Showing posts with label Refractory lining installation. Show all posts
Showing posts with label Refractory lining installation. Show all posts

January 19, 2011

Refractory Bricks – Shapes and Sizes


There is no limit to which a refractory brick can have different shapes and sizes to suit a particular design or lining requirement. Production of refractory shapes depends upon the design and size of furnaces or other service constructions where such refractories are to be used. Numerous shapes and sizes of refractory bricks are produced to meet the specific lining requirements of straight walled, cylindrical, arched, dome and other special types of construction work besides the shapes like wedges, keys, sleeves, nozzles, burner blocks, tiles etc. For example, only an iron blast furnace requires refractory bricks of so many types, shapes and sizes. However, most of the lining works are made of certain standard refractory shapes and sizes which are always available in the market. Special refractory shapes are only produced to meet the specific lining requirements of each furnace or refractory structures like some typical coke oven shapes, stopper heads, arch tiles etc. The shapes which are universally accepted and used are listed below (see figure):
Refractory Bricks - Shapes and Sizes image
Fig: Refractory Shapes
Standard Refractory Shapes
1. Straight (Rectangular)                
2. Side Arch
3. End Arch
4. Wedge
5. Key
6. Flat Circle
7. Combined Arch and Wedge
8. Circle
9. Splits
10. Dome Brick
11. Skew (End / Side)
12. Bullnose or Jamb Brick
13. Soap or Closer
Refractory Bricks shapes and sizes image
Fig: Refractory Brick Shapes / Sizes 
Refractory Ladle Well Block image
Fig: Ladle Well Block
Refractory Lining | Steel Technology - Stopper Sleeve image
Fig: Stopper Sleeve
Stopper Pin image
Fig: Stopper Pin
Refractory Stopper Head image
Fig: Stopper Head
(For a short definition of each shape see the ‘Glossaries > Refractories’ in the menu navigation bar above)
Standardization and rationalization of refractory shapes becomes important as a host of refractory shapes needed for lining even a single part of a production unit involving very complex and complicated designs necessitates use of numerous kinds of opening and aperture details besides inter-chamber dimensions et. As such one can not imagine preparation of moulds either by mechanical pressing or by hand / pneumatic moulding to suit production of large number of shapes with different design details without involving a very high cost of production. So, it is always preferable to design a lining with commonly used refractory shapes as they facilitate easy availability, reduce cost (moulds / liners are generally available with manufacturer), and easy to repair.  
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April 19, 2010

Some Basic Guidelines for Laying Refractory Brickwork or Lining

Certain basic rules exist for the laying installation of refractory bricks or lining. They generally apply for all designs and construction parts of any furnace, pipe, chute, chimney, foundation, tank or any other vessel etc. Some of these rules have been summarized below:
=> Refractory bricks must always be laid horizontally unless the design of the plant requires inclined positions or inclinations as is the case for crowns or inclined planes.
=> The construction dimensions in the design and drawings must always be observed taking the indicated tolerances into consideration. The first refractory layer (course) must be installed with extreme care, aligned and checked before giving the “go ahead” for further brick laying (lining) work.
=> All joints must be filled with the prescribed joint material. Thickness of the joints must be observed taking the indicated tolerances into consideration.
=> All joints must be filled over the entire surfaces with the joint material. It is permissible to apply the mortar with a ‘Collar’ because there is the danger of hollow spaces forming in the joints.
=> If, due to the size tolerances of the bricks, the prescribed joint thickness can not be accomplished without obtaining ‘Naked Surfaces’, the person responsible for the refractory design will have to decide if thicker joints can be allowed. This is only permitted as a better solution cannot be found by sorting or changing the shapes. A grinding of the bricks should only be a possibility in exceptional cases.
=> Expansion joints should never contain any contamination, e.g. by insertion of joint templates or by gluing.
=> Refractory bricks which have been already laid can only be readjusted in the direction of the bed or vertical joint.   
=> Readjustment of brickwork already laid is not possible if the mortar has started to harden to a greater degree. Depending on the type of mortar used, there will possibly be only few minutes for readjustment once the bricks have been positioned. Sometimes, it may be necessary to remove bricks not placed correctly, clean them, and re-install them once again with fresh refractory mortar.
=> Refractory bricks with smaller spalls, hair cracks or slight inclusions may only be installed (laid) provided these irregularities are insignificant for the proper functioning of the construction part. This also applies to the rear side of the hot slide layer and for the brickwork behind. The criteria for the acceptance or rejection are indicated in the specifications or must be agreed upon mutually by the customer, manufacturer, and supplier before the start of lining or brick laying work.
=> Brickwork out of refractory materials must be designed in such a way that no hollow space forms. Dust and fly ash can penetrate hollow spaces. This results in uncontrolled pressure buildup which may destroy the refractory brickwork. Damages can also occur by roaming gases.
(To be continued)
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March 23, 2010

Criteria for Furnace (or Kiln) Design and Selection of Refractories


The primary function of any refractory material is to withstand high temperature in a hostile environment. However, in actual application it is required to perform many other functions depending upon the place of use and prevailing service conditions.
The general requirement which a refractory material is to fulfill may be summarized as follows:
1. Ability to withstand high temperature.
2. Ability to withstand temperature fluctuation.
3. Ability to withstand the actions of processing materials and product of combustion.
4. Ability to withstand load under high temperature.
5. Ability to withstand impact and abrasion of solid, liquid and dust laden gases moving with high speed.
6. The refractory material should be volume stable.
7. It should not contaminate the finished product.
8. The refractory material should have low co-efficient of thermal expansion.
9. It should not conduct much heat.
For a proper design of any refractory lining system it is essential that the complete information of furnace or kiln type and prevailing service conditions are available.
The most important operational data required for the selection of refractories are as follows:
Furnace / Kiln Type            :  For which industry the furnace or the kiln is to be used.
Process                               :  Details of process to be adopted. Will the refractory material come in direct contact with slag, metal, dust, fluxing agent, gas or flame? Which part of the furnace or kiln will be subjected to the destructive actions of the above elements, etc.
Fuel                                      :  Type of fuel to be used for generation of heat energy. How the furnace will be heated.
Operation                            :  How the furnace (kiln) will be operated: continuous or intermittent. What is the extent of temperature fluctuation and over what period of time. To what extent the refractories will be exposed to thermal shock.
Operation - Temperature :  What will be the highest temperature to which refractories will be exposed. What will be the peaks.
Limiting - Temperature     :  What are the maximum and minimum temperatures of the furnace or kiln design components e.g. steel shell temperature etc.
Heat Loss                            :  What heat loss will take place? Is the heat to be conducted through refractories or retained within the furnace?
Surrounding Conditions   :  What are the surrounding conditions such as heat flux calculations, influence of any adjacent plant or component, maximum and minimum ambient temperatures, wind speed, radiation co-efficient etc.
Furnace Atmosphere          :  Is it neutral, oxidizing, reducing or changing?
Furnace Pressure               :  What operation pressure is expected? Is the furnace part under suction or under positive pressure.
In actual situation the refractories may have to work under some or all of the above conditions. They may act simultaneously and demand suitable refractories to withstand the destructive forces. No single refractory material can satisfy the entire requirement. Hence, a compromise is made and the most demanding requirements are first met at the cost of other lesser requirements. For example, in a hot air or gas carrying system the thermal conductivity would be the vital criteria. Therefore from every saving point of view insulating properties of the refractory material becomes more important than other properties for design considerations.
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September 18, 2009

3 Things You Must Do To Get Better Performance Of Refractories


Nothing counts like the ‘performance’. Getting or giving a better performance is one thing which everyone tries to do. Reasons obvious! For getting better performance of refractories from an installation one must take care of the following three simple but very important things:
1. Proper Selection of Refractories.
2. Proper Installation-Application.
3. Proper Operation Practice.
Selection of Refractories
Though there are specific refractories for different applications, operation practices lead to certain criteria on which, depends the life of refractories. As such these need to be properly considered. Customers should disclose the actual operating practices and conditions so that some important properties, required to such conditions can be taken care during the selection and manufacturing stage of refractories. Among various physical, chemical, thermo-chemical and thermo-mechanical properties of Refractories, there are a few properties which contribute markedly to its performance. These are called ‘Key Properties’. For ensuring better performance and quality these key properties should be tested.          
Application - Installation of Refractories
Depending on the method of application or installation there has to be a set of guidelines in respect to laying of refractory bricks, their dimensions, selection of mortars, expansion joints and many other minute but very important things. So from case to case basis the supplier of refractories should specify this properly and also ensure that the methods are actually being followed. Transportation, handling, timely arrival of refractory bricks, mortars, skill of masonry work, proper equipment for application e.g. mixer machine for castable, vibrator for installation, forma etc. are very important. Maintaining proper expansion gaps, correct dimension of bricks and monolithics, fixing anchors etc. all are very important to achieve better life of refractories. Once the installation of refractories is over, the initial heating of the lining before starting the actual operation is of prime importance. Customers should demand the initial heating schedule from the refractory supplier.
Operational Practices
Proper operation is not only important for getting right quality output but also, help in getting the optimum life of refractory lining, less downtime, maximum availability of the furnace and thus, the benefit of lower cost of refractories per tone of finished product. Customers must be aware of the reasons which can damage the refractories arising because of improper operations. During the training of the furnace operators, apart from the method of the furnace operation etc. they must be given some knowledge regarding the proper usage and importance of refractories also.   


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July 27, 2009

Blast Furnace (BF) - Refractory Lining Pattern

Refractory Technology: Different temperature zones of a Blast Furnace image Fig: Blast Furnace Temperature Zones

Refractory Technology: Blast Furnace image
Fig: Typical areas of a Blast Furnace
Blast Furnace - An Introduction
Blast Furnace is the focus of any integrated steel plant. Blast furnace is used to reduce the iron ore to iron. The charge, which consists of iron ore, coke and limestone etc. in the form of lumps and different ratios, is fed from the top. Air heated in the blast furnace stoves, is applied from the bottom of the furnace. The hot blast comes in contact with the descending charge in furnace and the iron ore gets reduced to iron due to reducing conditions on account of CO2 and CO in the furnace. CO provides further heat and a very high temperature is developed because of which the iron gets melted which, along with the slag is collected in the hearth from where these are tapped separately from different tap holes.
Ironmaking technology in general made great strides particularly, during the past few decades and as a result of which many alternative ironmaking processes such as Finmet, Fastmet, Hismelt, Romelt, COREX®, and FINEX® etc. have emerged. Nevertheless, the classical Blast Furnace, which has been around the longest, continues to be the dominant method of ironmaking till now. Improvements in burden quality, burden distribution, casting technology, and computer assisted supervision were realized throughout the world. To a great extent these operational improvements made it possible to install very sophisticated refractory lining systems in blast furnaces. The application condition of different sections of a blast furnace is different due to the very nature of its geometry and also pyrometallurgical process occurring at different stages (see adjacent Blast Furnace figures). Therefore, the Blast Furnace Bottom, Hearth, Taphole, Tuyeres, Bosh, Belly, Stack, Cast house, Blast Furnace Stoves all require different quality of refractories depending on the respective application conditions.
Selection of appropriate refractory combination depends on in-depth knowledge of ironmaking system and the physical, mechanical and chemical properties of the proposed refractories. An improper understanding of the above factors often leads to a refractory failure which, subsequently, becomes a complex problem to solve. Refractory linings whether it is of a Blast Furnace or any other furnace, usually fail due to any number or combination of such factors. For the convenience of understanding, here we will discuss the types of refractory lining required in a blast furnace area wise as well as the trend in the refractory lining pattern that has been observed during the last few years.
Furnace RefractoriesRefractory Technology: Blast Furnace refractory lining pattern graphics
Fig: Conventional and New Refractory Lining along with Wear Mechanism
Now-a-days the campaign life of Blast Furnace is measured in terms of 10 - 15 yrs rather than 4 - 5 yrs while on the other hand, the trend is to replace smaller Blast Furnaces with large capacity Blast Furnaces, which are being subjected to even more stringent operating conditions. To achieve these goals, it is necessary to have a good combination of high grade refractories combined with highly efficient cooling systems and tight control on furnace operation to ensure high productivity without excessive wall working and with minimization of massive “slips” in the blast furnace which can cause excessive premature damage to the refractory linings. It is known that the bottom and a part of the hearth are corroded mainly by pig iron, slag and alkalies. Refractory bricks in these areas are subjected to high load and temperature. So it requires a refractory lining which should have high strength, lower creep in compression value and higher RUL and PCE values. Many furnaces still use low iron, dense 42-62% Alumina, Mullite refractory bricks, conventional Carbon blocks etc. in the bottom and lower hearth while the present trend is to replace it with super micro-pore Graphite bricks.
Research and data shows that Blast Furnace hearth life mainly depends on the following factors:
1. Operational Factors such as,
(a) High productivity leading to High heat loads
    (b) High fluid velocity causing more erosion
    (c) High coal injection means lower permeability
None of the above factors is under the control of furnace operator and hence, the only solution for this can be a robust refractory lining.
2. Refractory Lining System Design The entire refractory lining is also subjected to thermal stress which also plays a dominant role especially when the design is inadequate. The refractory lining system or design must take care of the following things -
(a) Optimize thermal resistance
(b) Provide expansion relief
(c) Prevent cracking
(d) Eliminate built-in barriers.
3. Refractory Properties
(a) High thermal conductivity
(b) Alkali resistance
(c) Low permeability
(d) Low thermal expansion
(e) Low elasticity.
The recent development of micro-porous carbon bricks and improvement in the quality of semi-graphite and graphite bricks has led to higher infiltration resistance to iron and slags, and thermal conductivity. The problem of brittle layer formation around 800OC isotherm by alkali condensation and thermal stresses have been addressed to by using smaller blocks, optimum expansion allowances etc. The carbon refractories are covered by fireclay or mullite bricks to protect it against oxidation. The design of this ‘Ceramic Cup’ is important, as the isotherms are altered depending on the quality and thickness of the cup material.
The stack bricks are particularly; exposed to high abrasion and erosion by charge material from top as well as high velocity fume and dust particles going out due to high blast pressure in a CO environment. Therefore, the application condition demands refractory materials which should have high strength, low permeability, high abrasion resistance and resistance to CO disintegration. Superduty fireclay refractory brick or dense alumina brick having Al2O3 around 39 - 42% can impart these characteristics required for stack application. The tuyere and bosh are attacked by temperature change, abrasion and alkalies; and the belly and lower shaft by thermal shock, abrasion and carbon monoxide attack etc. In the critical areas of the furnace, i.e. tuyere, bosh, belly and lower stack, silicon carbide, SiC-Si3N4 and corundum refractories have replaced carbon and 62% Al2O3 or Mullite bricks – taking advantage of the high thermal conductivity of SiC in combination with the stave coolers. However due to the problem of water leakage around taphole and tuyere area many blast furnaces are lined with high alumina or Alumina-Chrome corundum refractories.
Hot Blast Stove Refractories
The hot blast system, incorporating either three or four hot blast stoves per blast furnace, is the other major refractory installation in the blast furnace complex. With today’s large blast furnaces, the main trend in hot-blast stoves is toward high temperature and pressure ventilation with dome temperature around 1550OC, blast temperatures of 1250 - 1400OC, and furnace pressures of 3 - 5 kg/cm2. Therefore, selection of refractories for hot blast stoves depends primarily on their creep resistance properties, bulk density, specific heat, thermal shock resistance, cold crushing strength, thermal expansion and dimensional accuracy. Blast furnace stoves are generally designed by high alumina bricks and checkers. Silica bricks have been introduced in high temperature stoves operating over 1300OC and where the temperature is never allowed to drop below 600OC as silica bricks display poor thermal shock resistance at such low temperatures. Alternatively silica checker bricks can be used can be used in high temperature zone, high alumina bricks in the middle temperature range and hard fired fireclay bricks and other high strength bricks at the bottom checker level.
Table: Blast Furnace Refractories
Area
Present
Trend
Stack
39-42% Al2O3
Super-duty fireclay
Belly
39-42% Al2O3
Corundum, SiC-Si3N4
Bosh
62% Al2O3, Mullite
SiC-Si3N4
Tuyere
62% Al2O3, Mullite
SiC self-bonded, Al-Chrome (Corundum)
Lower Hearth
42-62% Al2O3, Mullite, Conventional Carbon block
Carbon/Graphite block with super micro-pores
Taphole
Fireclay tar bonded, High Alumina / SiC tar bonded
Fireclay tar bonded, High Alumina / SiC tar bonded
Main Trough
Pitch / water bonded, Clay / Grog / Tar bonded ramming masses, Castables
Ultra low cement castables, SiC / Alumina mixes, Gunning repairing technique
Tilting Spout
High alumina / SiC ramming masses / Low Cement Castables
High alumina / SiC / Carbon / ULCC
Hot Blast Stove
42-82% Al2O
70-82% Al2O3, 91% SiO2 checker bricks

Recent Articles –
Blast Furnace Trough Mix (Refractories)