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Energy-Rice Lake Coking Coal

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Brilliant solution:

Jeff Wallace of GTR Scales Ltd.,

in Arnprior, Ontario, supplied

CanmetENERGY with a 920i® interfaced to a high resolution Sartorius

base for their coke research lab in

Ottawa. “They wanted to place a given

amount of coke into a furnace and

know when they had burnt off 200

grams. Our sister company, DCH, did it

by manufacturing an equal arm balance. One end has the sample of coke

in the furnace and the other end rests

on the Sartorius. As the coke reacts,

the weight is transferred to the scale

platform, thus showing us what is

happening in the furnace.”

Global steel production is dependent on coal. Steel is an alloy based primarily on iron. As iron occurs only as iron oxides in the earth’s crust, the ores must be

converted, or reduced, using carbon. The primary source of this carbon is coking coal.

Nearly all of the coke produced in the world is fed into blast furnaces to make steel.

World crude steel production was 1.2 billion tons in 2009. Around 761 million tons of

coking coal was used in its production.

Canada annually exports about 30 million tons of coking coal and uses an additional

6 million tons domestically. On behalf of Canadian coal, steel, and metal producers,

CanmetENERGY conducts research and development on metallurgical coal and coke

technologies including energy recovery from coke production, metallurgical coke,

bio-coke, and research into Canadian coal. CanmetENERGY’s coal evaluation, preparation and carbonization facilities are available to industry on a fee-for-service basis to

assist with mine planning, marketing and economic investigations; to ensure low risk

to expensive facilities during coking; and to evaluate the quality of coke, coal and other

alternate fuels including biofuels for metallurgical purposes.

Kirby Wittich, CanmetENERGY research engineer, explains, “On every continent there

is metallurgical coal, junk coal and excellent coal. It depends on the particular seam. We

are looking for very particular bituminous coals. A very quick bench-top

test can be done. We grind the coal up and heat 1 gram of it to about 800⁰ C

in a small crucible. After two minutes we take the lid off. If it is coking coal,

we’ll see a little muffin. If it is not coking coal, it may look exactly as it did

before—just powder.

“Some coal may coke at a certain temperature, and another at a different

range. When we mix those together we have a mixture that cokes at a wider

temperature range. The price difference between coking coal and coal that

would be used in a combustion furnace can be five to ten times. If a mine

shows that they have coking coal, then often a huge investment is made to

mine that coal.”

There are two kinds of coke producers: integrated and merchant. Integrated

coke producers are affiliated or owned by a steel manufacturer; merchant

producers are those who produce coke to be sold on the open market.

Kirby tells us half of CanmetENERGY’s

tests are done for steelmakers and half are

for Canadian coal mines that sell coking

coal to steelmakers. “We test the coal

they send us in the proportions they suggest. But instead of a 4 or 6 meter high

furnace, we test it in a furnace a little

over 1 meter high by adjusting conditions. Among other things, we are testing

to find the force of the wall pressure on

the coke oven, because most of the coke

ovens in the world are old. If there is too

Brilliant solution:

Jeff Wallace of GTR Scales Ltd.,

in Arnprior, Ontario, supplied

CanmetENERGY with a 920i® interfaced to a high resolution Sartorius

base for their coke research lab in

Ottawa. “They wanted to place a given

amount of coke into a furnace and

know when they had burnt off 200

grams. Our sister company, DCH, did it

by manufacturing an equal arm balance. One end has the sample of coke

in the furnace and the other end rests

on the Sartorius. As the coke reacts,

the weight is transferred to the scale

platform, thus showing us what is

happening in the furnace.”

much pressure on the oven wall, it will

crack and leak, and they take many millions to fix.”

Possibly the single biggest concern for

all coke producers is their ability to meet

the requirements of the Clean Air Act

Amendments of 1990 (CAAA ’90). A

cracked oven wall produces emissions,

and emissions bring huge fines. Coke is

produced in a coke battery that is composed of many coke ovens stacked in rows

into which coal is loaded. The generally

accepted guideline is that a battery of coke

ovens has a 20- to 30-year life span. This

premise does not hold up when the merchant coke producer segment is analyzed.

The average age of U.S. merchant batteries

is 40 years. The reason for this is partly

the merchant mentality. An integrated

producer views their coke plant as a disposable asset, producing raw material. In

the end, for an integrated producer, coke

is a “make-or-buy” decision.

The merchant producer knows that his

battery is his livelihood and will take extraordinary steps to maintain his facility.

For example, the oldest merchant battery

operating today was built in 1902 and

still has a future due to continuing facility

renovation and oven rebuilds. The CAAA

’90 has also resulted in the delaying of

the deterioration cycle of coke ovens. The

mechanisms that result in leakage are the

same that cause failure of ovens, so when

leakage is systematically eliminated, the

result is longer battery life.

Coke producers convert metallurgical or

coking coal to coke by driving off small

hydro-carbon molecular units to leave

almost pure carbon. The physical properties of coking coal cause the coal to soften,

liquefy, then resolidify into hard porous

lumps when heated in the absence of air.

Coking coal must also have low sulphur

and phosphorous contents.

The coking process takes place over long

periods of time—between 12-36 hours

in coke ovens. The heat is transferred

from the heated brick walls into the coal

charge. From about 375°C to 475°C, the

coal decomposes to form plastic layers near each wall. At about 475°C to

600°C, there is a marked evolution of tar

and aromatic hydrocarbon compounds,

followed by resolidification of the

plastic mass into semi-coke. At 600°C to

1100°C, the coke stabilization phase begins. This is characterized by contraction

of coke mass, structural development

of coke, and final hydrogen evolution.

During the plastic stage, the plastic

layers move from each wall toward the

center of the oven, trapping the liberated

gas and creating gas pressure build-up,

which is transferred to the heating wall.

Once the plastic layers have met at the

center of the oven, the entire mass has

been carbonized. The incandescent coke

mass is pushed from the oven and is

then quenched with water or nitrogen to

cool it before storage, or it is transferred

directly to the blast furnace for use in

iron making.

Optimal operation of the blast furnace

demands the highest quality of raw materials. The carbon content of coke therefore plays a crucial role in terms of its

effect in the furnace and on the hot metal

quality. A blast furnace fed with high

quality coke requires less coke input and

results in higher quality hot metal and

better productivity. Overall costs may

be lower, as fewer impurities in the coke

means smaller amounts of flux must be

used. Coke producers use widely differing coals and employ many procedures

to enhance the quality of the coke and to

enhance the coke oven productivity and

battery life.

GTR Scales’ unique 920i® and Sartorius

application for CanmetENERGY is

helping create the cleanest, most efficient

coke for the steel-making industry, ensuring blue skies in the future.▪

References:

Dusel, Martin, 4, March 2008, “The Coke Crisis.”

www.accci.org/Dusel.pdf

Ailor, David C, 8, Oct. 2003,”Principal

Environmental Issues Facing the U.S. Coke Industry”

www.accci.org/Ailor.pdf

www.canmetenergy.gc.ca

www.worldcoal.org/coal/uses-of-coal/coal-steel

www1.eere.energy.gov/industry/steel/pdfs/

roadmap_chap2.pdf


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