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Uusiutuvan energian vaihteleva tarjona haastaa perinteiset voimalaitokset joustamaan. Teknologian tutkimuskeskus VTT:n SmartFlex-tutkimusprojektissa (Smart and Flexible Thermal-Power Production, SmartFlex) kehitetään älykkäitä valvonta- ja säätötyökaluja hyödyntäen uusia tekoälypohjaisia ratkaisuja sekä tietopohjaisia lähestymistapoja.

In industrial applications, data is widely utilized to enable cost savings through optimized production. However, in a technical research organization, experimental data is often available in large quantities yet not fully utilized. The work presents a case study of the development of a digital twin for a pilot-scale fibre process research environment (SUORA), located in Jyväskylä, Finland. Using the digital twin, discrete laboratory analyses could be partially replaced with real-time quality parameter estimations. To evaluate the replicability of the approach, multiple quality parameters were studied, including dryness (former, press and web), as well as web basis weight, density and thickness. To construct the digital twin, data spanning over five years was collected, consisting of process measurements and laboratory analysis results. Representative operating periods were selected by the process operators, and the respective data converted into a single dataset. Using the dataset, feature selection was carried out for each quality parameter separately, showing the most descriptive process measurements. With the identified features, gradient boosting models were trained, showing good agreement with test data. In addition, isolation forest models were trained to assess the quality of the input data. With this approach, the operator was able to estimate also the prediction quality. The digital twin was deployed in the pilot control room (Fig. 1, left), with input data from the process control system fed to the models at a constant interval (Fig. 1, right). As the main benefit, the digital twin enables better estimation of the current process state, allowing desired steady-state conditions to be reached more easily. During the future trials with the pilot environment further model validation and end-user experience evaluation will be conducted.

Thermal energy storage (TES) plays a crucial role improving the efficiency of solar power utilization. Molten salt (MS) has gained a strong position as a thermal fluid in applications where solar power is stored and used overnight to provide dispatchable energy production. Novel process and operating concepts are being developed for TES systems that require reliable engineering tools. System-wide dynamic simulation provides a virtual test bench and analysis tool for assisting in process and control design and operational issues. Proper characterization of the thermal fluids in simulation tools is critical for successful simulation studies. In this paper, we report the experimental and modelling work related to counter-current heat exchange and free drainage test runs in CIEMAT's multi-purpose MS test loop at Plataforma Solar de Almería in Spain. We present a general method to define MS and non-condensable gas within a homogeneous pressure-flow solver. We present modelling of an indirect MS TES system connected to a thermal oil loop through TEMA type heat exchangers, model calibration with half of the experimental data, and finally, validation simulations against rest of the data. All these experimental data are previously unpublished. The model predicts the system behaviour with good agreement regarding temperatures, pressures, flow rates and liquid levels. The simulations suggest that the heat exchangers’ shell sides suffer from trapped non-condensable gas which significantly affects heat transfer, heat loss to ambient air and hydrodynamic losses. Our results contribute to thermal-hydraulic, system-wide modelling and simulation of MS processes. Furthermore, the results have practical implications for MS TES facilities with respect to system design, analysis and operation.

Concentrated solar power (CSP) is a renewable energy technology, which is able to provide dispatchable power according to demand. Dispatchability is typically achieved by decoupling solar thermal collection and power production with a thermal energy storage system. However, storage solutions for direct steam generating CSP technologies are still in a development phase. Hybrid system, in which solar field is integrated to a conventional power plant, is another option to produce renewable load-following power. The main idea in a hybrid system is to compensate the variation in solar thermal production with the steam boiler. In addition to dispatchable nature of power production, hybrid system offers several other possible benefits with respect to stand-alone CSP plant, such as reduced fuel consumption and emissions, enhanced plant efficiency and reduced production costs. However, the highly dynamic nature of the process imposes some challenges for the design and operation of the system, in particular in the case of significant solar share. Dynamic analysis of the system is foreseen to be utmost important in the plant design phase in order to take into account all the dynamic interactions in the process, which could affect for example the balance of different boiler heat transfer surfaces and turbine sections. The project "Combination of Concentrated Solar Power (CSP) with Circulating Fluidized Bed (CFB) power plants" (COMBO-CFB) aimed at developing innovative, flexible and high-efficient hybrid concept, which is able to balance the distributed intermittent production. The concept development included both experimental work and dynamic modelling and simulation. The research focused on the capacity building in terms of different CSP technologies, hybrid concepts and thermochemical processes, and in technical feasibility of the hybrid concepts, including the benefits provided by different concepts, challenges and possible future improvements. Three different hybrid concepts were studied in detail, namely: 1) Feedwater preheating concept, 2) Cold reheat line concept, and 3) High pressure turbine concept.

This paper presents a dynamic simulation study of the operation of a Power-to-Gas process. The process consists of three parallel 3MW alkaline electrolyzers driven by real-life national grid frequency data. These feed H2- and O2- compressor trains and storages processes followed by a methanation reactor. The process is controlled on two levels, where on the lower level stabilizing controllers are utilized to control e.g. flows and pressures by manipulation of e.g. valves and compressors. On the higher level, an operational scheduling of the electrolyzer operation is used. On this level the process can be operated as a primary grid frequency control reserve. To meet the local grid balancing needs, scheduling when to operate in frequency control could be determined beforehand from cost-efficient bidding in the local Electricity Spot and Regulation Power Markets. We assess a 24 hour period, in which the process operates to and from frequency control, from the point of view of how well the process can dampen variations. More precisely the effect of this operational scheduling on the electrolyzers, H2-storage system and CO2-methanation reactor is studied. Modelling of the process is done with a commercial, dynamic process simulator, Apros[...].

This paper addresses the operational profitability and benefits of co-production and dynamics in renewable Power-to-Fuel or Power-to-Chemical processes, when utilized to stabilize the power grid. To reach climate neutrality, the transport sector must switch to climate-neutral or climate-positive fuels or power. This can be done by a proper mix of electric vehicles where the power is based on renewable electricity, hydrogen vehicles where the hydrogen is based on side-product hydrogen or renewable power based processes, or by using in existing vehicle fleet renewable biofuels instead of fossil fuels. For hydrogen-based or hydrocarbon-based chemical industry, similar change needs are obvious. Today, renewable fuels can be produced with biomass based plants or in bio-refineries. If biomass cannot be utilized or there is a lack of some sustainable chemicals like hydrogen in the bio-process, new so called Power-to-X plants could be used to produce renewable fuels or chemicals of non-biomass origin (X refers to the end product of the plant). These processes are utilizing hydro, solar or wind power via electrolysis for production of the needed additional hydrogen fraction. Optimized day- or week-ahead planning can increase considerably the value of renewable Power-to-X plant operation. Such optimal operation can enhance commercial viability of the Power-to-X plants, and in this way introduce these climate-positive, mid-sized and distributed units into a smart grid. In this paper, we show examples on the value of such optimal dynamic operation together with the value of the dynamics of key unit processes and intermediate storages, while at the same time reaching a high share of sustainable solar and wind power in the end product.

Two concentrated solar power (CSP) concepts utilizing supercritical carbon dioxide (sCO2) Brayton cycle are dynamically simulated and compared regarding their overall performance and detailed sub-process behaviour. Concept 1 uses sCO2 both as heat transfer fluid (HTF) in the solar field and as working fluid in the power cycle, whereas Concept 2 uses molten salt as HTF and additionally takes advantage of a two-tank molten salt storage system to guarantee continuous power production. Concept 1 has been studied before, whereas Concept 2 presents a novel idea to combine high efficiency of sCO2 as the working fluid and the dispatchable nature of molten salt solar systems. Dynamic simulation software Aprosr was used to model and simulate the concepts, providing detailed results and insights on the system behaviour.

In literature CO2 liquidization is well studied with steady state modeling. Steady state modeling gives an overview of the process but it doesn’t give information about process behavior during transients. In this master’s thesis three dynamic models of CO2 liquidization were made and tested. Models were straight multi-stage compression model and two compression liquid pumping models, one with and one without cold energy recovery. Models were made with Apros software, models were also used to verify that Apros is capable to model phase changes and over critical state of CO2. Models were verified against compressor manufacturer’s data and simulation results presented in literature. From the models made in this thesis, straight compression model was found to be the most energy efficient and fastest to react to transients. Also Aproswas found to be capable tool for dynamic liquidization modeling.