Percent Increase in Power (%)
Percent Increase in Efficiency (%)
Cost/KW US$/KW
25.00
250.00
20.00
200.00
15.00
150.00
10.00
100.00
5.00
50.00
0.00
Evaporative Refrigeration Inlet Ice Storage Inter-stage Heated and Steam Injection Evaporative
Cooling Cooling Cooling Compressor Moisturized Cooling +Steam
Cooling Compressed Air Injection
Injection
Figure 2-45. Comparison of various cycles based on percent change in power and efficiency and cost $/KW.
Humidified Compressed Air lnjection System are about the same. This is due to the fact that though the initial cost to install the Compressed AirSystem， for a turbine of about 100 MW， is about .3.7 million as compared toabout .1.7 million for a steam injection system， the power generated by the Heated and Humidified Compressed Air lnjection System is much higher.
The rate of return on the steam injection system is higher than the Compressed Air lnjection System. This is due to the fact that though the efficiency of the steam injection system and the compressed air injectionsystem is about thesame， however， the initial cost of the steam injected system being over 50% lower than the compressed air injection system accounts for the difference.
The calculations for fuel gas savings have been based on an internationalprice offuel， at about .S.2.50 per million BT. (.S.2.64 per million .J).The plant availability was taken at97%， which is the availability throughout industry for most frame type plants. The cost of sale of new power was based on the average price of .S.0.04 per .W-Hr.
Some of the major restrictions in putting these cycles on existing units can be described as follows:
1. GeneJαtoJ PoweJ Output Cαpαcity.The generator， as a general rule of thumb is oversi.ed by about 20% above the turbine rated load. The changes have to be limited to that region by limiting the steam or Compressed Air lnjection.
2. TuJbine
FiJinfTe內peJαtuJe. The turbine firing temperature， the tem-perature of the gas measured at the inlet of the first stageno..les， is limited to the design firing temperatures as increase in firing tempera-tures would greatly reduce the life of the turbine hot section.
3. Injection PJessuJe. The injection pressure must be between 75-100 psia (5-7 Bar) above the Compressor Discharge Pressure. ln the case of theHeated and Humidified Compressed Air injectedsystem， the air must be saturated.
4. Nozzle AJeα o the FiJst TuJbine Stαfe (ExpαndeJ Stαfe). This is a verycritical parameter and limits the total airflow into the turbinesection， thus this limits the amount of steam injection or the amount of the heated and humidified compressed air injection.
5. SuJfe ContJol. The injection systems will all require major modifica-tions to the control system to prevent injection till the units have reached full load and stabili.ed operation.During shutdown， the system must first shut off the injection system. These changes are very necessary to prevent the units from surging.
6. NOxE內issions . The amount NOx emissions is very critical in most regions where gas turbines are being utili.ed for power generation. The present cap is about 22 ppm; the aim is to go down to as low as 9 ppm. The techniques offered here all are NOxemission friendly， in that they do not increase the present levels of NOx， in fact in thecase of the injection systems， both steam， and heated and humidi-fied compressed air will lower the NOx emissions making the planteven more environmentally friendly， especially in this critical loca-tion. 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：燃氣渦輪工程手冊 Gas Turbine Engineering Handbook 1(43)
