Integrated Method of Monitoring and Optimization of Steam Methane Reformer Process

Reforming of natural gas with steam represents the most energy-intensive part of ammonia production. An integrated numerical model for calculating composition of primary reforming products with cross-checking of outlet methane molar concentration, heat duty, maximum tube wall temperature, tube pressure drops, and approach to equilibrium was set up involving production parameters. In particular, the model was used for continuous monitoring and optimization of a steam methane reformer (SMR) catalyst in ammonia production. The calculations involve the solution of material and energy balance equations along with reaction kinetic expressions. Open source code based on Matlab file was used for modelling and calculation of various physical properties of the reacting gases. One of the main contributions is development of the rapid integrated method for data exchange between any distributed control system (DCS) and the model to accomplish continuous monitoring and optimization of SMR catalyst and reformer tubes. Integrated memory block was proposed for rapid synchronization between commercial DCS with the model solver. The developed model was verified with the industrial top-fired SMR unit in ammonia production located in Petrokemija, Croatia. Practical application of proposed solution can ensure overall energy savings of up to 3% in ammonia production.

Creep Failure of Reformer Tubes in a Petrochemical Plant

This paper investigates a failure in HP-Mod radiant tubes in a petrochemical plant. Tubes fail after 90,000 h of working at 950 °C. Observed failure is in the form of excessive bulging and longitudinal cracking in reformer tubes. Cracks are also largely branched. The microstructure of service-exposed tubes was evaluated using optical and scanning electron microscopes (SEM). Energy-dispersive X-ray spectroscopy (EDS) was used to analyze and characterize different phases in the microstructure. The results of this study showed that carbides are coarsened at both the inner and the outer surface due to the long exposure to a carburizing environment. Metallography examinations also revealed that there are many creep voids that are nucleated on carbide phases and scattered in between dendrites. Cracks appeared to form as a result of creep void coalescence. Failure is therefore attributed to creep due to a long exposure to a high temperature.

Aging Phenomena during In-Service Creep Exposure of Heat-Resistant Steels

An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbide takes place at high exposure temperature (910 °C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage.

Property Degradation and Residual Life Assessment of Service Exposed Reformer Tubes

Reformer furnaces are widely used in a hydrogen plant to obtain hydrogen from hydrocarbon. The radiantt coils tubes are the most critical components of a reformer furnace, which can be heated up to 850 °C or higher temperature for long time during service. The failure of tubes usually happened before the designed life due to over-heating or unexpected damage, which usually leads to unplanned shutdown of plant and great losses. Thus, it is important to assess the damage conditions and residual life of furnace tubes. This study is an attempt to investigate the property degradation and residual life for service exposed reformer tubes of a hydrogen reformer furnace after 6 years service. Microstructural and mechanical experiments were carried out to reveal the property degradation, included optical observations, scanning electron microscope (SEM) observations, room temperature tensile tests, high temperature tensile tests, and stress rupture tests. Finite element analysis was also used to investigated the influence factors on the stress of tubes. The residual life of furnace tube was estimated based on these experimental and simulation results.

Microstructural Characterization and Property Evaluation of Service Exposed Reformer Tubes

This study investigated the microstructural characteristics and property degradation of service-exposed reformer tubes. The reformer tubes were graded into three damage levels based on on-site ultrasonic testing. The microstructural and mechanical experiments were carried out included optical observations, scanning electron microscope (SEM) observations, room temperature tensile tests, high temperature tensile tests, and stress rupture tests. The results showed that the coarsen of carbides occurred during service. A decrease of tensile elongation was observed. The mechanical properties and rupture behaviours of reformer tubes for different inspection levels were also obtained. The results showed that the ultrasonic inspection levels of tubes could be significantly influenced by carbide morphology of tube materials. A residual life of 8.3 years was estimated for these tubes.