Diseño de la unidad de destilación criogénica para la obtención de helio a partir de gas natural

Abstract

This work deals with the production of helium. This is a gas which is scare in nature, expensive and has a diverse demand such as magnetic resonance imaging (MRI), pipeline leak detection, repairing of equipment that need an inert atmosphere and missiles fuel. More precisely this study consists of the design of a cryogenic distillation unit for helium production. Any cryogenic distillation unit can have four settings. In this project the setting constituted by two column has been chosen: one high pressure column; where helium is separated from the rest of the components, and one low pressure column, where the remaining components (nitrogen and methane) are separated from each other. At the same time, one liquid-vapor separator and three coil-wound heat exchangers has been designed. The raw material used is the cheapest currently available: Natural Gas. Using this raw material permits obtaining nitrogen and methane as byproducts. Main results from this study are: 1. The technical study -see Chapter 3- reveals that both high and low pressure columns should have similar dimensions. The reason for this similarity is that helium is a very volatile gas and therefore evaporates easily. On the contrary, nitrogen and methane has similar boiling points. Thus, in theory, the second column should be bigger. However, since the second column has two feeding streams its size not as big as it’s supposed to be. 2. The area of the main heat exchanger, a coil-wound type, goes from 45 to 3 m2. The difference in the heat exchange area depends on the difference in temperature between the input and the output streams. 3. Given the cryogenic character of all relevant fluids in this process some measures need to be taken, in order to maximize the safety of the working environment. For instance, proper clothing, adequate ventilation, N2 and methane concentration control in the environment or control the percentage of methane in order to avoid labor ricks xviii 4. Environmental hazards have also been considered and some preventive measures have been proposed –see Chapter 4. 5. As expected, the most important part of the investment is the fix capital, in particular, the equipment. 6. The economic study –see Chapter 5- shows that the production of byproducts (nitrogen and methane) make an important contribution to the sales income