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[marchese85]

hello
I need help. I have to simulate a batch distillation to recover of heteroazeotrope ethylacetate-water. I'm using HYSYS 3.2. The process is discontinuous and I have built a simulation in dynamic state .The process consists of several stages:
1) charge the boiler with the initial mixture and send the vapour to boiling feed
2) i work in conditions of total reflux until reaching a steady profile of T
3) draw the distillate and bottom product
I built the model and i simulated the boiler with a separator. I set (in the tab dynamic) the volume and the initial conditions of flash (20 ° C and 101.4 kPa), but just starts the integrator, the pressure drops sharply to values of 10 kPa and appears in some cases, the following message

negative pressures have been detected.Values will be set to 0.01 kPa and the system will attempt to continue (this may be caused by sudden large changes and large step sizes

I tried to reduce the step size but without results.
On the supply current I inserted a valve (as suggested by the dynamic assistant) but i noted that the pressure drop increases up to 100 kPa.
how can I initialize the valve on the feed line? The mass flow of feed must be zero.

p.s. sorry for my bad english
thanks in advance