A new simple and efficient flash algorithm for T-V specifications

CISMONDI DUARTE, M.; OURIQUE, J.; MATAR NDIAYE, P.; TAVARES, F.W.

Alicante

Conferencia; EQUIFASE 2015: X Conferencia Iberoamericana sobre Equilibrio entre Fases para el Diseño de Procesos; 2015

Flashcalculations play a major role in the application of chemical engineeringthermodynamics, both in the upstream and downstream industries. In the early80?s, Michelsen proposed an efficient successive-substitution algorithm for thetemperature and pressure specification (T-P), which is the most common androutinely applied in practice. At present, such type of algorithm isimplemented probably in most commercial simulators, as well as in a diversityof codes developed in academia, involving flash calculations.Thespecification of volume instead of pressure, along with temperature (T-v), fora fluid of known composition, can also be very important in many applications.These applications can be as diverse as storage tanks and simulation of flow ina reservoir, when considering the latter as an interconnected net of cavitieswith fixed volumes. Michelsen?s practical recommendation, for this as well asfor other alternative specifications, has been to run the well-known and well-behavedT-P flash on an inner loop, while adjusting the pressure on an outer loop,until matching the specification. Other authors have recently proposed and implementednew specific and more sophisticated methods, based on minimizing the Helmholtzfree energy at specified T-v conditions, through complex modern optimizationapproaches.Inthis work, we propose a new algorithm for T-v flash calculations, which isbased on results from adapting the classic successive substitution method forT-P flash, with equivalent simplicity, and therefore making it very attractivefor engineering calculations, especially when speed may be important.Complementary aspects like initialization of variables and stability analysis arealso discussed, providing recommendations. Results are presented for differentmulticomponent fluids, including the analysis of a synthetic gas condensatebehavior, the effect of temperature on storage tanks and the search ofconvenient conditions for separating the condensable fraction from a naturalgas.