Feed rate adjustment

Compositional control for other than azeotropic compositions can be achieved with both batch and semibatch emulsion processes. Continuous addition of the faster reacting monomer, styrene, can be practiced for batch systems, with the feed rate adjusted by computer through gas chromatographic monitoring during the course of the reaction (54). A calorimetric method to control the monomer feed rate has also been described (8). For semibatch processes, adding the monomers at a rate that is slower than copolymerization can achieve equilibrium. It has been found that constant composition in the emulsion can be achieved after ca 20% of the monomers have been charged (55). 

After the column was lined out, liquid samples were taken from the butenes condenser and from the reboiler. The composition of these samples served as a guide to indicate which adjustments in operating conditions were necessary to obtain the desired column operation. If the reboiler liquid contained 1-butene or isobutene, its temperature was increased, provided there was no butadiene in the overhead. If butadiene appeared in the overhead, the internal hydrocarbon reflux was increased by increasing the pressure or decreasing the solvent feed tray temperature. Solvent-to-hydrocarbon feed rate adjustments were also effective in giving desired changes in bottoms and overhead compositions. 

The decision whether to correct deviations to a target value, or an absolute average value, is application related. In cases where the overall output has to coincide with a total amount dispensed, or when subsequent flow stream attenuation will smooth minor irregularities, then correction of any shortfall or overfeed is included in feed rate adjustments. For applications where the historical feed rate has immutable consequences, then any corrections should only seek to recover from the offset to the target feed rate and not compensate for past deviations. There is no benefit in compensatory over- or underfeeding when it is not possible to rectify a prior deviation. It cannot be too strongly emphasized that flow reliability is paramount. No control system, however sophisticated, can compensate for an inconsistent feeder performance. 

Since acrylic polymerizations liberate considerable heat, violent or mnaway reactions are avoided by gradual addition of the reactants to the kettie. Usually the monomers are added by a gravity feed from weighing or measuring tanks situated close to the kettie. The rate of monomer addition is adjusted to permit removal of heat with full flow of water in the condenser and a partial flow in the cooling jacket. Flow in the jacket can be increased to control the polymerization in cases of erroneous feed rates or other unexpected circumstances. A supply of inhibitor is kept on hand to stop the polymerization if the cooling becomes inadequate. 

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

Stea.dy-Sta.teFeedforwa.rd, The simplest form of feedforward (FF) control utilizes a steady-state energy or mass balance to determine the appropriate manipulated variable adjustment. This form of feedforward control does not account for the process dynamics of the disturbance or manipulated variables on the controlled variable. Consider the steam heater shown ia Figure 15. If a steady-state feedforward control is designed to compensate for feed rate disturbances, then a steady-state energy balance around the heater yields ... 

Molten sodium is injected into the retort at a prescribed rate and the temperature of the system is controlled by adjusting the furnace power or with external cooling. The variables that control the quaUty and physical properties of the powder are the reduction temperature and its uniformity, diluent type and concentration, sodium feed rate, and stirring efficiency. Optimizing a variable for one powder attribute can adversely affect another property. For example, a high reduction temperature tends to favor improved chemical quaUty but lowers the surface area of the powder. 

One such approach is called cascade control, which is routinely used in most modern computer control systems. Consider a chemical reactor, where reac tor temperature is to be controlled by coolant flow to the jacket of the reac tor (Fig. 8-34). The reac tor temperature can be influenced by changes in disturbance variables such as feed rate or feed temperature a feedback controller could be employed to compensate for such disturbances by adjusting a valve on me coolant flow to the reac tor jacket. However, suppose an increase occurs in the... 

The objective of crusher control is usually to maximize crusher throughput at some specified product size, without overloading the crusher. Usually onlv three variables can be adjusted feed rate, crusher opening, and feed size in the case of a secondary crusher. Four modes of control for a crusher are (1) Setting overload control,... 

Running unbal- Redesign feed distributor anced—vibration. different bowl speed (usually slower) due to uneven feeding effective vibration monitor/shutdown device Adjust feed rate to get uniform distribution ... 

This is accomplished by constant feed concentrations through adjustment of the feed rate to keep C constant at various temperatures. After plotting the rate versus temperature, the curve can be differentiated, giving the derivative of 3r/3T. The change of the thermodynamic values of (-AH)/pc are minor and can be neglected and used as a constant multiplier of the measured slope. The 0 = V/F must be calculated for each measurement and also multiplied by the measured slope at the constant value of the concentration C. The technique is similar to the measurement of the activation energy discussed in Chapter 5.2. 

Mixers are designed to handle a relatively narrow band of incoming product flow rate. Therefore, care must be exercised to ensure that the actual feed rate is maintained within acceptable limits. The O M manuals provided by the vendor will provide the feed-rate limitations for various products. Normally, these rates must be adjusted for viscosity and temperature variations. 

In Figure 6.6 we have used sugar feed rate as an example of a pre-set feed pattern. In practice we can adjust a wide variety of parameters during the incubation. 

Experimental Procedure. For the initial start-up of the continuous tirred tank reactor, the mixing speed and bath temperature were adjusted with the reactor full of solvent. The polymer seed and monomer feed rates were then adjusted simultaneously. 

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