| OCR Text |
Show TRACE ELEMENTS IN COAL-DERIVED LIQUIDS Coal Liquefaction: Coal-derived liquids can be produced by different techniques, which may be classified under one of the following three general categories: pyrolysis, direct liquefaction, and indirect liquefaction. In all coal conversion processes, the coal is subjected to a thermal degradation resulting in a partial or total destruction of its macromolecular structure. In the indirect liquefaction processes coal is gasified first. The gaseous products are then catalytically converted to hydrocarbons and other organic molecules. The liquid products are usually clean and suitable for production of transportation fuels. Pyrolysis is a process primarily used for the production of metallurgical coke, as a by-product of which coal tars are generated. The liquid yield is usually low and the produced coal-derived liquids are low in their trace metal content. In direct liquefaction or hydroliquefaction processes, coal is dissolved in a solvent under hydrogen pressure where a catalyst nay also be present. Advanced direct coal liquefaction processes include Solvent Refined Coal (SRC), H-Coal, and Exxon Donor Solvent (EOS) processes. More advanced processes, such as two stage liquefaction, are under development and are expected to become the dominating processes of the future. In the SRC-I process, pulverized coal is mixed at high temperatures and pressures with a process-derived solvent and hydrogen. After the coal dissolves, most of its ash and sulfur settle out and are removed by 1.5.5 |
