1. Heat integration between two biodiesel processes using a simple methodAnita Kovač Kralj, 2008, izvirni znanstveni članek Opis: Biodiesel is a cleanburning alternative fuel, produced from domestic, renewable resources. Biodiesel can be blended at any level with petroleum diesel to create a biodiesel blend. It can be used in compressionignition (diesel) engines with little or no modification. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics. This paper presents heat integration between two biodiesel processes. Biodiesel can be produced by the esterification of different fatty acids (high and low boiling point) with alcohols. This simple method for heat integration is based on three possible steps. Simultaneous integration between processes can be performed using a stagewise model with a mixed integer nonlinear programming (MINLP) algorithm (step 3), which can include alternatives suggested by pinch analysis of heat transfer between the processes (step 2). The internal integration of individual processes can be performed in step 1. The fraction can be calculated for maximum integration between processes. Integration between the processes can be carried out using all three steps or by the first and third steps or by the last step only, depending on the problems' complexities. This method includes streams of different processes which are heated or cooled using a utility only. The existing heaters and coolers can be left unchanged in their original processes or can be used for integrating heat between processes, with hot and cold utilities being saved. This approach is illustrated by integrating two simulated biodiesel processes.The objective was to maximize additional annual profit for integration between processes by USD8300/a. Ključne besede: chemical processing, biodiesel producing, heat integration, nonlinear programming Objavljeno: 31.05.2012; Ogledov: 1187; Prenosov: 43 Povezava na celotno besedilo 
2. Energy saving and modifications in the methanol process, using the NLP model optimizationAnita Kovač Kralj, Peter Glavič, 2006, objavljeni znanstveni prispevek na konferenci Opis: The opportunities for additional profit depend very much on the existing plant and energy system. Heat and power integration can reduce fuel usage in chemical processes. Nonlinear programming contains equations which enable structural and parametric optimization. The NLP model is formulated using an optimum energy target of process integration and electricity generation using a gas turbine with separator. The reactor acts as a combustion chamber of the gas turbine plant, producing a lot of energy. The simultaneous NLP approach can account for capital cost, integration of combined heat and power, process modification and additional production of tradeoffs, and can thus yield a better solution. The combined production of electricity, heat and chemical products can lead to better process efficiency. The methanol plant was optimized using a mathematical nonlinear programming model by including an additional flowrate of hydrogen in crude methanol recycle and increasing the methanol production by 2,5%. The electricity can be generated in methanol recycle using a gas turbine. The total additional profit is 2,5 MEUR/a. Ključne besede: chemical engineering, methanol production, simultaneous process optimization, nonlinear programming, cogeneration, product increase Objavljeno: 30.05.2012; Ogledov: 1457; Prenosov: 12 Povezava na celotno besedilo 
3. CO2 separation from purge gas and flue gas in the methanol process, using NLP model optimizationAnita Kovač Kralj, Peter Glavič, 2007, izvirni znanstveni članek Opis: The concentration of CO2 in the atmosphere has to be stabilized, requiring a reduction in current emission rates in existing plants. This will be done by reducing the environmental burden imposed in such areas as materials input andCO2 emission reduction and using cleaner production, resources, and energy recycling. Any opportunities for emission reduction and CO2 reuse largely depend on existing plant and energy systems. CO2 can be separated from the outlet stream (purge gas) and from flue gas by a membrane or absorption system(absorber and regenerator) or adsorption system and reused as a reactantin a reactor system. Therefore, product yield can be increased and CO2emissions reduced, simultaneously. CO2 emissions can be reduced at the source. The authors of this paper studied CO2 reuse in a methanol process, in which electricity can be generated using an open gas turbine, followed by a separator. Simultaneous optimization of a process structure and its parametersusing simplified nonlinear programming (NLP) ensures an additional annual profit, influenced by reusing the flow rate of CO2. The additional electricity cogeneration and additional flow rates of the raw material could generate an additional profit of 2.79 MEUR/a. Ključne besede: chemical processing, methanol production, optimization, nonlinear programming, CO2 emissions, CO2 reuse Objavljeno: 31.05.2012; Ogledov: 1217; Prenosov: 51 Povezava na celotno besedilo 
4. H2 separation and use in fuel cells and CO2 separation and reuse as a reactant in the existing methanol processAnita Kovač Kralj, Peter Glavič, 2007, izvirni znanstveni članek Opis: Fuelcell efficiencies yield substantial reductions in the emissions of climatechange gases and promise an end to exclusive reliance on carbon fuels for energy. Fuel cells, CO2 reuse, process heat integration, and open gas turbine electricity cogeneration can be optimized simultaneously, using a nonlinear programming (NLP) algorithm. The simplified NLP model contains equations of structural and parametric optimization. This NLP model is used tooptimize complex and energyintensive continuous processes. This procedure does not guarantee a global cost optimum, but it does lead to good, perhaps nearoptimum, designs. The plant, which produces methanol, has a surplus of hydrogen (H2) and CO2 flow rates in purge gas. H2 is separated from the purge gas by an existing pressure swing adsorption (PSA) column. Pure H2 can be usedas fuel in fuel cells. CO2 can be separated from the outlet stream (purge gas) by a membrane or absorption system (absorber and regenerator) or an adsorption system and reused as a reactant in a reactor system. Therefore, theproduct yield can be increased and CO2 emissions can be reduced, simultaneously. CO2 emissions can then be reduced at the source. The retrofitted process can be operated within existing parameters. Using a methanol process as a case study, the CO2 emission flow rate can be reduced by4800 t/a. The additional electricity cogeneration in the gas turbine and in fuel cells and additional flow rates of the raw material could generate an additional profit of 2.54 MEUR/a. Ključne besede: chemical processing, methanol production, optimization, nonlinear programming, CO2 reuse, fuel cells, heat integration, energy cogeneration Objavljeno: 31.05.2012; Ogledov: 1565; Prenosov: 44 Povezava na celotno besedilo 
5. MINLP optimization of a singlestorey industrial steel buildingTomaž Žula, Zdravko Kravanja, Stojan Kravanja, 2008, izvirni znanstveni članek Opis: The paper presents the topology and standard sizes optimization of a singlestorey industrial steel building, made from standard hot rolled I sections. The structure consists of main portal frames, connected with purlins. The structural optimization is performed by the MixedInteger Nonlinear programming approach (MINLP). The MINLP performs a discrete topology and standard dimension optimization simultaneously with continuous parameters. Since the discrete/continuous optimization problem of the industrial building is nonconvex and highly nonlinear, the Modified Outer Approximation/EqualityRelaxation (OA/ER) algorithm has been used for the optimization. Alongside the optimum structure mass, the optimum topology with the optimum number of portal frames and purlins as well as all standard crosssection sizes have been obtained. The paper includes the theoretical basis and a practical example with the results of the optimization. Ključne besede: civil engineering, topology optimization, sizing optimization, nonlinear programming, MINLP Objavljeno: 31.05.2012; Ogledov: 1322; Prenosov: 30 Povezava na celotno besedilo 
6. An integrated strategy for the hierarchical multilevel MINLP synthesis of overall process flowsheets using the combined synthesis/analysis approachNataša Iršič Bedenik, Bojan Pahor, Zdravko Kravanja, 2004, izvirni znanstveni članek Opis: This paper describes an integrated strategy for a hierarchical multilevel mixedinteger nonlinear programming (MINLP) synthesis of overall process schemes using a combined synthesis/analysis approach. The synthesis is carried out by multilevelhierarchical MINLP optimization of the flexible superstructure, whilst the analysis is performed in the economic attainable region (EAR). The role of the MINLP synthesis step is to obtain a feasible and optimal solution of the multiD process problem, and the role of the subsequent EAR analysis step is to verify the MINLP solution and in the feedback loop to propose any profitable superstructure modifications for the next MINLP. The main objective of the integrated synthesis is to exploit the interactions between the reactor network, separator network and the remaining part of the heat/energy integrated process scheme. Ključne besede: multilevel MINLP, MINLP synthesis, attainable region, economic attainable region, concentration attainable region, continous stirred tank reactor, plug flow reactor, recycle reactor, nonlinear programming, mixed integer nonlinear programme Objavljeno: 01.06.2012; Ogledov: 1731; Prenosov: 65 Povezava na celotno besedilo 
7. A strategy for MINLP synthesis of flexible and operable processesZorka NovakPintarič, Zdravko Kravanja, 2004, izvirni znanstveni članek Opis: Abstract This paper presents a sequential twostage strategy for the stochastic synthesis of chemical processes in which flexibility and static operability (the ability to adjust manipulated variables) are taken into account. In the first stage, the optimal flexible structure and optimal oversizing of the process units are determined in order to assure feasibility of design for a fixed degree of flexibility. In the second stage, the structural alternatives and additional manipulative variables are included in the mathematical model in order to introduce additional degrees of freedom for efficient control. The expected value of the objective function is approximated in both stages by a novel method, which relies on optimization at the central basic point (CBP). The latter is determined by a simple setup procedure based on calculations of the objective functionćs conditional expectations for uncertain parameters. The feasibility is assured by simultaneous consideration of critical vertices. The important feature of the proposed stochastic model is that its size depends mainly on the number of design variables and not on the number of uncertain parameters. The strategy is illustrated by two examples for heat exchanger network synthesis. Ključne besede: chemical processing, process synthesis, MINLP, mixed integer nonlinear programming, flexibility, operability, controllability, steady state model Objavljeno: 01.06.2012; Ogledov: 1552; Prenosov: 55 Povezava na celotno besedilo 
8. Estimation of solid solubilities in supercritical carbon dioxide: PengRobinson adjustable binary parameters in the near critical regionMojca Škerget, Zorka NovakPintarič, Željko Knez, Zdravko Kravanja, 2002, izvirni znanstveni članek Opis: The density dependence of the binary parameters of the PengRobinson equation of state in near the critical region was examined. Published solubility data of eight compounds in pure CO2 have been fitted to the PengRobinson equation in combination with one and two parameters van der Waals mixing rules and in combination with the three parameter density dependent mixing rule of Mohamed and Holder. A systematic study has been done to determine the influence of different terms in the mixing rules. In order to obtain density dependence, binary parameters were calculated for each isotherm at particular experimental point separately in the way to equalise experimental and calculated solubility data. The system was formulated as an equationoriented model and solved by means of a nonlinear programming optimisation algorithm. For all compounds the binary interaction parameters thus obtained were found to vary strongly with pressure in the range from 75 bar to approximately 150 bar, i.e. near the critical end point (CEP) of the low temperature branch of the three phase solidliquidgas (SLG) curve. At higher pressures, the parameter is practically independent on pressure. In general, for the systems investigated, kij increases linearly with increasing density and reaches a constant value at higher densities in the range from 700 to 800 kg/m3, depending on the system under investigation. Ključne besede: solid liquid equilibria, equation of state, mixing rules, binary parameters, near critical region, nonlinear programming, thermodynamic model, supercritical fluids, CO2, solubility Objavljeno: 01.06.2012; Ogledov: 1363; Prenosov: 66 Povezava na celotno besedilo 
9. Cost optimal project schedulingUroš Klanšek, Mirko Pšunder, 2008, izvirni znanstveni članek Opis: This paper presents the cost optimal project scheduling. The optimization was performed by the nonlinear programming approach, NLP The nonlinear total project cost objective function is subjected to the rigorous system of the activity preceden ce relationship constraints, the activity duration constraints and the project duration constraints. The set of activity precedence relationship constraints was defined to comprise FinishtoStart, StarttoStart, StarttoFinish and FinishtoFinish precedence relationships between activities. The activity duration constraints determine relationships between minimum, maximum and possible duration of the project activities. The project duration constraints define the maximum feasible project duration. A numerical example is presented at the end of the paper in order to present the applicability of the proposed approach. Ključne besede: project management, scheduling, optimization, nonlinear programming, NLP Objavljeno: 10.07.2015; Ogledov: 649; Prenosov: 166 Celotno besedilo (444,81 KB) Gradivo ima več datotek! Več...

10. Mixedinteger nonlinear programming based optimal time scheduling of construction projects under nonconvex costsRok Cajzek, Uroš Klanšek, 2016, izvirni znanstveni članek Opis: Optimal project scheduling under nonconvex timecost relations represents a challenging problem in construction management. The nonconvex timecost relations may appear in a construction project when several different duration options are available for its activities due to alternative technological processes enabled for their realization or wide accessibility of production resources. The source of nonconvexity of the project scheduling optimization problem can also be the project penalty or bonusduration relations arranged within the construction contract. The aim of this paper is to present the mixedinteger nonlinear programming (MINLP) based optimal time scheduling of construction projects under nonconvex costs. For this purpose, the MINLP model was developed and applied. A numerical example from literature and an example of construction project timecost tradeoff analysis under practical nonconvex penalty function are given in the paper to demonstrate advantages of MINLP optimization. The example from literature first presented the capability of the MINLP approach to obtain the optimal solution for difficult, highly combinatorial nonconvex discrete project scheduling problem. Thereupon, the following example revealed that the optimal project timecost curve may take very nonuniform shape on account of discrete nature of activity direct cost options and nonconvex relation between project duration and total cost. In this way, the presented study intends to provide practitioners with new information from the field of optimization techniques for project scheduling as well as an alternative view on performance of total cost when project duration is changed. Ključne besede: extreme environments, construction management, discrete optimization, mixedinteger nonlinear programming, nonconvex costs, time scheduling Objavljeno: 12.07.2017; Ogledov: 327; Prenosov: 206 Celotno besedilo (807,33 KB) Gradivo ima več datotek! Več...
