Influence of gas composition on the reactivity of cokes

The NSC reactivity test is often criticised for not being able to accurately predict the performance of cokes in the blast furnace. One explanation proposed for this inaccuracy is that the gas used in the NSC test, pure carbon dioxide, is different to the gas that coke is exposed to in blast furnaces, which is a complex mixture including carbon monoxide, carbon dioxide and nitrogen. The aim of this work was to see to what extent different cokes behaved differently during the NSC test under different gases.Nine Australian coals, used in coking blends, were selected to cover a wide range of rank, maceral composition and elemental composition of the mineral matter. These coals were coked and their relative reactivities in a series of gas mixtures were compared. The time for the reaction of the coke in a 30% CO₂/70% CO mixture was set to eight hours to give about the same weight loss as two hours exposure to 100% CO₂.The main conclusion of this study was that gas composition (using mixtures of CO, CO₂ and N₂) had little effect on the relative rate of gasification of cokes over a wide compositional range of gas and of coke (although of course the absolute reaction rate decreased with decreasing CO₂ levels). The previous studies that suggested changes in gas composition affect the relative reaction rate of different cokes were misleading because they performed the studies at constant burnoff time (2 h) rather than ensuring the cokes were reacted to about the same weight loss.Thus any differences between the behaviour of cokes in the NSC test and in the blast furnace are not due to differences in gas composition between the two.The CSR value was found to be a combination of strength and reactivity: for the data in this study, CSR was determined by a two-component fit involving CRI and the I600/10 index (the strength of the unreacted coke as measured by the CSR tumble test).     

利用神木不粘性块煤炼制炭质还原剂

本文介绍利用神木不粘结性块煤炼制优质铁合金专用焦，通过对块焦的筛分组成分析、工业分析和灰分分析，焦炭的反应性能、比电阻、强度、石墨化程度研究，证明该煤炼制的块焦具有比电阻高，灰分、硫、磷、铝和高温下石墨化程度低的优点。该焦可代替冶金焦冶炼铁合金。     

Comparative study of reactivity to CO2 of cokes used in stone wool production

The reactivity towards CO₂ of seven types of commercial coke used in stone wool production has been measured in a thermo gravimetric analyser (TGA). The cokes originated from Western and Eastern Europe and from China. For three of the cokes, the porosity, density and surface area were determined. The directly measured porosities of the cokes was slightly low, indicating that there are pores that are not connected with the outer surface. This is supported by the measured densities and microphotos.The measurements showed that the Chinese cokes were the least reactive while the European cokes made on American coal were the most reactive. The reactivity of the one Eastern European coke in the measurements had an intermediate reactivity.Simulations with a cupola model show that 25% more coke is needed for stone wool production if the coke is changed to a type with half the reactivity towards O₂ and CO₂.The TGA method proved to be a good method for ranking the coke with respect to reactivity with CO₂.     

Effect of coal blending ratio on CO<Subscript>2</Subscript> coke gasification

Coke gasification is largely influenced by the raw coal, catalyst, and blending ratios, pore structure, and specific surface area of the raw coal. In this study, several properties of cokes related to their reactivity were measured using coke reactivity test apparatus (CRTA), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer-Emmet-Teller (BET) surface area analysis, and energy dispersive X-ray spectroscopy (EDS) to investigate the characteristics of coke gasification. The results indicated that the reactivity of coke in the temperature range from 950 to 1,050 °C was affected by the type of coke and its specific surface area rather than the general properties of the coke, although the overall reactivities at the other temperatures were uniform. EDS analysis showed that the catalyst acted on the reactivity of cokes at low temperatures, whereas the BET analysis indicated that the reactivity at high temperature was influenced by the specific surface area.     

Effect of pore diffusion on reactivity of lump coke

The gasification of fine-grained and lump coke in CO₂ atmosphere was measured in a laboratory reactor. Owing to the effect of pore diffusion, the reactivity of lump coke at 1050 °C was found to be considerably lower than that of fine-grained coke at otherwise the same conditions. The diffusion effect is more significant for cokes produced by a stamping method than for cokes from top charges. To express the gasification of lump coke, a simplified mathematical model considering the effect of pore diffusion on gasification rate was adopted. Kinetic parameters were determined from experiments with fine-grained coke, while effective diffusivity was evaluated from experiments with a single coke particle. The model fits experimental data of lump coke well. The relation between reactivity and textural characteristics was also examined: the correlation between effective diffusivity and the fraction of largest pore volume was found.     

Carbonization of aromatic hydrocarbons—VI: Carbonization of heterocyclic compounds catalyzed by aluminum chloride

Carbonization properties of heterocyclic compounds were studied in the presence of aluminum chloride to observe the effects of carbonization reactivity difference due to the kinds of heteroatoms and the ring structures on the structural properties of the carbon. The amount of catalyst was shown to have a significant influence on the properties of cokes. Some of the heterocyclic compounds gave graphitizable needle cokes with a suitable amount of the catalyst, some gave graphitizable mosaic cokes and the others gave non-graphitizable isotropic cokes. The tendency to give a graphitizable needle coke decreased in the order of sulfur, nitrogen and oxygen as for the heteroatom, and did in fluorene, anthracene and phenanthrene types as for the ring structure. Such a tendency is compared with that observed in carbonization under high pressure. A large part of sulfur and nitrogen atoms was left in the coke after carbonization, and no correlation was observed between the remaining amount and the structure of the coke.     

溶损反应动力学对焦炭溶损后强度的影响

为了分析溶损反应动力学行为对焦炭反应后强度的影响,在1 050℃～1 300℃的范围内,对三种典型焦炭进行了等温溶损反应实验.当焦炭的溶损失重率为25%时停止反应,通过I型转鼓检测焦炭的溶损后强度.结果表明,不同反应性的焦炭发生最严重的劣化梯度反应时的温度不同,高反应性焦炭为1 100℃左右,低于其他两种焦炭.虽然高反应性焦炭发生最严重的劣化梯度反应后的强度很低,但改变反应温度使反应速率加快或减慢都能使高反应性焦炭的反应后强度显著地提高.     

Mineral matter effects on air-oxidation of cokes from a coking coal

Indigenous mineral matter in coal affects the chemical reactivity of resulting cokes through both catalytic graphitization and catalytic gasification. The significance of both catalytic effects on air-oxidation was examined using cokes from a medium-volatile bituminous coking coal with 9 wt% mineral matter. Catalytic graphitization by mineral matter enhanced the reactivity of the resulting coke in spite of the formation of highly crystalline carbons. This effect, however, was less than that of catalytic gasification by mineral matter. The coke from the acid-treated predemineralized coal exhibited no catalytic effects but was the most reactive. The implications of these results are discussed in detail.     

单种煤结焦性能评价与焦炭质量预测

根据11种单种煤的性质,在实验室20kg小焦炉上进行了11种单种煤和8种配煤方案的炼焦实验,并对焦炭进行了筛分组成、冷态强度、焦炭热性质等分析,初步建立了焦炭质量预测模型。实验结果表明:单一的煤质指标与焦炭强度的关系不是很明显,选用煤质多因素指标进行焦炭质量预测,其预测效果较好;单一的煤质指标(Vd、R0max、Ad)与焦炭反应性之间有较好的关系,且焦炭的反应性随反应温度的升高而增大。     

Effect of coal weathering on technological properties of cokes produced at different scales

The effect of weathering (natural oxidation) on the technological properties of cokes obtained at three different scales (laboratory, pilot plant and semi-industrial), from two medium volatile bituminous coals stored at INCAR open stockyard for several months, has been studied in this work. The results show that the procedure developed at laboratory scale is useful for studying the evolution of coke quality because the trends of the main quality indexes (mechanical strength and reactivity to CO₂) are in agreement with those of the cokes produced at larger scales. Furthermore, it was found that the total porosity and the micropores specific surface area of the cokes vary with the scale of carbonization, and that they increase as follows: semi-industrial<pilot plant<<laboratory. All of which are related to the evolution of the mechanical strength and reactivity to the CO₂.     

A semi-industrial scale study of petroleum coke as an additive in cokemaking

The addition of petroleum coke to a typical industrial coal blend used in the production of metallurgical coke was studied. Cokes were produced at semi-industrial scale at the INCAR coking plant, using petroleum coke of different particle size distribution as an additive. Special attention was paid to changes caused in the textural properties (porosity, pore size distribution, fissures at the interface between metallurgical coke and petroleum coke) which have been found to be responsible for variations in the metallurgical coke quality parameters (e.g., mechanical strength and reactivity towards CO₂). Variation in porosity was found to depend on particle size and the proportion of the additive. The decrease in the microporosity (i.e., pore radius<3.7 nm) of the metallurgical cokes observed when petroleum coke is added to the coal blend, is postulated to be one of the main factors responsible for the decrease in the reactivity of these cokes. The variation of the mechanical strength indices can be explained by the changes in porosity and the quality of the interfaces between petroleum coke and metallurgical coke.     

Study of the reaction of cokes with KOH under nitrogen

Five cokes of increasing content of anisotropic carbon were prepared. Polished surfaces of these cokes were characterized by optical microscopy in terms of components of optical texture. These surfaces were reacted with KOH at 873, 1073 and 1273 K in an inert atmosphere for 2 h and the resultant topography monitored by scanning electron microscopy (SEM). The extent of potassium take-up by coke particles was measured and the diffusion of potassium was detected by EDAX. Microstrength testing was made on the cokes before and after reaction with the alkali. Coke reactivity measurements were obtained for untreated and treated cokes. Results indicate that in an inert atmosphere the alkali reacts preferentially on the prismatic edges of anisotropic carbon and that the rates of reaction increase with increasing temperature. Potassium is able to diffuse into the interior of the more anisotropic coke particles and this casues weakening of the coke. The reactivity measurements indicate that for the more anisotropic cokes the effect of potassium as a catalyst in the solution-loss reaction is more pronounced than for the least anisotropic coke. These conclusions suggest that metallurgical coke in the blast furnace in the presence of alkali materials can lose strength by direct reaction over and above considerations of gasification processes.     

Gasification reactivities of metallurgical cokes with carbon dioxide,steam and their mixtures

Gasification reactivities of cokes with carbon dioxide, steam and their mixtures at 1200 °C were investigated, using seven single cokes made in a laboratory furnace from single coals of different properties, and also one commercial coke. The reactivity with steam was significantly higher than that with carbon dioxide. The reactivities of the mixture increased proportionally with increasing steam content above 10%; however, the reactivity below 10% steam content was smaller than that with pure carbon dioxide, the minimum reactivity being observed at a steam content of 2–4%. The reactivities of the compounds corresponding to optical texture were determined by analysing the coke microscopically before and after gasification. In general, except for one coke, the inert texture was the most reactive. Increasing size of the optical unit decreased the gasification reactivity, fibrous and leaflet textures were the least reactive. Gasification with steam developed pores within the inner region of the coke, whereas carbon dioxide reacted with the coke at or near the surface, producing a relatively smooth surface. Some proposals are suggested for better coke production.     

Catalytic graphitization of cokes by indigeneous mineral matter

Indigeneous mineral matter in coals acts catalytically towards graphitization during heat treatment of coals to 2273 K. Nineteen coals of a wide range of rank were demineralized by acid extraction. Original and demineralized coals were carbonized in the range 1073–2273 K, and the resulting cokes examined by optical microscopy, X-ray diffraction and phase-contrast high resolution electron microscopy. Optical microscopy indicated the extent of formation of anisotropic carbon in the resultant cokes. The (002) X-ray diffraction profiles indicated three types of catalytic effect, for which electron microscopy demonstrated different crystallite structures and interrelations. The importance of catalytic graphitization in metallurgical cokes in relation to their strength and reactivity is discussed.     

用电阻率计算焦炭的反应性

用测定焦炭电阻率的方法来计算焦炭的反应性。反应性的计算值与实测值比较证明,焦炭的电阻率与反应性之间有很好的相关性。     

添加炭素物料改善焦炭性能的研究

通过向炼焦配煤中添加石油焦、人造石墨和天然石墨并炼焦处理，研究了添加炭素物料对焦炭性能的影响，结果发现，添加少量炭素物料有效地提高了焦炭强度并降低了焦炭的反应性。     

Comparison of steam-gasification characteristics of coal char and petroleum coke char in drop tube furnace

The steam-gasification reaction characteristics of coal and petroleum coke (PC) were studied in the drop tube fur-nace (DTF). The effects of various factors such as types of carbonaceous material, gasification temperature (1100–1400 °C) and mass ratio of steam to char (0.4:1, 0.6:1 and 1:1 separately) on gasification gas or solid products were investigated. The results showed that for al carbonaceous materials studied, H2 content exhibited the larg-est part of gasification gaseous products and CH4 had the smal est part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon con-version of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of al char samples increased with increasing steam/char ratio. For al the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic ef-fects when the gasification reaction of char was held in DTF. The calculating method for the equilibrium shift in this study wil be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer (L002/d002) numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.     

Influence of coal forced oxidation on technological properties of cokes produced at laboratory scale

The effect of coal oxidation in air at 140 °C on the technological properties of cokes obtained at laboratory scale from two medium volatile bituminous coals has been studied. The proximate and ultimate analyses do not show important changes with coal oxidation time. However oxidation clearly has a strong effect on the plastic properties of the coals in view of the fact that the Gieseler fluidity eventually disappears. From this point variations in plastic properties can still be detected by FSI. Other changes, such as a shortening of the length of the saturated fragments of the aliphatic chains, a decrease in the aliphatic hydrogen content and an increase in the oxygen-containing groups are detected by PA-FTIR. It was also found that the main coke quality indices (mechanical strength and reactivity to CO₂) of both coke series are impaired with coal oxidation. A close relationship between reactivity to CO₂ and the micropore specific surface area of the cokes has been corroborated.     

Enhancements in nickel-catalyzed hydrogasification of carbon by surface treatments

A pitch coke was given 4 types of pretreatment to modify the surface state; air oxidation, heatingquenching, steam treatment and hydrogen treatment. The treated cokes were impregnated with nickel and gasified in an atmospheric hydrogen flow. The catalytic reactivity of the pitch coke was enhanced by these pretreatments. Several properties of pretreated cokes were compared and it seemed that highly hydrophilic or acidic surfaces of carbon were unfavorable to metal-catalyzed hydrogasification. The reactivity enhancement was ascribed to an increase in the hydrogen adsorption capacity of nickel on the pretreated coke. The oxygen-containing surface groups are presumed to inhibit the spillover of atomic hydrogen from nickel to carbon. The effect of 1 type of pretreatment. heating-quenching, seems to relate to the expansion in pore volume.     

Influence of coal forced oxidation on technological properties of cokes produced at laboratory scale

The effect of coal oxidation in air at 140 °C on the technological properties of cokes obtained at laboratory scale from two medium volatile bituminous coals has been studied. The proximate and ultimate analyses do not show important changes with coal oxidation time. However oxidation clearly has a strong effect on the plastic properties of the coals in view of the fact that the Gieseler fluidity eventually disappears. From this point variations in plastic properties can still be detected by FSI. Other changes, such as a shortening of the length of the saturated fragments of the aliphatic chains, a decrease in the aliphatic hydrogen content and an increase in the oxygen-containing groups are detected by PA-FTIR. It was also found that the main coke quality indices (mechanical strength and reactivity to CO₂) of both coke series are impaired with coal oxidation. A close relationship between reactivity to CO₂ and the micropore specific surface area of the cokes has been corroborated.