Tube Skin Temperature Research Articles

Improving Cracking Severity in an Ethane Thermal Cracker Based on Dynamic Optimization Considering Process Limitations

The main goal of this research is to improve cracking severity in an industrial ethane thermal cracker in a domestic plant. In the first step, the considered cracker is modeled based on the mass and energy balance equations considering a molecular kinetic model. To develop an accurate model, a detailed thermal model is adopted to predict the tube skin temperature. To prove the accuracy of the developed model and considered assumptions, the simulation results are compared with the available plant data. In the next step, a sensitivity analysis is performed to investigate the effects of coil outlet temperature and steam to ethane ratio on the cracking severity factors including ethane conversion and production rate. Based on the results of sensitivity analysis although increasing steam to ethane ratio decreases ethane conversion, it improves ethylene yield. Then, a dynamic optimization problem is formulated to maximize ethylene production and minimize production decay during the process run time considering feed temperature, furnace temperature, and steam to ethane ratio as decision variables. The results show that applying the optimal condition to the system improves ethylene production by about 9.44%.

Experimental Investigation of Polymer-Induced Fouling of Heater Tubes in the First-Ever Polymer Flood Pilot on Alaska North Slope

Summary Polymer flooding is being pilot tested for the first time in the Schrader Bluff viscous oil reservoir at the Milne Point Field on Alaska North Slope (ANS). One of the major concerns of the operator is the impact of polymer on the oil production system after polymer breakthrough, especially the polymer-induced fouling issues in the heat exchanger. This study investigates the propensity of polymer fouling on the heater tubes as a function of different variables, with the ultimate goal of determining safe and efficient operating conditions. A unique experimental setup was designed and developed in-house to simulate the fouling process on the heating tube. The influence of heating tube skin temperature, tube material, and polymer concentration on fouling tendency was investigated. Each test was run five times with the same tube, and in each run, the freshly prepared synthetic brine and polymer solution was heated from 77°F to 122°F to mimic field-operating conditions. The heating time and fouling amount were recorded for each run. Cloud point measurement has also been conducted to find the critical temperature at which the polymer in solution becomes unstable and precipitates out. The morphology and composition of the deposit samples were analyzed by environmental scanning electron microscopy (ESEM) and X-ray diffraction (XRD), respectively. It was found that the presence of polymer in produced fluids would aggravate the fouling issues on both carbon steel and stainless steel surfaces at all tested skin temperatures. Only higher skin temperatures of 250°F and 350°F could cause polymer-induced fouling issues on the copper tube surface, and the fouling tendency increased with polymer concentration. At the lower skin temperatures of 165°F, no polymer-induced fouling was identified on the copper tube. A critical temperature that is related to the cloud point of the polymer solution was believed to exist, below which polymer-induced fouling would not occur and only mineral scale was deposited but above which the polymer would aggravate the fouling issue. The cloud point of the tested polymer solution was determined to be between 220°F and 230°F. From a practical safer design standpoint, we recommend a value of 220°F for operational purposes on the pilot site. The heating efficiency of the tube would be decreased gradually as more fouling material accumulates on its surface. If polymer precipitated and deposited on the surface, it would bond to the mineral crystals to form a robust three-dimensional network structure, resulting in a rigid polymer-induced fouling. The study results have provided practical guidance to the field operator for the ongoing polymer flooding pilot test on ANS.

Zone method based coupled simulation of industrial steam cracking furnaces

Coupled furnace/reactor simulations were conducted to study industrial steam cracking furnaces. Zone method was performed for the firebox side, and the one-dimensional reactor model COILSIM1D was used for the reactor side. In the firebox model, the Hottel zone method model was used to calculate the radiation heat transfer. The flow and combustion model were based on the results of computational fluid dynamics (CFD) simulations. A comparison was made among the results of zone method simulation, CFD simulations, and industry or design data, and the zone method simulation results were found to agree well with industry or design data. For the secondary burners installed 0.6 m away from the primary burners, the tube skin temperature and heat flux obtained with the zone method were higher than that under CFD simulation in the middle of reactor tube, and after 15 m they were lower than that obtained with CFD simulation. The higher process gas temperature led to a faster increase in ethene yield using the zone method compared with CFD simulation, whereas a shift in the maximum propene yield upstream of the reactor occurred with the zone method. This method was suitable for real-time operation optimization of industrial steam cracking units.

3D-Printed Graphene/Polydimethylsiloxane Composites for Stretchable and Strain-Insensitive Temperature Sensors.

Materials possessing exceptional temperature sensitivity and high stretchability are of importance for real-time temperature monitoring on three-dimensional components with complex geometries, when operating under various external deformation modes. Herein, we develop a stretchable temperature sensor consisting of cellular graphene/polydimethylsiloxane composite. The first of its kind, graphene-based polymer composites with desired microstructures are produced through a direct 3D ink-writing technique. The resultant composites possess long-range-ordered and precisely controlled cellular structure. Temperature-sensing properties of three cellular structures, including grid, triangular, and hexagonal porous structures are studied. It is found that all three cellular composites present more stable sensitivities than solid composites under external strains because of the fine porous structure that can effectively share the external strain, and the composites with a grid structure delivered particularly a stable sensing performance, showing only ∼15% sensitivity decrease at a large tensile strain of 20%. Taking full advantage of the composites with a grid structure in terms of sensitivity, durability, and stability, practical applications of the composite are demonstrated to monitor the cooling process of a heated tube and measure skin temperature accompanying an arbitrary wristwork.

Novel cracking coil design based on positive constructing of synergetic flowing field

A novel insert-hollow cross disk (HCD) combined with twisted tape is embedded in a cracking coil to enhance the propane cracking process by positive constructing of synergetic flowing field. Quantitative analysis of appropriate insert arrangement has been conducted based on contrastive CFD simulation results in the bare and novel coil. The characteristic exchanging flow between the central zone and the near wall area induced by inserts in the novel coil can play an effective role in improving the radial synergy among heat, mass and velocity. This leads to an obvious yield increase of 0.50% and 10.23% of ethylene and propylene comparing with the bare coil. And the average tube skin temperature is declined by 28.45 k. Moreover, the Nu and Sh are increased by 10.96% and 2.98% respectively and the overall PEC factor has a rise of 8.00% in the novel coil. This confirms the effective strengthening effect by the novel coil.Furthermore, the field synergy theory is applied to evaluate the synergy improvement for the heat and mass transfer process. Comparing with the bare coil, the synergy angles for heat as well as mass transfer in the novel coil have a maximum decrease of 21.76% and 23.14% in the downstream of the twisted tape (z/L = 0.23) and HCD insert (z/L = 0.60), respectively. This could explain the enhanced heat and mass transfer as well as the product distribution due to the synergic flow field in the novel coil with the assemble inserts group.

Cold End Corrosion Avoiding by Using a New Type of Air Combustion Pre-Heater

This paper analyzes the possibility of reducing the cold end corrosion in boilers and furnaces by using a new type of air combustion pre-heater. Cold end corrosion appears due to catalytic oxidation of the sulfur dioxide to sulfur trioxide and then due to the sulfuric acid condensation at dew point. Calculating dew points of various acid gases and options for reducing cold end corrosion of heat recovery exchangers are presented. For avoiding the cold end corrosion we design a new type of air combustion pre-heater for boilers and furnaces. Also, the tube skin temperature of the first row of pipes of the actual air pre-heater was simulated with this computer program, in order to determine whether this temperature is lower than acid dew point of flue gas. With the simulation for this configuration of the actual combustion air pre-heater, the skin temperature for the first row (for the combustion air flow) of tubes from the upper bundle was TS = 134 °C. A way to reduce the cold end corrosion in the combustion air pre-heaters is raising the temperature of the combustion air at the air pre-heater entrance. This solution involves taking a quantity of preheated air, recirculation and then reintroducing it in the air pre-heater. In the same time, this solution avoiding to use the steam radiator, mounted after the fan, for pre-heating the combustion air from 1°C to 45°C. Thus, the furnaces equipped with the new combustion air pre-heater and modern low NOx burners made a fuel economy about 3%.

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.

A rigorous mathematical model for online prediction of tube skin temperature in an industrial top-fired steam methane reformer

During the steam reformer operation, monitoring of tube skin temperature is extremely important to any program concerned with maximizing furnace tube life and maintaining safe furnace operation. It can also be an important tool in troubleshooting, debottlenecking and optimizing the plant’s operations. As a result of having reliable tube skin temperature data, the heat flux profile can be adjusted to correct the unit performance for prevention of overheating, hot spots formation and thermal aging of tubes and pigtails before failure. The present study details a rigorous and reliable online model to predict the skin temperature of tubes in an industrial top-fired primary reformer. The model is designed to run online and has a solution time of less than 1.5min starting from a poor initial guess that can be determined automatically from plant data. The model predicts the most important variables such as heat flux, composition and conversion profiles along the tube length, process gas temperature, maximum tube-wall temperature and tube pressure drop based on considering mass transfer limitation in catalyst pellets using a one-dimensional heterogeneous model. The predictions of model were compared with two previously reported works and operating data from the top-fired steam reformer of an industrial ammonia plant under normal conditions which showed a well compatibility. The model results demonstrated a maximum skin temperature of 905°C at location 2.6m from top of tube length at plant rates greater than 90% of full capacity. Applying the model in the plant to adjust the tube skin temperature resulted in 605.4Nm3/h of natural gas fuel saving. The outcome from this work is not only valuable in terms of operation, but can also prevents the overheating and failure of tubes and pigtails which extends the life of these constitutes in the reformer. Before implementing modifications in reformer design or its configuration, it is important to evaluate the maximum temperature of reformer tube.

Investigating the Effect of Fuel Rate Variation in an Industrial Thermal Cracking Furnace With Alternative Arrangement of Wall Burners Using Computational Fluid Dynamics Simulation

A new arrangement of side-wall burners of an industrial furnace was studied by three-dimensional computational fluid dynamics (CFD) simulation. This simulation was conducted on ten calculation domain. Finite rate/eddy dissipation model was used as a combustion model. Discrete ordinate model (DOM) was considered as radiation model. Furthermore, weighted sum of gray gas model (WSGGM) was used to calculate radiative gas properties. Tube skin temperature and heat flux profiles were obtained by solving mass, momentum, and energy equations. Moreover, fuel rate variation was considered as an effective parameter. A base flow rate of fuel (m˙=0.0695kg/s) was assigned and different ratios (0.25 m˙, 0.5 m˙, 2 m˙, and 4 m˙) were assigned to investigate the heat distribution over the furnace. Resulted temperature and heat profiles were obtained in nonuniform mode using the proposed wall burner arrangement. According to the results, despite increased heat transfer coefficient of about 34% for m˙–4 m˙, temperature profile for this rate is too high and is harmful for tube metallurgy. Also, the proper range for fuel rate variation was determined as 0.5–2 m˙. In this range, heat transfer coefficient and Nusselt number for m˙–2 m˙ were increased by 21% and for m˙–0.25 m˙ were decreased by about 28%.

CFD Simulation of Propane Thermal Cracking Furnace and Reactor: A Case Study

Abstract In the present work, a different new arrangement of side-wall burners of an industrial furnace with varying fuel flow rate was studied by three-dimensional CFD simulation. Tube skin temperature and heat flux profiles were obtained by solving mass, momentum and energy equations of the furnace by Ansys Fluent software. A reasonable fuel flow rate ($$\dot m$$=0.0695 kg/s) was assigned and effect of different ratio of this rate (0.25$$\dot m$$, 0.5$$\dot m$$, 2$$\dot m$$, 4$$\dot m$$) was investigated on reactor tube skin temperature profiles. Heat and temperature non-uniform distribution was observed by proposed arrangement. It was found that proper range for fuel rate was 0.5$$\dot m$$ to 2$$\dot m$$. Temperature profiles were used in one dimensional plug flow reactor model equations to consider fuel rate variations on reactor performance. By the proposed burner arrangement, Propane conversion and Ethylene yield obtained 6.25 % and 7.2 % more than the base case. Furthermore coil outlet temperature (COT) decreased about 7 °C. Also, feed flowrate was taken as an effective parameter on reactor process under no coke formation condition. Results showed that by increasing fuel rate, outlet Propylene yield decreased, while, process gas temperature, pressure drop, process severity (propane conversion) and Ethylene yield increased along the reactor tube i. e. for 0.5$$\dot m$$ to 2$$\dot m$$ at 0.8 kg/s reactor flowrate, Propylene yield decreased 15.95 % and reached to zero, whereas Ethylene yield increased 16.5 %. Also, in any fuel rate, by increasing reactor feed flowrate, even though the reactor coil outlet temperature decreased, the desired product yields increased. At 0.95 kg/s reactor flowrate, maximum Ethylene yield was obtained about 45.5 % at 1$$\dot m$$ kg/s; while, Propylene yield production at 0.5$$\dot m$$ kg/s fuel rate was 22.41 %.

Coupled simulation of convection section with dual stage steam feed mixing of an industrial ethylene cracking furnace

A complete coupled simulation of the convection chamber and tubes with dual stage steam feed mixing of an industrial ethylene cracking furnace has been carried out with the computational fluid dynamics (CFD) method for the first time. In the convection chamber, the standard k–ε model and discrete ordinates (DO) radiation model were respectively used in the descriptions of turbulence characteristics and radiative heat transfer. In the tubes, renormalization group (RNG) k–ε model and volume of fluid (VOF) model were respectively applied to the turbulence flow and the liquid–vapor two phases flow. Simulation results agree well with the industrial data. Based on the coupled result, a dynamic simulation was calculated in the feedstock preheater (FPH). Simulation results show that the velocity and temperature fields are inhomogeneous distributions along the width direction due to the asymmetrical structure of convection chamber. Two recirculation zones occur at the corner both near and away from the entrance to the convection chamber, which will cause a longer residence time of flue gas and local overheating in furnace wall of convection chamber. The process gas temperature, tube skin temperature and heat flux profiles are respectively different along the axial and radial direction of the high temperature coil (HTC-I). The changes of flow pattern from bubble flow to spray flow are effected by gravity and centrifugal force during evaporation. The results will be helpful for the design and operation in cracking furnace.

Multiscale modeling of turbulent combustion and NOx emission in steam crackers

AbstractA 3D RANS simulation of lean premixed turbulent combustion in an industrial scale steam cracking furnace is performed. Turbulence is represented by a renormalization group (RNG) k − ε model, while combustion is modeled with a skeletal mechanism. The eddy dissipation concept (EDC) model is used to account for turbulence/combustion interaction. The turbulent combustion regime is identified as a “thin flame regime with pockets” or a “corrugated flamelet regime”. A weighted sum of gray gases model (WSGGM) is used to account for the gas radiative properties. The radiative transfer equation is solved using the P‐1 and discrete ordinates method in the conservative finite volume formulation. NOx calculations are performed as a postprocessing step, with the flow field, temperature, and species concentrations fixed. The formation of NO through thermal, prompt, and N2O intermediate mechanisms is considered. The in situ adaptive tabulation technique is used to decrease the computational time required to treat the combustion chemistry. The effect of radiation models on the predicted furnace wall, tube skin, and flue gas temperature profiles and heat fluxes toward the reactor tubes, as well as on the predicted species and NO concentration profiles and structure of the furnace flames under normal firing conditions, is discussed. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Impact of radiation models in CFD simulations of steam cracking furnaces

The endothermic thermal cracking process of hydrocarbons takes place in tubular reactor coils suspended in large gas-fired pyrolysis furnaces. Heat transfer to the reactor tubes is mostly due to radiation from the furnace refractory walls and the flue gas. A three-dimensional (3-D) simulation of the flow in an industrial scale steam cracking furnace is performed. The renormalization group (RNG) k − ɛ turbulence model is used. The combustion kinetics is modeled by a three-step reaction mechanism, while turbulence–chemistry interaction is taken into account through the Finite Rate/Eddy-Dissipation model. The Discrete Ordinates model (DOM), the P-1 and the Rosseland Radiation model are used for modeling of the radiative heat transfer. The results of using the different radiation models are compared mutually with adiabatic simulation results. The absorption coefficient of the gas mixture is calculated by means of a Weighted-Sum-of-Gray-Gas model (WSGGM). The effect is discussed of the use of different radiation models on the predicted wall, tube skin and flue gas temperature profiles and heat fluxes towards the reactor tubes, as well as on the predicted species concentration profiles and structure of the furnace flames under normal firing conditions.

Combustion and Pyrolysis Reactions in a Naphtha Cracking Furnace

AbstractNumerical simulation on combustion and pyrolysis reactions in a tubular reactor is carried out on a 100,000 t/a naphtha cracking furnace. A complex arrangement of bottom burners is contained in the furnace model. The hydrodynamic and radiation models are included for calculating the flue gas flow pattern and heat transfer. A molecular reactions model is applied on the basis of a two‐dimensional tubular reactor model. The results calculated indicate that there is recirculation of the flue gas at each side of the reactor tubes due to the high inlet velocity from the bottom burners, which contributes to the uniformity of flue gas temperature in the furnace. Higher temperature profiles of the tube skin are mainly located 15–20 m along the tubular reactor. The calculated pyrolysis product yield and the tube skin temperatures are in good agreement with experimental data.

CFD simulations of steam cracking furnaces using detailed combustion mechanisms

A three-dimensional mathematical model has been developed for the simulation of flow, temperature and concentration fields in the radiation section of industrial scale steam cracking units. The model takes into account turbulence–chemistry interactions through the Eddy Dissipation Concept (EDC) model and makes use of Detailed Reaction Kinetics (DRK), which allows the detailed investigation of the flame structure. Furthermore, simulation results obtained with the EDC-DRK model are compared with simulation results obtained with a simplified model combining the Eddy Break Up (EBU)/finite rate formulation with Simplified Reaction Kinetics (SRK). When the EBU-SRK model is used, much faster fuel oxidation and products formation is predicted. The location of the peak temperature is shifted towards the burner, resulting in a smaller flame and the confinement of the combustion process into a smaller area. This is most likely because of the inherent deficiency of the simplified model to correctly predict the overall (effective) burning rate when the turbulent mixing rate and the reaction rate are comparable. It is shown that when neither the “fast-chemistry” nor the “slow-chemistry” approximation is satisfied, the overall burning rate is overpredicted. The smaller flame volumes obtained with the EBU-SRK model have important effects on the predicted temperature distribution in the furnace as well as on other significant design parameters like the refractory wall and tube skin temperatures. It is suggested that more sophisticated turbulence–chemistry interaction models like the EDC model and more Detailed Reaction Kinetics should be used for combustion modeling in steam cracking furnaces under normal firing conditions.

Systematics and modelling representations of LPG thermal cracking for olefin production

Pyrolysis of hydrocarbons is an important commercial process for the production of ethylene, propylene and 1,3 butadiene. These low molecular weight olefins are among the most important base chemicals for the petrochemical industries for polymer production. A simulation program of the reaction kinetics and coke formation inside the coils of a thermal cracking unit can provide information on the effects of operating conditions on the product distribution. The aim of this study was to develop a mechanistic reaction model for the pyrolysis of LPG that can be used to predict the yields of the major products from a given LPG sample with commercial indices. A complete reaction network, using a rigorous kinetic model, for the decomposition of the LPG feed has been developed, which is used for the simulation of industrial LPG crackers. This model has been adapted using industrial data for the pyrolysis yields of LPG. The present paper attends on the asymptotic coking mechanism and describes the development of a kinetic coking model in the pyrolysis of LPG. Detailed and accurate information about the product distribution, growth of coke layer, the evolution of the tube skin temperatures can be obtained from this simulation. Simulations of this kind can be used to optimize the furnace operation. They can be used as a guide for the adaptation of the operating variables aiming at prolonging the run length of the furnace. The reactor model, as well as kinetic scheme, is tested in an industrial cracking furnace.

Optimization of Steam Reformers: Heat Flux Distribution and Carbon Formation

Optimal heat flux distributions along the axial position of steam reformer tubes are analyzed, aiming to maximize the outlet methane conversion without violating the upper bounds specified for the tube skin temperature, Tw(z) and the local heat flux, Q(z). The possible occurrence of the carbon deposition phenomenon is considered as an additional constraint in the optimization problem by means of a kinetic criterion which accounts for the rate of carbon formation (rC,net).The problem of finding the axial heat flux profile that leads to maximum methane conversion (or minimum tube skin temperature for specified production) without violating the upper limits imposed for Tw(z), Q(z) and rC,net is in principle a complex optimization process. In this work, a relatively simple semi-analytical method, that requires only iterative reactor simulations, is proposed.At conditions of fresh catalyst and for operations with typical feed compositions and temperatures, the carbon formation constraint is not active. For low values of the maximum allowable local heat flux (Qall), the optimal heating policies are monotonically increasing Tw(z) trajectories. Conversely, for higher Qall values the optimal Tw(z) shows an initial increase in the first tube section followed by an isothermal section. Decreasing axial wall temperature profiles or Tw(z) curves with maximum are clearly not optimal.When the catalyst is strongly deactivated, the optimal manipulation of Q(z), or Tw(z), is an appropriate procedure to achieve carbon free conditions. As this heating policy consists basically in reducing the firing in the top section of the reformer tube, it leads to unavoidable production losses.The shape of the catalyst activity axial profile has a considerable influence on the risk of carbon formation. Increasing activity distributions (similar to those found when sulfur poisoning takes place) may result in severe carbon formation in the reformer top. An optimal control of the heat input can contribute to minimize this practical operation problem.

Influence of the Sulfur Poisoning on the Performance of a Primary Steam Reformer

In the present paper, the effect of sulfur on the performance of the catalyst particle and the operation of an industrial side-fired reformer is analyzed, by coupling detailed mathematical models for the reactor and the sulfur poisoning. The model predicts the transient evolution of the main variables inside the catalyst pellet (e.g., poison coverages and reaction rates) and along the axial position (e.g., gas composition, sulfur distribution, gas and tube skin temperatures). The common simplified model, which neglects the reaction rates update as the poisoning proceeds, is compared with the model proposed in this article. The deactivation phenomenon causes methane reaction rates that present maxima along the catalyst coordinate, moreover effectiveness factors higher than the unity are found close to the reactor entrance. When the poison is removed from the feedstock, non-monotonic sulfur distributions appear inside the particle and simultaneous sulfur migration towards the surface and the center of the pellet is observed. Non-isothermal deactivation conditions similar to those found in industrial reformers are simulated, i.e., the heat input is assumed constant during the poisoning. The increments in the gas and tube skin temperatures are maximum at those axial positions where the observed methane reaction rate becomes equal to its value at conditions of fresh catalyst. The proposed mathematical model is a useful tool to describe the dynamic behavior of the macroscopic reactor variables in terms of the local phenomena that take place within the catalyst particles. In practice, this model can be utilized to evaluate key variables such as: the outlet sulfur content (to minimize poisoning downstream the reformer), the maximum tube skin temperature (to extend the tube-life time) and the axial distribution of the process gas temperature and composition (to prevent carbon formation in the top section of the reactor).

Influence of the Heat-Flux Profiles on the Operation of Primary Steam Reformers

The influence of the heat-flux axial profiles on the main variables of an industrial primary steam reformer (i.e., outlet methane conversion, process gas temperature, tube-skin temperature, and equilibrium approach) has been studied. By means of adjustments of the heat flux along the tube length, two different optimization problems have been proposed: (a) maximum methane conversion for a given maximum allowable tube-skin temperature and (b) minimum tube-skin temperature for a fixed methane conversion, both for constant heat duty. The defined optimization problems have been solved using a one-dimensional heterogeneous model. This mathematical formulation accounts for the strong mass-transfer resistances by an appropriate solution of the material balances within the catalyst. An equivalent annular model has been used to represent the complex geometry of the catalyst particle. The simulation and optimization results indicate that the heat flux strongly influences the reactor performance. Indeed, adequate selections of the heat-flux distribution along the reactor length would increase the production rate and/or extend the tube lifetime significantly.

Mitigation of Fouling in Bitumen Furnaces by Pigging

Processing of Athabasca oil sands bitumen requires preheating of the feed to temperatures in the range of 350−500 °C. At these temperatures significant amounts of solid foulant can be deposited on the walls of the furnaces. Ultimately, buildup of the deposit causes premature shutdown of the process, either because of excessively high tube skin temperatures or because of high pressure drop across the furnace. Steam/air de-coking, which has been practiced in the past, is unable to eliminate all the deposit since the foulant contains significant quantities of non-carbonaceous material. Currently, the preferred method to address this problem is pigging assisted by high-pressure water. The feed to the furnaces typically contains close to 0.5 wt % inorganic solids originating from the mineral matrix from which the bitumen is extracted. Elemental analysis of the feed identifies 300−450 ppm iron, much of which can be attributed to the components of the inorganic matrix, such as pyrite, iron carbonate, and iron-bearing clays. However, it is expected that soluble organic iron species, such as naphthenates and carboxylates, are more likely to decompose at the temperatures in the furnaces and to convert to iron sulfide and deposit within the furnace. Samples of foulant were collected from two furnace pigging operations, one at the Suncor Energy Inc. coker furnace and one at the Syncrude Canada Ltd. LC Finer furnace. The samples were taken at timed intervals that allowed a profile of the foulant within the cross-section of the furnace tube to be completed. After washing and drying, the foulant samples were analyzed for carbon, sulfur, and a variety of metals and inspected by optical petrography. Coker furnace foulants exhibited high concentrations of both carbonaceous material and iron sulfide. The iron sulfide concentration was highest at the wall and declined as the distance from the wall increased. The carbon content showed the reverse trend, suggesting that coke formation became the more important factor as the deposition process proceeded. This reverse trend coincided with the increase in tube skin temperature. Fluid and skin temperatures are much lower in the LC Finer furnace than in the coker furnace; therefore, the tendency to coke formation is reduced. As a result, the composition of the foulant from the LC Finer furnace was more constant and consisted almost entirely of iron sulfide. It was estimated that the amount of iron deposited as foulant corresponded to about 0.05 wt % of the total iron in the feed that passed through these furnaces.