High HP Gearbox for Petrochemical Application

With a gearbox that large, I can see why the quote process is not as easy as for gearboxes up to a few hundred HP. I suspect few gearboxes in the 3000HP range are standards so the manufacturers spend some time doing a quote. But here are a couple possibilities:

Talk to a few different power transmission manufacturers reps. We all know that sometimes you find a rep with extensive industry experience and knowledge. The right one could probably give you a ballpark figure based on experience without even getting the gearbox companies (like Falk) involved.

Another possibility is look at the used equipment websites. Since you know the basic input/output characteristics you may find some in the close ratio and load range. Then take that cost of a serviceable, name brand, used gearbox and double it to get the cost of new. This 1/2 price rule for good used equipment is oftentimes close.

Either of these methods may just get you to a guesstimate or swag level but I do understand that this is often where a project starts.

With a speed increase of only 2.4, I would look into V belts and sheaves. At this low ratio it may be significantly cheaper than a gearbox. Yes they do make very large cast multi-groove sheaves. I would also consider a 3600 RPM motor and no gearbox. The overall cost may be lower. I have never purchased one that large but some large motor shops can do non typical RPM motors. One advantage is the higher RPM means lower torque for the same HP. This sometimes has cost benefits.

Contact any of the standard gearbox manufacturers

MAAg/Flender/CMD/...

The gear box in about 2.2MW is a bit larger, but this is the size we generally handle (our requirements are upto 3MW). Only we have a much higher ratio (1:8) and multi stage, helical.

Our couplings are Flexible Bibby (and also some times disc couplings)

Your application might be not off the shelf, and that is what is delaying the process. But that is what can not be helped. Our specification to Vendor design freezing for new gearboxes typically takes a month, few times may be upto six months. And the price negotiations start somewhere around the end.

Unless this is off the shelf, it may just be a bit difficult to get a quick quotation.

I will advice you to go to the websites and ask for the quotation. Flender and CMD we are closely associated with and may be able to cater the need.

Just had one small doubt on retrospection:

Your pump is 3600RPM, Motor is 1500 RPM (ie 1475)

Are you trying to marry a 60Hz system with a 50Hz system?

You could have as well gone ahead with a 3000 RPM compressor with a direct 2 pole motor.

But then maybe it has been decided by someone without looking at the operating frequency. Ordered pump, now searching for motor? It happens too often to be comfortable. I make the mess and you clean it up. (What about a VFD?) I can see quite a few 3MVA VFDs around.

On a smaller scale I have been involved with a similar question about screw compressors for refrigeration. The choice was between 1800 rpm diesel driving 3600 rpm screw via a 2:1 gear increaser, versus direct drive to a larger screw. The price of the main components was about equal, but the extra confetti for the gear increaser (oil cooler, piping), plus the labor of designing and aligning two pairs of shafts, made the second option better.

For a 50 Hz system, 3000 rpm direct drive would seem the most natural choice, if a screw of the proper size can be obtained.

"in cervisia carmen" I'm intrigued, what does this mean?

It is indeed correct that the screw was chosen prior to the understanding of the electrical system (50Hz). I am working with the screw vendor to see if there is a 3000rpm option that will get us the same performance curves.

I would love to just go direct coupled or find a screw manufacturer who can accomodate this need. The gearbox issue just seems to add unneeded complexity, engineering time, and unknown costs.

You guys have been very helpful as well as insightful for some of the things that need to be considered. Always appreciated.

Brian