Vessels, process mechanical design

Industrial processes proposed for the extraction of natural products with near-critical solvents work in a pressure range between 50 bar and 500 bar, and in some exceptional cases up to LOOO bar. Therefore this type of extraction must be regarded as a high pressure process. The pressure vessels are very important, since it is in these that the initial extraction takes place and also in which the saturated solvent is separated from the product. The design and operation of the pressure vessels have a decisive influence on the successful performance of equipment for extracting natural products with near-critical solvents. While the calculation of the necessary wall thicknesses is based on well-established codes of practice for pressure vessels, the mechanical design and especially the operation itself are specific to the type of extraction process considered. 

Escoe, A. K. (1994) Mechanical Design of Process Equipment, Vol. 1. 2nd edn Piping and Pressure Vessels (Gulf). 

Mechanical design of the adsorber then takes up the remainder of the engineering effort to produce a workable adsorption process design. Once a vessel is sized to provide the required inventory of adsorbenf we need to provide the mechanical details, which include flow distribution devices, bed supports and the required vessel wall thickness to withstand the working pressure and added stresses encountered during regeneration and repeated de-pressurization and re-pressurization. 

Mechanical design specification sheets (Appendix B) summarize the information that a fabricator needs in addition to the general specifications of the vessel codes. Not all of the data on the specification summary are necessarily in the province of the process engineer it may depend on the stage of the design and on who else in the organization is available to do the work. 

Unfortunately, project schedules may require that SRV sizing be carried out long before the fabricator has finished the mechanical design and certified the MAWP of his vessel. The process engineer must then use some pressure on which to base the relieving rate calculations. Paragraph 1.2.3.2 (c), API 520 states that the design pressure may be used in place of the MAWP in all cases where the MAWP has not been established. 

The concept is to use frister cycle times (seconds) than those used by the conventional PSA cycles (minutes) in order to obtain a step change in the productivity of the process (volume of product/volume of adsorbent our). Some of these designs use a conventional PSA cycle but they are operated faster by appropriate changes in the mechanical designs [6]. Others, propose novel process schemes in order to accommodate t cycle times [7-9]. An example of the second case is a RPSA process for air separation where a single adsorber vessel is packed with two or more (even numbers) shallow layers of small zeolite particles (-0.5 mm). The layers are separated... 

The fluid-bed process differs from the fixed-bed and moving-bed processes, insofar as the powdered catalyst is circulated essentially as a fluid with the feedstock. The several fluid catalytic cracking processes in use differ primarily in mechanical design. Side-by-side reactor-regenerator construction along with unitary vessel construction (the reactor either above or below the regenerator) are the two main mechanical variations. 

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