Thongchai Srinophakun

GAPinch: genetic algorithm toolbox for water pinch technology

Abstract Wastewater in the chemical industry can be minimized by water reuse. The optimum water usage network leads to a minimum freshwater consumption and wastewater treatment. Genetic algorithm, an objective of this work, is developed for solving the wastewater minimization problem. The optimization model is formulated for both single and multiple contaminants in the class of mixed integer nonlinear programming (MINLP). In this model, there is a set of equality constraints from mass balance that drives the genetic algorithm from addressing the feasible solution. To elucidate this problem, all variables have to be divided into two groups: independent and dependent variables. The values of independent variables come from randomization, whereas the values of dependent variables come from simultaneous solutions of a set of equality constraints after assigning the values of independent variables. This method is applied to the steps of initialization, crossover and mutation. The developed program is the MATLABTM toolbox that consists of 29 m-file. The graphic user interface was created in order to make the program easy and convenient. After a user inputs the process condition of the problem into the blank form of GUI, the program will formulate the optimization model and solve for the solution automatically. Then, the optimum results are returned to the user. The program is tested with a process that contains a certain number of water-using operations in which water is used to remove a fixed content of contaminant. In the single contaminant system, this program and Lingo can find the minimum freshwater consumption, but the solutions are different in the configuration of water usage network. These alternative configurations give a wide-vision on the analysis of the system. In the multiple contaminants system, this program can find the same or better results in some test problems.

Design of raceway ponds for producing microalgae.

Background: A raceway pond for producing algal fuels must be designed to minimize the energy required for mixing, otherwise the net energy recovery in the biofuel will be low. Results & discussion: Computational fluid dynamics modeling was used to characterize the energy demands for mixing full-scale raceways of various configurations. The locations of the dead zones and the conditions required for eliminating them were identified. The existing geometric configurations of the raceways were compared, to identify the best configuration. Conclusion: An inexpensive raceway configuration with a minimum of three semicircular deflector baffles and a modified end of the central divider was found to be the most energy efficient, while also being able to completely eliminate the dead zones.

Modified genetic algorithm for nonlinear data reconciliation

Nonlinear data reconciliation problem are inherently difficult to solve with conventional optimization methods because of the existence of a multimodal function with differentiated solutions. In this paper, the genetic algorithm (GA) of Wasanapradit [Wasanapradit, T. (2000). Solving nonlinear mixed integer programming using genetic algorithm. Master Thesis, King Mongkut University of Technology Thonburi, Bangkok, Thailand. Available: fengtcs@ku.ac.th] based on modified cross-generational probabilistic survival selection (CPSS) is explored for solving the steady state nonlinear data reconciliation (DR) problem. The DR problem is defined by a redescending estimator as the objective function, which is both a non-convex and discontinuous function. In the GA method, first the appropriate GA parameters are found and then the algorithm must be validated with the problem. The results show that the GA solves the redescending function without the complex calculations required by conventional optimization methods, but the calculation time is longer.

Simulation of power cycle with energy utilization diagram

The graphical representation named energy utilization diagram (EUD) is a very useful tool for exergy analysis of chemical processes. This technique can be applied to the power cycle, the combination of heat exchangers and power subsystems. The cooperation of EUD with the process simulator was introduced to retrieve the simulation results and thermodynamic properties. The ASPEN Plus simulator was used in this research for constructing the EUD routine by programming in Fortran block and external Fortran files. The Rankine power cycle and an improved Rankine cycle were selected as a case study for verifying this routine. The sensitivity analysis of the Rankine cycle showed that the exergy loss/net generated power ratio (EXL/NGP) decreased with these three conditions: pump discharge pressure increase, turbine discharge pressure decrease and steam temperature increase. The increase of the subcooled temperature in the condenser affected the increase of EXL/NGP. The ratio of EXL/NGP could be reduced by 12.61% compared to the base case after adjusting the operating condition. In addition, the modification of the Rankine cycle to the Kalina cycle could be achieved for the purpose of exergy reduction. The ratio of EXL/NGP could be reduced from 2.04805 in the Rankine cycle (improvement case) to 1.06036 in the Kalina cycle. Thus, the efficiency of the power cycle could be improved significantly.

Preliminary study of conformation and drug release mechanism of doxorubicin-conjugated glycol chitosan, via cis-aconityl linkage, by molecular modeling.

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.

A systematic formulation for HAZOP analysis based on structural model

Abstract The combination of an automatic HAZOP analysis with a structural model was introduced to obtain a systematic procedure for hazard and mal-operations identification. There are three stages of the proposed procedure. The first stage was used to analyze the conventional hazard and mal-operations for each process unit, whereas the second stage extended the analysis to adjacent units. The interaction style was used to identify the cause–consequence relationships between upstream and downstream unit with the concepts of the non-local path and the dummy parameters. Therefore, a generic HAZOP library will be additional modified. The third stage created the templates for hazard and mal-operations identification for operating arbitrary units. This proposed HAZOP analysis was verified with conventional HAZOP of the defatted soy flour pilot plant with three scenarios. The analysis scheme fulfilled the library of the case study and discovered 18 new consequences for the first scenario, 10 new consequences for the second scenario. For the third scenario, the analysis specified on an arbitrary flash drum by applying three guide-words (more, less and no) and found 46 causes and 83 consequences. The proposed methodology, therefore, can simplify and reveal the guidance for hazards and mal-operations identification.

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.

Performance comparison of different control strategies for heat exchanger networks

Abstract 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.

A Mixed Coding Scheme of a Particle Swarm Optimization and a Hybrid Genetic Algorithm with Sequential Quadratic Programming for Mixed Integer Nonlinear Programming in Common Chemical Engineering Practice

In this paper, mixed integer nonlinear programming (MINLP) is optimized by PSO_GA–SQP, the mixed coding of a particle swarm optimization (PSO), and a hybrid genetic algorithm and sequential quadratic programming (GA–SQP). The population is separated into two groups: discrete and continuous variables. The discrete variables are optimized by the adapted PSO, while the continuous variables are optimized by the GA–SQP using the discrete variable information from the adapted PSO. Therefore, the population can be set to a smaller size than usual to obtain a global solution. The proposed PSO_GA–SQP algorithm is verified using various MINLP problems including the designing of retrofit heat exchanger networks. The fitness values of the tested problems are able to reach the global optimum.

Extension of energy–utilisation diagram to power availability for exergy loss analysis

Energy–Utilisation Diagram (EUD) has been used to identify exergy loss in general process units, whereas Power Availability Diagram (PAD) provides the difference between exergy changes of two pressure exchangers. Two modifications of the original PAD are proposed for better exergy loss visualisation. Firstly, the energy donor curve is shifted to the location of energy acceptor. Secondly, arrows indicating the exergy change direction are inserted in the diagram. This research leads to Modified Power Availability Diagram (MPAD) that can identify the exergy loss. From the applied Rankine cycle, MPAD was changed in two forms as MCPAD (Modified Cycle Power Availability Diagram) and MSPAD (Modified Subsystem Power Availability Diagram). The results showed that MPAD can presents the exergy profile of the working fluid and MSPAD can reduce the complexity of EUD and show the exergy loss of each unit in the cycle. The advantages of MCPAD can present the graphical exergy distribution.