LOESCHE METHOD FOR MANUFACTURING ULTRA-FINE BLAST FURNACE SLAG

Dr. Holger Wulfert, Dr. Winfried Ruhkamp, Andre Bätz, Paul ErwerthMaterial Tests: Prof. Ludwig, Bauhaus University, Weimar, FIB

Blast furnace slag grain with reaction seam of CSH phases (taken by B. Möser, Bauhaus University, Weimar, FIB)

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1. Initial situation

Due to the high CO2 emissions that are associat-ed with the production of Portland cement clinker, a central objective of the cement manufacturer is to reduce the clinker proportion by using composite materials. One of the most important composite materials is blast furnace slag. The amounts of blast furnace slag that accumulate are used almost exclusively today as a composite material in cement or a concrete additive in concrete. The usual fi neness range of the blast furnace slag is between 3,500 and 6,000 Blaine.To be able to exploit the performance potential of blast furnace slag fully, material producers have expressed again and again the wish for a suitable preparation technique for creating the fi nest blast furnace slag.

Ultra-fi ne blast furnace slag could reduce one of the main weaknesses of cements containing blast furnace slag, that being too little early strength for many applications (Diagram 1).As is already apparent today, the ultra-fi ne blast furnace slag could be used for many different specialised products. Until now extremely fi nely ground blast furnace slag (> 10,000 Blaine) has been produced in ball mills (mostly in batch operation) in a very energy-intensive way. Generating such a high degree of fi neness requires an enormous amount of energy. The consequent high cost of the corre-sponding products has so far prevented a great-er market penetration, with the result being that binder systems based on the fi nest blast furnace slag have so far only been used in niche areas.

Against the backdrop of the situation described above, Loesche has developed a more energy-effi cient production of the fi nest blast furnace slag.The concept includes initially manufacturing a blast furnace slag of typical fi neness (4,500-6,500 Blaine) on a vertical roller mill, from which the fi nest blast furnace slag is separated in an extremely effective and economical manner. This low-cost production of the fi nest blast furnace slag will enable a wider market access for the corresponding products.

2. Tests for attaining ultra-fi ne BFS on pilot scale

Blast furnace slag produced in large-scale Loesche grinding plants usually has fi nenesses between 3500 and 6000 Blaine, max. 7000 Blaine.Investigations on grinding products from an industrial vertical roller mill showed that, depend-ing on the fi neness, grinding products contain ultrafi ne material components with degrees of fi neness of >10,000 Blaine, in the range of approx. 10 to 20 %.A way has been found to be able to use known and tested equipment and technologies to at-tain the ultra-fi ne content without signifi cantly increasing the specifi c power consumption.For this, the product is drawn out of the product silo and fed into a separate plant in order to attain the ultra-fi ne product.As a core part of this type of technology, a specialised cyclone is used for the fi nest dust.

The basic structure of such a system is illustrated in a simplifi ed fl owchart in fi gure 1.

GBFS-mortar mix 50% / 50% with CEM I 52,5 R

0

10

20

30

40

50

60

70

80

90

100

86.9

36.5

77.8

20.1

65.0

42.5

BFS with 5,000 Bl.

38.2

19.6

61.7

BFS with 3,600 Bl. BFS with 17,000 Bl.

2 d 7 d 28 d

Co

mp

ress

ive

stre

ngth

[M

Pa]

Diagram 1: Compressive strength development as a function of BFS-fi neness

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It is known that the fi neness of a fi nal product determines the geometric dimensions of the cy-clone to be used. Because of the relatively small dimensions, generating larger amounts of the product requires working with a larger number of cyclones, which are consolidated into so-called multi-cyclone batteries.

In the fi rst experimental tests, the following points were the focus:

• Proof of the general operational capability and control capability of the multi-cyclone facility regarding the achievable fi neness and the fi ne material yield.

• The use of a disperser, which transfers the grinding material from the grinding plant’s silo back into a gas/solid matter suspension with-out any agglomerates forming.

M

M

M

M

M

Feed silo

Supply

Multicyclone system Filter

9147 9397 9362

Feed to cyclone: Blaine

cm²/g 6000 5000 4500

Feed to cyclone: P50

µm 6.0 6.8 8.5

Portion of ultra fi ne material

% 18 14 10

Ultra fi ne mat. cm²/g 12000 11000 12000

Fines: P50 µm 2.1 2.2 2.1

Grit: Blaine cm²/g 4650 4050 3650

Grit: P50 µm 7.0 8.2 11.4

Table 1: Proportion of ultra-fi ne material and “grit” at different degrees of fi neness in feed

Figure 1: LOESCHE Cyclone-plant for producing of ultrafi ne materials

Disperser

Fan

Ultra fi ne

Grit

4

0

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60

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90

100

The gas/solid matter mixture is transported through the plant with the suction of a fan.The grinding product with a selectable fi neness, between 4500 and 6500 Blaine wherever possible,is stored in a bin and supplied to a disperser facil-ity via a rotary gate and speed-controlled screw conveyor. From here the gas/solid matter mixture reaches the multicyclone.

The ultra-fi ne material leaves the cyclones via the immersion tube and is transported to the fi lter. The material from the lower stream of the mul-ti-cyclone apparatus, called “grit”, has a fi neness in the range of conventional blast furnace slag and can be used as such (Tab.1 and 2).

Feed to cyclone: Blaine cm²/g 5000 4500

Feed to cyclone: P50 µm 6.8 8.5

Portion of ultra fi ne material % 14 9 10 5.5

Ultra fi ne mat.: Blaine cm²/g 11000 16000 12000 17000

Ultra fi ne mat.: P50 µm 2.2 1.7 2.1 1.6

Grit: Blaine cm²/g 4050 3950 3650 3850

Grit: P50 µm 8.2 8.3 11.4 10.7

Table 2: Manufacturing of various ultra-fi ne material at equal fi neness of the feeding material

Diagram 2: Compressive strengths of blended cements with blast furnace slag from a Loesche blast furnace slag grinding plant

36.0

6.5

15.1

Curing time [d]

32.4

43.1

20.2

45.1

53.155.8

2 d 7 d 28 d

1.00 CEM

0.50 BFS meal with 4000 BLAINE

0.70 BFS meal with 4000 BLAINE

Co

mp

ress

ive

stre

ngth

(N/m

m2) /

no

rm p

rism

s

Development of compressive strength compared to CEM I 42,5 R (1.00) and mixtures with 50 and 70 Ma.-% BFS meal(12,600 Blaine)

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3. Cycloning results and material tests of the ultra-fi ne blast furnace slag

In the Loesche test center many grinding and cycloning tests have been carried out with many different types of blast furnace slag over the past year.The throughput of the cycloning plant’s fi ne material is 20 to 80 kg/h.

The greater the fi neness of the feed material (grind-ing material), the higher the proportion of ultra-fi ne material. The higher the proportion of ultra-fi ne ma-terial, the lower its fi neness. These correlations are shown in tables 1 and 2. The degrees of fi neness are stated in Blaine. The authors are aware that the stated values may contain errors, since the Blaine procedure for high degrees of fi neness no longer produces any exact values. Thus the given values have a purely indic-ative value. For these degrees of fi neness it is common to characterise the material with P50 values that have been determined by laser granulometry with a CILAS device.

Of course the user is immediately faced with the question of how the “remaining blast furnace slag” proportion can be used.

Tables 1 and 2 show paired values:• Fineness of the ultra-fi ne material and • of the remaining “grit”.

The degrees of fi neness of the “grit” vary within the ranges of commonly used blast furnace slags.

This makes it clear that there is no waste product and the grit can be used completely normally as a composite material.

Diagrams 2 and 3 show compressive strengths of blended cements with typical degrees of blast furnace slag fi neness (4000 Blaine) and of ultra-fi ne blast furnace slag (12600 Blaine), attained from the 4000 Blaine material, that has been produced in a blast furnace slag grinding plant with a Loesche mill.

With technology of this type, the binder industry in question is made able to produce ultra-fi ne blast furnace slag in a cost-effi cient way.If prices are signifi cantly below those of the prod-ucts currently available on the market, a dynamic development of the demand in various applications is to be expected.

The fi rst manufacturing pilot plant is expected to go into operation in 2018.

Diagram 3: Compressive strengths of blended cements with ultra-fi ne blast furnace slag, attained from a grinding product from a blast furnace slag production plant

0

10

20

30

40

50

60

70

80

90

100

36.030.5

33.2

Curing time [d]

59.7

43.1

63.6

78.8

53.1

69.2

2 d 7 d 28 d

1.00 CEM

0.30 BFS meal 12600 Blaine

0.50 BFS meal 12600 Blaine

0.70 BFS meal 12600 Blaine

25.0

58.9

73.5

Co

mp

ress

ive

stre

ngth

(N/m

m2) /

no

rm p

rism

s

Development of compressive strength compared to CEM I 42,5 R (1.00) and mixtures with 30, 50 and 70 Ma.-% BFS meal (12,600 Blaine)

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M

M

M

M

MM

MM

M

M

M

M

M

M

M

M

M

M

Figure 2: Integrating a cycloning system into a Loesche blast furnace slag grinding plant

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Figure 2: Integrating a cycloning system into a Loesche blast furnace slag grinding plant

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LOESCHE GmbHHansaallee 243D-40549 Duesseldorf, GermanyTel. +49 - 211 - 5353 - 0Fax +49 - 211 - 5353 - 500Email loesche@loesche.dewww.loesche.com