Dynamic simulation of gas transmission pipelines in severe cryogenic conditions

Master Thesis

Chemical Engineering without orientation

Foreword

Today, simulation in processes can be an important tool to solve problems in various industries. A new idea that should be done in the real world by trial and error with a lot of costs and risks can be simulated in the environment of a strong software and the results can be used. Simulation can also be used to check and support the operation of a system. This thesis is a description of the implementation of an integrated simulation in gas transmission pipelines, and the main purpose of this simulation is to investigate and monitor the behavior of gas flow variables within the pipeline system, such as pressure, flow rate, speed and temperature. A change in ambient air temperature causes a change in gas consumption, and a change in gas consumption is equivalent to a change in the output flow rates of a pipeline system. Now, how will the behavior of the flow variables along the pipelines be? Is it possible for the gas pressure to drop so much in the branches of a pipeline system that it will eventually lead to a gas cut at that point? In this thesis, we try to investigate the effect of the increase in natural gas consumption resulting from a sharp drop in air temperature on the behavior of the natural gas fluid inside a pipeline system and to identify the points where there is a possibility of gas cutoff in these conditions. The second chapter is a review of past research. In the third chapter, the theory of simulation and governing equations of single-phase gas flow in dynamic mode are presented. The relationship between pipeline design and pressure drop in steady state is given and the effect of friction in different equipment is described. In the fourth chapter, Ardabil gas transmission pipeline system and OLGA simulation software are introduced and the working method is explained. The configuration of the pipeline system, pressure reduction stations, pressure boosting, pipeline specifications, topography and pipeline route are shown and the simulation model is described. In the fifth chapter, in order to obtain extreme cryogenic conditions, information on gas consumption and air temperature of different cities has been evaluated. An attempt has been made to understand the issue against the mentioned information, and gas usage patterns have been obtained as a function of air temperature and prepared for simulation in severe cryogenic conditions. The results of the simulation of the pipeline system in the OLGA software environment have been analyzed in two operating and cryogenic acute modes, and the pressure changes of the sampling points of the pipeline system have been evaluated against time changes as a reaction to the conditions applied in the simulation. Also, to analyze the condition of the pipeline system, the behavior of gas flow variables along the pipelines, in both operational and extreme cryogenic conditions, has been compared and investigated. The sixth chapter has been completed with summary and conclusion.

Abstract

In this research, the gas transmission pipeline system of Ardabil province is dynamically simulated. The purpose of this project is to determine the points of the pipelines where, with the decrease in air temperature in winters and the subsequent increase in gas consumption, the possibility of reducing the pressure in the pipelines and finally; There is a possibility of gas cut. Identifying these areas will be of great help to those involved in the gas supply sector to carry out preventive operations. The software used for this simulation is OLGA. This software is used to simulate the network of oil and gas transmission pipelines and process equipment. OLGA's dynamic capabilities increase its application range compared to static simulators. In this research, the topography and characteristics of gas transmission pipelines in Ardabil province, including fittings, valves, compressors and related equipment, are defined in the software. The natural gas fluid properties package was created by PVTsim software. The information of pressure, temperature and flow related to the winter of 2010 has been used in the simulation. First, the simulation has been performed dynamically in operational conditions to predict the duration of 12 hours. Then, the pattern of gas consumption in different cities of Ardabil province has been obtained by fractional degree day method.Assuming an air temperature of -20 degrees Celsius as an extreme freezing condition, the gas consumption of cities has been calculated at this temperature and a simulation has been performed with these new uses. The validation of the obtained results in operational conditions compared to the actual values ??of 2019 shows a good agreement. The simulation in extreme cold conditions shows that at the moment of 6.2 hours, in some branches of the 16-inch Parsabad pipeline, the pressure drops to the point of gas cut. The results of simulations are used to investigate and study the behavior of gas flow in pipelines and the profiles of pressure, temperature, flow rate and gas velocity are drawn. The results show that the trend of gas pressure changes in the pipelines is consistent with the topography of the routes; The gas of the 8-inch ankle pipeline has a reverse movement due to the gas flow with a higher pressure of the 20-inch reinforcement pipeline; As a result of the reduction of the flow rate passing through the compressor in severe cryogenic conditions, the compression ratio and temperature of the gas leaving the compressor increases and the pressure in the 16-inch pipeline drops greatly in severe cryogenic conditions. Then, as a solution, the valves of the auxiliary pipeline to transfer gas from the 30-inch pipeline of the power plant to the 25th kilometer of the 16-inch pipeline of Parsabad were placed in an open position and the simulation was performed. The results obtained in this case indicate the improvement of the situation and the increase of pressure in the 16 inch pipeline and the continuation of gas supply for 5.6 hours more than the previous situation. The results of this research can be used in the optimization, design and future development of the pipeline system.

Key words: simulation, dynamics, pipelines, gas consumption, pressure drop

Chapter one: the importance of natural gas; Gas transmission pipelines and simulation

1-1           Introduction

Natural gas is used as urban and industrial fuel and raw material in factories. Among the uses of natural gas as urban fuel, we can mention home heating, water heaters, and gas stoves. It is used as an industrial fuel in cement factories, clay bricks, glass making, industrial boilers and food industry factories. It is also used as a raw material for petrochemical industries to produce hydrogen and ammonia.

From an environmental point of view, natural gas is considered a clean fuel because it has important environmental advantages compared to other fossil fuels. The reason for the superiority of natural gas over crude oil or coal is that its pollution of sulfur dioxide, nitrogen dioxide and carbon dioxide is very low. This helps to reduce problems caused by acid rain, ozone layer destruction or problems caused by greenhouse gases [1]. The most important way to transfer natural gas from production points to consumption points is gas transmission pipelines. The simulation of gas flow inside the pipeline is used to investigate the condition and efficiency of pipelines in different conditions.

In this chapter, while referring to the position of Iran in the world's gas resources, the basic concepts of natural gas, including phase behavior, composition of natural gas, pipeline system and equipment used in pipelines and pressure boosting stations are discussed. Also, the importance and applications of simulating the flow of gas inside pipelines are stated.

1-2           Iran's position in the world's gas resources

Gas reserves are also divided into three categories, like oil reserves, established reserves, probable reserves and possible reserves. According to table (1-1), based on the latest reports until the end of 2010, the world's gas reserves are estimated at around 187.1 trillion cubic meters, with Russia having the largest gas resources in the world with 44.8 trillion cubic meters and a share of 23.9%, followed by Iran with 29.6 trillion cubic meters and a share of 15.8%, the second gas source in the world and Qatar with 25.3 trillion cubic meters and with a share of 13.5% of the world's reserves, they are the third largest source of gas in the world[2].

Abstract

In this study, Ardabil province natural gas pipelines system has been simulated dynamically.