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Showing posts with label Iron and Steel Technology. Show all posts
Showing posts with label Iron and Steel Technology. Show all posts

Refractory Bricks, Mortar and Castable for Reheating Furnace Lining

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17-Jun-2023

Reheating Furnaces serve the purpose of heating various intermediate products of Steel like- ingots, blooms or billets before rolling to give them different shapes of angles, channels, bars, slabs, rods & wires etc 

Read: What are Reheating Furnaces Area wise specifications of Refractory Bricks and Castables or Blocks which can be used for lining of reheating furnaces and the quality of Refractory Mortar which can be used for laying the bricks are given hereunder -

Reheating Furnace Hearth

  1. Dense high alumina bricks with low iron content. Alumina (Al2O3) 88-90%, Iron (Fe2O3) 1.8% (max), Bulk Density (BD) 3-3.2 gm/cc, Apparent Porosity (AP) 16-18%, CCS(kg/cm2) 800 (min), RUL(taOC) around 1550-1600, PLC at 1600OC/2hrs (+/-) 0.2% (max).

  1. Basic Magnesia, Mag-chrome bricks. MgO around 55-60%, Chrome (Cr2O3) around 12-15%, Silica (SiO2) 8% (max), AP 18-20%, CCS (kg/cm2) around 450-500, RUL (taOC) 1600 (min), PLC at 1600OC/2hrs (+/-) 0.5% (max).

Furnace Roof

Alumina (Al2O3) around 70%, Iron (Fe2O3) around 2.5-2.8%, BD 2.6-2.7 gm/cc, AP 21-23%, CCS (kg/cm2) 500 (min), RUL (taOC) around 1450-1500, PLC at 1500OC/2hrs (+/-) 2.5% (max).


Furnace Side-Wall and for General purpose

  1. Low porosity dense bricks. Alumina (Al2O3) 45%, Iron (Fe2O3) 1.6-1.8%, BD around 2.2 gm/cc, AP around 16%, CCS (kg/cm2) around 500, RUL (taOC) 1500 (min).
  2. Alumina (Al2O3) 40%, Iron (Fe2O3) 2.0-2.2%, BD 2.1 gm/cc (min), AP 22% (max), CCS (kg/cm2) around 350, RUL (taOC) 1400 (min).

Furnace Bottom, Blocks (Burner Block, Well Block, Seating Block, Seating Well Block) and Castables

  1. Medium purity Low Cement Castable (LCC). Alumina (Al2O3) around 90%, Iron (Fe2O3) 1.0-1.5%, BD 2.7-2.9 gm/cc, PCE 37 Orton (min), CCS (kg/cm2) at 110OC/24hrs 600 (min), at 1500OC/3hrs 550 (min), PLC at 1500OC/2hrs (+/-) 1.0% (max).
  2. Medium purity Castable conventional type. Alumina (Al2O3) around 60%, Iron (Fe2O3) 1.8% (max), BD 2.1 gm/cc (min), PCE 36 Orton (min), CCS (kg/cm2) at 110OC/24hrs 350 (min), at 1500OC/3hrs 450 (min), PLC at 1500OC/3hrs (+/-) 1.5% (max).

Furnace Door, Flue Stack, Heaters

Insulating Castables. Iron 1% (max), BD 1.0-1.2 gm/cc, CCS (kg/cm2) at 110OC/24hrs around 12-15.


Mortars

Have to be compatible with the laying brick quality (chemical spec).

All the data given above are tentative and should not be considered as ‘Typical Specification Data’. 

Methods of installation (Read: Refractory Installation Procedure and Heating Schedule to be followed after starting a Furnace) may be provided by the refractory supplier.

What are the Reheating Furnaces ? | Refractory Industry | Iron and Steel | Industry Guru

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09-Oct-2022

Reheating Furnaces are used for heating the intermediate products of steel like- ingots, blooms or billets at temperatures around 1000 - 12000C before rolling to give them different shapes of angles, channels, bars, slabs, rods & wires etc. The furnace is a chamber having inside refractory lining to conserve heat and generally includes a mechanism for transporting products continuously from one end to the other end. Heat for the furnace is provided by natural gas or fuel oil.

Reheat Furnace which is considered an accessory to the rolling mill is a critical factor in the quality of end-product. There are various types of reheating furnaces which can be differentiated on the bases of - (1) the method of heating, (2) method of charging the reheating furnace, (3) the movement of steel stock in the reheating furnace, and (4) the heat recovery methods.

Based on the method of heating, a reheating furnace can be Combustion Heating type or Electrical Heating type. The combustion heating type furnace can use solid, liquid, or gaseous fuel. Based on the method of charging, the reheating furnace can be classified as Batch type or Continuous type. In batch type reheating furnaces the charged material remains in a fixed position on the hearth until heated to rolling / forging temperature while in continuous type reheating furnaces the charged material moves in the reheating furnace and is heated to rolling temperature as it progresses in the furnace. Based on the movement of steel stock inside the furnace, continuous type reheating furnaces can be further classified as Pusher Furnace, Rotary Hearth Furnace, Walking Beam Furnace, Walking Hearth Furnace, and Roller Hearth Furnace.

Based on heat recovery method a reheating furnace can be either Regenerative type or Recuperative type. Regenerating type reheating furnace uses regenerative burners while Recuperative type reheating furnace uses recuperators for heat recovery from the exhaust gases.

(If you want to know in details about any of the above mentioned types of reheating furnaces then please let us know in the comment section below as we will bring separate post for the same).

In view of saving energy, requirement of Refractories with low thermal conductivity are required particularly for Door, Heaters, Flue-stack and further, for Hearths these criteria are corrosion, abrasion & spalling resistances with good strength. For these purposes, dense low-iron, high-alumina or chrome-magnesia bricks are best suited for Hearth. The side-wall and roof are lined with high-grog alumino-silicate bricks. Precast / Prefired (PCPF) blocks can be used for Burner-block, Seating Well Block, Well Block as well as for Furnace Bottom, made of low-iron high-alumina dense refractories having excellent spalling & abrasion resistances. The advantage of using PCPF blocks is that they can save time for both installation & for drying/preheating inducing more availability of the furnace. In the event of choosing Precast / Pre-fired (PCPF) blocks one has to take care of the design of these blocks which should be such that one person can handle them.

For more details refer to our post: Area wise Refractory specifications and lining procedure for reheating Furnaces

 

Importance of Tundish Design and Flow Modifier Refractories in Steel Making | Refractory Industry Guru

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 23-Sept-2020


www.industry.guru - Steel Tundish labelled image
To transfer finished melt steel from a ladle to mould in a continuous casting process, an intermediate vessel is used which is called tundish. The role of tundish is to deliver the molten metal to the moulds evenly and at a designed throughput rate and temperature without causing contamination by inclusions. Inclusion float out, slag vortexing, till end slab volume and residual metal in tundish are a strong function of tundish hydrodynamics. Tundish design as well as flow control devices / modifiers are known to have strong influence on tundish hydrodynamics. 



www.industry.guru - images of Tundish Flow Modifier Refractories


One of the major functions of steel making tundish is to enhance inclusion floatability and thereby, produce clean steel. For the removal of inclusion through floatation, wall adhesion and agglomeration the flow patterns inside the tundish play an important role, which in turn

Melt flow in any given tundish can be favourably altered by incorporating suitable tundish flow modifiers (TFM) and/or changing the design of the tundish. The flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel.

Now-a-days refractory makers are offering customized refractory solution. The new age tundish refractories facilitate temperature homogenization, removal of macro-inclusion, prevention of nozzle clogging etc. inside tundish. To streamline the flow and compress turbulence inside tundish various Flow Control Devices (FCD) are being used in place of traditional FCDs or tundish furniture like Dams, Weirs, Charge Pads, and Side Wall Pads etc. 


Industry Guru - Used Steel Tundish image
The next generation FCDs are popularly known as Tundish Flow Modifier (TFM), Tundish Flow Optimizer (TFO) etc. are precast refractory shapes made of Ultra Low Cement Castables (ULCC) having 85 - 90% alumina. The interior of tundish flow modifiers or flow optimizers as you say it, are designed in such a way that incoming steel gets a churning effect which results into inclusion flotation and subsequent absorption at the tundish powder level. Tundish argon diffusers are also being used to reduce inclusion in steel.

Eventually, it is tundish design from the viewpoint of metal flow and appropriate selection of refractory materials with their right positioning inside tundish that holds the key to the success of subsequent operations in steel making.


Iron Making in Mini Blast Furnace (MBF)

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The Blast Furnace ironmaking process had, until recently, been the unchallenged method of making hot metal on a large scale. Till 1990, the blast furnace route of ironmaking had about 97% (527mt) share of global iron production. Since then many other alternative processes of iron making have arisen e.g., Shaft Furnace DR processes (MIDREX, HyL), Rotary Kiln DR processes (SL/RN, CODIR, TDR), and recently the COREX Smelting Reduction process. The Mini Blast Furnace (MBF) is the most proven technology, as revealed by one recent global iron production data. While gas-based as well as coal-based DRI production routes produced 2.7% of total iron production in 1990 - 1991, the corresponding share held by MBF, operating mainly in Brazil, China and India, was 3.4%.

Iron and Steel Industry Guru
Mini Blast Furnaces (MBFs) are ideally suited to small scale operations. A Mini Blast Furnace (MBF), which can be viewed as is a miniature version of conventional large blast furnace, also has a few additional characteristic features known for their simplicity and economy. Since MBFs are small (working volume ranges between 100 - 370 m3 corresponding to production capacities of hot metal between 60000 - 200000 tpa) blast furnaces, the technology involved is not only well proven, but also very sophisticated. Smaller scales of operation allows the use of inferior grade coke and iron ore (sinter usage is difficult). Mini blast furnaces are becoming increasingly as an economic and reliable source of iron for foundries as well as for forward integration with steelmaking units in EAF / EOF (and sometimes even small BOF) based steel plants.

The products from mini blast furnaces are of the same quality as that of normal Blast Furnaces and are free of tramp elements - this is of particular advantage in steel making in mini steel plants. Use of 40 - 45% hot metal in EAF (Electric Arc Furnace) charge has thus become standard practice, which has helped to reduce the power consumption in Electric Arc Furnaces to 380 - 400 kwh/t liquid steel from 550 - 600 kwh/t. At the same time, sine the hot blast temperature in MBFs is lower than normal blast furnaces and the specific heat loss is more, the coke rate tends to be 100 - 150 kg/thm higher.

The biggest limitation of mini blast furnaces is that coal injection is normally difficult and the higher specific heat requirement has to be met entirely by coke (normally purchased from external sources).

In India, with the recent increasing demand of pig iron and steel, mini blats furnace technology has proliferated. Kalinga Iron Works is successfully operating three small blast furnaces with volumes less than 100m3 each, an MBF of 175m3 capacities was commissioned in Goa in 1992 and nine more mini blast furnaces with installed capacity of 0.80 Mtpa of foundry pig iron and 0.10 Mtpa of basic grade are already operational. These units are spread all over the country. If this trend continues, which is more likely to happen, Mini Blast Furnace Technology would play an increasingly important role in the rapid and wide spread growth of iron and steel making capacity in this country.

Brazil has a large hot metal production through mini blast furnaces which use charcoal as a reducer and an energy source. These companies are not integrated and their final product is pig iron. The growth in this sector started in Brazil in the early 1970's as a result of the availability of cheap and good quality raw materials (native wood charcoal and granulated iron ore). In addition, the return of the investment in the construction of Mini Blast Furnace was very fast. Nowadays, this sector is consolidated and has a fundamental role in the national and international iron and steelmaking sector since Brazil is a major supplier of primary iron.

Plant availability as well as the perfection achieved in technology, made Mini Blast Furnaces a well accepted iron making route in China. The situation in India could be similar in future. Presently, about one fifth of China’s total iron production is through about 55 - 60 MBFs. The furnaces in China use metallurgical coke, and the coke rates vary between 500 - 630 kg/thm. Extensive innovations have been introduced in the Chinese Mini Blast Furnaces including:
  • Injection of pulverized anthracite to the extent of 60 kg/thm, to bring down the coke rate by about 40 - 50 kg/thm.
  • Heat recovery from stove waste gas at 250-300OC for increasing the hot blast temperature by about 80OC.
  • Incorporation of self-preheating process stoves, enabling the generation of hot blast with a temperature of more than 1200OC.
  • Dry cleaning of furnace gas.

According to a published report some typical characteristics of raw materials used in Chinese Mini Blast Furnaces (MBFs) are given below:
Chemical Analysis (%)
Iron Ore
Sinter
Fe
40-45
53-54
FeO
--
11-12
CaO
8
10.5-12
SiO2
13-14
8.5-9
Al2O3
2
---
MgO
1
2.5
S
0.03-0.04
0.03-0.04
P
0.02
---
Tumbler index, %
81-82
Basicity
1.2-1.4

A typical range of iron oxide feed done in Chinese MBF is as follows:
Size (mm)
Percent
+70
2
-70, +60
2
-60, +40
8
-40, +25
12
-25, +10
49
-10, +5
20
-5
7

The coke characteristics used in China are:
Ash = 13.5 - 14.0
V.M. = 1.1 - 1.4
Sulphur = 0.25 - 0.75
Moisture = 7.5 - 8.0
M10 index = 17
M40 index = 75
Size = 25 - 60 mm