The challenges of integrating solar heat into industrial processes are discussed using the example of two plants. To this objective, the standardisation concept for a power transfer station developed in the Modulus project is explained using the example of the solar plant in Turnhout, Belgium. Test plans were defined for a standardised qualification during the production and installation of the power transfer station on site. The in-situ test plans were categorised according to characteristics that have a significant influence on the test procedure. In a next step, the developed test plans were transferred to the commissioning of the plant in Belgium. The findings and results of the commissioning are described in detail and possible problems that arose are analysed. Attention is then focussed on the largest solar thermal process heat plant in Seville, Spain and its design and technical features are discussed. To conclude, the results of the 2023 global market analysis for concentrating solar collectors are presented.
In this work, two different methods for measuring the efficiency of central receivers are analyzed by the case of the High Performance Molten Salt II Project (HPMS-II): the continuous power-on method, and the semi-analytical method. The main difference between the two methods is the procedure to calculate the thermal losses of the receiver: on the one hand, the continuous power-on method calculates the thermal losses from the measurement of the absorbed power by the molten salt for different measured incident powers on the receiver. Here, it is assumed that the thermal losses are independent of the incident power if the molten salt temperature is kept constant. On the other hand, the semi-analytical method calculates the thermal losses as the sum of convective and radiative losses, calculated directly from the Newton and Stefan-Boltzmann equations by measuring the temperature of the tube surface, the ambient temperature, and the wind speed. Therefore, the calculation of the thermal losses is independent from one method to another. The procedure of applying these methods during the experimental test campaign of the HPMS-II receiver is detailed in this paper. Additionally, an uncertainty analysis of both methods is conducted to determine the uncertainty expected for the receiver efficiency measurements.
Thermochemical energy storage (TCS) uses the reaction enthalpy of reversible chemical reactions. This storage technology contains a so far largely untouched potential: in comparison to sensible and latent thermal energy storage, TCS offers potentially higher storage densities, the possibility of long-term storage as well as the option to upgrade the thermal energy. This upgrade can be realised if the reaction system consists of a solid and a gaseous component. For these gas-solid reactions with the generic equation
AB(s) + HR A(s) + B(G)
the equilibrium temperature is dependent on the reaction gas partial pressure: the higher the partial pressure, the higher the reaction temperature. Consequently, the charging of the storage can take place at lower temperatures than the discharging by adjustment of the reaction gas partial pressure.
Currently, a number of water vapour-solid reactions are investigated as thermochemical storage materials [1-4]. Apart from a general suitability of a reaction system for thermochemical storage, special attention has to be paid to the cycling stability of the reaction. This is often done using thermogravimetric analysis [5]. However, past scale-ups have shown that behaviour of bulks differs from that of analysis amounts [6]. The bulk’s changing properties, however, have proven to be crucial for storage reactor design. The investigation of the cycling stability and reaction behaviour of reacting solid bulks has been our motivation to design and build a cycling test bench. In this experimental setup the gaseous reaction partner is water vapour and can be provided at pressures between 5 kPa and 0.5 MPa. Reactor temperatures can be up to 500 °C.
The aim of the presented studies is the automated cycling of about 100 ml solid storage material of reaction systems that have previously shown promise at analysis scale.
Das aus der Literatur bereits seit Jahrzenten grundsatzlich bekannte Prinzip der Warmetransformation verspricht im Vergleich zu thermisch betriebenen Warme-pumpen deutlich hohere Nutztemperaturen [1]. Die auch „chemische Warmepumpen“ genannten Systeme basieren auf dem Einsatz einer umkehrbaren Gas-Feststoff-Reaktion und sind somit ein Spezialfall der thermochemischen Energiespeicherung, bei dem die Hin- und Ruckreaktion auf verschiedenen Temperaturniveaus ablaufen: Im Vergleich zur endothermen Beladungsreaktion findet die exotherme Entladungs-reaktion bei einer hoheren Temperatur statt; die in der Reaktion gespeicherte thermische Energie wird somit in Bezug auf ihr Temperaturniveau „aufgewertet“.
Geeignete Stoffsysteme, die im Gramm-Masstab experimentell untersucht wurden, sind in der Literatur beschrieben [2]. Allerdings sind diese Ergebnisse zumeist nicht direkt ubertragbar auf grosskalige thermochemische Reaktoren. Ein moglicher „show stopper“ fur hohe thermische Belade- und Entladeleistungen ist vor allem der schlechte Warmetransport innerhalb der Feststoffschuttung. So sind in der Literatur bislang nur wenige Systeme in technisch relevanter Grosenordnung bei gleichzeitig hohen spezifischen thermischen Leistungen (kW/kg) beschrieben. In unserer Arbeit untersuchen wir ein Salzhydrat in Hinblick auf seine Eignung fur Warmetransformationsprozesse im Temperaturbereich von 180 °C bis 300 °C. Die Reaktionstemperatur wird uber die Variation des Drucks des gasformigen Reaktionspartners im Bereich von 1 kPa bis 0,6 MPa Wasserdampf eingestellt.
Im Rahmen des Beitrags mochten wir die technologischen Aspekte des thermodynamischen Prozesses der Warmetransformation diskutieren und insbesondere unsere aktuellen experimentellen Ergebnisse zur thermochemischen Warmetransformation im 1 kW-Masstab vorstellen.
Der effizienten Speicherung und Rekuperation thermischer Energie macht nicht selten die im Warmeubertrager auftretende Temperaturdifferenz (Gradigkeit) der Warmestrome einen Strich durch die Rechnung: Da es sowohl bei der Beladung als auch bei der Entladung beispielsweise eines sensiblen „Warmespeichers“ zu Temperaturgradienten kommt, ist die Entladetemperatur niedriger als die Beladetemperatur des Speichers. Dies schrankt die Einsatzmoglichkeiten thermischer Energiespeicher bei der Reintegration von Prozessabwarme ein.
Diese Problemstellung wird durch den Einsatz thermochemischer Systeme zur Speicherung und „Transformation“ von Energie adressiert. Dabei wird thermische Energie in Form chemischen Potentials der Reaktionspartner einer umkehrbaren chemischen Reaktion gespeichert. Die Nutzung der Druckabhangigkeit der Reaktionstemperatur einer Gas-Feststoff-Reaktion
A(s) + B(g) ⇌ AB(s) + ∆RH
ermoglicht dabei das Ausgleichen von Temperaturgradienten zwischen Beladung (endothermer Reaktion) und Entladung (exothermer Reaktion) des Energiespeichers: Ein Erhohen des Drucks des gasformigen Reaktionspartners fuhrt zu einer hoheren Reaktionstemperatur im Vergleich zur Speicherbeladung bei niedrigem Druck. Die chemische Reaktion erfullt dabei nicht nur die Speicherfunktion, sondern fuhrt zusatzlich zu einem Warmepumpeneffekt. Der durch die Druckerhohung erzeugte Temperaturhub kann nicht nur dazu dienen, die Gradigkeiten der Warmeubertrager zu kompensieren, sondern auch gespeicherte Energie daruber hinaus thermisch „aufzuwerten“. Neben der Antriebsart unterscheidet sich auch der Temperaturbereich dabei wesentlich vom Einsatzbereich konventioneller, von elektrischer Energie angetriebener Warmepumpen: Als Antrieb fur die Warmetransformation kann beispielsweise bei 100 °C anfallende Prozessabwarme genutzt und ein Warmestrom bei uber 200 °C thermisch aufgewertet werden. Eine Gruppe der in der Literatur bekannten thermochemischen Reaktionssysteme sind dabei die Hydrate anorganischer Salze [1].
Am Institut fur Technische Thermodynamik des Deutschen Zentrums fur Luft- und Raumfahrt (DLR) konnte die technische Umsetzung der Warmetransformation basierend auf dem Stoffsystem SrBr2/H2O in einem Reaktor im Technikumsmasstab (1000 g Speichermaterial) im Temperaturbereich von 200 °C bis 230 °C erstmals demonstriert werden. Erste Messergebnisse zeigen, dass sowohl die Beladung als auch die Entladung des Speichers bei einer Temperatur von 210 °C umsetzbar ist. Das Funktionsprinzip der Warmetransformation und der Unterschied zu konventionellen Warmepumpen soll anhand des Stoffsystems SrBr2/H2O erlautert werden. Die Messergebnisse aus dem Technikumsversuch werden den mittels thermogravimetrischer Analyse bestimmten thermodynamischen Daten des Reaktionssystems gegenubergestellt. Betrachtungen des Wirkungsgrads eines thermodynamischen Vergleichsprozesses sollen ferner das Potential sowie auch die Grenzen der Warmetransformation mittels thermochemischer Systeme verdeutlichen.
Literatur:
[1] YU, Y.Q.; ZHANG, P.; WU, J.Y.; WANG, R.Z. Energy upgrading by solid-gas reaction heat transformer: A critical review. Renewable and Sustainable Energy Reviews, 2008, Volume 12, 1302-1324.
To quantify the value of thermal energy as an “energy currency”, it needs more than solely the energy’s amount given in Joules: the temperature level at which, for example, excess heat is available from industrial processes determines whether this thermal energy can directly be re-integrated as process heat or is emitted to the ambient as waste heat. A further limitation is the temporal coupling of heat supply and heat demand. The latter can be resolved by using thermal energy storage systems, which, however, further “downgrade” the thermal energy in terms of its temperature level, and hence, lead to exergy losses. In this thesis, a energy storage system was developed based on the reversible chemical reaction of strontium bromide anhydrate to strontium bromide monohydrate. The phase transition from the anhydrous to the monohydrous phase allows for storage operation in the temperature range from 150°C to 300°C, which is particularly interesting for industrial applications. The temperature downgrade between charging and discharging can be compensated by means of the so-called thermochemical heat transformation: if the gas pressure is raised between charging and discharging, the stored thermal energy is released at a higher temperature compared to its transfer to the storage. Thermo-dynamically, this system corresponds to the coupling of an energy storage with a thermally driven heat pump. For the reaction system SrBr2/H2O, the pressure-dependent re-action temperatures of the hydration and dehydration reaction were experimentally investigated, and an empirical description of the reaction rate was derived from thermogravimetric measurements. The experimental proof-of-concept was performed with an effective thermal upgrade from 180°C (charging temperature at 1 kPa steam pressure) to 280°C (discharging temperature at 560 kPa steam pressure), using a reactor concept scalable for large industrial applications. The operating characteristics of the storage module were experimentally and numerically studied to quantitatively explain the performance-dominating processes in the storage reactor. By means of the experimentally validated simulation study, the limitation of the storage module’s thermal performance by heat transfer was proven. Subsequently, a thermal sensitivity study was executed, which shows that at the moment of maximum thermal power, the major contribution is attributed to the interface between the porous bulk and the heat exchanger wall - and not, as it is often assumed for other packed-bed storage geometries, within the porous medium. In addition to the proof-of-concept, the present study provides the necessary fundamentals for detailed potential analyses of various industrial thermal energy storage and heat transformation applications and the optimization of the storage integration.
The aim of the Modulus (Modular Heat Transfer Station) project is to achieve a cost reduction by standardizing the Balance of Plant (BoP) in the field of solar thermal process heat plants. A consortium of three parabolic trough collector manufacturers, one producer of conventional BoP plants, and two research institutes have joined forces to develop a conceptional approach: First, a worldwide research of existing process heat plants was carried out and the database "ship-plants.info" was evaluated. One partner analyzed in particular the plants that will be added in 2021. In the next step, the components of a BoP plant were listed in the power range from 0.5 to 10 MW, their potential for standardization was investigated and classified. Based on this, a standardized piping and instrumentation diagram (P&ID) was developed. This has already been used as a template for further detailing of the BoP for three process heat plants in Europe, which are presented in the third chapter. Finally, further standardization options for commissioning (functional and safety tests) and performance evaluation are discussed.
Currently, state of the art working fluids of conventional heat pumps are limited to maximum output temperatures of 140 °C, and thus cannot fulfill the need for high temperature heat pumps in industrial applications. This is why thermochemical reaction systems have come into the focus of interest: they offer the potential of high temperature energy storage and heat transformation, e.g. by making use of the pressure dependency of a gas-solid reaction. These reactions can in general be described by the following equation:
A(s) + B(g) ⇌ AB(s) + ΔRH.
Variation of the pressure of the gaseous reactant B results in a temperature shift of the exothermic reaction. In this way, the exothermic reaction (energy output) can be performed at higher temperatures than the endothermic reaction (energy input). In this contribution, the thermodynamic principle of thermally driven heat transformation and its main difference with respect to conventional or sorption based heat pumps is outlined.
The scope of this work is the potential of the SrBr2–H2O system as a possible candidate for thermochemical heat transformation. Constraints for a suitable reactor geometry and the possibility to combine thermal upgrade and thermal energy storage into one system are analyzed. Experimental results from a laboratory scale test reactor (~ 1,000 g) support the proof of concept of heat transformation in the region of 200 °C.
'/%3e%3c/g%3e%3cuse xlink:href='%23d' x='45.714'/%3e%3cuse xlink:href='%23e' transform='matrix(-1 0 0 1 479.792 0)'/%3e%3cg id='f' fill='%23fff'%3e%3cpath fill='%23039' d='M232.636 202.406v.005c0 2.212.85 4.227 2.212 5.69 1.365 1.466 3.245 2.377 5.302 2.377 2.067 0 3.944-.905 5.303-2.365 1.358-1.459 2.202-3.472 2.202-5.693v-10.768l-14.992-.013-.028 10.766'/%3e%3ccircle cx='236.074' cy='195.735' r='1.486'/%3e%3ccircle cx='244.392' cy='195.742' r='1.486'/%3e%3ccircle cx='240.225' cy='199.735' r='1.486'/%3e%3ccircle cx='236.074' cy='203.916' r='1.486'/%3e%3ccircle cx='244.383' cy='203.905' r='1.486'/%3e%3c/g%3e%3cuse xlink:href='%23f' y='-26.016'/%3e%3cuse xlink:href='%23f' x='-20.799'/%3e%3cuse xlink:href='%23f' x='20.745'/%3e%3cuse xlink:href='%23f' y='25.784'/%3e%3c/svg%3e)