Optimization of thermochemical heat storage systems by controlling operating parameters and using two reactors

Direct CO2 emissions from space heating and hot water production in buildings has been on a rising trend in recent decades. It is increasingly urgent to develop efficient and low-carbon heating technologies that can reduce energy consumption and shift the load to off-peak times. This work concerns thermochemical heat storage (TCHS), which has the potential to offer flexibility to bridge the energy supply and demand mismatches, and help with load shifting. One of the technical barriers for the use of TCHS is the variation of the outlet conditions for discharge process, which limits the implementation and competitiveness of the technology. Here we propose a new method to overcome the barrier. By using packed-bed based thermochemical reactors packed with silica gel, as an example, we use a Computational Fluid Dynamic (CFD) tool to understand the effectiveness of controlling and optimising the outlet conditions of the TCHS reactor. We demonstrated that, by optimizing the packed bed, a stable outlet temperature could be achieved. Furthermore, the whole TCHS performance could be enhanced, doubling the discharging power and prolonged discharge time by 4 times while keeping the same outlet temperature

Investigation of cryogenic energy storage for air conditioning applications

This research aims to develop an efficient air conditioning technology that exploits cold energy storage to reduce energy consumption and CO2 emissions and shift the cooling load to off peak times to achieve better national electricity grid stability. The investigation includes the use of commonly used cold storage materials (ice, Phase Change Materials PCM) to enhance the existing air conditioning systems and using cryogenic cold storage namely, liquid nitrogen/air (LN2/Lair) to provide air conditioning for domestic and office buildings. Computational Fluid Dynamic (CFD) modelling of the main two components in the cryogenic cooling system namely, cryogenic heat exchanger and expander were also carried out. An experimental test facility was developed to validate the CFD modelling of the liquid nitrogen evaporation process and assess its potential to provide cooling. Results showed that integrating existing Air Conditioning systems with cold storage tank can lead to energy saving of up to 26% and shifting the cooling load to off peak times, but this energy saving is highly dependent on the storage medium and its storage temperature. Also, using cryogenic fluids (LN2/Lair) to provide air conditioning for domestic and office buildings can recover up to 94% of the energy stored in LAir and up to 78% of the energy stored in LN2, and based on LN2/Lair prices of 3.5 pence per kg the system showed cost saving of the energy consumption of up to 73% when LAir is used and 67% when LN2 is used compared with the conventional system. The CFD modelling of cryogenic heat exchanger showed good agreement with the experimental work with maximum deviation 7.6%

A comprehensive material and experimental investigation of a packed bed latent heat storage system based on waste foundry sand

The EU's industrial sector discards about 18.9% of its energy as waste heat, much of which has the potential for recovery. This study addresses the challenge by focusing on the advancement of latent heat thermal energy storage (LHTES) using phase change materials (PCMs) encapsulated within industrial waste foundry sand (WFS). WFS, a problematic by-product, is repurposed as a supportive matrix for NaNO3 and solar salt PCMs, tailored for effective integration into high-temperature industrial processes. The paper provides a thorough mechanical and thermal examination of the WFS-salt PCMs, highlighting their improved thermal stability, performance, and compatibility with direct thermal energy systems. The composite PCMs demonstrated melting points well-suited for industrial waste heat applications and achieved an energy density of 542.0 ± 8.3 kJ/kg for NaNO3 and 516.0 ± 4.5 kJ/kg for solar salt, An experimental cascade PBLHS, based on these CPCMs, with a capacity of 262 MJ, designed to mimic an industrial heat source at 450 °C, was systematically tested to assess its energy density and efficiency over repeated charging/discharging and free cooling cycles. Its overall system efficiency is found to be 68.5%. These findings position WFS-salt PCMs as a promising and environmentally beneficial approach to enhance industrial energy efficiency and utilisation

Liquid air utilization in air conditioning and power generating in a commercial building

Current air conditioning (AC) systems use a vapour compression system that consume a great amount of energy particularly during the peak times where most electricity suppliers facing difficulties to meet the users demands. Shifting the peak cooling demands to off-peak times using cold energy storage systems is a promising technique leads to save energy and to reduce the CO2 emissions. This study presents new technology that uses the cold energy storage in form of liquid Air (LAir) or liquid nitrogen (LN2) to provide air conditioning and power to commercial buildings. Four different cryogenic cycles were modelled and analysis from a thermodynamic point view, and compared in terms of their, output power, cooling capacity, recovery efficiency, COP and how much energy could save when compared with the traditional AC system. The results showed that system performance when LAir is used is 21–25% higher than that of when LN2 is used, and the 4th configuration is the most effective cycle and it recovered up to 94% of the energy stored in LAir and 78% of the energy stored LN2. Compared to the conventional system at the current LAir and LN2 prices, the 1st, 2nd, 3rd and 4th cycles showed saving up to 15%, 24%, 31% and 37.5%, respectively, when LAir is used and −3.5%, 5%, 16% and 24%, consecutively, when LN2 is used.</p

From waste to value:Utilising waste foundry sand in thermal energy storage as a matrix material in composites

Waste foundry sand (WFS) is a by-product of the casting industry, which poses increasing economic and environmental issues due to the costs associated with landfill maintenance and stricter environmental regulations. This study proposes a novel solution for WFS as a material for thermal energy storage. The approach involves blending WFS with NaNO3 and a proprietary additive, X, to fabricate a composite phase change material (CPCM). The CPCM is found to be structurally stable up to 400 °C, and an optimal composition with a mass ratio of NaNO3:WFS:X = 0.6:0.3:0.1 is achieved. This composition yields an energy storage density of 628 ± 27 kJ/kg, and an average thermal conductivity of 1.38 W/mK over the temperature range of 25–400 °C. The CPCM also exhibits good mechanical strength and a low coefficient of thermal expansion compared to NaNO3. Currently, only a small portion of WFS is recycled, most commonly in building applications. The CPCM presented in this study has the potential for medium-to-high temperature heat storage in waste heat recovery applications, offering a sustainable solution for upcycling WFS.</p

A thermochemical energy storage based cooling and heating system:Modelling, experimental validation and lab-scale demonstration

Thermal (heat and cold) energy accounts for over 50% of global final energy consumption and is set to increase, and cooling contributes to 50% of the local electricity peak demands in many places of the world. Therefore, there is a need to develop efficient cooling and heating systems that not only can reduce the power consumption but also shift load to off peak times, offer a better network stability and reducing CO2 emissions at an affordable cost. This work present a thermochemical energy storage based system for cooling and heating provision. The system uses air hydration/dehydration with evaporation cooling concept to generate both cooling and heating, and it can be cascaded to give a wide range of outlet temperature to meet different applications. A single effect and a double effect of the proposed system were numerically investigated using a MATLAB model and experimentally tested under the lab conditions. The modelling results showed that the system level coefficient of performance (COP) depends on the inlet temperature, relative humidity and the recovered energy from the discharging process. At an inlet relative humidity of 45%, the system COP increased from 1.8 to 4.4 when the inlet temperature reduced from 37 °C to 29 °C. The experimental results showed that an outlet temperature of 10–12 °C and 5 °C with an inlet temperature of 30 °C can be obtained, respectively, meaning a temperature reduction respectively by 18–20 °C and 25 °C with the single-stage and double-stage configurations. These results agreed with the MATLAB modelling within 1–3 °C.</p

Multilayer Packed Bed Based Latent &amp; Sensible Heat Storage for Liquid Air Energy Storage Efficiency Enhancement

Energy storage technologies has a vital role to play in future renewable energy dominated power grids. Liquid Air Energy Storage (LAES), as one of such storage technologies, has attracted attention in recent years. Such a technology has an electrical-to-electrical round trip efficiency of ~50-60% if thermal integration is implemented particularly when a high-grade cold energy store (HGCS) is employed to capture and store cold energy during discharging for reuse charging process. Packed beds have been widely studied and demonstrated as the HGCS for the cryogenic energy storage due to low costs, long life-span and high safety. Most of these studied packed bed based HGCS is usually filled with a single sensible heat storage material, which gives a low energy density and unstable outlet temperature. Low-temperature encapsulated phase change material (PCM) has also been studied to address the two issues, which incurs a high-cost. This work examines the use of combined PCMs with sensible heat materials in one packed bed (as shown in Fig. 1). We shall show that such an approach is more cost-effective, but yet provides an enhanced stability of the outlet temperature as well as the overall performance of HGCS. Our particular focus in on the use of multilayer PCMs-sensible heat materials packed bed, investigating how this combination would affect the energy density, temperature profile, outlet temperature of the HGCS as well as the performance of the LAES system (e.g. roundtrip efficiency and liquid yield). We also optimized the number of the PCM layers in the packed bed based HGCS, considering both complexity and cost factors

Multilayer Packed Bed Based Latent &amp; Sensible Heat Storage for Liquid Air Energy Storage Efficiency Enhancement

Energy storage technologies has a vital role to play in future renewable energy dominated power grids. Liquid Air Energy Storage (LAES), as one of such storage technologies, has attracted attention in recent years. Such a technology has an electrical-to-electrical round trip efficiency of ~50-60% if thermal integration is implemented particularly when a high-grade cold energy store (HGCS) is employed to capture and store cold energy during discharging for reuse charging process. Packed beds have been widely studied and demonstrated as the HGCS for the cryogenic energy storage due to low costs, long life-span and high safety. Most of these studied packed bed based HGCS is usually filled with a single sensible heat storage material, which gives a low energy density and unstable outlet temperature. Low-temperature encapsulated phase change material (PCM) has also been studied to address the two issues, which incurs a high-cost. This work examines the use of combined PCMs with sensible heat materials in one packed bed (as shown in Fig. 1). We shall show that such an approach is more cost-effective, but yet provides an enhanced stability of the outlet temperature as well as the overall performance of HGCS. Our particular focus in on the use of multilayer PCMs-sensible heat materials packed bed, investigating how this combination would affect the energy density, temperature profile, outlet temperature of the HGCS as well as the performance of the LAES system (e.g. roundtrip efficiency and liquid yield). We also optimized the number of the PCM layers in the packed bed based HGCS, considering both complexity and cost factors