Molten salt gasification

This molten salt gasification process is the basis for the Rockwell International molten salt coal gasification process. A 900-kg-h l (1 ton/h) process development unit pilot plant has been built and is being tested under contract from the Department of Energy. This plant includes the gasifier and a complete sodium carbonate recovery and regeneration system. 

In the Rockgas (Rockwell International) molten salt gasification process (Figure 21.24), coal and sodium carbonate are first transported by compressed air (at 150-300 psi) into the bottom of the molten bed (ca. 980°C [1800°F] 300 psi) in the gasifier. This melt bed is composed of sodium carbonate along with any sodium sulfide and sulfate formed during the process (Rosemary and Trilling, 1978). 

An example of the gasification of biomass by partial oxidation in which air is supplied without zone separation in the gasifier is the molten salt process (Yosim and Barclay, 1976). In this process, shredded biomass and air are... 

A portion of the sodium carbonate melt is withdrawn from the molten salt reactor, quenched, and processed in an aqueous recovery system. The recovery system removes the ash and inorganic combustion products (mainly sodium salts such as NaCl and Na2S) retained in the melt. Unreacted sodium carbonate is returned to the molten salt furnace. The ash must be removed when the ash concentration in the melt approaches 20 to 25 wt % in order to preserve the melt fluidity. The inorganic combustion products must be removed before all of the sodium carbonate is completely converted to noncarbonate salts. For the case of a waste containing a valuable mineral resource, the valuable mineral resource is retained in the melt during the gasification process and may be recovered as a by-product of the regeneration process. 

Gasification of Waste Film. Two series of tests were conducted with waste X-ray film. The first series was performed in the bench-scale gasifier the second series was run in the molten salt test facility. Bench-scale gasification of film at 51% and 22% theoretical air produced product gases of 3.99 MJ m 3 (107 Btu/scf) and 6,67 MJ m 3 (179 Btu/scf), respectively. Small pellets of pure elemental silver (greater than 99,9% pure Ag) were recovered from these tests. 

Industrially, coal gasification processes are differentiated by the type of reaction system used to gasify the coal such as 1) fixed bed, 2) fluidized bed, 3) entrained bed, and 4) molten salt. The processes utilizing these reactor configurations are shown in Table 2.13 the typical gas distributions from some common systems shown in Table 2.14 [5,37],... 

A key component of the regeneration subsystem is the reducer. This component is a ceramic-lined vessel which contains the molten salt at temperatures approaching 2000°F. The component is common to several other sulfur dioxide and coal gasification processes and has been demonstrated at both 4-ft and 9-ft diameter size scales. In the reducer, both the oxidation of sulfide to sulfate and the reduction of sulfate to sulfide by the coke proceed simultaneously. 

Bed Height. The effect of the height of the molten salt bed on the kinetics is important for commercial design, which at present calls for bed heights of 10-20 ft. Ideally for ease of design, one would prefer that bed height have no effect on the kinetics of gasification. Physical limitations of the test equipment have allowed only a small amount of evidence to be obtained in this area. 

Gasification may be enhanced by the catalytic properties of the melt used. Molten salts, which are generally less corrosive and have lower melting points than molten metals, can strongly catalyze the steam-coal reaction and lead to very high conversion efficiencies. 

Molten salt processes, as the name implies, use a molten medium of an inorganic salt to generate the heat to decompose the coal into products and there are a number of applications of the molten bath gasification. 

Molten salts are not only useful as solvents in chemical synthesis, electrolysis, soldering, enameling, de-enameling, metal recycling and preparation, coal gasification, and desulfuration, but they are also reactants, catalysts, and ambients for heat storage and heat transfer, as well as electrolytes in fuel cells (molten carbonates). The solvent can participate in the reaction that is carried out in fluxes. BaTiOa is made in molten TiO, as a solvent and Bio(AlClJ, can only be made in a very acidic cryolite (NaAlClJ. 

Molten Salt Coal Gasification coal or coke 1700... 

Fig. 3 Solar-assisted coal gasification reactor with a salt molten process [14]...

Molten eutectic salt mixtures have been reported to be active catalysts in graphite and coal char gasification [4, 5]. A major reason probably is the contact between soot and catalyst which is increased by wetting of the soot with the catalyst. 

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