DD
D. Dell'Acqua
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Carbon capture and storage (CCS) requires captured CO2 to be purified and dried (i.e. conditioned) before it can be compressed or liquefied for transport, yet the adsorption dryers that remove water are routinely represented in process models as simplified separators with a fixed removal efficiency. Their regeneration energy, a contributor to the conditioning penalty that this study sets out to quantify, is left uncharacterised, because systematic dynamic data for commercial desiccants under CO2-conditioning conditions are largely absent from the open literature. This gap prevents reliable process design and, in particular, hides where the energy-optimal operating window of the dryer actually lies.
This thesis characterises two commercial adsorbents, silica gel and zeolite 4A, and integrates validated dryer models into complete conditioning chains that deliver a liquid or supercritical CO2 end product. Zeolite 4A is the industrial standard for this duty and, by virtue of its stronger affinity for water, is expected to outperform silica gel; it does so, however, at the cost of more demanding regeneration conditions, whereas silica gel regenerates at much lower temperatures and can potentially draw on low-grade waste heat. This raises the central question of whether, over the long run and at cyclic steady state, the milder regeneration requirements of silica gel make it the more efficient choice, or whether zeolite 4A retains its advantage.
Breakthrough experiments were carried out on a mixSorb L dynamic sorption analyser at pressures up to 10 bar across adsorption and regeneration temperatures, with a dedicated CO2-carrier run to bound competitive adsorption. Toth and dual-site Langmuir isotherms and LDF mass-transfer coefficients were fitted to the data in Python and validated in a cyclic bed model in Aspen Adsorption, which was then implemented in Aspen Plus flowsheets of three transport routes: subcritical liquefaction at 16 bar, low-pressure ship transport at 8 bar, and supercritical pipeline transport at 150 bar.
The results give explicit design rules: adsorb cold and at pressure, treat the dryer as a polishing step on a stream already dried by compression with intercooling, and regenerate hot with a minimal purge. Measuring the true working capacity and kinetics shows standard literature practice to be heavily oversized: a 2% purge suffices where 10% is customary, cutting dryer-loop energy fivefold, from 1.6 to 0.3 kWh/t, in the 16 bar case. At the process scale, the transport route dominates: roughly 30 kWh/t separates the chains, against 4 kWh/t or less between sorbents within a chain. Silica gel proves a genuine alternative to molecular sieves: where it can occupy the same downstream position as the zeolite, it matches its specific energy consumption while regenerating at less than half the temperature, so low-grade waste heat suffices. Its penalties in the other two routes are mechanical, set by the pressure tolerance of the pellet batch rather than by thermodynamics, which suggests a pressure-qualified grade would reduce the material choice to cost rather than energy. ...
This thesis characterises two commercial adsorbents, silica gel and zeolite 4A, and integrates validated dryer models into complete conditioning chains that deliver a liquid or supercritical CO2 end product. Zeolite 4A is the industrial standard for this duty and, by virtue of its stronger affinity for water, is expected to outperform silica gel; it does so, however, at the cost of more demanding regeneration conditions, whereas silica gel regenerates at much lower temperatures and can potentially draw on low-grade waste heat. This raises the central question of whether, over the long run and at cyclic steady state, the milder regeneration requirements of silica gel make it the more efficient choice, or whether zeolite 4A retains its advantage.
Breakthrough experiments were carried out on a mixSorb L dynamic sorption analyser at pressures up to 10 bar across adsorption and regeneration temperatures, with a dedicated CO2-carrier run to bound competitive adsorption. Toth and dual-site Langmuir isotherms and LDF mass-transfer coefficients were fitted to the data in Python and validated in a cyclic bed model in Aspen Adsorption, which was then implemented in Aspen Plus flowsheets of three transport routes: subcritical liquefaction at 16 bar, low-pressure ship transport at 8 bar, and supercritical pipeline transport at 150 bar.
The results give explicit design rules: adsorb cold and at pressure, treat the dryer as a polishing step on a stream already dried by compression with intercooling, and regenerate hot with a minimal purge. Measuring the true working capacity and kinetics shows standard literature practice to be heavily oversized: a 2% purge suffices where 10% is customary, cutting dryer-loop energy fivefold, from 1.6 to 0.3 kWh/t, in the 16 bar case. At the process scale, the transport route dominates: roughly 30 kWh/t separates the chains, against 4 kWh/t or less between sorbents within a chain. Silica gel proves a genuine alternative to molecular sieves: where it can occupy the same downstream position as the zeolite, it matches its specific energy consumption while regenerating at less than half the temperature, so low-grade waste heat suffices. Its penalties in the other two routes are mechanical, set by the pressure tolerance of the pellet batch rather than by thermodynamics, which suggests a pressure-qualified grade would reduce the material choice to cost rather than energy. ...
Carbon capture and storage (CCS) requires captured CO2 to be purified and dried (i.e. conditioned) before it can be compressed or liquefied for transport, yet the adsorption dryers that remove water are routinely represented in process models as simplified separators with a fixed removal efficiency. Their regeneration energy, a contributor to the conditioning penalty that this study sets out to quantify, is left uncharacterised, because systematic dynamic data for commercial desiccants under CO2-conditioning conditions are largely absent from the open literature. This gap prevents reliable process design and, in particular, hides where the energy-optimal operating window of the dryer actually lies.
This thesis characterises two commercial adsorbents, silica gel and zeolite 4A, and integrates validated dryer models into complete conditioning chains that deliver a liquid or supercritical CO2 end product. Zeolite 4A is the industrial standard for this duty and, by virtue of its stronger affinity for water, is expected to outperform silica gel; it does so, however, at the cost of more demanding regeneration conditions, whereas silica gel regenerates at much lower temperatures and can potentially draw on low-grade waste heat. This raises the central question of whether, over the long run and at cyclic steady state, the milder regeneration requirements of silica gel make it the more efficient choice, or whether zeolite 4A retains its advantage.
Breakthrough experiments were carried out on a mixSorb L dynamic sorption analyser at pressures up to 10 bar across adsorption and regeneration temperatures, with a dedicated CO2-carrier run to bound competitive adsorption. Toth and dual-site Langmuir isotherms and LDF mass-transfer coefficients were fitted to the data in Python and validated in a cyclic bed model in Aspen Adsorption, which was then implemented in Aspen Plus flowsheets of three transport routes: subcritical liquefaction at 16 bar, low-pressure ship transport at 8 bar, and supercritical pipeline transport at 150 bar.
The results give explicit design rules: adsorb cold and at pressure, treat the dryer as a polishing step on a stream already dried by compression with intercooling, and regenerate hot with a minimal purge. Measuring the true working capacity and kinetics shows standard literature practice to be heavily oversized: a 2% purge suffices where 10% is customary, cutting dryer-loop energy fivefold, from 1.6 to 0.3 kWh/t, in the 16 bar case. At the process scale, the transport route dominates: roughly 30 kWh/t separates the chains, against 4 kWh/t or less between sorbents within a chain. Silica gel proves a genuine alternative to molecular sieves: where it can occupy the same downstream position as the zeolite, it matches its specific energy consumption while regenerating at less than half the temperature, so low-grade waste heat suffices. Its penalties in the other two routes are mechanical, set by the pressure tolerance of the pellet batch rather than by thermodynamics, which suggests a pressure-qualified grade would reduce the material choice to cost rather than energy.
This thesis characterises two commercial adsorbents, silica gel and zeolite 4A, and integrates validated dryer models into complete conditioning chains that deliver a liquid or supercritical CO2 end product. Zeolite 4A is the industrial standard for this duty and, by virtue of its stronger affinity for water, is expected to outperform silica gel; it does so, however, at the cost of more demanding regeneration conditions, whereas silica gel regenerates at much lower temperatures and can potentially draw on low-grade waste heat. This raises the central question of whether, over the long run and at cyclic steady state, the milder regeneration requirements of silica gel make it the more efficient choice, or whether zeolite 4A retains its advantage.
Breakthrough experiments were carried out on a mixSorb L dynamic sorption analyser at pressures up to 10 bar across adsorption and regeneration temperatures, with a dedicated CO2-carrier run to bound competitive adsorption. Toth and dual-site Langmuir isotherms and LDF mass-transfer coefficients were fitted to the data in Python and validated in a cyclic bed model in Aspen Adsorption, which was then implemented in Aspen Plus flowsheets of three transport routes: subcritical liquefaction at 16 bar, low-pressure ship transport at 8 bar, and supercritical pipeline transport at 150 bar.
The results give explicit design rules: adsorb cold and at pressure, treat the dryer as a polishing step on a stream already dried by compression with intercooling, and regenerate hot with a minimal purge. Measuring the true working capacity and kinetics shows standard literature practice to be heavily oversized: a 2% purge suffices where 10% is customary, cutting dryer-loop energy fivefold, from 1.6 to 0.3 kWh/t, in the 16 bar case. At the process scale, the transport route dominates: roughly 30 kWh/t separates the chains, against 4 kWh/t or less between sorbents within a chain. Silica gel proves a genuine alternative to molecular sieves: where it can occupy the same downstream position as the zeolite, it matches its specific energy consumption while regenerating at less than half the temperature, so low-grade waste heat suffices. Its penalties in the other two routes are mechanical, set by the pressure tolerance of the pellet batch rather than by thermodynamics, which suggests a pressure-qualified grade would reduce the material choice to cost rather than energy.