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Showing posts with label Industry Guru. Show all posts
Showing posts with label Industry Guru. Show all posts

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

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 23-Sept-2020 - 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. - 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.

Kyanite - Properties and Indian Occurrences

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Kyanite which is an aluminium silicate with chemical formula Al2SiO5, belong to the Sillimanite group of minerals comprising Sillimanite, Kyanite, Andalusite, Dumortierite and Topaz. Kyanite is an important raw material for high alumina refractories. Especially, Raw Kyanite is extensively used for making high alumina insulation Refractory Bricks.

Apart from refractory industry kyanite particularly its blue variety, is also used as gem stone. The kyanite gem stone is believed to possess certain metaphysical properties with its ability to keep the mind calm and anxiety under control. The name Kyanite was derived from the Greek word Kyanos which means blue.

Mineralogy of Kyanite - image of Kyanite lumps
Raw Kyanite (Lumps)
Kyanite is found as subhedral and tabular to elongated, thin, bladed crystals having blue or light-green colour in the form of crystalline aggregates in schists, gneisses, granite pegmatite and occasionally in eclogites. The crystal system is Triclinic; optically kyanite is colourless and feebly pleochroic from pale-blue to colourless with one set of perfect cleavage, first and second order interference colour (yellow, grey and blue). The distinguishing features of kyanite are its higher refractive index than those of Sillimanite and Andalusite while birefringence is lower. The oblique extinction angle up to 32O together with the biaxial interference, negative optic sign, and large optic axial angle are also distinctive for kyanite. Its hardness varies from 4 to 7 (Moh’s scale) and specific gravity is around 3.6 - 3.7.

Indian Occurrences
In the Indian subcontinent very good gem quality kyanite is found Nepal.
Kyanite is formed at medium temperatures and high pressures in a regionally metamorphosed sequence of rocks and is found associated with minerals like - muscovite, quartz, garnet, staurolite and rutile. Kyanite is also found as detrital mineral. For the Use of Kyanite in Refractory Industry the Directorate General of Technical Development (DGTD) has recommended the following specification:

Al2O3 (min)
Fe2O3 (max)
PCE (min)
37 (Orton)
37 (Orton)

Recoverable reserves of medium to high grade kyanite in India and the current trend of production-utilization causes serious concern because of dwindling availability of this mineral in India. During 1960’s the hard, massive, lumpy variety of kyanite with Alumina content more than 61% and Iron content around 0.8% of Lapsa Buru mines in Kharswan (Bihar) was the largest deposit in the world. Today the source has dried up. Only poorer quality is now available which cannot be used as such. Deposits of kyanite available in a few other places some of which are being mined and supplied at present are -

Chemical Compositions of Indian Kyanite deposits

Na2O + K2O
Lapsa Buru (Bihar)
0.5 -1.3
0.2 -0.3
Singhbhum (Jharkhand)
Kudineerkati (Karnataka)
Sulia (Karnataka)
(West Bengal)
Khammam (A.P.)

HeidelbergCement India - Lackluster Q1 performance due to covid lockdown restrictions

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HeidelbergCement India Ltd on Wednesday reported a 38.07 per cent decline in net profit at ₹ 48.94 crore for the first quarter ended June 2020.
The company had reported a net profit of ₹ 79.03 crore in the April-June 2020 period of the preceding fiscal, HeidelbergCement India said in a BSE filing.
Total revenue from operations declined 30.80 per cent to ₹ 407.70 crore from ₹ 589.23 crore in the corresponding quarter of 2019-20.

The company said its sales volume declined due to suspension of operations during covid lockdown period. "Volume decreased by 32 per cent, primarily driven by the suspension of operations in April 2020. The decrease in volume impacted revenue and profitability during the quarter," said HeidelbergCement India, a subsidiary of HeidelbergCement Group.
Cement sales volume during the quarter was 857 KT as against 1,258 KT earlier. Total expenses were at Rs 342.99 crore as against Rs 479.25 crore in Q1 FY20, down 28.43 per cent.
In an interview to ET Jamshed Naval Cooper, MD of HeidelbergCement India Ltd said, capacity utilization will be hovering between 55% and 60%. Today many of the cement companies will have a very high breakeven.
You cannot keep a cement processing plant shut continuously. We made a big mistake of having a lockdown in the cement plant, he said. However, he is hopeful that after Diwali (which falls in November this year), most migrant labourers will return and capacity utilisation of cement plants should touch 70%.

Use of Kyanite as Refractory Raw Material

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Kyanite is one of the Alumino-Silicate group of minerals comprising Sillimanite, Kyanite, Andalusite, Dulmortierite, Topaz and Mullite all with similar chemical composition but different physical behavior and hence, uses. Kyanite, raw as well as calcined, have separate applications as refractory raw materials because of their distinct characters. 

Raw Kyanite

Industry Guru - image of raw kyanite
Raw Kyanite (Refractory Grade)
To be suitable for refractory raw material, kyanite should have very negligible amount of impurities which include free silica, alkali, iron oxides, calcium and magnesium. Kyanite, Sillimanite and Andalusite all these three minerals convert to Mullite and silica when they are calcined to temperatures between 1250OC and 1500OC. The inversion kyanite to mullite and silica (glass) begins at the periphery of grains and this rate of conversion depends the following:
>> Particle size
>> Firing temperature
>> Soaking time
>> Impurities present.
The heating of raw kyanite is accompanied with its volume expansion and a decrease in its specific gravity from 3.6 to 3.06, which takes place over a small range of temperature around up to 1350OC. 
Because of this property raw kyanite - 
  • Raw kyanite is extensively used for making high alumina insulation bricks, insulating mortars and castables.
  • Raw kyanite fines (pulverized) can be added to refractory mixes in different proportions as a measure to control or compensate the overall shrinkage due to other raw materials. 

Calcined Kyanite

Industry Guru - image of calcined kyanite lumps
Calcined Kyanite (lumps) to be used in making Refractories
In order to make it a volume stable refractory material, kyanite is pre-calcined at 1420OC to mullite and Cristobalite before use. Sometimes the lumps are very hard to crush after calcination. To avoid this, after calcination the kyanite lumps are, sometimes, quenched in water to make them crumble easily. Thereafter, it is ground, graded into various fractions as per requirement. These grains of calcined kyanite being volume stable are used with other raw materials for making refractory bricks and castables. The various refractory properties are:
P.C.E - above 1785OC or 35+ (Orton)
RUL (refractoriness under load) - 1750OC
Porosity = 24 - 25%
Properly calcined kyanite is a very good refractory raw material because of its high alumina percentage and low iron contents. As compared to other refractory raw materials kyanite can be sometimes, very handy for boosting alumina content and other refractory properties of the product at the same time maintaining its cost effectiveness.
Refractories made from calcined kyanite possess:
  • Higher modulus of rupture and creep resistance
  • Lower co-efficient of expansion
  • High thermal shock resistance
  • Increased durability, about three times that of ordinary bricks
  • Superior resistance to salt attacks and chemical corrosion
  • Very low co-efficient of spalling
Related Article: Kyanite - Properties and Indian Occurrences

HYL III and SL/RN - The two widely accepted Direct Reduction (DR) Processes of ironmaking

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Direct Reduced Iron (DRI) is obtained by reducing lumps as well as fines of iron ore in solid state at a relatively low temperature of around 1000OC. A large number of DR processes are available today. SL/RN and HYL are two such DR processes. While HYL is a batch-type gas based process and uses a countercurrent shaft-furnace, the SL/RN process utilizes rotary kiln to reduce lump ore, pellets and sand iron with coal. Here we will discuss about some key features, including advantages and disadvantages of these two DR processes.

Fig: HYL III Process Scheme

The HYL process was developed in Mexico and was the forerunner of the HYL III direct reduction technology. In HYL I process, a mixture of gases containing about 89% of reducing compounds is used. Each reduction module in HYL plant consists of four units - three “in line” and the fourth in “turn around” mode. The principal change made over HYL I in HYL III was the modification of the four fixed bed reactors by a single moving bed reactor, utilizing the same gas reforming plant, auxiliary equipment and quenching towers.  Actually HYL III technology is characterized by its wide flexibility for adapting to special needs, depending on available reducing gases, energy use and melt-shop requirements. Use of spent gases from direct ironmaking processes, coal gasification, energy optimization in DR plants and technology developments aimed to improve EAF productivity have been the objective of HYL. Some distinctive features of HYL III process are:

Fig: HYL III - COREX Off-Gas Process Scheme
=> The H2/CO of the reformed gas is 3, the temperature is about 930OC, the inside pressure of the countercurrent shaft-furnace is 450 kilopascals and the energy required for the reduction is basically the same as in the MIDREX process.
=> The selective elimination of H2O and CO2 from the reducing gas circuit allows maximum recycle of the reducing gases to the reduction reactor. Hence, the reducing gas make-up and the process natural gas consumption are minimized.
=> The reducing gas generation and the reduction sections of a HYL III unit are independent from an operational point of view. This feature offers important flexibility for adapting to different reducing gas sources. The process schemes based on use of alternative reducing gases from different sources and other DR/ Ironmaking sources have been proven in HYL III plants. Such alternate sources of reducing gas can be -
  • Coal gasification processes.
  • Coke oven gas.
  • Gases from Hydrocarbon gasification.
  • Partially spent gases from another DR plant.
  • COREX off-gases.
=> High pressure operation (4 atmospheres or more) enables the effective control of process conditions, with smaller equipment size for gas handling and lower energy requirements (9.0 - 10.0 GJ/t).
=> The process is much flexible as far as raw material use is concerned - while it operates best with 100% pellets, even 100% lump ore of a suitable type has been used, but it is suggested to use a mixture of pellets and lump ores.   
=> This technology offers the unique flexibility to produce three different product forms depending on the specific requirements of each user - Cold DRI, HBI and HYTEMP iron. Metallization can be controlled up to 95% and Carbon content 5.0%.
=> When combined with COREX off-gas as a source of reducing gas, the HYL III DR plant offers high productivity using available spent gas and benefits in steel production using HYTEMP® iron together with hot metal in EOF/BOF based steel mills.
=> The HYL III process features the flexibility of generating electric power, taking advantage of high pressure steam produced in the natural gas-steam reforming unit which can be used in a turbo generator or in a set of turbines, at a high generation capacity.
According a data of recent past, around 11 million tones of direct reduced iron (DRI) was produced in 2003 by this process in India, Grasim’s HYL plant at Raigad (Orissa) produced 0.75 million tones of HBI.     

SL/RN is the most widely accepted coal based DR process. It was jointly developed by Stelco, Lurgi Chemie, Republic Steel Company and National Lead Corporation in 1964. In this process, the materials charged into the kiln gravitate towards the discharge end during which they are progressively heated to the temperature of reduction of around 1000 - 1100OC. The product discharged from the kiln is cooled in an extremely cooled rotary cooler around 100OC before being subjected to magnetic separation to separate sponge iron from coal ash and char. Waste gases leaving the kiln at the inlet end pass through a dust chamber and a post combustion chamber, before being cooled and cleaned in electrostatic precipitators, scrubbers or bag filters. In SL/RN technology the clean gases can be used in waste heat boilers to recover the sensible heat and the steam generated can be utilized for heating purpose or for electric power generation. Some distinctive features of SL/RN process include:
=> Flexibility with regard to the type of iron bearing materials which can be used such as lump ore, pellets, ilmanite, iron sands and steel plant wastes.
=> Use of a wide variety of solid fuels ranging from anthracite to lignite and charcoal.
=> Improved heating of the charge by submerged air injection in pre-heating zone of the kiln. This process suffers, however, from relatively big heat loss and facility size.
=> SL/RN technology provides optimized coal injection facilities at the discharge end of the kiln.
=> Waste gas conditioning by controlled post combustion followed by power generation (the power generated is more than the requirement of the plant).
The original SL/RN process has been modified in a variety of ways, particularly in India where rotary kiln DR technology has been widely applied.