Hinckley C

Just Googled 'energy grades' top one came up with A to F for buildings, is that correct NDIY? Have a nice day. Seriously, no one is impressed with smart Alecs, if someone asks a question, why not answer it, we were all there once.

Tony

To avoid further unpleasantness here's my take on it. Burning gas produces heat. Converting heat to shaft power is inefficient, the higher the temperature the more efficient, but with current materials about 60% efficient at best. It's actually the temperature difference between highest and lowest, but we are stuck with the lower temperature, air or river used to condense the steam in a CCGT. Converting from shaft power to electricity and vice versa is very efficient with big motors or generators, and converting from shaft power or electricity to heat is 100% efficient. Thus shaft and electric are referred to as high grade, heat is lower, and the cooler the heat the lower it gets.

There are no daft questions, only daft or rude answers. This might be a daft answer, but I hope it's not rude

Edited By duncan webster on 10/07/2022 19:03:48

.

Thank you, Duncan … very civil

MichaelG,.

I tried again … and amongst all the ‘noise’ found this:

**LINK**

https://www.issuesofsustainability.org/helpndoc-content/TheGradingofanEnergySource.html

MichaelG.

Well, Low Grade energy has high entropy, and High Grade energy has low entropy. If only I understood entropy ...

It's like being back at school; still don't know what nine sevens are!

Don't worry, nobody understands entropy, just remember that like the national debt it always increases

Entropy always increases in a closed system. What happens in an unbounded system is still a very much open question.

But then obscure physical problems really have no place in this discussion.

Andrew.

CCGT with a thermal efficiency of 60% - just look who is claiming it. 20 years ago a near similar cycle with modern materials, high pressures and an HP turbine entry temperature of around 1800K I remember gave a value of 40%. For comparison, the last generation CEGB coal fired power stations were about 30%.

And I know what entropy is. It is anything but an obscure physical problem. It is a major reality in all our lives.

JA

Edited By JA on 12/07/2022 18:48:47

That made me smile.

David

Hello JA,

I think you got the wrong end of the stick! I fully agree that entropy is a very important factor in our lives. The obscure point was, "does entropy increase in an unbounded system" (think cosmology). As a physicist I have long believed that entropy doesn't increase in an unbounded system. I am happy to say that some of the younger generation of physicists would agree with me. It is good to have like minded thinkers!

Andrew.

Andrew

I don’t think I made the claim. Thinking about it I believe entropy can only exist in an enclosed system. I find astrophysics very confusing so I leave others to think about it. It is not even a good creation myth.

JA

I read your “obscure physical problem” as referring to entropy in general.

Edited By JA on 12/07/2022 19:55:47

Are you suggesting someone is making false claims re efficiency? Lying, even?

You need to look up the thermodynamics which restrict the efficiency of super-heated steam under pressure. It is that which limits the efficiency of any steam installation.

The closed circuit generating stations recuperate energy from the reduced pressure gas flow which has historically been dissipated in cooling towers (at coal-fired power stations). That accounts for the elevated efficiency values. OCGT generation is clearly (to those that understand the differences) is much lower, at around the same as coal-fired stations - but the do have advantages, all the same - faster, cheaper installation and less CO2 emissions per unit of generation, along with rapid start-up when required to generate (can be on-line in about 10 minutes in some situations, I believe

Look it all up. It is quite simple basic Physics, really - but a specialised area. Perhaps think here that many aeroplanes use jet engines for propulsion - but clearly the hot exhaust gases are immediately lost. Ever seen the temperature of exhausts when a military jet turns on the after-burners?

Hello JA,

My apologies for not making my input clear enough. I was strictly referring to unbound systems.I do agree that it is a difficult subject. I have worked on the problem off and on since my undergraduate days, well over 50 years ago and I still have difficulty in nailing the answer. But most of my results point to the belief that the Second Law is not obeyed for unbounded systems.

Andrew.

I think Flanders and Swan provided a good introduction to entropy, and set it to music!

Of course not. It is business.

JA

Edited By JasonB on 13/07/2022 19:54:49

CCGT stands for combined cycle gas turbine, it isn't a closed cycle, there is still hot exhaust gas and cooling towers.

The best coal fired stations were ~40%,CCGT are ~60%. I'm prepared to believe these figures but then I don't line my hat with tinfoil