Aspen Research Articles

Tree cavity occupancy by nesting vertebrates across cavity age

ABSTRACTCavity‐nesting birds and mammals exhibit species‐specific nest‐site selection for tree characteristics and cavity dimensions. Although trees and their cavities change as they age, with trees becoming softer and cavities becoming larger, it is not known how their value as nesting resources varies with age. In the context of wildlife and forest management, we investigated the relative value of generating a supply of fresh cavities, which are thought to be of high quality, versus protecting cavities as they age and expand in interior volume. For 21 years (1995–2016), we monitored the formation and occupancy of tree cavities used by >30 species of birds and mammals in interior British Columbia, Canada. Cavity occupancy by secondary users was highest 1 year post‐excavation (53%), then declined to 40% after 2 years, remained at 33 ± 7% (SD) between 3 and 16 years of age, and increased to 50% use from 17–20 years post‐excavation. Excavators that reused cavities (woodpeckers [Picidae], nuthatches [Sitta spp.]) strongly selected 1‐ and 2‐year‐old cavities, large‐bodied non‐excavators (ducks, raptors, squirrels) selected mid‐aged cavities, and mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) selected most strongly for the oldest cavities. Cavities created in living aspen trees (Populus spp.), especially those excavated by northern flickers (Colaptes auratus), maintained high occupancy by secondary users across cavity age, and provided the bulk of cavities used in this system. Altogether, these results show that a diverse excavator community is needed to generate a supply of fresh cavities in the ecosystem, and retention of the mid‐aged and older cavities will help support larger species. © 2017 The Wildlife Society.

Description of Deinococcus populi sp. nov. from the trunk surface of a Japanese aspen tree.

A bacterial strain designated PtRA-8T was isolated from the trunk surface of a Japanese aspen tree (Populus tremula var. sieboldii). Cells of strain PtRA-8T were aerobic, non-motile, non-spore forming, Gram-stain-negative rods, 1.0‒2.0µm in width and 3.0‒10.0µm in length. The pH range for growth was between 5.5 and 7.5, with an optimum at 6.5. The temperature range for growth was between 10 and 37°C, with an optimum at around 25‒30°C. Strain PtRA-8T was highly resistant to UV irradiation, similar to its Deinococcus relatives. The respiratory quinone was menaquinone MK-8. The major cellular fatty acids (> 10% of the total fatty acid content) were iso-C15:0 (17.8%), C16:0 (15.0%), iso-C17:0 (10.4%), and iso-C17:1 ω9c/C16:010-methyl (22.2%). The polar lipids consisted of four unidentified glycolipids, two unidentified aminolipids, two unidentified phospholipids, and three unidentified polar lipids. The peptidoglycan was A3β-type containing glutamic acid, glycine, alanine, and ornithine. The DNA G + C content of strain PtRA-8T was 68.2mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PtRA-8T was closely related to "Deinococcus radioresistens" 8AT (97.4%), Deinococcus metalli DSM 27521T (95.7%), and Deinococcus yunweiensis YIM 007T (94.5%). The DNA-DNA hybridization experiments between strain PtRA-8T and its relatives yielded relatedness values below 70%. Based on the polyphasic evidence, we concluded that strain PtRA-8T represents a novel species within the genus Deinococcus, for which the name Deinococcus populi is proposed. The type strain of D. populi is PtRA-8T (= DSM 29820T= NBRC 110763T; DPD TaxonNumber TA00271).

Integration Opportunities for Substitute Natural Gas (sng) Production in an Industrial Process Plant

This paper investigates opportunities for integration of a Substitute Natural Gas (SNG) process based on thermal gasification of lignocellulosic biomass in an industrial process plant currently importing natural gas (NG) for further processing to speciality chemicals. The assumed SNG process configuration is similar to that selected for the ongoing Gothenburg Biomass Gasification demonstration project (GoBiGas) and is modelled in Aspen Plus. The heat and power integration potentials are investigated using Pinch Analysis tools. Three cases have been investigated: the steam production potential from the SNG process excess heat, the electricity production potential by maximizing the heat recovery in the SNG process without additional fuel firing, and the electricity production potential with increased steam cycle efficiency and additional fuel firing. The results show that 217 MWLHV of woody biomass are required to substitute the site’s natural gas demand with SNG (162 MWLHV). The results indicate that excess heat from the SNG process has the potential to completely cover the site’s net steam demand (19 MW) or to produce enough electricity to cover the demand of the SNG process (21 MWel). The study also shows that it is possible to fully exploit the heat pockets in the SNG process Grand Composite Curve (GCC) resulting in an increase of the steam cycle electricity output. In this case, there is a potential to cover the site’s net steam demand and to produce 30 MWel with an efficiency of 1 MWel/MWadded heat. However, this configuration requires combustion of 36 MWLHV of additional fuel, resulting in a marginal generation efficiency of 0.80 MWel/MWfuel (i.e. comparing the obtained electricity production potentials with and without additional fuel firing).

Comparison of extractive and pressure-swing distillation for separation of tetrahydrofuran-water mixture

Tetrahydrofuran (THF) is widely used in many processes as solvent or chemical intermediate. It is necessary to separate mixture of THF-water, because in most commercial production processes, THF is produced from its water mixture. However, the above mixture cannot be separated with ordinary distillation, since THF and water can form azeotrope. Instead, extractive distillation (ED) and pressure-swing distillation (PSD) have been widely applied for commercial separation of mixture of THF-water. In this paper, Aspen Plus simulator is used to simulate extractive distillation and pressure-swing distillation process for separation of mixture of THF-water. Economic analysis is carried out by Aspen Process Economic Analyzer (APEA) for the two processes. The conclusion obtained based on the above process simulation and analysis is that the total annualized cost of the extractive distillation is slightly lower than that of pressure-swing distillation. The results obtained provide useful references for commercial separation of mixture of THF and water.

Global Optimization of Reactive Distillation Processes Using Bat Algorithm

Reactive distillation (RD) is an important process intensification approach with several advantages. It can improve the reaction selectivity and yield, overcome the thermodynamic restrictions, and reduce the cost/energy. However, the optimal design of RD relies on highly nonlinear and multivariable optimization including continuous and integer design variables. The objective function is generally non-convex with several constraints. For this problem, the conventional derivative-based optimization algorithms are faced with convergence problems and fail to guarantee the global optimal solution. Stochastic optimization algorithms appear to be a better alternative for the optimal design of RD because of the high robustness and efficiency. Bat algorithm (BA), which combines advantages of other existing algorithms, is a potential stochastic optimization algorithm. In this work, the BA was used to optimize the RD for the production of methyl acetate (MeAc). The link between Matlab and Aspen Plus was also created to ensure that each solution was provided from rigorous simulations. The total annual cost (TAC) was set as the objective function. Product purity constraints were achieved through Aspen plus instead of algorithms to simplify the process. BA can find the global optimal solution within less computation time than other stochastic algorithms or sequential optimization.

Simulation and optimization of salt-production process from desalination brine

A novel multi-salt crystallization process is presented to separate the salts from the desalination brine and is optimized using the gradual optimization integration strategy based on T-H diagram. Firstly, the process is simulated by Aspen Plus software to obtain the cold and hot load curve and the bottlenecks and unreasonable heat transfer processes are analysed. Secondly, considering the energy utilization and conversion procedure, the turbine and/or heat pump are introduced to improve the process. Then the parameters of production process and utility system are adjusted. Thirdly, the new stream information is obtained by process simulation and the new composite curves are drawn, which will guide the further adjustment of the system. If the new composite curves do not satisfy the process demand, then the above steps are repeated. Through several improvements, two approximate parallel hot and cold stream curves are constructed. The hot streams and cold streams are maximum possible matched, and the amount of utility and power consumption is significantly reduced. In a case study, two optimization schemes are adopted: the feed brine is preheated by the flash steam and the heat pump crystallization technology is introduced. The results show that the energy consumption of two optimized processes is 94.8 kW and 90.1 kW, and the total energy loss decreased 86.7 % and 87.3 %.

Modelling of an ozonation process for cyanide removal from blast furnace gas-washing water and analyses of process behaviour in different scenarios

In the steel sector, the control of cyanide in the wastewater of the gas washing system of blast furnaces is one of the main issues related to the wastewater quality. Although established treatment processes exist, the relevant costs, the stringent environmental regulation and the extremely complex and variable composition of gas washing water lead to investigate modifications of current treatments and to develop new ones. A cyanide treatment based on ozonation is one of the proposed and experimented methods within the European project “DynCyanide”. Starting from experimental data, a process model was developed through Aspen Plus® v.8.6, in order to test a wide range of operating conditions and wastewater features and to prove the robustness of the proposed process. The paper focuses on the process modelling and simulation phases. Water stream and ozonation are modelled through a number of theoretical reactors, by considering main and collateral reactions and a genetic algorithm is applied in order to reproduce at best the kinetics of these reactions. The validated model was applied for scenario analyses. Process knowledge was enhanced and, after finding the parameters and the compounds that reduce the ozonation efficiency, suggestions were obtained to improve the treatment performances. A temperature of 30°C and an initial pH value of 10 favour the cyanide ozonation; the batch mode of the treatment allows the removal of cyanide after 4.5 hours (3 cycles) using a limited ozone amount. If the wastewater contamination level is higher, a further cycle or a higher amount of ozone are needed.

Rigorous design optimisation for combined process of raw natural gas treating and co2 compression using surrogate models

Raw natural gas treating processes remove enormous CO2 and consume a lot of energy. The CO2 can be further compressed for storage or utilization to promote environmental protection. For the purpose of economic design of the combined process of raw natural gas treating and CO2 compression, a new superstructure combining CO2 removing and compression processes is presented. In the superstructure, the rich solvent is not regenerated in the distillation column but through a series of flash separators at different operating pressures and temperatures. The removed CO2 with varying pressures is then compressed to meet the transportation pressure separately. The optimal process structure and operating conditions are determined by minimizing the total annual cost (TAC). To obtain a good trade-off between calculation accuracy and efficiency, a surrogate based optimization framework is presented to address the NLP problem. The complex unit operation models are represented by the Kriging surrogate models, which are built from training data generated via Aspen HYSYS. The surrogate models are then incorporated into the mathematical superstructure framework for optimization. The case study results indicate that the proposed process achieves a significant TAC decrease (9 % - 21 %).

Optimal start-up strategies for a conventional distillation column using simulated annealing

The start-up process for a distillation column presents a challenging control problem in the chemical industry. To address this problem, reducing wasting time and duty consumption during the transient period are crucial issues. In this study, the separation of the dichloromethane, chloroform, and carbon tetrachloride system (CH2Cl2 + CHCl3 + CCl4) was investigated as a start-up example. The single column was used to obtain 83.1% CHCl3 and 99% CCl4. The distillation start-up steps were divided into the following four parts for investigation: feed control, bottom product discharge time, total reflux switch time, and medium temperature heating operation method of the reboiler duty. The feeding time depended on the sump level for safety, and the bottom product was discharged until reaching purity near the specification to avoid producing excess undesired products. Switch total reflux policies were presented using the minimum temperature difference or waiting until the top composition CHCl3 reached 50 wt%. Furthermore, the simulated annealing (SA) algorithm was applied to determine the optimal heating step. The objective function (j) and a set of variables during optimization (d) were subsequently designed, and a flow chart for the SA approach was developed and connected to Aspen Plus Dynamic software. Following the SA calculation, the modified cases with optimal heating steps exhibited better behavior than did the example case. These rules enabled the complicated evaluation process to be simplified for designing a start-up strategy.

Process Design and Analysis of Ethylene and Propylene Manufacturing from Shale Gas

In this paper, we develop two novel process designs for manufacturing ethylene and propylene from shale gas. In the first process design, raw shale gas is processed to produce the mixture of ethane-propane, which is then stream co-cracked to produce ethylene and propylene. In the second process design, ethane and propane are produced from shale gas separately; then, ethylene is mainly produced via the steam cracking of ethane, and propylene is mostly manufactured via the dehydrogenation of propane. We also consider a conventional naphtha cracking design, in order to compare the economic and environmental performance of manufacturing ethylene and propylene from shale gas with from naphtha. All process designs are modeled and simulated in Aspen HYSYS to obtain the mass and energy balances. On this basis, we conduct a comparative techno-economic and environmental analysis. The economic analysis indicates that the two proposed designs results in much lower production costs for ethylene and propylene than the conventional naphtha cracking design. However, in terms of life cycle GHG emissions, manufacturing ethylene and propylene via the naphtha cracking design is more attractive.

Increasing air humidity influences hydraulic efficiency but not functional vulnerability of xylem in hybrid aspen

Climate models predict greater increases in the frequency than in the amount of precipitation and a consequent rise in atmospheric humidity at high latitudes by the end of the century. We investigated the responses of hydraulic and relevant anatomical traits of xylem to elevated relative humidity of air on a 1-yr-old coppice of hybrid aspen (Populus×wettsteinii) growing in the experimental stand at the Free Air Humidity Manipulation site in Eastern Estonia. The hydraulic conductivity of stems was measured with a high pressure flow meter; artificial cavitation in the stem segments was induced by the air injection method. Specific conductivity of xylem decreased from 4.42 in the control to 3.94kgm−1s−1MPa−1 in the humidification treatment, while the trend was well correlated with increasing wood density. Humidified trees exhibited smaller leaf area at the same xylem cross-sectional area, resulting in 34% higher average Huber values compared to the control. Control and humidity-treated trees differed by neither native embolism level nor susceptibility to dehydration-induced cavitation. Increasing atmospheric humidity reduces the hydraulic efficiency of hybrid aspen trees expressed on a xylem area basis and causes substantial changes in resource allocation between photosynthetic and water transport tissues. This climate trend does not influence stem vulnerability to cavitation.

Diversity and distribution of epiphytic lichens and bryophytes on aspen (Populus tremula) in the middle boreal forests of Republic of Karelia (Russia)

The distribution of epiphytic bryophyte and lichen species growing on aspen in the middle boreal forests was studied in southern Karelia (Russia). These forests varied in time-since-disturbance from 80 to 450 years. Two hundred twenty two species of epiphytes, including 178 lichens, 32 mosses and 12 liverworts, were recorded on 192 aspen trees in forests over 24 ha, in the Karelian part of the Vodlozero National Park, Kivach Strict Nature Reserve, Kizhi Sanctuary and Petrozavodsk City. Arthonia biatoricola, A. excipienda and Biatoridium monasteriense were collected in Karelia for the first time. Eighteen rare species (lichens Anaptychia ciliaris, Arthonia vinosa, Bryoria nadvornikiana, Chaenotheca gracilenta, C. stemonea, Lecidea albofuscescens, Lobaria pulmonaria, Melanelixia subaurifera, Nephroma bellum, N. laevigatum, Phaeocalicium populneum, Ramalina thrausta, Rostania occultata, Scytinium subtile, Usnea barbata, mosses Neckera pennata, Plagiomnium drummondii and liverwort Lejeunea cavifolia) listed in the Red Data Book of Republic of Karelia (2007) were found. Relationships between epiphytic lichen and bryophyte species richness and certain environmental variables (at different trunk heights above ground and time-since-disturbance) were evaluated. Lichens and mosses on aspen trunks often occupy different ecological niches. Cover and diversity of bryophytes was high on trunk bases, while the number of lichen species and their cover were higher at a height of 1.3 m above ground level. The total number of lichen species on aspen increased on average from 40 to 60 species per ha with increasing time-since-disturbance from 100 to 450 years. A stabilization in lichen species number was observed at about 200 years since disturbance. No significant correlation was determined between bryophyte diversity on aspens and the time-since-disturbance.

Tree cavity densities and characteristics in managed and unmanaged Swedish boreal forest

ABSTRACTIn forests worldwide, ∼10−40% of bird and mammal species require cavities for nesting or roosting. Although knowledge of tree cavity availability and dynamics has increased during past decades, there is a striking lack of studies from boreal Europe. We studied the density and characteristics of cavities and cavity-bearing trees in three categories of forest in a north-Swedish landscape: clearcuts with tree retention, managed old (>100 years) forest, and unmanaged old forest. Unmanaged old forests had significantly higher mean density of cavities (2.4 ± 2.2(SD) ha−1) than managed old forest (1.1 ± 2.1 ha−1). On clearcuts the mean cavity density was 0.4 ± 2.3 ha−1. Eurasian aspen (Populus tremula) had a higher probability of containing excavated cavities than other tree species. There was a greater variety of entrance hole shapes and a higher proportion of cavities with larger entrances in old forest than on clearcuts. Although studies of breeding success will be necessary to more accurately assess the impact of forest management on cavity-nesting birds, our results show reduced cavity densities in managed forest. To ensure future provision of cavities, managers should retain existing cavity-bearing trees as well as trees suitable for cavity formation, particularly aspen and dead trees.

Plant Community Chemical Composition Influences Trembling Aspen (Populus tremuloides) Intake by Sheep.

Nutrients and plant secondary compounds in aspen (Populus tremuloides) may interact with nutrients in the surrounding vegetation to influence aspen use by herbivores. Thus, this study aimed to determine aspen intake and preference by sheep in response to supplementary nutrients or plant secondary compounds (PSC) present in aspen trees. Thirty-two lambs were randomly assigned to one of four molasses-based supplementary feeds to a basal diet of tall fescue hay (N=8) during three experiments. The supplements were as follows: (1) high-protein (60% canola meal), (2) a PSC (6% quebracho tannins), (3) 25% aspen bark, and (4) control (100% molasses). Supplements were fed from 0700 to 0900, then lambs were fed fresh aspen leaves collected from stands containing high (Experiment 1, 2) or low (Experiment 3) concentrations of phenolic glycosides (PG). In Experiment 2, lambs were simultaneously offered aspen, a forb (Lathyrus pauciflorus), and a grass (Bromus inermis) collected from the aspen understory. Animals supplemented with high protein or tannins showed greater intake of aspen leaves than animals supplemented with bark or the control diet (P<0.05), likely because some condensed tannins have a positive effect on protein nutrition and protein aids in PSC detoxification. Overall, animals supplemented with bark showed the lowest aspen intake, suggesting PSC in bark and aspen leaves had additive inhibitory effects on intake. In summary, these results suggest that not only the concentration but also the types and proportions of nutrients and chemical defenses available in the plant community influence aspen use by herbivores.

Stimulation and inhibition of enzymatic hydrolysis by organosolv lignins as determined by zeta potential and hydrophobicity

BackgroundLignin typically inhibits enzymatic hydrolysis of cellulosic biomass, but certain organosolv lignins or lignosulfonates enhance enzymatic hydrolysis. The hydrophobic and electrostatic interactions between lignin and cellulases play critical roles in the enzymatic hydrolysis process. However, how to incorporate these two interactions into the consideration of lignin effects has not been investigated.ResultsWe examined the physicochemical properties and the structures of ethanol organosolv lignins (EOL) from hardwood and softwood and ascertained the association between lignin properties and their inhibitory and stimulatory effects on enzymatic hydrolysis. The zeta potential and hydrophobicity of EOL lignin samples, isolated from organosolv pretreatment of cottonwood (CW), black willow (BW), aspen (AS), eucalyptus (EH), and loblolly pine (LP), were determined and correlated with their effects on enzymatic hydrolysis of Avicel. EOLs from CW, BW, and AS improved the 72 h hydrolysis yield by 8–12%, while EOLs from EH and LP decreased the 72 h hydrolysis yield by 6 and 16%, respectively. The results showed a strong correlation between the 72 h hydrolysis yield with hydrophobicity and zeta potential. The correlation indicated that the hydrophobicity of EOL had a negative effect and the negative zeta potential of EOL had a positive effect. HSQC NMR spectra showed that β-O-4 linkages in lignin react with ethanol to form an α-ethoxylated β-O-4ʹ substructure (Aʹ) during organosolv pretreatment. Considerable amounts of C2,6–H2,6 correlation in p-hydroxybenzoate (PB) units were observed for EOL–CW, EOL–BW, and EOL–AS, but not for EOL–EH and EOL–LP.ConclusionsThis study revealed that the effect of lignin on enzymatic hydrolysis is a function of both hydrophobic interactions and electrostatic repulsions. The lignin inhibition is controlled by lignin hydrophobicity and the lignin stimulation is governed by the negative zeta potential. The net effect of lignin depends on the combined influence of hydrophobicity and zeta potential. This study has potential implications in biomass pretreatment for the reduction of lignin inhibition by increasing lignin negative zeta potential and decreasing hydrophobicity.

Energy Study of Reactive-HIDiC Simulation for Ethyl Acetate Synthesis from Acetic Acid

In this paper the concept of Heat Integrated Distillation Column (HIDiC) and Reactive Distillation (RD) were used to study the ethyl acetate process by the simulation in Aspen Plus. The intensification concept of reactive-HIDiC was developed applying simulation concepts for the representation of the heat transfer phenomenology. An analysis of binary mixtures involved in the process was developed to determine the thermodynamic model. The thermodynamic properties were calculated with the NRTL-RK (Non-random two- liquids modified by Redlich-kwong) model to estimate the properties. The energy consumption was studied in a reactive distillation column and the intensified configuration r-HIDiC. The parameters of simulation and column configuration were established in order to compare the two configurations. The results showed the amount of energy consumed between the reactive distillation column and r-HIDiC column and compared to determine the energy savings. With the r-HIDiC column presented a decrease of energy consumption and increased concentration of valuable product on the top of column of the 7.8% compared to the reactive distillation column.

Equations for estimating above- and belowground biomass of Norway spruce, Scots pine, birch spp. and European aspen in Latvia

ABSTRACTThis study aims to derive allometric functions to estimate the above- and belowground biomass components of the most important tree species in Latvia. The study material included a total of 81 Norway spruce (Picea abies [L.] Karst), 102 Scots pine (Pinus sylvestris L.), 105 birch spp. (mainly silver birch (Betula pendula Roth)) and 84 European aspen (Populus tremula L.) trees sampled in 124 forest stands. The suitability of three mathematical models for the prediction of total aboveground biomass, stem biomass, total live and dead branch biomass, belowground biomass and small root biomass was evaluated. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change mean default values for the root-to-shoot ratio recommended for temperate and boreal ecological zones leads to the overestimation of root biomass of young trees, especially Scots pine and Norway spruce. Our findings indicate that biomass functions recommended for other Baltic Sea countries are not appropriate for the assessment of the biomass stock in Latvia’s forests because these lead to biased estimates. The biomass functions derived in our study are recommended for reporting the biomass stock in Latvia.

Hydrocarbon mixture fractionation direct sequence retrofitting and feed condition sensitivity analysis

The objective of this paper is to present the retrofit analysis for the hydrocarbon mixture (HM) direct sequence fractionation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient HM separation process methodology has been developed. The methodology consists of four hierarchical steps. In the Step 1, a simple and reliable short-cut method of process simulator (Aspen HYSYS) is used to simulate a direct HM sequence. The energy used to recover individual fractions in the base sequence is analysed and taken as a reference. In the Step 2, an optimal HM sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. Once the optimal HM sequence has been determined, the new optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the process sensitivity and energy used in the optimal HM sequence are analysed, the process sensitivity of optimal HM sequence is compared with the other three different sequences by changing their feed conditions. Better sensitivity sequence was achieved when compared optimal sequence with the other three sequences in Step 4, the sequence determined by the driving force method has better sensitivity compared to the three other sequences as well as less energy requirement. All of these findings show that the methodology is able to design better sensitivity and minimum energy distillation column sequence for HM fractionation process in an easy, practical and systematic manner.

Kinetic Based Simulation of Methane Steam Reforming and Water Gas Shift for Hydrogen Production Using Aspen Plus

This paper presents the kinetic-based simulation of methane steam reforming (MSR) from natural gas and water gas shift (WGS) reaction for hydrogen production. It is found that most simulations of these reactions were either done as balance or equilibrium based. Although it provides simplicity, such approach has limitations, especially for sensitivity analysis, control and optimisation. In order to improve and optimise the reactor performance, kinetic-based simulation is necessary. The kinetic data for MSR and WGS reactions were obtained from literature. The simulation was performed in Aspen Plus using RPLUG model blocks with rearranged Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model. The results of the simulation show good agreement with results found in the literature. Apart from that, sensitivity analysis was carried out to observe the effect of several parameters such as temperature, pressure, catalyst weight and ratio feed to the reactor performance.

Optimal retrofit of natural gas liquids separation direct sequence and feed condition sensitivity analysis

The objective of this paper is to present the retrofitting analysis for the direct sequence natural gas liquids (NGLs) separation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient NGLs separation process methodology is developed. Hence, the methodology consists of four hierarchical steps. In Step 1, a simple and reliable short-cut method for distillation column design of process simulator (Aspen HYSYS) is used to simulate a base (direct) NGLs sequence. The energy used to perform the separation is obtained that will be used for comparison purpose. In the Step 2, an optimal NGLs sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. The optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the energy used in the optimal NGLs sequence is analysed. Finally, the energy and sensitivity used in the optimal NGLs sequence is compared with the base sequence in Step 4. Several case studies involving several sequences have been used to test the performance of the developed methodology. A maximum energy saving of 11.7 MW was achieved when compared with the optimal (driving force) sequence with the direct sequence. For sensitivity analysis, the results show that the driving force sequence has the best sensitivity compared to other sequences. These findings show that the developed methodology is not only able to design energy efficient distillation columns sequence but also better process sensitivity with respect to the feed conditions for NGLs separation process in an easy, practical and systematic manner.