Abordagem simplificada para o projeto e análise preliminar de custos de sistemas de compressão de gás natural em plataformas

Abstract

Several stages of platform design demand complex tools and methods, sometimes requiring excessive personnel and time expenditure. Simplified analysis and models can contribute significantly to facilitate the project management. In the present work, two approaches are compared in the design of a gas compression system in platforms: a simplified one that uses approximations for the behavior of the substances and a lower level of detailing, and a conventional one, that uses Peng-Robinson equation of state (PR-EoS) to describe the thermodynamic behavior of systems and more calculation steps. The compression system modeling and simulation was performed in the Scilab software, validated with a simulation of the same system performed in Aspen Plus®. The gas has a typical composition of natural gas, containing C1 to C8, N2, CO2, H2S and H2O. Each stage involves a vessel, a compressor and a heat exchanger. In the simplified approach, it is assumed that the gas is considered to be formed from C1 and C2 with normalized compositions. The compressor is isentropic, and the heat exchanger uses ideal gas heat capacities, being considered only the sensitive heat. On the other hand, in the conventional approach, the phase equilibrium is modeled by a cubic state equation (ϕ-ϕ approach via EdE-PR), the compressor is adiabatic, considering a certain isentropic efficiency and the heat exchanger considers enthalpies calculated from conventional way via EdE-PR. Preliminary cost evaluations of the system for each approach were performed. In this sense, the CAPEX of the entire compression system and each individual equipment are compared for two typical natural gas compositions. Results for the two gas streams show that the deviations increase with the gas richness. Analyzing the two gas compositions and the deviations from the simplified model compared to the conventional model, it was found that the deviation in the total CAPEX never exceeded 10%, indicating the potential application of the simplified approach in providing fast and reliable cost estimates in a typical range of natural gas compositions.