Gas heating value

The chemistry of the oil-to-gas conversion has been estabUshed for several decades and can be described in general terms although the primary and secondary reactions can be truly complex (5). The composition of the gases produced from a wide variety of feedstocks depends not only on the severity of cracking but often to an equal or lesser extent on the feedstock type (5,62,63). In general terms, gas heating values are on the order of 30—50 MJ/m (950-1350 Btu/fT). 

Both control schemes react in a similar manner to disturbances in process fluid feed rate, feed temperature, feed composition, fuel gas heating value, etc. In fact, if the secondary controller is not properly tuned, the cascade control strategy can actually worsen control performance. Therefore, the key to an effective cascade control strategy is the proper selection of the secondary controlled variable considering the source and impact of particular disturbances and the associated process dynamics. 

Tables 2.5 and 2.6 provide a database on the key features of the technologies considered in this study along with the producer gas heating values and compositions. A considerable amount of data is missing, which is indicative of the need for comprehensive performance information to be organized into design practice literature to guide developers. These tables do, however, form the starting basis for the analysis presented in the sections that follow.

Objective function. The objective function for the reactor optimization is based on the difference between the value of the product gas (heating value and ammonia value) and the value of the feed gas (as a source of heat only) less the amortization of reactor capital costs. Other operating costs are omitted. As shown in Murase et al., the final consolidation of the objective function terms (corrected here) is... 

Kinetic data for the third experiment have not yet been analyzed, but It appears that product gas heat values depend mostly on hydrogen contents, and that the use of high steam/alr ratios promotes hydrogen formation via C + H2O CO + H2, followed by CO + H2O CO2 + H2. Small Increases In CHi content are also Indicated under such conditions. 

As can be observed from the temperature plots shown In Figure 6, rapid cooling of the system requires further Injection of air or oxygen In order to maintain reasonably high gas heat values and minimize fluctuation In heat value. 

Since R is related to volatile matter content (Figure 1), it would be reasonable to expect a correlation between this rank parameter and specific properties of by-product gas. Our results show that gas specific gravity and gas heating value can, in fact, be estimated fairly accurately from reflectance data. 

A similar correlation was obtained for R and the heating value of byproduct gas. Figure 14 compares gas heating value (B.t.u. per cubic foot) with R (r = —0.87) and demonstrates that the heating value of gas decreases gradually as coal rank increases through the 0.7-1.9 R range. 

Figure 15 compares the heating value of gas, as expressed in B.t.u. per pound of coal, to the R of the samples analyzed. In general, as the R of vitrinite in coal increases, the heating values decrease (r = —0.72). As indicated by the low coefficient of correlation in Figure 5 (r = —0.72), a close relationship between R and gas heating value does not exist. Therefore, any reference to these data can only be in very general terms. 

Figure 15. Relationship between reflectance and gas heating value.

The change from ideal gas to real gas heating values usually is less than Vi percent and normally is ignored. 

One of the major technical problems that had to be overcome to integrate the POLYBED system with the steam reformer was the variation in tail gas flow and composition. Because of the cyclic nature of the process, tail gas is rejected by the POLYBED unit during blowdown and purge with significant flow and composition variations. The fluctuations would have made it impossible to use the tail gas for fuel and a sophisticated system was developed to balance tail gas heating value. This buffer/mixing tank system has proven to be very reliable in holding heat input variation to 1% (2). ... 

The effect of water influx on product gas heating value and production rate is illustrated in Figure 5. These computed results are qualitatively consistent with experimental results from the Hanna tests. The optimum water influx ratio found by Gunn, et al. (1, 2) is not observed, but it is clear that such an optimum must exist at a smaller value of water influx ratio than investigated here. In the total absence of water only devolatilization will contribute to product gas heating value. 

Figure 5. Product gas heating value and production rate as functions of water...

TABLE 9.4 Comparison of Operating Temperatures and Pressures and Typical Product Gas Heating Values and Compositions of Selected Coal Gasification Processes... 

Concerning the hot gas filtration one of the ideas behind this is of course to allow gaseous tars to pass through the fitter and other tars to stick to the filter cake and not pass into the fme pore structure of the filter itself As the amount of benzene and tars is not insignificant from gas heating value point of view, this is very in ortant to achieve. 

Instead of using one or two process measnrements, all the measured process conditions (e.g., fuel feed rate, oxygen in the flue gas, heating value of the fuel, ambient air temperature, and so on) have been empirically correlated to predict the NO concentration in the fine gas. The empirical correlation is based on training an artificial neural network to predict the flue gas NO concentration from all the available data. 

Steam-Hydrocarbon Ratio. The next series of tests was made to show the effect of the steam-hydrocarbon ratio on gas composition (Figure 9) and to determine the minimum practical steam-hydrocarbon ratio. The trends shown are approximately the same as predicted by equilibrium calculations. The lack of complete temperature profile data makes it difficult to show how closely the trends agree with equilibrium predictions. Steam-hydrocarbon weight ratios as low as 1.6 (molar ratio of 7.7) were adequate to prevent carbon deposition. The product gas heating value at this low ratio was about 774 B.t.u./std. cu. ft. It could be raised to 957 B.t.u./std. cu. ft. if the exit gas carbon dioxide were reduced to 2 mole % by scrubbing. 

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