ANALYSIS AND SIMULATION OF AMMONIA SYNTHESIS REACTOR

Abstract

The growing need for fertiliser nitrogen to meet the demand of food grains for the rapidly increas-ing population gave a considerable fillip_ to the development of large size ammonia synthesis reactor to reduce capital and operating costs. The first ammonia reactor having a capacity of 30 Tons/day went on stream in Germany in 1913 and since then reactor size increased rapidly reaching upto 900 Tons/day in 1965 and upto 2000 Ton/day in 1975. its a consequence of the large size of ammonia reactor now in operation, the use of computer to control the operation has now becoce essential, when a computer is used for control, it is necessary to develop a mathematical model to realistically describe the performance of the reactor for feed forward and feed back control as well as off-line and on-line optimi cation. Ammonia is produced by catalytic reaction of hydrogen-and_nitrogen in the mole ratio of a-.7,7aroxi-mately 3:1 at elevated pressures (100 to 1000 kglcm2) and temperatures (400 to 650 °C). Single pass con-version from multibed reactors varies from 12 to D5 percent using doubly ipromoted iron catalyst. Since the reaction is exothermic reversible, it is essential 2 to carryout the reaction in various types of auto-thermic reactors with external heat exchange and quench type cooling and/or internal heat exchange in view of the critical behaviour, of ammonia synthesis reactor its analysis and simulation is most important. Van Heerden and Baddour and co-workers have presented the stability analysis of simplified single bed models. In a more recent study Shah has used a two bed adiabatic reactor model with cold shot cooling and external heat exchanger capacity. The nonidealities in rate equation and energy balance equation have also been accounted by him.. In this study a more general model for ammonia synthesis reactor is chosen for analysis and simula-tion. ICI type quench converter with three catalyst bed, bottom heat exchange and internal heat exchange capacity and with provisions for introducing quench gas at the inlet of each catalyst bed is chosen as the model. teaction rate, hbat capacity and heat of reactions relationships used in the present model are the same as used by Shah. The coupled non-linear mass and energy balance equations are solved numerically using Milne's predictor corrector method.