Aspen Research Articles

Process Optimisation of Biogas-Based Power-to-Methane Systems by Simulation

Increasing amounts of renewable energy produced by volatile sources like photovoltaic and wind turbines demand for higher energy storage capacities to achieve a sustainable energy generation and supply. Power-to-methane – storing excess energy via chemical conversion as methane – is one of the most interesting technologies to reach this goal, as it bundles the advantages of large storage capacities, fast response time and use of existing infrastructure. First commercial plants have been realised, but alternative concepts are still heavily researched and in demonstration stage. As most are using complex process setups or achieving low methane product concentrations, process optimisation and simplification is needed, but information on this topic is scarce. To close this gap, a power-to-methane process consisting of catalytic methanation and membrane gas upgrading using biogas as carbon dioxide source was simulated in ASPEN Plus®. Four different process setups were modelled to assess influences of fermentation setup, recycling of membrane off-gas and multistage membrane gas separation as well as pressure and GHSV. Models were parameterised with experimental results obtained from a demonstration plant. It was shown that a process without off-gas recycling requires less energy but leads to hydrogen losses of up to 25 %. Preventing this loss by recycling the off-gas leads to an increase of specific energy demand for hydrogen storage by 17 % and relative membrane area by 11 % for the base case.

Effect of Packing Structure on CO2 Capturing Process

The increasing concentration of carbon dioxide (CO2) in the atmosphere is a primary global environmental concern due to its detrimental impacts on climate change. A significant reduction in CO2 generation together with its capture and storage is an imperative need of the time. CO2 can be captured from power plants and other industries through various methods such as absorption, adsorption, membranes, physical and biological separation techniques. The most widely used systems are solvent based CO2 absorption method. The aim of this study was to analyze the effect of various random and structured packing materials in absorption column on CO2 removing efficiency. Aspen plus was used to develop the CO2 capture model for different packing materials with Monoethanolamine (MEA) solvent in order to optimize the system. It was found that the lowest re-boiler duty of 3,444 kJ/KgCO2 yield the highest rich CO2 loading of 0.475 (mole CO2/mole MEA) by using the BX type of structured packing having the highest surface area. The surface area of the different packing materials were inversely proportional to the temperature profiles along the column. Furthermore, the packing materials with higher surface areas yielded higher CO2 loading profiles and vice versa. The findings of this study and recommendation would help further research on optimization of solvent-based CO2 capturing technologies.

Multi-objective Optimisation of MTBE Reactive Distillation Process Parameters based on NSGA-II

Optimisation of reactive distillation (RD) process parameters is very important and complex because of a large number of variables and a strong coupling between them. A hybrid method of orthogonal numerical test and non-dominated sorting genetic algorithm II (NSGA-II) was presented for optimisation of the methyl tert-butyl ether (MTBE) RD process parameters such as the reflux ratio, the number of trays etc. on maximizing the conversion of isobutene and minimizing TAC of MTBE RD process simultaneously. Firstly, Aspen Plus was used to simulate MTBE RD process and the key parameters were selected by univariate sensitivity analysis. Secondly, the orthogonal test method was used to design the experiment scheme, and correlation formulations between the process parameters and objective functions (conversion of isobutene and total annual cost) were determined by second order regressions model according to the results of orthogonal numerical tests. Finally, based on the fitting function equations, NSGA-II was used to optimize the MTBE RD process parameters, and a non-dominated solution set was obtained and presented. The results indicate that the combination of orthogonal numerical test and the NSGA-II can not only reduce the number of experiments effectively, but also get the optimal and effective process parameters set for process design and operation.

Optimization of Shale Gas Sweetening Process Coupling with Claus Process Based on Energy Synthesis

As a sort of emerging unconventional energy, shale gas has extensive market outlook by virtue of its enormous reserves, and concerns for shale gas exploitation and processing have been raised nowadays. Raw shale gas must be processed to achieve certain specifications before it can be transmitted in pipelines or utilized by consumers. Sweetening is a gas conditioning process to decrease the concentration of acid gases such as hydrogen sulfide and carbon dioxide which are not preferred in sales gas in consideration of heating value specification and corrosion prevention. However, the after-treatment of acid gases is not discussed in many research of sweetening process. In this paper, a flowsheet of shale gas sweetening process is established using Aspen Plus v8.6. Dissolution of light gases and weak electrolyte, absorption of acid gases and reactions in electrolyte solution are considered simultaneously in process modelling. Diethanolamine (DEA) solution is employed as the solvent to separate acid gases from raw shale gas. The optimal feed stage of rich solvent regeneration and reflux ratio of regenerator are analysed to optimize the sweetening flowsheet. A three-stage Claus process is simulated coupling with shale gas sweetening process to convert hydrogen sulfide in acid gas to element sulphur for pollution reduction. A principle is proposed to determine the operating temperature of each Claus reactor which is a decisive parameter on sulfur recovery efficiency and performance of Claus process. Ultimately, the sulfur recovery efficiency of the three-stage Claus process proposed in this paper is 97.35 %. The effectivity of the principle is confirmed by the results reported in literatures. Energy synthesis is then adopted to integrate sweetening process with Claus process in both mass and energy flow. The coupled process provides with more streams than a single sweetening or Claus process, promoting the reasonability of energy utilization. Streams are extracted and matched for heat exchanger network (HEN) synthesis to reduce the energy consumption and total annual cost of the whole process.

Simulation and optimization study on aqueous mea-based co2 capture process

Chemical absorption with monoethanolamine (MEA) is the most common technology used in the CO2 removal unit for a power plant. However，the application is hindered by its high energy consumption for absorbent regeneration. In this study, a rate-based model of the typical MEA-based CO2 capture process was built for a power plant with Aspen Plus software. The thermodynamic model of ENRTL-RK was adopted. Temperature fields and the flow rates changes of components in absorber and stripper were obtained. And process analysis using the equilibrium stage model was performed to investigate the effects of operation parameters (CO2 loading in lean solution and stripper pressure) on the regeneration energy consumption. With heat pump technology adopted to assist lean solution regeneration, two processes were proposed and the reboiler duties decreased to 2.77 GJ/t CO2 and 2.38 GJ/t CO2, respectively, owing to the recovery of latent heat and part of sensible heat. Moreover, condenser duties were reduced obviously.

Dynamic Process Simulator Assisted Optimization of Operating Point Transition

Model-based dynamic optimization is an effective tool for control and optimization of chemical processes, especially during transitions in operation. This study considers the dynamic optimization of load transitions. Poor operating point transition strategy can increase the quantity of off-spec product coming with financial loss, and also can increase the risk of malfunctions. A novel methodology for operating point transition optimization is applied to a vacuum distillation column unit in which concentration of cumene-hydroperoxide intermediate occurs. Optimization task is based on Open Platform Communication (OPC) between a commercial process simulator (Aspen HYSYS) and MATLAB. Nonlinear Optimization with Mesh Adaptive Direct Search algorithm (NOMAD) is applied to solve the task. Load of the distillation column is decreased from 100% to 90% taking into account the time of transition, amount of off-spec product and energy consumption. Different objective functions result definitely different transition strategies, therefore the right choice of this function is crucial step in this process. The results show that the proposed optimization methodology can be applied efficiently based on a complex simulator of the technology.

Cogeneration system of power and h2 from black liquor through gasification and syngas chemical looping

One of the strategies to improve environmentally friendly energy harvesting can be realized by using biomass as a primary energy source for generating electricity and H2. In addition, high energy efficiency can be achieved by minimizing the exergy loss through process integration and exergy recovery. As an implementation, this study proposes a cogeneration system for black liquor (BL) to co-produce electricity and H2. The system primarily comprises of BL drying, circulating fluidized bed gasification, syngas chemical looping (SCL), and power generation. The Aspen Plus V8.8 software package is used for modelling and performing calculations of the proposed integrated system. Furthermore, thermodynamic analysis of gasification is performed by employing Gibbs energy minimization. The effects of target solid content on the required total work and compressor outlet pressure during drying and gasification with different steam-to-fuel ratios are evaluated. Moreover, the SCL process adopts three reactors, namely, the reducer, oxidizer, and combustor. Compared to the conventional processes, the integrated drying-gasification-SCL processes are significantly cleaner and more energy efficient. The proposed integrated system can achieve a net energy efficiency of about 70 %, with almost 100 % carbon capture.

Energy consumption optimization of a synthetic ammonia process based on oxygen purity

The energy consumption of an ammonia process is huge, and it occupies a large proportion in the industrial energy consumption. The air separation unit is an important energy-consuming unit in the process of ammonia synthesis. For the ammonia process with pure oxygen gasification, the purity of oxygen products in the air separation unit is generally 99.6%. If the oxygen purity from the air separation is reduced properly, its energy consumption will decrease effectively, and the energy consumption of the whole ammonia process may further decrease, as the nitrogen element is needed for ammonia synthesis. However, with the increase of the flow rate, the operating cost of the subsequent unit would increase, so there is an optimal purity that could minimize the energy consumption of the whole process. In this paper, the process simulation software, ASPEN PLUS, is used to model and analyse the process of ammonia synthesis to determine the process energy consumption with different inlet oxygen purity. With the reduction of oxygen purity, the oxygen compressor power consumption increases, nitrogen compressor power consumption decreases, and the refrigeration energy consumption of the purification unit increases. The relations between the three kinds of energy consumption and oxygen purity are linear. Combined with the relation between oxygen purity and the energy consumption of air separation unit, the optimal oxygen purity that makes the process energy consumption minimal is 92%. Compared with the current process used 99.6% purity oxygen, the energy saving is about 13.3% as much as air separation energy consumption.

Process Simulation and Evaluation of Ethane Recovery Process using Aspen-HYSYS

In this work, the process of ethane recovery plant was simulated for the purpose of Front End Engineering Design. The main objective is to carry out a series of simulation using Aspen HYSYS to compare recovery of ethane from Joule Thomson (JT) Valve, Turbo-Expander and Twister Technology. Twister technology offers high efficiency, more ethane recovery and lower temperature than JT valve and turbo-expander process. It lies somewhere between isenthalpic and isentropic process due to its mechanical configuration. Three processes were compared in terms of recovery of ethane. To conduct the simulations, a real gas plant composition and design data were utilized to perform the study for comparison among chosen technologies which are available for ethane recovery. The same parameters were used for the comparisons. Effect of operating conditions including pressure, temperature, and flow rate as well as carbon dioxide on the recovery of ethane was examined.

Phytochemical Screening of Quaking Aspen (Populus tremuloides) Extracts by UPLC-QTOF-MS and Evaluation of their Antimicrobial Activity.

The continual emergence of pathogen resistance is a recurring challenge and pushes for the development of antimicrobial compounds. Here, we investigated compounds from quaking aspen trees (Populus tremuloides) as potential antimicrobial agents. Several extractions using different solvents were realized, and corresponding antimicrobial activity was tested against eight microorganisms. Results revealed that polar extraction solvents including water, ethanol and methanol gave the best extraction yields (>15.07%). Minimal inhibition concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC) demonstrated that water extracts had the best antimicrobial activity by a weak to moderate inhibition of growth of all eight tested microorganisms in addition to having a bactericidal effect on three of them. The quaking aspen methanol extract also displayed antimicrobial activity but to a lower level than the water extract. Ultra-performance liquid chromatography quadrupole time-of flight mass spectrometry (UPLC-QTOF-MS) analysis led to the identification of 92 compounds, mainly polyphenols in both extracts, with 22 molecules previously known for their antimicrobial properties. According to the relative abundance, 4-hydroxybenzaldehyde (5.44% in methanol extract) and kaempferol (5.03% in water extract) were the most abundant antimicrobial compounds. Among antimicrobial molecules identified, nine were from the flavonoid family. The results of our study demonstrate the interest of using quaking aspen as source of antimicrobial compounds.

Field evidences for the positive effects of aerosols on tree growth.

Theoretical and eddy covariance studies demonstrate that aerosol-loading stimulates canopy photosynthesis, but field evidence for the aerosol effect on tree growth is limited. Here, we measured in situ daily stem growth rates of aspen trees under a wide range of aerosol-loading in China. The results showed that daily stem growth rates were positively correlated with aerosol-loading, even at exceptionally high aerosol levels. Using structural equation modeling analysis, we showed that variations in stem growth rates can be largely attributed to two environmental variables covarying with aerosol loading: diffuse fraction of radiation and vapor pressure deficit (VPD). Furthermore, we found that these two factors influence stem growth by influencing photosynthesis from different parts of canopy. Using field observations and a mechanistic photosynthesis model, we demonstrate that photosynthetic rates of both sun and shade leaves increased under high aerosol-loading conditions but for different reasons. For sun leaves, the photosynthetic increase was primarily attributed to the concurrent lower VPD; for shade leaves, the positive aerosol effect was tightly connected with increased diffuse light. Overall, our study provides the first field evidence of increased tree growth under high aerosol loading. We highlight the importance of understanding biophysical mechanisms of aerosol-meteorology interactions, and incorporating the different pathways of aerosol effects into earth system models to improve the prediction of large-scale aerosol impacts, and the associated vegetation-mediated climate feedbacks.

A Combined Evaporation and Microalgal Cultivation Approach for Efficient Treatment of Landfill Leachate: Batch and Continuous Experiments and Process Simulation

Leachate from landfill is one of the most relevant unsolved environmental issues, in particular related to the high ammonia content. In this work, the possibility of treating this waste stream with a combined approach that includes both physical and biological treatment was assessed. The process is composed by a first evaporation/condensation step in an innovative industrial technology (WastWa) developed by Solwa SrL, that allows separating an aqueous stream in which about half of the water volume and most of the ammonia are recovered, and a concentrated leachate stream. The ammonia-rich water stream can be then sent to a microalgal cultivation step for N removal, while the concentrated waste can either be partially used to provide micronutrients for microalgal growth or delivered to phytodepuration. The feasibility of the process was tested at lab scale by carrying out both batch and continuous experiments with Acutodesmus obliquus, a microalgal species isolated from a pond containing pretreated leachate from an urban landfill located in Lazio (Italy). This strain was cultivated both in untreated leachate and in the aqueous outlet stream of the WastWa unit. A simulation model of the microalgal growth process was implemented in Aspen Plus, keeping into account the chemical equilibrium and ionic speciation of the nutrients in solution as well as the pH. The model was able to reproduce well the experimental data, and can therefore be a useful tool to evaluate the feasibility of the proposed process at large-scale.

Dormancy by communication shutdown

Plant Science Trees become dormant in winter, with encapsulated buds protected against harsh conditions. Tylewicz et al. found that, as the days get shorter, communication channels between cells in aspen trees shut down. The blocked plasmodesmata sequester the dormant meristems from growth signals.

Ethylene signaling induces gelatinous layers with typical features of tension wood in hybrid aspen.

The phytohormone ethylene impacts secondary stem growth in plants by stimulating cambial activity, xylem development and fiber over vessel formation. We report the effect of ethylene on secondary cell wall formation and the molecular connection between ethylene signaling and wood formation. We applied exogenous ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) to wild-type and ethylene-insensitive hybrid aspen trees (Populus tremula×tremuloides) and studied secondary cell wall anatomy, chemistry and ultrastructure. We furthermore analyzed the transcriptome (RNA Seq) after ACC application to wild-type and ethylene-insensitive trees. We demonstrate that ACC and ethylene induce gelatinous layers (G-layers) and alter the fiber cell wall cellulose microfibril angle. G-layers are tertiary wall layers rich in cellulose, typically found in tension wood of aspen trees. A vast majority of transcripts affected by ACC are downstream of ethylene perception and include a large number of transcription factors (TFs). Motif-analyses reveal potential connections between ethylene TFs (Ethylene Response Factors (ERFs), ETHYLENE INSENSITIVE 3/ETHYLENE INSENSITIVE3-LIKE1 (EIN3/EIL1)) and wood formation. G-layer formation upon ethylene application suggests that the increase in ethylene biosynthesis observed during tension wood formation is important for its formation. Ethylene-regulated TFs of the ERF and EIN3/EIL1 type could transmit the ethylene signal.

Photoperiodic control of seasonal growth is mediated by ABA acting on cell-cell communication.

In temperate and boreal ecosystems, seasonal cycles of growth and dormancy allow perennial plants to adapt to winter conditions. We show, in hybrid aspen trees, that photoperiodic regulation of dormancy is mechanistically distinct from autumnal growth cessation. Dormancy sets in when symplastic intercellular communication through plasmodesmata is blocked by a process dependent on the phytohormone abscisic acid. The communication blockage prevents growth-promoting signals from accessing the meristem. Thus, precocious growth is disallowed during dormancy. The dormant period, which supports robust survival of the aspen tree in winter, is due to loss of access to growth-promoting signals.

Design of Naphtha Splitter Unit with Petlyuk Distillation Column Using Aspen HYSYS Simulation

Design of Naphtha Splitter Unit with Petlyuk Distillation Column Using Aspen HYSYS Simulation

Effect of environmental temperature on bending strength of the finger jointed aspen lumber.

Effect of environmental temperature on bending strength of the finger jointed aspen lumber.

Структура осинников Закамья Республики Татарстан

Приведены результаты исследований, отражающие характер распределения осинников Закамья Республики Татарстан по типам лесорастительных условий, возрасту, запасу стволовой древесины, классам бонитета и полноте The article focuses on the low forest cover of the Republic of Tatarstan, the need to maintain a regional forest resource base, the prospects for increasing the economic potential of forests without compromising their environmental functions. As one of the ways to achieve this goal, the prospects of increasing the productivity of the aspen formations of the Republic of Tatarstan through their reconstruction are considered. For the subsequent development of a complex of forestry measures for qualitative improvement of aspen trees, it is proposed to study the structural organization of the aspen. In this case, the example of the physical and geographical region of Zakamye of the Republic of Tatarstan. The specificity of this work is that the study of the area of the aspen propagation of Zakamye of the Republic of Tatarstan, the accumulation of the timber stock, the characteristics by class of bonitet and relative completeness – was carried out in the context of types of forest conditions by age groups. As a result, an informative set of data on the age structure of the aspen formations of Zakamye of the Republic of Tatarstan, the features of their localization in various types of forest habitat conditions, the laws of accumulation of wood volume was obtained. In the context of the types of forest growing conditions and groups of ages, characteristics of aspen plantations according to bonitet classes and relative completeness are given. The obtained information serves as a good information base for development of scientific and production solutions aimed at improving the ecological and resource potential of forests and, in particular, aspen formations of the Republic of Tatarstan.

The function of two type II metacaspases in woody tissues of Populus trees.

Metacaspases (MCs) are cysteine proteases that are implicated in programmed cell death of plants. AtMC9 (Arabidopsis thaliana Metacaspase9) is a member of the Arabidopsis MC family that controls the rapid autolysis of the xylem vessel elements, but its downstream targets in xylem remain uncharacterized. PttMC13 and PttMC14 were identified as AtMC9 homologs in hybrid aspen (Populustremula×tremuloides). A proteomic analysis was conducted in xylem tissues of transgenic hybrid aspen trees which carried either an overexpression or an RNA interference construct for PttMC13 and PttMC14. The proteomic analysis revealed modulation of levels of both previously known targets of metacaspases, such as Tudor staphylococcal nuclease, heat shock proteins and 14-3-3 proteins, as well as novel proteins, such as homologs of the PUTATIVE ASPARTIC PROTEASE3 (PASPA3) and the cysteine protease RD21 by PttMC13 and PttMC14. We identified here the pathways and processes that are modulated by PttMC13 and PttMC14 in xylem tissues. In particular, the results indicate involvement of PttMC13 and/or PttMC14 in downstream proteolytic processes and cell death of xylem elements. This work provides a valuable reference dataset on xylem-specific metacaspase functions for future functional and biochemical analyses.

Quaking aspen woodland after conifer control: Herbaceous dynamics

Abstract Western juniper (Juniperus occidentalis Hook.) woodlands are replacing low elevation (