Permeability blast furnace

Permeability Bulk sohd permeability is important in the iron and steel industiy where gas-solid reactions occur in the sinter plant and blast furnace. It also strongly influences compac tion processes where entrapped gas can impede compaction, and solids-handling equipment where restricted gas flow can impede product flowabihty. The permeabihty of a granular bed is inferred from measured pressure drop under controlled gas-flow conditions. 

South Blackwater and Ensham coal are shipped from Gladstone port in QLD, Australia to the Jindal COREX plant in India. The COREX process is a unique and modem process of iron making that has many distinct advantages over the conventional blast furnace iron making process. The COREX process does not required coking coal and uses only thermal coal for generating heat, reduction gas and adequate permeability. The properties of South Blackwater and Ensham coal used in the Jindal COREX plant are given in Table 1. 

Such fissuring causes premature coke abrasion and breakage, reducing permeability in the blast furnace melting zone and influencing the stability of the race-way. Formation and... 

With regard to protection against sulfate attack, the quality of the concrete is a crucial factor a low permeability is the best defence against this type of attack, since it reduces sulfate penetration. This can be obtained by decreasing the w/c ratio and using blended cement (i. e. pozzolanic or blast furnace slag cement that reduce the calcium hydroxide content and refine the pore stracture of the matrix). Finally, the severity of the attack depends on the content of CjA and, to a lesser extent, of C4AF in the cement. Standards in different countries provide for sulfate resistant cements with a C3A content below 3-5 %. 

Some suggest that for wind flow in the blast furnace the factor 1.75 should be double or triple this value. In the blast furnace literature, the term k/1.75 is called the burden permeability with values of 0.15-0.35 cm. 

Brouwers, 1998). In the presence of these additives the dissolved calcium hydroxide tends to react with the residual non-reacted fly ash, yielding additional amounts of C-S-H, and thus reducing the permeability of the paste. The optimum amounts of these additives to be interblended with Portland cement were found to be around 35 mass% of fly ash and about 8 mass% of silica fume (van Eijk and Brouwers, 1998). However, cement combined with 70 mass% of granulated blast furnace slag behaves not too differently from a cement that contains just Portland clinker alone (Faucon et al., 1996). 

Under equal conditions the diffusion coefficients for d vaiy greatly in different cements (see Table 20.4). In general, blended cements that contain blast furnace slag, fly ash or silica fume exhibit a lower permeability to chloride ions and are more suitable for protecting the steel reinforcement from corrosion (Jensen and Pratt, 1989 Aiya et al, 1990 Schiessl and Raupack, 1992 Deja, 1997 El Sayed et al, 1997 Wiens and Schiessl, 1997). An extremely low permeability was also found in alkali-activated slag cement activated with water glass (Deja, 1997). 

Impurities present in coke (moisture, volatile matter, ash, sulfur, phosphorous, and alkali contents) affect its performance in the blast furnace by decreasing its role as a fuel in terms of amounts of carbon available for direct and indirect reduction roles and also its role as a permeable support. 

Mineral admixtures can be used to reduce concrete permeability. These are typically fly ash, microsilica, or blast furnace slag and are also addressed by TRB [42], and by ASTM Committee C09 on Concrete. 

Reduced levels of return sinter will cause a decrease in bed permeabihty, reducing possible gas flow and hence, sinter machine capacity. On the other hand gas permeability is enhanced by increased levels of return sinter, but fuel value of the charge is reduced and peak bed temperature is lowered. This leads to poorer quality sinter with increased fines, which report to returns and reduce sinter bed permeability, thus reducing gas flow and machine capacity. The product sinter in this case is also weak and readily breaks up in the shaft of the blast furnace, reducing permeability and blast furnace throughput. Hence, there is an optimum level of recycle sinter and of fuel to maximise sinter machine capacity. This normally corresponds to a sulfide sulfur content of sinter feed of six to seven per cent and a minimum recycle ratio of 1 1 (recycle net sinter production), or 50 per cent of total sinter production. 

The porous concretes are preferably composed with blast-furnace slag cements, gap graded crushed aggregate with grain size above 5 mm and without fines or minimizing sand volume fraction with superplasticizers and fly ash. Pavements with increased porosity are built in a few layers with different tasks. A minimum required permeability between 7-10 m/s and 3-10 m/s was proposed by Beeldens and Brishant (2004). 

The final effects of carbonation are strongly dependent on the quality of Portland cement and on the permeability of the hardened cement paste. Cements with a small amount of alkalis are less exposed to carbonation, and the same concerns cements blended with fly ash and blast-furnace slag. Carbonation occurs at the highest rates at relative humidity about 40-70%. Near 0% or 100% there is Utde or no carbonation. 

Pure carbon monoxide is extracted from synthesis gas, blast-furnace gas, or coke-oven gas by the following techniques (1) absorption of carbon monoxide by an ammoniacal cuprous salt solution at elevated pressure, followed by desorption by pressure release (2) low-temperature condensation and fractionation (3) liquid methane scrubbing and separation and (4) permeable membrane. 

Figure 6.5.21 Sectional view of the interior of a blast furnace (schematically, hatched cohesive zone, where the metallic burden loses permeability, impeding gas flow).

Concretes prepared with blast furnace slag cement and pozzolanic cement have lower Ca(OH)2 content and pH of the pore solution, thus in principle providing less protection against carbonation or chloride induced corrosion with time. However, the pozzolanic reaction leads to a filling and refining of the pore system and thus to a less or much less permeable concrete. Due to the slow hydration reaction curing (keeping wet the concrete in its early age) is much more important to achieve low porosity. 

Gas permeabihty of burden in blast furnace can be reflected by pressure drop and characteristic value obtained in the process of experiment. The maximum pressure drop indicates the worst permeability and characteristic value indicates the overall permeability of burden. The maximum pressure drop and characteristic value decreased, the temperature at the maximum pressure drop increased, which illustrated the gas permeability of mixture was improved, as shown in Table V. The Figure 2 shows the pressure drop curves of iron ore and the mixtures of ore and A coal or C coal are similar, which illustrated the gas permeability of iron ore was not improved by mixing A coal or B coal, probably due to the poor high-temperature of the two lump coal. The gas permeability of iron ore was improved by mixing coke or B coal, but the gas permeability of iron ore mixed with B coal are worse than that of iron ore mixed with coke. 

Sinter reduction degradation lead to the deterioration of the blast furnace permeability. Therefore, the reduction degradation property of sinter has proved to be of great importance. The result of the reduction degradation property is shown in Fig.4. From the experimental result it can be seen that the reduction degradation index (RDI) of sinter 4 and 5 is higher, which indicates the tendency to produce less fines and dust. 

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