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: Fuel-cell efficiencies yield substantial reductions in the emissions of climate-change 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 energy-intensive continuous processes. This procedure does not guarantee a global cost optimum, but it does lead to good, perhaps near-optimum, 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: 1538; Prenosov: 40
Povezava na celotno besedilo
Energy metabolism, growth performance, body composition, meat quality and boar taint compounds in immunocastrated pigsNina Batorek Lukač
, 2015, doktorsko delo/naloga
Opis: In recent years, immunocastration, a vaccination against gonadotropin releasing hormone, has been proposed as an alternative to surgical castration of intact male pigs without anaesthesia. However, the effects of immunocastration on metabolic changes, nutritional requirements and growth potential have not been quantified. Thus in the present thesis, the meta-analytical approach was used to quantitatively synthesize the effects of immunocastration and four studies were conducted to evaluate the effects of quantitative and qualitative feed restriction on growth performance, heat production and energy metabolism, carcass and meat quality. Results show that boar taint compounds are dramatically reduced in immunocastrates, still they remain slightly higher than in surgical castrates. Immunocastrates are less feed efficient, fatter but grow more rapidly and may have better meat quality than entire males. Compared to surgical castrates, immunocastrates have superior performance with no difference in meat quality. It is more economical to fatten immunocastrates than surgical castrates, but production costs and carcass quality are less favourable than in entire males because of the huge increase in voluntary feed intake during the weeks preceding slaughter. Applying quantitative feed restriction after active immunization did not significantly affect growth performance or carcass composition; however, restrictively fed immunocastrates were closer to entire males, whereas ad libitum fed immunocastrates were closer to surgical castrates. Meat quality is also unchanged by the restriction. However, higher incidence of carcass lesions in restricted immunocastrates together with higher plasma cortisol level indicates more aggression prior to slaughter and can be considered as a negative aspect of the quantitative restriction. Total heat production, assumed to be the major factor contributing to the differences in feed efficiency of pigs, is changed after the immunocastration. Additional energy retained due to higher feed intake is directed towards lipid deposition. Increased fatness of immunocastrates is a result of increased daily lipid deposition caused by higher energy intake, lower fasting heat production and improved energy retention. Hence, dietary energy intake should be limited after immunocastration. Moreover, according to the results of the nitrogen balance study, dietary crude protein content could also be decreased. By reducing net energy concentration of the diet up to 10 % using higher fibre content, similar energy efficiency (gain to net energy intake ratio) may be achieved, with an advantage in terms of reduced lipid deposition, and no effect on growth rate after effective immunization. This is particularly important when immunocastrated pigs are fattened to higher body weights, i.e. when longer delays between full immunization and slaughter are practiced.
Ključne besede: pig, immunocastration, growth performance, carcass characteristics, meat quality, heat production, lipid metabolism, fat deposition, feed restriction
Objavljeno: 27.07.2015; Ogledov: 1242; Prenosov: 84
Celotno besedilo (19,44 MB)
SYNTHESIS OF PROCESSES AND PROCESS SUBSYSTEMS FOR ENTIRE LIFETIMEAndreja Nemet
, 2015, doktorska disertacija
Opis: Economically viable process designs should be, in addition to other criteria, profitable over their entire process lifetimes not only at the present time. An improved process design can be achieved by establishing an appropriate trade-off between product income, raw material, operating costs, and investment. The full lifetime of the processes and future prices have to be considered rather than optimising them on a yearly basis using current prices. Single-period optimisation and synthesis models for processes reflects current prices only. The prices can fluctuate rather quickly and the optimal solution may be very different from one year to the another. Therefore, the traditional superstructural synthesis approach applying a mixed-integer nonlinear programming model was upgraded: i) over time, by considering an entire lifetime, which can be described by a multi-period model and ii) the whole field of variation regarding uncertain future prices. A stochastic approach considering the statistical distribution of price projections over an entire lifetime was used on different case studies instead of the traditional deterministic approach accounting for nominal future price projection. The objective was the maximisation of the expected net present value of a process or the expected incremental net present value of different process subsystem.
The heat exchanger network has been one of the subsystem, which can significantly contribute to operating costs due to savings of external utility consumption. For this subsystem a deterministic and stochastic multi-period mixed-integer nonlinear programming (MINLP) synthesis models have been developed in order to account for future price projections. Considering higher energy prices gives rise to larger initial investments compared to solutions obtained with current prices. However, due to the uncertainties of utility prices' forecasts, retrofitting using an extension of HEN during future years of the lifespan might be a better strategy. The objective is to identify a design that is the most suitable for effective future extensions and preferably with the lowest sensitivity to energy price fluctuations, as there can be various designs featuring similar initial investment. The results supports that it is economically beneficial to consider future utility prices as the incremental investment is not only paid-off but additional savings are achieved.
Process-to-process Heat Integration can also significantly affect the trade-off between investment and operating cost. The aim of Total Site (TS) HEN synthesis was to develop a model synthesis for the TS that, besides many other important features, would also consider future utility prices. Two strategies for TS synthesis have been developed: i) sequential, when HI is performed within a process during the first step and then after a process-to-process HI has been performed, and ii) simultaneous, where the HI is performed within and between processes simultaneously. The second strategy can reveal additional opportunities for heat recovery that might not be identified when applying the first strategy. Comparison of the results obtained at consideration of current utility prices and forecasted utility prices indicates that is worth to account for future utility prices.
The separation processes also consume a significant amount of energy. The synthesis of a distillation column sequence integrated within its heat exchanger network was used as a case study for the separation of a multi-component stream into pure component products by considering future utility prices. This analysis has been performed in order to evaluate the magnitude of the influence of forecasted utility prices. It can be concluded that forecasted utility prices can be beneficial, however, the technical limits of the systems should be carefully observed.
The price fluctuation can also be observed for other prices not only utility prices, e.g. raw material cost, product price, etc
Ključne besede: future prices, forecasted prices, stochastic optimisation, mathematical programming, Heat Exchanger Network, Total Site, distillation column sequence, methanol production
Objavljeno: 04.05.2015; Ogledov: 820; Prenosov: 75
Celotno besedilo (4,74 MB)
Using steam as an alternative motive fluid in the existing turbine ejector system of the Ljubljana District Heating PlantDušan Strušnik
, Jurij Avsec
, 2013, izvirni znanstveni članek
Ključne besede: analysis, ejector, heat flow, oscillation, reconstruction, reliability of production, pump system, motive steam, turbine condenser
Objavljeno: 10.07.2015; Ogledov: 599; Prenosov: 21
Povezava na celotno besedilo
Multiple-effect evaporation in aluminosilicate technologyDušan Klinar
, Janvit Golob
, 2001, strokovni članek
Opis: The article presents an engineering approach to the development of an alternative production with the existing equipment. Zeolite production is becoming an alternative to the old »Bayer« process for aluminum hydrate production. By applying appropriate know-how old equipment was used for an economically as well as ecologically acceptable production. In this equipment adaptation among other production steps the multistage evaporation battery was the most critical part of the process. We applied semi empirical approach on the basis of Z. Rant ideas to find heat transfer coefficients and to determine which equipment elements are more relevant for efficient performance and need serious maintenance.
Ključne besede: chemical engineering, evaporation in silicate technology, bauxite alumina production, evaporators, process optimization, heat transfer, heat flow, empirical equations, heat transfer coefficients, zeolites
Objavljeno: 24.08.2017; Ogledov: 339; Prenosov: 45
Celotno besedilo (354,14 KB)
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