Coke Layer Research Articles

Metals flow analysis applied to the hydrogen production by catalytic gasification of plastics

Gasification processes can play a key role in the clean energy production from fossil and non-conventional fuels because of its transformation in a synthetic gas (syngas) rich in hydrogen and carbon monoxide. Fluidized bed reactors, both bubbling and circulating, allow to use a catalytic or reacting solid material in partial or total substitution of the bed in order to promote the dehydrogenation of the fuel. Depending on the operating conditions of reactor and of fuel type, the catalyst has a strong influence on the hydrogen yield; otherwise, the effect of catalyst add to a fluidized bed can decrease during the experimental run due to its progressive deactivation. The experimental tests demonstrated that the utilization of olivine as bed material, recognized in the literature as a good catalyst for gasification process of biomass and plastics, improves the dehydrogenation of the recycled polyethylene used as fuel by producing a hydrogen-rich syngas and a coke layer on the bed particles. The tests also indicated that the olivine was not capable to catalyse the dehydrogenation process for long time because of loss of metals diffused and linked to the carbonaceous solid (coke). A Substance Flow Analysis has been applied to the experimental data in order to evaluate the Hydrogen Recovery Efficiency for the gasification tests and to follow the repartition of metals (Fe, Ni, Mg) in the input/output streams and in the bed. The limited duration of the steady state regime as observed during the tests with olivine indicated a progressive reduction of the catalytic action correlated to the loss of metals. In other words, the use of olivine allows to obtain very high hydrogen concentration in the producer gas but for a limited time and without the possibility to recover its catalytic capacity by thermal or mechanical regeneration due to the progressive loss of metals responsible of polymer dehydrogenation. This experimental result is strictly correlated to the utilization of polyethylene as fuel. This evidence has been confirmed by analysis on olivine and fines elutriated by the reactor and showed, in this work, by a material balance on metals.

Solid-phase aminolysis in the ammonium polyphosphate– pentaerythritol–amine system

IR spectroscopy was used to study chemical transformations in the ammonium polyphosphate– pentaerythritol–amine system at 100-400°C. The reaction responsible for formation of the heat-stable coke layer is the aminolysis of the phosphates. The fire-retardant efficiency of the intumescent system depends on the heat stability of the amine and decreases in the series melamine > dicyandiamide (2-cyanoguanidine) > carbamide (urea).

Evaluating the effectiveness of using coke breeze in blast-furnace smelting

The expediency of using various amounts of nut coke in blast-furnace smelting is evaluated in relation to the quality of the skip coke. Data from blast-furnace operation are analyzed to obtain relations expressing the dependence of the consumption of nut coke on the unit consumption of skip coke and its abradability index M 10 . A blast furnace can run smoothly with the use of nut coke if its concentration in the charge does not exceed 20 kg/ton pig iron and the abradability index of the skip coke is satisfactory (M 10 ≤ 9.0%). The average value of the coke-substitution equivalent was determined to be 0.67 kg/kg nut coke. This interest stems from the possibility of reducing unproductive losses of coke, optimizing the gasdynamic regime in the smelting operation, and improving its technical-economic indices. Analytical studies (1) show that mixing nut coke with the iron-ore-bearing part of the blast-furnace charge improves the charge's gas permeability. The optimum dimensions of nut coke used for this purpose range from 10-15 mm to 35-40 mm. The gas permeability of the charge is most favorably affected by charging nut coke in such a way that it comprises 20-30% of the initial portion of the coke charge. Such an approach improves the charge's gas permeability by 11.5-13.5%. An analysis of the performance of blast furnaces at European plants operated with a low (down to 300 kg/ton pig iron) consumption of coke showed that lowering coke consumption from 350 to 270-290 kg/ton pig leads to a small (10%) increase in the thickness of the ore lenses and a significant decrease in the thickness of the layers of coke - from 48 to 34 cm. Nut coke is mixed with ore and charged into the peripheral zone of the furnace to keep it from descending into the lower layers of the cohesion zone (2). Due to an acute shortage of coke for the blast furnaces at the West Siberian Metallurgical Combine (ZSMK), the combine conducted commercial heats with the use of fine fractions of coke (36-25 mm) in the charge (3). Pig-iron output decreased 1.0-6.6% when such fines were used to make up as much as 22% of the charge, with the exact fines content of the charge depending on the smelting conditions. A decrease in iron output of this magnitude is equivalent to a 0.2-0.4% decrease in the production of pig iron for each 1% content of fines. Unit coke consumption increased 0.8-1.0%, or by 0.19-0.17% for each 1% content of fines. The use of coke breeze at the above-indicated rates also adversely affected the drainage capacity of the hearth. The technical-economic indices obtained on a furnace equipped with a rotary charge distributor showed that it is possible to maintain forced operation of the furnace when the content of the 36-25 mm of coke ranges up to 25%. The inclu- sion of more than 30% coke breeze reduces smelting rate and aggravates the operation of the hearth. Data obtained by the central test laboratory of the combine were used to analyze the use of nut coke as a substitute for regular metallurgical coke at plants in Germany, France, Belgium, the Netherlands, Russia, and Ukraine. The relationships

Investigations on Hydrotreating of Fischer Tropsch-Biowaxes for Generation of Bio-Products from Lignocellulosic Biomass

The present study describes the application of Fischer Tropsch biowaxes as a feedstock in a pilot-scale hydroprocessing unit at operating conditions very similar to industrial size hydrotreating plants of traditional refineries. The project focus on a future coprocessing of biowax/gasoil blends due to produce bio-products derived from lignocellulosic biomass: crack gases, naphtha, kerosene, diesel and a residual product. Hydro-processing plants operating at mild cracking conditions support the production of high amounts in middle distillates at reduced coke formation. Premium bio-diesel and bio-kerosene with excellent cold flow properties are the main objective of the investigations. Various test runs with different hydrotreating catalysts have been conducted due to determine the influence of waxy feedstock on catalyst behavior and product distribution. Depending on the catalyst selected, the fixed bed reactor streamed by hydrogen operates under specified cracking condition defined by the following parameters: reactor temperature, hydrogen pressure and weight hourly space velocity (WHSV). Test runs with selected catalysts - isodewaxing (IDW), hydro-desulphurization (HDS) and the catalytic deparaffination (CDP) catalyst - have been executed at constant process conditions in order to compare the product spectrum and properties of product groups. Highest amounts of bio-diesel and bio-kerosene with excellent cold flow properties can be obtained with the IDW catalyst. This NiW- based catalyst with special additives generates cleaved and reshaped molecular fragments via skeletal isomerisation increasing the isoparaffin content of naphtha and middle distillates. Further investigations with this catalyst type have been executed due to determine the catalyst aging effect in a separate long term test run. The loss of cracking severity during operation of the catalyst can be observed by a steady decline in conversion. Unsaturated hydrocarbons such as olefins and diolefines in the bio-feedstock support the formation of a coke layer on the catalyst surface resulting in reinforced deactivation. As the consequence naphtha and finally the crack gases and the kerosene fraction are shifted to higher molecular fragments increasing the diesel and residue yield. Physicochemical properties of the product groups obtained during the test run vary and especially the cold flow properties from the diesel and kerosene fraction degrade significant. Balancing the conversion decline of the catalyst in operation can be realized by increasing the reactor temperature and the hydrogen pressure, but the effect is time limited.

粒子配置を考慮した充填層の熱物質移動解析

Low reducing agent operation of large blast furnace has attracted a special attention from the background of the global warming. Because the coke ratio is reduced in this operation, causing a huge local ventilation resistance that causes operational problems, it has become increasingly necessary to understand the operation of blast furnace based on non-empirical phenomena. Among the most promising numerical approaches is a combination of the discrete element method (DEM) and computational fluid dynamics (CFD). In this study, particle-based model was newly developed, which considers heat transfer, mass transfer and chemical reactions in the shaft part of blast furnace. It became possible to analyze the three-dimensional discontinuous phenomena among particle with gas flow.Because this model was developed to expand the spatial scale more than conventional analysis, the discontinuous factors made it possible to simulate by the behavior of discrete particles. The particle arrangement and the packed bed structure were evaluated for studying the flow structure, temperature and composition distribution. Remarkable change in the heat and mass transfer characteristic appeared in the interface between coke and ore layer, and near the wall. The ore and coke particle mixture system, which was expected to improve reducing rate due to the dense packing, is relatively-ineffective. Rather, a low permeability resistance improved reducing rate, it means convection effect was larger. Degree of freedom of particle arrangement is high, and its large influence on temperature and reaction distribution, it was able to show the usefulness of this model.

Catalysed ethylbenzene dehydrogenation in CO2 or N2—Carbon deposits as the active phase

Bare alumina support transforms into an active catalyst for the dehydrogenation of ethylbenzene to styrene in CO2 or N2. During the first 15h time on stream in CO2, or the first 10h time on stream in N2, the alumina shows an increase in ethylbenzene conversion and styrene selectivity from 15% to 60% and from 60% to 92%, respectively, under industrially relevant conditions of 600°C and 10vol% ethylbenzene. Thereafter, the system slowly deactivates, but remains highly selective. TGA analysis shows an increase in coke content. The specific surface area and pore volume show a decrease with time on stream. TEM-imaging reveals that the spent catalyst surface is completely covered by several layers of coke. These results combined suggest that the carbon deposits on the alumina are responsible for the increase in activity and selectivity, and also are the cause of deactivation once a monolayer of carbon is deposited on the support surface. Similar trends are observed for zirconia support. Supported vanadium and chromium oxides on alumina all give similar results, but after a faster activity development. Also for these supported catalysts and even carbon samples, deposited coke is the active and selective phase.

Metal Dusting of Alumina-Forming Creep-Resistant Austenitic Stainless Steels

Three developmental alumina-forming austenitic stainless steels were exposed to metal dusting conditions at 650 °C in a gas of 50%CO–49%H2–1%H2O (a C: 36.7 and $$ p_{{{\text{O}}_{2} }} $$ : 2.83 × 10−26 atm) under thermal cycling conditions. Metal wastage measurement showed initially slow kinetics followed by a fast weight loss. This observation is attributed to the formation of protective chromia/alumina oxide scales in the early stage of the reaction, followed by local oxide failure/spallation during cyclic reaction. Metal dusting initiated from these local defects, and pitting-type attack was observed after 131 cycles of reaction. After 352 cycles, severe dusting had developed, forming heavy and distinctive “tentacles” of superficial coke. This carbon deposit was composed of fine carbon filaments. Examination by TEM of the coke-metal reaction front showed direct surface metal disintegration, indicating that the dusting follows the classical mechanism for austenitic materials. Etching with aqua regia revealed a carburised zone formed in the alloy underneath the coke layer. Analysis by TEM of this zone revealed the formation of ultra-fine, needle-shaped chromium carbide precipitates within a chromium depleted austenite matrix.

Petroleum coke and soft tailings sediment in constructed wetlands may contribute to the uptake of trace metals by algae and aquatic invertebrates

The fate of trace metals in pore water collected from wetland sediments and organisms exposed to petroleum coke were evaluated within in situ aquatic microcosms. Oil sands operators of Fort McMurray, Alberta, Canada produced 60 million tonnes of petroleum coke by 2008, containing elevated concentrations of sulphur and several trace metals commonly seen in oil sands materials. This material may be included in the construction of reclaimed wetlands. Microcosms were filled with a surface layer of petroleum coke over mine-waste sediments and embedded in a constructed wetland for three years to determine how these materials would affect the metal concentrations in the sediment pore water, colonizing wetland plants and benthic invertebrates. Petroleum coke treatments produced significantly elevated levels of Ni. We also found unexpectedly higher concentrations of metals in “consolidated tailings” waste materials, potentially due to the use of oil sands-produced gypsum, and higher background concentration of elements in the sediment used in the controls. A trend of higher concentrations of V, Ni, La, and Y was present in the tissues of the colonizing macrophytic alga Chara spp. Aeshnid dragonflies may also be accumulating V. These results indicate that the trace metals present in some oil sands waste materials could be taken up by aquatic macro-algae and some wetland invertebrates if these materials are included in reclaimed wetlands.

Stable low-temperature dry reforming of methane over mesoporous La2O3-ZrO2 supported Ni catalyst

A series of supported Ni catalysts was prepared using various supports and tested in low-temperature (400°C) dry reforming of methane. Ni/La2O3-ZrO2 showed near-to equilibrium yields of CO and H2 and the highest stability. This catalyst was studied in greater detail in order to determine the influence of the support morphology on the catalyst activity and stability. To this end, nonstructured, mesoporous, and macroporous La2O3-ZrO2 were prepared and characterized before and after loading with Ni. Among them, only Ni on the mesoporous support showed practically no change in activity over 180h on-stream, whereas the others deactivated. Formation of graphene-like coke layers on the catalysts and of NiO shell over Ni particles appears to be responsible for catalyst deactivation, while sintering of Ni did not play a major role. The enhanced stability of Ni on the mesoporous La2O3-ZrO2 is attributed to stronger interaction of the Ni particles with the support stemming from a pore confinement effect.

Coke Collapse Model and Collapse Profile Variation Law for Bell-Less Top BF

The mathematical model of minimum safety factor that investigated the collapse trends of coke layer under different charging parameters was established firstly on the basis of the slope stabilization theory in soil mechanics, and then the model of burden profile after coke collapse was improved by adopting the predetermination of quadratic curve and energy correction methods. The research will provide theoretical evidences for describing the coke profile more accurately and technical direction for choosing suitable charging parameters of blast furnace. The results show that: it is helpful to improve the stability of coke layer with increasing chute inclining angle and length of the coke flat; when the main falling point of ore moves toward furnace wall or the coke flat is wider, the curve radian of burden profile after coke collapse becomes smaller; the ore to coke ratio distribution agrees with the gas top temperature measurement well under considering coke collapse comparing with the result of ignoring coke collapse.

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

The efficacy of organophosphorus radicals as anticoking agents was subjected to a computational study in which a representative set of radicals derived from industrially relevant organophosphorus additives was used to explore competitive reaction pathways on the graphene-like coke surface formed during thermal cracking. The aim was to investigate the nature of the competing reactions of different organophosphorus radicals on coke surfaces, and elucidate their mode of attack and inhibiting effect on the forming coke layer by use of contemporary computational methods. Density functional calculations on benzene and a larger polyaromatic hydrocarbon, namely, ovalene, showed that organophosphorus radicals have a high propensity to add to the periphery of the coke surface, inhibiting methyl radical induced hydrogen abstraction, which is known to be a key step in coke growth. Low addition barriers reported for a phosphatidyl radical suggest competitive aptitude against coke formation. Moreover, organophosphorus additives bearing aromatic substituents, which were shown to interact with the coke surface through dispersive π-π stacking interactions, are suggested to play a nontrivial role in hindering further stacking among coke surfaces. This may be the underlying rationale behind experimental observation of softer coke in the presence of organophosphorus radicals. The ultimate goal is to provide information that will be useful in building single-event microkinetic models. This study presents pertinent information on potential reactions that could be taken up in these models.

Experimental Study of Softening and Melting Properties on Indonesia Vanadium-Titanium Sinters

As a raw material, Indonesia vanadium-titanium sinters are being applied to the blast furnace process for iron making in the typical iron and steel plant. In order to keep the health running of blast furnace process, in this work we have investigated the softening and melting properties of Indonesia vanadium-titanium sinters. We found that the content of vanadium-titanium magnetite in sinter is correlated with the softening and melting ranges for those sinters considered here. With the increasing of the vanadium-titanium magnetite in sinter, the starting softening temperature increases gradually and the final softening temperature increases as well, thereby the softening range becomes narrow. Both starting and final melting temperatures begin to ascent, and the variation of melting range is not obvious. In addition, we also found that the coke is wetted by the molten slag and iron. From the viewpoint of blast furnace process, the softening and melting zone has to move downward. In this zone of blast furnace the contact area of solid-liquid phase will get larger because of the close contract among the molten slag, iron and coke. On one hand, this kind of behavior can definitely speed up the reduction of iron oxide. On the other hand, it simultaneously worse the ventilation properties and affect the normal running of air flow, because a lot of iron and slag can not be got smoothly into the hearth through coke layer.

Feasibility of In-Situ Combustion in the SAGD Chamber

Summary Steam-assisted gravity drainage (SAGD) is a commercially successful bitumen-recovery method that has transformed some of the vast Canadian oil-sand deposits into recoverable reserves. Several SAGD projects have been developed in northern Alberta in the past few years, and many more are in the planning stages. As the projects mature, new operational problems are revealed, demanding new solutions. Because of operational restrictions, it is almost impossible to have the same growth rate in all steam chambers in a SAGD pattern. Hence, interference between a mature chamber and an adjoining immature chamber can become a problem. Steam leakage from the immature chamber into the mature chamber reduces the thermal efficiency of the project and requires a solution to prevent the steam dissipation. Filling the mature chamber with combustion gases is a possible solution for this problem. Carrying out in-situ combustion (ISC) in the mature chamber not only would create the needed combustion gases in the chamber, but also could recover a substantial part of the residual oil in the mature chamber. It is also likely that the combustion would create a reduced-permeability coke (toluene insoluble fraction) zone around the mature chamber, thus isolating it from the rest of the reservoir. To evaluate the merit of this idea, an elevated-pressure experiment was conducted using a 2D physical model. The conventional SAGD process was conducted in the model to develop a steam chamber. Air was then injected through a horizontal well near the top of the model into the SAGD chamber, and a combustion front was established around the air-injection well. By operating combustion in the depleted chamber, residual oil was mobilized and produced. Additional oil recovery was attained by more than 20% over the SAGD operation as a bonus. Initiation and propagation of combustion were confirmed by a large increase in the temperature in the combustion zone. After unpacking the model, it was found that a coke layer formed around the perimeter of the chamber.

Identifying optimal cleaning cycles for heat exchangers subject to fouling and ageing

Fouling of heat exchangers causes reduced heat transfer and other penalties. Regular cleaning represents one widely used fouling mitigation strategy, where the schedule of cleaning actions can be optimised to minimise the cost of fouling. This paper investigates, for the first time, the situation where there are two cleaning methods available so that the mode of cleaning has to be selected as well as the cleaning interval. Ageing is assumed to convert the initial deposit, labelled ‘gel’, into a harder and more conductive form, labelled ‘coke’, which cannot be removed by one of the cleaning methods. The second method can remove both the gel layer and the coke layer, but costs more and requires the unit to be off-line longer for cleaning. Experimental data demonstrating the effects of ageing are presented. The industrial application is the comparison of cleaning-in-place methods with off-line mechanical cleaning. A process model is constructed for an isolated counter-current heat exchanger subject to fouling, where ageing is described by a simple two-layer model. Solutions generated by an NLP-based approach prove to be superior to a simpler heuristic. A series of case studies demonstrate that combinations of chemical and mechanical cleaning can be superior to mechanical cleaning alone for certain combinations of parameters.

Hydroprocessing of Fischer–Tropsch biowaxes to second-generation biofuels

Upgrading of Fischer–Tropsch (FT) biowaxes to second-generation biofuels via hydroprocessing is the final step for increasing the fuel amount of the overall biomass conversion route: gasification of lignocellulosic biomass, FT synthesis, and hydroprocessing. The typical FT product portfolio consists of high molecular weight paraffinic waxes as the main product and FT fuels in the diesel and naphtha boiling range. OMV's objective and contribution to the project focus on achieving coprocessing of FT biowaxes with fossil feedstock using existing hydrotreating plants of crude oil refineries. Various test runs have been examined with a conventional refining catalyst under mild conditions (380–390°C, 5.8 MPa; WHSV, 0.7–1.3 h−1) in a pilot plant. Pure FT biowax is converted to gases, fuels, and an oil/waxy residue in a fixed-bed reactor with a porous catalyst layer technology. The presence of hydrogen in the reaction chamber reduces the fast deactivation of the catalyst caused by the formation of a coke layer around the catalyst particle surface and saturates cracked hydrocarbon fragments. Another approach is the creation of synthetic biodiesel components with excellent fuel properties for premium fuel application. Basically, premium diesel fuel differs from standard diesel quality by cetane number and cold flow properties. Hydroprocessed synthetic biodiesel (HPFT diesel) has compared to conventional diesel advantages in many aspects. Depending on the catalyst selected, premium diesel quality can be obtained by shifting cold flow operability properties of HPFT fuels to a range capable even under extreme cold conditions. In addition, a high-quality kerosene fraction is obtained to create bio jet fuels with an extremely deep freezing point, as low as −80°C. The isomerization degree, as well as the carbon number distribution of high paraffinic profile, and the branching degree have a major impact on the cold flow properties and cetane number. FT diesel has, compared to HPFT diesel, a slightly higher derived cetane number (DCN > 83) and a cloud point of −9°C, whereas HPFT diesel reaches values as low as −60°C. Although the HPFT naphtha obtained consists of high amounts of isoparaffins, the RON/ MON values are comparable to fossil straight-run naphtha. The reason is that the branching degree of isoparaffins from the naphtha fraction is not sufficiently high enough to reach the typical octane number values of gasoline products delivered at filling stations. Assuming the goal of launching a premium biodiesel or biokerosene fuel to the market, these hydroprocessed synthetic biofuels from FT biowaxes are ideal blending components.

Effect of Interface Resistance on Gas Flow in Blast Furnace

Any improvement in Blast Furnace productivity under a given set of operating conditions is fundamentally related to better flow distribution of gas through layered burden structure in Blast Furnace. Flow distribution and hence pressure drop of gas in granular zone of blast furnace is dependent on number and thickness of alternating layers of coke and metallic burden. A significant part of this total pressure drop in granular zone can be attributed to interfacial resistance between two successive layers. Whereas, pressure drop in porous layers of materials can be described by well known Ergun's equation in terms of all physical parameters, interface resistance needs specific treatment. Systematic study to investigate the effect of interfacial resistance on gas flow between two successive layers of different material has been attempted in this work. Laboratory scale experiments in scale down model of blast furnace were conducted to establish and quantify interface resistance for different layer configurations.

Inter-particle Percolation Segregation during Burden Descent in the Blast Furnace

Inter-particle percolation at the interfaces between burden layers directly influences the permeability of the burden in the shaft of the blast furnace. This paper studies inter-particle percolation of small particles (pellets) into large particles (coke) during the burden descent through small-scale experiments and simulations. A special device was designed for making it possible to consider the effect of the increase in cross-sectional area along with the burden descent. The simulations, which are based on the discrete element method, were first validated using one experimental case. An overall agreement was found between the experiments and the simulations. The velocity distribution of coke and pellet particles in the small bed, the trajectories along the height of the bed and the quantity of percolating particles at different heights of bed were investigated. The results show a considerable inter-particle percolation of pellets into the underlying coke layer at the wall area, but also a percolation over the whole radius of the system. These findings stress the importance of taking measures to prevent percolation by proper design of the charging programs in the operation of the blast furnace.

Modeling the Coke Formation in the Convection Section Tubes of a Steam Cracker

The presence of liquid hydrocarbon droplets in the convection section of a steam cracker may cause serious fouling problems due to coke formation, especially in high temperature zones. In order to investigate these fouling problems, a model has been developed and implemented in a CFD code to accurately simulate the behavior of a hydrocarbon droplet impinging on a hot surface. The impact energy of the droplet and the hot surface temperature are found to determine the impact behavior. On the basis of the newly developed model, the positions where droplets preferentially collide with the convection section tube walls and liquid material is deposited are determined. Furthermore, a kinetic model describing coke formation out of liquid hydrocarbon droplets in the temperature range of 450−700 K has been developed to calculate the rate of coke formation in each zone of the convection section tube. The calculated coke layer thickness on the most vulnerable tube locations and the industrially available values corre...

Thermal stress in wet slaking

A mathematical description of thermal stress in wet slaking is proposed. Calculations show that deeper cracks are formed in the coke layers directly exposed to the water supply than in lower layers. In large coke pieces, the crack depth may be a quarter of the radius. Water supply from below increases the number of pieces with deep cracks. The number of cracks formed may be reduced by increasing the wet-slaking time to 15–20 min. Other means of improving the slaking process are considered.

Burden distribution control and its optimisation under high pellet operation

Gas distribution control under high pellet blast furnace (BF) burden operation is more difficult than with sinter due to low angle of repose, high rolling characteristics and layer collapse tendency. Also heavier pellets exert a pushing effect on the preceding coke layer thereby forcing coke towards wall with the pellets also rolling down towards the centre. High pellet proportion at the centre promotes high peripheral flow affecting the burden layer profile and process stability. In order to achieve accurate gas distribution, changes in batch sequence discharge at the stock house and material discharge rate inside the furnace were altered. To avoid excessive rolling of pellets inside the furnace, ore and coke falling trajectory was monitored and optimised to enhance central gas flow without centre coke charging. With a high pellet content of up to 70–80%, BF-1 productivity up to 2·1 t m−3 per day and fuel rate down to 570 kg/tonne of hot metal was achieved.