Radiant Coils Research Articles

Eddy current analysis for predicting deterioration stages in alumina former radiant coils

The alumina former radiant coil is typically used as a high-temperature material. It is inevitable that the material undergoes deterioration after prolonged use. This deterioration is primarily caused by damage from the service environment and initiates carburization, resulting in a loss of its mechanical properties. Currently, the damage to the materials is only discovered when they are already broken and a precise non-destructive testing method to determine the extent of material deterioration before the damage occurs has not successfully been developed. Therefore, this research aims to study and analyze the deterioration and the causes of damage to alumina former radiant coil materials. Additionally, the study was conducted to establish a relationship between the extent of deterioration and the impedance phase angle using the eddy current test method. The experimental analysis included both as-received and in-service materials of alumina former radiant coil, which consisted of 45 % nickel by weight, 30 % chromium by weight and 4 % alumina by weight. The additional testing methods included microstructure and elemental analysis, deterioration distance measurement and impedance phase angle measurement. The results indicated that the deterioration was primarily caused by damage to the oxidation layer, facilitating the diffusion of carbon and initiating a carburization reaction on the surface of the coil. These factors unavoidably reduced the corrosion resistance of alumina former radiant coil materials. Furthermore, the reduction in chromium content as materials entered the deterioration stage led to increased hardness in the carburization zone and reduced hardness in the oxidation zone. This deterioration caused the material to exhibit ferromagnetic behavior. It was observed that as the area of deterioration increased, the size of the ferromagnetic regions also increased. Resulting in, the eddy current testing results show a variation in the impedance phase angle. Therefore, the relationship can be concluded that the impedance phase angle increases in the counterclockwise direction, corresponding to a greater extent of deterioration. The benefit of this paper is to forecast the level of the severity of deterioration quantitatively when using eddy current testing.

Investigation of stress-strain state of coil of tubular furnace radiant chamber at different arrangement of intermediate support

The coils of radiant chambers of tubular furnaces are operated under especially loaded conditions in terms of temperature stress distribution. It is in the radiant sections that the feed is heated to the required maximum temperatures. Also, part of the coil structure may be in close proximity to the burners and exposed to an open flame to form superheating zones. In this regard, the elements of the coil can deform and prematurely collapse. One of the most important roles is played by the support elements of the coil in the form of suspensions, brackets, etc., which serve to prevent sagging of the coil pipes. An important role is played by the optimal location of the support elements of the coils during design in order to prevent pipe sagging during operation. In the era of rapidly developing digital technologies, the problem of optimal location of support elements at the coil, taking into account the peculiarities of the design, operating parameters, and the intensity of thermal radiation, can help solve specialized software complexes. Special programs develop a coil model taking into account all the necessary parameters and characteristics, both material and technological process. This makes it possible to detect zones of concentration of increased stresses and maximum deformations. Therefore, the actual work is the modeling of the stress-strain coil of the radiant coil, taking into account the different locations of the support elements.

Contaminant removal from plastic waste pyrolysis oil via depth filtration and the impact on chemical recycling: A simple solution with significant impact

Recycling of mixed plastic waste via pyrolysis and subsequent steam cracking towards light olefins is a promising solution for the ever-growing plastic waste crisis. However, the pyrolytic recycling pathway is still not established on industrial scale due to the large variety of pyrolysis oil contaminants that hamper the application in (petro-)chemical processes. In short, plastic waste pyrolysis oils are unfeasible for steam crackers without upgrading. In this work, depth filtration for the removal of particulate contamination from a post-consumer mixed polyolefin (MPO) pyrolysis oil was performed using three different filter media with different porosity. Comprehensive analyses using SEM-EDX of the retained particles as well as ICP-OES and GC × GC-FID of the filtered oils allowed to understand the efficacy of filtration. Most of the particulate contamination was removed by filtration leading to a reduction from 69 mg/L in the unfiltered sample to < 2 mg/L in the filtered samples. Particle characterization confirmed that the main contamination is composed of iron, calcium and silicon-based contaminants in combination with carbon-based species. It was confirmed by ICP-OES that after filtration, important contaminants such as nickel, vanadium and lead were reduced below contamination thresholds for steam crackers indicating that filtration is an efficient, and potentially cost-effective upgrading technique for pyrolysis oils. When steam cracking the filtered oils, results show that radiant coil coke formation was reduced by 40–60% compared to the unfiltered oil without changes in product selectivity, confirming the strong impact of particulate contamination on coke formation during steam cracking.

Investigation of changes in the structure of heat-resistant iron-containing chromium-nickel alloy as a result of long-term operation

Pyrolysis furnaces operate in harsh temperature and power conditions. Radiant coils are the most vulnerable part in their design. The coil pipe operates in two modes: operational - at a constant pressure and temperature not exceeding 1050 &deg;С, and cleaning mode, which is characterized by increased pressure and higher temperature (about 1100 &deg;С) compared to the operating one, which leadsto a thermal force effect. Such operating conditions of coil pipes lead to changes in the structure and properties of the material. In this regard, chromium-nickel steels are widely used for the manufacture of coils, and for operation at higher temperatures (1000-1050 &deg;C), the content of chromium and nickel is increased, obtaining iron-containing chromium-nickel alloys, to ensure a stable austenitic structure. Identification of the dominant damaging mechanism makes it possible to determine the remaining resource and replace the coils in time to prevent possible emergencies. It is obvious that structural changes in the pipe metal will have a decisive influence on the performance of the structure as a whole. This paper presents the results of a study of the influence of some operational factors on the state of the metal of pipes of a standard furnace coil made of heat-resistant iron-containing chromium-nickel alloy. A change in the matrix microstructure in the form of partial homogenization of austenite was revealed. The fact of the occurrence of carbide reactions has been established. The presence of an oxidation zone mainly along the boundaries of dendrites was revealed, and the main types of oxides were determined. The dominant damaging mechanism of radiant tubes during operation has been determined.

Assessing the feasibility of chemical recycling via steam cracking of untreated plastic waste pyrolysis oils: Feedstock impurities, product yields and coke formation

Chemical recycling of plastic waste to base chemicals via pyrolysis and subsequent steam cracking of pyrolysis oils shows great potential to overcome the limitations in present means of plastic waste recycling. In this scenario, the largest concern is the feasibility. Are plastic waste pyrolysis products acceptable steam cracking feedstocks in terms of composition, product yields and coke formation? In this work, steam cracking of two post-consumer plastic waste pyrolysis oils blended with fossil naphtha was performed in a continuous bench-scale unit without prior treatment. Product yields and radiant coil coke formation were benchmarked to fossil naphtha as an industrial feedstock. Additionally, the plastic waste pyrolysis oils were thoroughly characterized. Analyses included two dimensional gas chromatography coupled to a flame ionization detector for the detailed hydrocarbon composition as well as specific analyses for heteroatoms, halogens and metals. It was found that both pyrolysis oils are rich in olefins (∼48 wt%) and that the main impurities are nitrogen, oxygen, chlorine, bromine, aluminum, calcium and sodium.Steam cracking of the plastic waste derived feedstocks led to ethylene yields of ∼23 wt% at a coil outlet temperature of 820 °C and ∼28 wt% at 850 °C, exceeding the ethylene yield of pure naphtha at both conditions (∼22 wt% and ∼27 wt%, respectively). High amounts of heavy products were formed when steam cracking both pyrolysis oils, respectively. Furthermore, a substantial coking tendency was observed for the more contaminated pyrolysis oil, indicating that next to unsaturated hydrocarbons, contaminants are a strong driver for coke formation.

Effect of variations internal pressure on cracking radiant coils distortion

In this paper, radiant tubes distortion of cracking furnaces plants has been modeled in operation conditions by the finite element method (FEM). The coils are made of 25Cr 35NiNb, and Baily-Norton formulation has been used for modeling the creep behavior. Tubes operational pressure and temperature have been achieved by since coils to complete the cracking process have a limitation in reducing skin temperature. If to economic reasons and to reach the appropriate timeframe for production and fulfillment of sales obligations, operation time before decoking increases from 60 days to 62 days, high operation temperature in the final two days passes from temperature calculated by normal numerical integration techniques and field observations, respectively. Analysis results have compared increasing values of coil tubes length in real conditions. Due to the coils operational process, the parameters affecting their distortion have been investigated. The phenomenon of ballooning and excessive distortion has also been studied by changing tubes internal pressure.

Performance investigation of a transcritical CO2 heat pump combined with the terminal of radiator and floor radiant coil for space heating in different climates, China

CO2 air-source heat pump is regarded as a promising technology for domestic hot water and automotive air-conditioning system. However, its coefficient of performance is not very satisfactory when it is used for space heating in winter, while this phenomenon is more obvious at the condition of taking conventional radiator as a heating terminal unit. To cope with this issue, a transcritical CO2 air-source heat pump system combined with the terminal of radiator and floor radiant coil for space heating was developed in this paper, for fulfilling the energy cascade utilization. The performance and feasibility of the studied system were investigated using Transient System Simulation Program and compared with a benchmark system in five locations with different climate zones, China. The results showed that, taken Shenyang as an example, the inlet water temperature of heat pump unit of the studied system and the benchmark system were 36 °C and 50 °C respectively. Also the average coefficient of performance and heating seasonal performance factor of CO2 air-source heat pump unit were 17%–28% and 9%–22% higher, respectively, compared with the benchmark system during the entire heating period. This study is helpful to improve the application of transcritical CO2 air-source heat pump for space heating in severe and cold zones in China.

Stress-deformed state of the coil of the pyrolysis furnace at deviation of the shape of pipes

A distinctive feature of the pyrolysis furnaces of hydrocarbon raw materials from other types of furnaces operated at the facilities of oil and gas chemical enterprises is the strict operating conditions necessary for the implementation of this process. At the same time, the temperature of the radiant coil in operating conditions can reach 1050 ° C. In this regard, the probability of failure of coils of pyrolysis furnaces due to defects and damages during operation is extremely high. In addition, variations in coil shape and dimensions that occur during manufacturing or operation can negatively affect the overall stress-strain state of the coil during operational loads. In this work, the influence of permissible deviations in the shape and dimensions of pipes used in the welding of the coil on its stress-strain state in working conditions is investigated.

Electric Spark Alloying of Radiant Coils for Pyrolysis Furnaces

Currently, the petrochemical industry uses furnaces to produce ethylene, the main element of which is radiant coils designed for the decomposition of straight-run gasoline into pyrolysis gas, which is the main product for producing ethylene. In radiant coils, the gasoline decomposition process must take place at a temperature of about 800 °C with a high heating rate in order to avoid coking of the coils. Heat is supplied by radiation from the inner lining of the furnaces heated by the flame of flat-flame gas burners. For radiant heat transfer to occur, the surface of the coils must have a high degree of blackness. This article presents the developed technology for coating heating surfaces with shungite and the results of increasing their emissivity to intensify radiant heat transfer. Measurements of the emissivity after electrospark alloying were carried out by the radiation method, according to which, according to Kirchhoff’s law, the emissivity is equal to the emissivity at equal temperatures.

Development of a CFD model for steam cracker radiant coil using molecular kinetics

ABSTRACTThere are several commercially available radiant coil designs for steam hydrocarbon crackers with various features which include, reduced coking, increased selectivity and higher heat transfer coefficient. A structured approach is required to qualify these radiant coil designs for commercial steam crackers. This work describes the development of a single radiant coil model using computational fluid dynamics (CFD) and focuses on investigating the impact of various turbulence model and wall functions. The model validation is carried out using experimental results reported in literature. The validated model was then used to simulate propane cracking by using a reduced molecular kinetic mechanism. Good agreement was found between the CFD results using reduced kinetic mechanism with those reported in literature using two-dimensional model with radical reaction mechanism.

PREPARATION AND SIMULATION OF THE ON-LINE SiO2/S COATING FOR COKING INHIBITION IN THE INDUSTRIAL CRACKING FURNACE

Abstract Coke formation inside radiant coils is one of the main problems during thermal cracking of hydrocarbons. The on-line preparation of the coating for coking inhibition is a promising technology because it provides more flexibility to the operators on site. The SiO2/S coating was prepared on the inner surface of coils in an 8-year-served GK-VI industrial cracking furnace. The effects of the coating preparation process on the operation of TLE were studied. The coking rates of the tube with and without coating preparation were evaluated by the trend change of tube metal temperature. Simulations of the coating deposition process were further carried out using the computational fluid dynamics approach. The results showed that a significant temperature increase at the outlets of TLEs during coating preparation were due to the accumulation of SiO2 and S in a loose form under the TLE operating conditions when the concentration of coating precursors was 7500 ppm (wt. %). In the three tests, coating precursors were mainly completely consumed in tubes and TLEs. For the coated tube, the run time was extended by 4-7 days because the catalytic coking was decreased. No significant changes in the distribution of products and molar yields of main products were observed. In the simulations, it was found that increasing the inlet flow rate led to a more uniform thickness and improved the mass content of sulfur in the coating. In the tube bend section, circumferential nonuniformities for the deposition were due to circumferential differences in the temperatures and mass fractions. The mass fraction of S in the coating was within the range of 0.02%-0.1%. The control step for the SiO2/S coating deposition was kinetic. Based on the simulation results, the optimized coating preparation parameters were determined, i.e., the inlet flow rate of 15t/h, the outlet temperature of 1093K and the inlet mass concentration of 3000 ppm (wt. %).

Computational Fluid Dynamics-Based Study of a High Emissivity Coil Coating in an Industrial Steam Cracker

To assess the effect of applying a high emissivity coating to the reactor coils in a steam cracking furnace, a complete energy balance was made for two cases based on simulations of the radiant section, reactors, convection section, and transfer line exchanger. A base case with a typical emissivity spectrum for a generic high-alloy steel was compared to a case with an artificially increased emissivity corresponding to a high emissivity coating. At the same cracking severity, coating the radiant coils increases the radiant section efficiency by 0.70% absolute, reduces the required furnace firing rate by 1.73%, and reduces the flue gas bridge wall temperature by 14 K. Minor changes to the convection section layout are required to compensate for the shift in duty to the radiant section: the reactor feed is still fully preheated to the targeted crossover temperature, but the production of high pressure steam is reduced.

Mitigating flow induced vibration in heater radiant coil

Vibration of process heater tubes in a fired heater can cause fretting-wear damage of the tubes at the locations of contact points with the supports. For the reboiler of a naphtha splitter in a naphtha hydrotreating unit, a scenario of fretting-wear damage was observed exactly at contact areas between the top return bends and the hanger supports, which likely indicated constant rubbing between them during vibration. A root-cause analysis of this tube vibration problem was carried out through a combined study of process simulation, Computational Fluid Dynamics (CFD) and vibration analysis. Results from CFD simulations revealed dual phase flow inducing pressure fluctuations inside the radiant tube. The predicted pressure fluctuations were further analyzed using Fast Fourier Transform (FFT) to identify the dominant frequency of pressure fluctuations. Some of the resulting dominant frequencies were within 20% band of the estimated natural frequency of the tube, which could lead to resonance mode. This predicted resonant vibration matched with the locations of severe grooving, as reported in the heater inspection report. A scenario of mitigating this resonance mode has also been presented through decreasing feed flow rates to the radiant tube coils and installing additional support at the mid-height of the radiant tube coils.

Atomic-Level Simulation Study of n-Hexane Pyrolysis on Silicon Carbide Surfaces.

Ethylene production plays a key role in the petrochemical industry. The severe operation conditions of ethylene thermal cracking, such as high-temperature and coke-formation, pose challenges for the development of new corrosion-resistant and coking-resistant materials for ethylene reactor radiant coils tubes (RCTs). We investigated the performance of ceramic materials such as silicon carbide (SiC) in severe pyrolysis conditions by using reactive force field molecular dynamics (ReaxFF MD) simulation method. Our results indicate that β-SiC surface remains fully stable at 1500 K, whereas increased temperature results in melted interface. At 2500 K, fully grown cross-linked-graphene-like polycyclic aromatic hydrocarbon coking structure on SiC surfaces was observed. Such coking was particularly severe in the carbon-side of the surface slab. The coking structures were mainly derived from surface atoms at the initial 3.0 ns, as a result of the loss of interfacial hydroxyl layer and further hydrothermal corrosion. The SiC substrate surface enhances the ethylene cracking rate and also leads to different intermediate-state compounds. Our fundamental research will have significant and broad impact on both petrochemical industry and academic research in materials science, petrochemistry, and combustion chemistry.

Integrated Operation and Cyclic Scheduling Optimization for an Ethylene Cracking Furnaces System

Multiple cracking furnaces in an ethylene plant run in parallel to produce ethylene, propylene, and other products from different hydrocarbon feedstocks. Because both coke formation in radiant coils and change of operation conditions with time have significant effects on the performance of cracking furnaces, it is better for the cyclic scheduling to be simultaneously optimized with the operation conditions. To match this real requirement, a mixed-integer dynamic optimization (MIDO) problem is presented for the optimization of both operation conditions and cyclic scheduling simultaneously, through which the optimal assignment, the processing time, the subcycle number, and the optimal operation conditions of different feeds in different cracking furnaces are determined at the same time. To solve the MIDO problem, it is discretized and converted into a large scale mixed-integer nonlinear programming (MINLP) problem. The two scheduling cases of a cracking furnaces system are illustrated showing a remarkable i...

Effect of severe operation conditions on the degradation state of radiant coils in pyrolysis furnaces

This work arose from the need to understand the degradation phenomena taking place in the radiant coils of pyrolysis furnaces of the petrochemical plant of REPSOL POLÍMEROS in Sines, Portugal, in order to extend their service lifetime.The radiation coils were studied through the finite element method, rendering stress and displacement analysis and calculation of the Larson–Miller parameter in severe operation conditions. The studied operation parameters were temperature increase, pressure increase, net coil weight increase through coking. Additionally, microstructural analysis of samples of H39WM and H46M alloys in as-supplied and used conditions was carried out.Attained results suggest that the operating lifetime of similar coils can be extended by tuning their temperature profile and especially the amount of coke weight loaded, both during current operation and on decoking. Frequent and standardized temperature readings are mandatory to assure a temperature profile below project temperature, determining the coke weight loaded at a given time would also allow a more accurate knowledge of the remaining furnace creep life.

Experimental Investigations on Thermal Performance of a New Floor Heating Device

Thermal performance experiments were carried on a new floor heating device in a thermal environmental chamber in order to provide design reference for engineering application. The new floor heating device can achieve heating demand with lower heat medium water temperature when compared with traditional floor radiant heating coil pipe. The device can combined with low grade thermal energy utilization system for high efficient heating.

Effect of coking in massive failure of tubes in an ethylene cracking furnace

The causes and characteristics of the massive failure of the radiant coil tubes in an ethylene cracking furnace, which failed during an emergency non-programmed stop, are investigated. The failed tubes had been in service for about three and a half years, while lifetime had been estimated in five years. Tensile testing showed severe in-service degradation of material mechanical properties. Longitudinal cracks on failed tubes are brittle and originate in the inner side of the tubes wall. All failed tubes display a thick layer of coke adhered to the inner wall. This coke comes easily broken by bending or tension stresses, but sustains compression.The origins of loads which lead to the fracture were replicated; cracks were lab-induced by longitudinal cutting and resulting openings measured. Mechanical modeling allowed concluding that loads that led to failures were due to differences between thermal expansion coefficients of tube alloy and the coke growth within them. When the furnace was cooled down, thermal contraction of tube metal was restricted by the thick coke layer. This layer grew in service in the pressure expanded tubes.The failures were due to a combination of circumferential loads induced by coke during fast cooling and low strength of tube material. Recommendations include monitoring coke thickness and comparing with critical thickness for tube rupture in case of an emergency stop. This way, operators will have a parameter useful to schedule decoke processes.

乙烯裂解炉辐射段技术的研究进展及工业应用

Radiant section is the key componet of the cracking furnace, and the cracking reaction of hydrocarbons occurs in the coils of radiant section. In the research of radiant section, the focus is how to obtain the proper product distribution and the high economic benefit. This review reports the research progress of cracking reaction in the radiant coils and the heat transfer in radiant section. The kinetic model of thermal cracking reaction, the heat transfer model and the combustion model are introduced. The factors influcing the thermal cracking reacion and the heat transfer are presented, and the application of the above research on the cracking furnace are introduced as well.

Energy-efficient air conditioning system with combination of radiant cooling and periodic total heat exchanger

The main thrust of this paper is directed toward a novel air conditioning system that can maintain a healthy indoor environment and be energy-efficient. This system consists of a low-temperature regenerative periodic total heat exchanger, radiant ceiling-cooling coil, and conventional air conditioner. The natural cold energy of the tap water in the cooling coil provides comfortable and uniform cooling, and the desiccant-packed bed in the total heat exchanger recovers the indoor energy to handle the fresh air. The performance of each component is discussed, and the actual performance of the whole system is investigated in an office at the Taipei Water Department. The results indicate that using a radiant ceiling-cooling coil to precool the indoor environment enables the traditional window-type air conditioner to reduce two-thirds of the original operating time. In addition, the test of the whole system was conducted in the same office, and it was observed that using this system to handle the incoming air could save 13%–19% of the energy consumption per month during a year-round operation compared to directly introducing untreated fresh air.