Solar Gasification of Biomass: Kinetics of Pyrolysis and Steam Gasification in Molten Salt

Abstract

The use of concentrated solar energy as a heat source for pyroiysis and gasification of biomass is an efficient means for production of hydrogen rich synthesis gas. Utilizing molten alkali carbonate salts as a reaction and heat transfer media promises enhanced stability to solar transients and faster reaction rates. The present study establishes and compares the reaction kinetics of pyroiysis and gasification of cellulose from 1124 K to 1235 K in an electric furnace. Data are presented in an inert environment and in a bath of a ternary eutectic blend of lithium, potassium, and sodium carbonate salts. Arrhenius rate expressions are derived frotn the data supported by a numerical model of heat and mass transfer. The molten salt increases the rate of pyroiysis by 74% and increases gasification rates by more than an order of magnitude while promoting a product gas composition nearer to thermodynamic equilibrium predictions. These results justify using molten carbonate salts as a combined catalyst and heat transfer media for solar gasification.

Economic assessment of solar and conventional biomass gasification technologies: Financial and policy implications under feedstock and product gas price uncertainty

“…The salt of choice is a eutectic blend of carbonate salts (Li 2 CO 3 /Na 2 CO 3 /K 2 CO 3 ). The melt temperature of the eutectic mixture is 673 K. This carbonate salt mixture is also favored because it has corrosion resistant properties that can aid in prolonging the life of the facility, and has been shown to catalyze the gasification reactions [8]. After the injection of biomass into the molten salt, the product is collected for future use while the biomass remnants (ash, sulfur) remains in solution until the salt cleaning mechanisms remove it from the slurry [10,12].…”

“…The new technologies assessed are variations of an externally-heated solar gasification reactor technology which uses molten salts as the gasification medium [7,8].…”

Review of Heat Transfer Research for Solar Thermochemical Applications

“…Solar thermochemical processes are suitable for production of fuels, in which solar energy is stored in form of chemical bonds, and chemical commodities for industrial, agricultural, and other applications. Examples of solar thermochemical processes for fuel production include upgrading fossil fuels [4][5][6] and biomass [7], thermal reduction of metal oxides [8][9][10][11][12], and direct water thermolysis [13]. While the majority of processes considered in the past were for production of hydrogen, production of both hydrogen and carbon monoxidethe components of the synthesis gas, which can be further processed to hydrocarbon fuels-is of current research focus.…”

Towards Solar Thermochemical Carbon Dioxide Capture via Calcium Oxide Looping: A Review

“…In 2005, industrial CO 2 use was estimated to be 6.3 Gt-CO 2 /yr (Metz et al, 2005). An emerging use of CO 2 is for the solar-driven production of synthesis gas, which in turn can be used to obtain synthetic hydrocarbon fuels (Steinfeld et al, 1998;Chueh et al, 2005;Leckel, 2009;Hathaway et al, 2011). Employment of CO 2 capture systems may become necessary in the near future to stabilize CO 2 concentration in the atmosphere if the world continues to rely on fossil fuels for energy production.…”