tteemmpp.. ((°°FF)) ccaasstteerr tteemmpp.. ((°°FF))

April 26 3,057.8 2,839.6 36.8 38.75 2,787.8 51.8

May 26 3,058.2 2,843.5 35.0 37.40 2,789.5 53.9

June 24 3,047.6 2,839.0 35.8 35.22 2,785.2 53.8

July 27 3,057.4 2,835.3 36.7 37.35 2,793.5 41.8

August 45 3,065.9 2,830.6 32.2 31.90 2,789.1 41.5

September 5 3,090.4 2,833.8 38.3 38.78 2,783.2 50.6

October 20 3,070.5 2,834.7 32.7 33.27 2,785.0 49.7

November 17 3,078.5 2,833.9 34.9 35.96 2,785.9 47.9

December 9 3,066.6 2,847.9 33.7 34.92 2,792.1 55.8

Average 199 3,062.7 2,836.6 34.7 35.56 2,788.4 48.2

Table 2

FFeebbrruuaarryy 22000077 ✦✦ 2299

RReessuullttss iinn LLaaddlleessThe end product at V & M Star is seamlesstube. About half the steel produced is of oneparticular grade. The molten steel tempera-tures, LMF processing times and LMF electri-cal consumptions were collected for all heatsof this steel grade processed with the first insu-lated ladle (No. 9) and the uninsulated ladle(No. 3). The results are summarized and com-

pared by month in Table 1 for ladle No. 9 andin Table 2 for ladle No. 3. The results are sum-marized and compared by working liningcampaign in Table 3 for ladle No. 9 and inTable 4 for ladle No. 3. Despite lower tap tem-peratures, ladle No. 9 used less LMF kWh andhad less temperature loss. Not shown in thesetables is the reduction in LMF power-on timeper heat. The average power-on time for ladle

Ladle No. 9 With Microporous Insulation Average Molten Steel Temperatures and LMF Energy Usedby Working Lining Campaign

NNoo.. ooff EEAAFF ttaapp tteemmpp.. LLMMFF eexxiitt tteemmpp.. %% LLMMFF LLMMFF kkWWhh// MMaaxx.. ccaasstteerr EExxiitt LLMMFF –– mmaaxx..CCaammppaaiiggnn hheeaattss ((°°FF)) ((°°FF)) ppoowweerr--oonn ttiimmee sstteeeell ttoonn tteemmpp.. ((°°FF)) ccaasstteerr tteemmpp.. ((°°FF))

1 29 3,067.8 2,838.5 27.3 28.68 2,800.9 37.7

2 17 3,072.0 2,838.4 32.0 33.81 2,792.3 46.1

3 27 3,053.6 2,844.5 31.8 32.74 2,798.4 46.1

4 16 3,045.4 2,837.9 34.4 35.23 2,792.8 45.2

5 19 3,044.6 2,843.1 34.9 34.88 2,790.8 52.3

6 39 3,057.5 2,833.2 31.8 32.58 2,792.6 40.6

7 21 3,038.7 2,834.7 32.9 32.77 2,797.5 37.2

8 3 3,044.7 2,833.0 25.5 25.98 2,777.7 55.3

9 33 3,063.2 2,836.9 27.2 27.45 2,790.5 46.4

10 3 3,061.7 2,840.3 36.0 36.35 2,791.3 49.0

11 36 3,068.5 2,835.3 28.6 29.52 2,793.4 41.9

Average 243 3,058.2 2,837.6 30.6 31.41 2,794.1 43.4

Table 3

Ladle No. 3 Without Insulation Average Molten Steel Temperatures and LMF Energy Used by WorkingLining Campaign

NNoo.. ooff EEAAFF ttaapp tteemmpp.. LLMMFF eexxiitt tteemmpp.. %% LLMMFF LLMMFF kkWWhh// MMaaxx.. ccaasstteerr EExxiitt LLMMFF –– mmaaxx..CCaammppaaiiggnn HHeeaattss ((°°FF)) ((°°FF)) ppoowweerr--oonn ttiimmee SStteeeell TToonn tteemmpp.. ((°°FF)) ccaasstteerr tteemmpp.. ((°°FF))

1 17 3,053.6 2,834.5 34.5 36.75 2,785.5 49.1

2 35 3,060.2 2,844.9 36.5 38.61 2,790.2 54.7

3 15 3,048.7 2,837.7 36.0 35.33 2,786.9 50.8

4 18 3,052.9 2,840.0 32.9 33.20 2,786.9 53.1

5 28 3,063.3 2,832.0 36.6 36.96 2,792.7 39.3

6 35 3,062.9 2,830.9 32.8 32.22 2,789.1 41.9

7 20 3,082.1 2,836.0 32.7 33.35 2,785.7 50.3

8 9 3,052.7 2,827.8 35.1 35.17 2,782.0 45.8

9 17 3,075.9 2,837.2 35.5 36.92 2,788.3 48.9

10 5 3,077.8 2,853.6 33.3 34.58 2,790.6 63.0

Average 199 3,062.7 2,836.6 34.7 35.56 2,788.4 48.2

Table 4

3300 ✦✦ IIrroonn && SStteeeell TTeecchhnnoollooggyy

No. 9 heats was 2.4 minutes less than for ladleNo. 3 heats (17.4 versus 19.8 minutes).

Tables 1–4 and Figures 1–2 show that the0.20-inch-thick microporous insulationinstalled in ladle No. 9 provided significantenergy savings compared to ladle No. 3 with-out insulation over a 10-month period (11working lining campaigns). Despite startingwith steel from the furnace that averaged4.5°F colder, ladle No. 9 required 4.1 percentless LMF power-on time per heat, which used4.15 (11.7 percent) less kWh/ton of steel elec-trical heating at the LMF to achieve exit tem-peratures similar to ladle No. 3. These sameladle No. 9 heats were delivered to the casteran average of 5.7°F hotter than ladle No. 3heats.

Ladle shell temperatures were periodicallymeasured with a handheld Raytek RayngerMX4 infrared thermometer from February toDecember 2005. During this period, eight of

the nine ladles were insulated with 0.20-inch-thick microporous insulation in the sidewallsand bottoms. The maximum ladle shell tem-peratures were measured in the bottom, lowerbarrel, upper barrel and slagline zones afterthe ladles returned from the caster and werelaid down for gate maintenance. The averagesof these maximum temperatures for insulatedand noninsulated ladles are compared inFigure 3. The average ladle shell temperaturereductions due to 0.20-inch-thick microp-orous insulation are shown in Figure 4.

RReessuullttss iinn TTuunnddiisshheessTundish No. 4 was insulated with 0.20-inch-thick microporous insulation in August 2005.Eight thermocouples were installed against thesteel tundish shell behind the insulation, andeight more were installed on top of the insula-tion directly above the other thermocouples.Six thermocouple pairs were installed in the

Average campaign kWh/ton of steel at LMF.

Figure 1K

Wh

per

ton

of s

teel

at

LMF

36.00

35.00

34.00

33.00

32.00

31.00

30.00

29.00Ladle No. 9 Ladle No. 3

31.41

35.56

Average campaign steel temperatures in ladle No. 9 versusNo. 3.

Figure 2

Cam

paig

n av

erag

e te

mpe

ratu

res

(°F

)

Location of steel ladle temperatures taken

Average maximum ladle shell temperatures.

Figure 3

Ave

rage

tem

pera

ture

s (°

F)

Location in the ladle shell

31.41

Reduction in average maximum ladle shell temperatures.

Figure 4

Tem

pera

ture

red

uctio

ns (

°F)

Location in the ladle shell

FFeebbrruuaarryy 22000077 ✦✦ 3311

sidewalls above each of the three tapholes.Two thermocouple pairs were installed in thebottom, midway between the tapholes. Thenormal backup lining of 70 percent aluminacastable was installed over the microporousinsulation, being 4 inches thick in the sidewallsand 5 inches thick in the bottom.

Tundish No. 42 was insulated with 0.25-inch-thick ceramic fiber insulation inSeptember 2005. Eight thermocouples wereinstalled against the steel tundish shell behindthe insulation, and eight were installed on topof the insulation in the same pattern as intundish No. 44. The same thickness of 70 per-cent alumina castable was installed over thefiber insulation.

Temperatures were measured with eachthermocouple during the middle of castingeach heat in several sequences that rangedfrom two to 15 heats each. Temperaturesreached a plateau after five heats in the side-walls and seven heats in the bottom.Significantly cooler shell temperatures andhotter refractory cold face temperatures weremeasured in tundish No. 44 with micro-

porous insulation compared to tundish No.42 with thicker ceramic fiber insulation.Results for the thermocouples between thetundish shell and the cold face of the insula-tion are compared in Tables 5–6 and Figures5–6. Results for thermocouples between theinsulation hot face and the refractory castablecold face are compared in Tables 7–8 andFigures 5–6.

Reduced heat loss from the molten steelthrough the steel tundish shell, along withincreased heat retention in the tundish refrac-tory lining, led to reduced heat loss from themolten steel during the casting process.Molten steel heat savings were quantified bycomparing heat sequences cast throughtundish No. 4 to sequences cast through othertundishes immediately before and aftertundish No. 4 from October 2005 to January2006. Only heats transferred from the LMF tothe caster in ladles with microporous insula-tion were used in this analysis.

Table 9 compares LMF exit temperatures tominimum and maximum tundish tempera-tures for the most commonly produced grade

Average Sidewall Tundish Shell Temperatures in°F With Different InsulationHHeeaatt iinn MMiiccrrooppoorroouuss CCeerraammiicc ffiibbeerrsseeqquueennccee iinnssuullaattiioonn iinnssuullaattiioonn DDiiffffeerreennccee

1 331 446 115

2 456 561 105

3 550 634 84

4 565 724 159

5 and up 660 715 55

Table 5Average Bottom Tundish Shell Temperatures in°F With Different InsulationHHeeaatt iinn MMiiccrrooppoorroouuss CCeerraammiicc ffiibbeerrsseeqquueennccee iinnssuullaattiioonn iinnssuullaattiioonn DDiiffffeerreennccee

1 271 434 163

2 393 458 65

3 399 535 136

4 405 642 237

5 466 628 162

6 504 668 164

7 and up 538 733 195

Table 6

Average Sidewall Refractory Cold FaceTemperatures in °F With Different InsulationHHeeaatt iinn MMiiccrrooppoorroouuss CCeerraammiicc ffiibbeerrsseeqquueennccee iinnssuullaattiioonn iinnssuullaattiioonn DDiiffffeerreennccee

1 767 815 –48

2 1,149 964 185

3 1,272 1,088 184

4 1,290 1,205 85

5 and up 1,538 1,322 216

Table 7Average Bottom Refractory Cold FaceTemperatures in °F With Different InsulationHHeeaatt iinn MMiiccrrooppoorroouuss CCeerraammiicc ffiibbeerrsseeqquueennccee iinnssuullaattiioonn iinnssuullaattiioonn DDiiffffeerreennccee

1 638 554 84

2 896 687 209

3 1,029 794 235

4 1,090 927 163

5 1,216 988 228

6 1,273 1,041 232

7 and up 1,328 1,117 211

Table 8

3322 ✦✦ IIrroonn && SStteeeell TTeecchhnnoollooggyy

of steel cast through tundish No. 4 and othertundishes. The first heats in each castingsequence exited the LMF and arrived at thetundish hotter and cooled faster in thetundish than later sequence heats. Thus, aver-age temperatures in a heat sequence werecompared with and without the first heat dataincluded.

Steel heats cast through tundish No. 4 withmicroporous insulation had higher averagetemperatures measured in the tundish thansteel cast through other tundishes withceramic fiber insulation. Molten steel lost anaverage of 3.9°F less between exiting the LMFand the coldest temperature measured in thetundishes sequences after the first heat.These same heats lost an average of 1.7°F (30percent) less temperature through the cast-ing process.

RReessuullttss iinn EElleeccttrriicc AArrcc FFuurrnnaacceessOn Sept. 6, 2005, new sidewall refractorieswere installed at V & M Star’s electric arc fur-nace. A 3-inch-thick layer of fired magnesiabrick was installed against the furnace shell inthe melting area of the furnace. A layer of0.20-inch-thick microporous insulation was

installed against the furnace shell in the sumparea of the furnace (Figure 7). A working lin-ing of 18-inch-thick magnesia-carbon brickwith a 3/4-inch-thick layer of magnesia dryvibratable backfill was installed throughoutthe entire furnace sidewall (Figure 8).

EAF sidewall temperatures had been meas-ured periodically since June 1, 2005, with aFLIR Systems Thermacam PM695 thermalimaging camera. The maximum furnace side-wall shell temperatures ranged from 525 to884°F in the melting area and 590 to 899°F inthe sump area. The same camera was used tomeasure EAF sidewall temperatures after theSept. 6, 2005, furnace reline. The averagemaximum sidewall temperatures before andafter the Sept. 6, 2005, reline are summarizedin Table 10.

The handheld Raytek Raynger MX4infrared thermometer confirmed the temper-atures seen by the thermal imaging camera.The 0.20-inch-thick layer of microporous insu-lation in the sump area significantly reducedits steel shell temperature through the end of2005. The 29°F reduction in melting areashell temperatures in the furnace reflectscooler autumn temperatures.

Thermocouple readings in tundish sidewalls.

Figure 5

Tundish sequence heat

Ave

rage

tem

pera

ture

s (°

F)

Thermocouple readings in tundish bottoms.

Figure 6

Ave

rage

tem

pera

ture

s (°

F)

Tundish sequence heat

Molten Steel Temperatures and Heat Loss Savings in °F for Tundish No. 4 Versus OthersSSeeqquueennccee hheeaattss LLMMFF TTuunnddiisshh TTuunnddiisshh TTuunnddiisshh HHeeaatt lloossss rreedduuccttiioonnuusseedd iinn aavveerraaggeess eexxiitt tteemmppss.. mmaaxxiimmuumm mmiinniimmuumm mmaaxx..––mmiinn.. wwiitthh mmiiccrrooppoorroouuss

Tundish No. 4 All heats 2,835.8 2,791.1 2,786.3 4.8 1.5°F in tundish

Others All heats 2,834.1 2,789.0 2,782.7 6.3

Tundish No. 4 Heats 2 and up 2,832.3 2,790.3 2,786.3 4.0 1.7°F in tundish

Others Heats 2 and up 2,832.1 2,787.9 2,782.2 5.7

Table 9

FFeebbrruuaarryy 22000077 ✦✦ 3333

CCoonncclluussiioonnss• Steel processed in a ladle insulated with

0.20 inch of microporous insulation wascompared to the same grade of steelprocessed in an uninsulated ladle over10 months and 11 working lining cam-paigns. An average of 2.4 minutes lessLMF power-on time was required forthe insulated ladle, which yielded an11.7 percent reduction in kWh/ton ofsteel. Despite tap temperatures thataveraged 4.5°F colder, the insulatedladle delivered molten steel to the cast-er an average 5.7°F hotter.

• Ladles insulated with 0.20-inch-thickmicroporous insulation had steel shellsan average of 73–112°F colder thanuninsulated ladles in their bottoms andsidewalls.

• A tundish with 0.20-inch-thick microp-orous insulation had a steel shell thatwas 55–237°F colder than a tundishinsulated with 0.25-inch-thick ceramicfiber insulation. The microporous insu-lation kept the tundish backup castable85–235°F hotter than the thickerceramic fiber insulation.

• The microporous insulation in onetundish reduced the steel heat loss anaverage of 1.7°F during sequence cast-ing compared to a tundish insulatedwith thicker ceramic fiber insulation,and an average of 3.9°F less steel heatloss between exiting the LMF andsequence casting.

• A 0.20-inch-thick layer of microporousinsulation in the sump area of the elec-

tric arc furnace kept its steel shell anaverage of 142°F colder than the previ-ous uninsulated furnace refractory lin-ing.

AAcckknnoowwlleeddggmmeennttssThe authors would like to thank the manyemployees of V & M Star that contributed tothis project by installing the microporousinsulation and measuring the tundish thermo-couple temperatures. The authors would alsolike to thank the employees of UniversalRefractories that helped to prepare thetundish linings for this project. The microp-orous insulation background information wasprovided by Microtherm International Ltd.

RReeffeerreennccee11.. Doty, J.R., “Microporous Insulation Use in Steel

Ladles and Ladle Covers,” ISSTech 2003, Indianapolis,Ind. ✦✦

This paper was presented at AISTech 2006 — The Iron & Steel TechnologyConference and Exposition, Cleveland, Ohio, and published in the AISTech 2006 Proceedings.

Installing 0.20-inch-thick microporous insulation.

Figure 7

Installing working lining brick and backfill.

Figure 8

Average EAF Shell Temperature MaximumTemperatures in °F Before and After Insulating

MMeellttiinngg aarreeaa IInnssuullaatteedd ssuummpp ooff ffuurrnnaaccee aarreeaa ooff ffuurrnnaaccee

June 1–Sept. 6, 2005, reline 669 722

Sept. 6–December 2005 640 580

Temperature reduction 29 142

Table 10