Overall Control Strategy Development

In the following, we will investigate the proper overall control strategy for the proposed design with the lowest TAC. Only a tray temperature control loop(s) will be used in the overall control strategy for wider industrial 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 of both columns with the assumed tray spacing of 0.6096 m. The diameter of the Cl and the C2 columns are calculated to be 1.61 and 1.25 m, respectively, and the weir heights of both columns are assumed to be 0.0508 m. 

Other equipment sizing followed the recommendations in Chapter 4. The volumes of the column base for the Cl column and also for the C2 column, and the reflux drum of the C2 column, are all sized to give 10 min holdup with 50% liquid level. The decanter is sized to be bigger to allow for two hquid phases to separate. The holdup time of 20 min for the decanter is used in the dynamic simulation. 

Pressure-driven simulation in Aspen Dynamics is used with the top stage pressures of the Cl column set at 1.1 atm to allow for some pressure drop in the condenser and decanter. The top pressure of the C2 column is set to be at atmospheric pressure. The pressure drops inside both columns are automatically calculated in Aspen Dynamics to account for liquid 

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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. 

Because the method tests purely by generating environments, it could be used to test any robot that is written for Player/Stage. Similarly, it can be used on a simple prototype in order to test and algorithm or an overall control strategy - a lot can be learned (fundamental algorithm flaws can be found) without needing a fully developed and mature implementation. 

There are many other aspects of distillation column control in a plantwide context. One of the earliest studies of these issues is the work of Downs (1992). According to Downs, the control strategy for each unit operation must be developed within the framework of the overall component inventory control structure. 7 He presents several... 

Remedy selection involves three principal steps i) development of an overall exposure control strategy (i.e., what to do), ii) selection of optimal remediation technologies to implement this strategy (i.e., how to do it), and iii) development of appropriate design and construction specifications. The general decision process for remedy selection is described in further detail below. 

As reported in Chap. 2, all aftertreatment devices have to be described mathematically with high accuracy. Therefore, aU chemical reactions and heat transfer phenomena are represented in a chemical and physical form. Since computational time has to be kept short, global reactions and rate formulations based on Lang-muir-Hinshelwood type are considered. Moreover, the calibration of the models represents a major step in the modeling work, requiring time and costs and directly affects the accuracy of the simulation of exhaust aftertreatment systems. For the development of control strategies, it is necessary to consider all affected aspects of the powertrain in form of a virtual test bench. The overall simulation tool includes the catalytic parts but also devices like sensors and ECU functions, which interact... 

The proposed hierarchical procedure for plant-wide control developed by Luyben and coworkers [14] is utilized, in our framework, as stepwise guidelines to perform the plant-wide process control strategy. The procedure essentially decomposes the plant-wide control problem into various levels and tries to satisfy the two fundamental chemical engineering principles, i.e. the overall conservation of energy and mass. The design procedure consists of the following main steps ... 

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