mutiple steam ejector valve open sequence query

[hswang2]

I have a recactor, condensor, and vaccum steam ejector. temperature. The operation manual is written in the following:
1. waits until pressure in the Reactor is less than 150 mbara and then opens XV-B (steam to the second ejector stage).
2. Then the sequence waits until pressure in Reactor is less than 70 mbara and open XV-A (steam to the first ejector stage). If the desired time is elapsed, nitrogen is admitted to Reactor up to 1200 mbara and the process goes to a “Hold” status waiting for the panel operator input.
In my understanding, it is supposed to put more medium steam to get much more vaccum in the reactor. But why the less pressure (70 mbara )in the reactor, the first ejector valve should open?
Thank you very much for your help.
Note.The vapours containing some lights and water removed from the chain starter go to condesor A where they are cooled and partially condensed, using cooling water. The condensate (if any) flows, by gravity, to Hot Well.
Reactor Vacuum System, is a three stage jet ejector provided with two inter-condensers and one after-condenser. Medium pressure steam (MS) is used as the motive fluid in the ejectors and cooling water is used in the condensers. All the condensate from the condensers flows, by gravity, to Hot Well . Nitrogen is introduced under pressure control in order to adjust the desired pressure in reactor.

 

[ash9144]

I'm not sure what you are asking. But steam ejectors should be put on line with the farthest down stream ejector first and the one closest to the process last. So by your sketch open the main steam CV to feed the ejector on the right hand side of the drawing first then XV-B, then XV-A.

 

[rmw]

It is so that as each ejector is started, it is started into the lowest discharge pressure possible. How would you accomplish this by reversing the order?

rmw

 

[hswang2]

The ejector discharge pressure and temp condtion in this vacuum systme is put in the new post.

The discharge pressure from condesor increase from left to right.

But I still don't understand the open valve sequence in the vaccum ejector system when system need more vaccum.

Please give me more guideline for this and thank you for your help.

 

[ash9144]

Open the one on the right side (farthest down stream). It discharges to the scrubber directly. Then open middle ejector it discharges to the first ejector then the scrubber. And so on. Your scrubber has the least amount of back pressure. You can't discharge one ejector to the next with it off line.

 

[EdStainless]

HS,
notice that is no valve for the last (discharge) ejector? It is always pulling vacuum.
There is nothing magical about the cut off pressures. It is simply based on the design for these ejectors. There is no reason to turn them on at higher pressure, they would have little effect.

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