Thursday, September 27, 2012

Bubble point / Dew point calculations using PRO/II

Bubble point / Dew point calculations using PRO/II

Bubble point / Dew point calculation for single component or mixture can be calculated as follows:

1. Select the required component from the components library and set up a PRO/II model as shown:

Wednesday, August 22, 2012

Depressuring Unit in PRO/II


The Depressuring Unit simulates the time-pressure-temperature relationships which occur when a vessel is depressured through a relief or control valve. The initial phase of the vessel contents may be either a vapor or a vapor-liquid mixture. Several different valve flow models and vessel configurations are available. Several heat input models are also available to simulate the pressuring of the vessel by a fire or other means. An optional external makeup stream may also be specified.
  1. Place a Depressuring Unit from Batch Tab and connect it with a feed and vapor stream
  2. Enter the Initial and Final Depressuring conditions which can be either based on time or pressure
  3. Enter the Calculation options which could be as shown in the figure or can even be left as default values
  4. Enter the Valve data. In this example, the Valve model is based on Supersonic Flow. Please refer to Help for further information about Valve constant – C
  5. Provide the vessel data. There are four options and the final one being Unspecified shape where the user can just enter the Vessel volume
  6. Enter the Heat input data, the various Heat Flow Models are shown in the figure
  7. Run and review results, user can also generate a plot from Output menu as shown

Monday, August 20, 2012

Viewing Binary Interaction Parameters in PRO/II

  1. Click on Launch TDM button in PRO/II
  2. After Thermo Data Manager opens click on the Binary radio button
  3. Then, from the drop down menu, select the Thermodynamic Method that applies to the interaction parameters that are to be viewed
  4. Select the databank for e.g. in the above figure we have selected SIMSCI databank in PRO/II 9.0
  5. Select the components and view the parameter values

Friday, April 6, 2012

Modeling Solvent Extraction Systems

Modeling Solvent Extraction Systems

There are a number of chemical processes used in the refining sector which use solvents to effect a separation of closely boiling systems. They include among others, extraction of aromatics from petroleum feedstocks, separation of C4 and C5 hydrocarbons, and solvent Deasphalting. Each of these processes need comprehensive sets of fitted interaction parameters for proper thermodynamic modeling.

Recent legislation has mandated lower aromatic levels in refinery products, so we will focus on the extraction of aromatics for this blog. There are a number of widely used competing solvent extraction systems and licensors. Typically the licensor has the necessary data at hand to predict or model the performance of their solvent with a given feed stream. A proven track record along with claims or guarantees as to capital and operating cost factor into the decision of an operator in selecting among the competing processes. Commonly used solvents for aromatic extraction include; N-formylmorpholine (NFM), N-methylpyrrolidone (NMP), sulfolane (TETRAHYDROTHIOPHENE 1,1-DIOXIDE) and tetra and triethylene glycols.

The components which are aprotic (not hydrogen bonding) solvents all have similar structures:

These solvents have a high selectivity for aromatics and tend to form liquid-liquid mixtures with other hydrocarbons. A good example for the amount of thermodynamic fitting necessary to accurately model a solvent extraction system would be the Sulfolane Data Bank recently developed by Simsci. Sulfolane was selected by Simsci as the first aromatic extraction system to be modeled as there are over currently 150 extraction units licensed worldwide. The first step in any modeling project is the collection of phase equilibria and process data. For many of these solvent systems published data exist in the open literature, often however the necessary data for modeling are not found in the published literature. The essential part of any solvent extraction model is an accurate representation of the ternaries of the solvent, the aromatics and the similar carbon number non-aromatics, either a paraffin or napthene. For the Sulfolane databank an extensive literature collection was developed at Simsci-Esscor over a period of a number of years.

PROII’s Ternary Plots Tool using a link to Excel, is an excellent way for the user to determine if the important ternaries for any extraction process actually accurately model the equilibria of a system. Both the size of the two phase region and the slope of the tielines need to be well represented. In addition to the viewing the reproduction of the actual phase equilibria, using this tool one can also plot column tray compositions as well. While the methodology was actually conceived as a tool for azeotrophic extractive distillation it works equally well for envisioning solvent extraction processes.

The plot below shows a ternary plot example from our SULFOLANE Databank.

Even once a databank has been developed it will be limited in the number of components having interaction available with the solvent our current databank contains the following components:

We provide VLE and LLE parameters for every binary pair of the above components. An equivalent effort must be made for each one of the other solvents to assure a viable process model is possible. Simsci-Esscor has also been assembling a Bibliography for NFM as an extraction solvent. A final comment as a reminder is in order here, the regression of each of the systems below should been done with the ternaries in mind, even thought the parameters are for the binary pairs.

Written by:

John R. Cunningham
NA Tech Support