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

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 for reheating Furnaces (to be published soon).

 

Slag Cement Association (SCA) announces Slag Cement Project 2020 Awards | Cement Industry News

 30-April-2021

First let us refresh our knowledge a little bit about Slag Cement and how it differs from Portland Cement.

Slag cement can be used in concrete, either as a separate cementitious component or as part of a portland cement concrete. Slag Cement works synergistically with portland cement to increase strength, reduce permeability, improve resistance to chemical attack and inhibit rebar corrosion. When used as part of a portland cement concrete, slag reacts with both the water (latent hydraulic reaction) and the hydrated cement paste (pozzolanic reaction), resulting in a more refined microstructure than that of a plain portland cement.  

However, there are some disadvantages of Blast Furnace Slag Cement Its initial strength is low, because of which it cannot be used in RCC works. As the initial setting time of Blast Furnace Slag Cement is high, this cement is not used for emergency or repair works as well.

The Slag Cement Association (SCA) is a nonprofit trade association representing producers and shippers of slag cement in the United States. Since 2010, been running its annual slag cement project of the year awards program. The slag cement awards recognize projects for excellence and innovation in concrete using slag cement.

SCA has recently announced the recipients of its 2020 Slag Cement Project of the Year Awards. Sixteen construction projects from across the United States were chosen to showcase the broad applications of slag cement and its impact on creating more durable and sustainable concrete.

In the architectural category, Lehigh Hanson used slag cement in the construction of a new four-story parking garage at the Chesapeake Beach Resort & Spa to allow an additional 700 vehicles to park on the resort’s premises. The other winning project in this category, slag cement was used for durability enhancement and potential sulfate and alkali silica reaction (ASR) mitigation by St. Marys Cement in the construction of Adventure Cove at the Columbus Zoo and Aquarium in Ohio.

Lehigh Hanson also won in the sustainability category for using slag cement in the construction of the 72-story One Manhattan Square residential building at the foot of the Manhattan Bridge in New York City.

The awards for innovative application has been given to LafargeHolicm for the replacement of a 323 m (1060-ft) superstructure above the historic Lake Tillery Bridge in the Piedmont area of North Carolina. Slag cement was used in the deck placements of the bridge to increase durability and to mitigate against alkali silica reaction (ASR) in the concrete. In addition, slag cement helped with holding the slump longer and increased the workability of the mixture to help the finishers battle the strong heat during the placements. Argos was also awarded for its work on the Nucor Steel of Florida project where slag cement helped exceed the specified compressive strength of 4000 pounds per square inch (psi) in 28 days in a 50 percent replacement mixture with 245 kg (540 lbs) of cementitious material and with a 0.49 maximum water-cementitious materials ratio (w/cm). Lasty, St. Mary’s Cement was recognized for the Pittsfield Charter Township Planning Commission Development, a large residential project which included apartments, rowhouses, mixed-use commercial buildings, and stormwater retention buildings. Up to 35 percent slag cement was used in the concrete mixture design for its workability, increased control of curing and hydration cycles, and long-term durability benefits.

The remaining SCA winners include:

Durability

• Akron Hazel Storage Basin (CSO Rack 10 & 11)—Lehigh Hanson;
• CVST River Bridge—Lehigh Hanson;
• Lakeland Linder – Site Prep for Intermodal Center—Argos; and
• Upper Sandusky Water Reclamation Facility—St. Marys Cement.

High Performance

• Avon Park Air Force Range – Juliet Ramp & Airfield Pavements—Argos;
• Jamestown Municipal Airport Runway and Taxiway Paving Project—LafargeHolcim;
• Kew Gardens Interchange—Lehigh Hanson; and
• Potomac River Bridge/I-81 Widening and Replacement—LafargeHolcim.

Green Design

• The Blonde Apartments at 8th and Main—Skyway Cement Company; and
• The Lumen at Playhouse Square—LafargeHolcim.

Besides, there are two 2020 Slag Cement Research Award Winners:

• Sustainability of Concrete in the Pacific Northwest—Hilary Chaimov, Oregon State University; and
• Innovative Application of Slag in Improving Sustainability, Flexibility, and Cost in Thin Panels—Arash Rahmatian, University of Houston-Downtown

 (Source: Slag Cement Association News; edited)

FLSmidth wins contract for full digitalization of three cement lines at Kirene in Senegal, West Africa

 19-April-2021

The Danish engineering company FLSmidth has received contract from Chinese construction giant CBMI Construction Co., Ltd., part of the Sinoma Group, to supply and install three complete control systems for two existing and one new cement line at Kirene in Senegal.

In cement industry sector FLSmidth has a strong presence in India, Brazil and Russia whereas FLSmidth's minerals segment is being contributed heavily by the growing urbanization and industrialization in the developing countries, particularly China and India.

Energy savings, higher fuel substitution rates and maintenance planning – digitalisation presents massive opportunities for the cement industry at a time when energy costs, over-capacity and new environmental regulations are major concerns to many plant owners. With a complete and integrated control system across all three lines at Kirene, CBMI Construction creates the digital foundation for its customer to make data-driven decisions on process optimization, stay on top of maintenance jobs and accelerate energy savings.

All three lines will have a shared digital infrastructure build on the FLSmidth ECS/ControlCenter™ platform.  On top of that comes the FLSmidth plant data management software, ECS/PlantDataManagement. The data management software is the operational interface to all data, allowing plant management to transform performance data into real-time KPIs and giving operators access to critical process information via tailored dashboards. 

According to CBMI Construction, the ECS software from FLSmidth is essential in operationalising the 12,000 data points at the new Kirene line (3) for the customer. “With a combination of extensive process knowledge and digital solutions that integrate across different equipment suppliers, FLSmidth is instrumental in securing the efficiency benefits our customer expects,” explains CBMI.

“With more than 1,500 active product and process control installations in the cement industry, this order reaffirms our strong digital expertise,” says Jens Adler, General Manager in Group Digital at FLSmidth. “The cement industry might be a little slow in adopting Industry 4.0 technologies, but digitalisation is transforming how many respond to increasing demands for emission reductions and efficiency. This is reflected in the emphasis on digital solutions as part of our MissionZero ambition to offer cement producers zero emission cement production by 2030,” Mr. Adler concludes.

Apart from the digital infrastructure, the new line (3) at Kirene will be equipped with ECS/CemScanner® and QCX/BlendExpert™ from FLSmidth to further optimize the performance of the plant. The order became effective in Q1 2021.

FLSmidth, headquartered in Copenhagen (Denmark), supplies the minerals and cement industries globally with everything from engineering, single machines and complete processing plants to maintenance, support services and operation of processing facilities. FLSmidth employs more than 12,000 people worldwide in offices in more than 50 countries worldwide. As reported by the company about 99 per cent revenue of FLSmidth comes from outside Denmark.

Contact Investor Relations

Nicolai Mauritzen, +4536181851, nicm@flsmidth.com

Contact Media Relations:

Rasmus Windfeld, +45 40 44 60 60, rwin@flsmidth.com

 (Source: FLSmidth via Globenewswire; edited)

Use of Sillimanite as Raw Material in Refractories

Sillimanite as a natural and untreated mineral is a very important raw material for high alumina refractories which are extensively used in Iron and steel, Petrochemical, Electrical, Cement, Zinc and Glass industries.

Sillimanite when heated above 1545­^OC converts to Mullite and the excess silica as glass, crystoballite or tridyamite. The formation of the glassy phase can be reduced by addition of a small percentage of technical or calcined pure alumina fines (like - HGRM 30 etc) which reacts with this excess silica to form mullite, which in turn help in enhancing the quality of the product.

Due to the very low expansion or contraction on heating, sillimanite need not be calcined before use. Unlike sillimanite from most of the sources in the World which are used as it is, the Rewa sillimanite (found in Madhya Pradesh, India), because of its impurities, should not be used as such. It is always better once to wash these lumps in the raw material yard itself and then after shifting to the Mill House and crushing, grinding pass through magnetic separator to eliminate the free iron impurities.

The ideal firing temperature of green refractory bricks made of sillimanite grains as a major raw material is 1450 - 1500^OC, to be fired either in a batch type or a tunnel kiln. The soaking time will vary depending upon the volume, shape, setting and other constituents of the bricks (particularly raw clay used and sintering aid, if any).

Sillimanite Refractories

Sillimanite refractories are characterized of high refractoriness, very low coefficient of thermal expansion, high refractoriness under load (RUL) and mechanical strength with great resistance to thermal shock (spalling resistance), abrasion and slag corrosion. Due to their exceptionally high resistance to spalling and corrosive actions of molten glass, chemical attacks of soda, borax and other frits, they are most suitable for Glass Melting Furnace (GMT), Oil fired Furnace, Cement Rotary Kiln, Blast Furnace, Electric Arc Furnace (EAF) roofs, Hot Metal Mixer, Combustion Chambers and Metallurgical operations done in Zinc Furnace, Gold Refining Furnace etc.

Particularly in Glass industry sillimanite refractories have got many applications, such as in glass melting tank furnaces (to be discussed in detail in a separate article) in all parts open to the products of combustion like combustion chambers, flues, door pillars which may have to support heavy load at high temperatures, recuperators and such other parts which are liable to be subjected to fluctuations of temperature. Assam Sillimanite once available in good quality and quantity, even for export, were used to be cut into blocks of various sizes from solid rock at the site of deposits itself which were then sent to the user’s site for their direct use in construction of Glass Melting tank Furnace bottom. But now it is a forgotten past! However, there are quite a few suppliers in India who manufacture these GT blocks, mostly using certain percentage of sillimanite sand or even sillimanite lumps after crushing and grinding. To name a few are Maithan Ceramics Limited (MCL), Tata Refractories Limited (TRL), OCL India Limited, ORIND (quality ?) etc. So far the properties like density (BD), porosity, mechanical strength, slag corrosion resistance and consistency of performance etc. are concerned, high capacity machine pressed bricks are far too superior to those made by pneumatic ramming. Although it is a general practice to give some ‘patching/finishing’ manually before inspection - dispatch to particularly big and complicated shape refractory bricks but from the customers’ point of view it is most important that during inspection it must be ensured that except for the ‘look’ only, the refractory brick (or block) does not depend much on the ‘finishing’, if at all, done on it. Patching is a wrong practice as it is done to camouflage the flaws which could be detected by seeing the brick.

For GT blocks the machine finish of the surface is very important. It must be evenly polished or ground to ensure that the warpage is negligible. One of the main criteria for acceptance of these blocks should be that in the assembly there should not be any open joint (the specification could be from 0.2mm - 0.3mm filler gauge up to a maximum 20 - 25mm depth from the top). This is a must to avoid the penetration and subsequent crystallization of glass and alkali vapours in these joints. To meet this criterion the manufacturer should have facilities for grinding of these blocks minimum in 4 faces and in some bricks up to 6 faces and then marked accordingly. 

Related Article: Indian Sillimanite - Mineralogy, Properties and Occurrence

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

 23-Sept-2020

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. 

Read: Continuous Casting Tundish Lining Refractories: Practices, Advantages and Disadvantages 

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. 

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

25-July-2020

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

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 32^O 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:

	Grade-I	Grade-II	Grade-III
Al2O3 (min)	58%	54%	46-48%
Fe2O3 (max)	1.5%	1.5%	2%
PCE (min)	37 (Orton)	37 (Orton)

  

Suggested Article: Use of Kyanite as Refractory Raw Material

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

	SiO2	Al2O3	Fe2O3	TiO2	CaO	MgO	Na2O + K2O	LOI
Lapsa Buru (Bihar)	34.8	61.1	0.5 -1.3	--	0.2 -0.3	0.2	--	0.5
Singhbhum (Jharkhand)	46.5	45.97	0.5	1.5	--	--	--	1.1
Kudineerkati (Karnataka)	40.32	58.15	1.7	Tr.	0.52	--	--	1.32
Sulia (Karnataka)	32.8	61	1.85	2.7	--	--	--	1.65
Purulia (West Bengal)	38.8	46.65	2	Tr.	--	--	--	1.65
Khammam (A.P.)	51.92	27	11.25	--	--	--	--	--