SUPERPRO-BASED AMMONIA PLANT RETROFIT

REACTOR OPTIMIZATION THROUGH ASPEN ASSISTANCE

NORTH CAROLINA STATE UNIVERSITYDEPARTMENT OF CHEMICAL ENGINEERING

SPRING 2004

R. BARNHILLE. FABRICIUSA. HERRMANND. JONES

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

KINETICS SUPPLIED

Equation:

Constants: K1 = k01exp(-E1/RT)

K2 = k02exp(-E2/RT)

K01 = 1.78954*104 kgmol/m3-hr-atm1.5

K02 = 2.5714*1016 kgmol-atm0.5/m3-hr

E1 = 20,800 kcal/kgmol

E2 = 47,400 kcal/kgmol

)1(

/

3

2

3

5.12

232

5.121

3

N

HNHHN

PK

PPKPPKfK

CHALLENGES WITH SUPERPRO

Rate equation proves to be incompatible with given data SuperPro only accepts

simplified kinetics However, SuperPro

offers extent of reaction option

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

ASPEN SIMULATION: STEP 1

Setup Aspen to run ammonia reaction with supplied kinetics

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

ASPEN SIMULATION: STEP 3

Simulate the reactor at an “initial composition” obtained

Record SuperPro required Data Temperature Pressure Reactor Size Extent of Reaction

SUPERPRO SIMULATION: STEP 1

Plug the results from Aspen reactor simulation into SuperPro simulation (shown on next two slides) Conduct mass and energy balances

SUPERPRO SIMULATION: STEP 1a

Set Aspen operating temperature of the reactor

SUPERPRO SIMULATION: STEP 1b

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

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

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)