Talk:Allam power cycle

Efficiency claim
< the Allam cycle can potentially achieve efficiencies up to about 59 percent (LHV) for natural gas and 51–52 percent (LHV) for gasified coal. >

It would be interesting to know if these numbers are AFTER making allowance for the work input required by the air separation unit. Reference 1, from which the numbers appear to be taken, does not make this clear.

More study than ought to be required turns up the fact that table 1 of reference 7, i.e.

http://www.modernpowersystems.com/features/featurenet-powers-co2-cycle-the-breakthrough-that-ccs-needs

makes it clear that the ASU input is allowed for.

86.148.153.183 (talk) 12:17, 21 March 2017 (UTC)

No Figure 1
The article says, " A simplified flowsheet for this cycle can be seen in Figure 1." but there is no Figure 1. That makes it sound like a copy/paste from another source. Isn't that a violation of Wikipedia rules? Anorlunda (talk) 19:15, 6 December 2020 (UTC)

Reduced cooling claim
The article implies and almost outright claims that the cooling requirements of an Allam cycle power system are significantly lower than for a combined cycle system, suggesting that combined cycle requires large amounts of cooling water and/or cooling towers where the Allam cycle does not. However, consider two roughly equivalent systems: a 55% efficient combined cycle plant and a 55% efficient Allam cycle plant. Both will reject 45% of their fuel heat to the environment. The cooling requirements are exactly the same. They will both evaporate the same amount of water from their cooling towers or heat the same amount of water in their river/ocean. By the way, nobody does once-through river cooling anymore in the developed world; it's all evaporation in cooling "towers" even if the towers are forced draft and very short.

Furthermore, the cooling requirements of supercritical CO2 are more challenging than the cooling requirements for steam. To achieve most of the supercritical CO2 benefit, one must reject heat at the super-critical point of 31.5 degrees C. Compare this to steam which rejects heat at 104.5 degrees C in the low pressure (~0.17 bar) stage of a typical steam turbine condenser. Some steam power plants run at slightly reduced efficiency on hot summer days compared to cold winter cooling conditions. If the humidity is high and air is ~40 degrees C rejecting heat at 105 C requires a larger heat exchanger. Imagine how that will impact a super-critical CO2 system which needs 70 degrees lower coolant or much narrower reject heat exchanger pinch point.

Cuhlik (talk) 14:56, 12 October 2017 (UTC)

Produces fresh water claim
The claim of producing significant amounts of fresh water is specious. If the system is burning gasified coal, there will be net water consumption in the coal gasification process as the hydrogen for producing coal gas comes from water molecules and the coal gasification process is not 100% efficient. That process generates CO2 which is not recovered by the Allam cycle.

But let's assume the optimistic situation where the Allam cycle is powered by pure methane CH4. In a 1 GWe system of 55% efficiency, 1/.55 GW thermal of methane will be burned. That's about 0.1 kg/second of CH4 of which 25% of the mass is hydrogen, so 0.025 kg/sec of hydrogen. That will produce (16+2)/2 times as much water mass or 0.225 kg/sec of water which is only a quarter liter per second of water from a very large power plant. This large power plant will produce only 19 cubic meters of water per day if run at baseload, 100% capacity factor. A natural gas powered system will produce slightly less as natural gas is not pure methane so contains somewhat less hydrogen per unit heating value.

Cuhlik (talk) 14:56, 12 October 2017 (UTC)

What happens to the CO2?
" the CO2 product is high-pressure and high purity, ready for sequestration or utilization without requiring further compression."

I linked sequestration to carbon capture and storage. --Timeshifter (talk) 11:37, 10 August 2021 (UTC)