Feasibility study of seasonal solar thermal energy storage in domestic dwellings in the UK

Seasonal solar thermal energy storage (SSTES) has been investigated widely to solve the mismatch between majority solar thermal energy in summer and majority heating demand in winter. To study the feasibility of SSTES in domestic dwellings in the UK, eight representative cities including Edinburgh, Newcastle, Belfast, Manchester, Birmingham, Cardiff, London and Plymouth have been selected in the present paper to study and compare the useful solar heat available on dwelling roofs and the heating demand of the dwellings. The heating demands of space and hot water in domestic dwellings with a range of overall heat loss coefficients (50 W/K, 150 W/K and 250 W/K) in different cities were calculated; then the useful heat obtained by the heat transfer fluid (HTF) flowing through tilted flat-plate solar collectors installed on the dwelling roof was calculated with varied HTF inlet temperature (30 °C, 40 °C and 50 °C). By comparing the available useful heat and heating demands, the critical solar collector area and storage capacity to meet 100% solar fraction have been obtained and discussed; the corresponding critical storage volume sizes using different storage technologies, including sensible heat water storage, latent heat storage and various thermochemical sorption cycles using different storage materials were estimated

An optimised chemisorption cycle for power generation using low grade heat

The integration of chemisorption cycle with turbine/expander opens up enormous opportunities of recovering low grade heat to meet different energy demands including heating, cooling and power generation. In the present study, a novel advanced resorption power generation (RPG) cycle with reheating process has been proposed for the first time to significantly improve the thermal efficiency and exergy efficiency of the basic RPG cycle. Such a reheating concept is built on the premise of chemisorption monovariant characteristic and identification of the optimal desorption temperature aiming at producing the maximum work output under the given working conditions. The identified optimal desorption temperature might be lower than the available heat source temperature, and the desorbed ammonia vapour is subsequently reheated to the heat source temperature before it undergoes vapour expansion for power generation. This study explored the potential of the proposed advanced RPG cycle and investigated the system performance using three representative resorption sorbent pairs, including manganese chloride – sodium bromide, manganese chloride – strontium chloride, and strontium chloride – sodium bromide, all with ammonia as the refrigerant. The application of reheating concept can improve the total work output of RPG cycle by 10–600%, depending on different sorbent pairs and different heat source temperatures studied in this work, e.g., when the heat source temperature is at 200 °C, the thermal efficiency is increased by 1.4–4.5 times and the exergy efficiency is boosted by 2.0–8.3 times. Another valuable merit of the proposed RPG cycle is that there is a great potential of considerable amount of additional cooling output without compromising the maximum work output, leading to further improvement of system efficiency. Compared to other bottoming cycles for power generations, the proposed advanced RPG cycle exhibits the highest thermal efficiency when the heat source temperature is between 120 °C and 200 °C

Experimental parametric evaluation of adsorption characteristics for silica gel - water based open-bed system for seasonal thermal energy storage

This study aims to investigate the potential of using commercial silica gel as an energy storage material in a bulk-scale open bed adsorption-based system to achieve efficient domestic heating using renewable energy sources. Designing an efficient thermal energy storage (TES) system for practical use requires understanding of the sorption properties of the adsorbent and the effects of different operating and physical parameters on the sorption process. One critical parameter that significantly affects the energy storage density when scaling up from a laboratory to a prototype system is the amount of adsorbent in the reactor. Surprisingly, this aspect has been overlooked in previous studies. To address this research gap, a laboratory-scale test rig was designed and constructed. This rig enables the evaluation of the effects of different operating parameters (such as relative humidity, flow rate, and regeneration temperature) and physical parameters (such as the quantity of adsorbent and particle diameter) on the energy storage density of silica gel and the temperature lift in the process. The water adsorption capacity of the silica gel was measured in-house to assist in future theoretical modelling of a prototype TES system. Optimum operating conditions were determined for the system, with a relative humidity of 80 %, an air flow rate of 100 L/min, and material regeneration at 120 °C. The system's performance in terms of material energy storage density and maximum temperature lift was observed for varying amounts of adsorbent, particle diameter, and regeneration temperature at these optimal operating conditions. Finally, the required storage volume to meet domestic space heating demands was estimated based on optimal discharging conditions and compared to other experimental and theoretical studies involving silica gel-based energy storage systems

Investigation of equilibrium and dynamic performance of SrCl2-expanded graphite composite in chemisorption refrigeration system

This work experimentally investigated adsorption equilibrium and reaction kinetics of ammonia adsorption/desorption on the composite of strontium chloride (SrCl2) impregnated into expanded graphite, and also discussed the potential influence of the addition of expanded graphite on the SrCl2-NH3 reaction characteristics. The measured and analysed results can be very useful information to design the system and operating conditions using the similar chemisorption composites. Equilibrium concentration characteristics of ammonia within the studied composite were measured using the heat sources at 90 °C, 100 °C and 110 °C for the decomposition process, where the degree of conversion achieved 50%, 78% and 96% respectively. Therefore, the equilibrium equation reflecting the relationship between temperature, pressure and concentration was developed, and a pseudo-equilibrium zone was found, which should be useful information to setup the system operating condition for the desired global transformation. It was suspected that the addition of expanded graphite altered the reaction equilibrium due to the pore effect and the salt-confinement. The concept of two-stage kinetic model was proposed and kinetic parameters were determined by fitting experimental data. The developed kinetic equations can predict dynamic cyclic performance of a reactive bed in similar geometric structure with reasonable accuracy. Such a chemisorption cycle using the SrCl2-expnaded graphite (mass ratio 2:1) composite can be used for cooling application, and the maximum SCP value can be achieved as high as 656 W/kg at t = 2.5 min, and the COP can be 0.3 after one hour of synthesis process under the condition of Tev = 0 °C, Tcon = 20 °C, Theat = 110 °C

Hydrogen rich syngas production through sewage sludge pyrolysis: A comprehensive experimental investigation and performance optimisation using statistical analysis

Bioenergy is anticipated to play a significant role in the United Kingdom’s Net Zero 2050 scenario. This study aims to explore the possibility of producing hydrogen-rich syngas using sewage sludge from a wastewater treatment plant located in England, United Kingdom. The primary objective of this study is to experimentally produce hydrogen-rich syngas from sewage sludge through pre-treatment, drying, and pyrolysis. Furthermore, statistical methods have been employed to optimise the performance of the pyrolyser. The individual desirability scores for lower heating value (LHV) and cold gas efficiency (CGE) were estimated to be 0.83902 and 0.85307, respectively. Combining these scores, the overall desirability of the model reached 0.8460, indicating favourable predictive performance. The optimal operational conditions are reported to be a feed rate of 3.0488 revolutions per minute (rpm) and an operational temperature of 800°C. Under these conditions, the highest calculated CGE of 66.31% and the peak LHV value of 18.36 MJ/ m^3 were achieved

Chemisorption power generation driven by low grade heat – Theoretical analysis and comparison with pumpless ORC

Sorption cycles have been extensively developed for waste heat recovery to deliver cooling, heating, and electricity. Chemisorption cycles using metallic salts as sorbents and ammonia as working fluid have been explored in this work for the maximum potential of pure power generation. In order to get better understanding and more insights, resorption power generation cycle (RPGC) has been theoretically investigated and compared with pumpless organic Rankine cycle (PORC). The PORC operates without a liquid pump in conventional ORC and shares the similar configuration with RPGC. Three different organic fluids (pentane, R123 and R245fa) used in PORCs and four different reactant salts (manganese chloride, strontium chloride, barium chloride and sodium bromide) used in RPGCs have been analysed and evaluated in terms of the power generation capacity, thermal efficiency and energy density under the conditions of heat source temperature from 60 °C to 180 °C and heat sink temperature at 30 °C. The PORCs have higher thermal efficiency of work output for most cases in the studied scenarios, while RPGCs are evidently superior on energy density, at least as twice large as that of the PORCs studied. RPGC and PORC both have intermittent and dynamic operation, and the former one has the potential to have multiple energy productions or perform as energy storage

A chemisorption power generation cycle with multi-stage expansion driven by low grade heat

Ammonia-based chemisorption cycle driven by low grade heat exhibits vast potential for power generation because there exists huge pressure difference between the two salt-adsorbent-filled reactors. However, the intrinsic feature of ammonia as a wet fluid and the difficult match between chemisorption cycle and expansion device impede the development of such a power generation system and also increase the difficulty of practical implementation. To explore maximum benefits of this technology, the present work has proposed and studied a new resorption power generation cycle that applies multiple expansion. The application of multiple expansion integrated with reheating processes aims to overcome the limitation of the ammonia being wet fluid and fully harness the huge pressure difference that chemisorption can offer for power generation, leading to the improvement of energy efficiency. The performance of the proposed multiple expansion resorption power generation cycle using three typical resorption salt pairs, including sodium bromide – manganese chloride, strontium chloride – manganese chloride and sodium bromide – strontium chloride, have been investigated not just based on theoretical thermodynamics but also with the consideration of practical factors to obtain better understanding and more insights for a real system design. The multiple expansion resorption power generation using sodium bromide – manganese chloride and sodium bromide – strontium chloride pairs can achieve 100–600 kJ/kg (ammonia) work output when heat source temperature is from 30 °C to 150 °C; the multiple expansion using strontium chloride – manganese chloride pair has higher average work output per one expansion stage than that using the other two pairs. The cyclic energy efficiency can be achieved as 0.06–0.15 when implementing 2–4 expansions in a more practical scenario where the equilibrium pressure drop is set to 2 bar and the heat source temperature is in the range of 80–150 °C. Such efficiencies are circa 27–62% of Carnot efficiency under the same thermal conditions