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This paper, which describes an advanced two-stage gasification system, consists of two parts: part 1 describes the experimental results, and part 2 describes the process evaluation. In part 1, Avco's concept of two-stage coal gasification that utilizes very rapid coal pyrolysis is reviewed. Its potential technical and economic advantages are also reviewed. A moderately large-scale (1 ton of coal/h) entrained flow reactor facility was designed, constructed, and operated to obtain critical rapid pyrolysis kinetic data at conditions approaching those applicable for commercial reactors. Major factors that limit the product gas yield were identified and were optimized to the extent possible so as to maximize the coal carbon conversion to synthesis gas. Extensive intrusive diagnostics were used to study the effects of coal rank, coal carbon loading, and pyrolyzer inlet gas temperature on coal carbon conversion, exit gas temperature, and exit gas composition. The experiments were conducted under well-defined heating rate and mixing conditions in the pyrolyzer; hence, the data are not device specific and should have a general application. The system design studies (part 2) show that, when the experimental data on the rapid pyrolysis operation are incorporated into a two-stage gasification process design, distinct economic advantages over available single-stage processes can be projected. The results show that Avco's two-stage process has about a 6% advantage for coal conversion to methanol over currently available major gasification processes as well as a 10-15% reduction in the oxygen consumption for a near-term process design. For an advanced system, the reduction in oxygen consumption is projected to be 20-25%.

Baker, C. G. J.; Bergougnou, M. A. Can. J . Chem. Eng. 1972, 50, 695. Kim, S. D.; Baker, C. 0. J.; Bergougnou, M. A. Can. J. Chem. Eng. 1975, 53, 134. KO&, K.; MarWka, S.; Ueyama, K.; Matsurra, A.; Yamashlta. F.; Iwamoto, S.; Kato, Y.; Inoue. H.; Shloeta. M.; Suzuki, S.: Akehata, T. J . Chem.The effect of pH on the removal of pyritic sulfur in airlwater chemical coal cleaning was investigated. The pH was varied by adding sulfuric acid or sodium carbonate to a coal-water slurry. The effect of nearby neutral pH (-7) was determined in a buffer solution of sodium dihydrogen phosphate and disodium hydrogen phosphate. Data were taken in the temperature range of 130 to 190 OC, oxygen partial pressure of 0.32 to 1.36 MPa, and reaction times up to 3600 s. The rate of pyrite oxidation was found to be minimum at the nearby neutral conditions. Under otherwise identical conditions, the rate of pyrite oxidation was greater in basic pH than in acidic pH. The enhancement in the rate of pyrite oxidation is explained on the basis of electrochemil reactions. Under nearly neutral conditions, the overall reaction is shown to be controlled by the surface reaction, whereas under acidic as well as basic conditions, diffusion of oxygen through the product ash layer as well as the surface chemical reaction seems to be important.