This contribution presents a developed generic mixed integer linear programming (MILP) model for optimizing biogas supply network to generate electricity over monthly time-periods by maximizing the economic performance. Dry matter content and methane yield for each feedstock are included, which more accurately represents a realistic network. The model is applied to an illustrative case study of an agricultural biogas production plant in Slovenia. Optimal results show poultry manure and bedding and corn silage as the selected feedstocks to meet the production of 999?kW of electricity. Technologies selected include anaerobic digester, press-based dewatering and combined heat and power plant (CHP), while water, and heat required for the anaerobic digestion plant itself are “recycled”. A profit after tax of about 254,625 $/y is obtained. Furthermore, sensitivity analysis in terms of prices of electricity and digestate, dry matter content and utilization of crop residues is performed.
COBISS.SI-ID: 21533462
This paper describes an upgraded concept of the sustainability metric named Sustainability Profit (SP) from various micro- and macroeconomic perspectives and how it can be used for the synthesis of production systems in order to increase their circularity. An upgraded concept of SP is presented from three different perspectives: a microeconomic one, representing the company level, a macroeconomic perspective, combining the company and country (government) levels, and a wider macroeconomic one, with the addition of individuals (employees). Basic indicators of circularity, which measure the share of materials and energy reuse, are incorporated in order to synthesize more sustainable systems involving reuse of materials and energy. The concept is demonstrated on two case studies of supply network synthesis. The first case study is a supply network of fossil and renewable electricity production from various energy sources with fixed electricity demand, and the second case study is a larger-scale, renewable-based supply network for producing food, biofuels and electricity, and is applied to Central Europe. The results indicate that, by maximizing SP using the upgraded concept, overall circularity is favoured, and trade-offs between different sustainability pillars are obtained. The study could further be extended to account for uncertainty and more detailed Eco- and Social profit analysis and circularity measures as a good decision support tool in evaluating sustainable production systems.
COBISS.SI-ID: 21620246
The inventive method and device enable the pyrolysis process in a reactor, which is, from the construction point, significantly simplified, since a direct volume transfer of heat to biomass does not require a special portable surface of the reactor. The objective of the invention is to implement a controlled pyrolysis process in a reactor, the mechanical implementation of which will be simple enough and thus economical, thereby enabling the construction of a device that will compete on the market for devices intended for agriculture or individual farms. The invention, with its advantages, enables the mechanical implementation of a reactor with controlled air supply zones and a variable retention time depending on the individual partial volume of the reactor and the rate of biomass dosing and removal of char or ash from it. In the reactor, we can carry out the pyrolysis process or combustion without mechanical adjustments, and we can only perform it by setting process parameters. The inventive method of implementing the pyrolysis reaction enables accurate monitoring and regulation of the process parameters for biochar formation, by which we can influence and at the same time guarantee the desired biochar characteristics. The reaction system also allows the addition and homogenization of various biochar additives in the form of solutions. The invention allows the efficient capture of excess heat, generated by combustion of gases formed during the pyrolysis process. Hot gases from the area of complete combustion are supplied to the gas-water heat exchanger, where useful heat is captured into hot water as a portable medium to the users.
COBISS.SI-ID: 26239544
This study focuses on synthesizing large-scale heat exchanger networks (HENs) using mathematical programming to achieve near globally optimal solutions based on a two-step MILP/MINLP approach. In the first step a mixed-integer linear programming (MILP) model, TransHEN, is used that obtains a pglobally optimal solution at selected ?Tmin. By utilisation of this model, the most promising matches are selected based on feasibility and viability. The second step entails using the matches selected in the TransHEN of Step 1 in a mixed-integer nonlinear programming (MINLP) model, HENsyn, using a reduced superstructure, to generate a feasible HEN. This study presents also a simultaneous Total Site synthesis with direct heat transfer between processes. The newly developed procedure has been tested on two case studies. For Case study 1 the results obtained lie within the range of best solutions obtained by other authors. Case study 2, consisting of 173 process stream and involving multiple hot utilities, shows the applicability of the developed method to handle large-scale HEN problems.
COBISS.SI-ID: 21528598
This paper proposes a general superstructure and a Mixed-Integer Nonlinear Programming (MINLP) model for the synthesis and simultaneous optimisation and Heat Integration (HI) of Single- and Multiple-Effect Evaporation (SEE/MEE) systems including Mechanical Vapour Recompression (MVR) and the background process. The proposed superstructure also includes different flow patterns (forward feed, backward feed, parallel feed and mixed feed), Flashing of Condensates (FCs), single- and multi-stage MVR systems and various HI opportunities for preheating of feed stream (e.g. with condensates, bled vapours, and hot streams from the background process). The newly proposed SEE/MEE-FC-MVR superstructure is combined with a Heat Exchanger Network (HEN) superstructure for performing simultaneous optimisation and HI. On the basis of this combined superstructure, an MINLP model with tight bounds on the variables is developed and implemented for its solution in the General Algebraic Modeling System (GAMS). The model is solved using a two-step solution strategy. The proposed model enables to explore simultaneously all interconnections within the proposed superstructure in order to find the configuration with the optimal trade-offs between capital and energy costs.
COBISS.SI-ID: 21495574