Sulfur Absorption

At ID21 beamline p-XANES and p-XRF maps have been obtained along the same transects analyzed at ID18F. The maps were carried out in area of 100 x 100 pm with a resolution of 1 x 1 pm. The sulfur oxidation state was determined by scanning the energy of the exciting beam across the sulfur absorption K-edge (total-S = 2.55 KeV sulfide-S = 2.472 KeV sulfate-S = 2.482 KeV). 

There are two more quantities that must be defined to complete the description of the fluidized bed combustor viz., the carbon combustion efficiency, ncCE> sulfur absorption efficiency, nsAE- These are ... 

The above calculation is quite tedious and gets complicated by the fact that the properties which ultimately control the magnitude of these fourteen unknown quantities further depend on the physical and chemical parameters of the system such as reaction rate constants, initial size distribution of the feed, bed temperature, elutriation constants, heat and mass transfer coefficients, particle growth factors for char and limestone particles, flow rates of solid and gaseous reactants. In a complete analysis of a fluidized bed combustor with sulfur absorption by limestone, the influence of all the above parameters must be evaluated to enable us to optimize the system. In the present report we have limited the scope of our calculations by considering only the initial size of the limestone particles and the reaction rate constant for the sulfation reaction. 

The concentration profile of oxygen in the bed is fixed by establishing apriori a value for b as 4.5 and that of a as obtained from the assumed values of carbon conversion and sulfur absorption efficiencies. For a given oxygen profile the reaction rate constant, k3(To), and the size of the dolomite feed are varied. The changes in both of these parameters affect the value... 

Figure 8 represents the variation in limestone requirement as a function of sulfur absorption efficiency for various values of k3(To). The results emphasize that for a given value of k3(To), if the Imestone feed rate is increased which for a bed of fixed size implies a reduction in residence time, the sulfur absorption efficiency is correspondingly decreased. The implication of this result for an actual operating plant is important. It is Implicit in these plots that if the limestone feed rate is held constant, nsAE> increases with an Increase in k3(TQ). 

Figure 9 illustrates the effect of changing limestone average size, r , in the feed stream on the dependence of limestone feed rate, F, and on sulfur absorption efficiency, risAE plots refer to a constant value of 1c3(Tq). 

These results suggest that if the feed size of limestone is kept fixed, an increase in the limestone feed rate will result in the reduction of sulfur absorption efficiency- These results also emphasize that if the same sulfur retention is to be obtained when the size of the limestone particles is decreased the feed rate must be increased. However, for the same feed rate of limestone, a decrease in the size of limestone particles results in an increased sulfur retention. This may be explained on the basis of an increase in the overall surface area per unit volume of the bed when the average diameter of the particles decreases. It may be noted from Figure 9 that regardless of the limestone particle size, if sufficient residence time is allowed for limestone particles in the bed, it is possible to obtain sufficiently high sulfur retention. 

The influence of carbon conversion efficiency on the requirement of limestone for a fixed value of sulfur absorption efficiency is also computed. The generation of sulfur dioxide is found to be directly related to the amount of carbon combusted. 

The generation rate of sulfur dioxide reduces with the decrease in carbon conversion efficiency and hence the limestone requirement also decreases. A reduction in the carbon conversion efficiency from 99.5 to 70.0% causes a reduction in dolomite requirement from 27.5 to 18.9 g/s for a 99% sulfur absorption efficiency. 

Fig. 8.18 Sulfur absorption in the flue system of a coal-fired power plant (EVS, Heilbronn, Germany) left) absorber right) limestone processing and gypsum recovery (briquetting) systems...

The small intestine is the major site of sulfur absorption. 

Haldor Tops0e, Inc., 1986, Tops0e Sulfur Absorption Catalysts, HYZ, Brochure HTZ-10/86. 

Steam reforming process used in ammonia plants. Natural gas feed. Sulfur absorption on activated carbon secondary reforming high temperature shift catalysts used. Reformer-pressure increasing from atmospheric to 9bar. Plant capacity increasing from 150 tpy to 300 tpy. 

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