1 4-section top fired stoves successfully applied in new blast furnace

On September 12, 2017, project division of HBIS organized MCC CERI, Tanggang International Engineering Co, Yuxing Limited, Shandong Lunai Refractory Co, Annec Co to attend a technical exchange and discussion meeting. Specailits of the meeting pointed out that as the conical dome of existing 3-section top fired stove is located at the top of hot blast outlet leading to damages to the conical dome under high temperature and the damage rate is up to 90%. Besides, ironmaking experts gave positive comments to the stable structure and long service life of 4-section top fired optimised by Yuxing Limited. After the meeting, Yuxing 4-section top fired stove technology was approved to applied in the 3 newly built blast furnaces with volume 3580m3.

At present, 4-section top fired stoves for 3x3580m3 BFs have commissioned (see pictures below).

In addition, 2x2000m3 BFs at Hebei Tangshan Jinxi Steel and 1350m3 BF at Liaoning Xinpenghui Steel are also adopting 4-section top fired stoves.

                                                                                     Figure 2: Schematic drawing of 3-section top fired (Left one) and 4-section top fired stove (Right one)

2 4-section top fired stoves applied in rebuild projects

In 2003, 3-section top fired stoves were introduced into China. After more than a decade of development, the type of hot blast stoves has gradually changed from internal combustion chamber and external combustion chamber stove to top fired. At present, the market share of top fired hot blast stoves in China is more than 80%. The newly built blast furnaces and blast furnaces with capacity replacement have been 100% equipped with various types of top fired stoves. Top fired stoves have dominated the ironmaking industry in China.

However, early 3-section top fired stoves, after more than 10 years of operation under high hot blast temperature, have revealed significant shortcomings of hot blast outlet suffering high temperature and getting red hot, failure of the conical dome, severe cracking of stove shell, dislocation of gas nozzles of burner and reduction in hot blast temperature, which are subject to frequent repairs leading to huge costs to the clients.

Since 2008, Yuxing Limited has performed rebuild of the combustion chamber and pre-combustion chamber of 3-section top fired stoves with rebuild nos of over 100.

Typical rebuild projects

1) In April 2017, 9 early 3-section top fired stoves rebuild with 4-section fired stoves as replacement for 3x2500m3 BFs at Hebei Zhongtie Plant (See picture below)

                                                                                       Fig 3: Early 3-section top fired stoves rebuild with 4-section fired stoves as replacement

2) Early 3-section top fired stoves rebuild with 4-section fired stoves as replacement for 2x1080m3 BFs at Hebei Anfeng Steel

3) Early 3-section top fired stoves rebuild with 4-section fired stoves as replacement for 1350m3 BF at Chifeng Yuanlian Steel (See Figure 4)

                                                                                    Figure 4: Early 3-section top fired stoves rebuild with 4-section fired stoves as replacement

4) Early 3-section top fired stoves rebuild with 4-section fired stoves as replacement for 2x1350m3 BFs at Liaoning Jiachen Steel

3 Feature of 4-section top fired stove

3-section top fired consists of zones from top to bottom: precombustion chamber (gas and air premixed chamber), combustion chamber (conical dome and hot blast outlet wall), and checker chamber (checker brick chamber and cold blast chamber). Labyrinth connection is adopted between sections. During the use of this kind of stove, there are frequent issues of structural damages of precombustion chamber and combustion chamber, local high temperature of stove shell at hot blast outlet of combustion chamber, conical dome failure and so on. The investigation found that in the use process of this kind of stove, in addition to the 100% damage of gas nozzles of combustion chamber, the most deadly common problem mainly focuses on the stability of hot blast outlet and the conical dome leading to the damage of combustion chamber, and the direct impact is reduction in hot blast temperature. The reason of frequent damages to this zone results from stress and stress concentration existing in this area. For this reason, Yuxing Limited has developed 4-section top fired stove.

It can be seen from the structural schematic diagram of 3-section and 4-section top fired stove that after the conical dome of 3-section top fired stove is independent from hot blast outlet wall then a new precombustion chamber, a conical dome, hot blast outlet straight wall and checkerwork are formed. This becomes 4-section top fired stove. Refractory linings are supported directly on stove shell and the connection between section uses labyrinth.

In the conical stove shell with diameter of the upper part smaller than that of lower zone, the refractory lining is independent from hot blast outlet wall and the connection between both elements uses labyrinth. The thermal stress of brickwork at top of hot blast outlet can be relieved free. In this regard, the thermal stress is equal to the gravity. Besides, this structure is unaffected by construction, materials and performance factors. The elimination of the thermal stress prevents hot blast outlet and the dome from damages, and the risk in dome failure and stove shell getting red hot will be reduced to zero.

4 Development trend of top fired stove

Since 2017, there have been 13 blast furnaces using Yuxing top fired stoves among which 11 blast furnaces using Yuxing 4-section top fired stoves and 2 blast furnaces employing Yuxing catenary top fired stoves. However, the dome of all these stoves is independent from hot blast outlet straight section. As a result, the thermal stress stemming from the expansion of refractories and the concentrated stress are transferred to the stove shell, and the stability of the dome and hot blast outlet straight section are thus ensured. High hot blast temperature can be used stably for a long time without any hidden dangers, and stove shell will not crack due to the impact of the comprehensive stress and the damage and collapse of refractories can be avoided.

Hebei Province is a big iron and steel province in China, whose iron and steel production capacity occupies 30%-40% of China's iron and steel production capacity. The development of large blast furnaces in Hebei Province directly influences and drives the trend of upgrading and development of China's iron and steel equipment. Yuxing Limited has performed a number of 4-section top fired stove projects for over 20 blast furnaces in Hebei province. This proved that Yuxing 4-section top fired stove is the mainstream technology for the development of high hot blast temperature top fired stove for large blast furnace.

In a new round of capacity replacement projects, clients are prone to choosing top fired stove with the dome independent from hot blast outlet wall. The design of top fired stoves is developing towards the direction of unrestricted stress release and elimination of design risk factors. 4-section top fired stoves which thoroughly solves the structural defects of early 3-section top fired stoves will become a new trend in the development of large blast furnace stove with stable structure, long life and high hot blast temperature in the future.