Dynamic Simulation of a Compressor Located in a Natural Gas Processing Unit Using EMSO Simulator

Abstract

Abstract Nowadays, a profound knowledge of all the stages involved in large scale processing of oil, natural gas or other fuels is necessary, due to the increased preoccupation with how to use the natural resources in a responsible way. The facilities for processing natural gas can be divided in two main parts, the first one responsible for the condensation of larger hydrocarbons (ethane, propane, butane, and the like) and the second one for the distillation of these larger hydrocarbons obtained. The first part of these facilities achieves a minimum temperature of -90°C due to a propane refrigeration system. This work studies a centrifugal compressor situated in the propane refrigeration system of a Natural Gas Liquid Recovery Unit (LRU) located in Macae (Rio de Janeiro, Brazil) -Petrobras Transporte S.A. (Transpetro). This compressor is one of the most complex and important equipments of the LRU. The main contribution of this paper is to propose a dynamic model for this centrifugal compressor based on mass and energy balance coupled with thermodynamics equations for the nonidealities of the gas. This dynamic model was used to simulate real conditions in some situations observed in the LRU, analyzing its open loop behavior and investigating its automatic control (controller tuning and closed loop behavior). The situations studied consisted in applying step disturbances to the centrifugal compressor and then interpreting the results in the light of the developed model. The modeling, simulation and control investigations were achieved using a Brazilian simulator called EMSO (Environment for Modeling, Simulation and Optimization), which is a graphical environment that can be freely modified by all users. In this environment, the language is fully object-oriented, allowing the user to develop complex dynamic or steady models by composing them with existent small models or build specific models by deriving standard ones. EMSO was developed by the ALSOC Project (Free Environment for Simulation, Optimization and Control of Processes) which supplies this software without costs for partners and universities, aiming therefore to standardize and spread out its use. The present work provides information on the operation and control of the compressor allowing the further development of abnormal situation management tools that will support the control system and provide an easier and safer operation of the LRU.