Institute for Environmental Chemistry

1. Design and Operation Modeling and Simulation References Conclusion Background and Objectives Control and Optimization Acknowledgements Figure 1: The general Aim of the Thermal Battery House heating (central and water) PROCESS ENGINEERING OF A NEW THERMOCHEMICAL HEAT STORAGE SYSTEM Thermal Battery House heating Electricity for house Fopah Lele, Armand1; Rönnebeck, Thomas1; N‘Tsoukpoe, Edem K.1; Rohde, Christian1; Schmidt, Thomas1*; Ruck, Wolfgang1 Heat Loss (Waste Energy) 1Leuphana University of Lüneburg, Institute for Sustainable and Environmental Chemistry, Scharnhorststr. 1, Building. 13, 21335 Lüneburg – Germany *Tel: +49 (0) 41316772951, Fax: +49 (0) 41316772822 E-mails: thschmid@inkubator.leuphana.de. CHP Plant Storage of thermal energy is now needed if we want to achieve greater energy efficiency and a wide use of this resource. Especially in European’s households it is a very important factor in the improvement of living conditions and environment conservation. The demand of heat storage capacity in Germany will increase due to the fluctuating renewable energy sources. This new heating system to use the waste heat from a, for example, micro – CHP [1] for room heating, could be one solution. Reversible thermochemical solid-gas reactions [2] are fulfilling these conditions. However, the reactor itself and mandatory additional reactor components like heat exchangers are adding additional mass, which increases the percentage of latent heat. To face those limitations and provide a good efficiency it is rational to use a small amount of environmental energy and lift on a usable level. That is why a good process engineering would give the possibility to reduce the waste and dissipation. In the way of rethink systems engineering approach to combat complexity in product development, we ensure quality of our reactor by integrated verification and validation process through CAD program (figure 2 & 3). Netting plates or tubes of heat exchanger. This for diffusion enhancement involving total wet of the bed material (i.e. the grains and the pellet in radial and vertical directions). Reactor size reduction by keeping a high energy density involves the set up of operating conditions from material-scale to the reactor level. the supplied heat from the micro-CHP exhaust heat to the battery will be performed at ∆T = 10°C. According to Novak et al. [3], the usable temperature range of exhaust heat from the micro-CHP is [90°C – 120°C]. This fits with the objective of our thermal battery with 80 kWh storage capacity and a volume of 1m3for a 10 years lifetime with 200 cycles per year. Theoretical thermodynamic calculations based on equilibrium pressure of water steam over the material, condensing temperature lead us to an outlet temperature of about 40°C. Institute for Environmental Chemistry Figure 3: The SolidWorks Design Reactor (Virtual concept) Figure 2: The Labs scale Reactor (Physical product) The thermochemical energy storage is due to chemical reaction. From a scientific point of view, the difficulty lies in coupling heat, mass and chemical reaction. Comsol Multiphysics has been choose for this task because of its ability to couple those physical phenomena. As example at material scale, we model heat transfer (conduction and convection) in the material bed. Figure 5 shows the bed is highly heated at a limited depth and this led us to choose the reactor‘s diameter. In chemical reaction simulation, we are trying to figure out the kinetic behavior through the modified Prout-Tompkins equation [5]: At reactor level, transport phenomena at different parts of the system are performed to evaluate required parameters like temperatures, masses and diffusion coefficient. Concerning heat exchanger, previous studies [4] have revealed that it occupies a significant weight and volume of the bed, thereby causing a reduction in the gravimetric and volumetric density of the storage bed. Hence there is a need to investigate different compact heat exchanger for effective heat tranfer of the storage bed. Figure 4 is an example. 1 cm Figure 4: Heat transfer from tube to plate of the Heat Exchanger Figure 5: 2D multiphysics simulation with Comsol 4.3 • - The need to deliver innovative product leads to increased complexity and makes ensuring product quality more difficult. • - Boiler tank system with high volume used to provide outlet temperature in the range of [30°c – 60°C] for households applications. • - Reducing dimension by keeping yield (i.e. small volume with high density) is a great scientific challenge. • - Only rethink engineering process might bring solution to this scientific dilemma. • - With this new process engineering, the expected COP = stored heat / (consumed electricity + waste energy) is 4.85 (theoretical calculations). • - The thermal battery: new thermochemical heat storage system due the rethink process will bring a solution for better life conditions and efficient renewable energy. Adjusting our process for a good optimization lead us to common goal as cost minimizing, throughput maximizing, and/or efficiency. Figure 6 shows a result in the research of affordable thermochemical materials without violating some constraint like operating range of the battery for the micro-CHP. The use of water as transport means makes the transport cheaper. Requirement to the overall system’s optimization, particularly the amount of thermochemical material per volume, heat exchanging and process performance is needed. This implies dynamic simulation. Our battery connected to the CHP will also use electricity from the latter (electric coefficient of micro-CHP is 35% and thermal coefficient of micro-CHP is 60% ). However, this process allows a slight reduction (i.e. 4.5%) of electrical power coefficient. Figure 6: Different materials testing and operating range for the battery [6] [1] Cakir U., ComakliK., YükselF., The role of cogeneration systems in sustainability of energy, Energy Conversion and Management 63 (2012), pp 196 - 202. [2] Opel, O. et al., Thermochemical storage materials research – TGA/DSC – Hydration studies, International Conference (IC-SES), 20-24 February 2011, Belfast, UK. [3] Nowak W., Arthkamp J., Weddeling K., “BHKW-Grundlagen”, ASUE-Arbeitgemeinschaft für Sparsamen und Umweltfreundlichen Energieverbrauch e.V. (Juni 2010), seite 11. [4] Raju M., Kumar S., System Simulation Modeling and Heat Transfer in Sodium Alanate Based Hydrogen Storage Systems. (2010) Submitted to International J. Hydrogen Energy. [5] Vyazovkin S.,et al., “ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data” ThermochemicaActa 520 (2011) 1-19. [6] Bertsch F., Mette B., Asenbeck S., Kerskes H., Müller-Steinhagen (ITT and DLR): Low temperature chemical heat storage-an investigation of hydration reactions, Effstock 2009. We are grateful to the EU-Foerdert Niedersachsen to have financed this research project Innovation-Inkubator/Thermische Batterie. Innovations-Inkubator Lüneburg