ABSTRACT
This study investigates a solar-driven absorption heat transformer (AHT) with the LiBr/H2O pair. Four different solar thermal technologies are examined for producing useful heat which is then stored in a tank and feeds the AHT for industrial heat production. The examined solar thermal collectors are the simple flat plate collector (SFPC), the advanced flat plate collector (AFPC), the evacuated flat plate collector (EFPC), and the evacuated tube collector (ETC). Practically, the heat transformer upgrades the solar useful output through a thermochemical absorption cycle. This work uses a validated thermodynamic program created in Engineering Equation Solver, while the unsteady investigation is carried out through TRNSYS software by connecting the tools properly, exploiting their interoperability. During this analysis, the impact of some critical parameters on the system behavior is studied to calculate the industrial heat production and the system efficiency by conducting a dynamic simulation of a typical summer typical week in Athens (Greece). Specifically, the impact of the solar collectors’ mass flow rate, the load mass flow rate, the solar field area, and the tank’s volume are defined for all the collector types. Finally, a yearly simulation is conducted for the main scenario (100 m2 solar field with a tank of 8 m3) indicating that the selection of EFPC is the best choice energetically and economically compared to others. Specifically, in this scenario, the yearly industrial heating production is calculated at 36879 kWh, the yearly system energy efficiency at 21.17 %, the yearly system exergetic efficiency at 5.86 %, the levelized cost of heating at 0.0702 €/kWh, and the yearly CO2 emissions avoidance at 8504 kg CO2. The reported data shows that the proposed systems are more sustainable compared to a benchmark scenario with a natural boiler system. Finally, it is useful to state that the use of ETC and AFPC are also sustainable choices, but they are less effective compared to EFPC.
KEYWORDS
Solar thermal collector, Absorption heat transformer, LiBr/Water, Heat upgrade, Industrial heat
LINK: https://www.sciencedirect.com/science/article/pii/S0960148125019809?via%3Dihub
ABSTRACT
Waste heat recovery and upgrading is an effective measure for facing the energy problems in the industrial sector. This could even be more impactful when combined/boosted with compatible renewable energy systems. The objective of the present work is the comparison of three different collector types coupled to an absorption heat transformer for industrial process heat production. The absorption heat transformer operates with LiBr/water as a working pair and aims to upgrade the heat with a thermochemical process to cover a wide range of different temperature needs in the industrial sector from 80 °C up to 160 °C. The novelty of the present work is based on the systematic investigation and comparison of three different solar thermal collectors innovatively feeding an absorption heat transformer. Simple flat plate collectors, advanced flat plate collectors, and evacuated tube collectors are the investigated solar technologies. The investigation is conducted with a developed model in the Engineering Equation Solver tool. For industrial process heat temperatures from 95 °C up to 120 °C, the simple flat plate collector is the best choice, for greater temperatures up to 140 °C, the advanced flat plate collector is the best solution, and for higher temperatures, the evacuated tube collector outperforms others. For a solar energy input of 80 kW in these cases, the process heat supply at 115 °C by the system using simple flat plate collectors is 11.01 kW, at 130 °C using advanced flat plate collectors is 13.11 kW, and at 150 °C with evacuated tube collectors is 14.12 kW. The respective exergy efficiency values of these systems are 3.43 %, 4.86 %, and 5.60 %, respectively.
KEYWORDS
Absorption heat transformer; Solar thermal collector; Thermochemical process; Heat Upgrade; Industrial heat
LINK: https://www.sciencedirect.com/science/article/pii/S1359431124003338
ABSTRACT
Thermochemical energy storage is an emerging technology being researched for harvesting waste heat and promoting integration of renewable energy in order to combat climate change. While many simple salts such as MgSO4⋅7H2O have been investigated thoroughly, there remains much work to be done in the domain of materials that take advantage of synergetic effects of multiple different cations located in the same crystal. To this end, a solid solution library of divalent metal sulfates of the formula M1-xM2xSO4·nH2O (M, M2 = Mg, Co, Ni, Cu, Zn) has been synthesized. Following X-ray powder diffraction to confirm phase purity, scanning electron microscopy provided insight into particle morphology. One of the most conspicuous features was the presence of star-shaped cracks in some of the materials, which may contribute to increased surface area and enhance reaction kinetics. The simultaneous thermal analysis of the mixed salt sulfates led to several conclusions. Corresponding to the high initial dehydration barrier of NiSO4⋅6H2O, incorporation of nickel into other sulfates led to lower degrees of dehydration at low temperatures. The opposite effect was observed with the addition of copper. Of great interest was the surprisingly facile dehydration of hydrated Mg0.25Zn0.75SO4, which exceeded that of both pure MgSO4⋅7H2O and ZnSO4⋅7H2O. This promising compound is one representative of three different compounds with 75 % zinc which all have the highest dehydration activity up to 100 °C of all compounds in the series of hydrates of M1-xZnxSO4·nH2O (M = Mg, Ni, Cu).
KEYWORDS
Thermochemical heat storage; Salt hydrate; Simultaneous thermal analysis; Magnesium sulfate.
LINK:
https://www.sciencedirect.com/science/article/pii/S2950345024000277
ABSTRACT
Industrial process heat production is critical to achieving sustainability in our society. Avoiding fossil fuels and reducing electricity consumption for heat production are critical aspects of creating sustainable industries. Exploiting waste heat streams by upgrading them into useful high-temperature heat is an interesting idea for reducing the CO2 footprint industrial processes. In line with this, the present study’s main objective is to investigate a novel thermochemical heat upgrade system based on the SrBr2/H2O working pair for the petrochemical industry, which is practically driven only by low-temperature waste heat streams. This innovative system, which exploits a waste heat stream of 200 °C and upgrades it to 250 °C to make it suitable for industry utilization, achieves a nominal coefficient of performance of 0.605. The examined system is compared with three other alternatives, including a natural gas boiler with 86% efficiency, a hybrid solar thermal unit with an auxiliary natural gas boiler, and a high-temperature heat pump with a coefficient of performance of two. The nominal industrial heat production is 2.2 MW for the thermochemical heat upgrade system. The dynamic investigation is conducted under the climate conditions of Denmark and Greece. The high-temperature heat pump’s annual electricity consumption is 6.94 GWh. In contrast, the annual heat consumed by the natural gas boiler is 16.12 GWh, without integrating the solar thermal unit. For the hybrid system, the maximum daily contribution of the solar thermal system is 87% for the climate conditions of Denmark, and the annual useful heat generated by the concentrating solar system is 1.30 GWh for the Danish climate conditions and 2.82 GWh for the Greek climate conditions.
KEYWORDS
heat upgrade; thermochemical heat transformer; industrial process heat; solar thermal; natural gas boiler; sustainability
ABSTRACT
Combining organic Rankine cycles (ORCs) with absorption heat transformers (AHT) shows promise in improving energy efficiency. Heat transformers utilizing lithium bromide (LiBr) are a distinct subtype of AHT, employing a liquid absorbent to absorb and release heat, providing an efficient approach to transfer waste heat streams and enhance the performance of the heat recovery systems. By integrating with ORCs, LiBr heat transformers offer a more effective means of harnessing low to medium-grade waste heat sources and transforming them into usable energy. This study proposes integrating an AHT with an ORC to harness low-grade waste heat from AHT and raise its temperature. Additionally, it aims to utilize high-grade heat released from the AHT absorber in an ORC cycle to generate electrical power. Simulation results show that the coefficient of performance (COP) of the AHT reached 0.435, while the exergy-based COP calculated at 0.651 indicates an effective AHT design. The coupled ORC cycle produced a net electrical power of 307.4 kW with an energy efficiency of 13.95%. The total energy efficiency and exergy efficiency of the integrated system were measured at 6.07% and 35.46%, respectively. Parametric analysis revealed that the temperature of the condenser in the AHT cycle and the pressure of the condenser in the ORC cycle have an inverse effect on the system’s performance, whereas the high pressure of the ORC cycle exhibits a direct correlation with overall system performance indicators.
ABSTRACT
The objective of the present study is to examine a solar-driven absorption heat transformer operating with the LiBr/Water working pair. Selective flat plate solar thermal collectors coupled with an insulated sensible storage tank feed the absorption heat transformer for industrial heat production. Practically, the heat transformer upgrades the solar useful output through a thermochemical absorption cycle. This work uses a validated thermodynamic model developed in Engineering Equation Solver, while the transient investigation is conducted with TRNSYS software by connecting the tools properly, exploiting their interoperability. During this analysis, the impact of different parameters on the system performance is investigated aiming to calculate the industrial heat production and the overall system efficiency. Specifically, the effect of the solar field mass flow rate, the load mass flow rate, the solar field area, and the storage tank volume are calculated. A simulation for a summer week in Athens (Greece) indicates that the use of a 100 m2 solar field with a tank of 8 m3 leads to the production of 580 kWh of industrial heat at 120°C. The average coefficient of performance for the heat transformer was found at 0.47, the average solar collector efficiency at 25.6%, the solar to heat conversion efficiency at 12%, and the overall exergy efficiency at 3.1%.