Thermal Operation Maps for Lamm–Honigmann Thermo-Chemical Energy Storage—A Quasi-Stationary Model for Process Analysis

dc.contributor.authorThiele, Elisabeth
dc.contributor.authorZiegler, Felix
dc.description.abstractThe Lamm–Honigmann energy storage is a sorption-based storage that can be arbitrarily charged and discharged with both heat and electrical power. The mechanical charging and discharging processes of this storage are characterized by an internal heat transfer between the main components, absorber/desorber and evaporator/condenser, that is driven by the working-fluid mass transferred between those components with the help of an expansion or compression device, respectively. In this paper, thermal operation maps for the mechanical charging and discharging processes are developed from energy balances in order to predict power output and storage efficiency depending on the system state, which, in particular, is defined by the mass flow rate of vapor and the salt mass fraction of the absorbent. The conducted method is applied for the working-fluid pair LiBr/H2O. In a first step, a thermal efficiency is defined to account for second-order losses due to the internal heat transfer; e.g., for discharging from a salt mass fraction of 0.7 to one of 0.5 (kg LiBr)/(kg sol.) at a temperature of 130 °C, it is found that the reversible shaft work output is reduced by 1.1–2.9%/(K driving temperature difference). For lower operating temperatures, the reduction is larger; e.g., at 80 °C, the efficiency loss due to heat transfer rises to 3.5%/K for a salt mass fraction of 0.5 (kg LiBr)/(kg sol.). In a second step, a quasi-stationary assumption leads to the thermal operation map from which the discharging characteristics can be found; e.g., at an operating temperature of 130 °C for a constant power output of 0.4 kW/m2 heat exchanger area at volumetric and inner machine efficiencies of ηi=ηvol=0.8 and for an overall heat-transfer coefficient of 1500 W/(K m2), the mass flow rate has to rise continuously from 1.5 to 4.2 g/(s m2), while the thermal efficiency is reduced from 97% to 83% due to this rise and due to the dilution of the sorbent. For this discharging scenario, the corresponding discharge time is 4.4 (min·m2)/(kg salt). This results in an exergetic storage density of around 29 Wh/(kg salt mass). For a charge-to-discharge ratio of 2 (charging times equals two times discharging time) and with the same heat-transfer characteristic and machine efficiencies for constant power charging with adiabatic compression, the system is charged at around 0.75 kW/m2, resulting in a round-trip efficiency of around 27%. Besides those predictions for arbitrary charging and discharging scenarios, the derived thermal maps are especially useful for the dimensioning of the storage system and for the development of control strategies. It has to be noted that the operation maps do not illustrate the transient behavior of the system but its quasi-stationary state. However, it is shown, mathematically, that the system tends to return to this state when disturbed.en
dc.description.sponsorshipDFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berlinen
dc.subject.ddc620 Ingenieurwissenschaften und zugeordnete Tätigkeitende
dc.subject.otherthermochemical energy storageen
dc.subject.otherabsorption storageen
dc.subject.otherstorage and conversionen
dc.subject.otherCarnot batteryen
dc.subject.otherthermal operation mapen
dc.subject.othercontrol strategyen
dc.subject.otherstorage efficiencyen
dc.subject.otherstorage capacityen
dc.titleThermal Operation Maps for Lamm–Honigmann Thermo-Chemical Energy Storage—A Quasi-Stationary Model for Process Analysisen
tub.affiliationFak. 3 Prozesswissenschaften::Inst. Energietechnik::FG Maschinen- und Energieanlagentechnikde
tub.affiliation.facultyFak. 3 Prozesswissenschaftende
tub.affiliation.groupFG Maschinen- und Energieanlagentechnikde
tub.affiliation.instituteInst. Energietechnikde
tub.publisher.universityorinstitutionTechnische Universität Berlinen


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