SUPERPROBASED AMMONIA PLANT RETROFIT REACTOR OPTIMIZATION THROUGH ASPEN

SUPERPRO-BASED AMMONIA PLANT RETROFIT REACTOR OPTIMIZATION THROUGH ASPEN ASSISTANCE NORTH CAROLINA STATE UNIVERSITY DEPARTMENT OF CHEMICAL ENGINEERING SPRING 2004 R. BARNHILL E. FABRICIUS A. HERRMANN D. JONES

PROJECT OVERVIEW n n Objective: make 3000 metric tons of liquid ammonia per day Two options for Super. Pro simulation n Single-pressure process n Dual-pressure process Compare and contrast n Economics (capital and operational) n Environmental (emissions and solid/liquid) Determine the most profitable process

KINETICS SUPPLIED n Equation: n Constants: n n n K 1 = k 01 exp(-E 1/RT) K 2 = k 02 exp(-E 2/RT) K 01 = 1. 78954*104 kgmol/m 3 -hr-atm 1. 5 K 02 = 2. 5714*1016 kgmol-atm 0. 5/m 3 -hr E 1 = 20, 800 kcal/kgmol E 2 = 47, 400 kcal/kgmol

CHALLENGES WITH SUPERPRO n Rate equation proves to be incompatible with given data n n Super. Pro only accepts simplified kinetics However, Super. Pro offers extent of reaction option

ASPEN THEORY n Supply Super. Pro with extent of reaction n n Advantages n n n Optimize through analysis of critical parameters that affect the rate of reaction Basic Aspen simulation with one piece of equipment Aspen supports supplied kinetics Disadvantages n n Basic knowledge of Aspen required Iterative process between two simulation systems

ASPEN SIMULATION: STEP 1 n Setup Aspen to run ammonia reaction with supplied kinetics

ASPEN SIMULATION: STEP 2 n Run simulations varying critical parameters n n n Temperature Pressure Reactor Size Composition of inlet stream Study the relationship between the different parameters of the reaction n Plotting the information and studying trends works well

ASPEN SIMULATION: STEP 3 Simulate the reactor at an “initial composition” obtained n Record Super. Pro required Data n n n Temperature Pressure Reactor Size Extent of Reaction

SUPERPRO SIMULATION: STEP 1 n Plug the results from Aspen reactor simulation into Super. Pro simulation (shown on next two slides) n Conduct mass and energy balances

SUPERPRO SIMULATION: STEP 1 a n Set Aspen operating temperature of the reactor

SUPERPRO SIMULATION: STEP 1 b n Set the extent of reaction that agrees with the Aspen data

SUPERPRO SIMULATION: STEP 2 Study the effects that the new outlet stream (from the reactor) has on the inlet stream n Take new inlet stream data and plug back into Aspen and re-run the simulations n n This step is the final step in the cycle between Aspen and Super. Pro – this cycle is to be repeated several times until optimal results are obtained

SUMMARY AND KEY POINTS n Iterations between Aspen and Super. Pro require the use of multiple sets of data n n Keep accurate records Optimize the system based on costs n Cost of pressurizing the feed stream n n Cost of compressors Energy cost of the compressors Cost of cooling the reactor to the optimal temperature Cost of the reactor (size dependent)