2 replies to this topic

[dxmin112]

Hi,

 

I have a question regarding compressor motor.

 

I have been working on a dynamic simulation for compressor surge with Hysys as required for my project specification.

 

I am currently working with electric motor compressor, and struggling with ESD trip case.

 

The suction flow is about 1200m3/hr and speed and power are 10,000 rpm and 1000 kw accordingly.

 

With given inertia, my compressor speed reaches to 300 rpm from the initial speed of 10000 rpm in 1 minute

 

when I set the compressor power to be ramped down to zero in 0.1s. 

 

I would like to ask if this is realistic that the compressor speed (probably impeller) will decrease to 300 rpm from 10.000 rpm in one minute even though this time is Hysys time.

 

Addition to this, I asked one of my fiends who is working at a compressor manufacturer, and he said that the speed will decrease to zero in 2-3 minutes.

 

So, I also would like to ask if the speed of impeller decreases linearly or decreases with some arc graph.

 

Thank You

[trinhduchanh]

Hi dxmin 112,

 

I have wondered why your project requires centrifugal compressor ramp down to zero when ESD trip occurred. If your centrifugal compressor driven by electric motor and control speed by VFD then you can totally do that by ramp down function build in VFD. In my current project, we utilize MV drive from ABB and during solo run test for motor then we decelerate the motor speed from maximum allowance speed at 1800 rpm to zero within 1s setted in Ramp Down Function. But the fact ABB vendor don't recommend us setting value for decelerate quickly like that. It it can cause damage to VFD. When coupled motor with centrifugal compressor we only utilize Ramp Up function during start up compressor to bring up minimum speed with rate around 5rpm/second. If we want stop compresor to stand still position by normal stop or ESD trip then we use the Coast Down (not Ramp Down) Function to decelerate motor speed to standstill positon. It worked well and taked around 30 second. 

[GimliXJ]

I used a centrifugal compressor very similar to the size and rpm of the one you are looking to model for wet gas in a coker unit.  When it tripped, it would go to 0 rpm very quickly.  It felt like less than a minute but time feels like it speeds up during an unplanned shutdown.

 

To answer your first question, yes it sounds logical that the compressor would spin down that quickly.  Your second question, and I am purely guessing, is that you will have an arc'ish shape to the rpm vs. time graph.  My guess is that at the initially higher speeds there will be substantially more resistance on the impeller causing a faster deceleration.

 

Best of luck to you.