Comparison of Thermocline Molten Salt Storage Performances to Commercial Two-tank Configuration☆

Abstract This work deals with the assessment of thermocline heat storage performances when applied to solar thermal plants. The considered thermocline is based on molten salt heat transfer fluid (Solar Salts between 300 °C and 550 °C) and filled with quartzite. A 2-D finite element heat transfer model is developed to determine the temperatures inside the vessel with mass flows input/output. The model includes heat conductivity of molten salt and quartzite rocks, heat transfer between the molten salts and the quartzite, as well as heat loss to the environment. Results of the model are compared to available experimental data as well as analytic results showing good agreement. Then, the thermocline storage with the performances predicted by the 2-D code was integrated in a CSP plant previously modelled with the two-tank TES system. Plant management is kept equal to the two-tank configuration. A performance index is introduced to make a consistent comparison between the thermocline and the two-tank system: storage efficiency is defined as the heat withdrawn from the storage above 545 °C divided by the overall input in the storage. The defined index is equal to 100% for the two tank system as thermal losses have a negligible impact. On the contrary, in thermocline storage, part of heat stored in the molten salt is in the thermocline region and this molten salt is not accounted as useful. The thickness of the thermocline is about 4 to 6 meter height out of 14 meters making the storage performances in the range of 65%, hence significantly lower than in two-tank configuration. A sensitivity analysis on tank size and tank shape factor is performed to assess the optimal configuration for the thermocline

CAESAR: SEWGS integration into an IGCC plant

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ISIS Facchinetti: A Nearly Zero Energy Retrofit in Italy

The research presented here is about the energy retrofit of an existing high school building close to Varese (Italy). As the building was designed in the 60's with a peculiar architectural language, it has been protected by the conservation authorities. However, the construction system in exposed concrete and the large expanses of single glass make the energy performance of the building very poor. The Provincia di Varese, owner of the building, decided to realize an exemplary retrofit project, which would be the first renovated educational building in Italy in line with the future scenario of Nearly Zero-Energy Building expected from 2019 (2021 for private buildings) by the European Directive 2010/31/UE. In this work energetic and payback analysis are developed to delineate three different preliminary scenarios of intervention. The process has always followed discussions with the conservation authorities, which contributed to the definition of realistic scenarios. Interesting results are obtained: a potential energy demand reduction of 70% can be obtained with the passive solutions proposed; in combination with active strategies (efficient mechanical systems and controls) and with the integration of photovoltaic panels (BiPV), the overall energy need of the building can be reduced to nearly zero

Solar tower CSP plants with transcritical cycles based on CO2 mixtures: A sensitivity on storage and power block layouts

In this work three CO2-based binary mixtures, CO2 + C6F6, CO2 + C2H3N and CO2 + C4F8, are compared as innovative working fluids for closed power cycles in CSP plants. Adopted in transcritical cycles, they lead to cycle efficiencies higher than sCO2 cycles at minimum temperatures above 50 degrees C, a typical condition for arid regions with high solar radiation. The analysis considers four plant configurations: the first with direct storage, solar salts as HTF and cycle maximum temperatures of 550 degrees C, while the three other plants adopt sodium as HTF and an indirect storage system, designed for cycle maximum temperatures of 550 degrees C, 625 degrees C and 700 degrees C. Detailed models are used to characterize the solar fields optical performance, the receiver thermal efficiency and the HTF pump consumption, both at design and off-design conditions, for large scale plants located in Las Vegas. Different power block layouts are considered, spanning from the more efficient ones to cycles with a high heat recovery capacity. In addition, the impact of the mixtures on the design of heat exchangers is evidenced, with convincing results with respect to the heat transfer characteristics of CO2. Considering the resulting yearly performances and LCOE of each configuration, the adoption of indirect storage systems is considered a viable solution for high temperature solar plants. The three innovative mixtures allow for a reduction in LCOE with respect to sCO2 cycles (up to 10 $/MWh, depending on the configuration), capacity factors above 70% for the specific location, optimal solar multiples around 2.8 and 12 equivalent hours of TES

Green Hydrogen Production from Raw Biogas: A Techno-Economic Investigation of Conventional Processes Using Pressure Swing Adsorption Unit

This paper discusses the techno-economic assessment of hydrogen production from biogas with conventional systems. The work is part of the European project BIONICO, whose purpose is to develop and test a membrane reactor (MR) for hydrogen production from biogas. Within the BIONICO project, steam reforming (SR) and autothermal reforming (ATR), have been identified as well-known technologies for hydrogen production from biogas. Two biogases were examined: one produced by landfill and the other one by anaerobic digester. The purification unit required in the conventional plants has been studied and modeled in detail, using Aspen Adsorption. A pressure swing adsorption system (PSA) with two and four beds and a vacuum PSA (VPSA) made of four beds are compared. VPSA operates at sub-atmospheric pressure, thus increasing the recovery: results of the simulations show that the performances strongly depend on the design choices and on the gas feeding the purification unit. The best purity and recovery values were obtained with the VPSA system, which achieves a recovery between 50% and 60% at a vacuum pressure of 0.1 bar and a hydrogen purity of 99.999%. The SR and ATR plants were designed in Aspen Plus, integrating the studied VPSA model, and analyzing the behavior of the systems at the variation of the pressure and the type of input biogas. The SR system achieves a maximum efficiency, calculated on the LHV, of 52% at 12 bar, while the ATR of 28% at 18 bar. The economic analysis determined a hydrogen production cost of around 5 €/kg of hydrogen for the SR case

Application of Hydrogen Selective Membranes to IGCC

AbstractThis study considers the integration of Pd-based H2-selective membranes in integrated gasifier combined cycles (IGCC) from both technical and economical point of view. The selected gasification system is based on Shell technology. Two different dry feeding systems are investigated: the first is a state-of-the- art nitrogen-based lock hopper charger while the second uses CO2 as pressurization gas. The net electric efficiency of the two plants is evaluated as a function of the hydrogen recovery factor (HRF) and the membrane feed pressure in order to minimize the membrane surface area. 90% HRF and 54bar feed pressure are the best operating parameters which correspond to a net electric efficiency of 39% both for N2 and CO2 feeding system. The cost of CO2 avoided is calculated as a function of a parameter named MI which represents the membrane development in terms of performances and costs. Results show that an improvement of membrane technology is necessary to match the state-of-the-art CO2 capture plant, even though membranes show good potentiality for cost abatement

Outdoor Performance of Organic Photovoltaics: Comparative Analysis

Organic photovoltaic (OPV) solar cells represent an emerging and promising solution for low-cost clean energy production. Being flexible and semi-transparent and having significant advantages over conventional PV technologies, OPV modules represent an innovative solution even in applications that cannot be based on traditional PV systems. However, relatively low efficiencies, poor long-term stability, and thermal issues have so far prevented the commercialization of this technology. This paper describes two outdoor experimental campaigns that compared the operation of OPV modules with traditional PV modules—in particular crystalline silicon and copper–indium– selenium (CIS)—and assessed the OPV modules’ power generation potential in vertical installation and facing towards the cardinal directions