The accurate selection of property methods and thermodynamic models in Aspen Plus process simulation

Thread Content

The proper selection of property methods and thermodynamic models in Aspen Plus process simulation: Multiple thermodynamic models are used in Aspen Plus process simulation, and the appropriate selection and correct use of these models determine the accuracy, reliability of the calculation results, as well as the success of the simulation. Therefore, in the second lecture on Aspen process simulation, Xiao 7 has compiled for you the methods and criteria for selecting thermodynamic models in Aspen. In the process simulation of Aspen Plus, the calculation of thermodynamic properties is required for almost all unit operation models. To date, no single thermodynamic model has been able to apply to all material systems and all processes. Multiple thermodynamic models are required in process simulation, and the proper selection and correct use of these models determine the accuracy, reliability of the calculation results, as well as the success of the simulation. Property methods and thermodynamic models in Aspen: https://pic2.zhimg.com/v2-83a0e4fd295265059f53f99fefe0bfa5_b.jpg https://pic1.zhimg.com/v2-93738407bba340a5b4d2e32e90af9a0c_b.jpg The selection of properties is based on the characteristics of the system as well as empirical considerations related to operating temperature and pressure: https://pic1.zhimg.com/v2-8d6ce38e7d0bce09389d9cb1738bc818_b.jpg https://pic4.zhimg.com/v2-51a740a1d5bdd4b069e7446645bc2fb3_b.jpg https://pic4.zhimg.com/v2-261422c060707c7e653d200030e65a93_b.jpg https://pic2.zhimg.com/v2-c636e65ce9fbe7a474d74111a37c5add_b.png Taking the propylene, benzene, and isopropylbenzene systems as examples, since these are non-polar systems, property methods such as PENG-ROB, RK-SOAVE, PR-BM, and RKS-BM can be chosen taking into account real-world conditions. The choice of Aspen property methods depends on the type of components; for general chemical systems with pressures greater than 10 bars, equation of state models with advanced mixing rules are used, such as Wong-Sandler, MHV1, MHV2, or Mathias-Klotz-Prausnitz mixing rules. Other options include SR-POLAR, PRWS, RKSWS, PRMVH2, RKSMVH2, SRK, PSRK, HYSGLYCO, etc. Generally, to obtain the best results, many equation of state require binary interaction parameters. If you do not know the binary interaction parameter, use predictive equation of state such as SR-POLAR or PSRK. For refrigerants, REFPROP is the best choice. For pressures not exceeding 10 bars, the activity coefficient method is used, such as NRTL, Wilson, UNIQUAC, or UNIFAC. But several factors still need to be considered: whether the carboxylic acid is present ； Electrolyte system ； Henry component (incompressible component) ； Is HF present? ； Whether a two-liquid-phase system exists. Hydrocarbon systems include crude oil evaluation or virtual components. In a vacuum environment, BK10 (Braun K-10) or MXBONNEL (Maxwell-Bonnell) is generally used; in a non-vacuum environment, CHAO-SEA (Chao-Seader) or Grayson (Grayson-Streed) is usually employed. The state equation versions HYSSRK and HYSPR from HYSYS can also be used. If the system contains hydrogen, BK10 (Braun K-10) or equation of state models such as SRK (Soave-Redlich-Kwong) and PENG-ROB (Peng-Robinson) can also be used. Standard equation of state, such as PENG-ROB (Peng-Robinson), SRK (Soave-Redlich-Kwong), or LK-PLOCK (Lee-Kesler-Plocker), are generally used when crude oil evaluation or virtual components are not involved. The HYSYS versions of the equations of state, HYSSRK and HYSPR, can also be used. Special systems (water, amines, acid water, carboxylic acids, HF, electrolytes). Amines can be of the following types: AMINES: Kent-Eisenberg model ； ELENRTL: NRTL model for electrolytes with the Redlich-Kwong equation of state ； ENRTL-RK: An enhanced version of ELECNRTL. Like ELECNRTL, it utilizes asymmetric standard states. Mixtures containing carboxylic acids (such as acetic acid) are generally simulated using activity coefficients based on the Nothnagel or Hayden-O’Connel models for gas-phase association, such as NRTL-HOC or WILS-NTH. Organic acids such as acetic acid form dimers in the gas phase, and specific models are required to explain the behavior of the non-ideal phase. Electrolyte systems can use the ELENRTL model: an electrolyte NRTL model with a Redlich-Kwong equation of state (suitable for aqueous or mixed systems); ENRTL-RK: an enhanced version of ELECNRTL. Like ELECNRTL, it employs asymmetric standard states ； ENRTL-SR: Similar to ENRTL-RK, except that it uses a symmetric standard state (applicable to both aqueous and non-aqueous electrolyte systems) ； PITZER: Pitzer is applicable to aqueous electrolyte systems. Additionally, you can use the system’s built-in Electrolyte Wizard to help create the desired reactions and reactants. For gas-phase association, HF can be used with WILS-HF or ENRTL-HF, or any activity coefficient method that incorporates an HF equation of state. You can also use the built-in WILS-HF or ENRTL-HF property methods. But if you prefer a different activity coefficient equation (such as NRTL), you can also start by using the WILS-HF property method, and then go to Properties\Property Methods\Model Table to select the NRTL model. Furthermore, HF first forms hexamers in the gas phase, and a specific model is required to explain the state of this non-ideal phase; therefore, the equation of state model that can be used is ESHF. The refrigerant properties can be calculated using the REFPROP property method developed by NIST. The acid water system can use APISOUR: the API acid water method. Systems with only water STEAM-TA: ASME 1967 steam table statistics ； STEAM-NBS: 1984 NBS steam table ； STEAMNBS2: The 1984 NBS steam table; it is similar to STEAMNBS, but the root-search method is different ； IAPWS-95: Formulas proposed by IAPWS in 1995 for practical and scientific applications ； IAPWS-95: The currently recommended standard properties for water and steam. The refrigerant system can be modeled using the REFPROP property method developed by NIST. “For specific types of processes, in general chemical systems, a basic activity coefficient approach is sufficient, such as NRTL, WILSON, UNIQUAC, and their variations. For the preliminary design, either the original UNIFAC or the Dortmund-enhanced UNIFAC (UNIF-DMD) can be used. For pressures greater than 10 bars, state equations with advanced mixing rules are used, such as the Wong-Sandler, MHV1, MHV2, or Mathias-Klotz-Prausnitz mixing rules. Other options include SR-POLAR, PRWS, RKSWS, PRMVH2, RKSMVH2, SRK, PSRK, HYSGLYCO, etc. Electrolyte systems can be represented using the ELENRTL model: an electrolyte NRTL model with a Redlich-Kwong equation of state, suitable for aqueous or mixed systems. (1) ENRTL-RK: An enhanced version of ELECNRTL; like ELECNRTL, it employs an asymmetric standard state ； (2) ENRTL-SR: Similar to ENRTL-RK, except that it uses a symmetric standard state (which can be applied to aqueous or anhydrous electrolyte systems) ； (3) PITZER: Pitzer is applicable to aqueous electrolyte systems. Additionally, you can use the system’s built-in Electrolyte Wizard to help create the desired reactions and reactants. For general environmental applications, a basic activity coefficient approach is sufficient, such as NRTL, WILSON, UNIQUAC, and their variations. For the preliminary design, Dortmund’s improved UNIFAC (UNIF-DMD) can be used. The most important aspect of such applications is the ability to accurately represent the behavior of trace components; therefore, to ensure that the property method you choose can accurately describe the activity coefficient of the trace components of interest at infinite dilution, remember to check and adjust the appropriate binary interaction parameters. For natural gas processes, a fundamental equation based on cubic relationships is generally sufficient; examples include PENG-ROB or SRK. The state equations HYSSRK and HYSPR, which are part of the HYSYS software, can also be used. GERG2008 is used for the calculation of natural gas storage and transfer. For mining and metallurgy, SOLIDS or FACT physical property methods are selected in pyrometallurgy. The FACT method requires external ChemSage data files and ChemApp certificates, which can be configured in the Aspen/FACT/ChemApp interface. For hydrometallurgy, the ELECNRTL or ENRTL-RK property methods are sufficient. For oil and gas, a fundamental equation based on cubic relations is generally sufficient, such as PENG-ROB, RK-SOAVE, SRK, PR-BM, RKS-BM, HYSPR, HYSSRK, or PC-SAFT. In petrochemistry, property equations can be selected widely based on the contents involved in the process. Both the equation of state and activity coefficients may be used. Aggregation uses an aggregate property method; for example, PC-SAFT: PC-SAFT is suitable for copolymers. This model controls association ； POLYNRTL: Polymer-NRTL/Redlich-Kwong equation of state with Henry’s law ； POLYFH: Flory-Huggins/Redlich-Kwong equation of state with Henry’s law ； POLYSL: Sanchez-Lacombe ； POLYSRK: Redlich-Kwong-Soave equation of state with predicted polymerization ； POLYUF: obeys Henry’s law UNIFAC/Redlich-Kwong equation of state ； POLYUFV: obeying Henry’s law, UNIFAC free volume/Redlich-Kwong equation of state ； POLYPCSF: Perturbed-Chain statistical association fluid theory (PC-SAFT) ； EPNRTL: The Electrolyte-Polymer NRTL model consistent with the Redlich-Kwong equation of state. Suitable for aqueous solutions, mixed solutions, and also polymerization. These methods can be applied in the presence of Polymers Plus and Aspen Properties. The dynamics can be used with the combustion database via PR-BM or RKS-BM. For steam cycles, a steam table method (STEAM-TA, STEAMNBS, or IAPWS-95) can be used. IAPWS-95: The currently recommended standard properties for water and steam. Refining general property methods such as BK10, Chao-Seader, and Grayson-Streed are suitable for application in this type. Fundamental property equations for a cubic equation, such as Peng-Robinson or SRK, can also be used for simulation. General physical property methods used in pharmaceuticals, such as NRTL, UNIFAC, NRTL-SAC, COSMOSAC, or HANSEN, are suitable for application in this type.