Timo Laukkanen

Implementation aspects of interactive multiobjective optimization for modeling environments: the case of GAMS-NIMBUS

Interactive multiobjective optimization methods have provided promising results in the literature but still their implementations are rare. Here we introduce a core structure of interactive methods to enable their convenient implementation. We also demonstrate how this core structure can be applied when implementing an interactive method using a modeling environment. Many modeling environments contain tools for single objective optimization but not for interactive multiobjective optimization. Furthermore, as a concrete example, we present GAMS-NIMBUS Tool which is an implementation of the classification-based NIMBUS method for the GAMS modeling environment. So far, interactive methods have not been available in the GAMS environment, but with the GAMS-NIMBUS Tool we open up the possibility of solving multiobjective optimization problems modeled in the GAMS modeling environment. Finally, we give some examples of the benefits of applying an interactive method by using the GAMS-NIMBUS Tool for solving multiobjective optimization problems modeled in the GAMS environment.

Prediction of gas composition of Jatropha curcas Linn oil cake in entrained flow reactors using ASPEN PLUS simulation software.

A prediction for product gases of Jatropha curcas Linn (JCL) oil cake gasified in the entrained flow reactor is studied in this paper. ASPEN PLUS commercial software is used to carry out the simulation using Gibbs free energy minimisation with equilibrium phase. A series of simulations and analyses have been carried out to investigate the composition of product gases in JCL oil cake with reactor temperature ranging from 1000 to 1400°C. In the first prediction step, the gas composition of sawdust and rice husk are validated. After this, the simulation model is used to predict JCL oil cake gas composition. Mean error analysis is carried out to identify the maximum and minimum error of the simulation. The results show that with increasing reactor temperature, the amount of carbon monoxide (CO) and hydrogen (H2) increases while the amount of carbon dioxide (CO2) and methane (CH4) decreases. The results of the gas composition of JCL oil cake show that the CO content at a temperature of 1000°C ranges from 41.35% to 53.36%. Composition of other gases such as hydrogen (H2), carbon dioxide (CO2), methane (CH4) is 24.65–32.7%, 4.4–22.99% and 0.94%–19.62%, respectively.

Simultaneous precipitation of phosphorus in a kraft pulp mill wastewater treatment plant

Simultaneous precipitation (SP) using iron sulfates in the secondary treatment of elemental chlorine-free (ECF) kraft pulp mill wastewater was studied. In short-term pilot plant studies phosphorus reduction was improved from 58% up to 81% by adding 10 mg(Fe)/L ferrous sulfate in the activated sludge (AS) process. The phosphorus reduction in full-scale experiment was about 80% when less than 10 mg(Fe)/L was fed in with the influent of the AS plant. The reduction of phosphorus decreased with the dose of iron during the three month experiment. No notable change in either chemical oxygen demand (COD) or adsorbable organic halogen (AOX) reduction nor in the properties of sludge settling were observed during this SP experiment. Furthermore, no problems in sludge treatment due to increased iron concentrations in the waste sludge were reported. SP offers a simple way to decrease phosphorus discharges from AS plants instead of reliance on more expensive tertiary treatments.

Simulation and analysis of a combined cycle heat and power plant process

The regulations of process efficiency and stricter environmental policies require analysis of large-scale thermal energy systems to produce highly efficient, cost effective and low environmental impact energy. For analysis, it is beneficial to simulate an energy system. In this paper, simulation models are developed for the analysis of a combined cycle heat and power plant located in Göteborg, Sweden. With the help of simulation models, characteristics between district heating (DH) water temperature and key parameters such as overall district heat duty, electrical power and electrical efficiency has been developed. The characteristics are useful to estimate and maximize the key parameters during varying DH water temperature. According to a comparison between the full-load simulation models of 2006 and 2013 for the selected power plant, a loss of 2 MW is noticed for gas turbine and a loss of 2.18 MW of heat flow occurs for heat recovery steam generator in the year 2013. The feasibility analysis of modifying the connection between DH economizer and main DH line provides good performance indicators in a winter scenario. The conclusions in this paper are good references to plan and improve the performance of existing large-scale thermal power plants.