Naphtha Thermal Cracking Research Articles

Coke deposition and run length in industrial naphtha thermal cracking furnaces via a quasi‐steady state coupled CFD model

AbstractMathematical modelling of the thickness of the coke layer growing over months in millisecond cracking reactors is a dilemma in computational fluid dynamics (CFD) simulation. To address the time scale issue, a quasi‐steady state (QSS) approach was employed through a comprehensive coupled reactor/firebox CFD model in the current study. The model was applied to predict the time‐dependent behaviour of coke deposition and to determine the appropriate operating conditions for maximum olefin yields over an industrial furnace run length. A novel algorithm was designed to overcome the complexity of QSS simulation of the CFD model, which is a combination of reactive turbulence flow, combustion, and radiation models. The furnace parameters were studied as a function of two variables: the dilution steam‐to‐feed ratio and the liberated heat by the burners. The results indicated that the run length can be extended by up to 20% while retaining the main product yields. This study offers practical suggestions to maximize the run length in the operation.

An optimization model for the market-responsive operation of naphtha cracking process with price prediction

This study presents a new optimization-based framework for the optimal operation of the naphtha cracking process under uncertain market conditions. Two distinct decision models are embedded in the proposed framework: (i) product price prediction based on the machine learning techniques under market condition uncertainty for sales strategy, and (ii) mathematic model of naphtha cracking model for production planning strategy, both of which aim to maximize operating profit in the final optimization model. Based on the predicted price and the unit operation principles, the optimization model determines the major operation conditions of the naphtha cracking process. In particular, different price prediction models (multiple linear regression, artificial neural networks, and system dynamics) are compared to secure precise product prices. The rigorous mathematical model is developed by considering transport phenomena, thermal reaction, and coking effect and validated compared to real industrial data. As a result, the annual profit of the naphtha thermal cracking is expected to be 305,154 USD/year, which is 7.11% better than the reference case. This study could also be used as an auxiliary indicator for decision makers or businesses to identify production planning (i.e., optimal process operating conditions) and sales strategy (i.e., selling timing and quantity) in order to improve profits.

A coupled CFD simulation approach for investigating the pyrolysis process in industrial naphtha thermal cracking furnaces

In the steam thermal cracking of naphtha, the hydrocarbon stream flows inside tubular reactors and is exposed to flames of a series of burners in the firebox. In this paper, a full three-dimensional computational fluid dynamics (CFD) model was developed to investigate the process variables in the firebox and reactor coil of an industrial naphtha furnace. This comprehensive CFD model consists of a standard k-ε turbulence model accompanied by a molecular kinetic reaction for cracking, detailed combustion model, and radiative properties. In order to improve the steam cracking performance, the model is solved using a proposed iterative algorithm. With respect to temperature, product yield and specially propylene-to-ethylene ratio (P/E), the simulation results agreed well with industrial data obtained from a mega olefin plant of a petrochemical complex. The deviation of P/E results from industrial data was less than 2%. The obtained velocity, temperature, and concentration profiles were used to investigate the residence time, coking rate, coke concentration, and some other findings. The coke concentration at coil exit was 1.9 × 10 −3 %(mass) and the residence time is calculated to be 0.29 s. The results can be used as a scientific guide for process engineers.

Intensification of Ethylene Production from Naphtha via a Redox Oxy-Cracking Scheme: Process Simulations and Analysis

Abstract Ethylene production by the thermal cracking of naphtha is an energy-intensive process (up to 40 GJ heat per tonne ethylene), leading to significant formation of coke and nitrogen oxide (NOx), along with 1.8–2 kg of carbon dioxide (CO2) emission per kilogram of ethylene produced. We propose an alternative process for the redox oxy-cracking (ROC) of naphtha. In this two-step process, hydrogen (H2) from naphtha cracking is selectively combusted by a redox catalyst with its lattice oxygen first. The redox catalyst is subsequently re-oxidized by air and releases heat, which is used to satisfy the heat requirement for the cracking reactions. This intensified process reduces parasitic energy consumption and CO2 and NOx emissions. Moreover, the formation of ethylene and propylene can be enhanced due to the selective combustion of H2. In this study, the ROC process is simulated with ASPEN Plus® based on experimental data from recently developed redox catalysts. Compared with traditional naphtha cracking, the ROC process can provide up to 52% reduction in energy consumption and CO2 emissions. The upstream section of the process consumes approximately 67% less energy while producing 28% more ethylene and propylene for every kilogram of naphtha feedstock.

Simulation and Dynamic Optimization of an Industrial Naphtha Thermal Cracking Furnace Based on Time Variant Feeding Policy

Abstract The main goal of this research is modeling and simulation of ethylene production through naphtha thermal cracking in a coil furnace reactor. The naphtha cracking and decoking processes are modeled based on the mass, energy and momentum balance equations considering a detail kinetic model at pseudo-dynamic condition. To develop a reliable and applicable model, a detail thermal model is considered to predict tube skin temperature. To prove accuracy of developed model and considered assumptions, the simulation results are compared with the plant data. In addition, the results of coke burning in the decoking cycle by mixture of air and steam are presented. It is appeared that ethylene production decreases during the process run time gradually. The simulation results proved that increasing feed temperature, feed pressure and combustion chamber temperature during the process run time is a practical solution to maintain production capacity at an acceptable level. Finally, the optimal operating condition of thermal cracking process is calculated during the process run time based on the time variant feeding policy to achieve maximum ethylene production capacity. It is appeared that applying optimal condition on the system could increase ethylene production capacity from 15.31 ton.h‒1 to 15.49 ton.h‒1.

Anti-coking Effect of MnCr2O4 Spinel Coating during Light Naphtha Thermal Cracking

The research aimed at fabricating MnCr2O4 spinel coating on HP 40 alloy, and evaluating the influence of the spinel coating on coking behavior during thermal cracking of light naphtha. MnCr2O4 spinel coating formed on the alloy surface by selectively oxidized under low oxygen partial pressure atmosphere at 1050oC for 20h. The as-formed spinel coating was characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results show that the spinel scale is uniform and compact, with blade-like structures on the top. The coking behavior was studied from the morphology and microstructure of coke, and characterized by scanning electron microscope (SEM) and Raman spectra, respectively. The results show that, only globular coke presents on MnCr2O4 spinel coating compared with blank alloy, and the coke exhibits more disordered graphite structures. Thus, the spinel scale has a favorable anti-coking property.

Model for the simulation of light naphtha cracking in an inverted cyclone reactor

Light naphtha thermal cracking to produce ethylene and propylene in an inverted cyclone reactor has been proposed not only as an alternative for the cracked light naphtha recovery but also as a way to improve conventional cracking. A mathematical model was developed in order to assess the performan ce of this new process under changing operating conditions and design reactor parameters. A kinetic scheme for the naphtha cracking based on molecular reactions was selected and the mass and energy balances were performed. Rosenbrock's numerical method was used to find the numerical solutions to the model's equations. The simulation results allowed for a clear description of the light naphtha cracking behavior in an inverted cyclone reactor, showing that the heat exchange between solid and gas phases determines the conversion and product yields. Also, solid initial temperature and solid mass flow rate were found to be the operational parameters with the greatest impact on products formation while the steam temperature and steam/oil ratio are of lesser importance. In addition, injection angle determines the residence time, hence significantly affecting the overall performance.

Effect of selective oxidation and sulphur/phosphorus‐containing compounds on coking behaviour during light naphtha thermal cracking

AbstractThe investigation was aimed at evaluating the effect of selective oxidation and sulphur/phosphorus‐containing compounds on coking behaviour at the surface of HP40 alloy during thermal cracking of light naphtha. The surface morphology and composition of the selectively oxidized alloy were characterized by SEM, EDX, and XRD. Coking tests show that the coking rate of blank alloy decreased with sulphur/phosphorus‐containing compounds, while the effect of sulphur/phosphorus‐containing compounds on coking rate for selectively oxidized alloy is complex, and a mass concentration of µg/g results in the lowest coking rate. The morphology and microstructure of cokes were investigated by SEM and Raman spectra. SEM and Raman spectra analyses indicated that either selective oxidation or sulphur/phosphorus‐containing compounds resulted in more disordered graphite structures and amorphous carbon.

Inhibitory effect of MnCr2O4 spinel coating on coke formation during light naphtha thermal cracking

MnCr2O4 spinel coating can significantly affect coke morphology and coke microstructure.

Techno-economic analysis of petrochemical complex retrofitted with simulated moving-bed for olefins and aromatics production

This article presents a preliminary result on deciding whether to use simulated moving-bed (SMB) technology in a conventional petrochemical complex (cPCC) to increase olefins and aromatics production. A process model including an SMB unit, naphtha hydro-treating (NHT), naphtha thermal cracking (NTC), and naphtha catalytic reforming (NCR) was constructed to evaluate the economic feasibility of the retrofit petrochemical complex (rPCC) with the SMB unit for 2500kt/yr naphtha treatment. The chemical reaction kinetics of NTC and NCR were used to estimate the increase of olefins and aromatics production. The incremental total capital investment for the SMB and additional NHT areas, estimated by the factorial method, was 97.5$M. The incremental total production cost concerning utility and fixed costs was 25$M/yr. It was found that the rPCC has economic benefits, because the return on investment (ROI) after tax, payback period (PBP), and internal rate of return (IRR) are 18%, 3.7yr, and 20%, respectively. The SMB recovery of n-paraffins was most influenced on ROI and IRR in sensitivity analysis.

Effect of normal paraffins separation from naphtha on reaction kinetics for olefins and aromatics production

The objective of this study is to investigate the effect of the normal paraffins (n-paraffins) separation by the simulated moving-bed (SMB) on reaction kinetics of the naphtha thermal cracking (NTC) and catalytic reforming (NCR) for the olefins and aromatics production, respectively. First a process simulation of the SMB unit integrated to the petrochemical complex (PCC) was performed. Chemical reaction kinetics of NTC and NCR were proposed and validated. And a retrofit PCC with the SMB unit (rPCC) was compared to a conventional PCC (cPCC) in terms of products composition, flow rate, and energy consumption. It was found that olefins and aromatics yields of NTC and NCR can increase by 14wt% (41kt/yr) and 11wt% (127kt/yr) for the naphtha capacity of 2475kt/yr, respectively. However, the total energy consumption of rPCC increased by about 67.8MW (or 25%) because of the desorbent recovery in the SMB unit.

Treating Methanol‐to‐Olefin Quench Water by Minihydrocyclone Clarification and Steam Stripper Purification

AbstractIn the chemical industry, methanol‐to‐olefin (MTO) technology is a novel process for producing ethylene and propylene from naphtha thermal cracking. The process of recovering MTO quench water by minihydrocyclone and steam stripping treatment was successfully applied in industrial plants. The fine catalyst in the quench water is removed by the two‐stage minihydrocyclone separation. The method and equipment for this system present various advantages: the quench water can be recycled in the cooling system and prevents heat loss in heat transfer systems; and the stripping tower can be blocked by the catalyst. Maintenance activities are reduced and a stable operation cycle is extended. The proposed treatment process improves the economic efficiency of the MTO device.

Investigation of ethylene production in naphtha thermal cracking plant in presence of steam and carbon dioxide

In the present study, a mathematical model for naphtha thermal cracking in the presence of steam is developed. This model can predict the behavior of cracking unit of the olefin plant. In this plant a mixture of steam and naphtha passes through cracking tubes. The major role of steam is partial removal of coke that causes different problems along the reactor such as low heat transfer and high pressure drop. In this study another diluting media such as carbon dioxide is employed instead of steam in order to investigate the effect of carbon dioxide on main products yield and operating conditions. Carbon dioxide was shown to improve not only naphtha conversion but also the yield of ethylene and other main products. It also increases the heat transfer to the coils due to the fact that in presence of carbon dioxide the coke thickness along the reactor reduces dramatically. This analysis suggests that the run length of the reactor in presence of carbon dioxide is 25% higher than that in presence of steam. It is also observed that using carbon dioxide reduces tube wall temperature, resulting in less operating and maintenance costs.

Genetic algorithm model development for prediction of main products in thermal cracking of naphtha: Comparison with kinetic modeling

A novel model for prediction of the main product yields of thermal cracking of naphtha was proposed using genetic algorithms (GAs). Researchers mainly use statistical approach and artificial neural network as empirical models for modeling the thermal crackers; however, in the present study, a new application of genetic algorithm in the modeling is proposed. A polynomial model is linked with a genetic algorithm optimization procedure for a more accurate estimation of the set of model parameters compare to a Design of Experiment (DoE) derived model. A semi-mechanistic kinetic model, as a conventional method, based on free radical chain reactions was also developed using experimental results. This semi-mechanistic kinetic model contains 96 reactions. The performance of mathematical method and GA tuned model was compared with each other and the ANOVA calculation was carried out. Moreover, GA tuned model significantly improved the accuracy of the fit. This model can be used to recommend operating conditions for further experimental works in naphtha thermal cracking especially in the kinetic studies.

Thermal catalytic cracking of naphtha over multi wall carbon nanotube catalysts

The effects of temperature and Fe loading over multi wall carbon nano tube catalysts in thermal catalytic cracking of naphtha to produce light olefins have been studied in this paper. The CCD method was utilized and a set of experiments were designed and carried out. The temperature and loading varied from 572 to 628°C and 0.34 to 11.66wt.% Fe, respectively. In order to determine the effects of the variation of the operating conditions on the yield distributions, a set of statistical models were utilized and the maximum point of the yield of each product was determined. The maximum yield of ethylene (18.84wt.% of product) and propylene (12.85wt.% of product) was obtained at 628°C and 10.6wt.% loading of Fe over CNTs. Finally, thermal cracking of naphtha was carried out and was compared with thermal catalytic cracking of naphtha. As a result, at 620°C, the yield of ethylene and propylene in thermal-catalytic cracking was 6.3% and 4.7%, respectively, more than those in thermal cracking of naphtha.

Effect of Potassium Acetate on Coke Growth during Light Naphtha Thermal Cracking

Potassium acetate was used as a coking inhibitor to reduce coking during light naphtha cracking on a Cr25Ni35 alloy specimen that had already been used for 8 years. The effects of the mass concentration of potassium acetate on the morphology and structure of coke were investigated by high-resolution scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results show that the oxide scale formed on the inner surface of the cracking tube after 8 years of service is mainly composed of (Fe, Ni, Cr) spinels and the needlelike intermetallic compound of Cr and Fe. Changes of the surface conditions accelerate catalytic coking. The amount of coke decreases with increasing mass concentration of potassium acetate in a 1-h cracking period. The amount of coke was found to decrease by about 60% when the mass concentration was 400 ppm. The diameters of filamentous coke were about 100, 60, 45, and 35 nm when the mass concentrations of potassium acetate were 0, 100, 200, and 400 ppm, respectively. However, the gasification reaction was found to have little effect on the length of catalytic coke. The gasification reaction catalyzed by potassium acetate removes the noncatalytic coke surrounding the filamentous coke, and filamentous cokes at different concentrations are carbon nanofibers with a solid structure. Coke is mainly composed of amorphous carbon.

Aluminized Steel and Zinc Coating for Reduction of Coke Formation in Thermal Cracking of Naphtha

Rate of coke formation during steam pyrolysis of naphtha has been investigated in a laboratory CSTR reactor both for uncoated SS321 and metal coating constructed with thermal spray method with metal powders of aluminum, aluminum-magnesium and zinc. Rate of coke formation was studied in different temperatures and amount of coke as a function of run time has been studied too. The results of the study show that passivating the surface of SS321 with a coating of aluminum and aluminum-magnesium can significantly reduce the rate of coke deposition during naphtha pyrolysis. The results obtained from zinc coated show decoking carry out during thermal cracking. The scanning electron microscope (SEM) was carried out for morphology studied of coke deposited on the different metal surfaces.

The Use of ANN and the Mathematical Model for Prediction of the Main Product Yields in the Thermal Cracking of Naphtha

Thermal cracking of naphtha has such numerous reaction routes that the detailed reaction mechanism has not yet been determined. In this regard, a model of artificial neural networks (ANNs), using back propagation (BP), is developed for modeling thermal cracking of naphtha. The optimum structure of the neural network was determined by a trial-and-error method. Different structures were tried with several neurons in the hidden layer. The model investigates the influence of the coil outlet temperature, the pressure of the reactor, the steam ratio (H2O/naphtha), and the residence time on the pyrolysis product yields. A good agreement was found between model results and experimental data. A comparison between the results of the mathematical model and the designed ANN was also conducted and the relative absolute error was calculated. Performance of the ANN model was better than the mathematical model.

Modeling and Control of a Naphtha Thermal Cracking Pilot Plant

A computer-controlled pilot plant has been constructed to study the dynamical behavior and control of the thermal cracking furnace. The governing equations that describe the furnace dynamics are presented, and, based on these equations and a kinetic model, software that simulates the steady-state behavior of the system has been developed. The furnace is divided into eight zones that can be heated independently, and, therefore, any desired temperature profile can be applied. The variables to be measured are the furnace zone temperature, coil outlet temperature (COT), and product yield. Two different control strategies (namely, COT control and furnace wall temperature control) are applied using digital proportional−integral−differential (PID) controllers. The results show that, by applying a predetermined temperature profile along the furnace wall in the wall temperature control strategy, the same yield that is obtained by COT control can be achieved with the lower maximum furnace wall temperature. Finally, based on a performance index, the optimal temperature profile has been obtained and it is applied to the pilot through the designed control system.

Simulation and Optimization of a Naphtha Thermal Cracking Pilot Plant

In thermal cracking plants, it is desired to apply an optimal temperature profile along the reactor to minimize the operation cost. In this article a simulator is developed by the use of a mathematical model, which describes the static operation of a naphtha thermal cracking pilot plant. The model is used to predict the steady state profiles of the gas temperature and product yields. Using a dynamic programming technique, an optimal temperature profile along the reactor is obtained. The effects of operating variables such as steam to hydrocarbon ratio (S/HC), coil outlet temperature (COT) and feed flow rate on product yield are investigated. Pilot plant simulation results are compared with the industrial data and the results indicate that they follow the same trend.