Dynamic Simulation and Start-up Scenario a Pilot Distillation Column for Separating C6-C8 Hydrocarbons

A pilot distillation column was fabricated for multipurpose functions, such as separation testing compared with a real plant distillation column, and sample preparation for other projects. The packing efficiency of this column was developed by changing the packing material. Packing efficiency is normally an important key index, especially after a revamp. Aspen Dynamic was used to generate the best procedure for the start-up operation, covering three variables: the distillate rate, the reflux rate and the bottom rate. The start-up procedure according to these three parameters was divided into six scenarios. In addition, the effect of reflux rate and feed location was the operating conditions, including temperature profile of the column, benzene concentration in the overhead stream, and liquid levels in the reflux drum and sump. The test run data matched well, with 0.6 Murphree efficiency. The optimal procedure for the start-up operation was found to be a distillate rate – bottom rate – reflux rate scenario, which took just 9 h to reach a steady state

Design of a Stacked-layer Tubular Photobioreactor for Microalgae Cultivation

A tubular photobioreactor is one of the most effective methods of microalgae cultivation because of the high solar receiver area and better biomass productivity. However, the pressure drop along the tubular solar receiver induces a relatively high dead zone. An optimal design is necessary to maximize biomass productivity. In this article, the proposed model can reduce the dead zone by up to 15% under a pressure drop of 106 Pa. To optimize the area requirement, three configurations with different stacking angles of 30, 45, and 60°, are simulated. The optimal 60° stacked-layer model is then connected to an airlift device to demonstrate the complete system. This model can circulate seawater inside the reactor at an average velocity of 0.188 m/s with 0.07 m/s of air inlet velocity. The radial flow can force the microalgae from the inner part of the tube to the outer part and back again throughout the entire stacked section. This turbulence will enhance biomass productivity because the microalgae are moved from the darker interior of the tube to the periphery where they are exposed to solar radiation. The optimal stacked-layer tubular photobioreactor has a slope of 60° with four stacked layers. This modification promotes the circulation of microalgae in both axial and radial directions

Transesterification of Biodiesel by Molecular Modeling and Simulation

Transesterification of alkyl esters plays an important role in biodiesel production, and a critical substance in this mechanism is triacylglycerol. A molecular modeling technique is used in this study to determine the geometrical parmeters of triacylglycerol via semi-empirical AM1, PM3 and ab initio HF/6-31G with the GaussView 03W and GAUSSAIN 03W pieces of software. The results obtained from these three models showed that the geometrical parameters of the triacylglycerol molecules are in the same range. Hence, these molecular models can be used in the simulation of the transesterification mechanism. There are six possible mechanisms for the biodiesel transesterifications. Each type of mechanism contains six reaction steps. Using the B3LYP/6-31G//PM3 method, the transesterification mechanism was simulated to determine the best possible pathway

Energy and Exergy Analysis of Steam Boiler and Autoclave in Fiber Cement Process

The fiber cement composite production process consumes extremely high fuel especially boiler and autoclave leading to the release of a lot of waste energy. In this study, the concept of energy and exergy utilization is analyzed and illustrated in the form of the Sankey diagram. It was found that the energy and exergy efficiencies of the boiler were 72.04 and 69.98%, respectively. The exergy destruction of the boiler system is 30% or 3.89 MW. Which can also be represented in the Power Available Diagram (PAD). In the exergy analysis, there are 2 methods in reducing the energy loss of the boiler by increasing the steam outlet temperature or reducing the temperature of the exhaust gas of the boiler. For the autoclave system, the energy analysis showed the total energy input at 43.67 GJ/batch. The three main energy losses are; the exhaust steam (49.74% or 23.74 GJ/batch), condensate (16.42% or 7.83 GJ/batch) and autoclave shell heat loss (13.67% or 6.25 GJ/batch). For the exergy, the exergy destruction in the autoclave is at 87.14%. However, the PAD of the autoclave cannot present the relation of the exergy loss. The main causes of the exergy destruction are the three main energy losses; the exhaust steam (50.80%), condensate (16.47%) and autoclave shell loss (10.01%) respectively

Simulation of Doxorubicin Delivery via Glucosamine(ethylene glycol) Carrier

This article focuses on the molecular modeling of the release of doxorubicin from capsules composed of glucosamine(ethylene glycol) oligomers. Doxorubicin forms micelle structures with glucosamine(ethylene glycol), and the drug release mechanism can be studied through the modeling of oligomeric bond breaking under acidic, neutral, or basic conditions. Under these conditions, the activation energies were calculated to be 145.51, 135.78, and 287.60 kcal/mol, respectively, at the B3LYP/6-31G//PM3 level. Based on these values, doxorubicin can be released into acidic and neutral solutions but not into basic solution. Ethylene glycol chain length in glucosamine(ethylene glycol) also effects drug release. As the length of ethylene glycol increases, the amount of drug released increases under acidic conditions, but decreases under neutral and basic conditions. When the drug is released from glucosamine(ethylene glycol) oligomers, the drug molecule and glucosamine(ethylene glycol) molecules form a micelle structure. Studies found that, as the length of the ethylene glycol chains increases, the micelle structure is more easily formed. The ethylene glycol group can deliver doxorubicin to cancer cells in micelle form

Preliminary Study of Conformation and Drug Release Mechanism of Doxorubicin-Conjugated Glycol Chitosan, via cis-Aconityl Linkage, by Molecular Modeling

Abstract: An investigation of the structure and drug release mechanism of a drug delivery system is proposed on the basis of semi-empirical and ab initio computations in vacuum stage. Cis-aconityl linkage is used to improve the interaction between an anti-cancer agent, doxorubicin, and a glycol chitosan biopolymer. It has been found that the doxorubicin-conjugated glycol chitosan carrier has more stability. The stability is increased when the lengths of the polyethylene glycol (PEG) chains in the glycol chitosan biopolymer are increased. Cis-aconityl can release doxorubicin under appropriate environmental conditions. Relative energies of this mechanism in an acid condition, as determined by B3LYP/6-31G//PM3, are 122.41, 119.27, 160.18 and 222.22 kcal/mol, and by the B3LYP/6-31G//HF/6-31G method are 54.23, 109.28, 219.98 and 980.49 kcal/mol, with mono-, di-, tri-, and quanta-ethylene glycol, respectively. In a normal condition, the relative energies are above 300 kcal/mol for all reactions. Therefore, cis-aconityl will release doxorubicin in an acid solution but not in a normal condition. The glycol chitosan polymer can be degraded in an acid solution as well. Long PEG chains influence the release mechanism of doxorubicin. The proposed length of the PEG chain is di-ethylene glycol. These simulation results agree well with various reported experimental data

Performance comparison of different control strategies for heat exchanger networks

In this article, the dynamic responses of heat exchanger networks to disturbance and setpoint change were studied. Various control strategies, including: proportional integral, model predictive control, passivity approach, and passivity-based model predictive control were used to monitor all outlet temperatures. The performance of controllers was analyzed through two procedures: 1) inducing a ±5% step disturbance in the supply temperature, or 2) tracking a ±5°C target temperature. The performance criteria used to evaluate these various control modes was settling time and percentage overshoot. According to the results, the passivity-based model predictive controllers produced the best performance to reject the disturbance and the model predictive control proved to be the best controller to track the setpoint. Whereas, the ensuing performance results of both the PI and passivity controllers were discovered to be only acceptable

Design and Implementation of Energy Recovery System from Autoclaves in Fiber Cement Industry

The fiber cement composite process has extremely high fuel consumption and a lot of waste energy released. This study focuses on the recovery methods from two waste heat streams; the condensate and the exhaust steam from the autoclaves. An analysis of the heat loss from the autoclave shell showed that the optimum insulation thickness is 0.085 mm. To recover heat from either condensate or exhaust steams, a pinch location can recover the waste heat for fresh boiler feed water at 100°C. Introduction of multiple heat exchanger optimization and control proposed two series of shell and tube exchangers for the condensate and the exhaust steams. The fuel consumption from the heat recovery can approximately be reduced to 8.37 MTHB/year with a payback period of one and a half year

Passive Controller Design of Mass Exchanger Network

This work mainly focuses on applying the passivity concept to a mass exchanger network. Development of the mass exchanger state space model with controller design is proposed. The state space equations of the mass exchanger model have been developed based on assumptions a of lumped parameter system, including well mixing rich and lean streams, a linear equilibrium relation over the operating range and isothermal and isobaric conditions. The mass exchanger model is characterized as a non-passive system due to its positive passivity index, and according a weighting function is introduced to shift the system to passive region along with the controller tuning. A case study of a five-streams mass exchanger network with four control loops is demonstrated using a weihing function to again counter the non-passive characterstic. Multi-loop passive PI controllers of the mass exchanger network are developed. This passive control configuration is tested by both disturbance rejection and set-point tracking. The designed passive controllers are able to completely eliminate the impact of disturbance effects, and all control loops show good performance to track 4, 15, 3 and 1.5% change of the set-points