1,720,988 research outputs found
Exergy analysis of municipal solid waste incineration processes. The use of O2-enriched air and the oxy-combustion process
No full textThis work provides a complete exergy analysis of municipal solid waste incineration process. The work was based on a previous study, and was enriched considering the possibility to increase the O2 %mol in the combustion air, up to oxy-combustion conditions. Two configurations have been considered, with and without flue gas recirculation, and the environmental aspects of oxy-combustion were taken into account, as well as its exergetic cost. The flue gas was used in a boiler for high pressure steam production, expanded in three turbines for power generation. The exergy analysis allowed to identify the process units characterized by major irreversibility and exergy loss as waste. The results showed that the flue gas recirculation led to an exergy efficiency increase of the whole process of about 3% (from 31.1% up to 34% at adiabatic flame temperature equal to 1200 °C). The O2 %mol increase in the combustion air allowed to reduce the flue gas flowrate, leading to environmental benefits. Oxygen-enriched air adoption led to limited exergetic improvements, due to the exergy cost of the air separation unit. The specific energy generation of the plant increased at fixed combustion chamber temperature adopting flue gas recirculation
Production of metallic iron nanoparticles in a baffled stirred tank reactor. Optimization via computational fluid dynamics simulation
No full textThe aim of this work is to optimize iron nanoparticle production in stirred tank reactors equipped with two classical impellers: Rushton and four-pitched blade turbines, which are largely used in batch industrial synthesis and efficient scale-up. The main operative parameters of nanoparticle synthesis are the precursor initial concentration, reducing agent/precursor molar ratio, impeller–tank clearance, and impeller rotational velocity. These parameters were varied during the synthesis to find the optimal operating values based on the Fe(0) (%) production, zeta potential, particle size distribution, and powder X-ray diffraction pattern obtained. We found that the optimal operating conditions for nanoparticle production were an impeller velocity of 1500 rpm, initial iron precursor concentration of 20 mM, molar ratio of reducing agent to iron precursor of 3 mol/mol, and impeller clearance of 0.25 and 0.4 times the vessel diameter for Rushton and four-pitched blade impellers, respectively. Setting these conditions achieved a total conversion of 0.94–0.98 and yielded a product with a unimodal size distribution and average diameters in the range 30–50 nm. The computational fluid dynamics results agreed with the expectations, and the obtained mixing Damkohler numbers show that the process is mixed controlled
Green fuel production by coupling plastic waste oxy-combustion and PtG technologies. Economic, energy, exergy and CO2-cycle analysis
No full textThis study deals with the simulation of a waste to energy plant, with the implementation of a power to gas unit that converts the CO2 produced by the incineration of the municipal solid waste in methane. The simulation study was supported by the environmental, i.e. CO2-cycle analysis, economic and exergetic analysis. Three plant configurations were considered, in which the difference between the use of combustion air and pure oxygen as oxidant was analyzed. The work shows that a WtE plant implemented with a PtG unit is able to produce up to 1317 Nm3/h of methane with 940 kg/h of plastic waste feed, with a fuel cost for the base scenario of 5 $/MWh. Finally, in this work the energy and exergy analysis were carried on different scenarios resulting in a maximum value for energy and exergy efficiency of 36% and 26.4%, respectively
Hexavalent chromium reduction in manganese-rich soils by ZVI nanoparticles: the influence of natural organic matter and manganese oxides
Full text linkHexavalent chromium reduction by nano Zero-Valent Iron
(nZVI) has been proved fast and efficient, mainly due to
nanoparticles large specific surface area and high chemical
reactivity. In this work the influence of natural organic
matter and manganese oxide was investigated, through a
set of experimental tests carried out on a real polluted soils
naturally rich in manganese. Soil samples were
characterized in terms of initial concentration of Cr,
Cr(VI), Mn, pH, and TOC and three different nZVI
solutions were used (120, 360 and 600 mg nZVI L-1
) for
the treatment. At selected interval times (0, 5, 10, 15, 30,
60, 120 min) a slurry sample was filtered and Cr(VI)
residual concentration and pH were measured. The same
procedure was carried out on an artificial spiked soil,
characterized by a similar TOC and poor of Mn.
Furthermore the two soils were mixed with different
amounts of leonardite, to evaluate the influence of NOM
on treatment efficiency
Multi wall carbon nanotubes application for treatment of Cr(VI)-contaminated groundwater; Modeling of batch & column experiments
No full textMulti wall carbon nanotubes (MWCNTs) are carbonaceous nanomaterials with novel adsorption properties. In this study MWCNTs were used as adsorbents for hexavalent chromium, Cr(VI), and the influence of operating parameters, on adsorption process, such as pH, MWCNTs and Cr(VI) concentration, and contact time have been investigated. Batch and column experiments were carried out in order to investigate the removal efficiency of MWCNTs for different Cr(VI) concentrations related to groundwater polluted by either anthropogenic activities or by geogenic processes. The experimental results showed that pH was the most crucial factor for adsorption efficiency. Cr(VI) adsorption was inversely proportional with pH value and more specifically adsorption was significantly decreased for pH values higher than 7. The effect of adsorbent's concentration showed the high adsorption capacity of MWCNTs. The adsorption process was very fast since was almost completed within 1 h. Different isotherm models have been adopted to interpret the experimental equilibrium data, as well as two mass-transfer based model were used to describe the dynamic behavior of Cr(VI) sorption phenomenon in column experiments
Modeling and economic evaluation of carbon capture and storage technologies integrated into synthetic natural gas and power-to-gas plants
No full textThe production of synthetic natural gas from coal and biomass gasification made it possible to obtain a product that can be used to replace easily the standard natural gas in the existing infrastructures. This paper follows and presents a study that was conducted on a synthetic natural gas plant integrated with carbon capture and storage technologies. The recent growth in the use of energy coming from renewable sources requires that balancing measures be taken for electricity grids, which, as can be easily imagined, is best accomplished by using multiple energy storage technologies. In particular, the power-to-gas technology allows renewable electrical energy to be transformed into methane via electrolysis and subsequent methanation. Moreover, the production of synthetic natural gas can be enhanced by using concentrated CO2 emitted by synthetic natural gas plants, coupling the coal gasification and methanation processes within the same plant. This paper compares and evaluates two distinct process configurations and their implementation with power-to-gas technology in Aspen Plus v.8. During the study, it was analyzed how the introduction of carbon capture and storage technologies affect the overall energy balance, as well as the individual performances of each configuration. The two cases proved to have similar efficiency; it was also observed that the integration of and carbon capture and storage technologies resulted in a negligible reduction in the efficiency of the system (approximately 1%). The integration of power-to-gas technologies led to a decrease in the efficiency of the system up to 30%. Based on the current emission allowances specified in the rules of the regulated market of CO2, it was also assessed how such technologies would be sustainable in terms of costs derived from the production of gas. An analysis was in fact performed to estimate the costs associated with this type of plant and the results showed that the introduction of carbon capture and storage technologies in synthetic natural gas plants had a lower impact on the costs related to both the plant and the synthetic natural gas. In this respect, a sensitivity analysis of the most influent factors was performed as well. The results showed that, when it comes to the production of gas in in the power-to-gas process, the specific cost strongly depends on the price of electricity and the operating hours
Economic, environmental and exergy analysis of the decarbonisation of cement production cycle
No full textThe aim of this study is to analyze the exergetic, environmental, and economic impact of the use of alternative fuels (Plasmix), instead of coal on the clinker production to valorise a non-recyclable waste and to limit global CO2 emissions. The cement production process was implemented in AspenPlus® environment, simulating different scenarios with the possibility to conduct the non recyclable plastic waste incineration in oxy-combustion conditions. Three scenarios were considered: without and with flue gas recirculation from the pre-heating tower and the oxy-combustion layout. Sensitive analyses were carried out to optimize cyclonic pre-heater tower working. Exergetic and economic analyses were performed, and the relevant impacts on economic profitability were analysed. The study reports the advantages and disadvantages of the different scenarios in terms of exergy efficiency, energy requirements, economic impact and pollutants emissions savings. Oxy-combustion layout resulted in 18.4% savings in terms of CO2 emissions but, at the same time, a lower Return of Investment (11.79%) with respect to the scenario with flue gas recirculation (11.82%). The exergy analysis of third scenario re returned the maximum obtainable value of the exergy efficiency (58.4%)
Exergy and energy analysis of three biogas upgrading processes
No full textThe aim of this work was to provide a complete exergy and energy analysis of three biogas upgrading technologies: amine scrubbing, water scrubbing and membrane separation processes. Biogas production and treatment represents a key-process for the application of Circular Economy principles, since allows to reuse/reconvert industrial by-products or agro-industrial waste in a product that can be used in different energy demanding sectors, after proper cleaning and upgrading processes. The three technologies here reported have been implemented in Aspen Plus flowsheets, and were used to upgrade a biogas to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid. Each units of all the simulated processes have been analysed calculating total exergy feed, total exergy produced and exergy loss, distinguishing that lost for irreversibility and as waste. Water scrubbing was characterized by the highest values of exergy efficiency (94.5%) and methane recovery (99%), whereas the lowest exergy efficiency belonged to membrane separation (90.8%) that returned also the largest specific energy consumption (0.94 kWh/m3 STP). Conversely, amine scrubbing was characterized by the lowest specific energy consumption value (0.204 kWh/m3 STP) but by an exergy efficiency of 91.1%
Exergy and energy analysis of biogas upgrading by pressure swing adsorption. Dynamic analysis of the process
No full textThe aim of this work was to provide a complete exergy and energy analysis of a biogas upgrading technology: pressure swing adsorption. This technology has going to be widely used in Europe, because allowed to reach very high methane recovery (93.4%) and Wobbe Index (50.81 MJ/m3 STP) values. In this study, the upgrading process has been implemented in Aspen Plus and Aspen Adsorption dynamics simulation environment and the biogas was upgraded to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid. The upgrading technology has been analysed in terms of process efficiency, also considering CH4 total loss, energy and utilities requirements in dynamic conditions. Each units of the simulated process have been analysed calculating total exergy feed, total exergy produced and exergy loss, distinguishing that lost for irreversibility and as waste. The obtained CH4 recovery at steady cycle state was 93.4%, the CH4 purity in the obtained biomethane was 97.13% whereas the productivity reached a value of 0.143 kg/h·kgads reaching an overall exergy efficiency of 88%
Continuous production of KNO3 nanosalts for the fertilization of soil by means of a Spinning Disk Reactor
Full text linkIn this study the production of high soluble material
nanoparticles was successfully performed by means of a
spinning disk reactor (SDR). This result was possible due
to the use of a potassium nitrate saturated solution, which
was continuously recycled back to the reactor after
removal of the produced solid nanoparticles.
Several process configurations were checked. It appears to
be mandatory that the recycled saturated solution must be
free of residual nanoparticles since their presence would
lead to heterogeneous nucleation. In this respect, a small
amount of nitric acid was added to the stream to permit the
residual nanoparticle dissolution. Moreover, a spiral
wounded piping system was developed in order to increase
both the contact time and the mixing condition of the
saturated solution with the added acid before entering the
SD
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