Boosting biomethane production makes it possible to offset the required energy in a wastewater treatment plant. In this research, using batch biomethane potential assays, various techniques including ...pretreatment, co-digestion, and digestion temperature rise were evaluated to increase the methane productivity of municipal sewage sludge (SS). Between thermal and sonication pretreatment methods, thermal pretreatment was shown to be more efficient and there was no need to pretreat SS for more than 0.5 h. Thermophilic digestion of SS led to 160.8% rise in the methane productivity, compared to mesophilic digestion. The most suitable co-substrate for co-digestion with SS was food waste (FW). FW and SS had little negative synergistic effect, however higher FW concentration caused to higher specific methane yield. Thermal pretreatment was not effective on FW. To evaluate the techniques, a combined cooling, heat and power plant was suggested. The energy recovery balance was positive for all the techniques, but co-digestion was not successful to reduce the levelized cost of energy (LCOE). Unlike co-digestion, thermal pretreatment and digestion temperature rise decreased the LCOE. The thermophilic digestion of SS, pretreated at 90 °C for 0.5 h, resulted in the lowest amount of LCOE by 43.70% reduction, compared to the mesophilic single digestion of non-treated SS.
•Evaluation of various techniques to increase biogas productivity of sewage sludge.•For the same energy applied, thermal pretreatment was more effective than sonication.•Digestion temperature rise led to significant increase in the methane productivity.•Co-digestion with food waste could not reduce the levelized cost of energy (LCOE).•Thermal pretreatment before thermophilic digestion significantly decreased the LCOE.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
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•A multigeneration system fueled by a geothermal source is proposed.•Absorption heat transformer and chiller have the highest irreversibilities.•The overall system performance in ...winter is better than that of summer.•The system has considerably high heating, cooling, and freshwater capacities.•Thermoeconomic indexes are significantly lower compared to similar systems.
Population growth, economic challenges, and the environmental crisis force scientists and designers to pay more attention to clean, sustainable, and renewable-based energy systems. In this regard, due to the unlimited geothermal potential in many countries, the geothermal energy resource can be an economical alternative. Therefore, in the present work, a novel multi-generation system, based on a 100% geothermal resource, for power, cooling, heating, and desalination has been designed and analyzed, thoroughly. The system is evaluated from the energy, exergy, and thermo-economic viewpoints, and providing high heating/cooling potentials while reducing the thermoeconomic indexes is the major achievement of this study. The results demonstrate that the system's net power output, freshwater production rate, heating, and cooling capacities are 78.47 kW, 92.1 m3/day, 6251 kW, and 4991 kW, respectively. Moreover, the highest amount of exergy destruction occurs in the absorption heat transformer (42%) and the absorption chiller (35%), respectively. In addition, the chiller’s absorber has the highest cost rate of exergy destruction, and the turbine and the evaporator of the organic Rankine cycle have the highest investment costs. It is found that energy and exergy efficiencies are 60.55% and 17.05%, respectively for summer, and 70.58% and 43.59%, respectively for winter, and the system's total cost rate is 44.12 $/h with the payback period of 5.63 years. Furthermore, the parametric study shows that increasing the ambient temperature and decreasing the terminal temperature difference of the heat transformer’s evaporator lead to higher exergy efficiency and lower total system cost rate.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
New exergetic concepts such as endogenous/exogenous and avoidable/unavoidable exergy destruction and new exergoeconomics ideas provide valuable information about the potential of optimization of the ...system. In this work, a tri-generation cycle, with 30 MW power production, 40 MW heat generation and 2 MW cooling capacity, is analyzed by conventional and new exergetic and exergoeconomic concepts. It is found from the whole cycle analysis that an amount of almost 29% of the total exergy destruction and overall cost rates associated with exergy destruction in the cycle are endogenous-avoidable. Both conventional and advanced exegy analyses suggest that the combustion chamber has the highest contribution on the overall exergy destruction and the cost rates associated with exergy destruction of the cycle. In HRSG, over 71% of the exergy destruction is unavoidable. Air pre-heater is introduced with the higher improvement priority compared to HRSG. Also, a new definition for the exergoeconomic factor is introduced which suggests that the components of refrigeration cycle and combustion chamber have the lowest values of the exergoeconomic factor, therefore, the corresponding exergy destruction cost rates should be reduced. It is concluded that employing the new exergetic and exergoeconomic concepts provide valuable information for improving the overall system.
•A tri-generation cycle is analyzed using advanced exergoeconomic concepts.•29% of the total exergy destruction in the cycle is endogenous-avoidable.•29% of cost rates associated with exergy destruction is endogenous-avoidable.•New exergoeconomic concept provide valuable information for improving the system.•Refrigeration cycle components have the lowest values of the exergoeconomic factor.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
•NG/diesel RCCI engine was simulated by Converge CFD model.•By increasing the PR, the lower reactivity of NG causes lower combustion rate.•Increasing first injected fuel quantity results in higher HC ...and CO emissions.•Narrower spray angles have higher values of HC and CO emissions.
Reactivity controlled compression ignition (RCCI) combustion mode is an attractive combustion strategy due to its potential in satisfying the strict emission standards. In this study, the effects of direct injection (DI) strategies on the combustion and emission characteristics of a modified light duty RCCI engine, fueled with natural gas (NG) and diesel were numerically investigated. In this way, Converge CFD code employing a detail chemical kinetics mechanism was used for 3D simulation of combustion process and emissions prediction. NG with higher octane number (ON) is mixed with air through intake port, while diesel fuel with lower ON is directly injected into the combustion chamber during compression stroke by means of split injection strategy. The effects of several parameters, including the premixed ratio (PR) of NG, diesel fuel fraction in first and second injection pulses, first and second start of injection timing (SOI1 and 2), injection pressure and the spray angle on the engine performance and emission characteristics are investigated. The results indicate that these parameters have significant effects on the light duty RCCI engine performance and engine out emissions. Also, it was demonstrated that by decreasing the first injection pressure from 450 to 300bar, the gross indicated efficiency increases by 5% and CA50 is retarded by 4 CAD. Moreover, by reducing the spray angle from 144° to 100°, the gross indicated efficiency decreases by 4% and CA50 is advanced by 6 CAD. The results showed that reduction in NOx emission is achievable, while controlling HC and CO emissions, by means of increasing the NG fraction, advancing the SOI1, increasing the fuel fraction in first DI injection with lower injection pressure and employing a wider injector spray angle.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A numerical study is performed by KIVA-CHEMKIN code to compare the combustion, performance and emission characteristics of neat biodiesel (B100) and biodiesel blend including a mixture of 20% ...biodiesel and 80% diesel (B20) resulting from the PCCI combustion mode in a light-duty diesel engine. For the biodiesel reaction mechanism, multi-chemistry surrogate mechanism using methyl decanoate (MD) and methyl-9-decenoate (MD9D) is used in this study. The results show that PCCI combustion like high temperature conventional combustion cannot cover the lower ISFC of the biodiesel blend fuel compared to the diesel fuel. A detailed analysis of combustion and emissions, involving the role of formaldehyde (CH2O) and hydroxyl (OH) radicals as well as O and H radicals, was performed in the PCCI combustion stages and emissions formation for the B100 and B20 fuels. The results indicate that higher concentration of formaldehyde as well as lower concentration of hydroxyl radicals for the B20 case advances low temperature heat release (LTHR) and retards high temperature heat release (HTHR) respectively compared to the B100 case. In addition, O and OH radicals as well as cylinder temperature are effective parameters regarding higher NO and CO concentrations for the B20 case compared to the B100 case.
•PCCI combustion and emission characteristics of B100 and B20 are investigated.•Overall concentration of emissions for B20 is higher compared to B100.•B100 and B20 include 7% and 10% of heavy HC among the total HC, respectively.•B20 is more preferred compared to the B100 for the diesel oxidation catalyst.•The conversion of soot to CO is possible due to presence of O and OH radicals.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
Exergoeconomic assessment of a multigeneration system, which is fed with a mixture of natural gas and syngas produced from municipal solid waste gasification process, has been conducted under ...climatic restrictions of both hot and cold seasons. In the basic state of the 1st scenario, for the constant net power of 30 MW and 50% mixing ratio, exergy efficiency and total cost rate of the system are 27.92% and 1328 USD/h in summer, and 33.81% and 1246 USD/h, in winter, respectively. Moreover, the total relative cost difference in the summer is considerably higher than that in the winter. In the basic state of the 2nd scenario, for the constant fuel mass flow rate of 1.5 kg/s, the system's annual exergy efficiency, annual total cost rate, and payback period are 30.79%, 1166.4 USD/h, and 2 years, respectively. The optimization has been performed based on the genetic algorithm considering two objective functions. The optimization results revealed that, the system's annual exergy efficiency and annual total cost rate got improved from 30.79% to 32.37%, and from 1166.4 USD/h to 796.52 USD/h, respectively, while the payback period increases from 2 to 2.1 years. The complete results of parametric studies are also provided for both scenarios.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
•A new multi zone model is developed for HCCI combustion modeling.•New heat transfer model is used for prediction of heat transfer in HCCI engines.•Model can predict engine combustion, performance ...and emission characteristics well.•Appropriate mass and heat transfer models cause to accurate prediction of CO, UHC and NOx.
Heat transfer from engine walls has an important role on engine combustion, performance and emission characteristics. The main focus of this study is offering a new relation for calculation of convective heat transfer from in-cylinder charge to combustion chamber walls of HCCI engines and providing the ability of new model in comparison with the previous models. Therefore, a multi zone model is developed for homogeneous charge compression ignition engine simulation. Model consists of four different types of zones including core zone, boundary layer zone, outer zones, which are between core and boundary layer, and crevice zone. Conductive heat transfer and mass transfer are considered between neighboring zones. For accurate calculation of initial conditions at inlet valve closing, multi zone model is coupled with a single zone model, which simulates gas exchange process. Various correlations are used as convective heat transfer correlations. Woschni, modified Woschni, Hohenberg and Annand correlations are used as convective heat transfer models. The new convection model, developed by authors, is used, too. Comparative analyses are done to recognize the accurate correlation for prediction of engine combustion, performance and emission characteristics in a wide range of operating conditions. The results indicate that utilization of various heat transfer models, except for new convective heat transfer model, leads to significant differences in prediction of in-cylinder pressure and exhaust emissions. Using Woschni, Chang and new model, convective heat transfer coefficient increases near top dead center, sharply. Chang and Woschni correlations over predict in-cylinder peak pressure slightly. Annand and Hohenberg correlations compute convective heat transfer coefficient higher than other correlations which cause to incomplete combustion. Therefore, by employing Annand and Hohenberg models, peak in-cylinder pressure is lower than the corresponding measured values and the predicted values for carbon monoxide and unburned hydrocarbons are higher than the corresponding experimental values. Finally, it can be concluded that the new heat transfer model can be employed in multi zone chemical kinetics model to estimate convective heat transfer of HCCI engines more accurately.
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IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPUK
Nowadays, computer models have contributed to a better understanding and solution of long standing practical combustion problems in HCCI (homogenous charge compression ignition) engines. In this ...study, a new multi zone model is developed for HCCI engines simulation. Model contains four different types of zones, which are core, boundary layer, zones between them, and crevice zone. Heat and mass transfer are considered between all of zones. For accurate calculation of initial conditions at IVC, multi zone model is coupled with a single zone model, which simulates gas exchange process. The developed model is validated by using two types of fuels, n-heptane as a fuel with low octane number and methane as a fuel with high octane number. Semi detailed chemical kinetics mechanisms of fuels are used for their combustion simulation. A new heat transfer model is used for calculating convective heat transfer, which enhanced the model ability in prediction of combustion and performance characteristics of engine accurately. Model results are in good agreement with experimental data in prediction of in-cylinder pressure, NOx, CO and UHC emissions. Accurate mass transfer model caused to accurate prediction of UHC (maximum error is 20.2%) and CO (maximum error is 1.8%). Near zero NOx, which is lower than 10 ppm for all of examined cases, is predicted well, too.
•A new multi zone model is developed for HCCI (homogenous charge compression ignition) combustion modeling.•Gas exchange model is coupled with MZCM for calculation of initial conditions at IVC.•Model can predict engine combustion, performance and emission characteristics well.•Appropriate mass transfer model causes to accurate prediction of CO, UHC and NOx.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
•Thermal pretreatment and thermophilic digestion of sewage sludge were evaluated.•Thermophilic digestion significantly increased the biomethane productivity.•Energy recovery balance of the applied ...techniques were positive.•Thermophilic digestion drastically decreased the levelized cost of energy.
In a municipal wastewater treatment plant, the anaerobic digesters are able to support the whole or a portion of the required fuel to offset the energy demand. Also, by implementing some techniques on municipal sewage sludge, leading to biomethane productivity enhancement, it is possible to generate surplus power. In this work, using batch biomethane potential assays, thermal pretreatment at 70 °C & 90 °C for the durations of 0.5 h, 1 h, 2 h, 3 h, and 4 h, and digestion temperature rise from the mesophilic to the thermophilic conditions have been studied to boost the biomethane productivity of the sewage sludge. Also a combined cooling, heat, and power generating plant was suggested to evaluate the techniques thermo-economically. It was shown that, compared to the non-treated mesophilic digestion of the sewage sludge, thermal pretreatment at 70 °C and 90 °C for 0.5 h, and thermophilic digestion were able to raise the biomethane productivity by 13.63%, 59.82%, and 160.8%, respectively. In this regard, the thermodynamic and the thermo- economic model of the plant was developed. The energy analysis of the system revealed that not only the studied methods, but also the mesophilic digestion of the non-treated sewage sludge result in a positive energy recovery balance in the plant. The exergo-economic analysis indicated that the major origin of cost in the system is the anaerobic digester. Implementing thermal pretreatment at 90 °C for 30 min and digestion temperature rise led to decrease in the required volume of the digester, and subsequently, in the total system cost rate. Additionally, all the applied techniques provided more fuel compared to the non-treated mesophilic case, and consequently they could reduce the levelized cost of energy in the plant. Among the studied techniques, the most effective one was digestion temperature rise which decreased the total cost rate and the levelized cost of energy by 30.31% and 41.29%, respectively.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
Premixed charge compression ignition (PCCI) is one of the most important strategies of low-temperature combustion, in which a high level of EGR can be employed to reduce the combustion temperature ...and to extend the ignition delay period. Due to low-temperature combustion, these engines have low exhaust NOx but the CO and UHC emission levels are high. One approach to control these emissions in PCCI combustion is the use of biodiesel fuel because of its different physical and chemical properties compared to that of diesel fuel. The purpose of the current study is the optimization of the combustion, performance and emission characteristics of biodiesel-fueled PCCI engine using the design of experiments (DOE) methodology and a 3D CFD model coupled to a semi-detailed chemical kinetics mechanism. The chemical kinetics mechanism contains 69 species and 192 reactions. After validation of the model, the effects of five parameters including the start of injection, fuel injection pressure, exhaust gas recirculation, swirl ratio, and biodiesel content on PCCI engine performance and emissions are studied. The parametric study results are analyzed to find the upper and lower levels of DOE study. Then, the importance of each parameter, as well as their interactive effects on the performance and emissions, is determined using the DOE method. The results of the parametric study indicate that the most important parameters affecting the engine IMEP and exhaust HC, CO, and NOx emissions are EGR and SOI, respectively. Meanwhile, the results of the DOE study show that the interactive effect of EGR and SOI has the most significant impact on engine performance and emissions. Hence, to achieve the highest IMEP, EGR should be at its highest level and the fuel should be injected as early as possible. Also, earlier fuel injection and lower EGR percentages should be employed to reduce HC, CO, and soot emissions.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
