LDPE production developments require processing equipment with increased capacities and existing applications uprating. They include large reciprocating compressors with several cylinders operating at very high pressures. Selection of piping size, as these special components have very long delivery time, including reactors and intercoolers, requires a careful analysis to be performed at an early stage of a project to properly estimate the costs. A preliminary evaluation should be made during the bid stage using compressor data sheet and P&I diagram. A specific pre-study linked to compressor sizing program can be used for preliminary cost estimation. Prior to piping purchase order issue, based on the first issue of real layout around compressor, the above evaluation has to be confirmed by a preliminary pulsation study. Once the plant arrangement will be finalized, the final acoustic study will have to be performed. Usually such study will only result in minor adjustments to the design not involving the piping size.
RESUMOEste trabalho avalia a vida remanescente dos tubos catalisadores de um forno reformador devido ao fato do fim da vida de projeto de 100.000 horas estar próximo.O principal mecanismo de dano destes tubos é a fluência, por isso a análise seguiu roteiro da Part 10 do documento API-579/ASME FFS-1 (2007).O material dos tubos é uma liga HP modificada, para a qual existe escassez de dados de propriedades na literatura. Por isso, as propriedades de fluência necessárias para a avaliação foram determinadas experimentalmente utilizando correlação de dados de ensaios de tração a quente e fluência.Os resultados indicam que os tubos não necessitam ser substituídos de imediato e que sua vida residual é estimada em 22,3 anos operando na temperatura de projeto Palavras-chave: Forno reformador, HP modificado, fluência. ABSTRACTThis work evaluates remaining life of catalyst tubes of a reformer furnace due to achieving end of design life (100.000 hours).The main damage mechanism in this case is creep, hence the analysis was based in the procedure of API-579/ASME FFS-1 -Part 10 (2007).The tubes material is the alloy HP modified, which there isn't enough creep properties data on literature. Therefore, these properties have been defined based on experimental data from hot tensile and creep tests.The results showed that is not necessary to replace the tubes immediately and the remaining life is about 22 years operating at design temperature.
Today market requires machinery with ever larger performance increasing compression system vibrations risks. Knowledge of dampers pulsation-forces phenomena and best practices allows their minimization. Loads acting on foundation are early defined allowing a proper design, while “Cylinder-Gas-loads” depending upon compressor data-sheet cannot be adjusted unless to change requirements. Considering their high amplitudes and frequencies spectrum, some exciting frequencies often coincides with system mechanical natural frequencies. This involves expensive efforts in preliminary Cylinder Manifold response studies to guide compressor General Arrangement design. Specific software that includes Compressor standard elements selection and that allow building dampers by parametric inputs is cost effective in model creation. Together with the cost benefits it facilitates the designer to simulate multiple configurations rebuilding the model in a short time and exploring several solutions to optimize the system vibration control. A FEM specialist is not required for the Model build-up, the Software allow automatically applying cylinder gas loads, run analysis and compare results vs allowable ones. In case of allowable limits exceeding or design changes, G&A Designer can easily change input and iterate the loop till satisfactory results are achieved in a timely and quality manner, optimizing dampers and supports.
In recent years, also because of the overall contraction of the market, all compressor manufacturers are differentiating their products by offering solutions that optimize/minimize costs while maintaining the same robustness and reliability. To achieve this goal, the main guidelines are “Power Density” and “Efficiency”. On hyper compressors for LDPE plants, the absorbed power of the valves has a key role in overall efficiency and, thanks to dedicated development programs aimed to design more and more efficient valves, represents one of the disciplines where it is still possible to improve the performance. The absorbed power of this type of valves is strictly correlated to their behavior which is challenging to predict because it depends on many factors. The expected macroscopic gas parameters, such as pressure, temperature and gas composition often are not sufficient to properly evaluate valve behavior in the field. In fact valve operation is highly dependent on local phenomena such as localized pressure losses and presence of vortexes which are in turn influenced by the geometry of the valve and by its behavior. To better understand all these phenomena it is needed to characterize these valves through experimental tests aimed at defining, with a good precision and accuracy, the valve dimensionless parameters Cd (drag coefficient) and Ks (flow coefficient) as a function of the geometry of the valve itself. If the coefficients Cd and Ks are not accurate, the expected behavior of the valve and, as a consequence the valve losses, may be completely different from the evidence of the field and could not properly explain some unexpected power consumption. Therefore, through a dedicated characterization of the valves design, it is possible to improve the predictability of the valve, also in terms of power consumption, that contributes to a better evaluation of the total absorbed power by the compressor, which allows designers to reduce their margins of uncertainty.
The behavior of the valves of Hypercompressors on LDPE plants is challenging to predict because it depends on many factors and often the expected and macroscopic gas parameters, such as pressure, temperature and gas composition are not sufficient to properly evaluate the valve behavior in the field. In fact valve operation is highly dependent on local phenomena such as localized pressure losses and presence of vortexes which are in turn influenced by the geometry of the valve and by its behavior. To better understand all these phenomena it is needed to characterize these valves through experimental tests aimed at defining, with a good accuracy, the valve dimensionless parameters Cd (drag coefficient) and Ks (flow coefficient) as a function of the geometry of the valve itself. If the coefficients Cd and Ks are not accurate, the expected behavior of the valve may be completely different from the evidence of the field and could not properly explain certain types of failure modes. With a more accurate evaluation of Cd and Ks, some types of damage which in first hypothesis would seem caused by factors external to the valve, in reality are proven to be intrinsically related to valve design and often dependent on valve malfunctioning. As a final step, through to a deep understanding of the valve behavior in the field an improvement of valve reliability and efficiency can be achieved through optimization of the design for various operating conditions.
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