https://doi.org/10.1016/j.ijggc.2015.12.009
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The flow rate of steam to the reboiler is increased rapidly to 200% at t = 0 and remains at this value for 41 min, while all other plant parameters remain constant. Plant data continue to be obtained for an additional 50 min after steam had been ramped down, in order to observe any further effects on the response of the plant.
It is important to note that the plant may not have fully reached a steady-state operating condition at the start of this scenario, with the initial capture rate at 85% and a lean loading of 0.250 mol/mol.
Lean loading at the desorber outlet is observed to decrease steadily from 0.250 mol/mol after the flow rate of steam is increased at t = 0, eventually stabilising at around 0.2 mol CO2/mol amine (Fig. 14b). These titration data are shifted to the time at which each sample would reach the absorber inlet in Fig. 14c. The online solvent sensor output displays similar behaviour, but the decrease in lean loading appears less rapid. As the sensor is located after the main solvent tank, any rapid changes in lean loading at the desorber outlet are dampened when that packet of solvent reaches the sensor, due to mixing in the solvent tank, as previously explained. The continuous measurement suggests that the lean loading at the absorber inlet begins to decrease before any solvent which has undergone a greater degree of regeneration due to increased steam flow is expected to reach the absorber inlet. As the plant is not initially at baseload, it is not possible to attribute the observed increase in capture rate and decrease in lean loading at the absorber inlet between t = 0 and t = 25 min to the frequency response operation.
Fig. 14. (a) Gas, liquid and steam flow rates as percentage of previously-defined baseload operation, frequency response scenario. (b) Rich and lean solvent CO2 loading, desorber and reboiler temperatures frequency response scenario. (c) Lean and rich solvent loading bench measurements, time-shifted to absorber inlet and outlet respectively, continuous lean loading measurement, CO2 capture rate, frequency response scenario. (d) Predicted real-time solvent capacity and CO2 capture rate, frequency response scenario.
Fig. 14c and d shows that, when solvent which has undergone a greater degree of regeneration due to increased steam flow starts entering the absorber from t = 26 min onwards, the increase in solvent working capacity results in an increase in capture rate from 88% to 90%. Steam flow is turned down to 100% of baseload at t = 41 min. The response of the capture rate, starting at t = 70 min, corresponds to an increase in lean solvent loading at the absorber inlet (Fig. 14c).
A titration lean loading measurement at t = 66 min (Fig. 14b)/t = 93 min (Fig. 14c) appears to be anomalous as there is no significant change in the capture rate, and it deviates significantly from the online lean loading measurement at this point in time.
The calculated real-time solvent working capacity (Fig. 14d) follows well the trend of the capture rate over the course of the whole experiment. Accurate monitoring and prediction of real-time working capacity via continuous loading measurements at the absorber inlet and outlet could prove to be a key metric in future advanced control systems for dynamic post-combustion capture.
As there is no significant change in absorber temperature profile, the maximum dT over the course of the experiment being an increase of 1.68 °C at height of 3.6 m, absorber temperature data are not reported for this scenario.
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