Otimização energoeconômica de uma unidade de processamento de gás natural

Abstract

In view of the growth in the use of natural gas in the national and global energy matrix, the importance of studies dealing with its processing increases. The Natural Gas Processing Unit (NGPU) is responsible for separating natural gas and its contaminants into components of commercial interest, for example, Natural Gas Liquid (NGL) and Sale Gas (SG). This processing can be carried out by means of different layouts of units, each with different characteristics regarding energy consumption, raw material, separation efficiency and safety levels. Among the different processing unit layouts, it is possible to mention considerable differences regarding the cooling mechanism used in such a way that the combination of turboexpander with mechanical refrigeration (TEMR) stood out for its profitability and recovery efficiency. However, it is necessary to evaluate the energetic behavior of the mechanism with different qualities of the natural gas that feeds the unit. In this work, an optimization study of a unit represented by the TEMR scheme contained in the base case was carried out by minimizing the specific energy consumption [kWh/kg of SG] including the restriction of a minimum limit of 90% of C3+ recovery and by manipulation of the following parameters: temperatures of the heat exchanger outlet flows, fractionating column pressures, splitter ratio, compressor and expander outlet pressures and reboilers temperatures. Three different natural gas riches were analyzed: 11.2% ( “Very rich”, composition 1), 8.9% (“rich”, composition 2) and 5.5% of C3+ (“poor”, composition 3). The results were submitted to evaluation criteria: energy, economic, recovery, production, safety and quality performance. There was a reduction in specific energy consumption [kWh/kg of SG] of 10.7% for the “very rich” input current, 12.9% for “rich” and 21.1% for “poor” and a consequent increase in the margin economic [R$/h] for the three types of feed gas stream by 0.03%, 0.05% and 0.35%, respectively. In addition, the reduction in specific energy consumption implied a reduction in aspects of the adopted safety criterion (higher process pressure and higher thermal load required in the chillers) and a decrease in the recovery performance of the flowchart by up to 3.8%; and met the regulated characteristics (quality) of the Sale Gas