https://doi.org/10.1016/j.ijggc.2015.12.009
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A novel liquid sensor which differs from previous online measurement techniques (e.g. van Eckeveld et al., 2014) has been developed in-house at Edinburgh University. The sensor is used for continuous measurement of solvent lean loading in three of the dynamic scenarios.
It uses in situ measurements of physical properties to determine solvent loading and amine concentration, using proprietary intellectual property which is under development at the time of writing. Knowledge of the solvent CO2 loading in real-time can provide CCS plant operators with more frequent solvent analysis measurements, enabling them to react rapidly to perturbations or disturbances and develop automated process control systems for dynamic plant operation. Anecdotal evidence suggests that the established state-of the art for determination of solvent CO2 loading is accomplished via the use of an online auto-titrator which can take around 20 min or longer. As demonstrated in this work, plant conditions can change significantly within this period of time, therefore a more rapid method of solvent loading determination must be developed in order to incorporate solvent physical properties into future plant control systems.
The online sensor provides a continuous measurement of solvent loading and amine concentration. Further discussion of the operating principle is not possible as the technology is considered commercially sensitive.
Two locations are tested in this study, as illustrated in Fig. 4, Fig. 5, where the online solvent lean loading sensor takes a slipstream of liquid from the lean solvent line.

Fig. 4. Liquid loop for online solvent sensor – location upstream of solvent tank.

Fig. 5. Liquid loop for online solvent sensor – downstream of solvent tank.
For the “gas turbine startup” and “power output maximisation by capture plant decoupling” scenario, the sensor is located in the lean solvent line upstream of the solvent tank, between the desorber sump outlet and the main solvent tank. For the scenarios “power output maximisation by reboiler steam decoupling” and “frequency response” it is located downstream of the solvent tank and the main solvent pump. The sensor output is time-shifted to the point at which each “packet” of lean solvent analysed exits the desorber sump, for comparison with titration measurements. The sensor was unavailable for the “gas-turbine shutdown scenario”.
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