Whether A Pump with Gear Box (to increase pump speed) is Feasible? 1

[icecool]

Dear Sir,
I am trying to understand that whether a Pump who is flowing a High Temperature Fluid (Therminol) will be feasible with a Gear Box. The Gear Box will be used to increase the pump speed from 3000 rpm to 3600 rpm.
The reason behind increasing the speed is high Pump TDH and as per manufacturers it is not in their configurations. As per my understanding the increase in pump speed will help in to get higher TDH. I have enough NPSH available.

Any help is highly appreciated. Pump parameter are mention below

Flow rate 1100 m3/s
TDH : 321m
Temperature : 300 Degree C
Discharge pressure : 36 bar
Country : India

Thanks,

 

[BigInch]

Well yes. Pumps have gear boxes because they may need to run at speeds different than their motor's speed.


Learn from the mistakes of others. You don't have time to make them all yourself.

 

[LittleInch]

Or you could just use a 60 Htz supply, but many things change when you increase speed, sometimes by factors of squared or cubed, so you need to be very sure that your pump (and motor) can in fact handle the additional head or flow and speed (bearings, seals, impellor, casing, etc), not to mention power from the motor. Gearboxes also have some losses. The phrase "as per manufacturers it is not in their configurations" would worry me a lot. Just because the pumps works now at 3000, doesn't mean it will do what you think at 3600.

If you do this and it is outside the pump capabilities you could destroy your pump and spend much much more cleaning up the mess than just getting a new pump....

Are you trying to increase head or decrease it?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[icecool]

LittleInch

I am trying to increase the TDH.

I have the same concern for increasing speed from O&M point of view. I can understand your concern.

I am just looking after all the available options. But, if I don't have a choice then I may have to do it.

The increasing motor speed is another option but may need to include frequency convertor (as India is 50Hz power supply). Which may create more complication than gear box as I prefer to have a mechanical device than have a electronic convertor.

Thanks

 

[LittleInch]

What are you trying to increase flow and TDH to? you always have a choice, it's just that the alternatives are not palatable to those with the money, but you need to make sure you put all your concerns down in writing so when it blows up / doesn't work then you have some measure of support.

What power is your existing motor or are you changing that also?

Have you considered a bigger impellor in the same casing?

Your flow will Increase in proportion, but head increase as squared (+44%) and power by cubed (+85%).

Get the right sized pump and motor or you will just spend much more time and money fixing this catastrophe in the making.

Why do you want to increase head anyway?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[icecool]

What power is your existing motor or are you changing that also? : approximately 900kW

Have you considered a bigger impellor in the same casing? I already tried bigger impeller in the same casing but it won't fit.

Your flow will Increase in proportion, but head increase as squared (+44%) and power by cubed (+85%). : I agreed

Why do you want to increase head anyway? My overall system pressure drop increases due to installation of a new equipment.

Can somebody answer that.:

1. What are the O&M problems will face if increase the number of pumps apart from costing.

2. will then be a control/balance flow issue.

3. What kind of issues a VFD will create?

4. installing bigger pumps in series vs small parallel pumps?? which option is practicable and proven on bigger sizes of the pump.

 

[rotw]

Flow rate 1100 m3/s
really ?

country : India
why should we care ??
If you refer to ambient conditions, then you could just mention them as such.

 

[icecool]

No..its typing mistake..it is 1100 m3/hr.

 

[desertfox]

Hi

I would be concerned about the reduction in output torque after the gearbox and also whether the motor will cope with the increased inertia load of the gearbox.

Desertfox

 

[icecool]

Dear desertfox,

Can you please elaborate "reduction in output torque after the gearbox and also whether the motor will cope with the increased inertia load of the gearbox".

Thanks

 

[Artisi]

Of course you can increase the pump speed via a gearbox. The considerations are:
1. Is the pump capable of operating at 3600 rpm in terms of NPSHa/r and within its hydraulic range of operation.
2. Ensure the motor is sized for the new pump duty including the reduction in overall efficiency for the gearbox drive.
Pump performance changes as follows:
Flow will increase N2/N1
Head will increase N2/N1^2
Power will increase N2/N1^3
3. The gearbox is rated for the application.

Can not see where the majority of earlier discussion is heading . Pump drive thru' a gearbox certainly isn't rocket science - just a normal engineering application.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[desertfox]

Hi icecool

The simplest way to show how the torque reduction will occur is using the formula for power:-

2*pi*N*T/60 = power

Transpose the formula to find T :- power*60/(2*pi*N)= T

using the original speed and power := Tmax= 900000*60/(2*pi*3000)= 2864.78Nm
Apply the same logic with your new speed and the torque (max) decreases to 2387.32Nm which is about 83% of the original torque.
Now consider your adding a gearbox which the motor will also have to provide torque for to overcome friction, rotational inertia of the gearbox to bring it up to speed and last but not least an increased flow rate.

 

[dcasto]

Just install the right size motor with a vfd that can increase the 50 HZ to 60 HZ, is still cheaper than a new motor, stater and a gear box. The savings gained from the VFD on energy input and power factor more than offsets the cost of the VFD over a gear and starter.

 

[rotw]

dcasto,

The existing motor still needs to be verified that it is suitable for conversion to VFD application.

or not ?

 

[MikeHalloran]

>>>The reason behind increasing the speed is high Pump TDH and as per manufacturers it is not in their configurations.<<<

Three hundred plus meters seems like a lot of head for what I assume is a recirculating loop through a couple of heat exchangers.

Are you sure that you don't want to _decrease_ the TDH?

Did you actually measure the TDH and the flowrate, or are you working from nameplate data?



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

icecool,

when you put two pumps in parallel without some sort of flow control on each, one will pump more than the other - see multiple posts here on parallel pumping issues.

You gave us some data at the top and I agree with Mike - It looks very high TDH for a hot oil re-circ system - what is your new duty?

Series pumps could be used - you need to make sure the second pump inlet side seals are suitably rated for the high inlet pressure, but you can add head this way.

If your additional head is quite small a VFD might be an option, but the motor needs to be rated for the duty. There are other issues with VFDs such as electrical issues about feedback of the frequency and the extra speed might take you pump into less efficient operation.

New pump and motor still sounds like the best plan to me.....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[icecool]

Dear LittleInch

Basically this is a solar thermal power plant. The high temperature oil is goes through the solar field and collect heat and back to steam generator and transfer energy to water.

The high TDH value is mainly due to plant size and low efficiency of solar. It is a confirmed value. Currently, I am working with another small plant which has similar flow rate but the TDH was little less.

 

[LittleInch]

So do you have all the info you wanted?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[icecool]

Dear LittleInch,

I do. Thanks everyone. I have theoretical answer of the questions. But I am still not sure from O&M easiness.

Also, I found a supplier who can support me on this.

Thanks,
Lokesh

 

[Artisi]

Irrespective of who is going to help you, you must initially establish if the pump and system hydraulics are within the pump capabilities, otherwise the pump / system will fail.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)