Simulating Change in a Steady-State Simulator

Craig Spears

April 30, 2008


With feed streams changing, and with the ever watchful eye on the bottom line, you need to have simulation software that can help steer you in the right direction.

In 2006 Bryan Research & Engineering, Inc. and Crosstex Energy Services, L.P. published an article for Hydrocarbon Engineering titled “Steady-State Simulators are Developing a Dynamic Personality.” This article helps step through one case of designing a ProMax simulation utilizing our Scenario Tool to model changing conditions, and finding an optimum operating condition.

The first step is to model the current plant accurately. This step cannot be stressed enough, because without verifying that your model matches your plant data, how can any changes be successfully modeled?

Sizing and ratings for all equipment should also be set and verified. These calculations will give you information about how close you are to capacity, and whether your exchangers can handle the load being given to them under new cases. Exchangers should have calculators set to drive the percent overdesign to zero. Even if the exchanger was designed with a ten percent overdesign, remember that once it’s placed in the field, all area available to it is being used for heat exchange. Adjusting the outlet temperature or duty of the exchanger to give an overdesign of zero will best match the exchanger operation.

The scenarios should then be decided, and set within our Scenario Tool. The process requirements should be set: overhead specifications, product quality, etc… Also, choosing the variables that might be limiting for any changes made to a process is paramount. Some to think of: actual pressure drops in an exchanger, calculated nozzle sizes in an exchanger, tray flooding in towers, etc...

Once these are set, run the Scenario Tool, and then check the results. Which cases improve plant production or profitability? Which decrease the energy consumption? How much more inlet flow can the plant handle? The possibilities are endless and you can almost always make your company money.

This is not a process that can completely do away with dynamic simulators, as the time element is completely missing. ProMax can tell you what the result will be, but cannot tell you how long it will take to get there. Reminds me a little of thermodynamics.

Authored by Craig Spears - BR&E Sales Department