High Temperature Thermochemical Heat Storage for Concentrated Solar Power Using Gas–Solid Reactions

Abstract

High temperature thermal storage technologies that can be easily integrated into future concentrated solar power plants are a key factor for increasing the market potential of solar power production. Storing thermal energy by reversible ga.i-solid reactions has the potential of achieving high storage densities while being adjustable to various plant configurations. In this paper the Ca(OH)2lCaO reaction system is investigated theoretically. It can achieve storage den.'iities above 300 kWhlm^ while operating in a temperature range between 400 and 600° C. Reactor concepts with indirect and direct heat transfer are being evaluated. The low thermal conductivity of the fixed bed of solid reactants turned out to considerably limit the performance of a storage tank with indirect heat input through the reactor walls. A one-dimensional model for the storage reactor is established and solved with the Finite Element Method. The reactor concept with direct heat transfer by flowing the gaseous reactant plus additional inert gas through the solid reactants did not show any limitation due to heat transfer. If reaction kinetics are fast enough, the reactor performance in case of the Ca(OH)2lCaO reaction system is limited by the thermal capacity of the gaseous stream to take-up heat of reaction. However, to limit pressure drop and the according losses for compression of the gas stream, the size of the storage system is restricted in a fixed bed configuration.

Multi-physical continuum models of thermochemical heat storage and transformation in porous media and powder beds—A review

“…Validation of a numerical model similar to the previous one [98] was presented in Schaube et al [87] based on an extensive experimental characterisation of a laboratory scale (60 g of material) CaO/Ca(OH) 2 reactor [177]. The comparison to experimental data concentrated on heat transfer, integral reaction rate and maximum temperatures during the exothermic hydration reaction.…”

“…was investigated in Schaube et al [98] in the context of concentrating solar power plants for an operating temperature range of 400-600°C. Computed storage densities well exceeded 300 kW h m À3 .…”

“…Reactor concepts can be categorised in different ways [21,98]. Indirect reactor concepts avoid contact between the heat transfer fluid (HTF) and the solid reactant by compartmentalising the system into a separate HTF loop and the reactive material pair.…”

“…Based on the model and numerical implementation developed in Nagel et al [88], an open and direct CaO/Ca(OH) 2 reactor was simulated in Shao et al [179] using a one-dimensional model. Constitutive specifications of the model from its general state [88] were included based on experimental data and combined numerical-experimental work of a similar modelling approach [98,87,177]. Both the charging and discharging of the reactor was simulated.…”

Application of Chemical Heat Pumps for Temperature

“…Three literature sources with applicable property data were obtained (Samms and Evans 1968;Schaube 2011;Schaube et al 2012). The calcium oxide hydration/dehydration reaction equilibrium temperature versus pressure data from each of these sources was reproduced in Figure 7, which projects these data onto a benchmark plot of equilibrium readings to verify the mathematical expressions used in the calculations.…”