Revamping Vs. Renew - Oil fired Turbine Engine for Pump

[gasoperations]

Guys
There is a situation like this. A 50 yrs. old Oil Fired Turbine Engine for Crude Oil Loading Pump ( 600 rmp ) is still in use ( yes still working for Ship Loading ). Generally Pump is still in good working condition. Only turbine is in bad shape in terms of increased and costly repairs. Now finally management is thinking to replace these historic Pumping system with something different. Following options are being considered:

1. Convert the turbine engines from Oil fired to Gas fired and upgrade the required control system. ( Pump & Reducer gear box will remain the same ). A lot of work and budget has already been spent on Oil to gas conversion project and some of the material is already on site. Actual site activities for Conversion project are not not started yet.

2. Replace the Turbine Engine with Electrical driven Motor ( Low speed / Variable speed control ). Could retrofitting for old low speed pump be with existing obsolete reducing gear box with new Low speed / variable speed motor be practical???

3. Replace the whole system with new Motor & Pump.

Any thoughts / Comments / advise to arrive at most suitable and cost benefit analysis of this situation??

Thanks in advance

 

[waross]

A low speed motor will be expensive. Can you use a 3600 or 5000 RPM motor with the existing gearbox?
Another option may be to over-speed an electric motor.
If you are using a VFD, consider a 1500/1800 RPM motor fed double voltage and double frequency. This will produce 600 HP from a 300 HP, 60 Hz motor.
If you go more than 2:1 on speed ratio, consult with both the VFD manufacturer and the motor manufacturer as to suitability.
However if there is any doubt about the remaining life and dependability of the existing pump and gear box consider a complete new installation. The cost saving should be significant to consider reusing 50 year old gear.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gasoperations]

@ waross
The low speed shaft speed is 6000 rpm and speed variation of the turbine is used for capacity control of the pump.
Could you please elaborate what benefit can be expected by over speeding a 1500/1800 rpm motor as our requirement is to run a pump at max. 600 rpm ( speed variation is required from 65% to 100% of 600 rmp ).

Thanks

 

[waross]

If a VFD is used to run a motor at double voltage and double frequency, the available HP is doubled.
It may be worth while to inquire with some manufacturers as to whether a 1500 RPM motor or a 3000 RPM motor may be safe mechanically at 6000 RPM.
A 150 HP motor rated at 1500/1800 RPM will theoretically develop 600 HP at 6000 RPM if the rotor and bearings will withstand the speed.
Hopefully jraef will post in. He is one of our VFD application experts.
Generally the price of motors increases as the speed drops.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Is it 600 or 6000 RPM? Two entirely different beasts.

A new pump + motor system (with a VFD, if you want variable speed), seems better option than trying to retrofit into the old system.

Muthu

http://www.edison.co.in

 

[ScottyUK]

Edison - 600 rpm pump, with reduction gearbox.

What is the power required by the pump? Our crude loading pump motors are 2000kW, so it's an MV application where a VFD isn't a cheap commodity item.

You need to look at the lifetime costs of operating and maintaining the options, including any contracted-out support from OEM's and any major component replacements during the lifetime. For example, I would anticipate a full VFD replacement before you reach 25 years.

 

[gasoperations]

The Turbine rated capacity if 1500 BHP. Could not get the exact pump power. But data for operating point of pump is as under:
42000 GPM @ 165 feet total head
25000 GPM @ 200 feet total head
Hope this may help

@ Waross the point is if low speed motor is expansive than high speed motor, why use it and go into over speed region for motor operation. VFD will be required for speed regulation anyway for low speed or high speed motor selected. Unless I am missing something here.

 

[waross]

I misread the post as 600 HP required.
At 1500 HP, it is unlikely that a motor will withstand much over-speed, so my suggestion is probably moot.
But to explain my suggestion, even though it is probably unusable:
The voltage limitation of a low voltage motor is generally limited more by the "Volts per Hertz ratio" than by the insulation strength.
If you double the frequency (Hertz) than you can double the applied voltage.
The motor will still take rated Amps and develop rated torque, but at twice the speed the HP is doubled.
a few years ago, some compressor skid manufacturers were building sets with a 100 HP, 240 Volt motor, and with the help of a nominal 100 HP/480 Volt VFD they were applying 480 Volts and 120 Hertz to develop 200 HP. (The sets were connected to 480 Volt systems.)
By running a 3000 RPM motor at double frequency and double voltage, a 750 HP motor will develop 1500 HP at 6000 RPM.
This is more theoretical than practical for your application.
This works for smaller motors, but I doubt that a 750 HP motor will withstand the mechanical stresses of 6000 RPM operation.
In that size range you may not find an off the shelf VFD that will run at 200% frequency.
The voltage would not be as much of an issue. The manufacturer can easily connect the coil groups for 50% voltage when the motor is built.

A new motor and a new gearbox may be your best solution. Bear in mind that the pump may have to be replaced at some time and compare the price of a complete pump and motor with the price of a motor and gearbox only.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gasoperations]

I will try to workout economics of total replacement vs replacement of Turbine with either low speed motor or high speed with gear box.

Thanks guys for inputs