Info

"Klass, Kroenke, and Landahl (1981); Ng (1979). A plug-flow reactor, 0.48 cm ID, was used. The glucose concentration was 3.2 to 3.5 wt %. The WHSV is the weight hourly space velocity in grams of glucose per hour per liter of reactor volume. The critical temperature and pressure of water are 374.1°C and 22.119 MPa.

"Klass, Kroenke, and Landahl (1981); Ng (1979). A plug-flow reactor, 0.48 cm ID, was used. The glucose concentration was 3.2 to 3.5 wt %. The WHSV is the weight hourly space velocity in grams of glucose per hour per liter of reactor volume. The critical temperature and pressure of water are 374.1°C and 22.119 MPa.

from food processing (Elliott et ah, 1991, 1993). Continuous, fixed-bed catalytic reactor systems have been operated on three scales ranging from 0.03 to 33 L/h. The residence time in the supported metallic catalyst bed is less than 10 min at 360°C and 20,365 kPa at liquid hourly space velocities of 1.8 to 4.6 L of feedstock/L of catalyst/h depending on the feedstock. Aqueous effluents with low residual COD (chemical oxygen demand) and a product gas of medium-energy quality have been produced. Catalysts have been demonstrated to have reasonable stability for up to six weeks. Ruthenium appears to be a more stable catalyst than nickel. The product gas contains 25 to 50 mol % carbon dioxide, 45 to 70 mol % methane, and less than 5 mol % hydrogen with as much as 2 mol % ethane. The by-product water stream carries residual organics and has a COD of 40 to 500 ppm. The medium-energy product gas is produced directly in contrast to medium-energy, gas-phase processes that require either oxygen in place of air or the dual reactor system to keep the nitrogen in air separated from the product.

Hydrogasification

In this process, gasification is carried out in the presence of hydrogen. Most of the research on hydrogasification has targeted methane as the final product. One approach involves the sequential production of synthesis gas and then methanation of the carbon monoxide with hydrogen to yield methane. Another route involves the direct reaction of the feed with hydrogen (Feldmann et al,

1981). In this process (Fig. 9.7), shredded feed is converted with hydrogen-containing gas to a gas containing relatively high methane concentrations in the first-stage reactor. The product char from the first stage is used in a second-stage reactor to generate the hydrogen-rich synthesis gas for the first stage. From experimental results obtained with the first-stage hydrogasifier operated in the free-fall and moving-bed modes at 1.72 MPa and 870°C with pure hydrogen, calculations shown in Table 9.8 were made to estimate the composition and yield of the high-methane gas produced when the first stage is integrated with an entrained-char gasifier as the second stage. Note that although the methane content of the raw product gas is projected to be higher in the moving-bed reactor than in the falling-bed reactor, the gas from the first stage must still be reacted in a shift converter to adjust the H2/CO ratio, scrubbed to remove C02, and methanated to obtain SNG.

Other research shows that internally generated hydrogen for hydroconversion can be obtained in a single-stage, noncatalytic, fluidized bed reactor (Babu, Tran, and Singh, 1980). In this work, hydroconversion was envisaged to occur in a series of steps: nearly instantaneous thermal decomposition of biomass followed by gas-phase hydrogenation of volatile products to yield hydrocarbon

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FIGURE 9.7 Methane production by hydrogasification. From Feldmann et al. (1981).

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FIGURE 9.7 Methane production by hydrogasification. From Feldmann et al. (1981).

TABLE 9.8 Gas Composition and Yield from Integrated Hydrogasification Process at Stage 1°

Product Free fall Moving bed

Composition, mol %

TABLE 9.8 Gas Composition and Yield from Integrated Hydrogasification Process at Stage 1°

Product Free fall Moving bed

Composition, mol %

H2

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