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Insights from an exergy analysis of a green chemistry chitosan biorefinery
No full textChitosan is a biopolymer with a wide range of applications; however, its production from chitin involves using toxic chemical solvents and high energy consumption. In this study, we propose a new greener route for producing chitosan from shrimp exoskeletons. Our design reduces chemical solvents and freshwater consumption while adhering to Green Chemistry principles. Through process simulation and exergy analysis, we identified critical stages with high irreversibility and achieved a global energy efficiency of 75%, outperforming the conventional chitosan extraction process. An exergy analysis is then conducted to identify sources of energy inefficiencies and reveal process irreversibilities. With a processing capacity of 6507 kg/h of shrimp shells, our proposed biorefinery produces valuable byproducts such as astaxanthin and minerals/proteins. The exergy analysis determined drying, dilution, and washing units as critical stages with the highest irreversibility. Our results demonstrate the potential of applying Green Chemistry principles to improve the sustainability of chitosan production from aquaculture waste streams
Tuning mechanical behavior and deformation mechanisms in high-manganese steels via carbon content modification
No full textIn this paper, two high-manganese steels with comparable grain sizes and manganese contents, namely 34Mn0.1C and 32Mn0.6C, were investigated to explore the effect of carbon content on the mechanical behavior and deformation mechanisms at both room temperature (RT) and liquid nitrogen temperature (LNT). The results indicate that increasing the carbon content promotes the transition of deformation mechanism from dislocation slip to deformation twinning, which is similar to the effect of reducing the deformation temperature. At RT, the strength and elongation are effectively improved by increasing the carbon content, which is attributed to the transformation of deformation mode. Specifically, the yield strength, the ultimate tensile strength and the total elongation increase from 262 MPa, 595 MPa and 50.4% for the 34Mn0.1C steel to 360 MPa, 846 MPa and 87.4% for the 32Mn0.6C steel, respectively. However, at LNT, the 32Mn0.6C steel exhibites higher strength but lower elongation than the 34Mn0.1C steel. The total elongation decreases from 70.6% to 52.3%, which is because the high carbon content and cryogenic temperature induce the rapid activation of deformation twins, leading to premature fracture
Comparative assessment of different aluminum alloys for neutron beam window applications
No full textThe choice of an aluminum alloy window along a neutron beam requires careful consideration depending on the requirements of the instrument end station. The windows should generally be thin to minimize loss of neutrons from the beam due to scattering and absorption but still thick enough to be structurally sound for safety requirements. The microstructure of the material is dependent on the alloy and the preparation method and may introduce scattering artifacts or smearing of the instrument resolution that are not desirable. In this manuscript, SANS and total cross section measurements of several different aluminum alloys will be presented and compared in order to provide some useful insight to engineers working on future neutron instrument design.</p
An ADMM-based dual decomposition mechanism for integrating crew scheduling and rostering in an urban rail transit line
No full textThe crew planning problem is a key step in the urban rail transit (URT) planning process and has a critical impact on the operational efficiency of a URT line. In general, the crew planning problem consists of two subproblems, crew scheduling and crew rostering, which are usually solved in a sequential manner. Such an approach may, however, lead to a poor-quality crew plan overall. We therefore study the integrated optimization of crew scheduling and crew rostering and propose an effective dual decomposition approach. In particular, we formulate the integrated problem as an integer programming model using a space–time-state network representation, where the objective of the model is to minimize the weighted sum of total travel cost and penalties associated with imbalances in the workloads of the crew members. Then, an Alternating Direction Method of Multipliers (ADMM)-based dual decomposition mechanism that decomposes the model into a set of independent crew member-specific subproblems is introduced, where each of these subproblems is efficiently solved by a tailored time-dependent shortest path algorithm. To improve the performance of ADMM approach, two enhancement strategies are also designed to accelerate convergence. A set of real-life instances based on a rail transit line in Chengdu, China, is used to verify the effectiveness of the proposed model and algorithm. Computational results show that the ADMM-based approach with enhancements significantly outperforms a conventional Lagrangian Relaxation-based approach, yielding improved convergence and significantly smaller optimality gaps. Finally, on a set of real-life instances, the proposed ADMM-based approach with enhancements obtains an optimality gap of, on average, 4.2%. This is substantially better than Lagrangian Relaxation, which provides optimality gaps of, on average, 34.73%.</p
Pyrolysis kinetics of bio-based polyurethane: Evaluating the kinetic parameters, thermodynamic parameters, and complementary product gas analysis using TG/FTIR and TG/GC-MS
No full textIn this study, the pyrolysis behavior and reaction kinetics of bio-based polyurethane (BPU) was investigated in comparison to the individual components enzymatic lignin (EL) and polyurethane (PU). The produced gas composition during their pyrolysis were investigated using thermogravimetric (TG) analysis combined with FTIR and TG coupled with TG-GC/MS. TG analysis indicated that the decomposition of BPU was comparable with that of PU. However, the larger peak temperatures in DTA curves and residue mass for BPU than that for PU indicated that the incorporation of EL improved its thermal resistance. Most of the absorbance bands in FTIR for both samples were similar, except of the absorbance at 1500-1750 cm−1 for PU and 1000-1150 cm−1 for BPU. The dominant evolved products were N-containing compounds for PU and BPU, however, the phenols and furans were detected during BPU pyrolysis. Based on the Flynn-Wall-Ozawa model, the average activation energy was determined as 176.1 kJ mol−1 for BPU, which was larger than 159.5 kJ mol−1 for PU and smaller than that of 298.5 kJ mol−1 for EL. For PU and BPU, the experimental curves were comparable with F1.5 model at the conversion rate in the α range of 0.1–0.5 and F3 model beyond that range
Design and techno-economic analysis of a molten-salt driven energy conversion system for sustainable process heat supply
No full textStoring off-peak cheap electricity from wind/solar farms for high-temperature heat storage in different mediums and using that for steam or high-temperature heat supply is a promising concept. A major issue for implementing high-temperature molten salt-based process heating systems is designing an appropriate heat exchanger system that can minimize the technical and operational risks and maximize the economic benefits. This study focuses on designing an optimal energy conversion unit based on this approach and conducts a techno-economic analysis of the developed system for a case study in Denmark to prove its proficiency. The system comprises a kettle boiler heat exchanger compatible with a high-temperature Sodium Hydroxide (NaOH) salt, and the case study is a cardboard factory demanding saturated steam at 10 bar, placed in the sustainable industrial business park GreenLab Skive. The results for the developed energy storage/conversion system with the given specifications and the salt are compared to an optimal design of the system when a conventional molten salt (solar salt mixture) is used. The results prove that the cost-effectiveness of the concept, in general, will be much dependent on the cost of charging electricity, and the system will only be promising if cheap off-grid electricity could be used during the whole charging process. It was found that the system with the benchmark salt NaOH for medium temperature use of ∼180 °C will be able to offer an LCOH of 67 €/MWh at an average cost of charging electricity of 63.6 €/MWh. The solar salt-cased energy conversion unit is less attractive economically but yet promising economically at cheap electricity charging rat
A comparative study on the embodied carbon and operational carbon of a radiant cooling system and an all-air system
No full textGreenhouse gas emissions worldwide must be reduced to prevent the further acceleration of global warming. Therefore, there is an urgent need to reduce carbon emissions in the building sector. Radiant cooling systems have been proven to be an energy-efficient and resource-effective heating and cooling solution for buildings. These features of radiant cooling systems are expected to reduce building operational carbon emissions. The objective of this study was to quantify the effect of radiant cooling systems on building supply chain carbon emissions. The classification of whole life cycle stages of a building was based on EN 15978:2011. Dynamic building simulations were carried out to verify the effects of radiant cooling system on building operational carbon emissions. The studied radiant cooling system type was a Thermally Active Building System (TABS). A model with packaged variable air volume system (VAV) with reheat was simulated as a reference case for comparison. The building model was based on the medium office of the prototype building developed by the U.S. Department of Energy. The whole life carbon (A1-A3, B4, B6, C3, C4) was 8.4 kgCO2-eq/m2/year for the all-air system and slightly lower, 7.9 kgCO2-eq/m2/year for the TABS
Insights on the additive formulation for the energy-efficient production of fused calcium magnesium phosphate fertilizer from waste sludge
No full textThe production of the fused calcium magnesium phosphate fertilizer (FCMP) from sludge is a sustainable alternative to phosphate ore route. However, the distinct compositions of sludge and extensive energy input make the process under great uncertainty for the commercialization. In this study, a new method was proposed to determine the optimal addition amount of CaO and MgO to sludge, realizing the high phosphorus (P) availability and simultaneously reducing the melting point of the system for energy saving. The effect of P content on the product structure and P availability was first investigated at different metal oxide addition levels. The modified non-bridging oxygen to tetrahedral cation equation (NBO/T) was used to establish the linear relationship between the NBO/T and the P availability. The threshold value of the modified NBO/T ≥ 2.3 guaranteed a P-availability beyond 90%. Further, FTIR and Raman spectra showed that there was a strong correlation between the modified NBO/T and the actual glass structure. Finally, on the reference value of NBO/T = 2.30, the system exhibited the minimum melting point at 1292 °C when MgO/CaO = 0.83. This method offers a powerful tool to guide the optimal amount of CaO and MgO addition to sludge ash by simple calculations.</div
Robust Multi-objective Optimal Dispatching Model for a Novel Island Micro Energy Grid Incorporating Biomass Waste Energy Conversion System, Desalination and Power-to-hydrogen Devices
No full textTo realize renewable and self-sustainable energy supply in island region, based on geographical characteristics with abundant renewable resources, an optimal model for island micro energy grid (MEG) is designed incorporating biomass waste energy conversion system (ECS), desalination, and power-to-hydrogen (BSP-MEG) Firstly, the mathematical model is designed, including models of power generators, ECS, desalination and power-to-hydrogen (P2H) devices, etc. Next, the multi-objective scheduling optimization model is designed, containing conventional scheduling model (Scheduling optimization objectives and constraints established with minimum operation and environment costs) and stochastic scheduling model (Minimum Conditional Value-at-Risk objective specific to volatility and uncertainty of renewable generations based on robust stochastic optimization method). Then, to solve the multi-objective optimization problem (MOP), a hybrid differential evolution algorithm is proposed based on local optimal and external archiving strategies. Finally, the MEG of YongXing Island is selected as an example. The results show (1) BSP-MEG effectively realized multi-energy cooperative optimization, and promote intra-day peak shaving. (2) BSP-MEG reduced operating costs, environmental costs and Conditional Value-at-Risk (CVaR) by 78.2%, 61.8% and 77.9% respectively, while curtailment rate by 25.6 to 0.9%. (3) Whether in general scenario or worst, BSP-MEG can realize self-production and self-sale of energy and material, of which risk resistance ability is better. (4) By designing local optimal and external archiving strategies, hybrid differential evolution algorithm performs better in solving complex MOP. In general, the optimization model proposed in this paper can improve the utilization of renewable resources, alleviate the shortage of fresh water, and help realize renewable and sustainable energy supply
Co-enhancing effects of zero valent iron and magnetite on anaerobic methanogenesis of food waste at transition temperature (45 °C) and various organic loading rates
No full textDeoiling of food waste (FW) after hydrothermal pretreatment occurs at high temperatures, and more energy is required for substrate cooling before the anaerobic digestion (AD) process. AD at the transition temperature (for example 45 °C) is good for energy saving and carbon emission reducing when treating deoiling FW. However, the metabolic activity of methanogens must increase at the transition temperatures. This study proposes the use of zero-valent iron (Fe0) and magnetite (Fe3O4) to boost CH4 yield from deoiling FW. The results showed a co-enhancing effect on CH4 yield upgradation when using Fe0 and Fe3O4 simultaneously, and the highest CH4 yield reached 536.23 mLCH4/gVS, which was 67.5 % higher than that of Fe0 alone (320.14 mLCH4/gVS). In addition, a high organic loading was favorable for increasing the CH4 yield from deoiling FW. Microbial diversity analysis suggested that the dominant methanogenic pathway at 45 °C was hydrogenotrophic methanogenesis. Herein, a potential metabolic pathway analysis revealed that the co-enhancing effects of Fe0 and Fe3O4 enhanced syntrophic methanogenesis and possibly boosted electron transfer efficiency