Adding Material Streams

Sidestream Column. The RadFrac block in Aspen Plus can be used for the ordinary distillation column with one feed stream and two outlet streams (distillate and bottoms). This block can also be used for multiple feed streams or more than two ordinary outlet streams. For example, the extractive distillation column in Section 3.1 demonstrated that two feed streams can be connected to the RadFrac block. In a similar way, more outlet streams can be drawn out of the RadFrac block as a sidestream column. The sidestream draw-off can be either a liquid stream or a vapor stream. AU these varieties of different columns can easily be configured by adding material streams to the flowsheet with the RadFrac block (see previous Fig. 3.5). 

A simulation of a DWC based on the equivalent Petlyuk column has two recycle loops, which requires two recycle blocks (R1 and R2), as shown in Figure 9.6b. The prefractionator column (Pref) has neither reboiler nor condenser, which can be simulated using an absorber column. This column has two recycle streams, which includes a recycled vapor stream to a prefractionator (Vapor pre in) at the bottom, and the recycled liquid stream to the prefractionator (Liquid pre in) at the top. These two streams need the initial estimates to solve the Pref column. A distillation unit for the main column, the material streams. Feed, Vapor pre out. Liquid pre out. Liquid Main out. Vapor Main out. Distillate, Side, and Bottom for Main column are added to the flow sheet. Two recycle blocks need to be added to the flow sheet one recycle block (Rl) for the Liquid Main out and another (R2) for Vapor Main out to initialize the recycle stream. Once the Pref is solved, the main column is simulated with an estimated number of stages and stage locations from the shortcut calculation. 

Material Streams are used to transport the material components from process units in the simulation. A material stream can be added to the flowsheet in one of three ways ... 

In designing a conventional single column, the RadFrac model in Aspen Plus is used. To use a. MultiFrac model with a Peflyuk configuration, select the appropriate icon and drop it onto the process flow diagram as shown in Figure 12.2. Then feed, distillate, and bottoms material streams are added as shown in Figure 12.3. The model block is labeled DWC. 

Because of economic considerations, an increasing volume of resin is shipped in the natural or uncolored state. Color must be added at the plant level before the material is fed to the processing machine. This, along with the fact that most processing operations produce scrap which must be reintroduced into the material stream, has led to numerous systems for blending these various ingredients. 

Sepro Conta.iner, The Sepro container consists of a collapsible plastic bag fitted into a standard three-piece, tin-plated container such as a 202 X 214, 202 x 406, or 202 x 509 can. The product is placed within the bag, and the propellant is added through the bottom of the container, which is fitted with a one-way valve. There is no limitation on the viscosity of the product but compatibiUty with the plastic bag must be considered. A free-dowing hquid can be dispensed either as a stream or a fine spray, depending on the type of valve employed. A viscous material is often dispensed as a stream. This system has been used for caulking compounds, postfoaming gels, and depilatories. 

Flocculating agents differ from other materials used in the chemical process industries in that their effect not only depends on the amount added, but also on the concentration of the solution and the point at which it is added. The process streams to which flocculants are added often vary in composition over relatively short time periods. This presents special problems in process control. 

Possible interferences and variation of results from modified techniques can be avoided by titrating the sample in exacdy the same way and by employing approximately the same amounts of materials as in the initial standardization of the ferrous sulfate against a known quantity of nitric acid. The ferrous sulfate solution is added in a thin stream until the initially yellowish solution turns brown. The titration is complete when the faint brownish-tinged end point is reached. 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Chlorination of Hydrocarbons or Chlorinated Hydrocarbons. Chlorination at pyrolytic temperatures is often referred to as chlorinolysis because it involves a simultaneous breakdown of the organics and chlorination of the molecular fragments. A number of processes have been described for the production of carbon tetrachloride by the chlorinolysis of various hydrocarbon or chlorinated hydrocarbon waste streams (22—24), but most hterature reports the use of methane as the primary feed. The quantity of carbon tetrachloride produced depends somewhat on the nature of the hydrocarbon starting material but more on the conditions of chlorination. The principal by-product is perchloroethylene with small amounts of hexachloroethane, hexachlorobutadiene, and hexachloroben2ene. In the Hbls process, a 5 1 mixture by volume of chlorine and methane reacts at 650°C the temperature is maintained by control of the gas flow rate. A heat exchanger cools the exit gas to 450°C, and more methane is added to the gas stream in a second reactor. The use of a fluidi2ed-bed-type reactor is known (25,26). Carbon can be chlorinated to carbon tetrachloride in a fluidi2ed bed (27). 

The material balance table can be supplemented with temperatures, pressures, phases, and stream enthalpies (or internal energies). Utility flows and conditions should be added to the process information. 

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