COMPUTER SIMULATION, SECOND-LAW ANALYSIS, AND ECONOMICS OF COAL GASIFICATION PROCESSES

The efficiency and economics of the Synthane Gasification process are evaluated and discussed in this study. The efficiency of the Synthane process was determined using the "availability analysis" approach to process evaluation.; In order to accurately apply the availability analysis, it is essential that the absolute enthalpy and entropy values of each stream be determined. In this study, methods for predicting the enthalpy and entropy of coal, char, tar and ash, as a function of temperature and material composition, were developed. Comparisons of the results of the method developed for the evaluation of enthalpy with literature values were found to agree within an average of 8.49 per cent for chars and 8.55 per cent for coals. The standard entropy of coal and char was approximated by comparing the behavior of the standard entropies of a number of aliphatic and aromatic hydrocarbons as a function of the elemental composition of the hydrocarbon.; A computer simulation of the Synthane process was developed which allowed for the effect of changes in plant operating parameters on both the efficiency and economics to be studied. The simulation included a three-section model of the Synthane fluidized bed gasifier.; Results of the availability analysis include an overall exergetic efficiency of 61.2 per cent for the operation of the Synthane plant with a Pittsburgh Seam feed coal, and an overall exergetic efficiency of 61.1 per cent for a Wyodak Seam feed coal. Increasing the ratio of steam to oxygen fed to the gasifier from 6.83 to 10.0 was found to increase the overall exergetic efficiency from 61.2 per cent to 64.6 per cent with a Pittsburgh feed coal. Utilizing an alternate methanator design similar to one presented in an IGT HYGAS process design was found to increase the overall efficiency to 62.3 per cent with the Pittsburgh feed coal and to 61.9 per cent for the Wyodak feed coal.; The production cost of the synthetic natural gas (SNG) product from the Synthane process was found to be {dollar}4.61/GJ with the Pittsburgh feed coal, and {dollar}6.23/GJ with the Wyodak feed coal, in third quarter 1979 dollars. The SNG production cost was found to decrease from {dollar}4.61/GJ to {dollar}4.37/GJ when the ratio of steam to oxygen fed to the gasifier was increased from 6.83 to 10.0. A 50 per cent increase in coal cost was found to increase the SNG production cost by 15 per cent and 18 per cent for the Pittsburgh and Wyodak feed coals, respectively, while a 100 per cent increase in coal cost increased the SNG production cost by 30 per cent and 36 per cent, respectively. Changing to the alternate (HYGAS) methanator design resulted in a decrease of {dollar}0.21/GJ in the SNG production cost for the Pittsburgh feed coal, and a decrease of {dollar}0.26/GJ for the Wyodak coal.