Cyclic Assessment of Magnesium Oxide with Additives as a Thermochemical Material to Improve the Mechanical Strength and Chemical Reaction

Abstract

Heat storage with a thermochemical reaction has the advantages of a high heat storage density and no heat loss compared to conventional methods such as the sensible and latent heat. This method is promising to use in a thermal energy network because it is an efficient solution which addresses the time mismatch problem with regard to heat production and consumption. In this paper, we investigated Magnesium oxide (MgO) with different additives as a thermochemical material (TCM) coupled with the effects of several additives in an effort to improve the structural strength and reaction rate and reduce the initiation time. As additives in an MgO composite, Bentonite, Magnesium sulfate (MgSO4), and Zeolite 13X were chosen. With a cyclic scheduling experimental setup for the heat charging and discharging of the MgO composites, Bentonite as an additive improved the structural strength, and Zeolite 13X enhanced the reaction rate and led to faster reactions compared to only MgO as a TCM. With MgSO4 as an additive, however, the TCM composite showed a high reactivity during the a few cycles, and then rapidly became inactive due to byproducts side reaction. The results indicated that Bentonite and Zeolite additives, in an MgO composite, as a TCM can improve the mechanical strength and chemical reaction, optimum ratio is necessary to compromise promoting the thermochemical reaction.

Investigation on Long Term Operation of Thermochemical Heat Storage with MgO-Based Composite Honeycombs

“…In this study, our system is used to repeat cycles for a long period of heat charging and discharging. The operational procedure is similar to our previous study [20], however, a new operational sequence for heat charging and discharging are applied by considering several changes due to the open system supplied by gas and steam.…”

“…The design concept of the proposed system was to enable a long-term cycling operation and evaluation for the multiple TCM honeycombs. To differentiate this study from our previous setup [20], which was conducted in an enclosed chamber to measure the intrinsic material properties, this study aims to evaluate the thermochemical heat storage properties for a structure nearer to that in a common industrial process. The Piping and Instrument Diagram (P&ID) of the entire system is shown in Figure 2.…”

“…Our previous study [20] investigated the optimum compositions of MgO as TCM including several additives. As a result, we finally manufactured a honeycomb using the combination of the materials Mg(OH) 2 90 wt% and zeolite 13X 10 wt%.…”

“…Li et al [26] found that adding bentonite to make a zeolite based honeycomb can produce a honeycomb with ease, due to the lubrication, and prevents cracking. In our previous study [20], results showed that a suitable combination of Mg(OH) 2 /zeolite 13X/bentonite can produce a honeycomb with sufficient strength while maintaining the thermochemical performance. Based on these results, this study aims to carry out the assessment of the long-term operational feasibility of recovering waste heat with thermochemical heat storage using MgO-based composite honeycombs especially for steel industry.…”

“…In order to assess the economic feasibility, 87 cycles of heat transport tests were carried out between the waste incinerator and the industrial drying process for one year [19]. Our previous research [20] has focused on understanding the characteristics of TCM and finding the optimal composition for making a TCM honeycomb in order to utilize the waste heat from the steel industry. The target TCM was composed of MgO/Mg(OH) 2 for high heat charging density due to the chemical reaction and zeolite 13X for using a fast reaction by adsorption/desorption.…”