Driving Compressors with Electric Motors or Diesel Generators

Sure.

Energy losses of Alternator - Considering efficiency of 87%, you may save 13% losses of alternator. + Distribution losses about 0.25 - 0.5%, so total 13.5% alternator losses shall be saved.

Out of 1 kwh useful power , total mechanical energy input = 1/0.87 = 1.15 kwh.

power wasted = 1.15 - 1 = 0.15 units. for obtaioning 1 kwh of energy.

This is equivalant to 180*0.15 = 27 ml of diesel loss per kwh.

Considering load factor of 70%, total power usage 3 * 522 * 0.7 = 1096 kw/hr.

Diesel loss = 27ml * 1096 = 29.59 ltr/hr. = 29.59*0.48 USD/hr. = 14.2 USD/hr.

for 20 hr / day operation, this turns to be 14.2 * 20 *(365 - 60 ) = 86620 USD /yr.

= 4.33 Million Rs./yr.

Yes you would recieve some energy conversion (disel to electricity to compressed air VS disel to compressed air) benefits immediately. The question is, what is your infrastructure cost?

If the motors run all the time basically, you might. Is all the power from the current generators already allocated? Would your new disel motor be more efficient? What is the capital outlay difference between installing the disel version and electrical version (including installation cost and life cycle maintenance projections)?

Yes, more questions than answers, but if you are really looking at the real cost, you need to do a life cycle analysis including the future and present cost of money and financing (if any). Most folks just take a guess and don't really analyze their situation fully before deciding. And many decisions are not based on 'real' economics either.

Or my surly attitude could be due to a lack of coffee this morning :)

Capital cost exactly don't know the figures. But definitely, I suppose Engine would cost less then the Engine Alternator set.

Practical aspect is Control. How easily you can control your load. May be ELECTRICITY IS MORE USER FRIENDLY> You may use drives to save fuel further. You may close & re start the system as & when required, more times then the engine system. You may divert the diesel electricity else when compressors not in use?

But if only cost savings are envisaged, may be you need to pay the conversion cost.

1) Check for controls- electrical motor may be more friendly
2) Protections
3) Vibration isolation
4) Any auxiliaries (that includes lamp loads) being run by the alternators in addition to the compressors?

5) Not depending on external power supply (ie all the running will be by the engine)

If all of the above are agreeable definitely you save $s by running the compressor directly with the engine. Especially since, most likely, the compressors are going to be constant output and hence constant load.

Expect a lot more wear on the compressor end due to the impulsive nature of the diesel as opposed to the ac motor which runs considerably smoother.

Gas Turbines are regularly started by Diesel Engines. The vibration (or the impulsive nature of the diesel ) is isolated through hydraulic couplings.

This aspect was brought out in the prev post : vibration isolation.

Every energy conversion has losses, usually realized as heat. Any conversion that can be eliminated will make the overall conversion process more efficient. That is the answer in the most basic form. As per the previous posts, there are other factors to consider in evaluating whether the efficiencies gained will be worthwhile.