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Author Topic: Zero carbon gas power plant?  (Read 322 times)
dan_b
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« on: July 10, 2018, 10:41:11 AM »

How does this work?

https://cleantechnica.com/2018/07/09/net-power-claims-its-generating-plant-can-burn-natural-gas-without-releasing-any-carbon-dioxide/
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brackwell
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« Reply #1 on: July 10, 2018, 10:56:33 AM »

"The remaining, pure stream of CO2 can be buried underground."  so at the end of the day it is just a more efficient gas plant ?
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Philip R
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« Reply #2 on: July 10, 2018, 11:03:39 AM »

This is old news. Cleantechnica are behind the curve. The Allam cycle has been discussed on the BBC news website, The Engineer and on this forum over three months ago.
Its uses a supercritical C02 Cycle, It does not use a steam Rankine cycle.
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Philip R
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« Reply #3 on: July 10, 2018, 11:11:47 AM »

Mr Allam is English Born and went to work in the US for Air products, which whom he started work on the aforementioned cycle.
Theoretically it should run slightly more efficiently than gas CCGT and a few % lower on coal, but higher % efficiency than conventional pulverised fuel coal or supercritical coal powerred steam Rankine cycle.
The other great thing about it is the pure CO2 exhaust, so no future cider shortages, and more importantly. Because it burns oxygen and not air, there are no NOx gases in the exhast due to oxidation of atmospheric nitrogen.
Mr Allam deserves a Nobel Prize.
Philip R.
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dan_b
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« Reply #4 on: July 10, 2018, 11:12:47 AM »

Well it was news to me and I still don't understand it. What's the bit about supercritical CO2 being used in the turbine?
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brackwell
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« Reply #5 on: July 10, 2018, 11:41:08 AM »

So where is the pure oxygen for the burning coming from?
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Philip R
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« Reply #6 on: July 10, 2018, 11:45:22 AM »

Hi Dan,

My explanation is very simple. CO2 exists in a fourth state of supercriticality at temperature above about 31 deg C and 73 bar. Neither gas or fluid but in between. ( Water and steam does this too and about 3506 psi and very hot, can't remember the numbers but learned about it at Power  plant training school over 30 years ago.)

The Allam cycle burns natural gas or coal derived syngas, with oxygen diluted with cooled exhaust CO2, a sort of exhaust gas recirculation, in a gas turbine.( Co2 dilution is required otherwise the combustion temperatures would melt the turbine.) The exhaust , comprising of CO2 and superheated steam is cooled to recover water and CO2 for recirc and disposal ( Sequestration or enhanced oil recovery, or whatever).

The oxygen comes from an air seperation unit.(ASU). Similar to those found at liquid gasses plants dotted around the UK and elsewhere.
The power used to run the ASU has been factorred into the eficiency estimate.

Not Using steam cycles eliminate the loses associated with having to condense expanded steam back to water, as in conventional steam plants.

Philip R
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pdf27
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« Reply #7 on: July 10, 2018, 12:33:56 PM »

So essentially a nearly closed-cycle gas turbine? If I'm remembering the maths correctly running supercritical gives you a big boost to power density but not to the amount of energy you can extract from the gas, so there may well still be a benefit to running a separate steam cycle (as per CCGT) to extract more work from the residual heat.

I'd be curious to see how the costs stack up when compared to amine washing for CO2 extraction. In theory the plant should be significantly simpler and cheaper, but the absolute difference isn't likely to be all that big - and amine washing can be dealt with as a bolt-on to an existing CCGT while this would have to be essentially built up from scratch - something to be avoided where practicable.

NOx isn't too big a concern - the amount created by modern CCGTs is rather low and could be almost entirely eliminated by post-treatment if we cared enough about it. Compared to other sources (cars) it should be a low priority.
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Nickel2
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« Reply #8 on: July 10, 2018, 03:06:28 PM »

Irony alert!
 Wink Wink Wink

Perhaps they ought to capture the CO2 to help the desperate shortage in the food and drinks industries...

 flyingpig
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Philip R
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« Reply #9 on: July 10, 2018, 03:22:30 PM »

Co2 shortage nearly over. Plants back in production again after outages.
Just the supply chain to backfill now.
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dimengineer
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« Reply #10 on: July 10, 2018, 04:18:56 PM »

Co2 shortage nearly over. Plants back in production again after outages.
Just the supply chain to backfill now.

Yes, the Press just loved all that "We're Doomed, Doomed, Doomed" "The world will end, there will be plagues of Locusts, and football fans might be a bit short of lager" facepalm
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