HYSYS simulation of CO2 removal by amine absorption from a gas based power plant

Abstract A simplified combined cycle gas power plant and a MEA (monoethanol amine

Simulation of Condensation in Biogas containing Ammonia

Condensation in raw biogas during compression is a problem because the CO2 and water in the liquid phase is very corrosive. Raw biogas typically contains 60 mol-% methane, 40 mol-% CO2, is saturated with water and may contain contaminants as ammonia (NH3). In case of NH3, it is of interest whether it has influence on the dew point (condensation) temperature. The aim of this work is to calculate the dew point under different conditions using different equilibrium models. Phase envelopes showing the two-phase area are also calculated. For dry mixtures of methane and CO2 with up to 1 mol-% NH3 (a high value for biogas), the different models gave similar results. When the NH3 increased from 0 to 1 mol-%, the dew point temperature increased with approximately 3 K. When water was included, the amount of calculated NH3 dissolved in water varied considerably with the model. The electrolyte based models Sour PR, Sour SRK and Electrolyte NRTL did not calculate reasonable dew point temperatures, but the dissolved amounts of NH3 and CO2 were more reasonable using the electrolyte models compared to using PR or SRK. For biogas simulation including NH3, a simple equation of state as PR or SRK can be recommended to determine the dew point. If accurate composition of the condensed liquid is to be calculated, an electrolyte based model like Sour PR, Sour SRK or the Electrolyte NRTL is recommended.publishedVersio

Simulation-based Cost Optimization tool for CO2 Absorption Processes: Iterative Detailed Factor (IDF) Scheme

A simple, fast, and accurate process simulation based cost estimation and optimization scheme was developed in Aspen HYSYS based on a detailed factorial methodology for solvent-based CO2 absorption and desorption processes. This was implemented with the aid of the spreadsheet function in the software. The aim is to drastically reduce the time to obtain cost estimates in subsequent iterations of simulation due to parametric changes, studying new solvents/blends and process modifications. All equipment costs in a reference case are obtained from Aspen In-Plant Cost Estimator V12. The equipment cost for subsequent iterations are evaluated based on cost exponents. Equipment that are not affected by any change in the process are assigned a cost exponent of 1.0 and the others 0.65, except the absorber packing height which is 1.1. The capital cost obtained for new calculations with the Iterative Detailed Factor (IDF) model are in good agreement with all the reference cases. The IDF tool was able to accurately estimate the cost optimum minimum approach temperature based on CO2 capture cost, with an error of less than 0.2%.publishedVersio

Simulation and Impact of different Optimization Parameters on CO2 Capture Cost

The influence of different process parameters/factors on CO2 capture cost, in a standard amine based CO2 capture process was studied through process simulation and cost estimation. The most influential factor was found to be the CO2 capture efficiency. This led to investigation of routes for capturing more than 85% of CO2. The routes are by merely increasing the solvent flow or by increasing the absorber packing height. The cost-efficient route was found to be by increasing the packing height of the absorber. This resulted in 20% less cost compared to capturing 90% CO2 by increasing only the solvent flow. The cost optimum absorber packing height was 12 m (12 stages). The cost optimum temperature difference in the lean/rich heat exchanger was 5 °C. A case with a combination of the two cost optimum parameters achieved a 4% decrease in capture cost compared to the base case. The results highlight the significance of performing cost optimization of CO2 capture processes.publishedVersio

Applicability of NRTL Model for Prediction of the Viscosity of Alkanolamine + Water Mixtures

This study discusses the applicability of the non-random two-liquid (NRTL) model to represent viscosity for MEA (monoethanol amine) + H2O and AMP (2-amino-2-methyl-1-propanol) + MEA (monoethanol amine) + H2O mixtures under different amine concentrations at temperature ranges of 293.15 K– 363.15 K and 293.15 K – 343.15 K respectively. The NRTL model is adopted to determine excess Gibbs free energy of mixing and the Eyring’s viscosity model based on absolute rate theory is used to obtain excess free energy of activation for viscous flow. The correlations are proposed for the viscous flow as a function of concentration of the components, temperature and Gibbs free energy. Correlations are capable of representing measured viscosities at 1.3% and 0.3% of absolute average relative deviation (AARD %) for MEA + H2O and AMP + MEA + H2O mixtures respectively. These deviations are acceptable for engineering calculations and correlations can be used in process design and simulations like Aspen HYSYS and ASPEN Plus

Simulation of Condensation in Compressed Raw Biogas Using Aspen HYSYS

Raw biogas typically contains 60 % methane, 40 % CO2, small amounts of other components and is saturated with water. It is a question whether raw biogas can be compressed to high pressures without condensation. The aim of this work is to calculate the condensation limit under different conditions with varied temperature, pressure and gas composition using different equilibrium models. Traditionally, gas mixtures of methane, CO2 and water are calculated in a process simulation program with standard models like Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). PR and SRK with the a-function replaced with a Twu a-function were also evaluated. For mixtures with only methane and CO2 (dry biogas) all the models gave similar results. Under normal ambient temperatures (above 0 °C), a dry mixture with more than 40 % methane will not give any condensation. For biogas saturated with water, the different models gave similar results up to about 70 bar when binary coefficients were included, but above this pressure there were significant deviations between the models. The PR and SRK with standard or Twu a-function gave reasonable results for the dew-point predictions, but above about 70 bar the uncertainty increases.Simulation of Condensation in Compressed Raw Biogas Using Aspen HYSYSpublishedVersio

Impact of Uncertainty of Physical Properties on CO2 Absorption Design

The mass transfer coefficients, interfacial area and pressure drop of a packed bed are essential properties that need to be evaluated prior to the design of a CO2 absorption column. Various mathematical models have been proposed to predict these properties under different process conditions. This work has compared several mathematical models for pressure drop, mass transfer coefficients and interfacial area and discussed how the uncertainty of physical properties and process conditions affect the evaluation of packed bed height in a CO2 absorption column. A case study has been performed to study the propagation of uncertainty in input variables through the packed bed height design equations. Here, it was found as 12% from uncertainty in physical properties and 60% from uncertainty in choice of mathematical model of the calculated packed bed height. A recommended safety factor for the absorption packing height is 60 % for a generic packing, but this safety factor can be reduced considerably if experimental data for pressure drop and mass transfer coefficients are available for the specific packing

Simulation of Condensation in Compressed Raw Biogas Using Aspen HYSYS

Raw biogas typically contains 60 % methane, 40 % CO2, small amounts of other components and is saturated with water. It is a question whether raw biogas can be compressed to high pressures without condensation. The aim of this work is to calculate the condensation limit under different conditions with varied temperature, pressure and gas composition using different equilibrium models. Traditionally, gas mixtures of methane, CO2 and water are calculated in a process simulation program with standard models like Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). PR and SRK with the a-function replaced with a Twu a-function were also evaluated. For mixtures with only methane and CO2 (dry biogas) all the models gave similar results. Under normal ambient temperatures (above 0 °C), a dry mixture with more than 40 % methane will not give any condensation. For biogas saturated with water, the different models gave similar results up to about 70 bar when binary coefficients were included, but above this pressure there were significant deviations between the models. The PR and SRK with standard or Twu a-function gave reasonable results for the dew-point predictions, but above about 70 bar the uncertainty increases

Simulation of Condensation in Compressed Raw Biogas Using Aspen HYSYS

Raw biogas typically contains 60 % methane, 40 % CO2, small amounts of other components and is saturated with water. It is a question whether raw biogas can be compressed to high pressures without condensation. The aim of this work is to calculate the condensation limit under different conditions with varied temperature, pressure and gas composition using different equilibrium models. Traditionally, gas mixtures of methane, CO2 and water are calculated in a process simulation program with standard models like Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). PR and SRK with the a-function replaced with a Twu a-function were also evaluated. For mixtures with only methane and CO2 (dry biogas) all the models gave similar results. Under normal ambient temperatures (above 0 °C), a dry mixture with more than 40 % methane will not give any condensation. For biogas saturated with water, the different models gave similar results up to about 70 bar when binary coefficients were included, but above this pressure there were significant deviations between the models. The PR and SRK with standard or Twu a-function gave reasonable results for the dew-point predictions, but above about 70 bar the uncertainty increases