Low Ash Metallurgical coke(LAM Coke / Met-Coke) is solid carbonaceous material obtained from destructive distillation of low ash, low sulphur Bituminous coal. Coke is formed when the coal is heated in the absence of air. The residue obtained from the carbonization of a non-coking coal such as sub Bituminous coal. Lignite or Anthracite is normally called char. Coke contains carbon as its principal constituent, together with mineral matter & residual volatile matter. Coke is used as a fuel & reducing agent in smelting iron ore in blast furnace. Since, it is one of the basic raw materials used to produce pig iron, which in turn is used to manufacture Steel. This is the prime reason behind the integral steel plants having their own LAM Coke manufacturing plant on premises.
Traditionally, chemistry, size & strength (both cold as well as hot) have been considered the most important properties for use in the blast furnace. The quality of the constituent coal determines the characteristics of the resultant coke.
The Volatile constituents of the coal- including water, coal-gas & coal-tar are driven off by baking in an airless oven at temperatures as high as 2,000 degree Celsius. This fuses together the fixed carbon & residual ash. Most coke in modern facilities is produced in “by-product” coke ovens. Today, the hydrocarbons are considered to be by-products of modern coke-making facilities (though they are usually captured & used to produce valuable products). Non by-products coek ovens, burn hydrocarbon off-gases on site to provide the heat needed to drive the carbonization process.
Uses of met coke :
Met coke is used where high quality and resilient carbon is required. The applications where met coke is required includes oxygen exclusion, conductive flooring, electrolytic processes, friction materials, ceramic packing media, foundry coatings, heat-treatment, foundry carbon raiser, reducing agents, corrosion materials and drilling applications.
|Size||20 or 25 or 30 -60 or 80 or 90 mm or 100 mm (Any other size can be customized)|
The Metallurgical Coke for blast Furnaces for making iron :
Metallurgical Coke For Blast furnace Operation
A. PHYSICAL COKE PROPERTIES
A high quality coke is characterized by a definite set of physical and chemical properties that vary within a narrow limit thereby ensuring consistency in the quality.
Coke is the only solid material remaining below the cohesive zone in the blast furnace (refer Figure-A for various zones of operation in blast furnace). Hence, coke must provide the strength to support the burden and create the void spaces required to maintain the permeability of the bed. Hence, for stable blast furnace operation, the physical properties of coke are of paramount importance.
\he stability measures the ability of coke to withstand breakup at room temperature and reflects coke handling behaviour outside the blast furnace and coke breakage in the upper part of the blast furnace.
B. Chemical Properties
With physically stable raw materials in the blast furnace, further control of the process is achieved through control of the chemical properties. The most important chemical properties of coke are moisture, fixed carbon, and the content of minor elements
Moisture affects energy requirements and higher moisture will carry fines that on drying either leaves the furnace top or contribute to the coke fine loading, thereby offsetting the value of controlling the CSR and stability values. Moisture is mostly controlled by battery operations.
Fixed carbon is the fuel portion of the coke; the higher the fixed carbon, the higher is the thermal value of coke. Fixed carbon is controlled by the rank of the coal and the amount of mineral matter in the coal.
Coke ash content is also critical to blast furnace operation and hot metal quality. As the total ash increases or varies, the available fuel, carbon, decreases or varies which negatively affect the amount of energy and reducing gases available. Higher ash also results in a higher amount of slag, which requires extra energy to melt. Since ash is predominantly acidic, as it increases, additional flux is required to maintain constant slag chemistry so that sulfur can be removed. Also, the higher silica will result in higher silicon monoxide gas release during coke combustion and more silicon will be absorbed in the iron; the net result being an increase in hot metal silicon. The overall effect of high ash is more slag, lower metal yield, and less production. Ash is controlled by the coal depositional environment which affects the mode of distribution of mineral matter in coal.
The most significant minor elements in coke are sulfur, phosphorus and alkalis. Sulfur is removed by using limestone, which is calcined and then reacts to capture sulfur in the slag. Thus, the slag volume and chemistry control the amount of sulfur that can be removed from the blast furnace. Depending upon the coal sulfur forms, one half to two thirds of the coal sulfur will remain in the coke. Phosphorus in the coke is derived from phosphate minerals in the coal. It goes completely into the hot metal. It is not desired by the steel maker as it hardens the steel and causes surface defects. The last significant minor elements in coke are the alkalis, potassium and sodium oxides. Since these elements have low gasification temperatures, they form a recirculating load in the upper parts. The alkali attack refractory lining and also affects coke and iron ore resulting in loss of strength which ultimately affects blast furnace performance. The alkali content in the coke is controlled by the alkali content in the coal. This brief review of coke properties reveal that most of the properties are primarily controlled by coal and, to a lesser extent, by coke battery operation.. With this knowledge, it is, therefore can be inferred that to obtain high quality met-coke; emphasis should be made in the coal selection for making an economic coal blend charge.