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