Nut Coke Research Articles

Enhancement of Low-temperature Gasification and Reduction by Using Iron-coke in Laboratory Scale Tests

Iron-coke having various amount of M.Fe were produced in laboratory scale and the influence of M.Fe content in Iron-coke on reaction behavior under the condition simulating blast furnace has been investigated. Cold strength of Iron-coke products was decreased with an increase of mixing ratio of iron ore mostly due to a prevention of dilatation of coal particles by iron ore, resulting in weak bonding of coal particles. Nevertheless formed Iron-coke with iron ore in the fraction up to 30% would have enough strength for use in blast furnace as nut coke. Both CRI and JIS-reactivity were enhanced by increasing ratio of mixed iron ore, confirming the catalysis effect of M.Fe. The temperature at which carbon consumption started was lowered with an increase of T.Fe in coke. Formed Iron-coke containing 43% of T.Fe started reaction consuming its carbon at lower temperature than conventional coke by 150°C. Furthermore, consumed carbon ratio was improved by M.Fe installation to coke due to increasing gasification. Process evaluation with using Iron-coke in blast furnace was performed by BIS test. It was revealed that using formed Iron-coke having 43% of T.Fe for blast furnace resulted in an increase of shaft efficiency by 6.8%. It was found that to lower the reducing agent rate in blast furnace by decreasing the temperature of thermal reserve zone, lowering the beginning temperature of coke reaction was effective. Usage of Iron-coke having M.Fe catalyst within coke matrix is one of the methods.

Reduction of Pellets‐Nut Coke Mixture under Simulating Blast Furnace Conditions

AbstractIn recent years an intensive work has been carried out to decrease the coke losses of the blast furnace through mixing small‐sized coke called “nut coke” in the iron ore burden layers. In order to clarify the influence of nut coke on the pellets reducibility, industrial iron ore pellets were reduced with and without nut coke participation under different temperatures and atmospheres. Isothermal and non‐isothermal reduction tests under simulating blast furnace conditions were performed using an experimental laboratory rig. Furthermore, reflected light microscopy, scanning electron microscopy and X‐ray technique were applied to characterize the microstructure and different phases developed in the origin and reduced pellets. Pellets reduced isothermally without nut coke participation exhibited reduction retardation (RR) at elevated temperature (≥1373 K) whereas the presence of nut coke had a positive effect of preventing such phenomena. The non‐isothermal reduction of pellets showed that, as the amount of nut coke in pellets bed increased, the reducibility of pellets increased, too. The rate controlling mechanism of pellets and pellets‐nut coke mixtures was predicted from the correlation between apparent activation energy calculations and microstructure examination.

Influence of nut coke on iron ore sinter reducibility under simulated blast furnace conditions

One of the most important factors to increase the economic efficiency of the blast furnace process is to reduced coke losses (undersieve product known as nut coke). In recent years there has been increased interest in mixing nut coke in the sinter layers. In order to clarify the influence of nut coke on sinter reducibility, sinter and sinter–nut coke mixtures were isothermally reduced with 30%CO–70%N2 at 1173–1523 K using a muffle furnace supported by an on-line gas analyser. Reflected light microscopy, scanning electron microscopy and X-ray technique were used to characterise the microstructure and the different phases developed in the original and reduced sinter. Sinter reduced without nut coke participation exhibited reduction retardation at elevated temperatures (>1373 K) while the presence of nut coke prevented such phenomena. The rate controlling mechanism of sinter and sinter–nut coke mixture was predicted from the correlation between apparent activation energy calculations, mathematical modelling derived from gas–solid reaction model and microstructure examination.

Analysis of Traveling Behavior of Nut Coke Particles in Bell-type Charging Process of Blast Furnace by Using Discrete Element Method

The objective of this paper is to analyze the particle behavior in bell-type charging process of actual blast furnace by using Discrete Element Method (DEM). The circumferential balance of charged mass in the quad-hopper and the effect of the nut coke particle position in the quad-hopper on the traveling behavior and the segregation were discussed. The mass flow rate discharged from the rotating chute was fluctuated with the time, and the peak values gave when the directions of the chute movement became same as the one of the conveyor. It leads to the unbalance of charged particles in each part of the quad-hopper. The nut coke moved to the upward in the sintered ore particle layer during traveling to large bell from the quad-hopper due to the particle segregation, when they were segregated at the bottom of hopper. However their relative positions moved downward when they were segregated at the top, because the time for starting discharging of nut coke became faster. The installation of the damper at the way to the small bell from the hopper affects on the circumferential balance of mass of nut coke. Most of nut coke particles were charged at near the wall of blast furnace, and the small peak of the distribution of its specific charged mass was seen around 3.0 m in the radial distance from the center, it caused by the particle segregation during flowing on the particle layer. The relative radial distribution of the nut coke particles wasn't affected by their positions in the large bell and the total mass. Thus, keeping the circumferential balance of nut coke mass in the large bell is very important. The position of nut coke particle didn't affect on the segregation of sintered ore. The radial distributions of relative charged mass for all conditions were quite similar.

Technology for preparing coke for blast-furnace smelting and its efficiency

This article describes the use of coke of the Premium class on blast furnace No. 5 at the Enakievo Metallurgical Plant. It is shown that the use of this coke has increased furnace productivity by 5.7-6.9% and reduced the consumption of skip and nut coke by 3.2-4.1%.

Theoretical and experimental foundations for preparing coke for blast-furnace smelting

This article examines the preparation of coke for blast-furnace smelting by a method that most fully meets the requirements of blast-furnace technology: screening of the −36 mm fraction, the separation of nut coke of the 15‐36 mm fraction, and its charging into the furnace in a mixture with the iron-ore-bearing charge components. An analysis is made of trial use of coke of the Premium class on blast furnace No. 5 at the Enakievo Metallurgical Plant. Use of this coke makes it possible to reduce the consumption of skip coke by 3.2‐4.1%. Recent decades have seen significant progress in blast-furnace technology, advances made in this area having increased furnace productivity to 2.5‐3.5 tons/(m 3 ·day), reduced coke consumption to 250‐300 kg/ton pig iron, and lowered the pig’s sulfur content to 0.011‐0.015% [1]. The main reasons for these changes have been the wide-scale use of additional types of fuel and improvements in all of the original components of the technology: the quality of the charge materials, the slag and blast regimes, and the design of the furnace and other equipment. The most important factor in allowing these changes was an improvement in the quality of the coke, which has experienced an increase in the mechanical, thermal, chemical, abrasive, and other types of loads. Data from German researchers show that the strength properties of German coke has more than doubled in the last 20‐30 years. Abroad, the quality of skip coke is being improved while continuing to satisfy the other requirements of the smelting operation by improving the quality of the coke-bearing component of the charge, the coking regime, and the coke’s preparation for the blast furnace. In accordance with the requirements of modern blast-furnace technology, in most of the developed nations the minimum value of the index that characterizes the hot strength of coke (CSR) is 60‐65% or more, while the index that characterizes its reactivity is lower than 25‐30% [2].

Effect of coke reactivity and nut coke on blast furnace operation

Two measures for coke saving and increase in blast furnace efficiency related to coke characteristics – reactivity and size – are discussed in this paper. Modern blast furnace operation with low coke rate and high injection rate causes a change in coke quality requirements. A discussion has arisen recently about highly reactive coke. Here, a theoretical analysis of influence of coke reactivity on the thermal reserve zone, direct reduction and carbon consumption in the blast furnace has been undertaken. Experiments have been performed using non-standard test scenarios that simulate coke behaviour under real blast furnace operating conditions. Coke reactivity and microstructure have also been investigated under the impact of alkali and pulverised coal ash and char. Operation of many blast furnaces has proved the possibility of coke saving and increase in productivity when using small-sized coke (so-called nut coke) mixed with the burden, but the reasons for this phenomenon, and consequently the limit for nut coke consumption, are still not very clear. An analytical method and cold model simulations have been used to quantify the change in shaft permeability and furnace productivity when using nut coke.

Coke, char and organic waste behaviour in the blast furnace with high injection rate

Blast furnace operation with low coke rate, high amount of auxiliary hydrocarbons and use of nut coke causes a change in coke quality requirements. In particular, not burned in the raceway residues of injected substances (char and ash) can influence the coke behaviour. Therefore combustion efficiency of various organic wastes with and without pulverized coal injection (PCI) and coal char has been investigated under the raceway simulation conditions. Mixing of various substances improves their combustion efficiency. Study on coke gasification by carbon dioxide in the presence of char showed that with the increase of char concentration, coke strength reduction becomes smaller. The reactivity of char with CO 2 is higher than that of coke. Therefore char is consumed preferentially. In presence of injected char, total pore volume in coke and its wear resistance were increased. Coke reactivity and microstructure in the presence of various kinds of ash has been studied. Many ash spheres were observed on the surface of coke matrix and its size was dependent on ash properties.

99/03558 Quality of nut coke under modern conditions of its manufacture: Strakhov, V. M. et al. Koks Khim., 1998, (9), 26–30. (In Russian)

99/03558 Quality of nut coke under modern conditions of its manufacture: Strakhov, V. M. et al. Koks Khim., 1998, (9), 26–30. (In Russian)