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Decarbonisation of heat generation has become a priority for district heating network operators. In order to avoid the use of fossil-fired boilers, operators need to know peaks in heat demand in advance. Accurate thermal load forecasting is playing an increasingly important role in this respect. This paper presents the final results of the research project “deepDHC” (deep learning for district heating and cooling) funded by the German Federal Ministry for Economic Affairs and Climate Action (BMWK). The three-year project focused on systematically benchmarking thermal load forecasts for district heating networks, based on state-of-the-art machine learning methods. The analysis covers a variety of machine learning techniques, such as neural networks – including latest deep learning methods – (e.g. LSTM, TFT, ESN, RC), decision trees (random forests, adaptive boosting, XGB) and statistical methods (SARIMAX). In addition, the impact of combining methods by so-called “stacking” was investigated. Training and validation of the machine learning algorithms was based on historical operating data from the district heating network for the city of Ulm in Germany, in combination with historical weather data, and weather forecasts. Thermal load forecasts – typically for three days ahead – are presented and compared against one another. An automatic tuning routine was developed as part of the project, which enables regular re-training of the machine learning algorithms based on the latest operating data from the heating network. Furthermore, a web interface for real-time forecasting was developed and implemented at the power station.
The use of natural gas has continuously increased and reached 24.7% of the worldwide primary energy supply in 2020. The same trend applies to Liquefied Natural Gas (LNG), which contributed to 52% of overall natural gas trades in the same year. In this context, the recovery of the cold energy available at LNG receiving terminals during the process of regasification is of a critical importance.
This paper addresses the integration of the regasification process with an Organic Rankine Cycle (ORC) in order to exploit the available LNG cold energy, by condensing the organic fluid. In addition, a gas turbine exploits differences between regasification and distribution pressures. The analysis covers different organic fluids and two ORC heating source configurations: a) a low-temperature one, using seawater, and b) a high-temperature one, using exhaust gas. In addition, the integration of a natural gas-fired topping gas turbine, which uses the LNG cold energy by compressor inlet air cooling, was simulated. The performance of a medium size regasification terminal (50 kg/s) was evaluated as a function of both the regasification and the natural gas distribution pressures.
Dedicated models have been developed using Aspen Plus software to simulate the regasification process and the integrated topping cycles (Organic Rankine and Brayton), and their mutual energy integrations.
The analysis shows that ORC power outputs from 2 MW up to 4.5 MW in case a) and from 6 MW up to 9 MW in case b) can be reached. The topping gas turbine benefits from the inlet air cooling and can add a power output of 35 MW to 40 MW. R125 was the best working fluid for a low-temperature ORC, while R600a showed the best performance for a high-temperature application.
Für Fernwärmeversorger spielt die Lastprognose bei der Anlageneinsatzplanung eine zentrale Rolle. Benötigte Fernwärme oder auch -kälte lassen sich umso kostengünstiger, effizienter und emissionsärmer bereitstellen, je exakter die zu erwartende Last abgeschätzt werden kann. Ein neuartiges, an der Hochschule Kempten entwickeltes Verfahren namens »Deep DHC« kann die Genauigkeit dieser Lastprognosen deutlich erhöhen
High temperature fuel cells are considered a promising option for highly efficient distributed power generation. This paper presents a dynamic model of a solid oxide fuel cell (SOFC) system. Detailed models for all process components were developed and validated with experimental data, which is demonstrated using the burner model as an example. Focus of this paper is on SOFC system heat-up. Different strategies are discussed, and dynamic simulation results of heat-up processes are shown.
This paper presents a modeling framework to address the energy, economy, emissions and land use nexus when exploiting bioenergy in developing countries. The modeling framework combines a qualitative and a quantitative element. The qualitative element integrates two components: (1) technology roadmapping to identify long-term technology targets through expert judgment and (2) scenario analysis to investigate different future storylines. The quantitative element comprises four integrated tools, namely the energy system model (ESM), the land use and trade model (LUTM), an economic model, and an external climate model. An overview of the modeling framework, scenario analysis, structure of the models, modeling techniques, mathematical formulations and assumptions is presented and discussed. The modeling framework is applied to the particular context of Colombia, as a case study of a developing country with large bioenergy potential. In this study case, the impacts that an accelerated deployment of bioenergy technologies might cause on the energy demand and supply, emissions and land use until 2030 are evaluated. Results suggest that a plan to exploit bioenergy in Colombia should prioritize the deployment of technologies for biomethane production, power generation & CHP, which can reduce more GHG emissions and more emissions per incremental hectare of land than first-generation biofuels. Moreover, while the share of bioenergy in the primary energy demand decreases in all the analyzed scenarios, it is possible to envision significant increases in the share of bioenergy in road transport energy demand, power generation and natural gas supply for scenarios implementing roadmap goals. In addition, impacts of El Niño oscillation on the dependence of hydro for power generation can be partly mitigated by exploiting the complementarity of hydro and bioenergy, which might result in a reduction of up to 5–6% in the demand for fossil fuels used in power generation in dry years. However, despite the ambitious goals proposed here, bioenergy alone cannot significantly reduce emissions by 2030 (maximum 10% reduction relative to baseline) and effective climate change mitigation requires a portfolio of additional measures.
The growing concern about the role of man-made CO2 emissions with respect to global arming, in combination with the large increase in energy demand spurred by developing nations and a growing global population that is foreseen over the next 15 years have recently turned attention to potential CO2-neutral energy supply solutions.
Grid-compatible integration of typically fluctuating electrical energy sources, like wind and solar power, will be important in order to support the goal to reduce CO2 emissions. However, this will require substantial adjustments to the grids and power plant systems in order to cope with the upcoming new boundary conditions imposed by substantially increased utilization of renewable energies.
To respond to this imperative, GE and RWE Power have started to investigate new technologies for large-scale storage of electrical energy in Adiabatic Compressed Air Energy Storage power plants.
This concept offers efficient, local zero-emission storage based on compressed air held in underground caverns. The compression and expansion of air with turbomachinery help to balance power generation peaks that are not demand-driven on the one hand and consumption-induced load peaks on the other, allowing the optimal use of both traditional fossil fuels and renewables.
Before this concept can be implemented, however, numerous technical issues must be addressed, mainly in the field of turbomachinery and the heat storage device. This paper describes today’s technical capabilities of turbomachinery equipment, and evaluates the need for further development based on the requirements of advanced CAES technology. Ongoing development activities are described and initial results presented.
Methodology for biomass energy potential estimation: Projections of future potential in Colombia
(2014)
This paper presents a novel method to estimate the future biomass energy potential in countries with domestic markets unable to influence international markets. As a study case, the biomass energy potential in Colombia is estimated for the period 2010–2030.
The prediction model is a scenario-based optimization algorithm that maximizes the yearly profit of locally producing and importing commodities in a country subject to certain constraints (domestic demand, limited area, etc.) as well as to demographic, macroeconomic and market data (e.g. domestic and international prices of commodities). The bioenergy potential associated to the production of commodities is calculated according to a methodology presented by the same authors. In order to provide a modeling framework consistent with other state-of-the-art projections, global scenarios for analysis are selected from the literature rather than formulated. Selected global scenarios highlight the influence of global biofuel use on agricultural prices, production and demand.
Results predict a theoretical bioenergy potential in Colombia 56%–69% larger in 2030 than in 2010 (1.31–1.41 EJ). A sensitivity analysis shows that while a higher global biofuel use leads to a higher local bioenergy potential, its influence is less pronounced than that of agricultural yields, demand and specific energy of biomass resources.
This paper presents a novel approach to address uncertainty and improve reliability of the estimation of the biomass energy potential at a country level, particularly suitable for situations when quality and availability of data are limited. The proposed methodology improves the prediction reliability by following four steps: 1) using a simple accounting framework, 2) using a robust selection of probability density functions, 3) using a probabilistic propagation of uncertainty and 4) using sensitivity analysis to identify key variables contributing to uncertainty as well as a root cause analysis and a set of sub-models to improve estimation of key variables.
The application of the methodology to the energy scenario in Colombia shows that the improved estimation of the theoretical energy potential has an almost identical mean value compared to the preliminary estimate, but the uncertainty is significantly lower (less than 50%). Moreover, the mean value of the technical energy potential obtained through the methodology is 25% lower than the preliminary potential and the uncertainty reduces by one third.
Energy scenarios suggest that CO2 capture and storage (CCS) from power plants might contribute significantly to global greenhouse gas emission reduction. Since CCS from power generation is an emerging technology that has not been demonstrated on a commercial scale, related cost and performance information is still uncertain. This paper presents a detailed analysis of the impact of adding CO2 capture and compression process equipment to fossil-fuelled power plants. For coal-fired power generation, no single capture technology outperforms available alternative capture processes in terms of cost and performance.
Electricity generation from coal is still growing rapidly and energy scenarios from the IEA expect a possible increase from today's 1 600 GW of coal-fired power plants to over 2 600 GW until 2035. This trend will increase the lock-in of carbon intensive electricity sources, while IEA assessments show that two-thirds of total abatement from all sectors should come from the power sector alone to support a least-cost abatement strategy. Since coal-fired power plants have a fairly long lifetime, and in order to meet climate constraints, there is a need either to apply CCS retrofit to some of today's installed coal-fired power plants once the technology becomes available. Another option would be to retire some plants before the end of their lifetime. This working paper discusses criteria relevant to differentiating between the technical, cost-effective and realistic potential for CCS retrofit. The paper then discusses today's coal-fired power plant fleet from a statistical perspective, by looking at age, size and the expected performance of today's plant across several countries. The working paper also highlights the growing demand for applying CCS retrofitting to the coal-fired power plant fleet of the future.
In doing so this paper aims at emphasising the need for policy makers, innovators and power plant operators to quickly complete the development of the CCS technology and to identify key countries where retrofit applications will have the biggest extent and impact.
This working paper evaluates cost and performance trends related to carbon dioxide (CO2) capture from power generation, based on extensive analysis of data from major engineering studies published between 2006 and 2010. Since individual studies use different methodologies and boundary conditions, study estimates for over 50 CO2 capture installations are re-evaluated on a consistent basis and updated to current cost levels.
The paper discusses the need for further standardisation of evaluation methodologies and additional data for specific CO2 capture routes. Further analysis for non-OECD countries is considered crucial for global energy scenario models, and for improving the skills and knowledge developing countries need to evaluate the role of CCS in their national energy contexts.
Im Projekt KWK-Flex untersuchte die Hochschule Kempten innovative Methoden und Anlagenbetriebsstrategien zur flexiblen, stromgeführten Fahrweise von Kraft-Wärme-Kopplungs-(KWK)-Anlagen in Fernwärmeverbundnetzen im Kontext steigender Anteile erneuerbarer Energien. Solche KWK-Anlagenverbunde im Leistungsbereich ab einigen MW werden in Deutschland aufgrund ihrer hohen Brennstoffnutzungsgrade und der daraus folgenden Ressourcen- und Klimafreundlichkeit von mehreren hundert Stadtwerken bzw. Fernwärmeversorgern betrieben.
Bei der Methodenentwicklung und den daraus resultierenden optimierten Anlagenbe-triebsstrategien standen neben den Zielgrößen Dynamik und Flexibilität der Strombe-reitstellung insbesondere die Ressourceneffizienz, d.h. hohe Wirkungsgrade, geringe Emissionen und hohe Wirtschaftlichkeit, sowie eine hohe Versorgungssicherheit im Fokus. Als Schwerpunkte des Forschungsvorhabens wurde Untersuchungen zur in-stationären Prozesssimulation von KWK-Kraftwerken mit dem Ziel der Erhöhung der stromseitigen Anlagendynamik mit dem Einsatz numerischer Methoden zur optimierten Anlageneinsatzplanung der Kraftwerke in KWK-Verbunden kombiniert.
Das Projekt wurde am Institut für Energie- und Antriebstechnik (IEAT) der Hochschule Kempten mit Unterstützung der beiden assoziierten gewerblichen Partner Fernwärme Ulm GmbH (FUG) und ZAK Energie GmbH (ZAK) sowie dem Fernwärmeversorgerdachverband AGFW | Der Energieeffizienzverband für Wärme, Kälte u. KWK e.V. durchgeführt.
This paper describes the process of developing a technology roadmap for deploying bioenergy technologies at a country level. A method for energy technology roadmapping adapted to the conditions of developing countries is proposed. This method combines an acknowledged roadmapping framework from prior art, a new strategy to build consensus based on the Delphi method and a strong focus on analytical modeling for supporting expert judgment. This method aims to be simple, transparent and affordable. The proposed method is applied to Colombia for creating a plan to deploy sustainable bioenergy technologies in Colombia until 2030. This plan consists of a set of long-term goals, milestones, barriers and action items identified by over 30 experts for key bioenergy technology areas (viz. bioethanol, biodiesel, renewable diesel, biomethane, biogas, waste-to-energy and power generation and combined heat and power). Finally, the relevance of the process of developing a technology roadmap for bioenergy exploitation in Colombia in other developing countries is discussed.
Die verstärkte Einbindung fluktuierender erneuerbarer Energien erfordert hochflexible thermische Kraftwerke zur Netzstabilisierung und bedarfsgerechten Abdeckung der verbleibenden Netzlasten. Für einen effizienten Anlageneinsatz spielt dabei die möglichst genaue Kenntnis der zu erwartenden Fernwärmelast eine zentrale Rolle. Für die Fernwärmelastprognose können innovative Verfahren unter Verwendung moderner maschineller Lernverfahren zum Einsatz kommen, die im Folgenden vorgestellt werden.
Ökonomische Aspekte von CCS
(2015)
Brennstoffzellensysteme mit oxidkeramischer Brennstoffzelle (SOFC) eignen sich besonders für eine hocheffiziente und emissionsarme Energiebereitstellung. Aufgrund der für diesen Brennstoffzellentyp nur sehr begrenzt vorhandenen Betriebserfahrungen ist das Ziel der vorliegenden Arbeit, eine möglichst verallgemeinerbare dynamische Systemsimulation für SOFC-Kraftwerke zu entwickeln. Auf diese Weise können bereits im Vorfeld des Anlagenbetriebes Wechselwirkungen zwischen Teilsystemen analysiert sowie Strategien für einen ressourcensparenden Betrieb entworfen werden.
Die in dieser Arbeit vorgestellte Systemsimulation basiert auf einem gemeinsamen generischen Modellansatz für sämtliche Prozesseinheiten. Die Modelldetails der einzelnen Anlagenkomponenten orientieren sich an realen Bauteilen eines am Forschungszentrum Jülich im Aufbau befindlichen 20 kW Brennstoffzellensystems. Vor diesem Hintergrund stehen umfangreiche Messdaten zur Verfügung, mit denen alle entwickelten Komponentenmodelle validiert werden.
Dynamische Systemrechnungen für sämtliche Betriebszustände wie Aufheizen, Anfahren, Nenn- und Teillast sowie eine Außerbetriebnahme bilden den Schwerpunkt der Arbeit. Für den Aufheizvorgang werden in Bezug auf den Energie- sowie Zeitbedarf optimierte Betriebsstrategien ermittelt. Die simulierte Aufheizzeit von Raumtemperatur auf 600°C liegt für das betrachtete SOFC-System unter den gegebenen Randbedingungen bei mindestens fünf Stunden. Das anschließende elektrochemische Anfahren bis in den Nennlastzustand dauert rund eine Stunde. Wie die Untersuchungen zeigen, lassen sich in der Regel sowohl Lastreduzierungen als auch -erhöhungen unverzüglich durchführen, sofern sich das System nahe seiner Betriebstemperatur befindet. Ein stabiler Betrieb der SOFC-Anlage bei Teillast ist zudem selbst bei geringen Stromdichten möglich. Lediglich für einen mehrstündigen reinen Stand-by-Betrieb muss das System durch Wärmezufuhr auf Temperatur gehalten werden. Mit einem hohen Kühlluftzusatz lässt sich ein Abkühlvorgang im Rahmen einer Außerbetriebnahme derart forcieren, dass alle Systemkomponenten innerhalb eines Tages wieder Umgebungstemperatur erreichen.
Die Berechnungen erfolgen für ein SOFC-System mit separater Bereitstellung von Wasserdampf für die Vorreformierung. Die Simulation einer zusätzlichen Anlagenkonfiguration, in der mittels eines Ejektors Anodenabgas rezykliert wird, zeigt zudem Möglichkeiten einer weiteren Steigerung des Gesamtwirkungsgrades auf.
City busses and coaches are typically ventilated with high fresh air rates without monitoring of air quality according to recommendations and requirements of associations of public transport companies. The air quality of cabin air regarding humidity and CO2-concentration depends however on the number of passengers. Hence the air quality of the ambient air could be monitored and air conditioning units could be switched on re-circulation air, which is called here “monitored fresh air rate”. Average occupancy of city busses is 30 %. This means the cabin will be ventilated with a surplus of about 70 % of the required fresh air. This causes a high energy consumption which could be saved. The aim of this work is the monitoring of the cabin air quality with the help of sensors and development of appropriate control algorithms that could reduce energy consumption without any impairment of safety, comfort, stress and health.
Decarbonisation of district heating networks requires a heat generation and storage portfolio that allows for maximised integration of renewable energies. However, it is also essential to have a precise forecast of the thermal loads to be expected in the network and – based on this forecast – an optimised dispatch strategy in order to best match the available generation and storage portfolio with the actual heat demands in the grid. This paper presents a holistic approach that combines modelling and optimisation activities related to these three aspects: first, detailed process modelling and optimisation of power plants and thermal storages; second, a numerical model for dispatch optimisation; and third, machine-learning-based load forecasting. This work, which was performed as part of the publicly funded research projects “KWKflex” and “deepDHC”, was based on operating data from the district heating network of the city of Ulm in Germany. The paper presents the modelling, validation and simulation results of a stationary and instationary process simulation for a 58 MW thermal biomass-fired combined heat and power plant. The analysis identifies a potential to integrate additional renewable power of up to 17 MW thermal power by “power-to-heat” technologies into different parts of the process. The economic benefit is quantified with a mixed-integer linear programming dispatch optimisation model of the district heating network. In order to allow for real-time optimisation of the power plant and thermal energy storage dispatch, a machine-learning-based thermal load forecasting method was developed. The performance of different machine learning algorithms, including decision trees and deep learning techniques, is compared based on a 72-hour forecast horizon. In addition, the economic impact of uncertainties in thermal load prediction is analysed with the numerical dispatch optimisation tool.