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173 results on '"Ruuskanen, Vesa"'

33. Thermodynamic consistency of the equation of state of strongly interacting matter

Author

Randrup, Jorgen and Ruuskanen, Vesa P.

Subjects
Equation of State
Abstract

Addressing strongly interacting matter in the region of energy density where the hadronic gas phase coexists with the quark-gluon plasma phase, we discuss how thermodynamic consistency can be used to constrain the equation of state for uniform matter and we illustrate the method by constructing a T_c-dependent family of thermodynamically consistent equations of state based on simple spline interpolations between the gas and plasma phases.

Published
2003

42. Experimental comparison of regeneration methods for CO2 concentration from air using amine-based adsorbent

Author

Elfving, Jere, Kauppinen, Juho, Jegoroff, Mikko, Ruuskanen, Vesa, Järvinen, Lauri, Sainio, Tuomo, Lappeenrannan-Lahden teknillinen yliopisto LUT, Lappeenranta-Lahti University of Technology LUT, and fi=School of Energy Systems|en=School of Energy Systems

Subjects
Regenerability, Adsorbent regeneration, Working capacity, Direct air capture, CO2 adsorption, Specific Energy requirement
Abstract

Comparison of different regeneration options for direct air capture (DAC) has usually been limited to only consider pure CO2 production, limiting the process options to e.g. temperature-vacuum swing adsorption (TVSA) or steam-stripping. In this work, detailed experimental comparison is conducted of temperature swing adsorption (TSA/TCSA) and TVSA for DAC. Particularly, TVSA is assessed with air or inert gas purge flow (TVCSA) and without purge flow. The working capacity, regeneration specific energy requirement (SER) and adsorbent regenerability of these processes was compared. For all other studied regeneration options except TVSA without purge flow, over 85% regeneration was obtained already at 60 °C. Isobaric TSA at 60 °C had the lowest regeneration SER of 4.2 MJ/kgCO2. Coupling TSA with mild vacuum improved desorption rate and increased working capacity from 0.47 to 0.51 mmolCO2/gsorbent, requiring 7.5 MJ/kgCO2 for regeneration. Without purge flow, TVSA resulted in only 0.39 mmolCO2/gsorbent with the SER of 8.6 MJ/kgCO2 at 100 °C. Due to lower allowable regeneration temperature of 60 °C, mild vacuum TVSA with air flow also had a lower cyclic capacity decrease rate of 0.26%/cycle compared to 0.38%/cycle with TVSA without purge flow at 100 °C. However, using 100 °C with air flow in the TVSA process lead to a significant capacity decrease of 0.6%/cycle. Therefore, using either air or inert purge flow below 100 °C coupled with mild vacuum has benefits over the TVSA process with no inflow in terms of CO2 productivity, specific energy requirement and adsorbent regenerability. For utilization purposes that require low-concentration CO2, TVSA with purge flow should thus be considered as a viable regeneration option for direct air capture along with isobaric TSA. Publishers version

Published
2020

43. Effect of Power Quality on the Design of PEM Water Electrolysis Systems

Author

Koponen, Joonas, Ruuskanen, Vesa, Hehemann, Michael, Rauls, Edward, Kosonen, Antti, Ahola, Jero, and Stolten, Detlef

Subjects
ddc:620
Abstract

Water electrolyzer technologies may play a key role in the decarbonization of the fossil-fueled world economy. Electrolytic hydrogen production could bridge emission-free power generation and various energy end-use sectors to drive the energy system towards a net zero-emission level. In order to reduce the economic cost of the required energy transition, both the overall system efficiency in converting electrical energy into the chemical energy carried by hydrogen, and the material used to build electrolytic cell stacks, should be optimal. The effect of power quality on the specific energy consumption of proton exchange membrane (PEM) water electrolyzers is investigated with a semi-empirical cell model. An experimentally-defined polarization curve is applied to analyze cell-specific energy consumption as a function of time in the case of sinusoidal current ripples and ripples excited by an industrial 12-pulse thyristor bridge. The results show that the effective electrolyzer cell area should be up to five times as high as an ideal DC power supply when powered by the 12-pulse thyristor rectifier supply to match the specific energy consumption between the two power supply configurations. Therefore, the improvement of power quality is crucial for industrial PEM water electrolyzer systems. The presented approach is applicable to simulate the effect of power quality for different proton exchange membrane electolyzers.

Published
2020

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