Kinetic Modelling of Ammonia Synthesis Loop with Three Bed Synthesis Reactor

Abstract

This project focuses of ammonia synthesis loop modeling. The modeling has been done on different software and then results are compared. Software used include Aspen hysys, Aspen plus and Matlab. Ammonia is an essential component in nitrogenous fertilizers. More than 80 % of ammonia produced is used as fertilizers. Ammonia in industry is manufactured by Haber process which involve fixing of hydrogen in an exothermic reaction. The process has not changed for over a century however advancements in the field of reactor design and catalyst has made the process more economically feasible. Today the FFC uses S-300 series Haldor Topsoe converter with single pass conversion of 15 %. The reactor has two internal heat exchangers which uses feed as coolant. The reactor is operated at pressure range of 240-250 kg/cm2 and temperature range of 400-500 ºC. As heat exchangers are essential part of reactor operation, it has been simulated by calculating film heat transfer coefficients in its tube and shell. Overall heat transfer coefficient is obtained from film heat transfer coefficients, shell thermal resistance and fouling coefficient. Three beds are taken as three separate plug flow reactors connected in series. Rate equation are used in designing the reactors. Moreover chillers, coolers and boilers used to cool and liquify ammonia are also designed. The effect of temperature and pressure on the rate of reaction is investigated along the length of beds. The purpose of modelling is to simulate the process and pinpoint the most suitable operating conditions. These conditions are chosen based on compromise between cost, rate of reaction and conversion.