Combined cycles and overall energy efficiency

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In the previous part of this series, the author set a new benchmark for combined cycle energy efficiency at 65 %. Direct use of natural gas, and a national energy policy with new regulations, coupled with efforts to save crude oil with the help of shale gas and the efficient combined cycle is the need of the hour.

There are places where natural gas should continue to be burned while there are other places where we should use electricity. All electric homes can indirectly use shale gas through efficient power plants burning natural gas. However, directly heating our homes, our hot water, cooking our food by natural gas is more efficient. Such direct uses come at about 85 % efficiency versus only 50 % when considering part load efficiency of power plants and line and transformer losses even though peak plant efficiency might be 60 % with the new combined cycle power plants envisioned.

The point is this: there should be an integrated balance to consider when using gas or electricity. It would be hard to air condition our homes with gas, run our appliances, and use our computers directly with natural gas. The same approach should be used nationally. Any national energy policy must take into consideration safety, our environment, our drinking water, our atmosphere and other factors.  The new rules and regulations should not be restrictive either, and the following critical areas should be considered.

Adding ethanol to gasoline  

The endless mass of cars traveling on interstate highways transports only one person, the driver; and the 100 dollars a barrel for crude oil and the resulting $3.60 per gallon for gasoline has not stopped or slowed down the use of cars. As a result, the cost of gasoline is far too much, and the family budget leaves too little for other needs. Another example of questionable wisdom is the addition of 10 % ethanol in gasoline to reduce air pollution. But this mandate is not cost effective or pollution effective. We need a way to control pollution but ethanol alcohol is not the solution.


There are smaller and slightly more efficient gasoline cars available today but they are not as safe as the big ones. There are the midsize hybrid and the all electric cars: the Nissan Leaf and the Chevrolet Volt with its limp along home small recip engine included that requires premium fuel. Battery replacement costs are high, the electric car has too short a range between charges, the batteries take too long to charge compared to filling a gas tank, and chargers are costly to install in our homes and not available at many places.

How we can save crude oil

Efforts are being made to save crude oil with the help of shale gas and the efficient combined cycle. If we install 60 % plus efficient power plants to burn the new shale gas and generate low cost electric power, electric cars can use batteries charged by such power from these plants, and large amounts of crude can be saved. While the electric car has drawbacks, such as low mileage between charges, it has considerable potential for further development.

There is growing interest in alternative fuel vehicles but locations for compressed refueling stations are presently limited. There is little evidence that our government is pushing the efficient natural gas fueled combined and integrated cycles. TV ads promote domestic use of the new gas, but not for combined cycle power plants to power the electric cars.

Energy efficient road and rail systems

Large trucks that carry heavy loads on the freeways and interstate highways and also start and stop a lot in city traffic expend a considerable amount of kinetic energy. It would be more energy efficient to have generators hooked up to their wheels and pump this stopping and slow down energy to a bank of lithium batteries. This stored battery energy could then be used to fuel the truck later, and some crude could be saved.

School buses could also operate with such a battery system to save fuel by powering with compressed shale gas. Railway systems of all kinds could find a use for the battery storage and usage system and use shale gas fuel, some of which could be saved. Our hybrid cars are already taking advantage of storing and then releasing energy through generator and battery systems. Their main source of battery charging power would come from a central power plant burning shale gas. 

In order for the above systems to be economical there must be an ample supply of lithium batteries at a reasonable price. Other applications that can be considered are domestic use, factory and farm use, chemical and refinery plant use, shipyard use, improvement in power grid and power distribution systems and electrified rail systems.

New concepts, advanced engines

The year 2011 marked the start of the age of a new concept of power generation utilizing across the board the generation of electrical power by the advanced industrial gas turbine and the combined and integrated cycles coupled with wind and solar renewables. In closing, it is imperative to say that we need to recognize and use advanced gas turbines and the combined cycle power plants to provide more efficient power production. We should prudently and effectively develop fracking and the production of shale natural gas and shale crude oil and use these energy sources more wisely.

Ivan G. Rice was past chairman of the South Texas Section of ASME (1974 - 75), past chairman of the ASME Gas Turbine Division (now IGTI) (1975 - 76). A Life Fellow Member of ASME and Life Member of NSPE/TSPE, he has authored many articles and ASME papers on gas turbines, inter-cooling, reheat, HRSGs, steam cooling and steam injection.