GRATE-KILN PELLETIZING SYSTEM
GRATE-KILN SYSTEM 

VS

STRAIGHT GRATE
Grate - Kiln Benefits

1. Operational flexibility 

2. Superior product quality and more uniform 

quality

3. Significantly lower electrical power 

consumption 

4. Lower fuel consumption
Grate - Kiln Power Savings

If the power saving between is only 15 kW-hr/ton product, the 

savings in power costs alone would pay for the initial equipment 

cost of Metso’s Grate-Kiln System after only 20 years. 

kW-hr/ton

Difference

between

Grate-Kiln

& Straight

Grate

Savings per

year - $

millions

U.S.

Savings

after 10

Years - $

millions

U.S.

Savings

after 20

Years - $

millions

U.S.

10 8.4 84.0 168.0

15 12.6 126.0 252.0

20 16.8 168.0 336.0

25 21.0 210.0 420.0

Based upon 0.12 $U.S. per kW-hour
Grate - Kiln Fuel Savings

If the fuel saving between the grate-kiln and the straight grate is 

only 10,000 kCal/ton (about 14%), the savings over 20 years is 

about $100,000,000 U.S. 

Based upon fuel oil costs of 0.60 $U.S. per 

liter

kCal/ton Difference

between Grate-Kiln

& Straight Grate

Savings per year –

$ millions U.S.

Savings after 10

Years –

$ millions U.S.

Savings after 20

Years –

$ millions U.S.

5,000 2.47 24.7 49.4

10,000 4.94 49.4 98.8

15,000 7.41 74.1 148.2

20,000 9.88 98.8 197.6
G-K vs S-G FLEXIBILTY

DRYING PREHEATING INDURATION COOLING

STRAIGHT- GRATE

GRATE SPEED IS CONSTANT THROUGHOUT

A REQUIREMENT TO CHANGE RESIDENCE TIME IN ONE SECTION, SUCH 

AS DRYING, CHANGES THE RESIDENCE TIME IN EVERY OTHER SECTION.

HARDER TO OPTIMIZE EACH ZONE, BECAUSE ANY SPEED CHANGE 

EFFECTS ALL OTHER PARTS OF SYSTEM.

LESS FORGIVING OF CHANGES IN FEED OR UPSTREAM PROCESSING
G-K vs S-G FLEXIBILITY

GRATE-KILN

DRYING PREHEATING INDURATION

COOLING

INDEPENDENT VARIABLE SPEED CONTROL OF DRYING/PREHEATING, 

INDURATION, ANDCOOLING TO ACCOMODATE VARYING FEED CONDITIONS

EASY OPERATOR CONTROL. EASY TO SWITCH FROM ONE ORE TO ANOTHER 

WITHOUT PROCESS INTERRUPTION.
G-K vs S-G PELLET QUALITY

FIRED PELLETS /

HEARTH LAYER

STRAIGHT-GRATE

PELLETS

BECAUSE OF THE S-G STATIC BED, SOME PELLETS ARE OVERFIRED, SOME ARE 

UNDERFIRED.

THIS IS DUE TO THE TEMPERATURE GRADIENT THROUGH THE PELLET BED, WHICH IS 

CHARACTERISTIC OF A CROSS-FLOW STATIC BED

OVERFIRED

UNDERFIRED

PROCESS GAS FLOW

TEMPERATURE

PROFILE
PELLET QUALITY

IN A GRATE-KILN SYSTEM, THE KILN MIXES THE PELLETS SO ALL OF THE PELLETS SEE 

THE SAME TEMPERATURE A HOMOGENOUS PRODUCT IS THE RESULT

MORE HOMOGENEOUS PELLETS MEAN MORE STABLE BLAST FURNACE OR DRI PLANT 

OPERATION, AT POTENTIALLY HIGHER TEMPERATURES FOR IMPROVED PERFORMANCE. 

BECAUSE OF UNIFORM FIRING IN THE KILN, THE GRATE-KILN PRODUCES A 

PELLET THAT IS OF SUPERIOR QUALITY

GKS SG
PELLET QUALITY

0

10

20

30

40

50

60

0-50 50-

100

100-

150

150-

200

200-

250

250-

300

300-

350

350-

400

GKS

SG

DISTRIBUTION OF COMPRESSIVE STRENGTH

COMPRESSIVE STRENGTH, (kg)

%
PELLET QUALITY

• G-K REDUCIBILITY (% PER MINUTE ISO 4695) AVERAGED 1.05, 

WITH A MAXIMUM OF 1.44. 

• S-G REDUCIBILITY AVERAGED 0.82.

• REDUCIBILITY RELATES TO RATE OF REDUCTION, HIGHER IS 

BETTER.

• G-K FINES (LOW TEMPERATURE BREAKDOWN -0.5mm, ASTM 

1072) AVERAGED LESS THAN 3%. 

• S-G FINES AVERAGED GREATER THAN 5%.

• FEWER FINES MEANS BETTER PELLET QUALITY AND LESS 

RECYCLE.

TEST RESULTS OF GRATE-KILN AND STRAIGHT GRATE PELLETS FROM INDEPENDENT ISO 

LABORATORY. MULTIPLE PELLET SOURCES.
G-K vs S-G POWER CONSUMPTION

150 - 180 mm

GRATE 

CASTINGS

GREEN PELLETS

GRATE-KILN

250 - 450 mm

75 -150 mm

FIRED PELLETS /

HEARTH LAYER

STRAIGHT-GRATE

GREEN PELLETS

BECAUSE OF THE GREATER BED DEPTH, A S-G WILL ALWAYS HAVE A HIGHER PRESSURE DROP AND 

MORE POWER CONSUMPTION THAN A GRATE-KILN. FAN POWER DEMAND IS DIRECTLY 

PROPORTI0NAL TO BED DEPTH. 

GRATE

BARS
POWER CONSUMPTION

GRATE-KILN KWH/TON STRAIGHT-GRATE KWH/TON

EMPIRE MINE 21.4 HIBTAC 48.6

TILDEN MINE 24.6 MINORCA 37.5

USX MINNTAC 21.5 JINDAL 35.0

FERROMINERA 22.6 KIOCL 36.0

LKAB 18.0

A GRATE-KILN SYSTEM MAY OPERATE AT HALF THE POWER 

CONSUMPTION OF A STRAIGHT GRATE.

POWER CONSUMPTION FOR EQUIPMENT FROM THE INLET OF BALLING 

THROUGH LOADOUT.
FUEL CONSUMPTION

BECAUSE OF :

• MAXIMIZED USE OF PREHEATED COMBUSTION AIR 

• RADIANT HEAT TRANSFER IN THE KILN 

• LESS LEAKAGE AIR SINCE THE TRAVELING GRATE 

OPERATES AT AT CLOSE TO ATMOSPHERIC PRESSURE, NOT 

THE HIGH NEGATIVE PRESSURE OF STRAIGHT GRATES

• NO HEAT LOSS TO HEARTH LAYER

• SINGLE KILN BURNER MORE EFFICIENT THAN MUTLIPLE 

SMALL BURNERS

THE GRATE-KILN SYSTEM HAS A LOWER SPECIFIC FUEL 

CONSUMPTION RATE THAN A STRAIGHT GRATE-SYSTEM.
AVAILABILITY

• THE GRATE IS THE BIGGEST MAINTENANCE ITEM 

ON GRATE-KILN OR STRAIGHT-GRATE SYSTEM. 

• THE GRATE ON A GRATE KILN IS SMALLER, 

OPERATES AT LOWER TEMPERATURES AND 

THEREFORE REQUIRES LESS MAINTENANCE

• GRATE-KILN PLANTS IN THE USA OPERATE AT A 

+98.5% AVAILABILITY*

• 1 EXTRA DAY OF AVAILABILITY IS EQUAL TO AN 

EXTRA 21,000 TONS OF PELLETS (7,000,000 TPY 

PLANT)

*OF SCEHDULED RUNNING TIME
MAINTENANCE

GRATE-KILN STRAIGHT-GRATE

REFRACTORIES 75.0g/ton pellet 60.0g/ton pellet

ALLOY PARTS 8.2g/ton pellet 21.0g/ton pellet

MAJOR DIFFERENCES

GRATE CAR WELDING N/A ADDITIONAL STAFF
EQUIPMENT EVOLUTION

Grate

width 3.75m 5.65m 5.65m

length 29.0m 49m 73m

Kiln

diameter 3.05m 6.9m 7.47m 

length 36.6m 39.6m 40m 

Cooler

mean dia. 7.7m 20.1m 28m 

pallet width 1.3m 3.05m 3.65m 

Note: the 6,000,000 tpy system is currently under 

construction at LKAB and is scheduled for start-up in early 

2008.

1960’S 1970’S 2000’S

1,000,000 4,000,000 6,000,000

tpy tpy tpy
GRATE-KILN SYSTEM