The Vortex gas turbine is about exploring the idea of using super-heated air to heat the air inside the combustors of an gas turbine, and determining whether this might increase the efficiency of gas turbines.

Heating water by direct steam injectionThis idea might seem a bit far fetched, but in some industries heating water by direct steam injection is considered to be highly efficient. Click picture to see video on YouTube.

How it works

A stand-alone compressor (B) takes in air (A) and compresses it. The compressed air is heated in combustor 1 (C) by adding and burning (bio)fuel. The hot gases, ± 1450°C hot, expand in the combustor 2 of an gas turbine (F) and heat the airflow (D), already ± 450°C hot due to compression by the gas turbine's compressor (E).

The hot combined airflows (D+A) from the stand-alone compressor and the gas turbine expand in the turbines (G), driving both the gas turbine's compressor (E) and the generator (H). See picture 1.

Picture 1 - How does the Vortex Gas Turbine work?

How does a vortex gas turbine work?
Note: If the pressure of the air coming from the stand-alone compressor has to be the same or higher than the pressure of the air coming from the gas turbine's compressor, the higher pressure and the expansion of the hot air (A) might push back the air (D) coming from the gas turbine's compressor (E). This should not be too problematic because the density of air flow A should be lower because it is hotter (± 1450°C vs. ± 450°C).

To prevent the air coming from the stand-alone compressor (A) from pushing back (some of) the air (D) coming from the gas turbine's compressor, e.g. actuator operated valves can be placed between the gas turbine compressor and the combustor inlet and work in tandem. See picture 2.

Int resembles somewhat the working of an pulse jet engine or pulse detonation engine.

Picture 2 - Cross-section Vortex Gas Turbine Combustor

Cross-section view Vortex Gas Turbine Combustor

Potential efficiency

According to this site, thumb of rule is to allow 1 pound of steam for 6 pounds of water to be heated. If this thumb of rule also would apply to heating air with super heated air, a lot of energy might be saved.

For instance, the gas flow of an Siemens SGT-800 gas turbine (picture 3) is ± 132 kg/s. If the above thumb of rule would apply, an airflow of 22 kg/s (132 kg/s ÷ 6), at the right temperature and pressure, would be sufficient to heat the airflow of the SGT-800 gas turbine.

If you compare pictures 3 and 4, you will notice the exhaust gas flow of the SGT-100 gas turbine (picture 4) is ± 21 kg/s, almost the required volume of 22 kg/s.

The exhaust temperature of the SGT-100 is 531ºC versus the 544ºC of the SGT-800; both airflows are heated to almost the same temperature, about 1150ºC.

The compressor ratio of SGT-100 is 15,6 versus the 19 of the SGT-800. A difference of almost 4 bar.

Electrical efficiency of the SGT-100 is 31,0% so its energy consumption would be about 18 MW. Electrical efficiency of the SGT-800 is 37,5%, so its energy consumption should be ± 125 MW.

Picture 3 - Siemens SGT-800 gas turbine Picture 4 - Siemens SGT-100 gas turbine
Specifications Siemens SGT-800 gas turbine
Source: Siemens Industrial Gas Turbines Brochure
Specifications Siemens SGT-100 gas turbine

Possible energy savings

It takes ± 18 MW to produce an air flow of ± 21 kg/s and with an compressor pressure ratio of ± 16 bar and a temperature of ± 1150°C. This is very close to the likely needed airflow (A) of 22 kg/s, > 20 bar and ± 1450°C (higher temperature might damage the turbines).

The SGT-100 consumes ± 125 MW. So, even if an additional 72 MW of fuel would be needed to give airflow (A) the necessary pressure, volume and temperature to heat the airflow of the SGT-100 to its designated temperature, about 35 MW of energy might be saved.

This 72 MW is the combined energy consumption of four SGT-100 gas turbines!

So the margins seem to be there. Up to 110 MW (15 MW is still a 12% reduction in energy consumption) which should be enough energy to bring airflow (A) "up to par".

Also, as picture 5 shows the combined airflows would be 154 kg/s, 22 kg/s more than that of the SGT-800, so the energy output, both in a single as in an combined cycle will be higher.

Picture 5 - flowchart Vortex gas turbine

Flowchart Vortex gas turubine
Note: the numbers in picture 5 are estimates except for the airflows, and are just used to illustrate the airflows.

Feedback and help is very much appreciated

Tried to do the numbers myself with using an example (picture 6) I found on the the Engineering Toolbox, but gave up mainly because both airflow A and D have an compressor ratio of 19 bar or more, and couldn't figure out how to implement this in the calculations.

Picture 6 - Continuously heating by steam

Formula continuously heating by steam

Furthermore, because airflows A and D have an high compressor ratio and difference in temperature (± 450ºC vs. ± 1100ºC)  I wondered what the effect of these airflows hitting each other and the friction this could cause. Would this cause an triboelectric effect?

Please help and feel free to tweet or email your thoughts.