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STATEMENT OF PROBLEM:
What is a liquid ring vacuum pump? and how do you model it in ASPEN PLUS?
ANSWER:
A liquid ring vacuum pump is a specially designed compressor used to generate vacuum pressures of down to about 100 mmHg. It can handle a mixture of gas and liquid as feed at subatmospheric pressures and discharge it at ambient conditions
Modelling in ASPEN PLUS:
Neither the pump or the compressor models allow a two phase mixture feed. Therefore the following workaround should be used. The gas stream to be compressed (i.e. steam) should be fed into an MCOMPR block (2 stages with a inter-cooler).
The exiting stream from the compressor block is then mixed together with the sealing liquid (i.e. cooling water) stream, in a MIXER block. The outlet stream from the MIXER will have the correct composition.
However, the HP power requirement of the liquid ring vacuum pump (MCOMPR block) will be over estimated due to neglecting the cooling effect of the sealent liquid which is not fed to the compressor block.
In order to meet the process temperature, you will need a design spec that will vary the inter-cooler duty to meet the temperature spec you provide.
In this manner you will also obtain the power requirement due to the cooling feed stream (which is not taken into account in the MCOMPR).
Vapour Feed to the
liquid ring
vacuum
pump |--------| |-------------| |--------| |-------|
------->| MCOMPR |--->|Inter-cooler |--->| MCOMPR |------>| MIXER |----->outlet
| STAGE 1| |_____________| | STAGE 2| |_______| from
the
|________| |________| /|\ liq
ring
| vac
pump
--------|
Cooling Water Feed
to the liq. ring vac pump |
|
发表于 1970-1-1 08:00:00
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发表于 1970-1-1 08:00:00
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