Biomass-based, small-scale Combined Cooling, Heating and Power (CCHP) systems can increase the energy autonomy of building complexes while reducing their Greenhouse Gases (GHG) emissions. In combination with air-to-water Heat Pumps (HP), highly efficient energy systems can be designed, which allow for high flexibility in serving thermal and electric demands. This study presents an exergy evaluation of such a small-scale CCHP/HP system using a dynamic modelling approach based on gasification of various types of woody biomass. The transient model takes into account the effects of the biomass chemical composition as well as of ambient temperatures on the exergy performance of all key components for various CCHP system sizes supporting an HP system. The model has been applied in a case study for a historic building complex, where the CCHP sub-system would support an HP-subsystem allowing for downsizing the latter. The results show that smaller CCHP systems operate with higher exergy efficiency, because for larger systems the heat transfer from the engine and the operation of the absorption chiller are less exergy efficient. The electric load-following CCHP subsystem reaches exergy efficiencies of up to 13.3%, indicating huge improvement potential for system and sub-system design. It was also found that the biomass composition heavily influences the exergy efficiency of the gasifier and in turn changes the exergy efficiency of the syngas engine and the entire CCHP sub-system.

No one can disagree the growing attention to developing and utilizing high temperature fuel cells partly due to their potential for multi-service applications. Recently, much focus can be observed on examination of the integration of solid oxide fuel cell (SOFC) or molten carbonate fuel cell (MCFC) systems with other subsystems to propose polygeneration plants. Literature review prove that, to propose a poly generation concept based on SOFC and MCFC systems, there is not a typical way commonly used by researchers. So it is tried to categorize and survey the current challenges of the high temperature fuel cell polygeneration plants. In this regard, the most common concepts and some unique system designs are reviewed and investigated in terms of fuel type, plant scale, electrical efficiency, overall efficiency and other performance indicators. It is figured out that similar to the typical CCHP system, the most common polygeneration designs are those utilizing the potential of exhaust gases from the natural gas fed fuel cell system in a heat recovery unit and a refrigeration system. A notable observed trend in recent years is the coupling of biofuels with polygeneration concepts. We found that there are still great challenges regarding how to predict the fuel cell actual cell voltage influencing the overall efficiency of poly generation plants. It is also observed that attendance of researchers to analyze the polygeneration systems from the viewpoints of economic and environmental is less in comparison with the investigation of the systems from the thermodynamics point of view.& nbsp;

A techno-economic analysis is performed, assessing the production costs of Fischer-Tropsch syncrude and waxes of carbon number C20+. The products are obtained from the gasification of digestate from anaerobic digestion inside a dual fluidized bed gasifier (3.11 MWth). The results are compared against the same system fed with lignocellulosic biomass. The syngas is cleaned from impurities and conditioned to reach the desired H-2/CO molar ratio of 1.8 at the inlet of the Fischer-Tropsch reactor. The Fischer-Tropsch products distribution is based on experimental data of a cobalt-based catalyst. Two process configurations are studied: (1) the Fischer-Tropsch off-gas are employed to produce electricity; (2) the off-gas are recirculated to the gasifier for enhanced wax production. Co-production of steam is also investigated. The results show an advantageous production of Fischer-Tropsch compounds utilizing digestate over wood biomass. The highest plant efficiency (i.e., biomass-to-liquid fuel) of 56.3% is reached with digestate feedstock and off-gas recirculation, outputting 61.5 kg(wax)/t(dig). The minimum wax production cost is of 3.04 (sic)/kg(wax), assuming 7.5% discount rate and 25-years plant operation.

Polygeneration configurations for small power generation systems offer significant potential for energy saving and reducing carbon emissions in wastewater treatment facilities. In this work, a biogas-fed solid oxide fuel cell system operating in a wastewater treatment plant (located in Turin, Italy) is analyzed in terms of its potential improvements through novel polygeneration systems. In its present combined heat and power configuration, along with electrical power, thermal energy from the exhaust gas is recovered to provide required heat to the plant's anaerobic digester. The analysis is focusing on different energy efficiency solutions for this type of plant by using solar thermal collectors, microturbines, a trilateral Rankine cycle, and an absorption chiller. Results reveal that, despite of higher efficiency for the trigeneration case using both trilateral Rankine cycle and absorption chiller (up to 88.4%), the solar integrated system results in the lowest natural gas consumption, which is 38.5% lower than the baseline scenario. This same scenario is also the worst in economic terms due to the high capital costs of solar collectors. In a short-term cost trajectory of the solid oxide fuel cell technology, the most economically favorable scenario is the microturbine integrated case in which the calculated levelized cost of electricity is 0.11 (sic)/kWh, lower than grid electricity price, and with payback time of 6.5 years. Long-term cost trajectory is indeed generating effective investments for all of the four scenarios with payback time between 3 and 5 years in all cases. The analysis has been developed to the entire European Union area: the most suitable market conditions are found in Germany, Denmark, Slovakia, and Italy.

The research of renewable alternatives to decarbonize the transport sector and to reduce the consumption of fossil fuels pushes towards the development of more sustainable solutions for fuel production. Among the diesel substitutes, hydrotreated vegetable oil (HVO) is considered one of the most promising options, since it can be blended with fossil diesel without limitations. In this context, this paper assesses the technical and economic feasibility of producing HVO using waste vegetable oil (WVO) as feedstock, with the help of a simulation model that maximizes the integration of renewable energy sources. The process to synthesize HVO requires a large amount of hydrogen that, in this study, is supplied through an upstream high-temperature electrolysis process occurring in solid oxide electrolysis cells (SOECs), which are fed by low-carbon electricity. The use of waste oils as feedstock eliminates the competition with food crops (e.g. soybean or rapeseed) and promotes the recycling of substances that need to be disposed. The results of the study prove the technical feasibility of a plant with an annual capacity of 100 kt of HVO, having an energy efficiency of 80%. Also, the breakeven point of such investment would be reached before the fourth year of operation, considering a WVO price of 400 (sic)/t, which is assumed as target price. However, the uncertainty on the market prices of WVO, HVO and electricity, as well as on other fixed and variable production costs, can significantly affect the projected results.

The production of substitutes for liquid fossil fuels is of utmost importance for the decarbonization of the transport sector. This paper assesses the economic feasibility of producing hydrotreated vegetable oil (HVO) using waste vegetable oils as feedstock. The supply of hydrogen for the upgrading of the oil is obtained through a high-temperature electrolysis process, fed by low-carbon electricity. The use of waste materials eliminates the competition with food crops (e.g. soybean or rapeseed) and promotes the recycle of substances that should be treated for disposal. The results of the study show that the production cost of HVO with the considered plant are around 33% higher than that of fossil diesel. Moreover, the variable that has the strongest impact on the production cost of HVO is the price of the waste vegetable oil, which affects the final results more than the electricity price and the cost of the electrolyser.

The upgrading of biogas to biomethane, by removing contaminants and carbon dioxide, is a treatment that allows this gaseous fuel to reach the specifications suitable for the injection in the natural gas grid and the use as vehicle fuel. This pathway enables the conversion of wet biomass into a perfect substitute of natural gas. Biogas upgrading is usually performed through CO2 removal and the most diffused method is water scrubbing. However, the embedded CO2 could be directly recycled into methane through a high-temperature co-electrolysis process followed by a methanation step, thus increasing the yield of biomethane for the same biogas inlet. In this paper the environmental impacts of two routes for biomethane production are compared in the framework of the Life Cycle Assessment (LCA) methodology. A sensitivity analysis for different shares of renewable content in electricity has been carried out. The results show that the large need for electrical energy penalizes the electrolytic process for renewable contents of the electricity which are not close to 100%.

This work conveys the study of the production of synthetic fuels, in this case, methane and methanol, by means of comparing two processes that employ high-temperature water splitting based on solid oxide electrolysis cells (SOEC) technology. In both cases, the process consists of mixing hydrogen produced by electrolysis with carbon dioxide in order to achieve hydrogenation synthesis via a catalytic reactor. An energy analysis was performed with special care on thermal integration (minimization of external heat requirements) via pinch analysis, as well as a final estimation of power-to-fuel overall efficiency. The study demonstrates that power-to-methane and power-to-methanol process can achieve efficiency of up to approximate to 77% and approximate to 59%, respectively. The energy analysis (based on the process modelling developed for both the systems) and the heat exchange network design enabled the development of capital expenditure estimation. An economic analysis comparison for the production cost of both synthetic fuels was performed with the purpose of highlighting any potential risk associated with the systems. The economic analysis considered the impact on synthetic fuel cost of some parameters as electrolysis specific costs, the expenditure for carbon dioxide, electricity price, and yearly operating hours. The results show that for both systems, as expected, the SOEC electrolyzer is the greatest capital expenditure of the design. Methanol synthesis plant showed lower efficiency and higher investment costs; on the other hand, fossil-based methanol has higher costs ($/MWh) than fossil methane; thus, the breakeven point of electricity price (i.e., that making economically comparable synthetic and fossil fuel) is similar for the two considered cases. It was concluded that to produce an economically attractive market for methane and methanol, the production plants should maintain a utilization factor of approximately 50%, the cost of SOECs should be near to 1050 (sic)/kW and the electricity required to run the system needs to be supplied from renewable sources at a very low cost (below 40-50 $/MWh).

Biogas is a proven and valuable energy source today for the combined production of heat and electricity (CHP). One of the most reliable and efficient technologies for the CHP application using biogas is represented by microturbine (MT). This prime mover not only shows a very flexible behavior towards change in the fuel composition, but it also sticks out for its reliability, small size, and low weight. Moreover, micro humid air turbine (mHAT) cycle, which is still under development, provides a relatively simple and inexpensive solution to increasing the power output of the microturbines. In this paper, the thermodynamic model of a novel CHP system based on a 500 kW micro humid air turbine (mHAT) in a wastewater treatment plant (WWTP) is presented and discussed. Furthermore, some considerations regarding an appropriate biogas treatment system and heat recovery module are discussed. The results presented in this paper show how the proposed biogas-fed plant can achieve an electrical efficiency of 46.6% together with a CHP efficiency of 81.2%. The impact of integration with WWTPs is beneficial where both biogas and required water for inlet air humidification are available.

A novel integrated renewable-based energy system for production of synthetic diesel is proposed and simulated in this study. This system merges solid oxide electrolyser (SOE), entrained gasification (EG) and Fischer-Tropsch (FT) technologies. Two case scenarios are considered here. In the first case, the electrolyser unite produce syngas through co-electrolysis of steam and carbon dioxide, while in the second case only steam is electrolyzed. The effects of SOEC and EG operating pressure and temperatures on the system performance in each case are investigated and compared. It is shown that the operating condition of electrolyser subsystem has a more considerable effect on the performance of the integrated system as compared to the gasification subsystem. Also waste heat recovery results in about 43 and 2 percentage point increase in energy and exergy efficiency, respectively. It is also shown that internal recovering of oxygen has the best effect on the system performance.