Energy Conversion and Management

Journal: Energy Conversion and Management

Abbreviation

Energy convers. manag.

Publisher

Elsevier

ISSN

0196-8904
1879-2227

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Publications 1 - 10 of 32

The value of bulk energy storage for reducing CO2 emissions and water requirements from regional electricity systems
Ogland-Hand, Jonathan D.; Bielicki, Jeffrey M.; Wang, Yaoping; et al. (2019)
Energy Conversion and Management
Effects of using nanosecond repetitively pulsed discharge and turbulent jet ignition on internal combustion engine performance
Balmelli, Michelangelo; Hilfiker, Thomas; Biela, Jürgen; et al. (2024)
Energy Conversion and Management
Robust ignition of hard-to-ignite fuels is essential for future spark ignited internal combustion engines, particularly for introducing efficiency-enhancing diesel-like process parameters like air excess or high amounts of exhaust gas recirculation (EGR). On the one hand, novel plasma-based ignition systems like Nanosecond Repetitively Pulsed Discharge (NRPD) are promising in extending the ignition limits and the early flame development speed. On the other hand, Turbulent Jet Ignition is effective for shortening the combustion duration and decreasing the unburned hydrocarbon emissions. This article investigates experimentally the combination of NRPD ignition and TJI. The aim is to use a technology for robust inflammation (NRPD) in combination with a technology for fast combustion of the bulk charge (TJI). For this purpose, a turbocharged light-duty four-cylinder engine operated with natural gas is used. The engine can be fitted with a classical Open Chamber (OC) spark plug or with Pre-Chambers (PC). The PCs can be filled uniquely with fuel and air coming from the Main Chamber (MC) (“passive PC”), or additional fuel can be added to the PCs (“active PC”). The air-to-fuel ratio and EGR rate can be freely controlled. Five different combustion strategies are investigated with NRPD ignition and compared against an inductive discharge ignition system. The combustion strategies are passive PC with air and EGR dilution, active PC with air dilution, and Open Chamber (OC) with air and EGR dilution. HRR evaluations and a loss analyses are performed to interpret the results. Despite the faster inflammation present with NRPD ignition, similar peak efficiencies and emissions are reached in OC configuration using the inductive discharge and NRPD ignition systems, which are achieved by varying air-to-fuel ratios (AFR) and EGR rates. Above dilution levels for peak efficiency, the efficiency using NRPD ignition decreases at a slower pace and tolerates higher AFR and EGR rates, thanks to a more complete and shorter combustion. For the PC experiments using NRPD ignition, an efficiency increases and a reduction of emissions compared to inductive discharge ignition are present for the investigated AFR and EGR rates for both active and passive PC operations. The efficiency increase is present due to a stronger pre-chamber discharge and thanks to a faster end phase of combustion. Actively fueling the PC results in faster and more complete combustion that is over compensated by the increased wall heat losses, reducing the overall efficiency. The results show that passive PC with NRPD ignition may be an ideal ignition concept that maximizes engine efficiency and minimizes emissions.
An ecological and economic assessment of absorption-enhanced-reforming (AER) biomass gasification
Heffels, Tobias; McKenna, Russell; Fichtner, Wolf (2014)
Energy Conversion and Management
Biomass gasification with absorption enhanced reforming (AER) is a promising technology to produce a hydrogen-rich product gas that can be used to generate electricity, heat, substitute natural gas (SNG) and hydrogen (5.0 quality). To evaluate the production of the four products from an ecological and economic point of view, three different process configurations are considered. The plant setup involves two coupled fluidized beds: the steam gasifier and the regenerator. Subsequently the product gas can be used to operate a CHP plant (configuration one), be methanised (configuration two) or used to produce high-quality hydrogen (configuration three). Regarding ecological criteria, the global warming potential, the acidification potential and the cumulative energy demand of the processes are calculated, based on a life-cycle assessment approach. The economic analysis is based on the levelized costs of energy generation (LCOE). The AER-based processes are compared to conventional and renewable reference processes, which they might stand to substitute. The results show that the AER processes are beneficial from an ecological point of view as they are less carbon intensive (mitigating up to 800gCO2-eq.kW-1hel-1), require less fossil energy input (only about 0.5kWhfossilkW-1hel-1) and have a comparable acidification potential (300900mgSO2-eq.kW-1hel-1) to most reference processes. But the results depend heavily on the extent to which excess heat can be used to replace conventional heating processes, and hence on the exact location of the plant. The economic results show that under current German framework conditions, all plant configurations can only be profitable under very favourable site-specific conditions. The main parameters are the investments, accounting for 3740% of LCOE, the price of the available biomass (2732% of LCOE) and the revenues generated by selling excess heat. To reflect these dependencies in the economic results, spans between maximum and minimum LCOE-values are given: 1922€ctkW1hel-1, 1011€ctkW1hSNG-1 and 1416€ctkW1hH2-1. While the ecological performance of the considered plant configurations is largely independent of the plant size, the economics of this plant type depend on size and the number of installed plants. Hence future work should consider economies of scale and the learning effects when building multiple plants, and the impact these have on the generation costs.
Thermodynamic limitations to direct CO2 utilisation within a small-scale integrated biomass power cycle
Greencorn, Michael J.; David Jackson, S.; Hargreaves, Justin S.J.; et al. (2022)
Energy Conversion and Management
Partially recycling CO2-rich exhaust gases from a syngas fuelled internal combustion engine to a biomass gasifier has the capability to realise a new method for direct carbon dioxide utilisation (CDU) within a bioenergy system. Simulation of an integrated, air-blown biomass gasification power cycle was used to study thermodynamic aspects of this emerging CDU technology. Analysis of the system model at varying gasifier air ratios and exhaust recycling ratios revealed the potential for modest system improvements under limited recycling ratios. Compared to a representative base thermodynamic case with overall system efficiency of 28.14 %, employing exhaust gas recycling (EGR) enhanced gasification system efficiency to 29.24 % and reduced the specific emissions by 46.2 gCO2/kWh. Further investigation of the EGR-enhanced gasification system revealed the important coupling between gasification equilibrium temperature and exhaust gas temperature through the syngas lower heating value (LHV). Major limitations to the thermodynamic conditions of EGR-enhanced gasification as a CDU strategy result from the increased dilution of the syngas fuel by N2 and CO2 at high recycling ratios, restricting equilibrium temperatures and reducing gasification efficiency. N2 dilution in the system reduces the efficiency by up to 2.5 % depending on the gasifier air ratio, causing a corresponding increase to specific CO2 emissions. Thermodynamic modelling indicates pre-combustion N2 removal from an EGR-gasification system could decrease specific CO2 emissions by 9.73 %, emitting 118.5 g/kWh less CO2 than the basic system.
The value of CO2-Bulk energy storage with wind in transmission-constrained electric power systems
Ogland-Hand, Jonathan D.; Bielicki, Jeffrey M.; Adams, Benjamin; et al. (2021)
Energy Conversion and Management
High-voltage direct current (HVDC) transmission infrastructure can transmit electricity from regions with high-quality variable wind and solar resources to those with high electricity demand. In these situations, bulk energy storage (BES) could beneficially increase the utilization of HVDC transmission capacity. Here, we investigate that benefit for an emerging BES approach that uses geologically stored CO2 and sedimentary basin geothermal resources to time-shift variable electricity production. For a realistic case study of a 1 GW wind farm in Eastern Wyoming selling electricity to Los Angeles, California (U.S.A.), our results suggest that a generic CO2-BES design can increase the utilization of the HVDC transmission capacity, thereby increasing total revenue across combinations of electricity prices, wind conditions, and geothermal heat depletion. The CO2-BES facility could extract geothermal heat, dispatch geothermally generated electricity, and time-shift wind-generated electricity. With CO2-BES, total revenue always increases and the optimal HVDC transmission capacity increases in some combinations. To be profitable, the facility needs a modest $7.78/tCO2 to $10.20/tCO2, because its cost exceeds the increase in revenue. This last result highlights the need for further research to understand how to design a CO2-BES facility that is tailored to the geologic setting and its intended role in the energy system. (© 2020 Elsevier Ltd ).
Planetary boundaries assessment of deep decarbonisation options for building heating in the European Union
Weidner, Till; Guillén Gosálbez, Gonzalo (2023)
Energy Conversion and Management
Building heating is one of the sectors for which multiple decarbonisation options exist and current geopolitical tensions provide urgency to design adequate regional policies. Heat pumps and hydrogen boilers, alongside alternative district heating systems, are the most promising alternatives. Although a host of city or country-level studies exist, it remains controversial what role hydrogen should play for building heating in the European Union compared with electrification and how blue and green hydrogen differ in terms of costs and environmental impacts. This works assesses the optimal technology mix for staying within planetary boundaries, and the influence of international cooperation and political restrictions. To perform the analysis, a bottom-up optimisation model was developed incorporating life cycle assessment constraints and covering production, storage, transport of energy and carbon dioxide, as well as grid and non-grid connected end-users of heat. It was found that a building heating system within planetary boundaries is feasible through large-scale electrification via heat pumps, although at a higher cost than the current system with abatement costs of around 200 €/ton CO₂. Increasing interconnector capacity or onshore wind energy is found to be vital to staying within boundaries. A strong trade-off for hydrogen was identified, with blue hydrogen being cost-competitive but vastly unsustainable (when applied to heating) and green hydrogen being 2–3 times more expensive than electrification while still transgressing several planetary boundaries. The insights from this work indicate that heat pumps and renewable electricity should be prioritised over hydrogen-based heating in most cases and grid-stability and storage aspects explored further, while revealing a need for policy instruments to mitigate increased costs for consumers.
Assessing the energy potential of modernizing the European hydropower fleet
Quaranta, Emanuele; Aggidis, George; Boes, Robert; et al. (2021)
Energy Conversion and Management
About 50% of all hydropower plants (HPPs) worldwide were originally commissioned more than 40 years ago, so that the advanced age of the fleet is a major concern across all continents, and especially in Europe. The modernization of HPPs can generate several benefits in terms of generation, flexibility, safety, operation, and may have neutral or even positive implications for the environment. In this work, we appraise several options for the modernization of existing plants, with the exclusion of measures expected to increase the hydro-morphological pressure on water bodies (e.g. increase of withdrawals or new parallel waterways): dam heightening, head loss reduction in waterways, increase of weighted efficiency of electro-mechanical equipment, digitalization and inflow forecast, and floating photovoltaic (evaporation reduction). We provide an indicative estimation of the additional power and annual generation that could be obtained compared to the current condition. We estimate that the overall energy generation could be increased by 8.4% for European Union and 9.4% for the whole Europe by implementing the above-mentioned strategies. The additional energy gain achievable by increasing the inflow was discussed but not included in the above mentioned overall indicator, because it is very site-specific. The additional energy storage achievable by reservoir interconnection and coordinated operation has been estimated in literature as 169 TWh. This suggests that the modernization of HPPs can generate significant benefits in terms of energy, and should be considered as an important element of energy policy, also considering the additional benefits in terms of reliability and flexibility of the energy system that it may deliver. The modernization options considered here, insofar as not entailing a worsening of the hydro-morphological alterations, are also expected to cause limited or no conflict with the environmental objectives of water policies in Europe.
Mitigating future winter electricity deficits: A case study from Switzerland
Mellot, Adrien; Moretti, Christian; Tröndle, Tim; et al. (2024)
Energy Conversion and Management
The transition to a net-zero economy with increased electrification of transport and heating poses electricity supply challenges during the winter months, particularly in PV-dominated systems. This study explores comprehensively various strategies and their combinations to address potential winter electricity deficits in Switzerland. Our innovative modelling integrates three sectors (electricity, heat, and transport), neighbouring countries, and environmental life cycle considerations. Among potential strategies to mitigate Swiss winter electricity deficit, electricity imports from neighbouring countries are taken as the benchmark policy strategy. Our analysis reveals that only gas-fired power plants and alpine PV, if applied in isolation, are technology options that alleviate the Swiss winter deficit and reduce cost at the same time. Increasing other single power technologies individually, or importing hydrogen, alleviate the deficit, too, but they inflate energy system costs by 18%–34% compared to relying on electricity imports. Despite the strategies for mitigating the winter deficit assessed being substantially different, our study found no significant environmental concerns regarding local land requirements or critical raw material needs. However, each strategy might imply the need for certain fuel imports and can have a profound impact on determining cost-optimal heating strategies for buildings. With an additional 1.4 GW of gas-fired power plant fuelled by domestic bio-methane, 4 GW of alpine PV, 2.2 GW of wind turbines, and no cost increase compared to its current roadmap, Switzerland could have a fully renewable energy system with a reduced winter deficit and no fuel imports.
Flexibility provision in the Swiss integrated power, hydrogen, and methane infrastructure
Akbari, Behnam; Garrison, Jared; Raycheva, Elena; et al. (2024)
Energy Conversion and Management
The renewable energy transition hinges on balancing energy supply and demand across seasons. This paper investigates the potential flexibility of Switzerland’s integrated power, hydrogen, and methane infrastructure to balance temporal mismatches while complying with national energy policies for sustainability and security. It develops an optimization method for energy system expansion and operation planning, filling crucial research gaps by (1) explicitly modeling power and gas transmission networks to guide technology placement and pinpoint network expansions, and (2) incorporating flexibility in power demand via shedding and shifting and in hydrogen and methane demands via price elasticity. The findings suggest that a 6.7-fold capacity expansion of variable renewables (i.e., photovoltaic, wind, run-of-river) by 2050 offsets nuclear phase-out and demand growth. The winter power gap is filled by power imports, hydropower generation, and gas turbines fueled by cost-effective hydrogen or methane imports. However, fuel embargoes escalate winter hydrogen and methane prices, reducing demand by 3.8%–10.4% and increasing domestic fuel production from biomass and excess renewable power in summer. To bridge the seasonal hydrogen and methane supply–demand gaps, up to 1.9 terawatt-hours of gas cavern storage is deployed in geologically viable locations, while costly tank storage plays a minor role. Power-to-gas requirements and power trade restrictions necessitate further renewable expansion, including 8.0 to 9.5 gigawatts of wind installations.
Economic evaluation of the industrial solar production of lime
Meier, Anton; Gremaud, Nicolas; Steinfeld, Aldo (2005)
Energy Conversion and Management

Publications 1 - 10 of 32

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