Coal oxydesulfurized

A brief discussion of the rate-controlling step in coal oxydesulfurization is given on the basis of the shrinking core model. A diree-phase slurry reactor is designed by including die nonideal behavior of die solid phase. 

Desulfurization. The coals were treated in a 1-liter autoclave under conditions of the Ames oxydesulfurization process by leaching 100 g of coal with 400 ml of 0.3 M sodium carbonate for 1 hr. at 150 C under 200 psia oxygen partial pressure. The apparatus and detailed procedure for the leaching experiments were described elsewhere (4 5). 

The coals were desulfurized by leaching with a hot solution of sodium carbonate containing oxygen under pressure. The results of treating the coals under these oxydesulfurization conditions are presented in Table I. Substantial amounts of total sulfur were removed. The pyritic sulfur content was... 

Table I. Analysis of Different Coals Before and After Oxydesulfurization.a...

The calcium data on the residues from acid extractions also do not provide any significant correlation. However, the calcium data on the raw and treated coals point to an unusual correlation. Coals which have been oxydesulfurized by leaching with sodium carbonate solution tend to pick up calcium which is associated with the organic matrix. For example, at the 95%... 

Figure 3. Thermal oxidative degradation of untreated and oxydesulfurized Indiana Minshall Seam (HvCb) coal with diluent...

Treated (Oxydesulfurized coals that showed little or no change in organic sulfur were selected.)... 

Coal Pyrite (with Montano Rosebud Oxydesulfurized Coal) 250-380... 

Precombustion of sulfur from coal by selective oxidation is an important step in coal cleaning, without the need for a postcombustion cleanup step to remove sulfur oxides. This process, known as oxydesulfurization of coal, is a three-phase gas-liquid-solid system. As an example, a sparged reactor wiU be designed to oxydesulfurize 100 tons/day of coal in an aqueous slurry of coal with air. 

The mechanism of oxydesulfurization of coal has been extensively investigated by Vracar et al. (1970), Friedman and Warzinski (1977), Vetter (1967), and Joshi et al. (1982). The dissolution of sulfide minerals can be interpreted as an electrochemical surface reaction similar to the corrosion of metals. Oxygen is reduced at cathodic areas, and sulfides are dissolved liberating electrons to... 

The experimental conversion-time relationship was found to agree with Equation (CS9.3). Furthermore, the experimental value of t was found to be proportional to R. From these two observations, and also from the value of activation energy, it was concluded that the oxydesulfurization process of coal is chemical reaction controlled. For coal of 100 pm size, the time required for complete... 

Shah, Y.T. and R.S. Albal. "Chemical Cleaning of Coal-The Oxydesulfurization Process." a paper presented at NATO-ASI School. Izmir, Turkey (August 1981). 

Warzinski, R.P., J.A. Ruether, S, Friedman, and F.W. Steff-gen. "Survey of Coals Treated by Oxydesulfurization." Proc. Symp. on Coal Cleaning to Achieve Energy and Environmental Goals." Vol. 

Effect of pH. In another work> Joshi et al. (64) investigated the effect of acidic, alkaline as well as nautral pH conditions on the removal of pyritic sulfur in oxydesulfurization. The pH was varied by adding sulfuric acid or sodium carbonate to a coal-water slurry. The effect of neutral pH determined... 

At present, pyritic sulfur from coal can be easily removed by oxidation. The removal of organic sulfur generally requires severe operating conditions which also cause undesirable carbon loss. Future work must consider the removal of organic sulfur by the use of homogeneous catalysts under mild conditions. The processing of a low pH slurry could be an important factor in the commercialization of an oxydesulfurization process. 

---