There is a lot of interest in modelling flare networks dynamically these days. Although the HYSYS Dynamics pipe segment doesn't model all phenomena rigorously, you can do a pretty good job with it. What the pipe segment is lacking is the momentum balance and it does't account for kinetic energy. So, you should use it to evaluate what happens in the really short term after opening a relief valve. I mean, not what exactly happens in the first couple of seconds. The lack of kinetic energy term will affect the temperature results, but the deviations shouldn't be too larger. I have no direct comparison of dynamic cases, but steady state cases indicate it should be within a couple of degrees C.
With that out of the way, there are a couple of practical things that are good to know when you start modelling a flare network in dynamics.
- HYSYS Steady State has no network solver (except Aspen Hydraulics), so it may be just as easy to start in dynamics right away.
- Start with a case where you actually do have flow from all sources. It doesn't need to be the full flow, but some flow for sure.
- As the dynamic solver is more prone to failing once in a while, make sure you frequently save things.
- Build up the network a couple of pipes at a time.
- Do NOT try to put all the detail you have into the model. lump all the bends and tees and whatever else into a single fitting. A swage is a particularly nasty one to have. The problem being that a swage that enlarges the pipe diameter increases the pressure, so HYSYS Dynamics will translate that into a negative k-value and when your flow goes away from the flow where it was calculated, all sorts of odd things can happen.
- Use the full Churchill correlation on all pipes
- Do not forget to turn on the holdup calculations on all pipes, the default value is off.
- If you want to model the heat loss, best do so from the start. Make sure temperatures are behaving before you move on to model your next couple of pipes.
There may be a few more things to consider, I will add these as they come to mind, but the above ones should save you a lot of grief already.
With that out of the way, there are a couple of practical things that are good to know when you start modelling a flare network in dynamics.
- HYSYS Steady State has no network solver (except Aspen Hydraulics), so it may be just as easy to start in dynamics right away.
- Start with a case where you actually do have flow from all sources. It doesn't need to be the full flow, but some flow for sure.
- As the dynamic solver is more prone to failing once in a while, make sure you frequently save things.
- Build up the network a couple of pipes at a time.
- Do NOT try to put all the detail you have into the model. lump all the bends and tees and whatever else into a single fitting. A swage is a particularly nasty one to have. The problem being that a swage that enlarges the pipe diameter increases the pressure, so HYSYS Dynamics will translate that into a negative k-value and when your flow goes away from the flow where it was calculated, all sorts of odd things can happen.
- Use the full Churchill correlation on all pipes
- Do not forget to turn on the holdup calculations on all pipes, the default value is off.
- If you want to model the heat loss, best do so from the start. Make sure temperatures are behaving before you move on to model your next couple of pipes.
There may be a few more things to consider, I will add these as they come to mind, but the above ones should save you a lot of grief already.
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Examples of chemical process simulation in english or spanish in :
http://processimulation.blogspot.com/
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