Aspen Plus absorption

Next, we present results obtained by using Aspen Plus [23], Using the Uniquac-RK model with Henry components for supercritical gases ensures correct description of the absorption-desorption process. Table 11.7 shows the composition of streams around the reactor and the first separation step. 

Figure 6.8. Absorption column parameters in Aspen Plus.

This chapter introduced you to the many thermodynamic models available in Aspen Plus. The equations for short-cut distillation were summarized, and the Aspen Plus was used to solve a variety of distillation problems, with either short-cut methods (DSTWU) or plate-to-plate methods (RadFrac). You also learned how to solve gas absorption problems using Aspen Plus. 

This unit can simulate any type of separation processes, as distillation, absorption, stripping, or extraction columns, modelled as cascade of counter-current equilibrium stages. The model Radfrac in Aspen Plus is particular powerful. It is first built on the inside-out algorithm that increased dramatically the robustness in simulating distillation-based operations (Boston, 1980). Columns with multiple feeds, side streams products, stage heaters or coolers, can be treated, as illustrated in Fig. 3.13. The following capabilities are generally available ... 

In natural gas, methane is the main component, and other hydrocarbons such as ethane, propane and butane may be present in smaller quantities. Water, H2S and CO2 are also present as impurities in natural gas, and they have to be removed before pumping the natural gas through pipelines. An amine absorption process is commonly used for removing these impurities. Nowadays, membranes are being explored for natural gas processing (Baker and Lokhandwala, 2008 Ahmad et al, 2012 Niu and Rangaiah, 2014). This section presents simulation and optimization of such a membrane separation process for two objectives, using Aspen Plus, ACM, I-MODE and interface between Aspen Plus and Excel. As mentioned earlier, chemical processes can be simulated in Aspen Plus. In Section 4.3, a membrane model has been implemented in ACM, which can be added to Aspen Plus. 

An NGL plant was selected to analyze several distillation assisted heat pump processes when compared to conventional distillation. The depropanizer column which is the third column of the NGL plant was suitable for retrofitting by heat pump systems. This conventional process, along with top vapour recompression, bottom flashing and absorption heat pumps, were simulated using the Aspen Plus software, in order to determine economically the best alternative. Distillation with both top vapor recompression and bottom flashing heat pumps allows reduction of operation (energy) costs by 83.3% and 84%, respectively. This improves the economic potential (incorporating capital costs) by 53% and 54%, respectively. 

Fig. 4. Aspen Plus flow diagram for the absorption heat pump.

Aspen Plus amine package for C02 absorption reaction Water wash ... 

The kinetic model contains concentration terms given as activities. The overall reaction rate is not a simple power law but has absorption terms in LHHW form. This type of chemical kinetic cannot be used in the standard Aspen Plus reactive distillation model. The various formulas follow for the overall reaction rate (mol/s) ... 

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