11 replies to this topic

[akashlovey]

 

Here is a question ...

 

How do you start a centrifugal pump when pumping a cryogenic liquid?  The pump has a control valve in its discharge line and a control valve in the kickback line that goes from the discharge line to the suction drum.  The suction temperature (-180) is a cryogenic temperature and assuming discharge line is full of liquid but not at cryogenic temperature , assuming -100.  The pump is high pressure pump assuming 150 bar.  The suction drum operates at 10 barg.

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Edited by Art Montemayor, 27 March 2017 - 04:46 PM.
grammar, spelling, structure, meaning

[Bobby Strain]

Follow instructions provided by the pump supplier.

 

Bobby

[akashlovey]

The problem is i'm facing is that discharge line is not cool enough to start a pump ...usually it cools through kickback line due to pressure difference as its valve is open when pump is in stop condition . pump suction pressure is 15 bar while suction drum operates at 10 bar

[Art Montemayor]

Akashlovey:

 

The problem you are facing can be resolved easily by simply following Bobby Strain’s advice.

I’ve operated and handled many cryogenic pumps - both centrifugal and positive displacement - in my career and I never had any problems starting, stopping, or controlling them.  You have an inherent basic requirement to pre-cool the entire system - pumps and all associated piping and equipment - prior to trying to start any cryogenic pump.  Your diagram does not show this capability.  You don’t define how your control valve in the kickback line works.  Simply allowing for kickback doesn’t ensure that your total system will be inundated, flooded, or primed at the cryogenic temperature with LIQUID cryogen.  If you don’t ensure total LIQUID content in the suction and total pump casing and discharge line (devoid of any gas pockets) you will have a vapor-locked system and your pump won’t “pump”.  Pumps - and that means ANY pump - will only “pump” LIQUIDS.  They cannot - and will not - pump any 2-phase or gaseous fluid.  Cryogenic pumps are particularly very strict and fussy about this ruling.  One way to flood your system is to have a manual valve that allows for suction liquid to freely and fully inundate your system and allow all vaporized liquid to flow back to the suction drum vapor space while cooling down all components prior to startup.  This method, however, has the caveat that you must do something with the generated vapors.

 

If you consult your pump manufacturer for the required instructions, they should detail out the indicated required steps for starting your system and keeping it operating without vapor locking.  If you cannot get this service, then you have a major problem with your pump supplier.  I’ve operated liquid oxygen and nitrogen pumps with suction pressures as low as 5 psig and discharge pressures at 3,000 psig, pumping 24 hours a day and 7 days a week - continuously, without stopping.  So you might get the idea that I know what I’m talking about and follow Bobby’s advice.

 

[akashlovey]

Our pumps are vertical submerged cryogenic pumps , but cooling down down is done by only via suction line to pump casing and through pump to discharge line via kickback to suction drum vapour space . But such phenomena is not happening properly ,temperature in discharge line ( Temperature transmitter is placed just after pump discharge flange ) seems to gets stucked around -100 and then furthur cooldown is not happening. Kickback valve is there only for maintaining a minimum flow while operating pump . In rest case  it is fully open.

[Abm92]

You can open pump Discharge PSV bypass for some time and establish flow through it and cool the discharge line up to the required temperature.

[akashlovey]

You can open pump Discharge PSV bypass for some time and establish flow through it and cool the discharge line up to the required temperature.

We are already doing this process for cooldown of pump discharge but it is not a permanent solution ..in case of emergency we can't wait for cooldown of pump . we need permanent solution.

[Root]

1. you need some modification in pump discharge line, there is may be point for pressure guage on both pumps.
2. make interconnecting piping for both pumps and then chill standby pump with discharge of running one and keep it always open.
3. run standby pump anytime you need it.

cheers

[akashlovey]

 

1. you need some modification in pump discharge line, there is may be point for pressure guage on both pumps.
2. make interconnecting piping for both pumps and then chill standby pump with discharge of running one and keep it always open.
3. run standby pump anytime you need it.

cheers

 

We have 4 Pumps in parallel . The pumps which are not running gets comparatively less cooler . And all pumps discharge line are connected to same header.

[Root]

1st you need attache PID here for more discussion and 2nd you need to learn how to start your 1st pump, just open suction valve and release gas from discharge side to flare with vent drain line and leave it for some hours until you noticed icing on pump body and then start it.

follow same for other pumps. 

[Abm92]

The problem is i'm facing is that discharge line is not cool enough to start a pump ...usually it cools through kickback line due to pressure difference as its valve is open when pump is in stop condition . pump suction pressure is 15 bar while suction drum operates at 10 bar

How u get a 15bar suction pressure from 10 bar suction drum?

[akashlovey]

Due to liquid head present in suction drum. Suction drum vapour space is having 10 barg.