Home Refractory Knowledge Basic Refractories and Development of Osymen Refractories

Basic Refractories and Development of Osymen Refractories

Abstract

The importance of basic refractories during the development of steel, non-ferrous and cement industries was introduced. The process of magnesia-chrome bricks was expounded. The development history of basic refractories of Osymen as well as the research and application of magnesia-chrome bricks and chrome free bricks for RH vacuum refining furnaces, heavy non-ferrous smelting furnaces, and cement kilns was emphasized.

Key wordsbasic refractories; Osymen; magnesia-chrome bricks; chrome free bricks

 

1 Introduction

Basic refractories have high refractoriness under load and good resistance to basic slag and iron slag. Since the reform and opening-up in 1979, China’s heavy industries, such as steel, building materials and non-ferrous metals, has been deve-loped rapidly, increasing urgent demand for basic refractories. Representative magnesia-chrome refractories are widely used in cement rotary kilns, steelmaking furnaces, refining furnaces, non-ferrous metallurgical furnaces, lime kilns, metal mixers, etc.

 

2 Process of Magnesia-chrome Bricks

2.1 Silicate Bounded Magnesia-chrome Bricks

Silicate bonded magnesia-chrome bricks, known as ordinary magnesia-chrome refractories, have high impurity contents, which were prepared using ordinary chromium ore and mid-grade magnesia and firing at about 1 550 °C, with silicate bond between the grains. In the 1950s, magnesia-chrome products were bonded only by silicate, whose matrix mainly consisted of silicate phases, a small amount of forsterite, and other low melting point phases. Due to the low melting point of the matrix and the corresponding low sintering temperatures, they had poor slag resistance and corrosion resistance as well as low hot strength. The earliest improvement method of the bricks was increasing the calcination temperature to achieve a relatively stable bond. Figure 1 shows the SEM images of a silicate bonded magnesia-chrome brick.

Review-of-Basic-Refractories-and-Development-History-of-Osymen-Basic-Refractories-figure1

 Fig. 1 SEM images of silicate bonded magnesia-chrome brick

 

 

2.2 Direct Bonded Magnesia-chrome Bricks

In the 1960s, direct bonded magnesia-chrome bricks began to be industrially produced and applied. Considering the adverse effects of impurities, direct bonded magnesia-chrome bricks were prepared using high-grade chrome concentrate and high-purity magnesia to minimize the SiO2 and CaO contents, and firing at high temperatures above 1 700 °C. Periclase particles were directly bonded or bonded by spinel, with a few silicate phases at the boundaries, as shown in Fig. 2. Owning to the dense structure, direct bonded magnesia-chrome bricks performed good hot strength and slag resistance.

	Review of Basic Refractories and Development History of Osymen Basic Refractories figure2

Fig. 2 SEM images of direct bonded magnesia-chrome bricks

 

 

2.3 Fully Synthetic Magnesia-chrome Bricks (Co-clinker Magnesia-chrome Bricks)

Sintered synthetic magnesia-chrome clinker was prepared using light burned magnesite powder and chrome ore fine powder or fine particles, grinding to fines below 0.074 mm, pressing to balls at high pressures, and sintering at above 1 800 °C in tunnel kilns or rotary kilns. Magnesia-chrome bricks were prepared using the obtained clinker or adding some chrome ore and firing at 1500°C, which were known as fully synthetic magnesia-chrome bricks. The production was a typical European technology with complex processes. Spinel solid solution was evenly distributed in the synthetic iron-rich magnesia-chrome material, and the products had the advantages of stable performance, good thermal shock resistance and slag corrosion resistance.

 

2.4 Rebonded Magnesia-chrome Bricks and Semi-rebonded Magnesia-chrome Bricks

With the continuous development of black metallurgy (appearance of refining equipment) and non-ferrous metallurgy (such as copper, lead and zinc smelting) industries, higher requirements were put forward for the performance of magnesia-chrome bricks, and China began to explore their process route suitable for China’s resources. China has ample magnesite resources, with the MgO content ranging from 89% to 98%. High-purity magnesia produced with magnesite and light-burned magnesia powder has a low bulk density of 3.10-3.25 g·cm-3. China’s chrome ore resources are insufficient but have high impurity contents, mainly distributing in Tibet and Xinjiang, which is extremely inconvenient in mining and transportation. South African chrome ores have low impurity contents and high iron oxide contents. China needs to import a considerable amount of South African chrome ores as refractory raw materials. Based on the magnesite resources in China, the researchers tried to fabricate magnesia-chrome clinker with light burned magnesia and chrome ore sintering in ultra-high shaft kilns ( at ~2 000 °C) and found that the synthetic material adhered to the kiln lining. The magnesia-chrome clinker sintered with caustic magnesia and chrome ore in ultra-high shaft kilns had low bulk density. So the European technology of fully synthetic magnesia-chrome bricks was not suitable for China. China had independently developed and produced high-quality fused magnesia-chrome clinker, gradually forming systems of fused semi-rebonded and fused rebonded magnesia-chrome bricks. Magnesia-chrome bricks prepared completely with fused magnesia-chrome clinker are called rebonded magnesia-chrome refractories. Due to the pure starting materials and high firing temperatures above 1 750 °C, spinel and other components in the bricks were distributed evenly, with direct contact among the grains, endowing the bricks with good hot performance. SEM images of the rebonded magnesia-chrome refractories are shown in Fig. 3.

2.3 Fully Synthetic Magnesia-chrome Bricks (Co-clinker Magnesia-chrome Bricks)
Sintered synthetic magnesia-chrome clinker was prepared using light burned magnesite powder and chrome ore fine powder or fine particles, grinding to fines below 0.074 mm, pressing to balls at high pressures, and sintering at above 1 800 °C in tunnel kilns or rotary kilns. Magnesia-chrome bricks were prepared using the obtained clinker or adding some chrome ore and firing at 1 500 °C, which were known as fully synthetic magnesia-chrome bricks. The production was a typical European technology with complex processes. Spinel solid solution was evenly distributed in the synthetic iron-rich magnesia-chrome material, and the products had the advantages of stable performance, good thermal shock resistance and slag corrosion resistance.
2.4 Rebonded Magnesia-chrome Bricks and Semi-rebonded Magnesia-chrome Bricks
With the continuous development of black metallurgy (appearance of refining equipment) and non-ferrous metallurgy (such as copper, lead and zinc smelting) industries, higherrequirements were put forward for the performance of magnesia-chrome bricks, and China began to explore their process route suitable for China’s resources. China has ample magnesite resources, with the MgO content ranging from 89% to 98%. High-purity magnesia produced with magnesite and light-burned magnesia powder has a low bulk density of 3.10-3.25 g•cm-3. China’s chrome ore resources are insufficient but have high impurity contents, mainly distributing in Tibet and Xinjiang, which is extremely inconvenient in mining and transportation. South African chrome ores have low impurity contents and high iron oxide contents. China needs to import a considerable amount of South African chrome ores as refractory raw materials. Based on the magnesite resources in China, the researchers tried to fabricate magnesia-chrome clinker with light burned magnesia and chrome ore sintering in ultra-high shaft kilns ( at ~2 000 °C) and found that the synthetic material adhered to the kiln lining. The magnesia-chrome clinker sintered with caustic magnesia and chrome ore in ultra-high shaft kilns had low bulk density. So the European technology of fully synthetic magnesia-chrome bricks was not suitable for China. China had independently developed and produced high-quality fused magnesia-chrome clinker, gradually forming systems of fused semi-rebonded and fused rebonded magnesia-chrome bricks.Magnesia-chrome bricks prepared completely with fused magnesia-chrome clinker are called rebonded magnesia-chrome refractories. Due to the pure starting materials and high firing temperatures above 1 750 °C, spinel and other components in the bricks were distributed evenly, with direct contact among the grains, endowing the bricks with good hot performance. SEM images of the rebonded magnesia-chrome refractories are shown in Fig. 3.

Fig. 3 SEM images of rebonded magnesia-chrome refractories

Semi-rebonded magnesia-chrome refractories were prepared with fused magnesia-chrome clinker as particles, sintered fine powder or mixed powder of chrome concentrate and magnesia as the fine powder, firing at above 1 700 °C, and periclase crystals were mainly directly bonded. The refractories had the characteristics of both direct bonded magnesia-chrome refractories and fused rebonded magnesia-chrome refractories: the main phase of periclase was mostly directly bonded by periclase-spinel, and a little was bonded by silicate. The products had excellent slag corrosion resistance and good thermal shock resistance. SEM images of the semi-rebonded magnesia-chrome refractories are shown in Fig. 4.

Semi-rebonded magnesia-chrome refractories were prepared with fused magnesia-chrome clinker as particles, sintered fine powder or mixed powder of chrome concentrate and magnesia as the fine powder, firing at above 1 700 °C, and periclase crystals were mainly directly bonded. The refractories had the characteristics of both direct bonded magnesia-chrome refractories and fused rebonded magnesia-chrome refractories: the main phase of periclase was mostly directly bonded by periclase-spinel, and a little was bonded by silicate. The products had excellent slag corrosion resistance and good thermal shock resistance. SEM images of the semi-rebonded magnesia-chrome refractories are shown in Fig. 4.

Fig. 4 SEM images of semi-rebonded magnesia-chrome refractories

 

 

3 Development History of Basic Refractories
3.1 Exploration of Ordinary Basic Refractories

In January 1972, the second silica brick workshop of Luoyang Refractory Co., Ltd. (now named as Sinosteel Luonai) was changed to a magnesia brick workshop by the Department of Metallurgy. The first kiln of magnesia bricks was successfully prepared on July 10, with a yield of 96.14%. Subsequently, magnesia-chrome bricks with the refractoriness higher than 2 000 °C were successfully produced with sintered magnesia and chromite as raw materials, and magnesia alumina bricks were produced with sintered magnesia and underfired high alumina.In May 1973, the magnesia brick workshop of Sinosteel Luonai totally invested CNY 4.5 million for the the expansion project. The tunnel kiln fueled by heavy oil was dried on December 28, 1977 and began production on February 4, 1978. Positions 1-11 of the tunnel kiln were the drying zone (33 m in length) and positions 12-63 were the kiln body (156 m in length), of which positions 12-34 were the preheating zone, positions 35-44 were the firing zone, and positions 45-63 were the cooling zone. The kiln car had the dimensions of 3 m long, 3.1 m wide, and 1.72 m high. The kiln was 3.2 m wide, the height from the kiln car surface to the kiln crown was 1.1 m, and the gauge was 1.52 m. The fuel for the kiln was producer gas. Eight pairs of burners were installed in the firing zone. High pressure jet hot air device was provided between positions 45-46.In June 1975, to solve the loose effect and further improve the quality of bricks, new pre-reactive magnesia-chrome bricks were developed by a new method of secondary crushing, secondary ramming and secondary firing, which had high refractoriness under load, good thermal stability, high refractoriness, and long service life.From January to March 1980, Sinosteel Luonai undertook the National Seventh Five-year Plan and explored the process of fused magnesia-chrome clinker together with Luoyang Institute of Refractories Research Co., Ltd. A fusion section was set up and a 0.5 t electric furnace was installed in a magnesia brick workshop to produce fused magnesia and fused magnesia-chrome clinker, which created conditions for the production of fused products.In 1982, sheet steel covered unburned magnesia-chrome bricks were successfully prepared, filling a blank of refractories in China.In 1986, a 156 m tunnel kiln started operation using heavy oil instead of coke for direct kiln drying, which overcame the spalling of the kiln crown bricks, reduced the labor intensity, improved the operating environment, and shortened the drying time for 7 days.During this period, Sinosteel Luonai completed the hard exploration of magnesia-chrome bricks, but it was still in the initial stage of the research about silicate bonded magnesia-chrome bricks. The physical and chemical properties of ordinary magnesia-chrome bricks are listed in Table 1.

Table 1 Physical and chemical properties of ordinary magnesia-chrome bricks

Items

MGe-8

MGe-12

MGe-16

MgO /mass%

68.5

65.1

59.6

Cr2O3 /mass%

8.5

12.2

16.8

Apparent porosity /%

18.3

17.2

17.2

Cold compressive strength /MPa

37

40.0

42.3

Refractoriness under load (0.2 MPa) /°C≥

≥1600

≥1650

≥1650

 

 

3.2 Development and Progress of Magnesia- chrome Bricks

The production line of high-quality basic refractories was listed in the National Sixth Five-year Plan.

In 2004, the high temperature tunnel kiln was put into use, and various magnesia-chrome bricks representing the highest level in China at that time were prepared successively, such as direct bonded magnesia-chrome bricks, semi-rebounded magnesia-chrome bricks, fused rebounded magnesia-chrome bricks, fused magnesia-chrome bricks and fully synthetic magnesia-chrome bricks. They were initially applied to RH vacuum refining furnaces, large cement rotary kilns and non-ferrous converters, greatly improving their service life, which had been unanimously recognized by the market.

In 2016, dust removal and denitration systems were added to the kiln achieving ultra-low emissions. Osymen had the most advanced combined workshop, advanced cutting and grinding combination and salt immersion equipment, which could satisfy the pre-construction and assembly of any kilns.

 

 

4 Basic Refractories for RH Vacuum Refining Furnaces

4.1 RH Vacuum Refining Furnaces

RH vacuum hot steel circulating degassing method was successfully co-developed by Ruhrstahl and Heraeus, which was named as RH vacuum degassing. In this method, by vacuuming, the hot steel in the ladle entered the vacuum vessel, meanwhile, as the argon was blown into the inlet snorkel of the immersed snorkel, the hot steel entered the inlet snorkel and flowed back to the ladle through the outlet snorkel, then hydrogen and impurities in the hot steel were removed through the circulation. The function and refined steel types of RH had been gradually expanded, developing into a multi-functional vacuum refining technology that was dominant in secondary refining technology.In order to adapt to the stable production of ultra-low carbon steel and improve the operation capability of RH furnaces, especially with the increase of the production of some special steel, the circulation flow of RH furnaces was increased, the blowing gas was increased and the circulation speed of hot steel was accelerated. The increased blowing cold gases (argon, nitrogen and cold air) led to hot spalling and the increased molten slag absorption aggravated structural spalling and corrosion, resulting in more serious damage of lining materials.

 

4.2 Magnesia-chrome Bricks of OSYMEN for RH Refining

Magnesia-chrome bricks prepared with sintered magnesia-chrome clinker or fused magnesia-chrome clinker (or a portion of fused magnesia) were the first choice for the lining working layer of RH furnaces. The products were applied in major steel mills in China, and gradually replaced the foreign expensive basic refractories. The physical and chemical properties of direct bonded, semi-rebounded and rebounded magnesia-chrome bricks for RH furnaces are listed in Tables 2-4, respectively.

Table 2 Physical and chemical properties of direct bonded magnesia-chrome bricks for RH furnaces

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

DMK-8AS

78.0

1.2

8-11

17.0

3.17

50

>1700

6

DMK-8A

78.0

1.5

8-11

17.0

3.15

50

>1700

6

DMK-8B

78.0

2.0

8-11

18.0

3.10

45

>1680

7

DMK-12AS

72.0

1.2

12-15

17.0

3.17

50

>1700

6

DMK-12A

72.0

1.5

12-15

17.0

3.15

50

>1700

6

DMK-12B

72.0

2.0

12-15

18.0

3.10

45

>1680

7

DMK-16AS

65.0

1.2

16-19

17.0

3.18

50

>1700

6

DMK-16A

64.0

1.5

16-19

17.0

3.15

45

>1700

6

DMK-16B

62.0

2.0

16-19

18.0

3.10

40

>1680

7

DMK-20AS

59.0

1.2

20-23

18.0

3.20

45

>1700

6

DMK-20A

58.0

1.5

20-23

18.0

3.15

40

>1700

6

DMK-20B

56.0

2.0

20-23

19.0

3.10

35

>1700

7

 

Table 3 Physical and chemical properties of semi-rebonded magnesia-chrome bricks for RH furnaces

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

SRK-16A

62.0

1.2

16-18

16.0

3.15

50

>1700

5

SRK-16B

60.0

1.7

16-18

17.0

3.12

45

>1700

6

SRK-20A

58.0

1.2

20-22

16.0

3.18

45

>1700

5

SRK-20B

55.0

1.7

20-22

16.0

3.15

40

>1700

6

Table 4 Physical and chemical properties of rebonded magnesia-chrome bricks for RH furnacesTable

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

RMK-20AS

61.0

1.0

20-23

15.0

3.30

65

>1700

4

RMK-20A

60.0

1.2

20-23

16.0

3.25

60

>1700

4

RMK-20B

59.0

1.5

20-23

17.0

3.22

55

>1700

5

RMK-24AS

56.0

1.0

24-27

15.0

3.32

65

>1700

4

RMK-24A

56.0

1.2

24-27

16.0

3.27

60

>1700

4

RMK-24B

54.0

1.5

24-27

17.0

3.24

55

>1700

5

 

 

4.3 Chrome Free Materials of Osymen for RH furnaces

A granular structure was formed in the magnesia spinel bricks with the crystals embedded with each other, which reduced the wetting angle of steel slag to the bricks thus improving their corrosion resistance. The pore diameter was reduced by special processes, decreasing the penetration of steel slag to the bricks. Meanwhile, the bricks were toughened through high temperature firing, and the thermal shock resistance was enhanced.

 

5 Basic Refractories for Heavy Non-ferrous Smelting Furnaces

In 1983, non-ferrous metal metallurgy industry in China embarked on the track of rapid development and introduced a complete set of flash melting technology from abroad to improve the level of technical equipment, which rapidly increased the yield of non-ferrous metals. The lining of non-ferrous metallurgical furnaces was mainly damaged by the comprehensive action of the penetration and thermal stress of molten metal, metal oxides, sulfide or slag. The following conditions might occur when the molten metal, oxides, sulfide, or slag penetrated into the lining interior along the pores.
(1) Molten metal was oxidized, reduced or transformed into low melting point minerals, leading to corrosion, cracks or spalling of the lining.
(2) Molten metal or oxides were deposited, resulting in lining expansion and collapse.
(3) Because of the high fluidity, strong basic molten metal or slag seriously eroded and corroded the lining. For example, the melting point of copper is 1083°C.
During smelting, the molten metal would penetrate into the lining and oxidize accompanied by volume expansion. As copper was oxidized to Cu2O, it expanded by 0.64 times, and it expanded by 0.75 times when oxidizing to CuO. That is, due to the different temperatures on the section of lining for copper melting, the penetrated copper presented different forms and the generated volume changes led to cracks and even spalling of the lining. At certain temperatures, the copper oxides could react with some oxides in the refractories to generate liquid phase with low melting point, which destroyed the structure of bricks and formed melting corrosion, decreasing the service life of materials. For example, the copper oxides generated liquid phase with SiO2, MgO and Cr2O3 at 1060, 1135, and 1560°C, respectively.

 

5.1 Basic Refractories for Jinchuan Nickel Flash Furnace

The Jinchuan nickel flash furnace was the fifth large one in the world and the first large one in Asia at that time. It was put into production in 1993. Jinchuan Group Co., Ltd. produced 27 000 t of electrolytic nickel in 1994, of which the flash furnace smelted 17 000 t. To ensure the service life, imported refractories were used in the parts of the Jinchuan flash furnace that were prone to failure, and domestic refractories were used as far as possible in other parts, including a total of 1 256 t of domestic refractories accounting for 61.3% of the whole refractories, 722 t of magnesia-chrome bricks from Austria accounting for 35.2%, and 72 t of fused magnesia-chrome bricks from French accounting for 3.5%. Domestic basic refractory direct bonded magnesia-chrome bricks, fused magnesia-chrome bricks, sintered synthetic magnesia-chrome bricks, and the corresponding masonry materials were used in 1990, the bricks were trialed in slag cleaning furnace 1# similar to the nickel flash furnace, achieving good effects and realizing the localization of refractories for nickel flash furnaces.

 

5.2 Basic Refractories for Copper Oxygen-rich Autothermic Bath Smelting Technology of Baiyin Furnaces

Completely different from the production methods of conventional sintered refractories, the fusion-cast magnesia-chrome refractories were prepared with magnesia and chrome ore, adding a certain admixture, batching, melting in an arc furnace, casting to molds, annealing, then cutting, grinding and drilling. In 1996, fusion-cast magnesia-chrome bricks were success-fully used in Baiyin furnaces and could completely replace the import products, satisfying the requirements of key parts of the furnaces such as the melting tuyere, the tuyere zone, and the slag line, which played a positive role in promoting the development of copper oxygen-rich autothermic bath melting technology.

 

5.3 Localization of Refractories for Copper Smelting Flash Furnaces in Guixi Smelter

In the early 1980s, China built the first modern copper smelting factory: Jiangxi Copper Group Co., Ltd. Guixi Smelter (Guixi Smelter, hereinafter). The chemical reactions of the flash melting process were fierce with high speed, high thermal strength, and complex atmosphere in the furnace, which put forward strict demands for the lining refractories. Therefore, a complete set of refractories for the flash furnace lining were imported. In 1986, Guixi Smelter and Sinosteel Luonai jointly conducted comprehensive discussion and practice on the application of flash furnace lining refractories and furnace building technology, promoting the localization of refractories and improving the furnace structure combined with the production practice of Guixi Smelter, which ended the dependence on imports of refractories for flash furnace linings.

 

5.4 Development of Basic Refractories for Heavy Non-ferrous Smelting

With the rapidly increasing yield of non-ferrous metals after the reform and opening-up, China had become the largest non-ferrous metal country in the world. New technologies and new processes with advanced world levels had been applied in production, such as copper and lead flash melting technologies, copper and lead oxygen-rich bath melting technologies, oxygen bottom blowing lead and copper smelting processes with independent intellectual property, PS converters, ISA furnaces, and dual side-blown furnaces, which greatly improved the level of heavy metal smelting technology in China.

In view of these new processes, direct bonded magnesia-chrome bricks, semi rebonded magnesia-chrome bricks, and fused rebonded magnesia-chrome bricks for non-ferrous smelting developed and produced by Osymen were well used in these various furnaces, such as 400 heats of tuyere bricks for Guixi Smelter converters and bricks for non-ferrous side blowing furnaces accounting for more than 70% of the domestic market. Their physical and chemical properties are listed in Tables 5-7. The bottom blowing furnace oxygen lance and refractory bricks were produced with pre-synthetic spinel by the technology of secondary spinellization during sintering process, and their service life reached the foreign level of the same period.

With the increase of the consumption of non-ferrous metals, more and more waste and miscellaneous non-ferrous metals accumulated in the society. It was inevitable for sustainable development to strengthen the recycling of these non-ferrous metals and build large-scale renewable resources recycling and utilization distribution center. To adapt to various complex working conditions, it was urgent to further improve the corrosion resistance and the hot strength of magnesia-chrome refractories for non-ferrous industrial kilns. Pre-synthetic pure MgO-Cr2O3 spinel was added to strengthen the matrix, and an appropriate amount of micropowder was added to promote sintering considering that the increased Cr2O3 content would reduce the sintering properties. Magnesia-chrome refractories for non-ferrous smelting were produced using high quality high-content chromium ore or extra adding a certain amount of alumina chrome slag bricks, molding at high pressures, and firing at high or ultra-high temperatures by Osymen, which were widely used in various kilns of non-ferrous industry, such as converters, anode furnaces, flash furnaces, Kaldo furnaces, reverberatory furnaces, silver smelting furnaces, slag cleaning electric furnaces, insulation furnaces, shaft kilns, Baiyin furnaces, settling furnaces, side blowing furnaces, bottom blowing furnaces, top blowing furnaces, Ausmelt furnaces, electric furnaces, zinc volatilizing kilns, Feishang furnaces, and NGL furnaces.

Table 5 Physical and chemical properties of direct bonded magnesia-chrome bricks for non-ferrous industry

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

DMK-12AS

72.0

1.2

12-15

17.0

3.17

50

>1700

6

DMK-12A

72.0

1.5

12-15

17.0

3.15

50

>1700

6

DMK-12B

72.0

2.0

12-15

18.0

3.10

45

>1680

7

DMK-12C

70.0

2.5

12-15

18.5

3.05

40

>1650

7

DMK-12D

68.0

3.5

12-15

19.0

3.00

35

>1600

7

DMK-16AS

65.0

1.2

16-19

17.0

3.18

50

>1700

6

DMK-16A

64.0

1.5

16-19

17.0

3.15

45

>1700

6

DMK-16B

62.0

2.0

16-19

18.0

3.10

40

>1680

7

DMK-16C

61.0

2.5

16-19

18.5

3.05

35

>1650

7

DMK-16D

60.0

3.5

16-19

19.0

3.00

30

>1600

7

DMK-20AS

59.0

1.2

20-23

18.0

3.20

45

>1700

6

DMK-20A

58.0

1.5

20-23

18.0

3.15

40

>1700

6

DMK-20B

56.0

2.0

20-23

19.0

3.10

35

>1700

7

DMK-20C

55.0

2.5

20-23

20.0

3.05

35

>1700

7

DMK-20D

52.0

3.0

20-23

21.0

3.00

30

>1650

7

Table 6 Physical and chemical properties of semi-rebonded magnesia-chrome bricks for non-ferrous industry

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

SRK-12A

72.0

1.2

12-14

16.0

3.15

50

>1700

5

SRK-12B

70.0

1.7

12-14

16.0

3.10

45

>1700

6

SRK-16A

62.0

1.2

16-18

16.0

3.15

50

>1700

5

SRK-16B

60.0

1.7

16-18

17.0

3.12

45

>1700

6

SRK-20A

58.0

1.2

20-22

16.0

3.18

45

>1700

5

SRK-20B

55.0

1.7

20-22

16.0

3.15

40

>1700

6

 

Table 7 Physical and chemical properties of fused rebonded magnesia-chrome bricks for non-ferrous industry

OSYMEN

MgO

SiO2

Cr2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

1100°C Water

%

%

%

%

g/cm3

MPa

(Ta)°C

Cycles

RMK-16AS

65.0

1.0

16-19

15.0

3.28

65

>1700

5

RMK-16A

65.0

1.2

16-19

16.0

3.25

60

>1700

4

RMK-16B

63.0

1.5

16-19

17.0

3.20

55

>1700

5

RMK-16C

63.0

1.8

16-19

17.0

3.15

50

>1700

5

RMK-20AS

61.0

1.0

20-23

15.0

3.30

65

>1700

4

RMK-20A

60.0

1.2

20-23

16.0

3.25

60

>1700

4

RMK-20B

59.0

1.5

20-23

17.0

3.22

55

>1700

5

RMK-20C

58.0

1.8

20-23

17.0

3.20

50

>1700

5

 

6 Basic Refractories for Cement Kilns

Since the early 1980s, China had introduced complete sets of technical equipment of large dry-process cement kilns from abroad, which required refractories with good resistance to thermal stress damage, thermal fatigue, mechanical stress damage, and corrosion of alkali, sulfur and chlorine, as well as good coating adhesion performance. Ordinary magnesia-chrome bricks couldn’t meet the processing technology requirements of the firing zone and the transition zone of new dry-process cement rotary kilns, so that direct bonded magnesia-chrome bricks and magnesia spinel bricks were imported for the firing zone and the transition zone, respectively.

In the early 1990s, to improve their corrosion resistance to cement clinker, direct bonded magnesia-chrome bricks for the firing zone were manufactured mainly with a large proportion of fused magnesia-chrome synthetic materials, chrome concentrate, high purity magnesia and fused magnesia as raw materials by Osymen, which gave full play to the corrosion resistance and the expansion difference of various materials, producing micro- cracks during firing and cooling in the products, thus improving the thermal shock resistance and toughness. High pressure forming and ultra-high temperature firing improved the compressive strength, the bulk density and the refractoriness under load of the products. The ultra-fine powder addition miniaturized the pores, improving the thermal shock resistance and achieving good application performance. High-purity raw materials were adopted to prepare high-grade magnesium aluminate spinel bricks for the transition zone, and the impurity content was strictly controlled such as CaO and SiO2. Microcracks were generated during firing due to the expansion coefficient difference between periclase and spinel, thus enhancing the structural toughness of the products, cushioning the thermal stress, terminating the expansion of cracks, and improving the thermal shock resistance and structural spalling resistance. The properties of the direct bonded magnesia-chrome bricks and magnesium aluminate spinel bricks for cement kilns are listed in Tables 8-9.

Because of the excellent application effect, the manufacturers with large dry-process cement kilns in China began to use the high-grade basic refractories produced by Osymen, which had fully realized the localization of refractories for dry-process cement kilns.

Table 8 Properties of direct bonded magnesia-chrome bricks for cement kilns

OSYMEN

MgO

Al2O3+Cr2O3

A.P

B.D

C.C.S

R.U.L

TSR, 950 oC

TE

1100°C

TC

1000°C

%

%

%

g/cm3

MPa

(Ta)oC

Air Cycles

%

W/m.K

CMKS-4A

78.0

Cr2O3: 2-4

17.0

2.95

65

>1700

>100

1.05

2.5

CMKS-4B

76.0

Cr2O3:  2-4

18.0

2.92

60

>1680

>100

1.05

2.5

CMKS-9A

80.0

6-9

18.0

2.95

50

>1680

>100

1.03

2.5

CMKS-9B

78.0

6-9

19.0

2.92

45

>1660

>80

1.03

2.5

 

 

Table 9 Properties of magnesium aluminate spinel bricks for cement kilns

OSYMEN

MgO

Al2O3

A.P

B.D

C.C.S

R.U.L

T.S.R

950°C Air

T.E

1100°C

TC

1000°C

%

%

%

g/cm3

MPa

(Ta)oC

Cycles

%

W/m.K

CMAS-8AX

88.0

5-10

15.0

2.98

70

>1700

>100

1.20

3.0

CMAS-8AS

87.0

5-10

16.0

2.96

65

>1700

>100

1.20

3.0

CMAS-8A

86.0

5-10

17.0

2.94

65

>1700

>100

1.15

3.0

CMAS-8B

86.0

5-10

18.0

2.92

60

>1700

>100

1.15

3.0

CMAS-10AX

85.0

8-12

15.0

2.97

70

>1700

>100

1.20

3.0

CMAS-10AS

84.0

8-12

16.0

2.95

65

>1700

>100

1.20

3.0

CMAS-10A

82.0

8-12

16.0

2.93

65

>1700

>100

1.15

3.0

CMAS-10B

82.0

8-12

18.0

2.91

60

>1700

>100

1.15

3.0

CMAS-15AX

84.0

13-15

15.0

2.98

70

>1700

>100

1.20

3.0

CMAS-15AS

84.0

13-15

15.0

2.96

70

>1700

>100

1.20

3.0

CMAS-15A

80.0

13-15

16.0

2.94

65

>1700

>100

1.15

2.9

CMAS-15B

78.0

13-15

18.0

2.92

60

>1700

>100

1.15

2.8

CMAS-20AX

78.0

18-22

15.0

3.02

70

>1700

>100

1.20

2.8

CMAS-20AS

77.5

18-22

15.0

3.00

70

>1700

>100

1.20

2.8

CMAS-20A

77.3

18-22

16.0

2.98

65

>1700

>100

1.20

2.8

 

With the increasing environmental protection awareness, the application of chrome free basic bricks in cement kilns was rapidly expanded, and some developed countries almost stopped using magnesia-chrome bricks. Instead, dolomite bricks, magnesia calcium zirconate bricks, and magnesia spinel bricks were widely used for the firing zone, and magnesia spinel bricks and magnesia calcium zirconate bricks were widely used for the the transition zone. Meanwhile, Osymen began to study chrome free refractories for cement kilns.

 

7 Conclusion

Looking back, Osymen have played an important role in promoting the development of basic refractories in China. Based on the high-temperature industry, Osymen will moderately expand the relevant strategic emerging material industries, provide full life cycle services for the high-temperature industrial refractories, and achieve high-quality green development driven by innovation.

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Last updated: 2024-01-03
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