Reactor distribution control

The batch process is similar to the semibatch process except that most or all of the ingredients are added at the beginning of the reaction. Heat generation during a pure batch process makes reactor temperature control difficult, especially for high soHds latices. Seed, usually at 5—10% soHds, is routinely made via a batch process to produce a uniform particle-size distribution. Most kinetic studies and models are based on batch processes (69). 

Molecular Weight Distribution Control in Continuous-Flow Reactors... 

The reactor pressure is reduced to 0 psig to flash off any remaining water after a desired temperature is reached. Simultaneous ramp up of the heat source to a new setpoint is also carried out. The duration spent at this second setpoint is monitored using CUSUM plots to ensure the batch reaches a desired final reactor temperature within the prescribed batch time. The heat source subsequently is removed and the material is allowed to continue reacting until the final desired temperature is reached. The last stage involves the removal of the finished polymer as evidenced by the rise in the reactor pressure. Each reactor is equipped with sensors that measure the relevant temperature, pressure, and the heat source variable values. These sensors are interfaced to a distributed control system that monitors and controls the processing steps. 

Cylinders have the advantage that they are cheap to manufacture. In addition to varying the shape, the distribution of the active material within the pellets can be varied, as illustrated in Figure 6.7. For packed-bed reactors, the size and shape of the pellets and the distribution of active material within the pellets can be varied through the length of the reactor to control the rate of heat release (for exothermic reactions) or heat input (for endothermic reactions). This involves creating different zones in the reactor, each with its own catalyst designs. 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

G.R. Meira. Forced oscillations in continuous polymerization reactors and molecular weight distribution control. A survey. J. Macromol. Sci.- Rev. Macro-mol. Chem., 20(2) 207-241, 1981. 

In 1989, the NDF Company opened a facility in Georgetown, South Carolina to produce low density polyethylene. Manufacturing of the polyethylene is done in two 50-ton reactors that are encased individually within their own 8-story-high process unit. The main raw materials for the manufacturing operations include ethylene, hexane, and hutene. The polymerization is completed in the presence of a catalyst. The hase chemicals for the catalyst are aluminum alkyl and isopentane. The reactor and catalyst preparation areas are on a distributed control system (DCS). A simplihed process flow diagram is attached. 

The two requirements, small reactor size and maximization of desired product, may run counter to each other. In such a situation an economic analysis will yield the best compromise. In general, however, product distribution controls consequently, this chapter concerns primarily optimization with respect to product distribution, a factor which plays no role in single reactions. 

One major emphasis in this book is the focus of reactor design on the control of temperature, simply because temperature plays such a dominant role in reactor operation. However, in many reactors the control of other variables is the ultimate objective or determines the economic viability of the process. Some examples of these other properties include reactant or product compositions, particle size, viscosity, and molecular weight distribution. These issues are discussed and studied in subsequent chapters. 

Effective solutions to the problems of the vacuum residue hydrodesulfurization unit equipped with the fixed bed reactors, such as a hot spot, pressure-drop buildup, and catalyst deactivation by coke fouling, were discussed. Improving liquid distribution can prevent hot spot occurrence. Dispersing inorganic solids throughout the reactors can control a pressure-drop increase in the first bed. For a high conversion operation, controlling the conversion in each bed can minimize the coke deactivation in the fourth bed. 

The optimal control of the two-phase tubular reactors had been formulated by Kassem (1977). A distributed minimum principle was presented and the necessary conditions for optimality were derived. Based on these conditions for optimality a functional gradient aigorichm for synthesizing boundary and distributed controls were deduced. 

A wide variety of reactor processes have been reported in the literature and especially in patents. Most reactor designs are aimed at narrowing particle size distributions, controlling copolymer composition and/or particle morphologies, or reducing wall fouling and particle aggregation. 

Precipitation is an operation known for producing small crystals that are difficult to filter and dry. Batch precipitation is usually carried out in the form of a semibatch process, i.e., one or two reactants are continuously added to the reactor. The control of the particle size distribution in a precipitation process is very complicated because of the high level of supersaturation generated by the fast reaction. According to Mersmann [16], the important factors for sparingly soluble systems in isothermal precipitation are ... 

Number of Injection Points The hot spot within a multi-injection reactor is controlled mainly by the amount of injection points (Af). For a first approximation of the temperature rise at each injection point, a simplified system can be considered [34]. For the case of instantaneous mixing and reaction with an equally distributed flow among the injection points (1 2i = 22 = = = 2o/ )>... 

As mentioned earlier, the most commonly employed alkylene oxides for producing block nonionic surfactants are the very reactive three-membered cyclic ethers such as EO and PO. Particularly, EO is highly flammable, explosive in some condition, and also toxic and an irritant for skin and eyes. For these reasons, the reactor employed in the synthesis, described earlier, must be equipped with sophisticated safety devices, process monitoring systems, and distributed control systems (DCS) to keep the reaction in safety condition and avoid gas-phase decomposition and the so-called runaway... 

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