Stoichiometric reactor

The flowsheet is presented in Figure 2.11. This can be submitted to simulation by using a stoichiometric reactor and a black-box separator. Note that a... 

Table 7.6 gives details of the stoichiometric reactor in Aspen Plus. Note that the reaction 2 is expressed in term of a selectivity variable S, representing the degradation of EDC in heavies. This reaction is responsible also for chlorine production, further involved in other byproducts. The selectivity S may be related with the conversion X of EDC as follows ... 

Table 15.9 presents the main reactions that occur in the pretreatment reactor, modeled as a stoichiometric reactor, and the corresponding conversions. 

The fermentation section is modeled by means of two stoichiometric reactors placed in parallel, followed by a flash for separation of the vapor products (see Figure 5.12). The first reactor (SSCF) describes the saccharification and... 

The reactor modelling in flowsheeting has to supply a reliable description of the transformation of reactants into products, by-products and impurities. The stoichiometric approach is simple but sufficient for material balance purposes. In this example, the stoichiometric modelling needs to know (1) the conversion of the main reaction and (2) the selectivity of the secondary reaction. Hence, in a first attempt we can model the Reactor by a Stoichiometric Reactor model. 

As the main responsible for the changes in the material balance, the chemical reactor must be modelled accurately from this point of view. Basic flowsheeting reactors are the plug flow reactor (PFR) and continuous stirred tank reactor (CSTR), as shown in Fig. 3.17. The ideal models are not sufficient to describe the complexity of industrial reactors. A practical alternative is the combination of ideal flow models with stoichiometric reactors, or with some user programming. In this way the flow reactors can take into account the influence of recycles on conversion, while the stoichiometric types can serve to describe realistically selectivity effects, namely the formation of impurities, important for separations. Some standard models are described below. 

Unit operation model (black box models such as mixers, separators, component splitters, etc. models of phase separation and relaxation, heat-transfer model, multistage models, pumps and compressors, reactor models such as equilibrium reactor, stoichiometric reactor, tubular reactor, etc. see Chapter 2). 

Consider a single reaction. In the stoichiometric reactor models, one specifies the fractional conversion, of key reactant k. 

Figure 15.2 shows the flow sheet of the FP-FC system. The fuel forthe system is an aqueous solution of methanol at the molar ratio of methanol to water of 1 2 for the standard case. The fuel is evaporated in the vaporizer (VAP) at 150°C. In the reformer, the vaporized methanol and water react at 250 °C to form a hydrogen-rich gas, which contains also some CO2 and CO. The steam reformer is modeled as a Gibbs reactor assuming chemical equilibrium between the species at the outlet of the reactor. At the reforming temperature of 250 °C, the equilibrium conversion of methanol is almost 100%. The selectivity of methanol to CO2 is about 97% and to CO about 3%. In the mixer (MIX), the hydrogen-rich gas from the reformer is mixed with a small quantity of air, which is needed for the oxidation of CO present in the product gas from the reformer. The selective CO oxidation takes place in the COS reactor at 150 °C. The COS reactor is modeled as a stoichiometric reactor where 50% of the supplied O2 from the air is used for complete oxidation of CO and the remaining 50% of O2 reacts with H2. 

These two components are separated in a second distillation column (DC2) with AIBU3 being transferred over-head back to the stoichiometric reactor to serve as reaction partner for chain growth while the longer chain products are isolated as commercial products. 

A preferential oxidation (PROX) unit. This is modelled in the Aspen flow sheet code by two stoichiometric reactors, one to perform the PROX of carbon monoxide and the subsequent one to remove the remaining oxygen via reaction with hydrogen. These have been removed in the flow sheet shown below and shown as a single unit, as would be experienced in practice. 

Reactors. The way in which reactors are specified depends on a combination of the input information required and the reactor category. Generally there are four categories of reactor stoichiometric reactor, kinetic (plug flow or CSTR) reactor, equilibrium reactor, and batch reactor. All these reactor configurations require input concerning the thermal mode of operation adiabatic, isothermal, amount of heat removed or added. Additional information is also required. Each reactor type is considered separately below. 

In Problem 1 above, you should have simulated the reactor as a stoichiometric reactor with 75% per pass conversion. In order to estimate the volume of the reactor, it is necessary to have kinetics expressions. For the catalytic hydrodealkylation of toluene, assume that the reaction is kinetically controlled with the following kinetics ... 

Stoichiometric reactors, simulating, 435 Storage tanks. See also Product storage. 

Aspen is capable of modeling chemical reactions. It can handle single and multiple reactions. Material balance can be done in the stoichiometric reactor, Rsto/c from Reactors in the model library. Click on Material Streams, and connect the inlet and product streams. Click on Components and choose the components involved. Peng-Robinson EOS is selected as the thermodynamic fluid package. Doubleclick on the conversion reaction block. Click on the Specification tab enter pressure as 1 atm and temperature as 25°C. Then click on the Reactions tab, click on New and enter the components involved in the reaction, stoichiometric coefficient, and fractional conversion as shown in Figure 3.13. Close the stoichiometric windows and then double click on the inlet stream, specify temperature, pressure, flow rate, and composition. Click Run and then generate the stream table as shown in Figure 3.14. 

Aspen can handle multiple reactions. For material balance on multiple reactions, select a stoichiometric reactor (Rstoic) from the reactors subdirectory... 

Neglecting change in kinetic and potential energy, the change in the enthalpy of single reaction taking place in a stoichiometric reactor is... 

In order to implement the process steps into the Aspen Plus simulator, the stoichiometric reactor unit was used when the process involved a reaction system, and the flash unit was used for the LIME and ammonia fiber explosion (AFEX) pretreatments (in which there are no reactions). The operation conditions specified in these units, for each process, are shown in Table 2.6. 

Reactor Stoichiometric reactor model (RStoic) for reactions, tubular kinetic reactor (RPlug) to estimate temperature drop. Aluminium-oxide catalyst dominating reaction ethanol conversion... 

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