Control composition

We want to compare tray temperature control with two types of composition control. In both, the composition of the distillate propane product is measured directly and controlled at 2 mol% isobutane impurity. The first type is direct composition control in which a single PI controller is used with reboiler heat input manipulated. The second type uses a cascade composition-to-temperature control structure. 

Composition measurement typically has larger deadtime and lags than temperature control. We assume a 3 min deadtime in the composition measurement. 

Temperature control has the advantage of being fast, but it may not hold the product purity constant. Composition control is slow, but it will drive the product purity to the desired value. The next control structure studied is a cascade combination of composition and temperature control that achieves both fast control and the maintenance of product purity. 

The tray temperature controller is the secondary (slave) controller. It is set up in exactly the same way as we did in the previous section. It looks at tray temperature (Stage 9) and manipulates reboiler heat input. However, its SP is not fixed. The SP signal is the output signal of the composition controller, which is the primary (master) controller. 

Conceptually, product quality is determined by the heat balance of the column. The heat removal determines the internal reflux flow rate, whereas the heat addition determines the internal vapor rate. These internal vapor and liquid flow rates determine the degree of separation between two key components. 

Analyzer controllers in a feedback configuration can only be considered when the dead time caused by analysis update is less than the response time of the process. The composition controller provides a feedback correction in response to feed composition changes, pressure variations, or changes in tower efficiencies. 

Distillate composition can be controlled by a cascade temperature master on the upper part of the column, which manipulates the reflux flow L (left). Similarly, the bottoms composition can be controlled by a cascade temperature master located on the lower half of the column, throttling the reboiler heat input (right). 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Selective control configurations also require external feedback to protect them from reset windup. Part (d) has a combination of selective and cascade systems and in such configuration, the external reset (ER) signal (not shown) is taken from the measurement of the slave controller (FRC). 

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Compositional control ia suspension systems can be achieved with a corrected batch process. A suspension process has been described where styrene monomer is continuously added until 75—85% conversion, and then the excess acrylonittile monomer is removed by stripping with an iaert gas... 

Because these alloys are precipitation hardenable, they can be customized for specific requirements across a wide range of property combinations. Advances in composition control, processing, and recycling technology have broadened the capabiUties and expanded the range of appHcation. Data sheets pubhshed by the manufacturers and others (41) give compositions, properties, and typical appHcations. 

Table 1 fists many metal borides and their observed melting points. Most metals form mote than one boride phase and borides often form a continuous series of solid solutions with one another at elevated temperatures thus close composition control is necessary to achieve particular properties. The relatively small size of boron atoms facilitates diffusion. 

RGA Example In order to illustrate use of the RGA method, consider the following steady-state version of a transfer function model for a pilot-scale, methanol-water distillation column (Wood and Berry, Terminal Composition Control of a Binaiy Distillation Column, Chem. Eng. Sci, 28, 1707, 1973) Ku = 12.8, K = -18.9, K. i = 6.6, and Koo = —19.4. It follows that A = 2 and... 

Composition Control The first requirement for successflil control of a chemical reactor is to establish the proper stoichiometry, that is, to control the flow rates of the reac tants in the proportions needed... 

In the use of temperature measurement for control of the separation in a distillation column, repeatability is crucial but accuracy is not. Composition control for the overhead product would be based on a measurement of the temperature on one of the trays in the rectifying section. A target would be provided for this temperature. However, at periodic intervals, a sample of the overhead product is analyzed in the laboratory and the information provided to the process operator. Should this analysis be outside acceptable limits, the operator would adjust the set point for the temperature. This procedure effectively compensates for an inaccurate temperature measurement however, the success of this approach requires good repeatability from the temperature measurement. 

Detonation arresters are typically used in conjunction with other measures to decrease the risk of flame propagation. For example, in vapor control systems, the vapor is often enriched, diluted, or inerted, with appropriate instrumentation and control (see Effluent Disposal Systems, 1993). In cases where ignition sources are present or pre-dic table (such as most vapor destruct systems), the detonation arrester is used as a last-resort method anticipating possible failure of vapor composition control. Where vent collec tion systems have several vapor/oxidant sources, stream compositions can be highly variable and... 

Ishiyama, S. and Eto, M., Recent R D of C/C Composite Control Rod for HTGRs In Proceedings of 22nd Biennial Conf. on Carbon Pub. American Carbon Society, 1995, pp 161-162. 

Eto, M., Ishiyama, S., and Ugachi, H., Status of the research and development at JAERI on the C/C composite control rod for the HTGR. In Proceedings of the IAEA Specialists Meeting on Graphite Moderator Lifecycle Behavior, lAEA-TECHDOC-901, IAEA, Vienna, 1996. pp. 205 214. 

I. Verpoest, M. Desaeger, and R. Keunings, Composites, Controlled Interphases in Composite Materials, (H. Ishida, ed.), Elsevier Science Publishing Co. Inc., p. 653... 

Sputtering is an important thin-film process used extensively in the semiconductor and hard-coating industries and for decorative and jewelry coatings. PlP] Excellent coatings of refractory compounds and metals can be readily produced with good adhesion and composition control without the high temperature requirements of CVD. 

Figure 15. Variation in Dxh for garnet versns reciprocal temperature for experimental data sources listed in Table lb at a variety of pressures n = 33). A distinction is made between mantle solidus partition coefficients (Salters and Longhi 1999 Salters et al. 2002 McDade et al. 2003a,b) and the rest. Note the strong temperatnre dependence, which is qnalitatively similar to that incorporated in Equation (25b). The scatter is due to additional compositional controls.

Leeman WP, Phelps DW (1981) Partitioning of rare earths and other trace elements between sanidine and coexisting volcanic glass. J Geophys Res 86 10193-10199 Linnen RL, Keppler H (2002) Melt composition control of Zr/Hf fractionation in magmatic processes. Geochim Comsochim Acta 66 3293-3301... 

Lundstrom CC, Shaw H, Ryerson F, Phinney D, Gill J, Williams Q (1994) Compositional controls on on the partitioning of U, Th, Ba, Pb, Sr and Zr between clinopyroxene and haplobasaltic melts implications for uranium series disequilibria in basalts. Earth Planet Sci Lett 128 407-423 Lnndstrom CC (2003) Uranium-series disequilibria in mid-ocean ridge basalts observations and models of basalt genesis. Rev Mineral Geochem 52 175-214... 

Figure 6.14. Scheme of the experimental apparatus for gravimetric measurements described by Zavrazhnov et al. (2003) in their investigation of the phase composition control in chemical transport reactions. (1) quartz ampoule, (2) thermocouples, (3) two-zone furnace, (4) quartz rods, (5) wire for suspending the ampoule, (6) support, (7) weighing beam of the analytical balance,... 

Chemical transport reactions as a new variant of the phase composition control... 

In Fig. 8.7c the ratio of the two flows is changed by the output of a composition controller. This system is a combination of feedforward and feedback control. Finally in Fig. %.ld a feedforward system is shown that measures both the flow rate and the composition of the disturbance stream and changes the flow rate of the manipulated variable appropriately. The feedback controller can also change the ratio. Note that two composition measurements are required, one measuring the disturbance and one measuring the controlled stream. 

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