Calculation example
The enthalpy of vaporization/heat of condensation of water at 90°C is approx. 2278 kJ/kg. This means that 633 Wh of heat are required to vaporize 1 kg of water at 90°C. If 1 kg of water vapor condenses at 90°C in a heat exchanger, 633 Wh are also transferred. In power plants, this condensation heat is also used to vaporize water, which is then released as clouds visible from afar.
In the case of propane, the enthalpy of vaporization/heat of condensation at 90ºC is approx. 133kJ per kg. This means that to vaporize one kg of propane at 90ºC, an energy input of 36.9 Wh is required. When one kg of propane evaporates in a heat exchanger, this 41.6 Wh is transferred.
633 / 36.9 = 17.1
By using the condensation heat of the water vapor, 17.1 kg of propane could be vaporized per kg of water vapor.
However, this propane vapor would also be saturated and therefore not usable for a turbine, as droplet impact would occur. In addition, the propane would have an unnecessarily high pressure of approx. 37.6 bar at the dew point.
It would therefore be better to vaporize the propane at 50°C less and then overheat it by 50°C.
The enthalpy of vaporization of propane at 40°C is 307 kJ, which corresponds to 85.3 Wh per kg. To this must be added a further 23.5 Wh per kg for the specific heat capacity/overheating as 1kg of propane can absorb approx.
0.47Wh per 1K/1°C.
This means that propane has 93% of the specific heat capacity of water vapor.
Together this results in 108.8 Wh per kg for superheated propane vapor around 50 K/°C.
633 / 108.8 = 5,8
By using the heat of condensation of the water vapor, 5.8 kg of propane per kg of water vapor could be vaporized and superheated by 50 K or °C. Only the superheated part of the propane vapor is converted into work output in the turbine by using its specific heat capacity from the superheating. In the example, the condensation heat of 633 Wh from 1 kg of steam without superheating generates around 5.8 kg of propane steam with around 494.7 Wh.
Around 136.3 Wh are then used to superheat the propane vapor.
In order to transfer the same heat capacity of 136.3 Wh to 1 kg of water vapor, it would have to be overheated by 267 K/°C, as 1 kg of water vapor can only absorb 0.51 Wh per K or °C of overheating.
136.3 / 0.51 = 267
Nuclear power plants operating at low temperatures of 350°C could certainly double their efficiency by additionally utilizing the heat of condensation. Engineers could also use other gases and create more favorable conditions. Large amounts of additional electricity could be generated with the depicted variant alone. This finding could lead to further innovations and even higher levels of efficiency.
Just imagine how much CO2 could be saved if all coal-fired power plants generated the same amount of electricity using half as much coal.
Application example
French nuclear power plants of recent design
The type N4 nuclear reactor is a 3rd generation water-cooled and light-water moderated pressurized water reactor developed by the former French company Framatome. It has a thermal output of 4250 MWth, a net electrical output of 1450 MWe and thus an efficiency of 34.1 %. (Source: Wikipedia/IAEA).
They therefore generate 65.9% waste heat. These reactors are used in 2 units each in Chooz and Civaux.
Each of these units can currently theoretically produce 12000GW/h per year. However, the units cannot operate at full load, particularly in the summer, as the 2800 MW of waste heat can often not be released. Utilization of the condensing power process could halve this load on the cooling system. This would enable these units to produce electricity more reliably. In France, the construction of 14 new power plant units is currently being planned, although the cooling problem requires new sites. The latest unit in Flammanville alone costs 12.7 billion euros. The Finnish EPR of the latest design also cost over 10 billion euros. Both construction projects were delayed by around a decade.
The newly planned nuclear reactors would become redundant if the old reactors generated twice as much electricity using the condensing power process.
Nuclear power supporters and opponents can win with this.