Gasification steam decomposition rate

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 effect of the addition of a potassium promoter to a nickel steam reforming catalyst has been probed in terms of the propensity of the catalyst to resist carbon formation. It has been found that potassium facilitates a reduced accumulation of carbon by decreasing the rate of hydrocarbon decomposition on the catalyst and by increasing the rate of steam gasification of filamentary carbon from the catalyst. The effect of the promoter on the carbon removal reaction is evident in an enhancement of the pre-exponential factor in the rate equation by promotion of water adsorption on the catalyst surface. 

The role of CaO as a catalyst for the steam-char reaction can be inferred from the results obtained during mixed CO2-H2O gasification (figures 3 and 4). In many respects it is desirable to prevent the decomposition of CaCOj to CaO because of the high endothermic heats of reaction associated with this reaction. However, as we have shown, the steam gasification of oil shale char is about ten times slower when CaO is not present. A better evaluation of the importance of CaO requires a knowledge of the dependence of the reaction rate on the quantity of CaO present. 

In the case of the gasification of rubber wastes, Ogasawara et al.14 have studied the decomposition of used automotive tyres by treatment with steam at different temperatures. The main components detected in the effluent gases were H2, CO and CH4. As shown in Figure 3.4(a), the production rates of both hydrogen and carbon monoxide increase exponentially with the temperature. The H2/CO ratio is about 1.5 whereas CH4 is produced mainly at long reaction times. An oil fraction is also produced, containing mostly aliphatic hydrocarbons and alkylbenzenes. 

The mass flow rate of the gasifying agent steam WHaO.ga (all mass flows in kg/s) does not include the coal moisture Wh20,w and the decomposition water from coal pyrolysis WH20,pyr- The mass flow of residual steam in the raw gas is represented by WH20,rg [9]. In case of moving-bed gasification, sometimes only the injected steam is balanced [2]. 

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