The calcium-looping process is a promising technique for CO₂ capture from coal-fired power plants and for reducing GHG emissions from the power generation sector. This paper presents a calculation ...model of the carbonator, the key reactor of the Ca-looping process, where CO₂ is captured as a result of its reaction with CaO. The model presented is based on the Kunii–Levenspiel theory for circulating fluidized bed and on the recent findings on the properties of CaO as a CO₂ sorbent, while taking into account the effects of coal ash and sulfur species. This model can be used for process optimization and for the prediction of the performance of power plants based on the Ca-looping process. Also presented in this paper are the results of a sensitivity analysis of the primary parameters that influence the performance of the carbonator. These results confirm the feasibility of the Ca-looping process with reactors of reasonable size for industrial applications and highlight the importance of the properties of the Ca-based sorbent as they highly affect the carbonator's performance.
Late in summer 2003, extensive mass mortality of at least 25 rocky benthic macro-invertebrate species (mainly gorgonians and sponges) was observed in the entire Northwestern (NW) Mediterranean ...region, affecting several thousand kilometers of coastline. We were able to characterize the mortality event by studying six areas covering the main regions of the NW Mediterranean basin. The degree of impact on each study area was quantified at 49 sites by estimating the proportion of colonies affected in populations of several gorgonian species compared with reference data obtained in years without mortality signs. According to these data, the western areas (Catalan coast and Balearic Islands) were the least affected, while the central areas (Provence coast and Corsica-Sardinia) showed a moderate impact. The northernmost and eastern areas (Gulf of Genoa and Gulf of Naples) displayed the highest impact, with almost 80% of gorgonian colonies affected. The heat wave of 2003 in Europe caused an anomalous warming of seawater, which reached the highest temperatures ever recorded in the studied regions, between 1 and 3 °C above the climatic values (mean and maximum). Because this exceptional warming was observed in the depth ranges most affected by the mortality, it seems likely that the 2003 anomalous temperature played a key role in the observed mortality event. A correlation analysis between temperature conditions and degree of impact seems to support this hypothesis. Under the present climate warming trend, new mass mortality events may occur in the near future, possibly driving a major biodiversity crisis in the Mediterranean Sea.
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•Effect of design and operating parameters on CO2 capture efficiency investigated.•Calcined raw meal used as sorbent in the carbonator of the CaL process.•High solid-to-gas ratio ...(∼10 kg/Nm3) needed to achieve high capture efficiency.•Adiabatic carbonator suitable for achieving high capture efficiency.•Carbonator solids recirculation allows limiting specific heat duty for regeneration.
In this work, a 1D model of an entrained-flow carbonator of a Calcium looping process for cement plants is presented and the results of a sensitivity analysis on the main governing process parameters is discussed. Several design and operating parameters have been investigated through a wide sensitivity analysis, namely: adiabatic vs. cooled reactor, high gas velocity gooseneck reactor vs. low velocity downflow reactor, solid-to-gas ratio, sorbent capacity, reactor inlet temperature and solids recirculation. The effect of these design and process parameters on the CO2 capture efficiency and on Calcium looping process heat consumption is assessed.
The results of the calculations showed that with a proper combination of solid-to-gas ratio in the carbonator and sorbent carbonation capacity (e.g. ∼10 kg/Nm3 and ∼20% respectively), carbonator CO2 capture efficiencies of about 80% (i.e. total cement kiln CO2 capture efficiencies higher than 90%) can be obtained in a gooseneck-type carbonator with a length compatible with industrial applications in cement kilns (∼120 to 140 m). Further experimental investigations on this reactor concept, especially about fluid-dynamic behavior and the chemical properties of raw meal as CO2 sorbent, are needed to demonstrate the technical feasibility of the proposed process.
•Tail-end and integrated Calcium looping configurations assessed.•All CaL configurations involve significant fuel consumption, especially tail-end CaL.•Heat recovery steam cycle compensates the ...electric absorption of ASU and CPU.•Cost of cement increase: +67% and +74% for tail-end and integrated cases respectively.•Cost of CO2 avoided: 52 €/t and 58.6 €/t for tail-end and integrated cases respectively.
The scope of this work is to perform a techno-economic analysis of two Calcium Looping processes (CaL) for CO2 capture in cement plants. Both tail-end CaL system with fluidized bed reactors and integrated CaL system with entrained flow reactors have been considered in the analysis. The calculation of the heat and mass balances and the economic analysis are consistent with the methodology defined in the framework of the H2020 Cemcap project.
The analysis shows that the assessed CaL systems (especially the tail-end configuration) involve a significant increase of fuel consumption compared to a reference cement kiln without carbon capture. However, a large part of this additional energy input is exploited in a heat recovery steam cycle, which generates the electric power required to satisfy the consumption of the CO2 capture auxiliaries (i.e. the power absorbed by the air separation and CO2 compression and purification units). The integrated CaL process features a lower rise of equivalent fuel consumption (+59% compared to the reference) and a larger reduction of direct CO2 emission (-93% compared to the reference). The specific primary energy consumption for CO2 avoided (SPECCA), which takes into account also the indirect fuel consumption/savings and indirect emissions/avoided emissions due to electricity exchange (import/export) with the grid, ranges between 3.17–3.27 MJLHV/kgCO2 for the integrated system vs. 3.76–4.42 MJLHV/kgCO2 for tail-end cases, depending on the scenario considered for the grid electricity mix.
The economic analysis highlights that CaL processes are capital intensive, which involve, roughly, a doubling of the Capex of the whole cement plant with CCS compared to a greenfield conventional cement plant. However, the obtained cost of CO2 avoided is competitive with alternative technologies and ranges between about 52 €/tCO2 of the tail-end configuration and 58.6 €/tCO2 of the integrated one.
•Greenfield PC plant with Calcium looping and sorbent storage assessed.•Sorbent storage allows reducing the size and cost of ASU, CPU and calciner.•Economic optimization performed for plants with ...weekly capacity factor of 55–67%.•In the assessed cases, the storage system reduces the cost of CO2 avoided by 16–25%.
In this work, a Calcium looping (CaL) system including high temperature sorbent storage is presented, allowing to reduce the size of the calciner and the associated capital-intensive equipment (ASU and CPU). Reduction of the capital costs is particularly important for power plants with low capacity factors, which is becoming increasingly frequent for fossil fuel power plants in electric energy mixes with increasing share of intermittent renewables. The process assessment is performed by: (i) defining pulverized coal power plant (PCPP) with CaL capture system with and without sorbent storage and their mass and energy balances at nominal load; (ii) defining a simple method to predict the performance of the plant at part-load; (iii) defining the economic model, including functions for the estimation of the plant equipment cost; (iv) performing yearly simulations of the systems to calculate yearly electricity production, CO2 emissions and levelized cost of electricity for different sizes of the calcination line and the storage system and (v) performing sensitivity analysis with different power production plans and carbon taxes. With this process, optimal size of the calciner and of the storage system minimizing the cost of electricity have been found.
The optimal plant design was found to correspond to a solids storage system sized to manage the weekly cycling and a calciner line sized on the average weekly load. However, to avoid excessively large solids storage system, sizing the calciner on the average daily load and the storage system to manage the daily cycling appears more feasible from the logistic viewpoint and leads to minor economic penalty compared with the optimal plant design. For the selected case sized on the daily cycling, reduction of the cost of CO2 avoided between 16% and 26% have been obtained compared to the reference CaL plant without solids storage, for representative medium and low capacity factor scenarios respectively.
Cloud Formation by Supernova Implosion Romano, Leonard E. C.; Behrendt, Manuel; Burkert, Andreas
Astrophysical journal/The Astrophysical journal,
04/2024, Letnik:
965, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract The deposition of energy and momentum by supernova explosions has been subject to numerous studies in the past few decades. However, while there has been some work that focused on the ...transition from the adiabatic to the radiative stage of a supernova remnant (SNR), the late radiative stage and merging with the interstellar medium (ISM) have received little attention. Here, we use three-dimensional, hydrodynamic simulations, focusing on the evolution of SNRs during the radiative phase, considering a wide range of physical explosion parameters ( n H , ISM ∈ 0.1 , 100 cm − 3 and E SN ∈ 1 , 14 × 10 51 erg ). We find that the radiative phase can be subdivided in four stages: A pressure-driven snowplow phase, during which the hot overpressurized bubble gas is evacuated and pushed into the cold shell; a momentum-conserving snowplow phase that is accompanied by a broadening of the shell; an implosion phase where cold material from the back of the shell is flooding the central vacuum; and a final cloud phase, during which the imploding gas is settling as a central, compact overdensity. The launching timescale for the implosion ranges from a few 100 kyr to a few Myr, while the cloud formation timescale ranges from a few to about 10 Myr. The highly chemically enriched clouds can become massive ( M cl ∼ 10 3 –10 4 M ⊙ ) and self-gravitating within a few Myr after their formation, providing an attractive, novel pathway for supernova-induced star and planet formation in the ISM.
We have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from Stromboli (pumice from the March ...15, 2007 paroxysmal eruption) and Etna (1992 lava flow). Isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate (
T
= 1,157–1,187 °C and
γ
·
i
= 4.26 s
−1
for Stromboli;
T
= 1,131–1,182 °C and
γ
·
i
= 0.53 s
−1
for Etna). Melt viscosity increased due to the decrease in temperature and the increase in crystal content. The mineralogical assemblage comprises
Sp
+
Plg
(dominant) ±
Cpx
with an overall crystal fraction (
ϕ
) between 0.06 and 0.27, increasing with undercooling and flow conditions. Both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process. Plagioclase nucleation incubation time strongly decreases with increasing Δ
T
and flow, while slow diffusion-limited growth characterizes low Δ
T
—low deformation rate experiments. Both Stromboli (high strain rate) and Etna (low strain rate) plagioclase growth rates (
G
) display relative small variations with Stromboli showing higher values (4.8 ± 1.9 × 10
−9
m s
−1
) compared to Etna (2.1 ± 1.6 × 10
−9
m s
−1
). Plagioclase average nucleation rates
J
continuously increase with undercooling from 1.4 × 10
6
to 6.7 × 10
6
m
−3
s
−1
for Stromboli and from 3.6 × 10
4
to 4.0 × 10
6
m
−3
s
−1
for Etna. The extremely low value of 3.6 × 10
4
m
−3
s
−1
recorded at the lowest undercooling experiment for Etna (Δ
T
= 20 °C) indicates that the crystallization process is growth-dominated and that possible effects of textural coarsening occur.
G
values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions. Stirring of the melt, simulating magma flow or convective conditions, facilitates nucleation and growth of crystals via mechanical transportation of matter, resulting in the higher
J
and
G
observed. Any modeling pertaining to magma dynamics in the conduit (e.g., ascent rate) and lava flow emplacement (e.g., flow rate, pāhoehoe–‘a‘ā transition) should therefore take the effects of dynamic crystallization into account.
Changes of intestinal permeability (IP) have been extensively investigated in inflammatory bowel diseases (IBD) and celiac disease (CD), underpinned by a known unbalance between microbiota, IP and ...immune responses in the gut. Recently the influence of IP on brain function has greatly been appreciated. Previous works showed an increased IP that preceded experimental autoimmune encephalomyelitis development and worsened during disease with disruption of TJ. Moreover, studying co-morbidity between Crohn's disease and MS, a report described increased IP in a minority of cases with MS. In a recent work we found that an alteration of IP is a relatively frequent event in relapsing-remitting MS, with a possible genetic influence on the determinants of IP changes (as inferable from data on twins); IP changes included a deficit of the active mechanism of absorption from intestinal lumen. The results led us to hypothesize that gut may contribute to the development of MS, as suggested by another previous work of our group: a population of CD8+CD161high T cells, belonging to the mucosal-associated invariant T (MAIT) cells, a gut- and liver-homing subset, proved to be of relevance for MS pathogenesis. We eventually suggest future lines of research on IP in MS: studies on IP changes in patients under first-line oral drugs may result useful to improve their therapeutic index; correlating IP and microbiota changes, or IP and blood-brain barrier changes may help clarify disease pathogenesis; exploiting the IP data to disclose co-morbidities in MS, especially with CD and IBD, may be important for patient care.
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