417
References
to the simple cycle (Fig. 11.14) is about 8 % points, independent of pressure ratio
and TIT. For a pressure ratio above 35, the efficiency is above 50 %. Difficulties
with steam injection are that the steam flow rate is rather high (of the order of 15 %
of the air flow rate at pressure ratio 30 and TIT = 1350 °C) and that the required
cooling air flow also becomes rather big (also of the order of 15 % for pressure ratio
30 and TIT = 1350 °C). Providing a simple-cycle gas turbine for steam injection
with these steam and cooling air flow rates is just impossible. State-of-the-art gas
turbines allowing steam injection are limited to steam injection flow rates in the
12 % order (e.g. GE LM6000 with steam injection). Adaption to higher steam flow
rates is technically possible, but requires a turbine adaption to a higher flow rate,
and as a consequence, efficiency loss when running without steam injection.
Steam-injected gas turbines are typically used with cogeneration plants (CHP:
combined heat and power). The gas turbine is used then to generate mechanical
power for driving an electric generator. Exhaust gases are used for the generation of
steam applied in process heating. Steam is only injected into the gas turbine when
heat is not required. The steam injection is rather exceptional and for this reason the
machine is not optimised for steam injection operation. The steam-loaded exhaust
gas is discharged into the atmosphere for the same reason. This means that there is
no gas cooler for recovery of the water corresponding to the injected steam, although
complete recovery is possible with natural gas (CH 4 ) as fuel as the combustion then
generates much water. With a steam-injected gas turbine continuously running in
steam-injected mode, steam cooling would be a profitable option. The cooling air
extraction from the compressor would be unnecessary and the steam flow rate to
be injected in the combustion chamber would be strongly reduced. Steam required
for cooling might also be mixed into the gas flow. Contrary to closed-loop steam
cooling, there is no technical implementation problem, the cooling circuit being the
same as with air cooling.
References
1. Baehr HD (1966) Thermodynamik, 2nd edn. Springer, Heidelberg
2. Chiesa P, Macchi E (2004) A thermodynamic analysis of different options to break 60 %
electrical efficiency in combined cycle power plants. J Eng Gas Turbines Power Trans ASME
126:770–785
3. Cohen H, Rogers GFC, Saravanamuttoo HIH (1996) Gas turbine theory, 4th edn. Longman
Group, London. ISBN 0-582-23632-0
4. El-Masri MA (1986) On thermodynamics of gas turbine cycles: part 2—A model for expansion
in cooled turbines. J Eng Gas Turbines Power trans ASME 108:151–159
5. Franco A, Casarosa C (2002) On some perspectives for increasing the efficiency of combined
cycle power plants. Appl Therm Eng 22:1501–1518
6. Fu WL, Wright LM, Han JC (2005) Heat transfer in two-pass rotating rectangular channels
(AR=1:2 and AR=1:4) with smooth walls. J Heat Transfer ASME 127:265–277
7. Razak AMY (2007) Industrial gas turbines; performance and operability. CRC Press, Florida.
ISBN 978-1-84569-205-6
References
to the simple cycle (Fig. 11.14) is about 8 % points, independent of pressure ratio
and TIT. For a pressure ratio above 35, the efficiency is above 50 %. Difficulties
with steam injection are that the steam flow rate is rather high (of the order of 15 %
of the air flow rate at pressure ratio 30 and TIT = 1350 °C) and that the required
cooling air flow also becomes rather big (also of the order of 15 % for pressure ratio
30 and TIT = 1350 °C). Providing a simple-cycle gas turbine for steam injection
with these steam and cooling air flow rates is just impossible. State-of-the-art gas
turbines allowing steam injection are limited to steam injection flow rates in the
12 % order (e.g. GE LM6000 with steam injection). Adaption to higher steam flow
rates is technically possible, but requires a turbine adaption to a higher flow rate,
and as a consequence, efficiency loss when running without steam injection.
Steam-injected gas turbines are typically used with cogeneration plants (CHP:
combined heat and power). The gas turbine is used then to generate mechanical
power for driving an electric generator. Exhaust gases are used for the generation of
steam applied in process heating. Steam is only injected into the gas turbine when
heat is not required. The steam injection is rather exceptional and for this reason the
machine is not optimised for steam injection operation. The steam-loaded exhaust
gas is discharged into the atmosphere for the same reason. This means that there is
no gas cooler for recovery of the water corresponding to the injected steam, although
complete recovery is possible with natural gas (CH 4 ) as fuel as the combustion then
generates much water. With a steam-injected gas turbine continuously running in
steam-injected mode, steam cooling would be a profitable option. The cooling air
extraction from the compressor would be unnecessary and the steam flow rate to
be injected in the combustion chamber would be strongly reduced. Steam required
for cooling might also be mixed into the gas flow. Contrary to closed-loop steam
cooling, there is no technical implementation problem, the cooling circuit being the
same as with air cooling.
References
1. Baehr HD (1966) Thermodynamik, 2nd edn. Springer, Heidelberg
2. Chiesa P, Macchi E (2004) A thermodynamic analysis of different options to break 60 %
electrical efficiency in combined cycle power plants. J Eng Gas Turbines Power Trans ASME
126:770–785
3. Cohen H, Rogers GFC, Saravanamuttoo HIH (1996) Gas turbine theory, 4th edn. Longman
Group, London. ISBN 0-582-23632-0
4. El-Masri MA (1986) On thermodynamics of gas turbine cycles: part 2—A model for expansion
in cooled turbines. J Eng Gas Turbines Power trans ASME 108:151–159
5. Franco A, Casarosa C (2002) On some perspectives for increasing the efficiency of combined
cycle power plants. Appl Therm Eng 22:1501–1518
6. Fu WL, Wright LM, Han JC (2005) Heat transfer in two-pass rotating rectangular channels
(AR=1:2 and AR=1:4) with smooth walls. J Heat Transfer ASME 127:265–277
7. Razak AMY (2007) Industrial gas turbines; performance and operability. CRC Press, Florida.
ISBN 978-1-84569-205-6