High-temperature Pitch Research Articles

Development of an encapsulation process for toxic waste and hazardous chemicals in a fluidized bed

Objectives. This paper presents research results on the encapsulation of a fluidized bed of liquid and solid toxic waste containing chemicals with a hazard class of 1–3.Methods. Soils contaminated with hexachlorobenzene and hexachlorocyclohexane were used as the seed material. Ceresin was selected as the encapsulant, which was sprayed onto the fluidized bed through a pneumatic nozzle at a temperature of 135°C. Before the spraying of the ceresin, binders were introduced into the fluidized bed of the seed material through pneumatic nozzles in the form of a melt of high-temperature coal-tar pitch and wastewater containing sodium and arsenic salts as well as heavy metal oxides. The experiments were carried out using a modified GLATT AGT-150 laboratory unit.Results. The results demonstrate that the mechanism for granule formation is a mixed mechanism. The binding of the seed material is carried out by both the pitch and salting out. In this case, the cavities in the agglomerates are partially filled with salt deposits, which increases the strength and integrity of the final product’s structure. Ranges for the process parameter values were established at the point at which there was no unwanted agglomeration in the fluidized bed, and dust formation did not exceed 5%. When the ratio of the bed mass to the mass of ceresin is equal to unity, a moisture-resistant free-flowing product of hazard class 5 is obtained, which is suitable for transportation and long-term storage. The average diameters of the initial particles and encapsulated granules were 0.5 and 1.5 mm, respectively.Conclusions. The present study demonstrates a potential process for the granulation– encapsulation of toxic waste and hazardous substances with a hazard class of 1–3 in a single fluid-bed apparatus, resulting in the formation of a moisture-resistant hazard class-5 granular product suitable for transportation and long-term storage. The results obtained can be used in the development of an industrial large-scale process for encapsulating waste of hazard classes 1–3.

Influence of the Coking Conditions on the Microstructure of Coke Produced from High-Temperature Pitch

Influence of the Coking Conditions on the Microstructure of Coke Produced from High-Temperature Pitch

Effect of pitch powder addition on the microstructure and properties of carbon blocks for blast furnace

The phase composition and microstructural evolution of pitch-containing matrix sample with additive of silicon had been compared with pitch-free or resin-containing matrix sample to illustrate the strengthening effect of pitch. Two different pitch powders (CARBORES@P and High temperature pitch) were then incorporated into carbon blocks, respectively and the effect of pitch powder addition on microstructure and properties of carbon blocks fired at 1000 °C and 1400 °C in a coke bed was evaluated systematically. The results showed that compared with amorphous carbonized resin, carbonized pitch was a kind of highly graphitized carbon and could react with silicon and form SiC whiskers at 1400 °C. In carbon blocks, pitch powder accelerated the formation of AlN at 1000 °C and growth of β-SiC whiskers at 1400 °C, respectively, which enhanced the cold compressive strength, thermal conductivity and hot metal erosion resistance of carbon blocks. Moreover, carbon blocks containing CARBORES@P pitch with higher carbon yield exhibited better properties because of formation of more ceramic whiskers. The strengthening mechanism of pitch powder for carbon blocks was attributed to the pore-blocking effect of pitch carbonization and more in-situ formed whiskers derived from the reaction between carbonized pitch with silicon at 1400 °C.

TECHNICZNO-TECHNOLOGICZNY ASPEKT PRZEŁADUNKU WYSOKOTEMPERATUROWEJ SMOŁY WĘGLOWEJ NA PRZYKŁADZIE PRZEDSIĘBIORSTWA X NA TERENIE PORTU MORSKIEGO SZCZECIN

TECHNICZNO-TECHNOLOGICZNY ASPEKT PRZEŁADUNKU WYSOKOTEMPERATUROWEJ SMOŁY WĘGLOWEJ NA PRZYKŁADZIE PRZEDSIĘBIORSTWA X NA TERENIE PORTU MORSKIEGO SZCZECIN

Influence of bonding carbon on low carbon Al2O3-C refractory composites

Abstract The carbonized behavior of binders (carbores pitch, mesophase pitch, high temperature pitch and phenolic resins) was investigated. Meanwhile, the influence of binders, Ni-catalyst and heat treatment on structure and properties of low carbon Al 2 O 3 -C materials was researched. Mesophase pitch and high molecular weight resin provided higher carbon yield. The synergistic interaction of pitch and phenolic resin provided the higher carbon yield than that of single component. Ni-catalyst changed structure and morphology of bonded carbon promoting the transition of amorphous carbon to crystalline carbon increasing carbon yield and degree of graphitization. High molecular weight phenolic resins, mesophase or carbores pitch and Ni-catalyst worked together providing low carbon Al 2 O 3 -C samples of excellent strength performance in a wide temperature range and high resistance of thermal shock. Embedding coke in N 2 could promote the generating of carbon fibers which obviously enhanced thermal shock resistance of low carbon (6% flake graphite) Al 2 O 3 -C materials after heat treatment.

Thermal solution of coal to obtain binder for refractories. 1. Binder production

Experimental coal-based pitch obtained by the controlled action of solvent (a hydrogen donor) on the thermally activated organic mass of coking coal is studied. The basic parameters required for the production of such pitch are determined: the temperature; the duration of the process; and the proportions of the components. The pitch produced matches high-temperature coke-plant pitch in terms of the yield of volatiles, the softening temperature, the content of toluene- and quinoline-insoluble materials, and structure. The maximum conversion and best quality of the pitch (in terms of the traditional characteristics) are obtained when using coal with the maximum vitrinite content and plastic-layer thickness. Pitch produced by the solution of coal is suitable for use as a binder in the production of refractories and its content of carcinogenic benzo(a)pyrene is an order of magnitude less than that of standard coal pitch, since it is obtained directly from coal, without the need for the high temperatures used in coking.

Heat treatment of anthracene oil under pressure

The heat treatment of the anthracene fraction of coal tar under pressure is investigated. In the production of synthetic pitch, the temperature is varied in the range 400–480°C. The duration of the process is 5 h, and the pressure is 3–5 MPa. After treatment at temperatures below 480°C, the pitch produced lacks the quinoline-insoluble fraction. Chemical analysis shows that increasing the treatment temperature results in consumption of cata-condensed aromatic hydrocarbons, with simultaneous accumulation of peri-condensed aromatic hydrocarbons. NMR and IR spectroscopy indicates simultaneous increase in the aromatic index and the degree of condensation of samples with increase in the treatment temperature, as the result of dealkylation and condensation. Optical analysis shows clearly expressed mesogenic properties of the synthetic pitch. Pitch produced by low-temperature synthesis forms needle coke, with a greater anisotropy and greater real density than coke obtained from pitch produced by high-temperature synthesis. With increase in pressure in the course of coking, the anisotropy and the real density decline for low-temperature pitch, but increase for high-temperature pitch.

Density, porous structure, and gas-dynamic characteristics of finely grained graphites (a review)

The results of the statistical processing of data on the determination of the apparent (ρa) and pycnometric (ρp) densities and the accessible (open) porosity (Pa) of samples cut out in parallel (||) and perpendicularly (⊥) to the axis of extrusion of the workpieces of fine-grained graphites (>90% of coke filler particles of size ρa|| by 1.2% (0.019 g/cm3) and Pa⊥ < Pa|| by 3.3% (0.9% in the absolute value) or by 1.3% (0.024 g/cm3) and (0.92%), respectively, for the same graphite with high-temperature pitch. The capabilities of mercury porosimetry in the study of the porous structure of graphites and other carbon materials are demonstrated.

Effect of Pressure on Carbonization of Coal Tar Pitch of Different Composition

The effect of carbonization pressure for coal tar pitch of different composition on pyrolysis product properties is studied. The aim of the work is evaluation of dynamics and routes of forming the main coal tar pitch pyrolysis products under pressure and determination of pyrolysis product properties. It is established that with an increase in initial carbonizing pressure there is an increase in coke residue yield by 88.5 and 7.7% for low-temperature and high-temperature pitches respectively. The effect of α-fraction on final product microstructure is demonstrated. With an increase in α-fraction content by a factor of 3.7 the coke residue yield increases by 88.5, 60, and 55% for an initial pressure of 21, 11, and 1 bar respectively. It is revealed that with an increase in initial pressure there is an increase in primary product content and formation of new compounds within pyrolysis products is facilitated.

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.

The choice of an effective form of a bottom reflector for uniform heating of high-temperature pitch

The article presents the results of a comparative analysis of the use of reflectors of various shapes on the uniformity of the temperature field of high-temperature pitch. Efficiency of the pitch heating system is regulated by strict requirements for the uniformity of temperature distribution in the tank. The decisions to intensify heat exchange alongside with the employment of the circular method of heating is justified. Numerical modeling of heat exchange in the tank using bottom reflectors is performed. It is proved that bottom reflectors will allow intensifying heat exchange in the tank and ensure heating uniformity without additional energy expenditures. It is shown that the use of a bottom reflector shaped like an inverted truncated cone will make it possible to reduce the temperature gradient throughout the tank height. The achieved results can be used for developing energy saving modes of the pitch storage site PJSC Ukrgrafit.

Production of isotropic coke by thermocracking of the anthracene fraction of coal tar

The properties of coke obtained by heat treatment of the anthracene fraction of coal tar under pressure (by thermocracking) are investigated. Pressures up to 5 MPa are used; the temperature is 500 or 550°C. For comparison, pitch coke is obtained from oxidized pitch with softening temperatures of 166.2 and 190.2°C. The coke yield from thermocracking is 70–75%. The following properties of the coke are determined: the actual density, the ash content, the yield of volatiles, the optical microstructure, the elementary composition, the change in volume on heating to 2400°C, the impurity composition, and the X-ray structural characteristics. High temperatures (at least 550°C) and heating rate of the anthracene fraction facilitate the formation of a large quantity of active radicals, which instantaneously form the three-dimensional coke structure, preventing the growth and coalescence of mesophase particles; isotropic coke is formed, with a microstructure score of 2.2. At 500°C, anisotropic coke is formed, with a microstructure score of 4.3. Despite the high softening temperature and the content of the α1 fraction, the high-temperature pitch does not form isotropic coke on carbonization. The macrostructure of the coke obtained by thermocracking is monolithic, with fine pores. The thermocracking conditions (temperature, pressure, presence of H2) facilitate partial destruction and hydrogenation of the heterocyclic compounds. As a result, the coke has a reduced N, S, and O content. For pitch coke, the nitrogen content is 20–40% higher. The lack of ash in the anthracene fraction of coal tar results in ash- and metal-free coke. The coke obtained by thermocracking also has satisfactory X-ray structural characteristics and undergoes practically no expansion on graphitization, in contrast to pitch coke. In view of the technological convenience (absence of liquid products, high coke yield) and the quality of the coke, the production of isotropic coke by thermocracking may be regarded as a promising means of supplying the raw material used to produce artificial graphite.

Choosing an effective insulation for reservoirs with high-temperature pitch

The article analyzes heat-insulating materials to reduce heat losses to the environment of reservoirs with a high-temperature pitch. At enterprises producing graphitized electrodes there are strict requirements for storage technology of high-temperature pitch, so thermal insulation in addition to power-saving features, enables the processes of heating of the pitch at a given temperature level. The article justifies the thermal insulation for vertical steel reservoirs. There is a comparison of the thermal insulation Nobasil LSP and TEMP-COAT. It was shown that reduction of heat losses would reduce a coolant flow by 30%. From the point of view of the economic reasonability the thermal insulation TEMP-COAT is recommended, because the payback period is 1.7 times smaller. These results can be used as bases for the design of energy-efficient modes of operation of pitch enterprise "Ukrgrafit."

Influence of the meso phase in high-temperature pitch on the properties of artificial graphite

A relation is established between the content of meso phase in high-temperature pitch and the condensation of coal tar used for pitch production. The influence of the meso-phase content in the high-temperature pitch on the quality of the artificial graphite produced is demonstrated.

Effects of the time of combined vibration grinding and the compacting pressure on the density and shrinkage of graphite MPG-7 workpieces

A technique for the manufacturing of graphite MPG-7 was developed on a laboratory scale with the use of the following new raw materials: uncalcined isotropic shale tar coke and three high-temperature pitches. The caking capacity and density of the test samples of MPG-7 after molding, burning, and graphitizing were determined. It was found that the optimum concentration of a binding agent determined from the caking capacity decreased from 40 to 28% as the volatile matter content of coke increased from 4.5 to 9.5% and the softening temperature of pitch decreased from 148 to 135°C. In this case, the total shrinkages of the test samples decreased from 60 to 54%, and their densities decreased from 1.98 to 1.76 g/cm3. The optimum time of combined vibration grinding was determined, and the range of compacting pressures was chosen. The relationships between the densities of the test samples burned under laboratory and production conditions, as well as between the densities of burned and graphitized samples, were obtained. These relationships make it possible to predict the density level of MPG-7 material reached under plant conditions.

Effects of Carbonization Pressure on Microstructure of Graphitized Pitch-derived Carbons

Graphitized pitch-derived carbons were prepared under carbonization pressures of 30MPa and 60MPa respectively,using high temperature pitch as raw material.Microstructure of the samples were investigated by SEM and TEM.Results indicate that the samples prepared at 30MPa and 60MPa are dominated by easy graphitized flow/flow domain type texture and non-graphitized mosaic/domain type texture,respectively.Nucleation,growth and amalgamation of carbonaceous mesophase spherule as well as microstructures of as-prepared materials are influenced by carbonization pressures.Carbonaceous mesophase spherule can amalgamate completely to form anisotropic flow type texture at the carbonization pressure of 30MPa,while amalgamation of carbonaceous mesophase spherule is blocked to form mosaic type texture at the carbonization pressure of 60MPa.TEM and SAED results show that main texture of the sample prepared at 30MPa is flow type texture,some isotropic textures exist at the rim of lamellar structures or among them.Samples prepared at 60MPa exhibit non-homogeneous microstructure where(002) rings distribute by spotted state.It can be concluded that uniformity and orientation of the sample prepared at 30MPa are better than those of the sample prepared at 60MPa.

Specific features of the use of unconventional carbon-containing components in the technology of powdered steels: Report 2. The influence of unconventional carbon-containing components on the sintering processes in the technology of powdered steel

The processes of sintering powdered carbon steels with the introduction of unconventional carbon-containing components into the charge (special artificial low-ash graphite, pyrocarbon, and high-temperature coal-tar pitch) are considered. It is shown that the features of the chemical and granulometric compositions and the crystalline structure of these components (to a greater extent than the conventionally used pencil lead) determine the acceleration of material homogenization during sintering, improve its structural characteristics, and increase its mechanical properties.

Specific features of application of nonconventional carbon-containing components in technology of powder steels. Report 1

The possibility is shown to decrease the cost of production of powder hot-deformed carbon steels through the use of unconventional carbon-containing components in the charge composition (artificial special low-ash graphite, pyrocarbon, high-temperature coal-tar pitch). The peculiarities of their chemical composition, grain-size distribution, and crystal structure in comparison with the traditionally used pencil lead dictate the increase in blend homogeneity and in density of cold-pressed moldings, and eventually improvement of properties of powder steels.

Reduction of oxide films during consolidation of the charge used to make powder semifinished products

This article examines one possible method of making iron-carbon materials in order to obtain materials with a low content of impurities (especially oxygen) and sufficiently high density. The proposed method is also evaluated from the viewpoint of producing materials with a low carbon content. The technology traditionally used to obtain powder materials is discussed and the prospects for combining the reduction of surface oxides and consolidation of the powder into a dense semifinished product are examined. Powders of graphites obtained by using special synthetic low-ash pitch (SSLG) and high-temperature coaltar pitch (HCP) as the carbon-bearing components (CBC) are employed to achieve the stated objective of this investigation. The shaping method chosen is hot pressing with resistance heating.

Heat treatment of medium-temperature Sasol–Lurgi gasifier coal-tar pitch for polymerizing to higher value products

Two coal-derived pitch samples, one a medium temperature pitch from a Sasol–Lurgi gasifier and the other from a high temperature coking process, have been heat treated to induce polymerization, both separately and as a mixture of pitches (co-pyrolysis). The initial pitch samples and the heat-treated samples have been examined by size exclusion chromatography (SEC) in 1-methyl-2-pyrrolidinone (NMP), by UV-fluorescence spectroscopy (UV-F), by solid state 13C NMR; elemental analyses of the initial pitch samples have been carried out. The Sasol–Lurgi pitch showed larger apparent sizes, more alkyl and carbonyl functions, and smaller polycyclic aromatic hydrocarbon (PAH) groups than the high temperature pitch. Co-pyrolysis of the two pitches indicated that polymerized product from the Sasol–Lurgi pitch can be used as an extender for high-temperature binder pitch.