Effects of chemicals and blending petroleum coke on the properties of low-rank Indonesian coal water mixtures

In this study, the effects of different chemical additives including dispersant and stabilizer on the solid loading, viscosity, rheological behaviour and static stability of coal water mixtures have been investigated. In the experiments, naphthalene sulfonate formaldehyde condensate (NSF) was selected as dispersant and carboxymethyl cellulose sodium salt (CMC-Na) and nano-stabilizer were employed as stabilizers. An Indonesian low-rank coal, taken from Berau, East Kalimantan, was used for the study. To obtain high-loaded slurry, Liaohe petroleum coke was used to blend with Indonesian coal sample. The results of the experiments showed that adding chemical additives and blending Liaohe petroleum coke can effectively improve the slurryability of Indonesian low-rank coal.     

Ignition behaviour of different rank coals in an entrained flow reactor

An experimental study to determine the temperature and mechanism of coal ignition was carried out by using an entrained flow reactor (EFR) at relatively high coal feed rates (0.5 g min⁻¹). Seven coals ranging in rank from subbituminous to semianthracite, were tested and the evolved gases (O₂, CO, CO₂, NO) were measured continuously. The ignition temperature was evaluated from the gas evolution profiles, and it was found to be inversely correlated to the reactivity of the coal, as reflected by the increasing values of the ignition temperature in the sequence: subbituminous, high volatile bituminous, low volatile bituminous and semianthracite coals. The mechanism of ignition varied from a heterogeneous mechanism for subbituminous, low volatile bituminous and semianthracite coals, to a homogeneous mechanism for high volatile bituminous coals. A thermogravimetric analyser (TGA) was also used to evaluate coal ignition behaviour. Both methods, TGA and EFR, were in agreement as regards the mechanism of coal ignition. From the SEM micrographs of the coal particles retrieved from the cyclone, it was possible to observe the external appearance of the particles before, during and after ignition. The micrographs confirmed the mechanism deduced from the gas profiles.     

Preparation of natural gas adsorbents from high-sulfur petroleum coke

HSPC (high-sulfur petroleum coke) has been used as precursor in the preparation of natural gas adsorbents with chemical activation. The effects of activating parameters, such as activating temperature and duration, on the pore-structure of adsorbents and methane uptake were investigated systematically in this study. The results show that the adsorbents derived from HSPC have comparable pore-structural characteristics and methane uptake to that derived from LSPC (low-sulfur petroleum coke). As evidenced by methane adsorption measurements, the highest deliverable capacity of methane, 129.7 v/v at 3.5 MPa and 25 °C, is obtained on HSR4 prepared at activating agent/coke mass ratio of 4:1. Furthermore, sulfur distribution analyses show that the sulfur in HSPC was almost removed by chemical activation and that sulfur content of as-synthesized adsorbent was as low as 0.18 wt% for HSR4. This study shows that HSPC could be used potentially as a good precursor to prepare high quality adsorbents with lower cost.     

Thermogravimetric study of coal and petroleum coke for co-gasification

As a preliminary study of gasification of coal and petroleum coke mixtures, thermogravimetric analyses were performed at various temperatures (1,100, 1,200, 1,300, and 1,400 °C) and the isothermal kinetics were analyzed and compared. The activation energies of coal, petroleum coke and coal/petroleum coke mixture were calculated by using both a shrinking core model and a modified volumetric model. The results showed that the activation energies for the anthracite and petroleum coke used in this study were 9.56 and 11.92 kcal/mol and reaction times were 15.8 and 27.0 min. In the case of mixed fuel, however, the activation energy (6.97 kcal/mol) and reaction time (17.0 min) were lower than the average value of the individual fuels, confirming that a synergistic effect was observed in the coprocessing of coal and petroleum coke. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Reaction rates for the oxidation of highly sulphurised petroleum cokes: the influence of thermogravimetric conditions and some coke properties

The reaction with air of a large number (22) of high-sulphur petroleum cokes was studied by temperature-ramped thermogravimetric analysis. The kinetic parameters for each coke were established, based on BET surface areas. The oxidation rates (kg_C m⁻² s⁻¹ atm⁻¹) were found to vary with sample mass. This was a result of limitations on oxygen transfer, despite the small masses and low heating rates used. Limitations were present both externally (from the crucible mouth to the bed surface) and internally (from the sample surface to the bed interior). A method to take these effects into account was adopted, based on an analysis of the relevant diffusion rates. Application of this method reconciled the rate data for four different sample masses, except at high temperatures. The formation of a partially fused ash crust is believed to be the reason for this latter effect.The activation energies of the cokes varied between 195 and 280 kJ mol⁻¹, and the absolute rates varied by a factor of 10. They were between 1000 and 10,000 times higher than the average reactivity of carbon as reported in the literature. The elevated apparent rates are believed to have two causes, one in the combustion process and the other in the interpretation of the results. The first cause is the strong catalytic effect of the inorganic components, although the ash contents ranged only from 0.3 to 1.5%. The most active metal is vanadium, which is present in significant concentrations. The effectiveness of V₂O₅ as a gasifying catalyst is believed to be due to its low melting point. Increasing sulphur content in the cokes produces no perceptible change in the combustion rates. The second cause for poor combustion correlation is the inadequacy of BET surface area for expressing combustion rates.     

石油焦质量下滑对预焙阳极的危害及控制

深入分析当前石油焦质量下滑的三大因素:杂质含量高、粉焦和丸状焦比例增加等,以及对炭阳极质量造成的危害,并有针对性的提出一些预防措施,旨在引起石化和炭素行业提高对石油焦质量的重视程度。     

Modification of petroleum coke by different additives and the impact on anode properties

Anodes, which provide the carbon required for aluminum production, are made from dry aggregates (petroleum coke, rejected anodes, and butts) with coal tar pitch as the binder. Good quality anodes require good interaction between coke and pitch, and this relies on good wetting properties. The objectives of this work are to analyze the wetting properties of four different cokes with and without modification using an additive and to test the effect of the modified coke on anode properties. A FTIR study was done to identify functional groups in non‐modified and modified coke samples since they play an important role on coke‐pitch interactions. The wetting tests were done using the sessile‐drop method to measure the contact angle between coke and pitch. The results showed that the additive improved the wettability of all four cokes by pitch. The least wettable coke was chosen to produce anodes. For anode production, the entire dry aggregate is modified. The additive was mixed with the dry aggregate using two different approaches (one day earlier and 5 min before mixing). The anodes were characterized before and after baking. The early treatment with the additive was found to be better for the modification of dry aggregate.

     

Mild coal extraction for the production of anode coke from Blue Gem coal

The quality and availability of petroleum coke used in the manufacture of carbon anodes for aluminum production is a growing concern to the industry. Coke quality and yields have progressively declined as changes in refinery practice and the move towards processing an increasing proportion of heavier sour crudes have affected coke properties, resulting in an increase in the metal impurities and sulfur content of the coke. An alternative supply of anode coke is required to supplement or eventually replace calcined petroleum coke. The significant domestic reserves of coal could represent a viable carbon resource for anode production, provided defined coke specifications can be met and at a cost that is economically viable.The principal objective of this study was to examine the feasibility of producing anode grade coke by the UKCAER process for the mild solvent extraction of coal. Blue Gem coal from Eastern Kentucky was dissolved in a high boiling point solvent, the mineral matter and unreacted products removed by filtration, and the clean coal liquid converted to coke. The performance of the coal in solvent extraction was compared to a very reactive coal from Western Kentucky. A simple solvent-extraction screening test was established to assess potential candidate materials and process variables without the need for prolonged and complex routines. The coals were assessed in more detail to determine the optimum process conditions by conducting larger scale extraction tests to yield sufficient material for conversion to coke. The green cokes were calcined and the products characterized. The composition and structure of the calcined cokes were compared to typical petroleum coke and assessed for their use in the fabrication of carbon anodes.     

Hydrodynamics in airlift loop section of petroleum coke combustor

Based on the combustion characteristics of petroleum coke, a coupled gas-solid fluidized bed combustor is proposed in this work. The overall circulating system of the fluidized bed mainly consists of a dense-phase airlift loop section and a dilute-phase riser section. In different operating conditions, the particle flow behaviors in the airlift loop section were investigated systematically by using optical fiber probe. The experimental results show that the airlift loop section can be divided into four regions, namely, the draft tube, the annulus, the bottom region and the particle diffluence region, in which the average cross-sectional solids fraction and the particle velocity are different. The overall solids fraction difference between the draft tube and the annulus provides a driving force for particle circulation flow in the airlift loop section, and the driving force increases with increasing the superficial gas velocity in the draft tube. The ratio of the particle mass flux in the annulus to that in the riser ranges from 8 to 16. The particle circular velocity in the annulus also increases with increasing the superficial gas velocity in the draft tube. Moreover, a model about the particle circular velocity is established on the basis of energy equilibrium principle.     

石油焦配煤炼焦试验研究

通过对石油焦的特性研究及配煤炼焦试验,考察其对配煤黏结性能及焦炭质量的影响,研究结果表明,添加石油焦会引起煤的黏结指数下降,加入石油焦配煤炼焦会降低焦炭灰分,提高焦炭硫分,降低焦炭冷强度,提高焦炭热强度。     

化学预氧化对高硫石油焦煅烧脱硫的影响

对高硫石油焦采用化学预氧化再经高温煅烧(1 300℃)进行脱硫处理,并采用XRD和SEM对脱硫前后石油焦样品的结构和表面微观形貌进行分析表征。实验结果表明:常压室温下多种化学氧化剂脱硫效果比较,A酸-过氧化氢混合溶液对石油焦脱硫效果最好,其脱硫率达到20.72%;经A酸-过氧化氢混合溶液化学预氧化再高温煅烧(1 300℃)脱硫处理的石油焦的脱硫率相对直接煅烧或者只进行氧化脱硫处理的样品有显著提高,脱硫率可达55%;A酸-过氧化氢混合溶液化学预氧化处理不会破坏煅烧后石油焦存在的石墨雏晶结构,并且促使石油焦表面形成细微裂纹,这有利于煅烧时焦内部硫的逸出以及生产过程中煅烧石油焦原料与煤沥青的结合。     

石油焦与煤混烧特性及动力学

以石油焦与煤的混合燃料为研究对象,采用TG—DTG—DSC联用实验技术对混合试样进行了燃烧热重实验。分析了混烧特性曲线,计算了各个燃烧特性指数,并采用差减微分法Freeman—Carroll计算了燃烧反应动力学参数。结果表明：各混合试样均只出现一个位于高温区段的DTG曲线峰和方向向下的DSC曲线的热量释放峰,混合试样的燃烧过程主要是高温阶段焦炭的着火燃烧过程;混合试样s2,S3及S5热量释放相对较少且不集中,燃烧时间长且不完全;混合试样S4及S6的热量释放集中且时间短,燃烧释放的热量相对较多;烟煤含量最多的混合试样s6的着火特性、燃尽特性指数及综合燃烧特性参数均高于其它混合试样以及石油焦的各个相应值,且试样s6的可燃特性指数也大于石油焦的可燃特性指数;混合试样活化能均小于石油焦燃烧的活化能,混合试样比石油焦更易着火燃烧;只要石油焦与煤的混合比例适当,石油焦掺烧烟煤后的燃烧特性优于石油焦单独燃烧特性,此为解决石油焦难以单独燃烧利用提供了方法。     

石油焦与煤粉燃烧性能差异的研究

石油焦作为石油工业副产品,具有低灰分质量分数、高挥发分质量分数、高发热值等特点,但对其燃烧价值的利用还很不充分。文中利用X射线衍射及扫描电镜对石油焦及烟煤和无烟煤进行微观结构的研究,同时利用热重分析方法对其燃烧性能进行系统研究发现:石油焦的芳香片层堆砌结构与无烟煤接近,但其丰富的气孔结构又有利于改善其燃烧过程。无烟煤中加入石油焦后,着火点温度从527℃降低到482.6℃;总质量分数从71.95%提高到76.82%,其燃烧效率得到提高。     

Study of a Chilean petroleum coke fluidized bed combustion fly ash and its potential application in copper, lead and hexavalent chromium removal

This work deals with the characterization of a circulated fluidized bed combustion (CFCB) Chilean petroleum coke fly ash (FA) from a petroleum coke power plant, and its potential use in neutralization and heavy metals removal from acid wastewaters. FA presents a high Ca and content, being anhydrite the major crystalline mineral phase, with minor proportions of calcite, portlandite and lime. Regarding to environmental characterization of this fly ash, leaching tests allowed concluding that FA is a non-hazardous residue. Heavy metals removal tests indicate that FA is able to remove Cu²⁺ and Pb²⁺ mainly due to a precipitation process, while Cr(VI) is being removed probably due to a reduction process to Cr(III), at high liquid to solid ratios. Cu²⁺, Pb²⁺ and Cr(VI) kinetic experimental data present acceptable fit to a pseudo-second order kinetic model. According to these results, FA may be used to remove heavy metals and neutralize acid wastewaters, suggesting a possible replacement of pure and costly alkaline materials.     

石油焦系活性炭2-甲基噻吩吸附性能研究

以石油焦为原料经高温炭化和水蒸气活化处理制备出石油焦基活性炭,经硝酸氧化处理后,采用静态吸附法测试了2-甲基噻吩在石油焦基活性炭上的吸附性能。研究结果显示,制备的活性炭比表面积高于800 m2·g-1,孔容大于0.45 cm3·g-1,经硝酸处理后比表面积和总孔容有所下降。样品经硝酸处理后,对2-甲基噻吩的饱和吸附量显著增加,硝酸处理40 min得到的活性炭对2-甲基噻吩的饱和吸附量最大。2-甲基噻吩在石油焦基活性炭上的吸附动力学均遵循拟二级动力学模型,饱和吸附量随吸附温度的增加而减小,热力学上表现为放热,熵减且是自发进行的过程。     

Low temperature oxidation of coals of different rank and different sulphur content

Five coals of different rank and of different content of sulphur were subjected to oxidation by peroxyacetic acid (PAA), 5% nitric acid, by oxygen in 0.5N Na₂CO₃ aqueous solution and the air oxidation for 7 days at 125 °C. The processes of oxidation were carried out for coal samples demineralised by the Radmacher method, and additionally for the pyrite-free coal samples. Proximate, elemental and spectral analyses of the initial coals and the products obtained from them were made. The most effective oxidising agents were 5% HNO₃ and PAA. As a result of oxidation, a significant part of the organic components of coal is converted into acid soluble products. Depending on the oxidising agent, the loss of sulphur in the solid oxidation products was different and the highest for the coal samples oxidised with HNO₃ and PAA. Formation of oxidised sulphur species (SO and -SO₂) was detected by IR spectroscopy. FTIR data also provide useful information on evolution of the molecular structure of different rank coals on oxidation, in particular in the carbonyl and aliphatic ranges (1800-1500 and 3500-2800 cm⁻¹).     

Investigations into the ignition behaviors of pulverized coals and coal blends in a drop tube furnace using flame monitoring techniques

This paper presents experimental investigations into the ignition behaviors of pulverized coals and coal blends in a drop tube furnace using a flame monitoring system. Seven different ranks of coals and coal blends of different mixing proportion were tested. Characteristic parameters including relative ignition temperature, maximum ignition points, oscillation frequency, fluctuation ratio and combustion dynamic energy were determined from the flame monitoring system. The ignition behaviors of the coals are established by combining the parameters. Results demonstrate that the parameters are suitable for distinguishing ignition behaviors from homogeneous, hetero-homogeneous to heterogeneous in the ignition section of a drop tube furnace. The ignition behaviors of a coal blend are found to have similar characteristics as the coal of higher volatile matter in the blend and depend on its proportion in the blend. The results from this study are used to predict the operation of a coal fired power plant in terms of fuel selection, fuel blending, and flame stability.     

煅前石油焦自动配料系统的应用

针对煅前石油焦配料过程存在的问题,索通发展股份有限公司通过采用自动掺配煅前焦收到了很好的效果,并采用PLC对配料过程进行了实时监控,实现了多种调节、控制方式.该系统投产以来,运行可靠、性价比高,对提高、稳定预焙阳极的质量,降低原材料成本起到很好的作用.     

Rapid preparation of CaB6 powders via induction heating from low-cost colemanite and petroleum coke

Calcium hexaboride (CaB₆) powders were successfully prepared at 1650?°C for 20?min by induction heating technology using low-cost natural colemanite and petroleum coke as starting materials. The effects of synthesis temperature, holding time, raw material ratio and milling duration on the formation of CaB₆ were investigated. The synthesis temperature and time for CaB₆ were reduced versus traditional carbothermal reduction methods. The final products obtained after repeated HCl pickling, washing, and drying have good crystallization with a uniform particle size distribution. This rapid preparation of CaB₆ can be ascribed to the rapid formation of the B₂O₃-CaO molten liquid phase that is conducive to the synthesis reaction under induced electromagnetic field. Thus, induction heating technology is a time-saving and energy efficient way to prepare CaB₆.     

Clean and efficient use of petroleum coke for combustion and power generation

Petroleum coke is a challenging fuel in terms of its low volatile content, high sulfur and nitrogen content, which give rise to undesirable emission characteristics. However, the low price and increased production of petroleum coke from high-sulfur feedstocks give a powerful economic stimulus to use it for power generation. In this study two strategies are explored for the clean combustion of petroleum coke by in situ removal of CO₂ and sulfur or in the longer term for hydrogen production with CO₂ recovery. CaO sorbent is used to absorb CO₂ and SO₂ in fluidized combustor or steam gas reformer, and is regenerated in a calciner. In the calciner, petroleum coke is fired with pure oxygen to provide the heat for regenerating the sorbent and give a CO₂ stream for subsequent utilization or sequestration. The SO₂ is retained in solid CaSO₄ and would not be emitted to the atmosphere. The high carbon content and low moisture content of petroleum coke ensure high purity of the CO₂ stream. The low ash content is also important since it reduces the possibility of ash fusion in the calciner. It also reduces the heat loss and the requirement for ash disposal, and hence contributes to high overall efficiency. Simulation results show that high efficiency can be achieved with incorporation of the proposed scheme for power generation, even after the penalty of CO₂ recovery. Thus, there is a potential for the abundant available and low cost, but environmentally challenging petroleum coke to become a fuel for clean combustion and power generation.