Coking Temperature Research Articles

Development of anode mixture composition from processing products of coal to produce carbon nanostructures by the plasma-arc method

It is discussed the use of coal processing products as a part of the anode mixture and their effect on the production of homogeneous carbon nanostructures by the plasma-arc method. The main aim of this research is to develop a theoretical basis and anode mixture composition, allowing to obtain morphologically uniform carbon nanostructures. It was used arc evaporation method for synthesis of nanostructures. Identification of carbon nanostructures and sizes was carried out by electron microscopy. Carbon nanoparticles, carbon filamentary structure and carbon fiber were obtained using the proposed components that make up the anode mixture, pitch coke, coal tar and coal medium temperature pitch. The carbon content in pitch coke and in the form of aromatics in the coal medium temperature pitch may allow to obtain more homogeneous morphologically carbon nanostructure. The research results can be used to improve the strength and corrosion resistance of metals. We propose to use the processing products of coal as part of the anode mixture to produce morphologically uniform carbon nanostructures by the plasma-arc method.

Assessing coke readiness

An article by Rubchevskii and his colleagues on the assessment of coke readiness in terms of its electrical resistivity is discussed [1]. It is shown that the assessment of coke readiness on the basis of the yield of volatiles is incorrect and that the article does not adequately analyze existing methods for the assessment of coke readiness, such as expert evaluation; the APIR-S system for measuring the surface temperature of the discharged coke cake; the difference in the yield of volatiles for coke breeze and coke (ΔV daf ); two-probe measurement of the resistivity; monthly temperature measurements in the heating channels and correction of the coking temperature; and temperature measurement over the length of the boundary walls. The assessment of coke readiness on the basis of ΔV daf , by the method employed at OAO EVRAZ NTMK, is shown to be effective. The various systems for measurement of the coke resistivity that are promoted in the article are unsuitable for coke-plant laboratories. The UESMETR-31 system (for monolithic samples) is very massive (~20 kg). The UESP-2 system for measuring the resistivity of powder, which is again quite massive (~15 kg), is the best suited to the assessment of coke readiness. However, its use is hindered by the enormous cost (200000 hryvnia) and various other defects mentioned in the article [1]. The comparative analysis of its performance in the article seems promotional rather than rigorous. Measurement of the resistivity of carbon powder (particle size 0.315–0.400 mm) in accordance with State Standard GOST 4668–75 requires the UESP-1 system, which consists of a complex set of devices and instruments. The conclusion reached is that coke’s yield of volatiles, which is the traditional characteristic used to assess its readiness, is no longer applicable for current coke ovens, as shown conclusively in [8–10]. For example, with temperature variation in the axial plane of the coke cake in the range 940–1290°C (five cases), the coke’s yield of volatiles V co daf is consistently low: 1.1, 1.0, 1.0, 1.0, 0.9 [10]. This is confirmed by data on the constant mass yield of volatiles with change in the coking period and the coke readiness [2, Table 4]. A comparison in [1] shows that measurement of the resistivity in accordance with State Standard GOST 4668–75 and its measurement by the authors’ method are equivalent means of assessing the coke readiness.

Low-Temperature Oxidation Characteristics and Its Effect on the Critical Coking Temperature of Heavy Oils

Air-assisted steam stimulation (huff and puff) is an innovative process for enhanced heavy oil recovery. In this paper, the low-temperature oxidation (LTO) and coking experiments were conducted to reveal the LTO characteristics of heavy oils and its effect on the oil critical coking temperature. The O2 consuming ability and oxidation activity of different oils, in a temperature range of 80–170 °C, were analyzed, including typical light and heavy oil samples. The experimental results show that heavy oils have a higher oxidation activity at low temperature than that of light oils. Heavy oils can effectively consume O2 in the injected air and produce a certain amount of CO2 under reservoir conditions. In terms of the difference in LTO characteristics of different oils, a more general LTO reaction kinetics model of crude oils in a reservoir was established. A parameter, Rdec (ratio of hydrocarbon oxides participating in decarbonylation to total hydrocarbon oxides produced from oxidation), is introduced to ind...

A Modified Model for Calculating Theoretical Flame Temperature in Blast Furnace and Its Application

The theoretical flame temperature (TFT) before tuyere, always highly concerned by blast furnace (BF) operators, is one of the most important parameters for evaluating the thermal state of hearth. However, some influencing parameters, for example, the SiO2 reduction by carbon, were always neglected or inaccurate when calculating the TFT. According to the definition of TFT, the temperature of coke into raceway and the reduction rate of SiO2 in ash of coke and pulverized coal were obtained by analyzing the samples before tuyere in blast furnace. Taking full account of different factors, a modified model for calculating the TFT in blast furnace was established. The effects of the oxygen enrichment rate, the reduction rate of SiO2 in raceway, the ash content in coke and pulverized coal and the pulverized coal injection (PCI) rate on TFT were determined quantitatively. The modified model was applied to selecting the used coal for PCI in blast furnace. Considering the different SiO2 contents of mixed coal, the calculated TFT remained a stable level. This showed that the selected coal could be suitable for PCI in blast furnace.

Effect of Pt and Gd on coke formation and regeneration during JP-8 cracking over ZSM-5 catalysts

Pt and Gd loaded ZSM-5 catalysts were synthesized by ion exchange method to investigate the effect of metal promoters on catalyst activity, coking and regeneration during military aviation fuel (JP-8) cracking into petroleum gas (PG) at 723K. Multiple cracking and regeneration cycles were performed over the ZSM-5 based catalysts and their crystalline structure, oxidation profile, coke band and acidity were characterized. It was revealed that addition of Gd metal to the ZSM-5 catalyst prevented formation of complex aromatic coke and increased the number of Lewis acid sites, while Pt promoted ZSM-5 catalyst showed a decrease in the coke oxidation temperature. The effect of Pt and Gd promoters enhanced the coke burn-off ability, formed hydrogen rich carbon species and reduced oxidation temperature of coke substantially. Furthermore, agglomeration of Pt particles was partially impeded by coexisting Gd metal on the regenerated ZSM-5 catalyst. Synergetic effects of Pt and Gd promoters stabilized the PG yield and product distribution over the Pt–Gd/ZSM-5 catalyst during the cracking and regeneration cycles.

Determining the electrical resistivity of coke powder

In order to improve means of determining the electrical resistivity of coke powder, existing methods are analyzed. Their basic deficiency is that it is difficult to identify and eliminate the influence of transient electrical resistance between the electrodes and the coke-powder sample, because it is impossible to ensure constant packing density of the powder column at constant pressure. Therefore, to eliminate fluctuations in the transient resistance, constant packing density of the sample is required. That may be ensured if the pressure varies over the sample. The influence of transient resistances on the measurement result may be eliminated by improving the pressing system and constructing a two-probe cell and also by replacing the potentiometer, milliammeter, voltmeter, rheostat, and battery with an up-to-date measuring module. Recommendations for improvement in the apparatus and method used in determining the resistivity of coke are developed, for use in a prototype system. In improving the resistivity determination, the constant parameters are the sample mass; the volume of the sample (and hence its density); and the current passing through the sample. The variable is the pressure applied to the coke sample. A method of determining the electrical resistivity of coke powder is developed, and three improved systems are created. Two undergo industrial tests at PAO Zaporozhkoks and ChAO Makeevkoks. The tests confirm the known dependence of the resistivity on the final coke temperature (in the range 900–1150°C) and the possibility of using the resistivity in judging the condition of the coke and correcting the coking temperature of the batch. Since the final coking temperature determines the size and strength of the coke particles, other conditions being equal, the condition of the coke (its readiness for use) may be assessed on the basis of a set of physicochemical characteristics.

Numerical Simulation Analysis of the Optimized and Transformed 200MW Pulverized Coal Fired Boiler Burner

With the use of computational fluid mechanics software – FLUENT, the numerical simulation computation of combustion process inside a certain 200MW corner tangential firing boiler whose combustor is transformed by the multi-grade efficient low-nitrogen combustion technology was conducted, thus the furnace temperature, velocity, mixture and NOx concentration field at rated conditions before and after the transformation were obtained. The calculation results were highly identical with the industrial test results. The results show that after using the multi-grade efficient low-nitrogen combustion technology, the NOx emissions significantly lowered down with the drop of about 40% compared with the emissions before transformation, while the furnace coking and high temperature corrosion were effectively controlled, achieving good economic and social benefits and providing a reference to the design and transformation of the same types of boilers.

Microstructure and mechanical properties of low-carbon MgO–C refractories bonded by an Fe nanosheet-modified phenol resin

The effect of adding Fe nanosheets on the microstructure of phenol resin and low-carbon MgO–C refractories was investigated. The results indicate that well-crystallised carbon nanotubes (CNTs) of 50–100nm in diameter and of micrometre scale in length could be generated at 1000°C. The yield of CNTs decreases and the diameter of CNTs increases significantly as the coking temperature increases. The growth mechanism of vapour–solid (V–S) is transformed into the vapour–liquid–solid (V–L–S) mechanism at 1200°C for CNTs in low-carbon MgO–C refractories. The mechanical properties and thermal shock resistance at 1000–1400°C of the specimens with 0.5wt% Fe nanosheets are greatly improved compared with specimens without Fe nanosheets. The largest magnitudes in the cold crushing strength (CCS), the cold modulus of rupture (CMOR), the hot modulus of rupture (HMOR), and the residual cold modulus of rupture (CMORst) are 25%, 44%, 24%, and 30%, respectively. The results are attributed to in situ formation of CNTs and the subsequent generation of bridging and crack deflection mechanisms in the matrix. However, as the coking temperature increases, the yield of the CNTs becomes lower and their diameter becomes larger. Thus, the favourable contribution on the thermal shock resistance decreases gradually.

Thickness Optimization for Petroleum Coke in Microwave Dehydrating Based on the Analysis of Dynamic Absorption Efficiency

AbstractAn analytical approach is proposed to optimize the thickness of petroleum coke for achieving maximum microwave power absorption in microwave heating based on analysis of reflection loss (RL). The microwave RL of the petroleum coke layer was studied over the moisture content range of 1%–5% at 20 °C and the petroleum coke (10% moisture content) in the temperature range of 20 to 100 °C at 2.45 GHz. The results show that RL depends sensitively on the thickness of the petroleum coke and the absorption peak shifts towards a larger thickness as the moisture content of the petroleum coke increases. There exists a matching thickness corresponding to the maximum microwave absorption, the maximum absorbing peak decreases when the thickness of petroleum coke exceeds the matching thickness. We also show that the absorption peak is found to move towards a smaller thickness region with increasing petroleum coke temperature.

Influence of modifiers and coking conditions on the yield and quality of pitch coke

In the coking of pitch with different softening temperatures, coke particles of different type and structure are added. The coking temperature is 500 and 1200°C. The yield and quality of the pitch coke and compositions obtained are determined. In all cases, the introduction of coke particles is found to increase the yield and change the structure of the coke composition obtained. The microstructure of the composite coke may be regulated by introducing small coke particles of different structure in the high-temperature pitch prior to coking: particles of regular pitch coke increase the proportion of isotropic and finely fibrous structures; particles of acicular coke facilitate the appearance of fibrous and needle structures.

Research on Coking Behavior over Catalysts for Toluene Disproportionation

Effects of pressure of toluene, reaction temperature and nature of catalysts on coking over catalysts in toluene disproportionation are studied by using the method of thermogravimetry. Experiment results show that during the toluene disproportionation, the coking amount over catalysts increases with partial pressure of toluene and reaction temperature and the initial coking temperature decreases with partial pressure of toluene. Coking results mainly from the relatively stronger acid sites on the surface of the catalyst. Both HZSM-5 and HM catalysts have efficiency for toluene disproportionation, but HZM-5 catalyst has higher catalytic activity and stability.

Assessing coke on the basis of the yield of volatiles

Existing methods of assessing coke in production conditions are analyzed. Significant deficiencies are noted in the gravimetric method of determining the yield of volatiles and in methods of determining the temperature of the coke leaving the coking chamber. Assessment of coke on the basis of a modified method of determining the yield of volatiles (by volume) at 1150°C is proposed. In the coke shops at PAO Zaporozhkoks, samples of industrial coke are assessed by the proposed method. A close correlation is found between the yield of volatiles (by volume) and two important coking characteristics: the final temperature and the coking rate. Determination of the yield of volatiles by volume is currently used in the central laboratory at PAO Zaporozhkoks in continually assessing the coke produced and correcting the coking temperature.

Influence of batch properties and the final coking temperature on the coke yield

At PAO Zaporozhkoks, the coke yield is determined experimentally as a function of the batch properties and the final coking temperature, in box coking. An empirical formula for the coke yield is obtained. With increase in the yield of volatiles from dry batch by 1%, the coke yield falls by 0.71%. With increase in the final coking temperature by 50°C, the coke yield falls by 0.35%.

Raman spectroscopic characterization of novel carbon‐bonded filter compositions for steel melt filtration

In this work, Raman scattering results on novel carbon‐bonded filter compositions are presented. Such filters are already used for steel melt filtration; however, the potential of this carbon‐bonded Al2O3–C system regarding material characteristics and filtration efficiency has not been fully understood yet. In order to investigate thermally induced structural changes of the filter compositions, micro‐Raman spectroscopy was applied. Analyzing the position, intensity, and full width at half maximum of G and D peaks in the Raman spectra, it could be determined that the carbon appears in graphitic form and the graphitic cluster size was estimated. We found an increase of the lateral cluster size La with increasing coking temperature. Copyright © 2013 John Wiley & Sons, Ltd.

Thermal regulation of the hearth by means of a blast-furnace model

A mathematical model of the lower heat-transfer zone is developed on the basis of heat-transfer theory and operational data for blast furnaces in Europe, the Commonwealth of Independent States, China, and the United States. This model may be used to determine the theoretical combustion temperature of coke. On that basis, a relation is derived between the theoretical combustion temperature of coke, the yield of blast-furnace gases, and the degree of direct reduction of iron, when coal-dust fuel is employed.

Mesoporous Siliconiobium Phosphate as a Pure Brønsted Acid Catalyst with Excellent Performance for the Dehydration of Glycerol to Acrolein

The development of solid acid catalysts that contain a high density of Brønsted acid sites with suitable acidity, as well as a long lifetime, is one of great challenges for the efficient dehydration of glycerol to acrolein. Herein, we report on a mesoporous siliconiobium phosphate (NbPSi-0.5) composite, which is a promising solid Brønsted acid that is a potential candidate for such a high-performance catalyst. A variety of characterization results confirm that NbPSi-0.5 contains nearly pure Brønsted acid sites and has well-defined large mesopores. In addition, NbPSi-0.5 contains a similar amount of acid sites and exhibits weaker acidity than that of the highly acidic niobium phosphate and HZSM-5 zeolite. NbPSi-0.5 is quite stable and has a high activity for the dehydration of glycerol. The stability of NbPSi-0.5 is about three times higher than that of the reported catalyst. The significantly enhanced catalytic performance of NbPSi-0.5 can be attributed to 1) nearly pure Brønsted acidity, which suppresses side reactions that lead to coke formation; 2) a significant reduction of pore blocking due to the mesopores; and 3) a decrease in the amount and oxidation temperature of coke.

In situ formation of carbon nanotubes and ceramic whiskers in Al2O3–C refractories with addition of Ni-catalyzed phenolic resin

Microstructure and mechanical properties of Al2O3–C refractories using Ni-catalyzed phenolic resin as binder coked in the temperature range from 800°C to 1400°C are investigated in the present work. The results showed that only amorphous carbon formed from as-received phenolic resin, while crystalline graphite carbons, particularly multi-walled carbon nanotubes (MWCNTs) were gradually obtained from Ni-catalyzed phenolic resin with increasing the pyrolysis temperature from 450°C to 1050°C. The morphology and quantity of in situ formed carbon nanotubes (CNTs) in Al2O3–C matrix specimens were closely associated with the coking temperature. The mechanical properties such as cold modulus of rupture (CMOR), flexural modulus (E), force and displacement of Al2O3–C refractory specimens with addition of Ni-catalyzed phenolic resin were greatly improved compared with those with as-received phenolic resin. The improvement was attributed to the in situ catalytic formation of CNTs and more ceramic whiskers in the specimens containing Ni-catalyzed phenolic resin.

Investigation on shot-coke-forming propensity and controlling of coke morphology during heavy oil coking

A systematic study was undertaken to reveal shot‐coke formation pathway and to find solutions to minimize and even eliminate shot‐coke formation during heavy oil delayed coking. The heavy oil used as coking feedstock was in the form of vacuum residue. Shot-coke-forming propensity was characterized by dynamic monitoring optical texture in the coke product, and coke morphology was macroscopically recorded by photography. Results show that the pathway for shot‐coke formation is distinctively stepwise: Feedstock→Formation of anisotropic spherules→Limited growth of the spherules in the viscous coking system→Mosaic optical texture in the solidifying bulk coke→Formation of primary shot coke→Formation of secondary shot coke. Coking feedstocks with higher asphaltene content, higher carbon residues, and higher heteroatom content have higher propensity to form shot coke. Particularly, when a coking feedstock has an asphaltene/Conradson carbon residue mass ratio greater than 0.5, H/C molar ratio less than 1.5, and colloidal stability parameter less than 3.5, it could be tentatively called shot-coke-forming feedstock, which shows dominant mosaic optical texture in the coke derived from typical delayed coking conditions. Hydrogen donating additives such as suitable FCC slurry (raw, i.e. without HDA/HDS treatment) are economically advantageous in reducing shot-coke-forming propensity. Feedstock blending, decreasing coking temperature, increasing coking pressure, increasing recycle ratio, and employing hydrogen donating additives are potentially effective measures for controlling shot‐coke formation.

Experimental investigation on heat transfer and pressure drop of kerosene at supercritical pressure in square and circular tube with artificial roughness

An experiment on supercritical kerosene heat transfer and flow characteristics in square and circular flow channels with ribbed roughness was carried out at Xi’an Jiaotong University. The wall temperature distribution and pressure drops in the tubes were obtained in the experiment. The coking characteristic of the square tube was also analyzed, with the method of wall temperature variation with the time. Experimental conditions included pressures of 5–22MPa, velocities of 15–60m/s, and maximum heat flux of 40,000kW/m2. Four different ribbed structure square tubes and two ribbed circular tubes were tested. Compared with the smooth tube, the experimental results showed the ribbed roughness can improve the heat transfer performance while the pressure drop in the tubes is increased. It was found that of either the square tube or the circular tube, the tube with the ratio of rib pitch to height 7.5 can get the best integrated heat transfer and pressure drop effect. With the increase of velocity, the coking is significantly improved, and the initial coking temperatures for the square smooth and ribbed tube are about 370°C and 410°C, respectively. The introduction of ribbed roughness also has the benefit of the coking weakening. The heat flux when coking occured in the ribbed roughness square tube was much higher than that of the smooth square tube. For assessing the engineering application, and for deeper understanding of the rib effect on the heat transfer and pressure drop, more ribbed structures need to be investigated.

Novel Al2O3‐C Refractories with Less Residual Carbon Due to Nanoscaled Additives for Continuous Steel Casting Applications

AbstractA new generation of thermal shock resistant Al2O3‐C refractories with approximately 30% less residual carbon and functionalized due to nanoscaled additives based on carbon nanotubes (CNTs) and alumina nanosheets (α‐Al2O3) were developed and investigated after coking at 1000 and 1400 °C. With the aid of electron backscatter diffraction analyses (EBSD) on fracture surfaces of the carbon bonded samples, Al3CON was identified on the nanosheet shapes already at 1000 °C coking temperature. The Al3CON new phase based on the reaction between alumina nanosheets and CNTs offers a chemical interconnecting phase for the carbon as well as for the oxide alumina filler. The new refractory composite structure presents excellent thermo‐mechanical properties in spite the lower carbon content. In addition, due to EDS and EBSD analyses amorphous whiskers and platelets within the system of SiO were observed in samples coked at 1000 °C, that were transformed to crystalline β‐SiC‐whiskers in samples coked at 1400 °C.