Blast furnace coke requirements

Worldwide demand for blast furnace coke has decreased over the past decade. Although, as shown in Figure 1, blast furnace hot metal production (pig iron) increased by about 4% from 1980 to 1990, coke production decreased by about 2% over the same time period (3). This discrepancy of increased hot metal and decreased coke production is accounted for by steady improvement in the amounts of coke required to produce pig iron. Increased technical capabihties, although not universally implemented, have allowed for about a 10% decrease in coke rate, ie, coke consumed per pig iron produced, because of better specification of coke quaUty and improvements in blast furnace instmmentation, understanding, and operation methods (4). As more blast furnaces implement injection of coal into blast furnaces, additional reduction in coke rate is expected. In some countries that have aggressively adopted coal injection techniques, coke rates have been lowered by 25% (4). 

Foundry Coke This coke must meet specifications not required of blast furnace coke. The volatile matter should not exceed 1.0 percent, the sulfur should not exceed 0.7 percent, the ash should not exceed 8.0 percent, and the size should exceed 100 mm (4 in). 

Coking produces a blast furnace coke feed substantially free of sulfur. However, the gaseous product, coke oven gas, has a sulfur gas content of 900-1, lOOg/m (at 15°C, 1 atm) [31]. This is mainly hydrogen sulfide, which may be removed either by the vacuum carbonate or Stretford processes. The sulfur gas removal efficiency of the Koppers Company s vacuum carbonate process is about 90%, which produces sulfuric acid, whereas the Stretford process can achieve 99% containment to a sulfur product (Chaps. 3 and 9). The choice of desulfurization process depends on the efficiency required and the sulfur product desired. Condensible hydrocarbons such as benzene (and other aromatics) and phenols have always been recovered by condensation, etc. [34]. 

Of these three roles, the first two can be substituted by oil, gas, plastics, and coal, which are injected at the tuyeres as generating energy and a carbon source. Such a substitution brings about a reduction in coke rates for the blast furnace. (Coke rate is the weight of coke required to produce 1 ton of iron). However, there is no other satisfactory material available, which can replace, fully or partially. 

Table 6 Required chemical properties of blast furnace coke...

The composition of blast furnace coke with respect to its Ume, silica and alumina contents also needs to be taken into account when calculating the required sinter composition and corresponding flux additives to give the required blast furnace slag composition. 

USS installed three 9004ip conq>ressors and the as iated piping to boost the incoming coke oven gas pressure from 68.9 kPa (10 psig) to 379 kPa (55 psig) for injection into the furnaces. Since n(H enough coke oven gas would be available to completely satisfy the blast furnace injection requirements, USS purchased instrumentation and equipment so that natural gas could be added to supplement the coke oven gas [24]. 

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as ... 

DRI, in peUet/lump or HBI form, can be added to the blast furnace burden to increase furnace productivity and reduce coke requirements. It can be used for short-term increases in blast furnace output when a faciUty is short of hot metal during times of high steel demand, or when one of several blast furnaces is down for a reline. It also can be justified if the increased output is sufficient to allow operation of fewer blast furnaces long-term. 

Out of the 900 million tons of coal produced in the United States for domestic purposes in 1992, about 34 million tons were used for coking [10]. The overw helmmg majority of coal is consumed by the electric utilities. Nevertheless, in 1990, the United States steel industry required about 23 million tons of coke which was produced by the byproduct recovery slot oven [15] For a typical blast furnace, this translates to 0 5 tons of coke per ton of iron metal. 

There are two process routes for making steel in the UK today the electric arc furnace and the basic oxygen converter. The latter requires a charge of molten iron, which is produced in blast furnaces. The raw materials for producing molten iron are iron ore, coking coal, and fluxes (materials that help the chemical process) - mainly limestone. 

The production of steel begins when iron ore is fed into a blast furnace (Fig. 16.39). The furnace, which is approximately 40 m high, is continuously replenished from the top with a mixture of ore, coke, and limestone. Each kilogram of iron produced requires about 1.75 kg of ore, 0.75 kg of coke, and 0.25 kg of limestone. The limestone, which is primarily calcium carbonate, undergoes thermal decomposition to calcium oxide (lime) and carbon dioxide. The calcium oxide, which contains the Lewis base O2", helps to remove the acidic (nonmetal oxide) and amphoteric impurities from the ore ... 

Natural gas has replaced coal to a great extent for domestic and industrial heating. This is a consequence of installation of very large pipelines from producing to consuming places, the rise in solid fuel price, convenience, cleanliness, controllability and versatility as a fuel. The by-product gaseous fuels, coke oven gas and blast furnace gas are well-known important fuel for the ferrous industry, and require no further elaboration. 

Low-Sliaft Furnace. These furnaces are circular or oval in cross section. The oval shape permits greater hearth area without increasing the required depth of penetration of the blast supplied through Ihe tuyeres. Such lumaces are designed for liner raw materials and low-grade coke or lignite. Once considered ideal lor small-scale iron production, only a limited number have been installed. The operating principles are essentially similar to those of a blast furnace. 

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