Control Strategy Development

The heterogeneous azeotropic column system using isobutyl acetate as the entrainer will be studied in detail in this section. The overall control strategy of this system will be developed in order to maintain bottom and top product specifications in spite of feed flowrate and feed composition changes. In the control strategy development, we will assume no online composition measurement is available. The composition control loops will be inferred by some tray temperature control strategy. This type of control strategy can easily be implemented in industry for wider applications. 

The Aspen Plus steady-state simulation in the last section is exported to the dynamic simulation of Aspen Dynamics. The tray sizing option in Aspen Plus is utilized to calculate the column diameter to be 0.3259 m and the tray spacing is 0.6096 m. Other equipment sizing recommended by Luyben is used here. The volume of the reboiler is sized to give 10 min holdup with 50% liquid level. The decanter is sized to be bigger to allow for two liquid phases to separate. The holdup time of 20 min is used in the dynamic simulation. Pressure-driven simulation in Aspen Dynamics is used with the top pressure of the azeotropic column controlled at 1.1 atm to allow for some pressure drop in the condenser and decanter to give the decanter at atmospheric pressure. The pressure drop inside the colunm is automatically calculated in Aspen Dynamics. Since the tray pressures in the colunms are different than the constant atmospheric pressure assumption used in steady-state simulation, the established base-case condition in Aspen Dynamics will be slightly different than Table 9.11. The final base-case steady-state condition used for control study can be seen in Table 9.15. 

There are two inventory control strategies that can be used for this system. The first inventory control strategy (Inventory Strategy 1) uses entrainer makeup flow to control the organic phase level in the decanter. This inventory control strategy was successfully used in Chien 

ACETIC ACID-WATER (ISOBUTYL ACETATE AS THE ENTRAINER) 

TABLE 9.15 Base-Case Condition of the Optimal Flowsheet for Dynamic Tests. 

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Combustion control is currently a hot area of research in the U.S. and abroad. In addition to basic research at a number of universities, joint industry-university S T efforts are also underway to implement the control strategies developed by researchers in industry applications. Though some of the demonstrations have been made using gaseous fuels, the techniques can be extended to liquid fuels as well, and efforts are underway to accomplish this. It is hoped that future engines will perform equally well in off-design conditions, with improved reliability and easier maintenance, and reduced operational costs. 

The outputs of the sensors were used in two closed-loop control strategies developed for combustor performance optimization [7]. The objective of the first strategy, based on an adaptive least-mean squares (LMS) algorithm, was to maximize the magnitude and coherence of temperature oscillations at the forcing frequency /o in the measured region. The LMS algorithm was used to determine... 

Core, J.E. Hanrahan, P.L. Cooper, J.A. "Air Particulate Control Strategy Development A New Approach Using Chemical Mass Balance Methods." This symposium. 

Presented as an overview of the State of Oregon s unique approach to particulate control strategy development, this review was prepared to provide those responsible for airshed management with new information on source impact assessment methods. (This material is available in the form of an audio-visual program suitable for presentation before public, regulatory or private Interest groups). 

Using the validated dispersion model as the key tool in the strategy development, efforts turned to Step 5, Control Strategy Development. Table I presents predictions of 1987 particulate air quality based on future year emission data bases, and incorporates all of the identified inventory corrections, and emission growth projections. 

It is clear from the data presented in this chapter that the effects of control strategies developed for CFCs and halons are already measurable. Although loss of stratospheric ozone with accompanying increases in ultraviolet radiation in some locations have clearly occurred, the tropospheric concentrations of CFCs are not increasing nearly as fast as in the past. Indeed, the concentrations of CFC-11 and CFC-113 appear to have peaked and have started to decline. The equivalent effective stratospheric chlorine concentrations are predicted to have peaked about 1997 and to return to levels found around 1980 at about the year 2050 (World Meteorological Organization, 1995). The significance of the 1980 level is that these levels resulted in detectable Antarctic ozone depletion. 

A number of different approaches have been taken to understanding the VOC-NO chemistry and its application to control strategy developments. These include the use of environmental chambers, models ranging from simple linear rollback to complex Eulerian models, and field studies. 

In short, while a number of field studies and routine monitoring over the years have been directed to examining the relationship between emissions and air quality, with obvious implications for control strategy development, interpretation of the data is not straightforward or unambiguous. With these caveats in mind, we briefly discuss a few of the many studies that have been carried out. 

The Generic Model Control (GMC) is a model-based control strategy developed by Lee and Sullivan in 1988 [41], It can be shown that GMC is an input-output linearization technique for processes with unitary relative order [31],... 

The control strategy developed in this work makes use of the principle that the temperature change from inlet to outlet in a heat exchanger remains constant when the mass flow rate and power... 

Unsteady-state or dynamic simulation accounts for process transients, from an initial state to a final state. Dynamic models for complex chemical processes typically consist of large systems of ordinary differential equations and algebraic equations. Therefore, dynamic process simulation is computationally intensive. Dynamic simulators typically contain three units (i) thermodynamic and physical properties packages, (ii) unit operation models, (hi) numerical solvers. Dynamic simulation is used for batch process design and development, control strategy development, control system check-out, the optimization of plant operations, process reliability/availability/safety studies, process improvement, process start-up and shutdown. There are countless dynamic process simulators available on the market. One of them has the commercial name Hysis [2.3]. 

Core, J. E., Hanrahan, P. L., and Cooper, J, A. (1981 Air Pollution Control Strategy Development A New Approach Using Chemical Mass Balance Methods in Atmospheric Aerosol Source/Air Quality Relations, in Macias, E. S and Hopke, D. (Eds.). Symposiim Series No. 167, American Chemical Society, Wa.s iington. D.C., p. 107. 

Core JE, Hanrahan PL and Cooper JA (1981) Air particulate control strategy development - a new approach using chemical mass balance methods. In Macias ES and Hopke PK, eds. Atmospheric Aerosols Source/Air Quality Relationships. ACS Symposium Series 167. Washington, DC. 

Chemical sensors will be used and control strategies developed to ensure that all energetic materials are fully hydrolyzed and that process and operator safety is maintained. Other objectives of the system performance evaluation are summarized below (Bonnett, 2000) ... 

Pressure-driven simulation in Aspen Dynamics is used in the control strategy development. Before converting the Aspen Plus simulation to Aspen Dynamics, sizing of all equipments is needed. The tray sizing tool in Aspen Plus is used to calculate the column diameters of both columns to be 0.78 m and 0.82 m for the first and the second column, respectively. Tray spacing and weir height of both columns are assumed to be 0.6096 m and 0.0508 m. 

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