Sulfur Based Thermochemical Energy Storage for Concentrated Solar Power

Abstract

A sulfur based thermochemical energy storage cycle for baseload power generation is being developed under the support of US DOE Sunshot program. Solar heat is stored in elemental sulfur via thermal decomposition of sulfuric acid and disproportionation of sulfur dioxide into elemental sulfur and sulfuric acid. Heat energy is recovered upon sulfur combustion. On-sun decomposition of sulfuric acid in a solar furnace has been demonstrated between 650 and 850°C. Near equilibrium conversion was obtained at high temperature but conversion was reduced due to catalyst poisoning at the lower temperatures. Sulfur dioxide disproportionation modeling showed the reaction driving force is maximized at the high system pressure and low system temperature. The effect of system pressure was validated experimentally. However, the disproportionation rate was found to increase with system temperature as a result of increased reaction kinetics. Homogenous iodide catalysts were used to further enhance the degree of disproportionation and the reaction rate. The process steps required to recover the catalyst for reuse have been verified.

Review of technology: Thermochemical energy storage for concentrated solar power plants

“…The areas closer to the quartz are heated up to much higher temperatures than the middle or end of the honeycomb. With increasing operating temperatures the gap between the temperature of the front and back widens: at 650ºC, the front and back differ by little less than 100ºC; when operating at 850ºC the difference increases to over 200ºC [15]. Due to a short residence time of 0.5 seconds on average, the average temperature of the honeycomb is used for analysis.…”

“…Due to the products being liquids formed from gases, they will be favored by higher pressures in accordance to Le Chatelier's principle. Simulations show that the disproportionation rate increases predictably with pressure up to 30 bar, at which point it stops presenting significant changes [15]. Albeit, modelling tends to ignore many of the physical interactions which occur in the reactor vessel.…”

“…This explains why experimental results have yielded data slightly lower than the theoretical models. Current operation conditions oscillate around 15 bar [15].…”

“…It is customary and recommendable to operate several reactors in series and decreasing the temperature in each successive reactor [15] ( Figure 6). This is done in order to shift the equilibrium towards a higher production of H 2 SO 4 taking advantage of the tendency of exothermic reactions to be favored by lower temperatures.…”

Sulfur-based thermal energy storage system using intermodal containment: Design and performance analysis

“…The nominal cost of sulfur, typically $0.06-0.16/kg [12,13], is far less than typical molten salts and low temperature oils which cost between $1.19/kg -$5.00/kg and $0.30/kg -$5.00/kg [14]. Wong et al [15] have previously demonstrated the use of an elemental sulfur based thermochemical storage cycle with energy stored via decomposition of sulfuric acid and recovered via combustion of elemental sulfur. Additionally, both Clark and Dowling [16] as well as Wentworth and Chen [17] have proposed TES using elemental sulfur and sulfur based compounds, respectively, in an isobaric configuration.…”