Volume 12, Issue 4 - Special Issue of 29th Symposium of Malaysian Chemical Engineers (SOMChE) 2016 - Process System Engineering, Guest Editors: Agus Saptoro, Jobrun Nandong, Mohd Azlan Bin Hussain, Syamsul Rizal Abd. Shukor

This special issue presents a set of twelve selected papers from 29th Symposium of Malaysian Chemical Engineers (SOMChE) 2016 on the area of process system engineering. SOMChE 2016 itself was held in Miri Marriott Resort & Spa, Miri, Sarawak, Malaysia from 1st to 3rd December 2016. This symposium was co-organised by Department of Chemical Engineering, Curtin University Malaysia and Institution of Chemical Engineers (IChemE), Malaysia. Since the theme of the symposium is “Engineering Solutions for Sustainable Development”, its papers are related to the latest advances and best practices of engineering solutions in industry and academic for sustainable food, water, energy and environment. Consequently, the selected papers in this special issues focus on how process system engineering is employed to address energy, environmental and economic issues faced by process industries. Each paper in this special issue had undergone double peer review to ensure its quality. We believe that this issue will serve as a book of knowledge and an essential literature, which will lead to not only scientific and engineering progress but also other novel processes and new products. We express our gratitude to the authors, reviewers and editors of this journal who make the publications of these papers possible.

Circulating fluidized beds (CFB) play a major role in the chemical industry especially as heterogeneous catalytic reactors. Research on hydrodynamic properties of Liquid – Solid CFBs (LSCFB) is significantly under-reported as compared to Gas – Solid CFBs (GSCFB). Steadily, prominent research is being established in fields like food industry (whey protein recovery), waste management (removal of heavy metals from radioactive wastes) and others, which use LSCFBs. In this context, it is important to have significant knowledge about the changes occurring in hydrodynamic properties like solid hold-up, rate of solid circulation etc., on changing certain critical physical properties such as inventory height. An LSCFB of height 2.95 m and riser outer diameter 0.1 m was chosen and the effect of inventory height on the properties was studied by taking the initial inventory heights as 15 cm, 25 cm and 35 cm. The hydrodynamic studies concentrated on axial solid holdup, average solid holdup, solid circulation rate and slip velocity. On increasing the inventory, uniformity of axial solid holdup was confirmed along with studying holdup patterns. Solid flux was seen to follow an inverse relationship to holdup, as expected. The change in slip velocity with varying inventory was also checked, and was found to decrease with inventory. The distribution parameter, C o of the drift flux model was used to determine the extent of non-uniformity in solid distribution. C o was calculated to be less than unity in the range of 0.983–0.994, suggesting non-uniformity in solid distribution, with higher solid concentration by the walls compared to the core.

The dehydration unit of a plant that processes natural gas uses triethylene glycol (TEG) as an absorbent to remove water from the gas to prevent blockages in pipes due to the formation of hydrates. Although TEG is recyclable, it is usually lost in the system due to vaporization and carryover, which results in economic issues. Therefore, it is necessary to optimize the dehydration process to achieve the allowable water concentration in the gas, to minimize the use of energy, and to minimize the loss of TEG. Experimental set was designed using Design Expert software by utilising data from Farashband gas processing plant, Iran and subsequently, fed to ASPEN HYSYS to construct and simulate the dehydration process. The chosen affecting parameters to the process were the (1) lean glycol circulation rate, (2) the temperature of the reboiler, and (3) the number of trays in the contactor column. Whereas, the response parameters included the (1) amount of glycol that was lost, (2) the reboiler duty, (3) the concentration of water in the dry gas, and the (4) temperature at which the hydrate formed. Then, these data were optimized using the response surface methodology (RSM). The results indicated that the optimum conditions within the experimental range conducted in this study of process parameters chosen, of the lean glycol circulation rate, the temperature of the reboiler, and the number of trays in the glycol contactor column for the gas dehydration process for the plant were 3944 kg/hr, 180 °C, and three trays, respectively.

Locally weighted partial least square (LW-PLS) model has been commonly used to develop adaptive soft sensors and process monitoring for numerous industries which include pharmaceutical, petrochemical, semiconductor, wastewater treatment system and biochemical. The advantages of LW-PLS model are its ability to deal with a large number of input variables, collinearity among the variables and outliers. Nevertheless, since most industrial processes are highly nonlinear, a traditional LW-PLS which is based on a linear model becomes incapable of handling nonlinear processes. Hence, an improved LW-PLS model is required to enhance the adaptive soft sensors in dealing with data nonlinearity. In this work, Kernel function which has nonlinear features was incorporated into LW-PLS model and this proposed model is named locally weighted kernel partial least square (LW-KPLS). Comparisons between LW-PLS and LW-KPLS models in terms of predictive performance and their computational loads were carried out by evaluating both models using data generated from a simulated plant. From the results, it is apparent that in terms of predictive performance LW-KPLS is superior compared to LW-PLS. However, it is found that computational load of LW-KPLS is higher than LW-PLS. After adapting ensemble method with LW-KPLS, computational loads of both models were found to be comparable. These indicate that LW-KPLS performs better than LW-PLS in nonlinear process applications. In addition, evaluation on localization parameter in both LW-PLS and LW-KPLS is also carried out.

In this paper, the comparison of turbulence models for fluid flow past single sphere under supercritical conditions is reported. Firstly, Dixon et al.’s models [1], which are under non-supercritical conditions, were used as benchmarks to validate the simulated results. Two turbulence models namely RNG k-ε and SST k-ω models parameters were fine-tuned accordingly in order to obtain almost comparable results generated by Dixon et al.’s models [1]. The simulation works were then extended to simulate flow of supercritical carbon dioxide. The second part of this paper, therefore, presents a comparative study of the turbulence models i. e. standard k-ε , RNG k-ε , realizable k-ε and SST k-ω models. This study emphasises on the predictions and evaluations of the velocity profiles at different flow regimes namely recirculation, recovery and near-wake. Simulations were carried out to determine the velocity profiles at subcritical and supercritical conditions by varying Reynolds numbers (2000 and 20,000), pressures (65 and 80 bar) and temperatures (283.15 and 308.15K). Simulation results indicate that the predicted results are consistent with the literature data. Interesting flow features were identified for all the simulations. The results of this study also reveal that the SST k-ω turbulence model was able to better capture the flow characteristics near-wake of the sphere.

Sustainable biomass supply chain management (SBSCM) problem is a multi-objective optimisation (MOO) problem since the objectives of each sustainability dimension and (or) each components under a same sustainability dimension can be conflicting. It is unlikely to have a single solution that could simultaneously satisfy all objectives. Therefore, achieving optimum for one objective requires compromise of other objectives. Several approaches have been developed to solve MOO problems. The simplest way reported from the academicians is to transform MOO problem into single objective optimisation (SOO) problem by converting all objectives into a similar form of objectives. However, converting environmental impacts into economic form might produce sub-optimal solution as the optimal result is highly dependent on the magnitude of the penalty cost. This paper presents a systematic approach which integrates both economic and environmental concerns in the supply chain by using the concept of analytic hierarchy process (AHP). Instead of merely focusing on carbon emission, this paper incorporates other environmental indicators as well, i. e., global warming potential (GWP), ozone depletion potential (ODP), acidification potential (AP), photochemical ozone creation potential (POCP), nutrification potential (NP), aquatic toxicity potential (ATP), terrestrial toxicity potential (TTP), abiotic depletion potential (ADP), water footprint and land footprint. On top of that, this paper also proposes a graphical illustration method to present the sustainability performance of the results. Both economic sustainability and environmental sustainability are expressed in a vector form. With the aid of this graphical representation, the tendency of the process towards each sustainability dimension can be clearly seen. A case study in Johor state is used to demonstrate the proposed method and a palm biomass supply chain with high sustainability performance (λSCM${\lambda ^{SCM}}$= 0.8437) is synthesised in this paper.

Hydrogen is considered as an environmental friendly energy carrier but its actual impact on the environment depends on the way it is produced. A strategy of plant-wide modelling and advanced process control with optimization is currently developed for the Hydrogen production via the Iodine-Sulphur thermochemical cycle process. The objectives of this paper are two-folds: (1) to optimize the trade-off between steady-state profitability and dynamic operability of the Bunsen section subject to multiple constraints, and (2) to design practical control strategy based on the multi-scale control concept. A multi-scale modelling for the Bunsen section in the Hydrogen production via the Iodine-Sulphur thermochemical cycle process is presented. Based on this multi-scale model, a practical control design is developed and applied to Bunsen section. The suitable sets of control variables and manipulated variables are chosen via a sensitivity study incorporating the multivariate Response Surface Analysis method. By dint of simulation study, it can be shown that the proposed control strategy is able to produce a good closed-loop performance where its robustness depends strongly on the selected schemes of Bunsen section. It is worth highlighting that, the proposed multi-scale control strategy demonstrates robust performance in the face of the worst case uncertainty scenario.

Distillation is the most commonly used separation and purification technique in the chemical and allied industries despite that it has been known as the most energy-consuming unit in process industry. The need to reduce this energy consumption has become one of the important focuses in the efficient design and optimization of distillation processes. In the present work, we propose an improved Lewis-Matheson stage-by-stage procedure by incorporating the Fenske equation to enhance the estimation of the non-key component distributions, and thus avoiding infeasible solutions to the stage-by-stage system of equations of mass and energy balances. A modified theta method is also included in the design procedure to satisfy the feed stage matching criteria which help reduces the computational time while increasing the accuracy of feed composition matching. By using the proposed modified Lewis-Matheson method, an optimization is conducted in Matlab environment where the problem formulation takes into account both sets of design and operating parameters with specified product purity as the constraint. The objective function of the optimization is to minimize the Total Annualized Cost (TAC), which includes both capital and operating costs. The effectiveness of the proposed design procedure is demonstrated using an industrial-scale natural gas liquids (NGLs) depropanizer fractionation unit.

Major components of triglycerides in palm oil are palmitic acid, oleic acid, and linoleic acid, in which the presence of these components effects the final purity of a biodiesel. Since reaction process and type of catalyst influence the composition of the free fatty acid (FFA) ASPEN HYSYS was used to simulate a biodiesel production process. Furthermore, higher yield of biodiesel was desired to increase its efficiency as fuel application. Palm oil was taken as the raw material at different components of FFA wt% by using sulphated zirconium (SZ) as the catalyst. Three simulations of biodiesel production processes were performed using ASPEN HYSYS based on 99 % of conversion factor to determine the energy consumption and the results were compared. The conversion factor for each component and the mixture of all of the components was discussed. Results showed that triolein with 0.12 wt% of oleic acid produced 99.75 % of biodiesel, while tripalmitin with 0.5 wt% of palmitic acid is the most abundant FFA in palm oil producing 99.67 % of biodiesel. The total energy consumption in the three processes were different because, different types of feedstocks and unit operations arrangements have been used.

Two-fluid model approach to simulate gas-liquid airlift reactors is widely implemented but have yet to reach a consensus on the closure model to account the gas-liquid interphase forces. Proper selection of a closure model is required in order to accurately capture the hydrodynamics in the complex of the two-phase system. Our work concerns the evaluation of the interfacial forces models (i. e. drag, lift and turbulent dispersion force) and their effects on local gas holdup and liquid velocity. A transient three-dimensional airlift reactor simulation was carried out using computational fluid dynamics by implementing the dispersed standard k-ε turbulence model. Four drag models governed by spherical bubble, bubble deformation and Rayleigh-Taylor were being evaluated in our work. The significance on the inclusion of the lift model on predictive accuracy on the flow field was also studied as well. Whereas, two turbulent dispersion force models were selected to evaluate on their performance in improving the predictive accuracy of the local hydrodynamics. Results showed that the drag governed by Rayleigh-Taylor which accounts the bubble swarm effect had better predictions on the gas holdup in the downcomer and improved predictions in radial gas holdup. The inclusion of the lift model improved local gas holdup predictions at higher heights of the reactor and shifted the bubble plume towards the centre region of the riser. Meanwhile, the turbulent dispersion models improved the overall results of predicted local gas holdup with closer agreement obtained when the drift velocity model was considered in the simulation. The axial liquid velocity was well predicted for all cases. The consideration of the drag, lift and turbulent dispersion forces resulted in a closer agreement with experimental data.

The work proposes two different approaches where the first one is based on the tools of the system theory and the other is strongly related to the principle of heat balance, in order to analyze the abnormal phenomena of the continuous styrene polymerization reactors, i. e. the multiplicity behavior in the wide range of operating conditions. More precisely, the multiplicity behavior of polystyrene production in a continuous stirred tank reactor (CSTR) is carried out by the numerical simulations through the Van Heerden diagram and the phase plane. Furthermore, the bifurcation diagrams in terms of two different inputs including jacket temperature and volumetric flow rate of initiator predict the appearance of multiplicity behavior as well as the saddle-node bifurcation points. The results, firstly, verify that the multiplicity behavior of the system appears under considered operating conditions. Secondly, the analysis of bifurcation behavior gives the theoretical prediction of multiplicity behavior once the operating conditions vary due to the soft constraints or the effect of noise and disturbance.

This research presents the numerical results of laminar forced convective heat transfer performance and the flow behaviour for Al 2 O 3 -water nanofluid in circular, 2:1 rectangular, 4:1 rectangular and square ducts. The nanoparticles concentration studied were 0.01%, 0.09%, 0.13%, 0.25%, 0.51%, 1.00% and 4.00%. Single phase constant and temperature-dependent properties were employed. For the case of constant properties, the thermal performance and pressure drop increase with the increase of nanofluid concentration and Reynolds number. For the temperature-dependent properties, the Nusselt number and pressure drop also increase when the Reynolds number increases. However, there is a slight decrement in the Nusselt number and no significant pressure drop increment when the nanofluid concentration is increased from 0.01% to 1.00%. When the concentration is further increased to 4.00%, the Nusselt number and pressure drop increase. For the temperature-dependent model, lower thermal performance and pressure drop are identified when compared to those of the constant properties. The maximum Nusselt number enhancement and pressure drop increment occur at the concentration of 4.00% and Reynolds number of 2000. They are 25.43% and 945.69% as well as 4.86% and 117.01% for constant and temperature-dependent properties, respectively. The thermal-hydraulic efficiency of nanofluid is found to be not as good as the pure water.

Hydrogen (H 2 ) has been recognized as one of the attractive energy carriers due to its clean and environmentally friendly characteristics where the burning of H 2 as a fuel produces zero waste emission. Water-gas shift reaction (WGSR) has been accepted as one promising pathway for producing hydrogen. Recently, membrane technology has emerged as a new way to improve high-purity H 2 production via the WGSR. A substantial amount of research works has so far focussed on the production of H 2 alone while often neglecting the emission of carbon dioxide ($CO_2$CO2), a greenhouse gas that is known to be the culprit responsible for global warming. Addressing the conflicting issues between clean H 2 fuel and environmentally adverse $CO_2$CO2 emission requires a systematic engineering approach to carbon capture to be incorporated directly into H 2 production plant. In view of this, the reuse of $CO_2$CO2 can be implemented by incorporating the dry methanation reaction. In the proposed reuse strategy, the WGSR uses carbon monoxide (CO) and water as the reactants while the dry methanation reaction uses $CO_2$CO2 and methane (CH 4 ) to produce CO and H 2 . Based on two case studies of industrial plants, this paper presents a rigorous evaluation of the technical and economic feasibility of the implementation of this reuse strategy by using H 2 selective membrane reactor (MR). Upon extensive analysis of different strategies with and without carbon capture technology, it is found that with the proposed carbon capture strategy, the industrial plants show positive improvement in terms of both technical and economic performances.