Neutrons for Heat Storage, NHS, (completed)

Funded by:

Nordforsk and KTH

Time period:

July 2017- December 2020

Project partners:

Technical University of Denmark (DTU)- Denmark

Institute for Energy Technology (IFE)- Norway

Amminex Emission Technology (AET)- Denmark

KTH (EGI)- Sweden

Background

The Neutrons for Heat Storage (NHS) project aims to develop a thermochemical heat storage system for low-temperature heat storage (40-80 °C). Thermochemical heat storage is one effective type of thermal energy storage technique, which allows significant TES capacities per weight of materials used. In the NHS project, reversible chemical reactions (absorption and desorption) between metal halides and ammonia (NH3) are used. 

The project is a Nordic collaboration between Technical University of Denmark (DTU) - Denmark, Institute for Energy Technology (IFE) - Norway; Amminex Emission Technology (AET) - Denmark and KTH- Sweden. DTU, IFE and AET are working on materials development and characterizing for this types of reaction systems. Their research therefore include developing novel metal halides, their thermos-physical property characterization as well as improving these characteristics by e.g. producing composites by combining with materials having better thermal conductivity. Based on the inputs from these materials’ research, the KTH partners are designing a bench-scale TCS system employing one chosen metal halide candidate, for the reversible absorption/desorption with NH3.
 

Thermochemical heat storage (TCS) with materials that undergo reversible chemical reactions is gaining momentum today among energy storage technologies. Materials that have such suitable reversible chemical reactions are called thermochemical heat storage materials (TCMs). TCMs primarily operate through absorption (i.e., chemical reaction involving the entire molecule) or adsorption (a physical sorption process involving only the surface of the molecule). Many TCS systems considered today involve water as a sorbate, in many absorption processes (e.g. with salts forming salt hydrates or hydroxides) and adsorption processes (e.g. with silica gel and Zeolite, which adsorb water). The reaction systems of ammonia and metal halides (e.g. SrCl₂, BrCl₂, and MgCl₂, among others) are an emerging category of TCMs undergoing chemical reactions (i.e., undergoing absorption/desorption, as explained in the simplified sketch in Figure 1). This particular branch of TCS technology allows the reversible storage of large quantities of thermal energy per both weight and price in various salts upon exothermic/endothermic absorption/desorption of NH₃. These reactions can be tailored to obtain optimal heat release (desorption) temperatures (e.g. for indoor comfort applications) thus with a competitive advantage over other TES counterparts like sensible TES, PCMs or even certain other TCMs.

Within this background, the DTU researchers, as a pre-study for the NHS project, have already built a lab-scale experimental set-up involving the chemical reaction pair SrCl₂-NH₃. This system is made of a single reactor operating in batch-mode between absorption and desorption between specifically SrCl₂·NH₃ and SrCl₂·8NH₃. This reactor is a packed bed of about 600 ml volume, where the salt is packed within honeycomb disks. This reactors serves as the TES unit, and can store about 100 Wh (92.1 kWh) heat at a given desorption cycle, which can then be released during absorption. The operational conditions of this reaction system can be changed by abiding to the equilibrium pressure conditions and the corresponding temperature of the specific reversible conversion between SrCl₂·NH₃ and SrCl₂·8NH₃.

Aim and objectives

The NHS project aims to develop and demonstrate novel cost effective and compact thermochemical heat storage systems based on ammonia (NH₃) absorbing salts (metal halides). Thus, the objective of the NHS project is to develop a cost efficient thermochemical heat storage system specifically optimized for the utilization of industrial, low-grade waste heat (temperature range 40-80 °C), to be then used in district heating. In this project, it is proposed to synthesize new ammonia salts and study their behavior in TES systems by neutron imaging. Neutrons are particularly ideal to characterize material containing hydrogen. The information collected via neutron imaging on the spatio-temporal development of the ammonia salts micro-/macrostructure will help to rationally design the TES reactors and heat exchanger in order to increase their efficiency and lifetime. Thus, the project is named NHS.

The specific objectives of the partners at DTU, IFE and Amminex Technologies are novel metal halides development, their and other existing metal halides’ thermos-physical properties and reaction kinetics characterization, as well as investigations on these materials’ thermal conductivity improvements. The objectives of the KTH project partners are to construct a bench-scale TCS system that allows continuous heat storage and release operation, also containing improved reactor-heat exchanger combined units. For this TCS system design, the materials design and characterization work of the rest of the project partners are serving as complementary and supplementary inputs.

Outcomes

At DTU and IFE (collaborating with AET)

• Successful synthesis of several new mixed metal halides (multicomponent alloys combining Ca, Cu, Y, Ba, Sr, with Cl) using several synthesis methods. However, no stable phase pure compounds were obtained so far. Therefore, it was decided for KTH to design their TCS system using the NH₃-SrCl₂ reaction pair.
• Experimental characterization of the obtained new metal halides using XRD and DSC
• Successful in situ neutron radiography and Tomography - Experimental characterization of the reaction progression in a reactor packed-bed cell (a honeycomb disk from of the DTU-reactor) using Neutron Radiography (NR) imaging
• Development and validation of a 3D-COMSOL simulation for the reactor cells (of a honeycomb disk reaction cell of the reactor at DTU) using experimental data

At KTH:

• Proposing the preliminary design of an NH₃-SrCl₂ TCS system for continuous operation using numerical modelling in Aspen PLUS (developed based on the master’s thesis project work by Michail Laios)
• Verification of the designed bench-scale TCS system numerical model (in Aspen PLUS) with experimental data from literature (based on the master’s thesis project work by Michail Laios)
• Preliminary calculations of the TCS reactor- heat exchanger combined unit design using CFD modelling in COMSOL Multiphysics

Publications

Anastasiia Karabanova, Perizat Berdiyeva, Didier Blanchard, Rune E. Johnsen, Stefano Deledda. Comparison between Numerical Simulation and Neutron Radiography of Ammonia Sorption in SrCl₂ for Application in Thermochemical Storage System for Waste Heat Recovery, Conference article for Eurotherm Seminar n-112: 15-17 May 2019, Spain.

P. Berdiyeva, A. Karabanova, D. Blanchard, R. E. Johnsen, B.C. Hauback S. Deledda, Neutron Imaging study of Strontium Chloride Ammine system for Heat Storage, Workshop on neutron imaging and scattering on engineering materials (Dec. 6.-7, 2018 in Copenhagen)

Saman Nimali Gunasekara, Michail Laios, Anastasiia Karabanova, Viktoria Martin and Didier Blanchard, 2019. Design of a bench-scale ammonia-SrCl₂ thermochemical storage system using numerical modelling. Eurotherm Seminar n-112  , Lleida, Spain. 15-17 May 2019.

Saman N. Gunasekara, Stefano Soprani, Anastasiia Karabanova, Viktoria Martin and Didier Blanchard, 2019. Numerical Design of a Reactor-Heat Exchanger Combined Unit for Ammonia-SrCl₂ Thermochemical Storage System. ISES SWC-2019 , 4-7 November, Santiago, Chile.

S. Soprani, “MODELING – TES system based on SrCl₂ - NH₃,” Roskilde, 2016 [an internal report at DTU]

Project contact persons

At KTH

Project Leader

Project Researcher

At DTU¹, IFE² and AET³:

Didier Blanchard ¹ - Senior Researcher, NHS project Manager and project leader at DTU

Anastasiia Karabanova ¹ - PhD Candidate- researcher involved in NHS

Stefano Deledda ² - Senior Scientist, NHS project leader at IFE

Perizat Berdiyeva ² - PhD Candidate- researcher involved in NHS

Benoit Charlas ³ - Researcher