Refractories for Byproduct Coke Oven Batteries Aug21

Refractories for Byproduct Coke Oven Batteries...

Refractories for Byproduct Coke Oven Batteries  A coke oven battery (COB) is basically a structure made of different varieties of refractory bricks and shapes held together by a steel framework. The battery is designed to operate at maximum temperatures up to 1450 deg C though it is constructed at ambient temperature. During operation, the maximum temperature can be expected to cycle downward by as much as 110 deg C as part of normal battery operation. Hence the battery must be constructed of refractory materials that can withstand the maximum as well as the cyclic temperatures, and that have known and predictable properties related to thermal expansion, strength and creep.  Coke oven batteries are normally operated for long periods like 25 to 30 years continuously. Therefore refractory bricks for lining a COB should have accurate shapes and precise dimensions, an excellent mechanical strength at high temperatures, hot modulus of rupture and excellent volumetric stability to work at temperatures of up to 1450 deg C.  Types of refractories used in different region of COB are shown in Tab 1. Tab 1 Type of bricks usually used in different zones of coke oven     Coke oven region Refractories     Roof Fireclay brick   Insulating brick Flue wall Silica brick Jamb (wall near oven door) insulating brick, Fireclay brick Curved wall Silica brick Regenerator   Wall Silica brick, Fireclay brick Checker Fireclay brick Sole flue Silica brick, Fireclay brick Door Precast brick Ascension pipe Precast brick Chimney flue Fireclay brick, Common brick Silica bricks have sufficiently high refractoriness under load (RUL)and reliable volumetric stability at high temperatures so a large volume of silica bricks of standard shapes are used to construct the coking and combustion chambers of COB. The roof, regenerator checkers and chimney flue of COB are constructed with...

Carbon blocks used for blast furnace hearth lining...

Carbon blocks used for blast furnace hearth lining  One of the largest users of refractory materials in a blast furnace (BF) is the BF hearth. This region of the BF exhibits more varied designs, conflicting practices and vastly different performance histories of the hearth lining.  The traditional materials used in hearth construction have been carbonaceous in nature. Various grades of amorphous and hot pressed carbon conventionally baked and hot pressed semi-graphite, semi-graphitized carbon and fully graphitized materials, are the basic refractories used in any modern BF hearth refractory lining design. However, the nomenclature of these materials must first be clarified, because they represent an entire family of materials with varying compositions, processing and resulting properties. The words, carbon and graphite, are often used interchangeably, but the two are not synonymous. The following briefly describes the major differences and characteristics of the carbonaceous materials used as refractories in the blast furnace. Carbon refractories – Carbon, formed carbon, manufactured carbon, amorphous carbon and baked carbon are the terms which refer to those refractories that result from the process of mixing carbonaceous filler materials such as calcined anthracite coal, petroleum coke or carbon black with binder materials such as coal tar or petroleum pitch. These mixtures are formed by moulding or extrusion, and the formed pieces conventionally baked in furnaces at temperatures between 800 deg C to 1400 deg C to carbonize the binder. The resulting product contains carbon particles with a carbon binder. Typically, conventionally baked carbon is manufactured in relatively large blocks. As the binders carbonize and the liquids volatilize, they escape through the block, resulting in porosity. This porosity results in a permeable material that can absorb elements from the BF environment such as alkalis. These contaminants use the same passages for entering the...

Crisis Management

Crisis Management  Crisis is an event which harms an organization, its facilities, its finances or its reputation within a short period of time. A crisis can occur as a result of an unpredictable event or as an unforeseeable consequence of some event that had been considered a potential risk. In either case, crisis almost invariably requires that decisions be made quickly to limit damage to the organization. Crisis management is the application of strategies designed to help the organization deal with a sudden and significant negative event. Crisis management is the art of making decisions to head off or mitigate the effects of such an event, often while the event itself is unfolding. This often means making decisions under stress and without the support of key pieces of information. Crisis management is the management and coordination of the organization’s response to an incident that threatens to harm, or has harmed, the organization’s people, structures, ability to operate, valuables and/or reputation. It takes into account management’s planning and automatic incident response, but must also dynamically deal with situations as they unfold, often in unpredictable ways. The study of crisis management originated with the large scale industrial and environmental disasters in the 1980s. Under the present day environment crisis management is an important and necessary component of managing an organization since in the current day situation, no organization is immune to crisis. Crisis may hit an organization in the shape of terrorist attack, industrial accidents, product recall or natural calamity etc. Crisis management is closely linked to public relations where the organization’s image and pride are at stake. Following three elements are common to a crisis. A threat to the organization The element of surprise A short decision time Crisis is a process of transformation where the...

Refractory lining of blast furnace Aug15

Refractory lining of blast furnace...

Refractory lining of blast furnace  A modern blast furnace (BF) is refractory lined to protect the furnace shell from the high temperatures and abrasive materials inside the furnace. The refractory lining is cooled to further enhance the protection against the dispatch of excess heat that can destroy the refractory lining. BF has a complex refractory system to provide a long, safe life that is necessary for the blast furnace availability and for permitting nearly continuous furnace operation and casting. Conditions within the blast furnace vary widely by region and the refractories are subjected to a variety of wear mechanisms. Details are given in Tab 1. The application condition of different regions of a blast furnace is not the same due to the very nature of its geometry and also due to the pyrometallurgical process occurring at different stages. There are diverse physical and chemical wear mechanisms in the different regions of the blast furnace and they are complex in nature. For example mechanical wear or abrasion occurs mainly in the upper stack region and is caused by the decent of the charge materials and by the dust laden gases. High thermal loads are a major factor in the lower stack and the belly regions. In the hearth region, horizontal and vertical flow of hot metal combined with thermal stresses often form undesirable elephant foot shaped cavitation. The refractory materials in these regions are to take care of these wear mechanisms to avoid damage due to them. Therefore, the BF stack (upper middle and lower), belly, bosh, raceway and tuyere region, hearth, and taphole all require different quality of refractories depending on the respective application conditions. Tab 1 Attack mechanisms in different regions of blast furnace       Region Attack mechanism Resulting damage       Upper stack Abrasion...

Stainless Steel Reinforcement Bars...

Stainless Steel Reinforcement Bars  Premature deterioration of reinforced concrete structures is a serious problem worldwide due to corrosion of the embedded steel. The affected reinforced concrete structures are mainly those which are situated in an aggressive marine environment, and road bridges to which de-icing salts are applied during winter periods. Corrosion of the steel is initiated when the chloride ion from the salt (sodium chloride) permeates through the concrete to the level of the reinforcement steel which is attacked on contact. The solution, now favoured by highways authorities in Europe and North America, is to use stainless steel for rebars that has proven to be highly resistant to chloride ion. Stainless steel reinforcement bars or simply called stainless steel rebars are more expensive than carbon steel rebars. They do not corrode for the design life of the structure which is normally taken as 125 years in the case of highway bridges. The reductions on ongoing repair and maintenance costs that are usually incurred in case of carbon steel rebars are significant. Environmentally, the reduced downtime for maintenance and repair impacts upon traffic flow and disruption thus making the use of stainless steel rebars highly attractive. Only a small percentage of the steel rebars needs to be stainless steel to achieve a significant increase in durability. Stainless steel rebars can readily be used with conventional carbon steel rebars in reinforced concrete without causing galvanic effects. Stainless steel rebars are cost effective when used in the elements of the concrete structure at highest risk to corrosion (with carbon steel used for the balance of the reinforcement) or, where repair is difficult and expensive. Further by using stainless steel rebars, the concrete mix can also be simplified as it not necessary to provide passivity to the steel...