Model application

InTech, Feb 2004 by Muravyev, Aleksandr I, Kelahan, Robert C, Kowallis, Paul C, Torgesen, Greg L

Process performance

The original reason to develop a dynamic model of the vent system was to analyze pressure profiles in the off-gas system after an incident that caused equipment damage. Minor alterations in the process, over the years, raised concerns that the off-gas system might not be adequately protected. Besides, they had to investigate the potential process sources for the incident. The main suspected reason was variation in composition of one of the furnace feed streams. The simulation provided an estimation of the feed inconsistencies potentially causing this effect. The maintenance improvements, based on these estimations, helped to decrease the risk of the accidents. Generally, the simulations demonstrated sufficient protection of the process in the abnormal situations. Nevertheless, the additional design step will help augment the process safety.

The dynamic model will help modify the plant venting system. The users ended up creating the model of a new pressure-relief device, and then they tested its behavior before installation. Using simulation, the users were able to evaluate the different configurations of the vent system with the new device and then determine the optimal parameters of the seal. Particularly, they estimated the optimal relieving points for the furnace/processing units depending on the furnace capacity and dynamics (volume and resistance) of the units.

By using extensive simulation, the responses of the existing and the modified vent system have undergone comparison at the most probable levels of furnace pressure excursions. Two typical magnitudes, moderate and severe, and several shapes of the pressure impulse (rates of the pressure rise), were simulated in different combinations. The plots present the pressure profiles for different points along the furnace/processing unit. The new system has shown superior performance, providing 10-12% less peak system pressure, with a more favorable (safe) sequence of the relief devices opening and higher resealing capabilities. The modified system has undergone successful implementation for one of the furnaces. The results of its functioning are close to those predicted in simulation. An implementation of the modernized vent system is Currently under way for two other furnace units.

Behind the byline

Aleksandr I. Muravyev works at MYNAH Technologies in Chesterfield, Mo. Robert C. Kelahan works at Monsanto Co.'s St. Louis office, and Paul C. Kowallis and Greg L. Torgesen work at Monsanto's Soda Springs, Idaho offices.