Specific Investment Cost Research Articles

Comparison of different optimized heat driven power-cycle configurations of a gas engine

Among different technologies in internal combustion engines, waste heat recovery from the lost energies has great potential to improve fuel economy and reduce CO2 emission. In the present work, to achieve the optimal design parameters for a waste heat recovery system of a gas engine, a multi-objective optimization evolutionary algorithm is employed. The system consists of different types and combinations of the Organic Rankine/Kalina cycle as the waste heat recovery system of gas engine exhaust gas and the waste heat of cooling water is recovered by the trilateral flash cycle. The objective functions are chosen to maximize exergy efficiency and minimize the specific investment cost of the system. Cyclohexane, Toluene, and Benzene have been investigated and compared to the organic Rankine cycle working fluid. To evaluate different cycle configurations and working fluids, the Pareto front solutions related to 18 studied cases are compared. Meanwhile, the “Linear Programming Technique for Multidimensional Analysis of Preference” decision-making approach has been used as an optimal point in all cases. This work is aimed to compare the optimal design operating conditions of the studied configurations to choose the best configuration for waste heat recovery from a gas engine. The results reveal that, among the decision parameters, the organic Rankine cycle turbine inlet temperature is the most important in terms of the specific investment cost of the system. Also, considering the exergy and energy efficiency of the system, organic Rankine cycle turbine inlet temperature as well as organic Rankine cycle and trilateral flash cycle turbine isentropic efficiencies are of great importance. The Pareto front comparison for each configuration indicates that toluene is the most suitable fluid for the organic Rankine cycle in all configurations. Comparing the selected optimal points in different combinations reveals that, the configuration of organic Rankine cycle with internal heat exchanger-trilateral flash cycle, due to its lower payback period and specific investment cost as well as the higher exergy efficiency and net power output in optimal point, is the prominent compared to the other combinations. Furthermore, the optimized configuration of the organic Rankine cycle with the internal heat exchanger-trilateral flash cycle shows a 14.31% increase in the exergy efficiency and an 8.2% decrease in the specific investment cost of the system compared to the base case. Employing the optimized configuration of the organic Rankine cycle with internal heat exchanger-trilateral flash cycle as waste heat recovery of the gas engine leads to a 7.8 kW increment of net power output, equivalent to an increase of 18.85% exergy efficiency of the whole system including engine and bottoming cycle. On the other hand, additional equipment to the engine, impose 3061$/kW specific investment cost which takes 2.2 years to be paid back.

A comparative study of the energy, exergetic and thermo-economic performance of a novelty combined Brayton S-CO2-ORC configurations as bottoming cycles

This paper presents a comparative study on the energy, exergetic and thermo-economic performance of a novelty thermal power system integrated by a supercritical CO2 Brayton cycle, and a recuperative organic Rankine cycle (RORC) or a simple organic Rankine cycle (SORC). A thermodynamic model was developed applying the mass, energy and exergy balances to all the equipment, allowing to calculate the exergy destruction in the components. In addition, a sensitivity analysis allowed studying the effect of the primary turbine inlet temperature (TIT, PHIGH, rP and TC) on the net power generated, the thermal and exergy efficiency, and some thermo-economic indicators such as the payback period (PBP), the specific investment cost (SIC), and the levelized cost of energy (LCOE), when cyclohexane, acetone and toluene are used as working fluids in the bottoming organic Rankine cycle. The parametric study results show that cyclohexane is the organic fluid that presents the best thermo-economic performance, and the optimization with the PSO method conclude a 2308.91 USD/kWh in the SIC, 0.22 USD/kWh in the LCOE, and 9.89 year in the PBP for the RORC system. Therefore, to obtain technical and economic viability, and increase the industrial applications of these thermal systems, thermo-economic optimizations must be proposed to obtain lower values of the evaluated performance indicators.

Thermo-economic analyses and evaluations of small-scale dual-pressure evaporation organic Rankine cycle system using pure fluids

Thermo-economic performance of small-scale (<1 MW) dual-pressure evaporation organic Rankine cycle (DPORC) system using pure fluids was studied. The effects of heat source conditions (flow rate and temperature), pinch point temperature differences (PPTDs), and heat sink condition on the thermo-economic performance of DPORC system were analyzed. The distribution characteristics of component costs were given. Traditional single-pressure evaporation ORC (SPORC) system was selected as the compared object to evaluate the thermo-economic performance of DPORC system. Results show that the minimized specific investment cost (SIC) of DPORC system substantially decreases with increasing flow rate and temperature of heat source. The DPORC system can obtain a better thermo-economic performance compared with SPORC system. For R245fa, the minimized SIC of DPORC system can be 0.6% lower than that of SPORC system, meanwhile its net power output also increases by 21.9%. The substantial increase of heat absorbers cost generally results in the minimized SIC of DPORC system is higher. Furthermore, the DPORC system has a larger application potential at the working conditions of the large flow rate of heat source and PPTD during heat absorption process. The working fluid with a high critical temperature is more suitable to adopt the DPORC system.

Exergy-Based Analysis and Optimization of an Integrated Solar Combined-Cycle Power Plant.

The transition towards higher shares of electricity generation from renewable energy sources is shown to be significantly slower in developing countries with low-cost fossil fuel resources. Integrating conventional power plants with concentrated solar power may facilitate the transition towards a more sustainable power production. In this paper, a novel natural gas-fired integrated solar combined-cycle power plant was proposed, evaluated, and optimized with exergy-based methods. The proposed system utilizes the advantages of combined-cycle power plants, direct steam generation, and linear Fresnel collectors to provide 475 MW baseload power in Aswan, Egypt. The proposed system is found to reach exergetic efficiencies of 50.7% and 58.1% for day and night operations, respectively. In economic analysis, a weighted average levelized cost of electricity of 40.0 $/MWh based on the number of day and night operation hours is identified. In exergoeconomic analysis, the costs of thermodynamic inefficiencies were identified and compared to the component cost rates. Different measures for component cost reduction and performance enhancement were identified and applied. Using iterative exergoeconomic optimization, the levelized cost of electricity is reduced to a weighted average of 39.2 $/MWh and a specific investment cost of 1088 $/kW. Finally, the proposed system is found to be competitive with existing integrated solar combined-cycle plants, while allowing a significantly higher solar share of 17% of the installed capacity.

Parametric optimisation of a combined supercritical CO2 (S-CO2) cycle and organic Rankine cycle (ORC) system for internal combustion engine (ICE) waste-heat recovery

Supercritical CO2 (S-CO2) power-cycle systems are a promising technology for waste-heat recovery from internal combustion engines (ICEs). However, the effective utilisation of the heat from both the exhaust gases and cooling circuit by a standalone S-CO2 cycle system remains a challenge due to the unmatched thermal load of these heat sources, while a large amount of unexploited heat is directly rejected in the system’s pre-cooler. In this paper, a combined-cycle system for ICE waste-heat recovery is presented that couples an S-CO2 cycle to a bottoming organic Rankine cycle (ORC), which recovers heat rejected from the S-CO2 cycle system, as well as thermal energy available from the jacket-water and exhaust-gas streams that have not been utilised by the S-CO2 cycle system. Parametric optimisation is implemented to determine operating conditions for both cycles from thermodynamic and economic perspectives. With a baseline case using a standalone S-CO2 cycle system for an ICE with a rated power output of 1170 kW, our investigation reveals that the combined-cycle system can deliver a maximum net power output of 215 kW at a minimum specific investment cost (SIC) of 4670 $/kW, which are 58% and 4% higher than those of the standalone S-CO2 cycle system, respectively. A range of ICEs of different sizes are also considered, with significant performance improvements indicating a promising potential of exploiting such combined-cycle systems. This work motivates the pursuit of further performance improvements to waste-heat recovery systems from ICEs and other similar applications.

Commercial Biogas Plants: Lessons for Ukraine

Ukraine has enough biomass resources for biogas production. However, this energy potential is not used sufficiently. This research is aimed at examining the current experience of commercial biogas systems in the Europe Union and its adaptation for Ukraine. Special attention was paid to economic indicators, such as specific investment costs, production costs (biogas, biomethane, and electricity), and incentives. Using statistical data for the European Union and Ukraine, the biogas potential for Ukraine (based on European experience) was determined. The economic competitiveness of biogas production was evaluated compared to alternatives, such as photovoltaic, wind power, biomass, conventional fuels, and liquid biofuels. The results showed that biogas complexes have higher specific investment costs and produce more expensive electricity. It was highlighted that agricultural residues and industrial waste are sustainable feedstocks for biogas systems. A perspective biogas plant is a plant that is an integrated part of the circular bioeconomy that is based on organic residues. Biomethane production (as a substitution for vehicle fuel) combined with capture and utilization of carbon dioxide is a more profitable pathway. Awareness and perception of the importance of biogas are key factors for the development of the biogas industry. To develop an effective strategy for the biogas industry, it is necessary to create a positive image in order to raise awareness and knowledge of biogas technologies.

Exergetic performance and comparative assessment of bottoming power cycles operating with carbon dioxide–based binary mixture as working fluid

This paper presents CO2-toluene (CO2-C7H8) binary mixture as working fluid to enhance the energetic and exergetic performance of CO2 bottoming power cycles in warm ambient conditions. A criterion for selection of CO2-based binary mixture is defined, and 0.9 CO2/0.1 C7H8 composition is decided based on the required minimum cycle temperature compatible with ambient conditions. Bottoming simple regenerative cycle (BSRC) and bottoming preheating cycle (BPHC) configurations are selected, and their realistic operating conditions are determined based on sensitivity analysis. The performance of bottoming cycles using CO2-C7H8 binary mixture is compared with the bottoming cycles using pure CO2 as working fluid at different ambient temperatures. It is observed that the cycles operating with pure CO2 can only perform better at lower ambient temperature conditions, whereas, at the increased ambient temperatures, bottoming cycles with CO2-C7H8 binary mixture outperform and produce significant gains in exergetic and energetic performance compared with pure CO2 bottoming cycles. A maximum gain of exergetic efficiency for BSRC and BPHC observed is 26.83% and 18.71%, respectively, at an operating ambient temperature of 313 K, whereas an overall gain in energetic efficiencies for BSRC and BPHC observed is 28.92% and 10.12%, respectively. Taking into consideration thermodynamic performance, overall UA (product of overall heat transfer coefficient and heat transfer area for the heat exchanger) and specific investment cost, BPHC configuration is suggested as reasonable choice for higher ambient temperature conditions.

Exergoeconomic analysis of zeotropic mixture on the new proposed organic Rankine cycle for energy production from geothermal resources

In this study, the performance of Isobutane/Isopentane (zeotropic mixture) is studied in the new proposed Organic Rankine Cycle (NORC). Operating parameters included temperatures of two series evaporators and regenerative, degree of superheating, and pinch point temperature difference in the first evaporator are optimized with multi-objective functions i.e., exergy as thermodynamic, Specific Investment Cost (SIC) as economic and exergoeconomic as the third objective function that considered exergy and SIC simultaneously. Optimization results for Isobutane/Isopentane indicate that the value of exergy has a sharp decrease when the mole fraction of Isobutane increases to 0.5, and after that, the exergy amount rises significantly and reaches a peak at 54.584% for pure Isobutane. Also, return on investment (ROI) is employed as an economic indicator to get the center of attention in economic proficiency by utilizing Isobutane/Isopentane in NORC configuration according to the exergoeconomic results for fifteen countries as two groups of developed and developing in order to compare profitability all around the world. The results represent that, by the growing of Isobutane mole fraction in Isobutane- Isopentane mixture, ROI indicator is reduced. The maximum and the minimum value of ROI are related to Germany (57.64%) and India (4.09%), respectively.

A study of effects on economic indicators for different heat source temperature on thermal storage‐based solar organic Rankine cycle system

AbstractThe solar organic Rankine cycle (ORC) system for power generation with thermal storage type may be one of the promising technologies for prolonging power generation. The thermal storage type of solar ORC system is feasible for investment due to higher power production. In addition, the heat source temperature of the ORC system plays an important role in the investment. The main aim of the study is to investigate the solar ORC with thermal storage systems from the thermoeconomic point of view. The paper provides recommendations for a suitable class of investment in which an ORC system can be economically feasible. Besides, the economics and thermoeconomic analysis is carried out in order to find the cost of electricity production from the solar ORC under various solar source temperatures. The cost of electricity generation is found to be in the range of $0.2/kWh to $0.6/kWh for 120°C and 90°C, respectively. For analysis, different financial scenarios are developed based on the total cost of the solar ORC units. The economic parameters, such as payback period, internal rate of return (IRR) and specific investment cost, are calculated. The payback period is found to be less than 6 years for the thermal storage type of solar ORC system with the IRR to be 15%. This shows that the investment is feasible for medium and large scale solar ORC with thermal storage systems.

Thermodynamic and economic investigation of an ionic liquid as a new proposed geothermal fluid in different organic Rankine cycles for energy production

Organic Rankine cycle (ORC) is a promising technology for electricity generation by utilizing heat sources at low to moderate temperatures. In the present work, an ionic liquid (1-butylpyridinium tetrafluoroborate, C9H14NBF4), a known green chemical and non-volatile compound with good thermal and chemical stability, and significant heat capacity are utilized as a geothermal fluid. Simulation and optimization were conducted for a basic ORC, a regenerative organic Rankine cycle (RORC) and a two-stage evaporative organic Rankine cycle (TSORC) by maximizing exergy efficiency and minimizing specific investment cost. The operating parameters considered in the optimization exercise were evaporative and regenerative temperatures, pinch point temperature difference of evaporators and the degree of superheat. Peng Robinson equation of state was used and isobutane (R-600a) and butane (R-600) were selected as working fluids. Comparisons were made between the performance of ORCs when C9H14NBF4 and water were individually used as a geothermal fluid. Utilization of an ionic liquid improved the performance of the three ORC configurations with the best performance generated from a basic ORC with exergy efficiency of 82.35% (R-600) and 87.70% (R-600a). From an economic viewpoint, the amount of specific investment cost (SIC) is comparatively lower when ionic liquid is used as a geothermal fluid.

Profitability Analysis and Capital Cost Estimation of a Thermochemical Energy Storage System Utilizing Fluidized Bed Reactors and the Reaction System MgO/Mg(OH)2

The storage of industrial waste heat through thermochemical energy storage (TCES) shows high potential to reduce the dependency on fossil fuels. In this paper the capital cost investment of a TCES system utilizing fluidized bed reactors and the reaction system MgO/Mg(OH) 2 is estimated and a profitability analysis is performed. The study estimate is based on a simulation study that considers the mass and energy balance of the proposed preliminary heat storage and release processes utilizing fluidized bed reactors. Furthermore, transport, operation and maintenance as well as utility costs were estimated in order to evaluate the profitability of the system. It is concluded that for the selected boundary conditions, the specific investment costs per kW stored heat are approximately 900 €/kW and that the systems should not be installed at sites where less than around 5 MW of waste heat are available. Finally, a sensitivity analysis was conducted, to identify the key process and economic parameters critical for a positive net present value.

Stochastic economic analysis of coal-alternative fuel production from municipal solid wastes employing hydrothermal carbonization in Zimbabwe.

Hydrothermal carbonization (HTC) is a promising technology for converting high moisture municipal solid waste (MSW) to a safe low-chlorine hydrochar. The key objective is to assess the economic viability of an HTC based MSW management system in Zimbabwe. Previous studies have only used deterministic estimates of hydrochar production costs disregarding uncertainties in their model parameters. Herein, a probabilistic economic analysis is introduced to quantify the uncertainty concerning costs. The goal is to determine factors that will consolidate the venture to achieve a certain level of return. The effectiveness of different investment strategies, namely, a government or private sector-run operation will be tested using Monte Carlo simulations. Results indicate a 55% and 18% probability for a positive Net Present Value (NPV) for a state-run and private operation respectively. A specific investment cost of US$54 - 67 per Mg of MSW treated, a return on investment (ROI) of 5.4-29.0% and internal rate of return (IRR) of 5.2-22.9% can be expected if the project is undertaken by government. The private sector can expect an ROI of -0.8-18.2% at a 90% confidence level and a lower IRR of -2.1-16.2% from US$57 - 71 per Mg of MSW invested. Contingency costs are US$25 per Mg and US$38 per Mg of MSW for the government and private sector respectively at a 100% confidence interval. A 70% rise in collection tariffs or a minimum selling price of US$91/Mg of the hydrochar would ensure a positive NPV for the government-run operation.

Effects of shell-and-tube heat exchanger arranged forms on the thermo-economic performance of organic Rankine cycle systems using hydrocarbons

Shell-and-tube heat exchangers are crucial and widely used components in organic Rankine cycle (ORC) systems. Heat exchanger arranged forms, namely, the organic fluid flows either inside or outside the tubes, substantially affect the purchased cost and exergy loss of heat exchangers; and thereby considerably influencing the system thermo-economic performance. Based on various heat exchanger arranged forms, the thermo-economic performance of ORC systems may differ remarkably and even result in opposite conclusions, such as in selecting optimal working fluids and ratios of component purchased cost. However, no published studies have focused on this specific issue. Influence degree exerted by the heat exchanger arranged form on the thermo-economic performance of ORC system remains unclear. Selection guidelines for the optimal arranged forms also need to be developed. This study analyzed the effects of heat exchanger arranged forms on the thermo-economic performance of subcritical ORC systems with shell-and-tube heat exchangers. Three common heat exchanger arranged forms were studied. Heat source temperatures are 100–200 °C, and five hydrocarbons are working fluids. Results show that the heat exchanger arranged forms substantially affect the specific investment cost (SIC) of ORC system, and the largest difference in SIC reaches 14.7% among various arranged forms. The optimal working fluid and system parameters, and ratios of component purchased costs also differ remarkably. Optimal heat exchanger arranged form depends on the working fluid and heat source temperature. This study provides the optimal heat exchanger arranged forms for five hydrocarbons at heat source temperatures of 100–200 °C.

Thermoeconomic Modelling and Parametric Study of a Simple ORC for the Recovery of Waste Heat in a 2 MW Gas Engine under Different Working Fluids

This paper presents a thermo-economic analysis of a simple organic Rankine cycle (SORC) as a waste heat recovery (WHR) systems of a 2 MW stationary gas engine evaluating different working fluids. Initially, a systematic methodology was implemented to select three organic fluids according to environmental and safety criteria, as well as critical system operational conditions. Then, thermodynamic, exergy, and exergo-economic models of the system were developed under certain defined considerations, and a set of parametric studies are presented considering key variables of the system such as pump efficiency, turbine efficiency, pinch point condenser, and evaporator. The results show the influence of these variables on the combined power of the system (gas engine plus ORC), ORC exergetic efficiency, specific fuel consumption (∆BSFC), and exergo indicators such as the payback period (PBP), levelized cost of energy (LCOE), and the specific investment cost (SIC). The results revealed that heat transfer equipment had the highest exergy destruction cost rates representing 81.25% of the total system cost. On the other hand, sensitivity analyses showed that acetone presented better energetic and exergetic performance when the efficiency of the turbine, evaporator, and condenser pinch point was increased. However, toluene was the fluid with the best results when pump efficiency was increased. In terms of the cost of exergy destroyed by equipment, the results revealed that acetone was the working fluid that positively impacted cost reduction when pump efficiency was improved; and toluene, when turbine efficiency was increased. Finally, the evaporator and condenser pinch point increased all the economic indicators of the system. In this sense, the working fluid with the best performance in economic terms was acetone, when the efficiency of the turbine, pinch condenser, and pinch evaporator was enhanced.

Cost Uncertainties in Energy System Optimization Models: A Quadratic Programming Approach for Avoiding Penny Switching Effects

Designing the future energy supply in accordance with ambitious climate change mitigation goals is a challenging issue. Common tools for planning and calculating future investments in renewable and sustainable technologies are often linear energy system models based on cost optimization. However, input data and the underlying assumptions of future developments are subject to uncertainties that negatively affect the robustness of results. This paper introduces a quadratic programming approach to modifying linear, bottom-up energy system optimization models to take cost uncertainties into account. This is accomplished by implementing specific investment costs as a function of the installed capacity of each technology. In contrast to established approaches such as stochastic programming or Monte Carlo simulation, the computation time of the quadratic programming approach is only slightly higher than that of linear programming. The model’s outcomes were found to show a wider range as well as a more robust allocation of the considered technologies than the linear model equivalent.

Thermo-economic performance evaluation of emerging liquid-separated condensation method in single-pressure and dual-pressure evaporation organic Rankine cycle systems

Liquid-separated condensation is an emerging and effective heat transfer enhancement method to reduce the condenser cost, which can help with the widespread application of organic Rankine cycle (ORC) systems. However, few related studies have focused on the shell-and-tube condenser even if it is widely used in ORC systems. The thermo-economic performance superiorities and applicable working conditions of shell-and-tube liquid-separated condenser should be investigated, especially in novel ORCs. This study introduced the liquid-separated condensation method into single-pressure and dual-pressure evaporation ORC systems with shell-and-tube condenser. R245fa, R600a, and R1234ze(E) were used as working fluids. Optimal liquid-separated thermodynamic states and decrements in condenser heat transfer area of one to four stages liquid-separated condensations were provided. Decrements in specific investment cost (SIC) of ORC system by adopting the liquid-separated condensation method were evaluated. Results show that the liquid-separated condensation method is more suitable for low tube diameter, low inlet velocity in tubes, high inlet velocity outside tubes, and low cooling water temperature rise. Optimal liquid-separated thermodynamic states remain constant with increasing the tube diameter and inlet velocities. The SIC of ORC system can be reduced by 4.6% at most by adopting the liquid-separated condensation over the conventional condensation method. Increasing the mass flow rate of heat source fluid and pinch point temperature difference during heat absorption process is beneficial to increase the superiority of liquid-separated condensation method. Compared with dual-pressure evaporation ORC, the effects of liquid-separated condensation method on reducing the SIC are more remarkable in single-pressure evaporation ORC.

Economic feasibility and sensitivity analysis of fish waste processing biorefinery

Abstract Due to still increasing fish waste production, there is an effort to develop an effective and environmentally friendly treatment technology. Anaerobic fermentation of fish waste represents a promising way of its effective environmental material-energy recycling. The process flow diagram was designed for the biorefinery in which fish waste is anaerobically co-fermented with cow dung to produce methane and concentrated liquid mineral fertiliser being primary products, and carbon dioxide, solid fertiliser and purified water being secondary ones. Specific capital investment cost of such a plant is 659 Eur t−1 of the treated substrate. Techno-economic analysis of the proposal showed that its technical maturity is limited by TRL7 being both for operating set of mineral liquid production by reverse osmosis, and for operating set of biomethane separation using membranes. Sensitivity analysis found that the profitability of such a proposal is strongly dependent on methane yield and primarily on the methane purchase price. The technology is profitable only if methane yield over 0.34 L kg−1 VS of fish waste and methane purchase price over 0.17 Eur kWh−1 are reached. So if there is no green subsidy, the technology is not profitable.

Thermoeconomic optimisation of small-scale organic Rankine cycle systems based on screw vs. piston expander maps in waste heat recovery applications

The high cost of organic Rankine cycle (ORC) systems is a key barrier to their implementation in waste-heat recovery (WHR) applications. In particular, the choice of the expansion device has a significant influence on this cost, strongly affecting the economic viability of an installation. In this work, numerical simulations and optimisation strategies are used to compare the performance and profitability of small-scale ORC systems using reciprocating-piston or single/two-stage screw expanders when recovering heat from the exhaust gases of a 185-kW internal combustion engine operating in baseload mode. The study goes beyond previous work by directly comparing these small-scale expanders for a broad range of working fluids, and by exploring the sensitivity of project viability to key parameters such as electricity price and onsite heat demand. For the piston expander, a lumped-mass model and optimisation based on artificial neural networks are used to generate performance maps, while performance and cost correlations from the literature are used for the screw expanders. The thermodynamic analysis shows that two-stage screw expanders typically deliver more power than either single-stage screw or piston expanders due to their higher conversion efficiency at the required pressure ratios. The best fluids for the proposed application are acetone and ethanol, as these provide a compromise between the exergy losses in the condenser and in the evaporator. The maximum net power output is found to be 17.7 kW, from an ORC engine operating with acetone and a two-stage screw expander. On the other hand, the thermoeconomic optimisation shows that reciprocating-piston expanders show a potential for lower specific costs, and since piston-expander technology is not mature, especially at these scales, this finding motivates further consideration of this component. A minimum specific investment cost of 1630 €/kW is observed for an ORC engine with a piston expander, again with acetone as the working fluid. This system, optimised for minimum cost, gives the shortest payback time of 4 years at an avoided electricity cost of 0.13 €/kWh. Finally, financial appraisals show a high sensitivity of the investment profitability to the value of produced electricity and to the heat-demand intensity.

Assessing sustainable biogas potentials—case study for Serbia

Biogas is efficient renewable energy source concerning greenhouse gases emission (GHG) reduction and waste disposal. The most abundant biogas substrates are originating from agriculture, i.e., energy plants and wastes such as manure, and respective production and utilization can be used to support rural development. Defining sustainable potentials, i.e., realistic value under defined conditions, of biogas production in some geographical region is important, as a background for policy development on a national, regional, and even local level. The objective of the study was defying method for its assessment. The characteristics of the proposed method are as follows: (1) biogas potential is expressed in electric power of cogeneration units that can operate with biogas produced from available feedstock. Available thermal energy, or biomethane production, can be calculated based on biogas potential; (2) the determined sustainable potential is based on environmental, technological, and socio-economic criteria; (3) the assessment is related to the actual substrates’ availability, whereby expected technological advancements are considered. Developed method has been tested in the form of a case study for Serbia and obtained outcomes compared with studies previously done by other authors. The potential is lower than previously assessed. The forecasted technology advancements and reduction of specific investment costs in the future can contribute to the increase of potential, higher share of wastes and by-products in substrates. New, smaller biogas plants would be constructed in undeveloped regions, what could contribute to rural development.

Digestate evaporation treatment in biogas plants: A techno-economic assessment by Monte Carlo, neural networks and decision trees

Abstract Biogas production is one of the most promising pathways toward fully utilizing green energy within a circular economy. The anaerobic digestion process is the industry standard technology for biogas production due to its lowered energy consumption and its reliance on microbiology. Even in such an environmental-friendly process, liquid digestate is still produced from the remains of digested bio-feedstock and will require treatment. With unsuitable treatment procedure for liquid digestate, the mass of bio-feedstock can potentially escape the circular supply chain within the economy. This paper recommends the implementation of evaporator systems to provide a sustainable liquid digestate treating mechanism within the economy. Studied evaporator systems are represented by vacuum evaporation in combination with ammonia scrubber, stripping and reverse osmosis. Nevertheless, complex multi-dimensional decisions should be made by stakeholders before implementing such systems. Our work utilizes a novel techno-economics model to study the techno-economics robustness in implementing recent state-of-art vacuum evaporation systems with exploitation of waste heat from combined heat and power (CHP) units in biogas plants (BGP). To take into the account the stochasticity of the real world and robustness of the analysis, we used the Monte-Carlo simulation technique to generate more than 20,000 of different possibilities for the implementation of the evaporation system. Favourable decision pathways are then selected using a novel methodology which utilizes the artificial neural network and a hyper-optimized decision tree classifier. Two pathways that give the highest probability of providing a fast payback period are identified. Descriptive statistics are also used to analyse the distributions of decision parameters that lead to success in implementing the evaporator system. The results highlighted that integration of evaporation system are favourable when transport costs and incentives for CHP units are large and while feed-in tariffs for electricity production and specific investment costs are low. The result of this work is expected to pave the way for BGP stakeholders and decision makers in implementing liquid digestate treating technologies within the currently existing infrastructure.