Reformer Tubes Research Articles

ICONE19-43248 Experimental study on method for heat transfer enhancement using a porous material

There are several methods for enhancement of heat transfer; for example, there are attaching various fins on the heat transfer surface, processing the surface roughly, and so on. When cooling high temperature circular or rectangular channels by forced convection of gas, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on the channel surface or inserting twisted tape in the channel. In the case of the gas heating type steam reformer, disk type fins are attached on the outside surface of the reformer tube, and the tube is inserted into the guide tube to increase an amount of heat transferred from the high temperature gas. However, it has to take into consideration the deterioration of the structure strength by attaching the fins on the tube surface with the design of the steam reformer. The objective of this study is to clarify performances of a method for heat transfer enhancement using porous material with high porosity. The experiment has been performed using an apparatus which simulated the passage structure of the steam reformer to obtain characteristics of heat transfer and pressure drop. From the results obtained in this experiment, the heat transfer rate by this method showed a good performance in the laminar flow region. It was also found that the method for heat transfer enhancement using porous material with high porosity is further improved under the high temperature condition as compared with the other methods for heat transfer enhancement.

Root cause analysis of primary reformer catastrophic failure: A case study

AbstractThis article describes the investigation of an incident of catastrophic failure of a primary reformer in an ammonia plant. The lessons learned from the root cause analysis of the event are of interest. The reformer is one of the critical unit operation in an ammonia plant. Under normal operating conditions, reformer tubes get aged and progressively develop “creep” in metal leading to a possible catastrophic failure. This event of total failure occurs when one tube fails and results in destroying the neighbouring tubes. Such a situation may occur during start up. A failure diagnosis model is developed, and several hypotheses were tested to determine most likely causes. The analysis revealed that, due to short supply of nitrogen, the start‐up procedure of the reformer was modified on expert's advice shortly before the operation. This change was not reviewed by the whole team. The important parameters in view of the changed procedures were not monitored. This communication gap resulted in severe damage to the reformer melting almost all of the tubes and convection zone coils. It may be observed that the primary reformer amounts to 25% cost of whole ammonia plant. The systematic root cause analysis, thus, clearly identified the reason of catastrophic failure as incomplete analysis and nonconformity of procedures. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2011

Optimizing reformer tube life through advanced inspection and remaining life assessment

AbstractSteam reformer tubes must withstand high temperature and pressures during operation and are made from centrifugally cast materials, typically HK‐40, HP modified, and microalloy materials. As operating conditions can result in various forms of damage, the identification and quantification of damage is of vital importance if tube life is to be predicted accurately. This article describes the recent developments in an inspection system, which uses multiple nondestructive testing techniques to provide the most comprehensive assessment of current tube condition. This is coupled with a sophisticated remaining life assessment software model, which not only predicts the remaining life of each tube in a furnace but can also calculate the effect of changes in future operating conditions on tube ageing. Field experiences and findings are also discussed in the article. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2010

Microstructural degradation of two cast heat resistant reformer tubes after long term service exposure

Microstructural evolution of a gas reformer tube made of the two dissimilar heat-resistant cast alloys, 25Cr–35Ni and 28Cr–48Ni–5W, was studied using light optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy point analysis. Specimens were cut from an ex-service, failed reformer tube aged 8 years. The phases and carbides at each section of the reformer tube were determined and compared with as-cast conditions. It was found that the specimens located far from the bottom or the roof of the reformer box had mainly meta-stable phases such as G-phase or M 23C 6 due to exposure to intermediate temperatures. Those inside the reformer box, however, had phases such as M 6C carbides which are more stable than M 23C 6, and NbC due to exposure to high temperatures above 1000 °C.

Variations of the microstructure and mechanical properties of HP40Nb hydrogen reformer tube with time at elevated temperature

Hydrogen reformer furnaces have been widely used in the petrochemical industry to produce the hydrogen-rich gas from a mixture of hydrocarbons and steam at high temperature. However, the degradation of material microstructure was frequently encountered in the tubes due to high temperature service, leading to their premature failure. The aim of this paper was to address the variations of the microstructure and mechanical properties of HP40Nb hydrogen reformer tubes after aging treatment and long-term service at temperature of 900°C. The results showed that the grain boundaries became coarsening due to the precipitation of the chromium-rich carbides and the secondary carbides precipitated in the matrix after aging treatment and long-term service. The mechanical properties of the HP40Nb tube obviously degraded after short-term service and then almost kept unchanged. The interdendritic carbide content can be used as a key index for the life predication of the used tube since there was a linear relationship between the logarithm of carbide content and the logarithm of time.

Damage characterization in two reformer heater tubes after nearly 10 years of service at different operative and maintenance conditions

Reformer furnaces are used in petrochemical industry to produce hydrogen. Their most critical components are radiant tubes, where extreme temperature and pressure conditions required the deployment of high alloyed austenitic HP grade steels, owing to their superior strength to creep rupture and good corrosion resistance. Nevertheless, these high strength alloys undergo damage when process conditions allow coke deposition and maintenance procedures are not carried properly. Two radiant tubes, coming from two different plants and made of HP40Nb and HP40Nb microalloy steels respectively, are investigated here to highlight the endured damage after 85,000–96,000 h of service at maximum temperature of ∼950 °C. Light optical microscopy (LOM) and scanning electron microscopy (SEM) analyses both confirmed significant aging in both tubes, as revealed by a substantial microstructural evolution consisting of phases transformation and precipitation, as well as cavitation and incipient microcracking in the bulk. Mechanical testing demonstrated the considerable worsening of mechanical properties following such a microstructural deterioration. However, noticeable differences between the two tubes were discovered as far as type and distribution of damage, and extent of the aged zone. The small differences in alloys composition seem not sufficient alone to explain such dissimilarity in behaviour because, in addition to creep damage, one tube showed also clear evidence of carburization. Instead it is argued that differences in process conditions (i.e. temperature, pressure chemical composition of process fluids and steam–hydrocarbon ratio) and cleaning maintenance for decoking (i.e. type and frequency) may have synergistically triggered different damage mechanisms responsible for the different form of degradation on each reformer tube.

Failure Analysis and Remaining Life Assessment of Methanol Reformer Tubes

High-quality failure analysis and good engineering judgment can turn plant shutdowns resulting from methanol reformer tube failures into an opportunity to improve the future performance of the reformer furnace. The plant down time can be used to evaluate remaining tube life and provide some insight into the effect of tube operating history, especially tube metal temperature on tube performance. The results can be used to minimize potential future failures and economic losses because of reformer shutdowns. In this article, the failure mechanism of a ruptured reformer tube is determined and an assessment of the remaining life of non-ruptured tubes in the reformer is discussed. Two assessment methods are reviewed (1) metallographic examination of ex-service material to characterize microstructure and creep damage and (2) modeling of creep damage accumulation using special-purpose finite-element software (WinTUBETM).

Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project: The Thermal Storage Media of Na2CO3–MgO Composite Materials

The molten-salt tubular absorber/reformer (MoSTAR) project aims to develop a novel type of “double-walled” tubular absorber/reformer with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate its performances on the sun with a 5 kWt dish-type solar concentrator. The new concept of double-walled reactor tubes is proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. This solar tubular absorber concept may be also applied to solar air receiver for solar thermal power generation. The MoSTAR project includes the development of molten-salt thermal storage media, the new design and the fabrication of absorber/reformer with the double-walled absorber tubes, and finally the solar demonstration on the 5 kWt dish concentrator of Inha University in Korea. In this paper, thermal storage media of the series of Na2CO3–MgO composite materials were tested in a double-walled reformer tube with a thermal storage capacity of about 0.3 kWh. The chemical reaction performances for dry reforming of methane during cooling or heat-discharge mode of the reactor tube were investigated using an electric furnace. The experimental results obtained under feed gas mixture of CH4/CO2=1:3 at a residence time of 0.3 s and at 1 atm showed that the single reactor tube with 90 wt % Na2CO3/10 wt % MgO composite material successfully maintained a high methane conversion above 90% with about 0.9 kW reforming scale based on high heating value during 45 min of the heat-discharge mode. The chemical reaction performances of the reactor tube were investigated also for the solar-simulating operation mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

Double-walled reformer tubes using high-temperature thermal storage of molten-salt/MgO composite for solar cavity-type reformer

Abstract Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na2CO3, K2CO3, and Li2CO3 composite materials with magnesia were tested as thermal storage media for CO2 reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na2CO3/MgO composite with various MgO contents was also estimated. Composite materials of Na2CO3 80–90 wt% and MgO 20–10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at >90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage.

Optimising reformer tube life by applying advanced inspection and remaining life assessment technology

Centrifugally cast materials, namely HK40, HP Modified, and Micro-Alloy materials, are used for tube materials in steam reformer tubes. The material undergoes various stresses resulting in damage which can manifest itself in several ways. The quantification of damage is of vital importance if tube life is to be predicted accurately. A comprehensive inspection system has been developed to assess the exact degree of damage. The technology utilises several NDE techniques, including ultrasonic and eddy current examinations. The combination of techniques provides valuable data for the prediction of the remaining life of tubes. Customised software for remaining life prediction directly utilises the inspection information, together with plant operating parameters, to provide a methodology for managing tube life scenarios. Field experiences and findings are discussed in the paper.

Low Temperature Methane Steam Reforming for Hydrogen Production for Fuel Cells

Thus, it is necessary to develop low temperature process to decrease the material cost for the reformer tube. Moreover, if the low temperature process is possible, the lifetime of the re-former tube will be extended considerably. Previously, we have reported that it is possible to operate SRM at 548

Creep and tensile behaviour of austenitic Fe–Cr–Ni stainless steels

The control of creep behaviour during service of reformer tubes made of HP-40 austenitic stainless steels is still limited by the knowledge of creep mechanisms in these alloys. Two different HP-40 alloys modified with a low-level addition of Nb were studied. Creep tests were carried out at 980 and 1050 °C with different stress levels, in the range of 20–50 MPa, and their results were plotted in a Norton-type diagram. Also, low strain rate tensile tests were performed at temperature of 950, 980 or 1000 °C. As low strain rate tensile tests showed a plateau at nearly constant stress for a given strain rate, they could be somehow linked with creep tests. Accordingly, tensile and creep results were plotted together on a Larson–Miller (LMP) diagram. The fracture modes of tensile and creep samples were investigated and the effect of different parameters such as sample dimensions, temperature and atmosphere, was also studied.

Microstructural and mechanical property changes in HK40 reformer tubes after long term use

The microstructural change in the steam reformer tubes which had been used for approximately 60,000–90,000 h in a hydrogen manufacturing plant was investigated and their effect on the remaining creep-rupture life was studied by performing lifetime prediction using Larson–Miller Curves. In addition solutionization treatment at 1100–1200 °C was attempted on the used tubes in order to study the possibilities of extending the remaining lifetime and of improving the mechanical properties of the used tubes. The results showed that the remaining lifetime of the HK40 reformer tubes was largely dependent upon the precipitation of σ phase under the current operating conditions of 32–34 kgf/cm 2 pressure at 800–1000 °C, showing extensive degradation of the mechanical properties. Observed was no major improvement in the creep-rupture properties of the used tubes treated by solutionizing treatment at 1100–1200 °C, but the tensile properties, especially elongation and impact resistance at room temperature, however were enhanced extensively. Also the σ phase was decomposed by the treatment, indicating that the materials reliability against the embrittlement at room temperature could be improved in a great deal.

Operation of an industrial steam reformer under severe condition: A simulation study

AbstractA rigorous two‐dimensional model is developed for simulating the operation of a less‐investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non‐availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. In all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer.

High-temperature carbonate/MgO composite materials as thermal storage media for double-walled solar reformer tubes

The composite materials of molten alkali-carbonate/MgO-ceramics are examined as thermal storage media in a tubular reformer using a double-walled reactor tube of a laboratory scale. The concept of a double-walled reformer tube is proposed as a solar tubular reformer and involves packing a molten salt/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. The composite materials of Na 2CO 3, K 2CO 3, and Li 2CO 3 with magnesia are tested as thermal storage media. The reforming performances of the composite materials are tested in the cooling mode of the double-walled reactor tube. The experimental result obtained under feed gas mixture of CH 4/CO 2 = 1:3 at 1 atm shows that the use of 80 wt%Na 2CO 3/20 wt%MgO composite material successfully delayed the cooling time of the catalyst bed by 5–19 min in comparison to the case without a composite material. In addition, the Li 2CO 3/MgO and Na 2CO 3/MgO composite materials relatively revealed good performances: they prolonged the cooling time by over 10 min in the gas hourly space velocity (GHSV) range of 5000–12,500 h −1. The application of the reactor tubes to solar tubular reformers is expected to realize stable operation of the solar reforming process under fluctuating insolation during cloud passage.

Wall-to-particle heat transfer in steam reformer tubes: CFD comparison of catalyst particles

Computational fluid dynamics (CFD) was used to simulate non-reacting heat transfer in a steam reforming packed reactor tube of tube-to-particle diameter ratio ( N ) equal to 4, with cylindrical multi-hole catalyst particles. These simulations extend those of our previous study [Nijemeisland, M., Dixon, A.G., Stitt, E.H., 2004. Catalyst design by CFD for heat transfer and reaction in steam reforming. Chemical Engineering Science 59, 5185–5191] to provide accurate tube wall temperatures, runs at constant pressure drop in addition to those at constant mass flow rate and simulations of particles with different sizes of holes. At constant pressure drop, particles with higher void fractions allowed higher mass flow rates, resulting in tube wall temperatures and radial temperature profiles in order: solid cylinders > one-hole particles > multi-hole particles. Little difference was seen between three-hole and four-hole particles. The particles with multiple holes gave a substantial reduction in tube wall temperature, with only a small decrease in core tube heat transfer. The effect of hole size was small, for the cases investigated in this study.

Process simulation of natural gas steam reforming: Fuel distribution optimisation in the furnace

This paper describes a two-step method to simulate the natural gas steam reforming for hydrogen production. The first step is to calculate reforming tube length and fuel distribution with equilibrium approach associated with heat transfer. The second step is to calculate and validate reforming performance with kinetic model. A short-cut simulation of hydrogen plant has also been performed to calculate inputs for the reformer model, such as total flow rate and composition of mixed fuel burning in the furnace chamber. Heat transfer, especially radiative heat transfer, is the key role in the steam reforming technology, due to the high heat fluxes involved. For this reason, energy modelling of the furnace chamber has been performed. The simulation evaluates the most important design variables, as tubes height, maximum tube-wall temperature, and tube pressure drop. The heat flux profile can be selected to have suitable metal temperatures to lengthen the reformer tube life. The model calculates the design parameters for reforming tube and fuel distribution among burners.

A three dimensional view of high temperature creep damage

A three dimensional view of creep voids in a hydrogen reformer tube is presented. By separating and reconstructing various microstructural features present, the proper representation of creep voids in 3D can be fully studied. Useful measurements of parameters such as void volume, void-to-void distance, and grain boundary angles were obtained. The data presented here represent the initial collection of creep void information for use in various creep void nucleation and growth models. Additional data are currently being collected for material subjected to different service conditions.

Temperature measurement of reformer tubes

An overview of the methodology for measuring the temperatures of process tubes in reformers using IR techniques is presented. The major sources of error are examined and advice is given on how best to avoid or correct for these errors. An uncertainty analysis is also given, providing the means for reformer operators to assess the risks associated with decisions based on the results of temperature measurements.

Simulation Study of Radial Heat and Mass Transfer Inside a Fixed Bed Catalytic Reactor

A rigorous two-dimensional model is developed for simulating the operation of a less-investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non-availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. Due to severe operating conditions, in all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer. Keywords—Steam Reforming, Direct Reduction, Heat Transfer, Two-Dimensional Model, Simulation I. INTRODUCTION TEAM reforming is the reaction of a hydrocarbon, especially methane, with the oxidants water vapor and/or carbon dioxide to produce hydrogen and carbon monoxide. The chemical reactions taking place in catalytic methane reforming are numerous, among which four reactions are more probable under the reforming conditions (Hyman, 1968): CH4 + H2O ↔ CO + 3H2