Process description for the A6G example simulation
- Last UpdatedJul 07, 2025
- 5 minute read
This simulation includes one equilibrium reactor (RX7) and three flash drums (D6, D7, and D8).
The feed to the synthesis loop (SRC1) comes from reformed natural gas and is equivalent to a natural gas consumption of six million square cubic feet per day (SCFD). We mix this fresh feed with a recycle stream from the flash drum immediately downstream of RX7 (D6). We send this mixed feed to the D7 flash drum.
D7 chills the fluid to remove excess ammonia (introduced by the recycle) from the vapor and to produce additional liquid ammonia. The resulting vapor product (S6) serves as the equilibrium reactor feed.
We want to study how the concentration of the inert components in the reactor feed affect the conversion to ammonia and by extension the concentration of ammonia in the final ammonia product. Therefore, we add a flowsheet variable (Rx_Feed_Inerts) to the simulation as well as a flowsheet equation (Eqn1) to determine this value. We calculate the Rx_Feed_Inerts variable as the sum of the compositions of the two inert components (argon and methane) in the reactor feed:
We use two heat exchangers to preheat the reactor feed. The first heat exchanger (X4) uses the feed to D7 as the hot, tube-side fluid. The second heat exchanger (FDEF) uses the reactor product (S9) as the hot, tube-side fluid.
We feed the reactor product to D6, which chills the reactor product and provides the primary separation. We split the vapor product of D6 between a purge stream (S18) and a recycle stream (S19). The purge stream helps reduce the accumulation of inert components in the synthesis loop, which affects the ammonia conversion in RX7. The recycle stream returns unreacted feed to the synthesis loop.
We add a Compressor (CP4) to the recycle stream to maintain pressure in the synthesis loop. We also add Valves (XV1, XV2, XV3, and XV4) on every feed stream to a flash drum to facilitate the pressure requirements for each flash drum.
We combine the liquid products from D7 and D6 in a final flash drum (D8) to produce the final liquid ammonia product (S16).
The following table shows the compositions and thermal condition of the feed to the synthesis loop.
Table 1: Feed conditions
|
Variable |
Description |
Value |
UOM |
|---|---|---|---|
|
SRC1.F* |
Molar flow rate |
3256.54 |
lbmol/h |
|
SCR1.P |
Pressure |
4955 |
psig |
|
SRC1.T |
Temperature |
95 |
°F |
|
SRC1.M[ARGON] |
Unnormalized molar feed composition of argon |
9.58 |
lbmol |
|
SRC1.M[H2] |
Unnormalized molar feed composition of hydrogen |
2424.3 |
lbmol |
|
SRC1.M[N2] |
Unnormalized molar feed composition of nitrogen |
807.5 |
lbmol |
|
SRC1.M[C1] |
Unnormalized molar feed composition of methane |
15.16 |
lbmol |
|
SRC1.M[NH3] |
Unnormalized molar feed composition of ammonia |
0 |
lbmol |
* You must switch specifications to set this value. See Process mode for the A6G example simulation for more information.
The following table shows the specified process conditions throughout the simulation. It shows only the values that differ from the default value.
Table 2: Process conditions
|
Variable |
Description |
Value |
UOM |
|---|---|---|---|
|
D7.P* |
Pressure of the D7 flash drum |
4840 |
psig |
|
D7.T* |
Temperature of the D7 flash drum |
40 |
°F |
|
X4.Tso* |
Shell-side outlet temperature for the X4 heat exchanger |
85 |
°F |
|
X4.DPs |
Shell-side pressure drop for the X4 heat exchanger |
50 |
psi |
|
X4.DPt |
Tube-side pressure drop for the X4 heat exchanger |
50 |
psi |
|
FDEF.Tto* |
Tube-side outlet temperature for the FDEF heat exchanger |
430 |
°F |
|
FDEF.DPs |
Shell-side pressure drop for the FDEF heat exchanger |
30 |
psi |
|
FDEF.DPt |
Tube-side pressure drop for the FDEF heat exchanger |
30 |
psi |
|
RX7.DP |
Pressure drop for the RX7 equilibrium reactor |
30 |
psi |
|
RX7.DT |
Approach temperature for the RX7 equilibrium reactor |
20 |
°F |
|
D6.P* |
Pressure of the D6 flash drum |
4660 |
psig |
|
D6.T* |
Temperature of the D6 flash drum |
85 |
°F |
|
D8.P* |
Pressure of the D8 flash drum |
350 |
psig |
* You must switch specifications to set this value. See Process mode for the A6G example simulation for more information.
The following table shows the equipment sizes and configuration throughout the simulation. It shows only the values that differ from the default value.
Table 3: Equipment sizes and configuration
|
Variable or Parameter |
Description |
Value |
UOM |
|---|---|---|---|
|
XV1.ManPos |
Manual position of the XV1 valve |
0.5 |
fraction |
|
D7.InletPressures* |
Parameter to determine whether the flash drum allows any feed inlet pressure or sets all feed inlet pressures equal to each other |
Balanced |
- |
|
D7.HeadRatio |
Ratio of the head length to the radius of the cylinder for the D7 flash drum |
0 |
- |
|
X4.HotSide |
Parameter to determine which side of the X4 heat exchanger is the hot side |
Tube |
- |
|
X4.Feed |
Parameter to determine whether the X4 heat exchanger includes feed ports for the shell side, the tube side, or both sides |
BothSide |
- |
|
FDEF.HotSide |
Parameter to determine which side of the FDEF heat exchanger is the hot side |
Tube |
- |
|
FDEF.Feed |
Parameter to determine whether the FDEF heat exchanger includes feed ports for the shell side, the tube side, or both sides |
BothSide |
- |
|
RX7.RxnModelType |
Parameter to determine which reaction submodel the RX7 reactor uses |
Models.EQAmmonia |
- |
|
XV2.ManPos |
Manual position of the XV2 valve |
0.5 |
fraction |
|
D6.InletPressures* |
Parameter to determine whether the flash drum allows any feed inlet pressure or sets all feed inlet pressures equal to each other |
Balanced |
- |
|
D6.HeadRatio |
Ratio of the head length to the radius of the cylinder for the D6 flash drum |
0 |
- |
|
XV3.ManPos |
Manual position of the XV3 valve |
0.5 |
fraction |
|
XV4.ManPos |
Manual position of the XV4 valve |
0.5 |
fraction |
|
D8.InletPressures* |
Parameter to determine whether the flash drum allows any feed inlet pressure or sets all feed inlet pressures equal to each other |
Balanced |
- |
|
D8.HeadRatio |
Ratio of the head length to the radius of the cylinder for the D8 flash drum |
0 |
- |
|
SP1.RatioSum** |
Summation of the outlet stream flow ratios for the SP1 splitter |
1 |
- |
|
Purge.F** |
Molar flowrate for the Purge sink |
70 |
lbmol/h |
|
CP4.eta |
Isentropic efficiency for the CP4 compressor |
0.95 |
fraction |
|
MX1.InletPressures* |
Parameter to determine whether the mixer allows any feed inlet pressure or sets all feed inlet pressures equal to each other |
Balanced |
- |
* You must switch specifications after you set this parameter value. See Process mode for the A6G example simulation for more information.
** You must switch specifications to set this value. See Process mode for the A6G example simulation for more information.