Steam optimization methods

The steam reforming of methane to produce syngas includes nine basic reactions. The global equilibrium yield (GEY) and the potential maximal equilibrium yield (PMEY) can be calculated by a new method proposed by this paper. The optimal reaction assemblage (ORA) can be constructed by an optimization method. Where hydrogen is the desired product, the ORA is composed of reactions (1) and (2) in the nine-reaction system. The observed peak yield (OPY) of hydrogen equals 2.410 (mole fraction), its PMEY and GEY equal 3.341 (mole fraction). If carbon monoxide is the desired product, the ORA includes only reaction (1) in the nine-reaction system and the OPY, GEY and PMEY of carbon monoxide equal 0.344, 0.2767 and 0.9789 (mole fraction) respectively. Construction of the ORA is the key and fundamental way to improve the yield of a desired product. In this paper, the method of constructing the ORA is developed. 

As mentioned earlier, the steam power industry requires a standard formulation that is both stable (in the sense of not changing for tens of years) and computationally fast. For 30 years, the IFC-67 formulation mentioned in Section III fulfilled that need. Through the years, however, some deficiencies in IFC-67 became apparent. Probably the worst problems related to inconsistencies at the boundaries between the regions of pressure-temperature space in which different equations defined the formulation. These inconsistencies can cause problems in iterative calculations near the boundaries. Also, with improvements in optimization methods and computer technology, it was believed that the computational speed of IFC-67 could be surpassed. In addition, there was a desire (driven by the increasing use of combustion turbines) to add standard properties for steam at temperatures higher than the upper limit of 800° C for IFC-67. 

A common process task involves heating a slurry by pumping it through a well-stirred tank. It is useful to know the temperature profile of the slurry in the agitated vessel. This information can be used to optimize the heat transfer process by performing simple sensitivity studies with the formulas presented below. Defining the inlet temperature of the slurry as T, and the temperature of the outer surface of the steam coil as U then by a macroscopic mass and energy balance for the system, a simplified calculation method is developed. 

Besides two different hydrolysis methods (i.e., acid hydrolysis and pretreatment without the addition of acid), two different pieces of pretreatment equipment were used to perform the experiments (Fig. 4). Acid hydrolysis was conducted in a microwave oven, while pretreatment was performed in a steam pretreatment unit. The microwave oven provides a closed system where the amount of water added is fixed and there is no loss of material during the process (17-18). On the other hand, the sampleshave to be rather diluted for the microwave oven to be efficient. Another disadvantage is that the microwaves penetrate the material only a few center-meters, and therefore this method is not feasible on a large scale. The microwave oven may, however, still be of interest in the laboratory as a screening method to analyze the composition of feedstock as well as to determine a range of optimal conditions for steam pretreatment. 

Benedict applied exergy costing to the design of an air separation plant in 1949 see (58). Gaggioli used the methods for the optimal selection of steam piping and its accompanying insulation (50, 59). Evans, Tribus, El-Sayed and co-workers (53, 54) have developed the fundamentals of the subject, under the title of Thermoeconomics, and present chapters in this volume. 

This problem contains 31 variables and 29 equality constraints (or governing equations) including the objective function. This gives rise to 2 variables as independent (or decision) variables. For a practical reason, the saturation pressure for steam, P, and the fraction of steam generated in the evaporator, which is reused for heating, a.., are selected as the independent variables. A random search technique (26) is adopted to locate the optimal point for each given e. The results are tabulated in Table I, and the trade-off curve is plotted in Figure 3. The relationship between these two objectives is obtained by the least square method as... 

To avoid pinholes and cracks, Matsukata et al. [46] optimized the density of the precursor phase by using a dry gel instead of a solution. This was achieved through the use of a slipcasting method. A dry porous alimina plate of 2.2 cm was dipped into a gel whereby the support surface was covered with an amorphous aluminosilicate phase. After drying, the sample was exposed to template vapor, triethylamine, ethylenediamine and steam (the Vapour-phase Transport Method). However, the zeolite layer (20 pm thick) consisted of a mkture of ZSM-5 and Ferrierite. Nitrogen and oxygen permeation were studied. 

Ghassempour et al." published an interesting work comparing MAE and ultrasonic extraction (USE) for the extraction of diazinon from soil and the stems of rice plants. After optimizing the conditions, better results (98% recovery) were obtained by MAE with hexane as solvent. The USE method gave 91% recovery with the same solvent. The reduced extraction time, minimal amount of solvent, the fact that the soil and steam moisture did not influence MAE when a solvent such as acetone is used, and higher recoveries, made MAE the method of choice in this study. 

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