Simulation of the coking phenomenon in the superheater of a steam cracker

CATEGORY: COKE
Chemical Engineering Science, Volume 110, 3 May 2014, Pages 31–43
Mackie-2013 “Pushing the boundaries”
Simulation of the coking phenomenon in the superheater of a steam cracker
Amit V. Mahulkar, Geraldine J. Heynderickx, Guy B. Marin
Laboratory for Chemical Technology, Ghent University, Technologiepark 914, B-9052 Gent, Belgium
Abstract
Coke formation in the convection section of a steam cracker occurs when heavy feeds are cracked. Authors present CFD simulations of coke formation in the mixture superheater tubes in the convection section of a steam cracker. They employed a gas condensate as hydrocarbon feed for the simulations. They chose representative chemical species based on their boiling points, to mimic the entire range of feed components. They simulated the liquid–vapor spray flow in the mixture superheater tube based on an Eulerian–Lagrangian approach using ANSYS FLUENT 13.0. Authors’ work provides guidelines to minimize the extent of coke formation in the steam cracker convection section when a heavy feed is cracked. It also provides possible remedies to completely eliminate the coking problem when cracking heavy feeds.
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Mathematical modelling of selected processes utilizing combustible process gases

CATEGORY: COKE
2013 14th International Carpathian Control Conference (ICCC), 26-29 May 2013, Page(s): 315 – 320, Rytro, Digital Object Identifier :10.1109/CarpathianCC.2013.6560561
Mathematical modelling of selected processes utilizing combustible process gases
Abstract
A number process technologies produce combustible gases as by-products. They vary in calorific value and are used to decrease the use of gases with higher calorific value. Coke oven gas from the coking process and process gases from an electric furnace in a copper plant are exemplify these gases. Coke oven gas used in the process of heating combustion air in a heat regenerator is the most common process. Because of low calorific value, the gases from the electric furnace require afterburning at the beginning of their utilization process. Authors present mathematical modeling of a coke oven battery regenerator and mathematical modeling of post combustion of the electric furnace process gases.
They elaborate the regenerator mathematical model for the simplified geometry of a real object making the assumptions for the heat transfer equations. They also provide a simplified geometry of a real object to model the post combustion process.
Research continues on solving problems with recycling of waste gasses. It focuses on the mathematical modeling and optimization of the operation of the recycling units. The authors describe mathematical models of the regenerative heat exchanger of the coke-oven and post combustion chamber of the waste gasses from the electric furnace.
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In situ detection of coke deposits on fixed-bed catalysts by a radio frequency-based method

CATEGORY: COKE
Sensors and Actuators B: Chemical, Volume 181, May 2013, Pages 681–689
In situ detection of coke deposits on fixed-bed catalysts by a radio frequency-based method
Dieter Rauch (a,b), Peter Fremerey (a,b), Andreas Jess (b), Ralf Moos (a)
a Department of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany
b Department of Chemical Engineering, University of Bayreuth, 95440 Bayreuth, Germany
Abstract
Describes an investigation into whether a contactless radio frequency-based method is suitable to monitor both coking and regeneration of industrial fixed-bed catalysts directly and during operation. The tubular steel reactor served as an electromagnetic cavity. Two waveguide feeds were used to impress and receive electromagnetic waves between 1 and 20 GHz.
Shifts of the resonance frequencies mirror the coke loading in the low loaded state. Strongly decreasing power transmission over the entire frequency range goes along with increasing coke load at higher coke loadings. Both the locally homogeneously distributed coking process and the coke burn-off process that starts in the reactor front and moves through the reactor can be observed by the radio frequency-based method.
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Investigation of Coke Formation in Steam Cracking of Atmospheric Gasoil

CATEGORY: COKE
Journal of Petroleum Science Research (JPSR) Volume 2 Issue 2, April 2013
Investigation of Coke Formation in Steam Cracking of Atmospheric Gasoil
Sorood Zahedi Abghari
zahedis@ripi.ir
Modeling and process control Department, Process Engineering Development Division, Research Institute of Petroleum Industry (RIPI)
Abstract
Researchers designed and conducted a number of experiments in a pilot plant to study the characteristics of atmospheric gasoil as a suitable feed stock of steam cracker processes. The experimental operating conditions were coil outlet temperature (COT), feed flow rate and steam ratio (STR).
A group of experiments were conducted to determine the coke formation rate. Researchers used a central composite design methodology to set up the experiments and analyze the results. They employed statistical teststo confirm the accuracy, consistency and reproducibility of experimental results. In addition, a statistical model was used to investigate the coke formation rate. To determine the yield distribution of main products a reaction network composed of 21 reactions in conjunction with the related kinetic reaction rates was developed. Based on the models and employing a suitable optimization algorithm, the best operating conditions were determined.
Free Full Text Source: http://www.jpsr.org/paperInfo.aspx?ID=5708

Structure and composition of hard coke deposited on industrial fluid catalytic cracking catalysts by solid state 13C nuclear magnetic resonance

CATEGORY: COKE
Applied Catalysis A: General, Volume 466, 10 September 2013, Pages 123–130
Structure and composition of hard coke deposited on industrial fluid catalytic cracking catalysts by solid state ¹³C nuclear magnetic resonance
Babita Behera, Piyush Gupta, Siddharth S. Ray
CSIR-Indian Institute of Petroleum, Dehradun 248005, India
Abstract
Reports results of a study of carbonaceous deposits (hard coke) using several solid state ¹³C nuclear magnetic resonance (NMR) techniques after demineralization of the spent and regenerated fluid catalytic cracking (FCC) catalysts obtained from Indian refineries. A variety of structural parameters, including aromaticity, H/C ratio, fraction of protonated f_a^P and non-protonated f_a^NP aromatic carbons, number of pericondensed rings per average molecule (N_peri), and aromatic condensation index (γ_ar) were derived from the NMR data.
Researchers rationalized observations of thirty-two and thirty-nine aromatic rings in coke from regenerated catalysts and five and nineteen rings in coke from spent catalysts using several parameters, including feed, temperature and process conditions of FCC reactor on the basis of condensation. They noted that the coke was more condensed in regenerated catalysts compared to spent catalysts.  This indicates that the temperature has a marked effect in the evolution of coke structure. Feeds and other process conditions, on the other hand, govern the nature and composition of coke.
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Effects of Alkali and Alkaline Earth Metals on NOx Reduction in Coke Combustion

CATEGORY: COKE
Advanced Materials Research (Volumes 634 - 638) Pages 522-525, DOI 10.4028/www.scientific.net/AMR.634-638.522 (2013)
Effects of Alkali and Alkaline Earth Metals on NOx Reduction in Coke Combustion
Yan Guang Chen, Hong Jing Han, Jia Lu, Dan Dan Li, Jin Lian Li, Shu Zhi Liu
Abstract
Researchers fabricated a series of coke samples with loading alkali and alkaline earth metals using the impregnation method.  They studied NOx emissions in a silica fixed bed reactor in the combustion process of raw coke and coke modified by Na, K, Ca and Mg.
Results reveal that Na, K, Ca and Mg have in-situ catalytic effects on the NOx reduction reactions.
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Process for Regenerating Coked Particles

PATENT
Process for Regenerating Coked Particles
United States Patent Application 20120043195
Inventors:
Corma Canos, Avelino (Valencia, ES)
Rundell, Douglas (Glen Ellyn, IL, US)
Sauvanaud, Laurent Louis Andre (Valencia, ES)
Yaluris, George (Park Ridge, IL)
Application Number:
13/264007
Publication Date:
02/23/2012
Assignee:
Bo Corporation North America Inc. (Naperville, Il, Us)
Bp Oil International Limited (Naperville, Il, Us)
Abstract:
A process for regenerating coked particles, which process comprises contacting a hydrocarbon feedstock with solid particles in a reaction zone to produce coked particles, which coked particles are transferred to a regeneration zone in which they are contacted with steam to produce hydrogen and at least one or more oxides of carbon, wherein the solid particles comprise one or more of the following components: (i) an aluminosilicate zeolite comprising one or more of Mn, Ti and Zn; (ii) a Ce-containing aluminosilicate zeolite with a Ce loading of at least 0.05 wt % and/or a molar ratio of total other rare earth elements:Ce in the range of from 0:1 to 5:1; (iii) a magnesium and aluminium-containing anionic clay; (iv) a material with the Perovskite structure.
This invention relates to a method of regenerating coked particles, and more specifically to a method of regenerating coked particles in processes such as hydrocarbon coking and catalytic cracking.
The upgrading of low value, high boiling point fractions of crude oil into lower boiling point hydrocarbons, which can be used in the production of higher value fuels such as gasoline, diesel and kerosene is an important aspect of crude oil refining, and a number of hydrocarbon coking and cracking processes have been developed in order to achieve this aim. Such processes are becoming increasingly important in the exploitation of heavy crude oil sources, such as tar sands and shale oils, and also in processing heavy crudes that are extracted from mature and declining oil wells.
Examples of coking and cracking processes commonly used in crude oil refineries include fluidised catalytic cracking (FCC), hydrocracking, delayed coking, visbreaking, flexicoking and fluid coking. A number of these processes are described in the Kirk-Othmer Encyclopaedia of Chemical Technology, Third Edition, volume 17, pages 205-217.
Coking processes are generally used to upgrade very heavy, low value fractions such as vacuum residues having high Conradson carbon content, typically above 5 wt %, to produce lighter hydrocarbon components and coke. In fluid coking, for example, the hydrocarbon feedstock is sprayed into a reactor comprising a fluidised bed of hot particles. On contact with the particles, the hydrocarbon undergoes a cracking reaction to produce light hydrocarbons such as C₁ to C₄ hydrocarbons, naphtha, distillates, and the additional formation of coke, which is subsequently removed. Often the added particles are coke particles, a portion of which can be ground to an appropriate size and returned to the coking reactor. Alternatively, or additionally, particles such as silica or sand particles can be used which are regenerated to remove coke before being returned to the coking reactor, as described for example in GB 792,763. In flexicoking, the coke and/or coked particles are gasified by contact with steam and/or oxygen in a regeneration zone, as described in the Kirk-Othmer Encyclopaedia of Chemical Technology, Vol 17, Third Edition, page 214.
Catalytic cracking processes, such as FCC, typically involve contacting the hydrocarbon feedstock with a solid acid catalyst at high temperature, which results in their catalytic decomposition into smaller hydrocarbons. The hydrocarbon feedstocks are typically lighter than those used for coking processes, having a lower Conradson carbon content, for example heavy gas oils or vacuum gas oils, or even some of the heavier gas oils produced in the aforementioned coking reactions.
In a typical FCC process, the catalyst is lifted up through the cracking reactor (also known as a “riser”) by the action of vapourised hydrocarbons in the feedstock, and also by the co-feeding of a fluidising or lifting gas. The smaller, lower boiling hydrocarbons leave the reactor together with the fluidising gas, where they are separated and typically further processed to produce fuel stocks. Another product of the reaction is solid carbonaceous residue, or coke, some of which deposits on the catalyst and contributes to its deactivation. To regenerate the catalyst, FCC processes typically remove catalyst from the reactor and feed it to a regenerator, where the coke is removed. Optionally, the catalyst undergoes a stripping step before being fed to the regeneration zone to remove any adsorbed product or unreacted hydrocarbons, which would otherwise reduce yields if left on the catalyst and fed to the regenerator.
Typically, in FCC and coking processes, coke is removed from catalyst particles by combustion in the presence of oxygen to produce predominantly carbon dioxide (CO₂). Heat generated by the combustion can be used to balance heat lost from the process during the endothermic cracking reactions. However, where large quantities of coke are formed, for example when processing oils having a high Conradson carbon content (which can be measured using analytical method ASTM D-189), the heat produced on combustion can rise to levels which can damage or destroy the catalyst and associated reactor equipment. Additionally, the regeneration unit may not be able to supply the quantity of oxygen required to oxidise the large quantity of coke on the catalyst. Therefore, processing of such oils cannot easily be achieved without either limiting the quantity of catalyst regenerated, or diluting the feedstock with oils having lower coking potential, for example feedstocks with lower Conradson carbon values.
One reported method of reducing heat generation is described in U.S. Pat. No. 4,888,156, which relates to the use of so-called catalyst coolers, in which the regenerator comprises heat exchange tubes that remove heat from the process, for example using a water coolant.
Yet another way to reduce the quantity of heat generated in the regeneration zone is to use a lean oxygen supply, such that only partial combustion of the coke occurs to produce carbon monoxide (CO). The CO produced can be further combusted in a separate reactor to produce CO₂ and additional heat, without causing catalyst damage. The additional heat from this second oxidation or combustion can be captured, for example through heating a steam supply. U.S. Pat. No. 6,660,683 provides a summary of the different types of oxidation mode that can be used in regenerating FCC catalysts.
A further process involving the use of combustion for regenerating coked catalyst is described by Hedrick et al, the Annual Meeting of the National Petrochemical and Refiners Association March 19-21 2006, who describe a process for upgrading heavy crude oils for distribution through a pipeline by catalytically cracking a portion of the heavy crude to produce lower boiling point hydrocarbons, which are blended (or “cut”) with the crude oil to improve its flow properties. The coked catalyst is regenerated by combustion or partial oxidation and recycled. Additionally, in US 2007/0034550, a process for improving flow properties of crude oil is described, in which a first crude stream is processed, including cracking in the presence of catalyst, in which the cracked stream is mixed with a second, unprocessed crude stream to increase the API value. The spent catalyst is regenerated by oxidation before recycle.
In the aforementioned cases, the main product of coke removal is CO₂, a so-called greenhouse gas, which is typically released into the atmosphere. It would be advantageous if the release of carbon dioxide into the atmosphere could be reduced. It would also be advantageous if the coke regeneration produced useful products that could be used in other processes, for example as feedstocks to chemicals or refinery processes.
An alternative method of removing coke from a catalyst or other solid is to react the coke with steam. For example, U.S. Pat. No. 2,518,775 describes a process in which coked FCC catalyst is reacted with steam and oxygen in a regenerator to produce predominantly carbon monoxide and hydrogen, which can be fed to a Fischer-Tropsch synthesis unit for producing hydrocarbons. U.S. Pat. No. 5,362,380 describes a process in which steam in the absence of oxygen is used to regenerate a coked FCC catalyst.
Carbon dioxide can be used to regenerate coked catalyst. For example, U.S. Pat. No. 4,425,259 and U.S. Pat. No. 4,450,241 describe FCC processes in which high Conradson carbon value feedstocks are contacted with an FCC catalyst modified with various metals, selected from Li, Na, K, Sr, V, Ta, Mo, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Sn and Bi. These aim to improve the reforming rate with CO₂ in the regenerator, which CO₂ is produced during combustion in the presence of oxygen. Additionally, they describe the addition of a CO₂-rich feed to the regenerator to produce CO from the combination of CO₂ and coke-derived carbon to mitigate the exotherm produced during regeneration.
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