Steam-to-oxygen ratio

It should also be pointed out that gasifiers operated at steam to oxygen ratios as low as possible provide the thermally most efficient and lowest cost route to the production of medium BTU gas (1). The co-production of pipeline gas in the gasification step improves the overall thermal efficiency of various liquefaction processes (Flscher-Tropsch, Methanol, Mobils MTG route) by 13 to 18 % (2). 

The steam-to-oxygen ratio rr/w in kg/m (STP) is another common characteristic value for gasification processes. If steam is serving as gasification agent in the process, the steam decomposition rate fHaO in % is calculated by Equation (4.19). 

The primary steam injection has little influence, since it is only 5.6-18.0% of the total steam. The same applies for the secondary O2, which is 2.7-10.1% of the total amount. The global steam-to-oxygen ratio adds up to 0.5-1.5kg/ m (STP). 

Other important parameters in the steam reforming process are temperature, which depends on the type of oxygenate, the steam-to-carbon ratio and the catalyst-to-feed ratio. For instance, methanol and acetic acid, which are simple oxygenated organic compounds, can be reformed at temperatures lower than 800 °C. On the other hand, more complex biomass-derived liquids may need higher temperatures and a large amount of steam to gasify efficiently the carbonaceous deposits formed by thermal decomposition. 

By proper adjustment of the oxygen-to-carbon and steam-to-carbon ratios, the partial combustion in the thermal zone [reaction (9.8)] supplies the heat for the subsequent endothermic SR reaction (9.1) [24]. The CO shift reaction (9.2) also takes place in the catalytic zone. 

A structured ruthenium catalyst (metal monolith supported) was investigated by Rabe et al. [70] in the ATR of methane using pure oxygen as oxidant. The catalytic activity tests were carried out at low temperature (<800 ° C) and high steam-to-carbon ratios (between 1.3 and 4). It was found that the lower operating temperature reduced the overall methane conversion and thus the reforming efficiency. However, the catalyst was stable during time on-stream tests without apparent carbon formation. 

The ratio of steam to oxygen (air) in the gasifier controls the peak temperature in the combustion zone. If a nonslagging operation is desired, sufficient steam is added to offset exothermic oxidation reactions with endothermic steam-carbon reactions to stay safely below the ash-fusion temperature. Slagging gasifiers operate at a higher temperature, and ash is removed in a molten state and then quenched in a water bath. 

It takes place between 400 and 600°C at 0.15.10 Pa absolote, in the presence of catalysts based on bismuth molybdate and phosphate, doped with various transition metals. Operations are conducted with oxygen to butenes mole ratios of about 1 and steam to butenes ratios of 30 to 50. Once-through conversion is up to 60 per cmt and molar butadiene selecti ity dose to 95 per cent. 

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