Maintaining Optimum Operating Conditions

As depicted in Fig. 9.5b, at a temperature of 10 °C, there are no heating costs, but also not much production of B. At temperatures above 103 °C, the cost of heating exceeds the revenue received from the production of B and then it is no longer profitable to produce. As depicted in Fig. 9.5b, the optimum temperature is 70 °C. These three conditions are marked by an X in both graphs. Maintaining the temperature as close as possible to 70 °C will be the task of automatic control, i.e., any time the reactor temperature deviates from 70 °C, the system will be brought back to continuously operate at 70 °C. 

9 Fundamentals of Mathematical Modeling, Simulation, and Process Control 

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Combustion controls such as oxygen trim help to maintain optimum operating conditions, especially on gaseous fuels. Instrumentation can give continuous visual and recorded information of selected boiler and plant functions. To be effective, it must be maintained and the data assessed and any required action taken before the information is stored. 

The use of vibration analysis is not restricted to predictive maintenance. This technique is useful for diagnostic applications as well. Vibration monitoring and analysis are the primary diagnostic tools for most mechanical systems that are used to manufacture products. When used properly, vibration data provide the means to maintain optimum operating conditions and efficiency of critical plant systems. Vibration analysis can be used to evaluate fluid flow through pipes or vessels, to detect leaks, and to perform a variety of non-destmctive testing functions that improve the reliability and performance of critical plant systems. 

Novel Processing Schemes Various separators have been proposed to separate the hydrogen-rich fuel in the reformate for cell use or to remove harmful species. At present, the separators are expensive, brittle, require large pressure differential, and are attacked by some hydrocarbons. There is a need to develop thinner, lower pressure drop, low cost membranes that can withstand separation from their support structure under changing thermal loads. Plasma reactors offer independence of reaction chemistry and optimum operating conditions that can be maintained over a wide range of feed rates and H2 composition. These processors have no catalyst and are compact. However, they are preliminary and have only been tested at a laboratory scale. 

With a given system of constant K, a decrease of E/R increases y, but decreases y. Therefore, an optimum operation condition has to be determined based on the various factors affecting the economy of the separation processes, such as the value of products, equipment costs, and operating costs. It is interesting to note that Y depends on the ratio E/R, but not on the values of E and R. Can we increase E and R indefinitely to maintain the same y as long as E/R is constant for a continuous extractor The answer is "no." We should remember that Eq. (10.13) is based on the assumption that the extractor is in equilibrium. Therefore, the increase of E and R will shorten the residence time as a result, the extractor cannot be operated in equilibrium and y will decrease. 

Any good analytical working curve requires first the establishment of optimum operating conditions, including spectral line selection, fuel and oxidant selection and control, sample uptake rate, and the positioning of the optical path and optical components. Once established, these conditions must be maintained throughout the acquisition of the analytical data. 

Thus, the operating conditions in electrokinetic remediation have to be selected to enhance the solubilization of the contaminants and/or maintain a high electroosmotic flow. Research is necessary to determine the optimum operating conditions in each contaminated soil, since the behavior largely depends on the chemical nature of the contaminants and the geochemical interactions of soil and interstitial fluid. 

It is important to consider not only the impurities themselves but also their interaction. The presence of one impurity may not be harmful, but its synergistic combination with others may be [144]. For example, silica itself is not harmful for membranes. Only in the presence of calcium and aluminum do precipitates form and damage the membrane irreversibly. The concentration of silica and/or the concentration of aluminum plus calcium can be adjusted to give the optimum operating conditions. For example, with an effective secondary brine purification, higher levels of silica can be tolerated. Similarly, if aluminum concentration is high, calcium or silica concentration must be reduced to maintain acceptable membrane performance. 

During the time an evaporator is in operation, solids often deposit on the heat-transfer surfaces, forming a scale. The continuous formation of the scale causes a gradual increase in the resistance to the flow of heat and, consequently, a reduction in the rate of heat transfer and rate of evaporation if the same temperature-difference driving forces are maintained. Under these conditions, the evaporation unit must be shut down and cleaned after an optimum operation time, and the cycle is then repeated. 

Tight temperature control is maintained in the reactor (3) to arrive at high yields using a multi-point hydrogen quench (4). In this way, conversion is controlled at the optimum level, which depends on reactor throughput, operating conditions and feed composition. 

To control an operating plant for minimum acid make-up, the Isobutane concentration in the reactor must be maintained at the maximum possible level. This means operating both the depropanizer and the deisobutanizer under optimum conditions. The operator should adjust tower feed rates and operating conditions, always using the isobutane concentration in either the total effluent hydrocarbon or the net effluent hydrocarbon from the reactor as his primary reference. Isobutane-to-olefin ratio, deisobutanizer overhead purity, depropanizer recycle purity, and refrigerant recycle purity are significant only as they relate to reaction zone isobutane concentration. 

Water affects the reaction rate through its effect on reaction kinetics and protein hydration, which is required for optimal enzyme conformation and activity. Enzymes need a small amount of water to maintain their activity however, increasing the water content can decrease the reaction rate as a result of hydrophilic hin-drance/barrier to the hydrophobic substrate, or because of denaturation of the enzyme (189). These opposite effects result in an optimum water content for each enzyme. In SCFs, both the water content of the enzyme support and water solubilized in the supercritical phase determine the enzyme activity. Water content of the enzyme support is, in turn, determined by the distribution/partition of water between the enzyme and solvent, which can be estimated from water adsorption isotherms (141, 152). The solubility of water in the supercritical phase, operating conditions, and composition of the system (i.e., ethanol content) can affect the water distribution and, hence, determine the total amount of water that needs to be introduced into the system to attain the optimum water content of the support. The optimum water content of the enzyme is not affected by the reaction media, as demonstrated by Marty et al. (152), for esterification reaction using immobilized lipase in n-hexane and SCC02- Enzyme activity in different solvents should, thus, be compared at similar water content of the enzyme support. 

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