https://doi.org/10.1016/j.ijggc.2015.12.009
“The mass inertia of the solvent inventory has an effect on the dynamic response of the plant. Solvent circulation time is obviously dependent on total solvent inventory, which is limited in this study to as little as practically possible. Circulation times at several different liquid flow rates are estimated by inducing a step-change in main pump output, and observing the time required for this to produce a liquid level change of 10% at several points in the liquid line. The solvent pump reaches its new setpoint within approx. 10 s and does not contribute significantly to the overall circulation time. The results are summarised in Table 3. Circulation times between each individual section of the plant, and relevant circulation times at 50% of solvent baseload flow rate are estimated using the measured values and indicated by *. Circulation times through sumps are estimated using (circulation time = liquid holdup/volumetric flow rate) (Fig. 2).
Table 3. Summary of plant solvent circulation times.
| Liquid flow rate (as percentage of baseload) | Circulation time from main solvent pump to top of absorber sump (min:sec) | Circulation time from top of absorber sump to top of desorber sump (min:sec) | Circulation time from top of desorber sump to top of 500 l liquid tank (min:sec) | Circulation time from top of liquid tank to main solvent pump (min:sec) | Total circulation time required (min:sec) | Circulation time from lean sample point to rich sample point* (min:sec) |
|---|---|---|---|---|---|---|
| 100 | 1:07 | 6:03 | 8:35 | 21:10 | 36:55 | 30:17* |
| 75 | 1:20 | 7:25 | 10:36 | 32:17 | 51:38 | 43:38* |
| 50* | 1:49* | 8:40* | 14:25* | 48:58* | 73:52* | 63:11* |
| 30 | 2:20 | 12:18 | 19:40 | 79:35 | 113:08 | 97:50* |
- *
-
Estimated values based on other measurements.
Fig. 2. Block diagram of plant solvent circulation times (in min:sec) for baseload solvent flow rate. * indicates estimated value based on other measurements.
Solvent circulation times have a direct impact on the dynamic response of the capture plant and affect the time delay between when a process parameter is changed and when the impact of that change is observed in solvent loading and plant capture rate. For example, after a change in steam flow rate to the reboiler, it takes approximately 30 min (Table 3) at 100% baseload flow rate for the change in lean solvent loading to be observed at the rich solvent sampling point based on solvent circulation times. The amount of solvent in the vessel sumps and solvent tank, and solvent mixing also has an impact on the dynamic response of the plant (Table 4).
Table 4. Estimated circulation times (in min:sec) between relevant plant locations.
| Empty Cell | 100% of baseload | 75% of baseload | 50% of baseload | 30% of baseload |
|---|---|---|---|---|
| Main solvent pump – absorber inlet | 0:20* | 0:27* | 0:40* | 0:55* |
| Absorber inlet – top of absorber sump | 0:47* | 0:53* | 1:09* | 1:25* |
| Top of absorber sump – rich sampling port (absorber sump outlet) | 2:10* | 2:55* | 3:24* | 5:08* |
| Rich sampling port (absorber sump outlet) – desorber inlet | 3:06* | 3:37* | 4:07* | 5:45* |
| Desorber inlet – top of desorber sump | 0:47* | 0:53* | 1:09* | 1:25* |
| Top of desorber sump – lean sampling port (desorber sump outlet) | 2:45* | 3:30* | 5:25* | 9:03* |
| Lean sampling port (desorber sump outlet) – top of 500l solvent tank | 5:50* | 7:06* | 9:00* | 10:37* |
| Top of 500 l solvent tank – main solvent pump | 21:10* | 32:17* | 48:58* | 79:35* |
| Total circulation time | 36:55 | 51:38 | 73:52* | 113:53 |
“