Electric Motor vs Steam or Gas Turbine

What is necessary to know is the type of plant and its design philosophy, there a few generalizations that can be made.

For example if there is no need for steam in the process it is unlikely that all the "stuff" that is needed to run a single turbine to turn a pump when an electric motor could be used. On the other hand if the plant is built where there is lots of fuel but no electricity supply then there will probably be steam that is available for process conditions and running a turbine or two.

I've been in generating stations where some BFPs (Boiler Feed Pumps) were powered by motors and others by turbines, in the end it all comes down to process conditions and economics.

I would run turbines to turn generators and use the current to run electric motors.

Is that not how it is done?

The bottom line is; which is the cheapest to use.

Good day,

I think these kind of decisions are financially influenced. I know that in some countries where there is abundance of coal and water with other processes also using steam, it would be easier to use steam turbine. The problem with steam turbine is that it has low efficiency versus gas turbines especially close cycle or tri-generation.

But running turbines require that the company has teams of operators and mainteners of the power generating plant with all associated auxilliary plant.

I would go for electric motor if all I need is to drive a pump and there is realiable power supply.

I am just reminded that the aircraft I travel is run by turbines. Also, 500MW Steam power plants depend on the boiler feed pumps that are run by small dedicated steam turbines. I don't think the turbines are less reliable if only they are looked after the way they are supposed to.

In case of power plants, use of steam turbines for boiler feed pumps improves the cycle efficiency and in other places also, it is more efficient and economical if turbines directly run the compressors / pumps (or whatever).

It is also a possibility that a site remote from the electric grid may not have required source capacity to start (may be even run) a large electric motor.

That depend so much on the industry.

Paper machines used to be line shaft driven from a steam turbine.

The modern configuration is all electric drives. They provide more flexibility and better speed regulation.

The move from turbine to sectional electric drives can cause some interesting issues as the turbine is off loaded both in HP and connected inertia. Since the overall process still uses the boilers, the power through the system has to be balanced. It also opens the opportunity for co-gen projects with bio-fuel as the source, and preferential feed-in tariffs for carbon neutral energy sources.

Reliability is important as to the service involved. Co-Ed made a decision that since it was running an electric power plant in New York City that it would always have electric power so everything in the new plant was electric motor driven. When the 1965 Blackout hit, the power drain tripped the entire plant and as "Big Alice" coasted to a stop, the lube oil tank ran dry and without a steam turbine driven lube oil pump available the bearings ran dry and bearings wore out and close clearances got too close and things went bump in the night. Consequentially Big Alice lost a lot of blading and had to be shut down for a long maintenance operation all because Co-Ed didn't utilize steam turbine alternate drivers for critical services like most power plants did. A statement of confidence in their ability to supply electricity which fell short of reality due to an unforeseen weakness in the grid. Overconfidence in a design has often led to severe consequences in reality, often something that experience more than book learning teaches an engineer to avoid.