1. 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

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

3. KINETICS SUPPLIED Equation: Constants: K 1 = k 01 exp(-E 1 /RT) K 2 = k 02 exp(-E 2 /RT) K 01 = 1.78954*10 4 kgmol/m 3 -hr-atm 1.5 K 02 = 2.5714*10 16 kgmol-atm 0.5 /m 3 -hr E 1 = 20,800 kcal/kgmol E 2 = 47,400 kcal/kgmol

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

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

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

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

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

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

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

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

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

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