PetroBob
Chemical
- Dec 23, 2005
- 60
I've been asked to model a sour water stripper that will use natural gas to strip H2S from sour water, using VMG Sim/Symmetry process modelling software. (My company moved away from using HYSYS due to the high cost and insufficient oil industry work in recent years; we only have VMG Sim now.)
How good a tool are process simulators like VMG Sim and HYSYS at modelling this process? We are only doing high level design at this stage, and the main information I need from the simulation is gas flowrate into the column and size of column. Are process simulators a good tool to determine the approximate gas flowrate? Or is it more efficient and more accurate to get this information from vendors?
Also we know that the effectiveness of the stripping is strongly affected by pH, we will likely be operating at around pH 6 (ie above the optimal pH of 5 or thereabouts for gas stripping for H2S removal). I know HYSYS and VMG Sim don't model water chemistry effects like this; is there a way I can fudge this pH effect eg by entering a lower efficiency for the trays or somesuch? I have a senior water chemist supporting this project.
Our first crack at modelling this (not considering pH effects) showed lower gas flowrates than we expected, and very efficient H2S removal which we're not convinced matches reality - despite setting the tray efficiency to 40% on all trays. I believe overall H2S removal would be in the range of 90 to 95% H2S removal (based on vendor's feedback) - whereas our modelled column removed H2S in water from inlet spec of 800 ppm H2S to outlet spec of 4 ppm at 60 degF (16 degC) which seems an unlikely efficiency even at perfect pH.
I ran a temperature sensitivity and got H2S in outlet ranging from 0.1 ppm (at 65 degC) to 11.5ppm (at 5 degC) - changing nothing else including gas flowrate. It all seems awesomely efficient! And temperature having less effect than I would expect. (I'd have thought that 5 degC would have very inefficient gas stripping compared with 65 degC.) Am I right to be suspicious of these results? How can I make my model be less
To cross-check my simulation building, is there any simple online guide that goes through the steps required to build a sour water stripper in HYSYS or VMG simulation? Or would someone be willing to give me a quick dotpoint list of the steps they'd take to build this model? Given I am way out of practise at doing process modelling (haven't had much oil work in years now due to the recession in our region), I never modelled a gas stripper even back when I was doing refinery design, and it's a long time since I did this at university. Any advice welcome!
How good a tool are process simulators like VMG Sim and HYSYS at modelling this process? We are only doing high level design at this stage, and the main information I need from the simulation is gas flowrate into the column and size of column. Are process simulators a good tool to determine the approximate gas flowrate? Or is it more efficient and more accurate to get this information from vendors?
Also we know that the effectiveness of the stripping is strongly affected by pH, we will likely be operating at around pH 6 (ie above the optimal pH of 5 or thereabouts for gas stripping for H2S removal). I know HYSYS and VMG Sim don't model water chemistry effects like this; is there a way I can fudge this pH effect eg by entering a lower efficiency for the trays or somesuch? I have a senior water chemist supporting this project.
Our first crack at modelling this (not considering pH effects) showed lower gas flowrates than we expected, and very efficient H2S removal which we're not convinced matches reality - despite setting the tray efficiency to 40% on all trays. I believe overall H2S removal would be in the range of 90 to 95% H2S removal (based on vendor's feedback) - whereas our modelled column removed H2S in water from inlet spec of 800 ppm H2S to outlet spec of 4 ppm at 60 degF (16 degC) which seems an unlikely efficiency even at perfect pH.
I ran a temperature sensitivity and got H2S in outlet ranging from 0.1 ppm (at 65 degC) to 11.5ppm (at 5 degC) - changing nothing else including gas flowrate. It all seems awesomely efficient! And temperature having less effect than I would expect. (I'd have thought that 5 degC would have very inefficient gas stripping compared with 65 degC.) Am I right to be suspicious of these results? How can I make my model be less
To cross-check my simulation building, is there any simple online guide that goes through the steps required to build a sour water stripper in HYSYS or VMG simulation? Or would someone be willing to give me a quick dotpoint list of the steps they'd take to build this model? Given I am way out of practise at doing process modelling (haven't had much oil work in years now due to the recession in our region), I never modelled a gas stripper even back when I was doing refinery design, and it's a long time since I did this at university. Any advice welcome!
